Tissue Biology
https://fenix.tecnico.ulisboa.pt/disciplinas/ETeci/2023-2024/1-semestre
Gabriel Monteiro
email: gabmonteiro@tecnico.ulisboa.pt
phone: 218 419 981
office: room 8-6.16 (Alameda, Torre sul)
Gabriel Monteiro, 23-24
1- Integration of cells into tissues. Cell-cell interaction, matrix-cell and
cellular
communication.
Function
and
composition
of
the
extracellular matrix ~1h
2- Architecture and functional role of tissues (epithelial, connective,
muscular and nervous) ~2h
3- Tissue dynamics: chemical, electrical and mechanical signaling. Cell
stress, inflammatory responses and cell death –~4h
Gabriel Monteiro, 23-24
Integration of cells into tissues
- Function and composition of the extracellular matrix
- Cell-cell interaction, matrix-cell and cellular communication
Gabriel Monteiro, 23-24
Integrating Cells into Tissues
Direct interactions between cells, as well as between cells and the extracellular matrix,
are critical to the development and function of multicellular organisms
Gabriel Monteiro, 23-24
Lodish et al., Molecular Cell Biology, W.H. Freeman
The cytoskeleton provides structural support and shape for the cell, organizes cytoplasm (polarity) and
permits directed movement of organelles, chromosomes, and the cell itself. Also, through association with
extracellular matrix and other cells it stabilizes tissues.
The polymerization/depolymerization (assembling/disassembling) of the cytoskeleton elements is precisely and tightly
regulated
Composition:
Microfilaments (f=7nm) G-actin which polymerizes to F-actin
Main functions: cell motility, cell contractility
actin
Microtubules (f=24nm) a and b tubulin,
Main functions: vesicular transport, mitosis, cilia and flagella
tubulin
Intermediate filaments (f=9-11nm) filamentous proteins (keratin, vimentin, lamin,
desmin, nestin, GFAP, etc)
Main functions: essentially as structural components
vimentin
Gabriel Monteiro, 23-24
Lodish et al., Molecular Cell Biology, W.H. Freeman
The extracellular matrix, ECM, is a complex structural entity surrounding and supporting cells that are
found within mammalian tissues.
Functions: mechanical strength (rigidity and compressibility), adhesion, migration, chemical
selectivity, proliferation, differentiation, apoptosis and cell shape. All of them depend on ECM
composition and density.
Composition:
- Structural proteins: e.g. collagens and non-collagenous proteins (e.g. elastin)
- Specialized (multiadhesive) proteins: e.g. fibronectin and laminin
- Glycosaminoglycans (GAGs): polysaccharides and Proteoglycans: a protein core attached to GAGs
- Signalling molecules (e.g. VEGF, BMP)
Gabriel Monteiro, 23-24
Non-collagenous ECM
proteins
Gabriel Monteiro, 23-24
Nat Rev Mol Cell Biol 15, 771–785 (2014)
Collagens
Gabriel Monteiro, 23-24
Nat Rev Mol Cell Biol 15, 771–785 (2014)
Collagens (28 types)
The collagen types (the major protein comprising the ECM and also from the animal kingdom) differ from
each other in structure, properties and function.
- Type I collagen is the most common (~90% of the body's collagen content), the main type found in the
skin, in bones and tendons and ligaments, being adapted mainly to resist stress.
- Type II collagen is abundant in cartilage, being able to associate with proteoglycans that contain
chondroitin sulfate, which gives it a reversible compressibility.
- Type III collagen, in turn, is found in tissues that suffer constant deformation, such as blood vessels and
the smooth muscle of the digestive tract and uterus.
- Type IV forms a two-dimensional reticulum and is a major component of the basal lamina.
- Collagens are mainly synthesized by fibroblasts but epithelial cells also synthesize them
Gabriel Monteiro, 23-24
Collagens (28 types)
Types I, II and III are the most abundant and form fibrils of similar structure
Most of collagens (rich in glycine and proline) are long (300nm) and thin (1.5nm) diameter rod-like proteins consisting of 3
coiled subunits composed in a characteristic right-handed triple helix
Lateral interactions of triple helices of collagens result in the
formation of collagen fibrils roughly 50-200 nm diameter. The
packing of collagen is such that adjacent molecules are displaced
~1/4 of their length (67nm).
Gabriel Monteiro, 23-24
Laminins and fibronectins form bridges between structural ECM molecules, and
connect the ECM to cells and to soluble molecules within the extracellular space
Fibronectin (dimers) bind many cells (via RGD-integrins)
to fibrous collagens and other ECM molecules
Laminin (heterotrimers) and type IV collagen form the
2-D network of basal lamina
Lodish et al., Molecular Cell Biology, W.H. Freeman
Gabriel Monteiro, 23-24
Tissue Engineering, JB Clemens & A. Blitterswijk, Academic press, 2023
Glycosaminoglycans (GAGs)
- hyaluronic acid, dermatan sulfate, chondroitin sulfate, heparin, heparan sulfate, and keratan sulfate;
-are long unbranched polysaccharides, highly negatively charged, containing a repeating disaccharide unit: Nacetylgalactosamine (GalNAc) or N-acetylglucosamine (GlcNAc), and a uronic acid such as glucuronate or iduronate
Gabriel Monteiro, 23-24
GAGs possess a variety of biologic activities including the ability to bind growth factors and chemokines/cytokines and
promote water retention.
GAGs confer high viscosity to the solution and low compressibility, which makes these molecules ideal for a lubricating fluid
in the joints. At the same time, their rigidity provides structural integrity to cells and provides passageways between cells,
allowing for cell migration.
Hyaluronic acid is unique among the GAGs in that it does not contain any sulfate and is not found covalently attached to
proteins as a proteoglycan. It has very large molecular weight (100,000–10,000,000) and can displace a large volume of water.
GAG
Hyaluronate
Chondroitin sulfate
Heparan sulfate
Heparin
Dermatan sulfate
Gabriel Monteiro, 23-24
Keratan sulfate
Localization
Comments
synovial fluid, vitreous humor, ECM of loose connective tissue
large polymers, shock
absorbing
cartilage, bone, heart valves
most abundant GAG
basement membranes, components of cell surfaces
contains higher acetylated
glucosamine than heparin
component of intracellular granules of mast cells
lining the arteries of the lungs, liver and skin
more sulfated than
heparan sulfates
skin, blood vessels, heart valves
cornea, bone, cartilage aggregated with chondroitin sulfates
Proteoglycans are proteins linked to GAGs (also called mucopolysaccharides).
- GAGs extend perpendicularly from the core in a brush-like structure. The linkage of GAGs
to the protein core involves a specific trisaccharide which is linked to the protein core
through an O-glycosidic bond to a S or T residue in the protein.
Gabriel Monteiro, 23-24
Lodish et al., Molecular Cell Biology, W.H. Freeman
Signalling molecules (growth factors, cytokines)
An advantage of utilizing the ECM in its intact state (decellularized tissue*) as a scaffold for tissue engineering is the presence
of all the attendant growth factors in the same relative amounts and three-dimensional ultrastructure that exist in nature. The
ECM protects these growth factors from degradation and efficiently presents them to resident or migrating cells.
*Decellularization is a technique by which a tissue or organ is processed by various physical, chemical, and/or enzymatic methods to remove all
the resident cells leaving behind only the extracellular matrix which later will serve as a bioscaffold.
Gabriel Monteiro, 23-24
Tissue Engineering, JB Clemens & A. Blitterswijk, Academic press, 2023
Commercially available products composed of intact ECM
Gabriel Monteiro, 23-24
Tissue Engineering, JB Clemens & A. Blitterswijk, Academic press, 2023
Composition and structure of ECMs
Gabriel Monteiro, 23-24
The FEBS Journal 288 (2021) 6850–6912
Physical properties of the extracellular matrix
(A) Topography encountered by a migrating cell
(B) Examples of varying fiber diameters and sizes of pores between ECM fibers
(C) Examples of fiber orientation: compare oriented fibers near ‘C’ with the other relatively non-oriented fibers
(D) Examples of varying fiber elasticity/stiffness represented as different degrees of fiber deformation as a cell
pulls on two fibers using cell processes and cellular contractility
(E) Ligand density (shown as black bristles) affecting the extent of cell spreading
(F) Basement membrane composition: a slice of the basement membrane indicating key molecular components
(G) Fibrous ECM composition: a slice of fibrillar ECM listing several key components
Gabriel Monteiro, 23-24
Development (2020) 147, dev175596
Examples of key components of the extracellular matrix
Gabriel Monteiro, 23-24
Development (2020) 147, dev175596
Cell-cell and cell-ECM adhesion and communication
is dependent on specialized structures (Gap junctions, Tight junctions, Adherens junctions, Focal
adhesions (or Adhesion plaques), Desmosomes, Hemidesmosomes) and molecules (Cell adhesion
molecules) associated with microfilaments and intermediate filaments
Gabriel Monteiro, 23-24
Gap junctions ("junções comunicantes")
- consist of assemblies of six (x2) connexins (>20 types), which form open channels through the
plasma membranes of adjacent cells where some ions and small molecules pass through
(movement of molecules smaller than 1 kDa or <2nm (e.g. peptide < 8 aa))
Gabriel Monteiro, 23-24
Lodish et al., Molecular Cell Biology, W.H. Freeman
Tight junctions (“junções apertadas")
- ribbon-like bands connecting adjacent cells that prevent leakage of fluid across the cell layer
- are formed by interactions between strands of transmembrane proteins (occludin and claudins)
on adjacent cells.
Gabriel Monteiro, 23-24
Tight junctions in epithelial cells of small intestine and glucose transport from intestine
lumen and blood
Gabriel Monteiro, 23-24
Lodish et al., Molecular Cell Biology, W.H. Freeman
Desmosomes (D), Hemidesmosomes (HD),
Adherens Junctions (AJ), Focal adhesion (FA)
- are dense protein plaques (D, HD) or belts (AJ, FA) that mediate
adhesion between cells (D and AJ) or between cells and ECM (HD
and FA). Desmosomes and Hemidesmosomes bind to intermediate
filaments and Adherens Junctions and Focal adhesions attach to
actin filaments (microfilaments).
Focal adhesion
Focal adhesion
D
Gabriel Monteiro, 23-24
Lodish et al., Molecular Cell Biology, W.H. Freeman
Stable cell-cell junctions mediated by the cadherins
Interactions between cadherins mediate two types of stable cell-cell adhesions:
- In adherens junctions, the cadherins are linked to bundles of actin filaments via the catenins
- In desmosomes, desmoplakin links members of the cadherin superfamily (desmogleins and desmocollins)
to intermediate filaments
Adherens Junction
Gabriel Monteiro, 23-24
Desmosome
ECM exerts control over many cellular fate processes through binding to a class of receptors, integrins.
Gabriel Monteiro, 23-24
Lodish et al., Molecular Cell Biology, W.H. Freeman
- The extracellular matrix is critically important for many cellular processes including growth, differentiation, survival,
and morphogenesis.
- Cells remodel and reshape the ECM by degrading and reassembling it, playing an active role in sculpting their
surrounding environment and directing their own phenotypes.
- Both mechanical and biochemical molecules influence ECM dynamics in multiple ways; by releasing small bioactive
signaling molecules, releasing growth factors stored within the ECM, eliciting structural changes to matrix proteins which
expose cryptic sites and by degrading matrix proteins directly.
- The dynamic reciprocal communication between cells and the ECM plays a fundamental role in tissue development,
homeostasis, and wound healing.
Gabriel Monteiro, 23-24
Current Opinion in Biotechnology 24: 830-833 (2013)
Take home messages
The cytoskeleton provides structural support and shape, and permits movement of organelles, chromosomes, and the cell
itself. Microfilaments (actin) - main functions: cell motility, cell contractility. Microtubules (tubulin) - main functions:
vesicular transport, mitosis. Intermediate filaments (filamentous proteins) - main functions: essentially as structural
components.
Cell-cell and cell-ECM adhesion is dependent on specialized structures - Gap junctions, Tight junctions, Adherens junctions,
Focal adhesions, Desmosomes, Hemidesmosomes - and molecules - Cell adhesion molecules - associated with
microfilaments and intermediate filaments.
ECM exerts control over many cellular fate processes through binding to cell receptors, e.g. integrins.
The dynamic reciprocal communication between cells and the ECM plays a fundamental role in many cellular processes.
Gabriel Monteiro, 23-24
Architecture and functional role of tissues
Gabriel Monteiro, 23-24
Tissue Biology
A tissue is a collection of cells and ECM that
perform a given function.
Gabriel Monteiro, 23-24
> 400-1000 cell types (grouped in 7 classes) in mature human body
PNAS 2023, 120:39 e2303077120
https://humancelltreemap.mis.mpg.de
Cell classes
https://humancelltreemap.mis.mpg.de
Gabriel Monteiro, 23-24
Epithelial cells:
- Grow in contiguous 2D sheets
- They have polarity
- Connected with their neighbors and
bound to basal lamina (cannot migrate)
Mesenchymal cells:
- They can migrate
- Their growth is contact-inhibited
- Can differentiate into osteoblasts,
chondrocytes, fibroblasts
Cell count and biomass distributions by cell type
(A) Even after removing
nonnucleated blood cells (≈29
trillion), white blood cells (≈3.4
trillion) still dominate the ≈7 trillion
nucleated cell count.
(B) Cell biomass is dominated by
skeletal myocytes, comprising
about half of cell biomass in the
body, even though they make up
<0.002%. Most of the remaining
23.5 kg of cell biomass are white
adipocytes.
Gabriel Monteiro, 23-24
PNAS 2023, 120:39 e2303077120
Cell types distributions across select tissues
Cell count and biomass distributions
across 18 broad cell types are shown
for the 32 most significant tissue
systems of the body. Most tissue
systems are dominated by the ≈140
distinct cell types making up the
epithelial cell class.
(total ECM ~25 kg).
Gabriel Monteiro, 23-24
PNAS 2023, 120:39 e2303077120
Epithelial tissue
Epithelial tissues are composed of closely aggregated polyhedral cells with very little extracellular substance but showing
strong adherence to each other (tight junctions, desmosomes, adherens junctions, gap junctions). Are not irrigated by blood
vessels.
Almost all epithelia are separated
from the connective tissue by the
basal lamina (or basement membrane)
Main functions:
Covering and lining of surfaces (e.g. skin, intestines), absorption (e.g. intestines), secretion (e.g. glands), sensation
(e.g. olfactory neuroepithelium)
Epithelia classification is based on:
- Number of cell layers: simple (one sheet) or stratified (multilayered)
- Cell (and also nucleus) shape: squamous (“pavimentoso”) (flattened), cuboid, columnar or pseudostratified (has only one
cell layer but looks like more)
- Presence of cell surface specializations (Microvilli that increase the cell surface area; and Cilia that allows a current of
fluid to be propelled in one direction)
Gabriel Monteiro, 23-24
Junqueira & Carneiro, Basic Histology, McGraw-Hill
Type
Simple
Cell form
Examples of distribution
Main function
Squamous
Lining vessels
(endothelium). Serous lining
of cavities: pericardium,
pleura, peritoneum
(mesothelium)
Facilitates the movement of
viscera (mesothelium), active
transport by pinocytosis (meso& endothelium), secretion of
biologically active molecules
(mesothelium)
Cuboid
Covering the ovary, thyroid
Covering, secretion, ciliated
epithelia in female reproductive
system
Columnar
Lining the intestine,
stomach, gallbladder
Protection, lubrication,
absorption, secretion
Pseudostratified Some columnar
Lining of trachea, bronchi,
and some cuboidal nasal cavity
Gabriel Monteiro, 23-24
Protection, secretion, ciliamediated transport of particles
trapped in mucus
Junqueira & Carneiro, Basic Histology, McGraw-Hill
Common types of covering epithelia in the human body
Common types of covering epithelia in the human body
Type
Stratified
Gabriel Monteiro, 23-24
Cell form
Examples of distribution
Main function
Surface layer squamous
keratinized (dry)
Epidermis
Protection, prevents water
loss
Surface layer squamous
nonkeratinized (moist)
Mouth, esophagus, larynx, vagina,
anal canal
Protection, secretion,
prevents water loss
Cuboid
Sweat glands, developing ovarian
follicles
Protection, secretion
Transitional (urothelium)
Bladder, ureters, renal calyces
Protection, distensibility; it
is cuboidal when is not
stretched or squamous
when the organ is
distended
Columnar
Conjunctiva
Protection
Junqueira & Carneiro, Basic Histology, McGraw-Hill
Endothelium lines blood and lymph
vessels
Section of a vein containing red blood cells. All
blood vessels are lined with a simple squamous
epithelium called endothelium (arrowheads)
Gabriel Monteiro, 23-24
Mesothelium lines certain body cavities
(pericardium, pleura, peritoneum)
The simple squamous epithelium that
covers the body cavities (the abdominal
cavity in this case) is called mesothelium
Junqueira & Carneiro, Basic Histology, McGraw-Hill
Connective tissue (“conjuntivo”)
Connective tissues are composed mainly of ECM (unlike other tissues). The wide variety reflects
variations in the composition and amount of cells and ECM. Are originated from the mesenchyme
(an embryonic tissue) that develops from mesoderm.
Main functions:
Provide and maintain form in the body, and structural and metabolic aid for other tissues
Blood
Gabriel Monteiro, 23-24
Cells of the connective tissue
Gabriel Monteiro, 23-24
Cell type
Function
Fibroblast, chondroblast, osteoblast
Production of ECM - Structural
Plasma cell
Production of antibodies – Immunological
Lymphocytes
Production of immunocompetent cells - Immunological
Eosinophils
Allergic, vasoactive, inflammatory processes – Immunological
Neutrophils
Phagocytosis - Defense
Macrophages
Secretion of cytokines - Defense
Mast cells and basophils
Liberation of active molecules (e.g. histamine) - Defense
Adipose (fat) cell
Storage of fats – Energy reservoir, heat production
Note: Adipocyte, megakaryocyte, and osteoclast cells are significantly larger than the other cells illustrated.
Junqueira & Carneiro, Basic Histology, McGraw-Hill
Fibroblasts synthesize and secrete ECM proteins, GAGs and proteoglycans and also
growth factors (involved in growth and differentiation).
In adults, fibroblasts rarely divide unless additional fibroblasts are needed
Active (left) and quiescent (right) fibroblasts.
Fibroblasts that are actively engaged in synthesis are
richer in mitochondria, Golgi complex, and rough ER
than are quiescent fibroblasts (fibrocytes).
Gabriel Monteiro, 23-24
Quiescent fibroblasts are elongated cells
with thin cytoplasmic extensions
Junqueira & Carneiro, Basic Histology, McGraw-Hill
Macrophages and the mononuclear phagocyte system
Macrophages are polymorphic phagocytic cells
Electron micrograph of a macrophage, lysosomes (L),
nucleus (N), nucleolus (Nu). The arrows indicate
phagocytic vacuoles.
Gabriel Monteiro, 23-24
Cell type
Location
Main function
Monocyte
Blood
Precursor of macrophages
Macrophage
Connective tissue
Production of cytokines involved in inflammation,
antigen processing and presentation
Kupffer cell
Liver
Same as macrophages
Microglia cell
Nerve tissue of CNS
Same as macrophages
Langerhans cell
Skin
Antigen processing and presentation
Dendritic cell
Lymph nodes
Antigen processing and presentation
Osteoclast
Bone
Digestion of the bone
Multinuclear giant cell
Connective tissue
Segregation and digestion of foreign bodies
Junqueira & Carneiro, Basic Histology, McGraw-Hill
Plasma cells (plasmocytes) are derived from B lymphocytes and produces antibodies
Ultrastructure of a plasma cell. The cell contains
a well-developed rough ER, with dilated
cisternae containing immunoglobulins
(antibodies). In plasma cells, the secreted
proteins do not aggregate into secretory
granules. Nu, nucleolus.
Gabriel Monteiro, 23-24
Electron micrograph of a plasma cell showing an
abundance of rough ER (R). Note that many cisternae
are dilated. Four profiles of the Golgi complex (G) are
observed near the nucleus (N). M, mitochondria.
Junqueira & Carneiro, Basic Histology, McGraw-Hill
Adipose tissue is rich in adipocytes which are also found isolated or in small groups in other
connective tissues is highly vascularized. It is the largest organ in the body… (in men 15-20% and in
women 20-25% of body weight)
Yellow/white (unilocular) adipose tissue stores energy as
triglycerides, 9.3 kcal/g (muscles and liver also store
energy but in glycogen form, 4.1 kcal/g).
Brown (multilocular) adipose tissue produces heat and
is abundant in newborns (and hibernating animals)
Photomicrograph of multilocular adipose tissue (lower portion) with its
characteristic cells containing central spherical nuclei and multiple lipid
droplets. For comparison, the upper part of the photomicrograph shows
unilocular tissue (showing adipocytes’ nuclei compressed against the cell
membrane).
Gabriel Monteiro, 23-24
Junqueira & Carneiro, Basic Histology, McGraw-Hill
Process of lipid storage and release by the adipocyte
endhotelial cell
capillary
Triglycerides are transported in blood from the intestine and liver by lipoproteins known as chylomicrons and VLDLs. In
adipose tissue capillaries, these lipoproteins are partly broken down by lipoprotein lipase, releasing fatty acids. The free fatty
acids diffuse from the capillary into the adipocyte, where they are re-esterified to glycerol phosphate, forming triglycerides.
These resulting triglycerides are stored in droplets until needed. Norepinephrine from nerve endings stimulates the cAMP
system, which activates hormone-sensitive lipase. Hormone-sensitive lipase hydrolyzes stored triglycerides to free fatty acids
and glycerol. These substances diffuse into the capillary, where free fatty acids are bound to the hydrophobic moiety of
albumin for transport to distant sites for use as an energy source.
Gabriel Monteiro, 23-24
Junqueira & Carneiro, Basic Histology, McGraw-Hill
Thermogenin dissipates the proton electrochemical gradient
Gabriel Monteiro, 23-24
Cartilage tissue is characterized by chondrocytes and an ECM enriched with GAGs and
proteoglycans. Variations in the ECM composition originate hyaline, elastic and fibrous
cartilages.
Photomicrograph of hyaline cartilage. In embryo serves as a temporary skeleton. In adults is located
in the articular surfaces of movable joints, in the walls of the larger respiratory passages (nose,
larynx, trachea, bronchi), in the ventral ends of ribs and at the ends of bones (epiphyseal plate)
Chondrocytes are located in matrix lacunae. The upper and lower parts of the figure show the
perichondrium stained pink. Note the gradual differentiation of cells from the perichondrium into
chondrocytes.
Gabriel Monteiro, 23-24
Junqueira & Carneiro, Basic Histology, McGraw-Hill
Bone tissue supports fleshy structures, protects vital organs (cranial and thoracic cavities) and harbours
the
bone marrow where blood is formed. Is highly vascularized and metabolically active. It serves as a reservoir of
ions (calcium, phosphate, etc).
Has a mineralized ECM and inside lacunae, osteocytes/osteoblasts which synthesize the organic ECM, and
osteoclasts which make reabsorption and remodeling of the bone tissue.
Photomicrograph of bone. The lacunae and canaliculi
filled with air deflect the light and appear dark, showing
the communication between these structures through
which nutrients derived from blood vessels flow.
Gabriel Monteiro, 23-24
Schematic drawing of a long-bone diaphysis. At the right
is a haversian system showing lamellae, a central blood
capillary (there are also small nerves, not shown).
Junqueira & Carneiro, Basic Histology, McGraw-Hill
Bone resorption
Lysosomal enzymes packaged in the Golgi complex and protons are released into the bone
matrix. The acidification facilitates the dissolution of calcium phosphate from bone and is
the optimal pH for the activity of lysosomal hydrolases (e.g. collagenases). Bone matrix is
thus removed and the products of bone resorption are taken up by the osteoclast’s
cytoplasm, probably digested further, and transferred to blood capillaries.
Gabriel Monteiro, 23-24
Junqueira & Carneiro, Basic Histology, McGraw-Hill
Blood consists of cells (erythrocytes, platelets (thrombocytes), and leukocytes) and plasma (ECM):
albumins, g-globulins, lipoproteins, prothrombin and fibrinogen, signaling molecules, water and ions.
(serum is plasma without the coagulated proteins)
Cell type
Main products and functions
Erythrocyte
Hemoglobin - CO2 and O2 transport
Platelet
Blood-clotting factors - Clotting of blood
Neutrophil
Rich in specific granules - Phagocytosis of bacteria
Eosinophil
Rich in specific granules - Defense against parasites; modulation of inflammation
processes
Basophil
Rich in specific granules - Inflammation mediation
Monocyte
Rich in specific granules - Phagocytosis of protozoa and virus and senescent cells
B lymphocyte
Immunoglobulins - Production of antibodies
T lymphocyte
Killing of virus infected cells and modulation of other leukocytes (interleukins)
Natural killer cell
Attacks some tumor and virus-infected cells
“Granules” are vesicles and lysosomes rich in enzymes, proteins carbohydrates and signaling molecules
Gabriel Monteiro, 23-24
Junqueira & Carneiro, Basic Histology, McGraw-Hill
Main components and functions of blood
Gabriel Monteiro, 23-24
Junqueira & Carneiro, Basic Histology, McGraw-Hill
CO2 and O2 transport by erythrocytes and plasma
80% of the CO2 is transported
as HCO3- (2/3 of it in plasma)
In tissues, CO2 is produced
Gabriel Monteiro, 23-24
Blood clotting
Gabriel Monteiro, 23-24
Bone marrow (myeloid tissue) is
found in the hollow interior of bones. It constitutes 4% of total body
weight, and is responsible for hematopoiesis (erythropoiesis, granulonopoiesis, monocytopoiesis,
megacaryocytopoiesis or thrombopoiesis).
- Network of stromal cells (fibroblasts, macrophages, adipocytes, osteoblasts,
osteoclasts, endothelial cells forming the sinusoids) and hematopoietic cells
- Produces 2.5x109 erythrocytes and 2.5x109 platelets and 50-100x109
granulocytes per day and per kg of body weight!
- Removes (like liver and spleen) damaged erythrocytes
- Is the place for B lymphocytes maturation
Section of active red bone marrow showing
some of its components. Six blood sinusoid
capillaries containing many erythrocytes are
indicated by arrowheads.
A femur showing its red bone marrow and a focus of yellow bone marrow consisting mainly of fat
cells (progressively substitutes red marrow in adults)
Gabriel Monteiro, 23-24
Junqueira & Carneiro, Basic Histology, McGraw-Hill
Lymphoid tissue. Circulating lymphocytes originate (lymphopoiesis) mainly in the thymus
and the peripheral lymphoid organs (spleen, lymph nodes, tonsils). Some migrate to thymus
where they become T-lymphocytes and other differentiate at bone marrow, B-lymphocytes
The lymphoid organs and lymphatic vessels are
widely distributed in the body. The lymphatic vessels
collect lymph from most parts of the body and
deliver it to the blood circulation primarily through
the thoracic duct.
Gabriel Monteiro, 23-24
Muscle tissue is divided in 3 types:
Cardiac muscle is composed of
irregular branched cells bound
together longitudinally by
intercalated disks.
Smooth muscle is an agglomerate of
fusiform cells.
Skeletal muscle is composed of
large, elongated, multinucleated
fibers.
Gabriel Monteiro, 23-24
- Skeletal muscle contracts quickly, forcefully and under voluntary control
- Long multinucleated fibers (cells), up to 35 cm in length and 10-100 µm in diameter, form
bundles, and result from the fusion of embryonic mononucleated myoblasts
- Can undergo limited regeneration (from inactive myoblasts)
Longitudinal section of striated
muscle fibers. The blood vessels
were injected with a plastic material
before the animal was killed.
Gabriel Monteiro, 23-24
Striated skeletal muscle in
longitudinal and cross
sections. The nuclei can be
seen in the periphery of
the cell.
Junqueira & Carneiro, Basic Histology, McGraw-Hill
Schematic representation of the thick (myosin) and thin
filament (actin, tropomyosin, and troponin (TnI, TnC, and TnT))
Gabriel Monteiro, 23-24
Junqueira & Carneiro, Basic Histology, McGraw-Hill
Sequential activation of gated ion channels at a neuromuscular junction
(or motor end-plate)
Arrival of an action potential at the terminus of a presynaptic motor neuron induces opening of voltage-gated Ca2+ channels
(step 1) and subsequent release of acetylcholine, which triggers opening of the ligand-gated nicotinic receptors in the muscle
plasma membrane (step 2). The resulting influx of Na+ produces a localized depolarization of the membrane, leading to
opening of voltage-gated Na+ channels and generation of an action potential (step 3). When the spreading depolarization
reaches T tubules, it triggers opening of voltage-gated Ca2+ channels and release of Ca2+ from the sarcoplasmic reticulum into
the cytosol (step 4). The rise in cytosolic Ca2+ causes muscle contraction (see next slide).
Gabriel Monteiro, 23-24
Lodish et al., Molecular Cell Biology, W.H. Freeman
Molecular mechanism of contraction
Muscle contraction, initiated by the binding of Ca2+ to the TnC unit of troponin, which exposes the myosin binding site on
actin (cross-hatched area). In a second step, the myosin head binds to actin and the ATP is hydrolysed yielding energy,
which produces a movement of the myosin head. As a consequence of this change in myosin, the bound thin filaments
slide over the thick filaments reducing the distance between the Z lines, thereby shortening of the whole muscle fiber.
Gabriel Monteiro, 23-24
Junqueira & Carneiro, Basic Histology, McGraw-Hill
- Cardiac muscle contracts vigorously, rhythmically and under involuntary control
- Cells are 85-100 µm in length and 15 µm in diameter
- Has almost no regenerative capacity beyond early childhood.
Photomicrograph of cardiac muscle. Note the crossstriation and the intercalated disks (arrowheads)
which are enriched in gap junctions to assure ionic
continuity between adjacent cells. Thus, muscle to
act as a syncytium allowing the signal to contract
to pass in a wave from cell to cell.
Gabriel Monteiro, 23-24
Junqueira & Carneiro, Basic Histology, McGraw-Hill
- Smooth muscle contracts slowly and under involuntary control
- Lengths from 20 to 500 µm
- Contraction does not rely in a paracrystalline organization of actin and myosin and
depends on the phosphorylation of myosin and of calcium binding protein, calmodulin, but
not dependent of tropomyosin
- Smooth muscle is capable of active regeneration
Photomicrographs of smooth muscle cells in cross
section (upper) and in longitudinal section (lower).
Note the centrally located nuclei.
Gabriel Monteiro, 23-24
Junqueira & Carneiro, Basic Histology, McGraw-Hill
Smooth muscle contraction and relaxation
contraction
Gabriel Monteiro, 23-24
Nerve tissue is composed of nerve cells (neurons) which sense, process and respond to features of both
internal and external environment, glial cells (neuroglia) which occupy space between neurons and modulate their
functions. Each neuron has many interconnections with other neurons.
General functional organization of CNS and PNS
Gabriel Monteiro, 23-24
Junqueira & Carneiro, Basic Histology, McGraw-Hill
Neurons are responsible for the reception, transmission, and processing of stimuli, the triggering of certain cell
activities, and release of neurotransmitters. Generally, receive information via their dendrites and transmit
information via their axons to other neurons or other cells forming synapses.
Where neurons and their target cells
meet, information is transmitted
across synapses by the release of
neurotransmitters.
Gabriel Monteiro, 23-24
Glial cells physically support neurons and perform many housekeeping functions
Glial cell type
Location
Main functions
Oligodendrocyte
CNS
Myelin production, electric insulation
Schwann cell
Peripheral nerves
Myelin production, electric insulation
Astrocyte
CNS
Structural support, repair processes, blood-brain
barrier, metabolic exchanges
Ependymal cell
CNS
Lining cavities of CNS
Microglia
CNS
Macrophagic activity
All these cells are derived from progenitor cells in neural tube except microglia which is formed at bone marrow
Gabriel Monteiro, 23-24
Junqueira & Carneiro, Basic Histology, McGraw-Hill
Membrane potential
Neurons have an electric charge difference across their plasma membranes. The difference in voltage across
membrane is called membrane potential. In an unstimulated neuron is called resting potential. Nerve impulses
are also called action potentials and travel along the plasma membrane
- The negative resting potential is created by the 3Na+/2K+ ATPase and K+ and Na+ ion channels.
- Na+- K+ pump moves 2 K+ ions inside the cell as 3 Na+ ions are pumped out.
- K+ ions diffuse out of the cell at a faster rate than Na+ ions diffuse into the cell because neurons have more K+ leakage channels than
Na+ leakage channels.
Gabriel Monteiro, 23-24
Action potentials (speed up to 100 m/s) result
from rapid changes in voltage-gated Na+ and K
+ channels.
An action potential is a rapid reversal in charge
across a portion of the plasma membrane
resulting from the sequential opening and
closing of voltage-gated sodium and potassium
channels. These changes in voltage-gated
channels occur when the plasma membrane
depolarizes to a threshold level.
Gabriel Monteiro, 23-24
Synapses are functional connections for
communication between neurons or
neurons and other cells
Synaptic transmission
begins with the arrival
of an action potential
Synapses can be
excitatory or
inhibitory (the
Gabriel Monteiro, 23-24
neuromuscular is always
excitatory)
Molecular mechanism of vesicle fusion
Synaptotagmin
SNAREs can be divided into two
categories: vesicle or v-SNAREs,
which are incorporated into the
membranes of transport vesicles
during budding, and target or tSNAREs, which are associated with
nerve terminal membranes.
Ca2+
SNARE complex
But other proteins are involved!
Gabriel Monteiro, 23-24
Annu. Rev. Biophys. 2015. 44:339–367
Take home message
A tissue is a collection of cells and ECM that perform a given function. There are 7 main classes of cells in the mature human
body: blood, myocyte, epithelial/endothelial, stem /germ/pericyte, adipocyte, neural/glia, and fibroblast/osteoid.
Epithelial tissues are composed of closely aggregated cells with very little extracellular space, showing strong adherence to
each other (e.g., tight junctions). They are not directly irrigated by blood vessels.
Connective tissues are composed mainly of ECM. They are originated from the mesenchyme. They provide and maintain
form in the body (e.g., bone and cartilage), and metabolic aid for other tissues (e.g., adipose tissue). Connective tissues are
highly vascularized.
Blood consists of cells (erythrocytes and leukocytes) and plasma (ECM, proteins, signaling molecules, water and ions). The
bone marrow is the place of hematopoiesis (blood formation).
Macrophages are polymorphic phagocytic cells that reside in several organs: blood, connective tissue, liver (e.g., Kupffer
cells), skin (e.g., Langerhans cells), bone (e.g., osteoclasts), and brain (e.g., microglia).
Circulating lymphocytes can migrate to the thymus (T-lymphocytes), where others mature in the bone marrow (Blymphocytes).
Gabriel Monteiro, 23-24
Take home message
Muscle tissue is divided in 3 types: skeletal, cardiac, and smooth muscle.
Skeletal muscle is composed of large, elongated, multinucleated fibers, that result from the fusion of mononucleated
myoblasts. It can undergo voluntary movement. Muscle contraction is initiated by the binding of Ca2+ to troponin, which
exposes the myosin binding site to actin, producing movement and the shortening of the whole muscle fiber.
Cardiac muscle contracts vigorously, rhythmically and under involuntary control. Highly vascularized, has limited
regenerative capacity. It is rich in gap junctions to assure ionic continuity between adjacent cells, and rhythmic contraction
to pass in a wave from cell to cell.
Smooth muscle contracts slowly and under involuntary control. Contraction does not rely on the movement of actin and
myosin fibers. It is dependent on the calcium binding protein calmodulin, activation of protein kinase G, and
dephosphorylation of myosin.
Nerve tissue is composed of neurons and glial cells. The central nervous system communicates with the peripheral nervous
system that receives signals from the environment.
Neurons have an electric charge difference across their plasma membrane. The difference in voltage across the membrane is
a membrane potential. In an unstimulated neuron it is called resting potential. Nerve impulses are also called action
potentials and travel along the plasma membrane until they reach a synapse. There, the opening of calcium channels causes
the release of neurotransmitters via synaptic vesicles.
Thus, an action potential is a rapid reversal in charge across the plasma membrane resulting from the sequential opening
and closing of voltage-gated Na+ and K+ channels. Vesicular transport and membrane fusion in synapses is mediated by the
SNARE complex: vSNAREs in the membrane of transport vesicles, and t-SNAREs associated with nerve terminal membranes.
Gabriel Monteiro, 23-24
Tissue dynamics
- Chemical, electrical and mechanical signaling
- Cell stress, inflammatory responses and cell death
Gabriel Monteiro, 23-24
Tissue Dynamics
The three dynamic states of tissues and the underlying cellular-fate processes
Gabriel Monteiro, 23-24
Tissue homeostasis (equilibrium): the normal steady-state function of tissue
- Some tissues produce cells (bone marrow, skin) as their main function, while others produce a secreted product (glands).
Some tissues primarily carry out mass-transfer operations (lungs, kidneys) while others are biochemical “refineries” (liver) or
can adapt to physiological need (hypertrophy of muscle)
Tissue repair: wounded tissue displays a healing process that is relevant to tissue engineering
- A biopsied piece or a graft of tissue is expected to initially
display a healing-type response after being placed in culture or
engrafted.
Tissue repair occurs in phases: Early in the process (days),
there is a coordination between cell proliferation, adhesion
and migration. Remodeling of the wound occurs later (weeks
to years) as a result of cell differentiation and ECM proper
formation.
The healing response is faster in fetus and slower in adults
Tissue formation: the formation of tissue involves developmental biology including morphogenesis (describes the
evolution and development of form). Morphological changes are important in the formation and subsequent function of the
tissue and are fundamental to tissue formation and repair
Gabriel Monteiro, 23-24
After fertilization of an egg, several cell divisions and differentiation (is the process where a cell changes from one cell
type to another) take place. This spherical mass reorganizes forming blastocyst containing a cavity, and starting
gastrulation which is a large-scale morphogenic process.
or embryonic stem cells (ESCs)
Gabriel Monteiro, 23-24
The underlying molecular-control mechanisms of morphogenic processes (which proceed on a characteristic
time scale) are not known in detail but they are dependent on the cell-fate processes (division, differentiation,
death, movement and adhesion) that rely on:
- direct cell-cell interactions
- cell-ECM interactions
- chemical signals
- mechanical signals
- electrical signals
Organ and tissue growth result from an integration of biophysical communication across biological scales, both in time and
space
Tissues and organs grow to the morphology required for their function with phenomenal precision. Many animals can even
regenerate differentiated tissues.
Gabriel Monteiro, 23-24
Common convergences between ubiquitous signalling pathways
influencing tissue maturation
transcription factors
Gabriel Monteiro, 23-24
Black arrows represent
activation while red hashes
represent inhibition; solid lines
represent putatively direct
interactions while dashed lines
represent indirect effects
Regenerative Medicine (2022) 7:44
Interpretation of morphogen signal
Morphogens (M) usually act by binding to transmembrane receptors
(R) and initiating signaling cascades, ultimately leading to the activation
of morphogen effectors, commonly transcription factors (TF), which
allow the expression of target genes (gene X).
Gabriel Monteiro, 23-24
As a morphogen (green circle) gradient is established,
naïve cells are exposed to differing concentrations of the
morphogen originating different cell types (red, white and
blue).
Annu. Rev. Biomed. Eng. 2016. 18:1–24
Morphogen concentration gradients are dynamic systems that can confer spatial information to cells, which can
respond to a fold change in ligand levels (i.e. rate of change), rather than absolute levels.
By analyzing Smad4 activation dynamics, nodal triggers a rapid, adaptive target response dependent on the rate
of ligand concentration change. On the contrary, BMP signaling dynamics were found to depend on absolute
ligand concentration.
Gabriel Monteiro, 23-24
Curr Opin Cell Biol 2021, 73:50–57
Control of bone cell differentiation
Differentiation of osteoclasts from
haematopoietic stem cells (HSCs) occurs
through a series of steps (osteoclastogenesis)
controlled by CSF-1 (produced by stromal
cell) and RANKL, which is located on the
surface of the osteoblasts (and T cells).
Differentiation of the osteoblasts from
mesenchymal stem cells (MSCs) occurs
through a series of steps controlled by the
Wnt signalling pathway. The osteoclasts
release sclerostin (SOST), which inhibits the
Wnt signalling to reduce osteoblastogenesis.
As the osteoblasts secrete bone (white
arrows), they gradually become buried in the
mineralized matrix where they are
transformed into star-shaped osteocytes
Gabriel Monteiro, 23-24
Cell Signalling Biology, M.J. Berridge, 2014, Portland Press
Electrical stimulation induces proliferation and differentiation in
mesenchymal stem cells and preosteoblasts
Electric field application leads to an increase of
intracellular Ca2+ and subsequent activation of
gene expression.
CREB/CRE cAMP response element-binding protein/cAMP
response element; ER endoplasmic reticulum; IP3 inositoltriphosphate; mTOR mammalian target of rapamycin; NF-AT
nuclear factor of activated T-cells; PI3K phosphatidylinositol 3kinase; PIP2 phosphatidylinositol- 4,5-bisphosphate; PIP3
phosphatidylinositol-3,4,5-trisphosphate; PLC phospholipase C;
SACC stretch-activated cation channel; VGCC voltage-gated
calcium channel.
Gabriel Monteiro, 23-24
Biomedical Materials & Devices, https://doi.org/10.1007/s44174-022-00028-x
Changes in Vmem within and among cells in a network
(A) Vmem is a measure of the resting membrane potential
across a plasma membrane of a cell created by pumps and
channels that regulate the movement of ions across the plasma
membrane. Resting Vmem can vary within a cell and during
phases of the cell cycle. However, the resting Vmem is generally
associated with the proliferative state of a cell, becoming
hyperpolarized with progressive differentiation.
(B) When cells are coupled in a series, voltage differential is
minimized through ionic currents flowing through gap
junctions.
(C) Recent work has shown that key properties of Vmem
regulation can be modeled through a simple integrated
feedback circuit that considers the additive effects of inwardly
rectifying (Kir) and leak (KL) potassium channels. Cm,
membrane capacitance; g, conductance of channel; E,
electromotive force of channel.
Gabriel Monteiro, 23-24
Development. 2021; 148(10): dev180794
Large-scale bioelectric patterns are instructive for shape
Bioelectric signaling controls tissue shape and structure Understanding of the bioelectric circuit that controls, for example, anterior–
posterior specification in a fragment of regenerating Planaria can be used to design drug cocktails that alter the anatomical structure thus
produced, such as inducing the posterior-facing blastema to build a secondary head in Planaria.
Abbreviations: hpa, hours postamputation; IVM, ivermectin; SCH, SCH-28080
Gabriel Monteiro, 23-24
Annu. Rev. Biomed. Eng. 2017. 19:353–87
Large-scale bioelectric patterns are instructive for shape
Depolarization of host tissues in the context of an eye transplant induces drastic overproliferation of nerve emerging from the implanted
organ in comparison to a control host. This technique can be used to pattern the ectopic nerve, inducing it to connect to specific regions by
patterning the activation of ion channels in the surrounding tissue.
Abbreviations: hpa, hours postamputation; IVM, ivermectin; SCH, SCH-28080
Gabriel Monteiro, 23-24
Annu. Rev. Biomed. Eng. 2017. 19:353–87
Information flow and molecular origins of mechanics
Intricacies involved with connecting molecular, cellular, and tissue scale behaviors and mechanisms. At
the molecular scale, there is molecular signaling which causes intermolecular force production. This
force production then feeds back into more molecular signaling. From the molecular scale, there are
resultant forces and cell shape changes/movements on the cellular scale, which induce signaling into
neighboring cells. The cellular scale can then feedback into molecular scale dynamics or result in tissue
scale movements or bulk mechanical property changes. Isolating any portion of this intricate feedback
loop is extremely difficult without considering all upstream and downstream effects.
Gabriel Monteiro, 23-24
Nat Rev Genet 2013, 14(10): 733–744
The different types of mechanical cues cells experience
(a) Fluid flow generates a shear stress parallel to the cell surface and in the direction of fluid flow.
(b, c) Compression(/stretching) occurs when a pushing force presses the cell inward causing it to be compacted.
(d) Cells are surrounded by matrix proteins. Cells respond to changes in matrix stiffness by tuning their internal contractility.
(e) A protrusive force is generated by the polymerization of actin at the leading edge. Actin monomers are added at the plus end which is oriented towards
the plasma membrane. A protrusive force pushes the cell membrane forward.
(f) Cells forming adhesions with adjacent cells can experience a tugging force from increased tension in the circumferential actin belt that connects the cells.
(g) Increased internal contractility of cells is derived from the molecular motor myosin binding and pulling the actin filaments in opposite directions, thereby
generating traction forces.
Gabriel Monteiro, 23-24
Biol. Cell. 2023;115:e202200108
Integrins and cadherins modulate the mechanical landscape of the cell
Integrin-based focal adhesions* (A) and cadherin-dependent adherens junctions (B) relay mechanical signals through a contractile
actin–myosin network (C) to actively modulate the mechanical landscape of the cell.
Focal adhesions and adherens junctions form the linkages of the cell to the ECM and to neighboring cells, respectively. Integrins and
cadherins are linked to the intracellular actin–myosin network and are thus intrinsically linked to each other.
*Focal adhesions share some similarities with desmosomes, although they differ in that integrins are linked to actin filaments rather than intermediate filaments
Gabriel Monteiro, 23-24
J Cell Sci (2016) 129, 1093-1100
Intracellular mechanosensation pathways that accelerate glycolysis
(b) Cell-cell adhesion forces are sensed through Ecadherin, which forms a complex with and activates
LKB1 as well as AMPK. AMPK and the membranecytoskeletal protein vinculin are phosphorylated by
LKB1 and Abl, respectively. Vinculin activity enhances
actin remodelling through the Rho/ROCK pathway,
whereas AMPK promotes glucose uptake and ATP
production in order to maintain energy supply to
adhesions.
LKB1, liver kinase B1; AMPK, AMP-activated protein kinase; Abl, tyrosine-protein kinase; FAK, focal adhesion kinase; MLC, myosin light
chain; MLCK, myosin light-chain kinase; p38, P38 mitogen-activated protein kinase; PIP2, phosphatidylinositol 4,5-bisphosphate; PIP3,
phosphatidylinositol (3,4,5)-trisphosphate; ROCK, Rho-associated kinase; RTK, receptor tyrosine kinase; Src, proto-oncogene tyrosineprotein kinase.
Gabriel Monteiro, 23-24
(d) Cell-matrix forces are sensed through integrins in
focal adhesion complexes, which promote actin fiber
remodelling (also simulation of RTKs promotes actin
remodelling (c)) through Rho/ROCK and JNK/p38
signaling. Actin fibre remodelling, integrates all three
signaling pathways, and enhances transcriptional
activity of YAP/TAZ as well as release of glycolytic
enzymes in the cytosol. The cytoskeleton also
sequesters TRIM21 from the cytosol, preventing
proteasomal-mediated degradation of PFK. These
processes culminate in acceleration of glucose
metabolism.
Nat Metab. 2021 ; 3(4): 456–468
Integrins alter cell metabolism in response to increased
matrix stiffness
(a) On soft matrices TRIM21 targets PFK1 for degradation.
Additionally, sterol regulatory element binding proteins (SREBP) are cleaved
and are then trafficked to the nucleus. In the nucleus, SREBP signals for
increased lipid synthesis.
(b) On stiff matrices, TRIM21 is sequestered by actin stress
fibers, which protects PFK1 from degradation and promotes
glycolysis. The transcriptional co-activators YAP/TAZ are
activated by stiff matrices and increase glutaminase (GSL1),
thereby promoting glutaminolysis.
A stiff matrix also promotes kindlin localization to the mitochondria
promoting proline synthesis.
Gabriel Monteiro, 23-24
Biol. Cell. 2023;115:e202200108
Reciprocal regulation of mechanics and metabolism in cancer
PFK
Under normal conditions, the compliant ECM suppresses JNK/p38 signaling,
and promotes either retainment of inactive YAP/TAZ in the cytosol or its
degradation by proteasomes. Cells show reduced actin cytoskeleton
assembly and TRIM21 binds to PFK promoting its degradation.
GLUT, glucose transporter; GLS1, glutaminase 1; Ub, ubiquitin, PFK, Phosphofrutokinase 1
Gabriel Monteiro, 23-24
In cancer, ECM stiffening accelerates glycolysis through JNK/p38 and YAP/TAZmediated metabolic reprogramming, and induces cytoskeleton remodelling,
(TRIM21 becomes inactive) resulting in the release of glycolytic enzymes in the
cytosol, thereby promoting glucose metabolism. Transcriptional programs of
glucose and glutamine metabolism are promoted. Glutamine metabolic and
glycolytic end-products feed into the TCA cycle, increasing the abundance of
oncometabolites (fumarate, succinate, and 2-HG).
Nat Metab. 2021 ; 3(4): 456–468
Molecular connectivity from the ECM to the nucleus and nuclear
membrane mechanotransduction
Nesprins bind to actin and to cytoskeletal cross-linkers
(plectin and kinesin) and with SUN proteins. The complex
SUN-nesprins act as the physical link connecting the
nucleus and the cytoskeleton.
a) The nuclear envelope protein conformational changes
responding to the exert force applied on the nucleus.
b) Nuclear membrane stretch in response to force opens
nuclear pore complexes, calcium channels, and activates
cPLA2 on the cytoplasmic side, thus increasing calcium
release, import of transcription factors (TFs), and
production of arachidonic acid in the nucleoplasm.
c) Mechanical forces applied to the nucleus may induce
chromatin opening and epigenetic changes, that promote
accessibility to TFs and regulate gene expression.
Gabriel Monteiro, 23-24
Adv. Sci. 2023, 10, 2204594
Osteogenic differentiation via mechanical and non-mechanical signals
Model of substrate mediated osteogenic differentiation wherein substrate stiffness (mechanical signal) activates
mechanotransduction pathway involving YAP/TAZ (1 A-1B) and non-mechanical signals from substrate leads to
osteogenesis via canonical BMPR signaling pathway (2).
Gabriel Monteiro, 23-24
Biomaterials Research 27: 55 (2023)
Neurogenesis via mechanotransduction
The nanotopography manipulates the focal adhesion signaling pathway and neurogenic differentiation
Gabriel Monteiro, 23-24
Biomaterials Research 27: 55 (2023)
Recalling…
Cell metabolism
Cells can use multiple metabolic pathways to produce energy, antioxidant power and intermediates for the
biosynthesis of macromolecules
Glycolysis provides precursors for the synthesis of amino
acids, nucleotides, fatty acids and for glycosylation. In
mitochondria, oxidative phosphorylation transfers electrons
produced by the tricarboxylic acid (TCA) cycle to the
respiratory complexes, which creates the electrochemical
gradient needed for ATP synthesis. This oxygen dependent
process can be fuelled by pyruvate, fatty acids (through
mitochondrial fatty acid oxidation) and amino acids.
Conversely, TCA cycle intermediates can be used for anabolic
processes such as amino acid and fatty acid synthesis. The
amino acid glutamine is an important fuel that can be used to
sustain the TCA cycle (oxidative glutamine metabolism) but
also to directly provide precursors for fatty acid synthesis and
for the synthesis of antioxidant molecules (reductive
glutamine metabolism).
Gabriel Monteiro, 23-24
Nat Rev Mol Cell Biol 22, 22–38 (2021)
Recalling…
Metabolism and differentiation
Nonproliferating tissues metabolize glucose to pyruvate via glycolysis and then completely oxidize pyruvate in the
mitochondria through the Krebs cycle in the process of oxidative phosphorylation. When oxygen is limiting, cells can
redirect pyruvate to generate lactate (anaerobic glycolysis). The Warburg effect is observed in proliferative tissues (normal
or cancer cells) that tend to convert glucose to lactate regardless of whether oxygen is present (aerobic glycolysis).
Gabriel Monteiro, 23-24
Science 324: 1029-1033 (2009) doi:10.1126/science.1160809
Take home message
We can define three dynamic states of tissues and the underlying cellular-fate processes: homeostasis, tissue repair, and
morphogenesis.
The formation of a complete organism from a single fertilized egg requires the generation of large numbers of cells, which
at the appropriate times acquire specialized functions and morphologies, while assembling into well-defined structures,
tissues, and organs.
Cell activity is guided by soluble factors, extracellular matrix, tension/pressure, and bioelectrical properties. These stimuli
orchestrate cell behavior during homeostasis, morphogenesis and regeneration. Normal balance is subverted during
oncogenic transformation and aging.
Morphogenesis depends on the cell-fate processes (division, differentiation, death, movement and adhesion) , which in
turn rely on direct cell-cell and cell-ECM interactions and chemical, mechanical and electrical signals integrated both in
time and space.
Besides the type of the chemical signal, its concentration and its rate of change define the cell response.
The resting membrane potential is generally associated with the proliferative state of a cell (e.g., hyperpolarized with
progressive differentiation). Electrical stimulation induces proliferation and differentiation due to voltage-sensitive sensors
(e.g., Ca2+ channels)
Gabriel Monteiro, 23-24
Take home message
Cells/tissues respond to different internal and external mechanical signals through focal adhesions (ECM-cell) and adherens
junctions (e-chaderins, cell-cell)
Mechano-dependent cell response (in a stiff substrate or subjected to a force) rely on ECM-cell interactions, which promote
release of glycolytic enzymes, avoid PFK binding by TRIM21, availability of YAP/TAZ which promote the glycolytic
metabolism and glutaminolysis. Also, cell-cell interactions activate AMKP that promote glucose uptake. In cancer, ECM
stiffening also accelerates glycolysis.
The nucleus senses the mechanical forces either directly or indirectly (due to interactions between the cytoskeleton and
nuclear proteins) altering the uptake of ions and transcription factors or altering chromatin structure/gene transcription
Substrate stiffness induces mechanical (via YAP/TAZ) and non-mechanical (via BMP) signals to promote osteogenic
differentiation both altering gene transcription via mechanotransduction. Also, neurogenesis can also occur via
mechanotransduction in response to the nanotopography/stifness.
Gabriel Monteiro, 23-24
Cell Stress, Inflammatory Responses and Cell Death
- Cells are capable of sensing various deleterious conditions, both normal
and pathological, and respond by mounting a variety of stress responses.
- If the stress signal is not too severe, the cell stops growing and enters a
state of senescence. Another example of an evolutionarily conserved
survival mechanism is autophagy, which enables cells to cope with
periods of starvation. If such stresses become too severe, the cell dies,
either through a process of necrosis or through apoptosis.
- Necrosis and apoptosis are clearly distinct but share some similarities in
that they are induced by similar stimuli and often employ the same
signalling mechanism. Necrosis occurs when the cell is overwhelmed by
the insult and rapidly disintegrates, causing release of the cellular
contents into the intercellular space where they can elicit an
inflammatory response. By contrast, apoptosis is a much more orderly
affair in that proteases and nucleases within the confines of an intact
plasma membrane disassemble the cell that gradually shrinks in size and
is then engulfed by neighbouring cells, thus avoiding any inflammatory
reactions.
Gabriel Monteiro, 23-24
Cell Signalling Biology, M.J. Berridge, 2014, Portland Press
For example, biological responses to reactive oxygen
and nitrogen species (RONS) mediated stress depend
on the dose
Biomedical Materials & Devices, https://doi.org/10.1007/s44174-022-00028-x
Cell death
How a normal cell may receive signals that trigger
cell death by several controlled biochemical
pathways resulting in apoptosis, autophagy,
necroptosis (which include oncosis and pyroptosis),
or the uncontrolled disruptive necrosis pathway
Gabriel Monteiro, 23-24
Tissue Engineering, JB Clemens & A. Blitterswijk, Academic press, 2023
Inflammation
The innate immune system is triggered by
signals derived from tissue damage and
invading pathogens to activate cells such
as the macrophages, neutrophils, mast
cells, platelets and endothelial cells that
contribute to a co-ordinated series of
responses to both remove the pathogens
and to repair damaged tissues.
1- Tissue damage
2- Endothelial cell damage
3- Platelet aggregation and clot formation
4- Endothelial permeability
5- Cell proliferation
6- Activation of macrophages
7- Activation of mast cells
8- Neutrophil recruitment and activation
9- Monocyte differentiation
Gabriel Monteiro, 23-24
Cell Signalling Biology, M.J. Berridge, 2014, Portland Press
Mechanisms of cell senescence
Normal cells can transform into a non-proliferating senescent state through two main mechanisms. Loss of telomeres results
in replicative senescence. A variety of cellular stresses, including the activation of oncogenes, results in stress-induced
senescence. Oncogenes such as Ras and Myc can activate tumour suppressors (e.g., p16, p53) to divert cells into stressinduced senescence.
These senescence pathways are avoided or switched off during the development of cancer cells. The expression of
telomerase avoids the replicative senescence pathway, whereas the inactivation of the tumour suppressors such as Rb, p16
or p53 prevents the emerging cell from being diverted into stress-induced senescence.
Gabriel Monteiro, 23-24
Cell Signalling Biology, M.J. Berridge, 2014, Portland Press
Molecular mechanisms of autophagy
Autophagy could be induced by various stress
conditions such as amino starvation, glucose depletion,
and others. The common target of these signaling
pathways is the ULK1 complex. Under normal condition,
mTORC1 inhibits ULK1 via phosphorylation. Under stress
condition, mTORC1 is suppressed, leading to activation
and recruitment of the ULK1 complex to PAS.
During an induction process, a membrane protrusion
buds off from the ER and breaks away from the ER to
form an isolation membrane that engulfs mitochondria
and ribosomes to form an autophagic vacuole, which
then fuses with a lysosome where degradation occurs.
fusion
Gabriel Monteiro, 23-24
MedComm. 2022;3:e150.
Autophagic-lysosomal
degradation
Apoptosis
The onset of apoptosis is controlled by a
number of interconnecting processes.
1- Cytokines such as FasL and TNFα act on death
receptors that engage the extrinsic pathway
2- It activates caspase 8
3- It can also recruit the intrinsic pathway by
activating Bid
4- The initiator caspases (e.g. caspases 8, 9 and
10) activate the executioner caspases
5- The intrinsic pathway depends upon an
interaction between ER and the mitochondria.
6- The Bcl-2 superfamily contains both pro- and
antiapoptotic factors that play a major role in
modulating the intrinsic pathway.
7- A number of cell signalling pathways can
modulate the apoptotic signalling network
8- Some of the signalling pathways modulate
apoptosis
9- Some of the pathways can regulate the
transcription of components of the apoptotic
signalsome
10- Genotoxic stress resulting in the activation of
the transcription factor p53
Gabriel Monteiro, 23-24
Cell Signalling Biology, M.J. Berridge, 2014, Portland Press
Strategies to promote vascularization, survival, and
functionality of engineered tissues
So far, the success of tissue engineering constructs is limited to avascular (cartilage, cornea) or thin tissues (bladder, skin),
exhibiting a slow metabolism, and mainly relying on passive oxygen diffusion into the tissue.
Upon implantation and until a proper vasculature is established, a tissue graft can only rely on passive diffusion to assure the
supply of oxygen and nutrients as well as the removal of metabolites. However, this process is limited to about 150-200 mm of
distance to the next supplier vessel. Consequently, a higher cell death rate is often observed in the core of the implant as
compared to the outer layer, which is closer to the host vasculature
The long-term survival of cell-based tissue grafts strongly depends on rapid neovascularization, which is a major hurdle for
clinical translation
Gabriel Monteiro, 23-24
Tissue Engineering, JB Clemens & A. Blitterswijk, Academic press, 2023
Strategies to promote vascularization, survival, and
functionality of engineered tissues
Neovascularization occurs through two different processes:
- formation of new vessels from pre-existing blood vessels, angiogenesis
- de novo formation of blood vessels from endothelial progenitor cells, vasculogenesis
Gabriel Monteiro, 23-24
Tissue Engineering, JB Clemens & A. Blitterswijk, Academic press, 2023
Recalling…
Proliferation of specific cell types: angiogenesis
A process of angiogenesis carries out the growth and repair of blood vessels, during which pre-existing blood vessels give
rise to new vessels. Differentiated endothelial cells that line the inner surface of blood vessels are normally in a quiescent
state (G0), but they return to the cell cycle in response to various growth factors.
In the initial response (stages A–C), a single endothelial cell
differentiates (in a response to VEGF-A released from a tumour)
into a tip cell to initiate the growth of a sprout. As the endothelial
cells (ECs) proliferate, this new sprout grows and new tip cells
appear (stages D and E) to form a branch. The newly formed
vessels then invade the tumour providing a new blood supply.
Gabriel Monteiro, 23-24
The newly differentiated cell tip cell releases platelet-derived
growth factor B (PDGF-B) to stimulate the proliferation of
neighbouring endothelial cells and pericytes and it recruits the
Notch signalling pathway to inhibit these other cells from
becoming tip cells.
Cell Signalling Biology, M.J. Berridge, 2014, Portland Press
Strategies to improve vascular ingrowth into tissue engineered constructs
e.g., VEGF, PDGF (promote angiogenesis),
TGFb (promote vessel maturation)
e.g., vascular or proangiogenic cells
e.g., synthetic or natural
scaffolds/ECM
Gabriel Monteiro, 23-24
Tissue Engineering, JB Clemens & A. Blitterswijk, Academic press, 2023
Common physiological trends in cell and tissue maturation
As metabolically provided energy is
diverted from proliferative activity to
physiological function, cell complexity,
and functional parameters are improved.
This increasing specialization necessitates
an investment of energy to manage cell
size, structure, and specialized structures
or organelles. The energetic outlay and
continued flux for this expenditure is
generally maintained by high-yield and
efficient oxidative phosphorylation from
lipids, short-chain fatty acids,
carbohydrates, amino acids, lactate,
and/or ketones, depending on the
specific tissue and stage of maturation in
question. Metabolic supply is provided by
increased perfusion and spatial zonation,
at which point the tissue can then exert
its hallmark function
*
Gabriel Monteiro, 23-24
*Hypertrophy is the increase in the size of cells
Regenerative Medicine (2022) 7:44
Factors influencing maturation of
myocardial
Factor
Gabriel Monteiro, 23-24
Effect on physiological
maturation
neural tissue
Factor
Effect on physiological
maturation
hepatic tissue
Factor
Effect on physiological
maturation
Regenerative Medicine (2022) 7:44
Signalling molecules in tissue engineering
Gabriel Monteiro, 23-24
Fundamentals of Tissue Engineering and Regenerative Medicine, Meyer U. et al. Springer 2009
In vitro approaches for spatially patterning gene expression
Varying levels of protein production in neighboring cells can
be achieved either (left) by providing cells with varying gene
dosages or (right) by inducing the expression of the same
gene dosage to variable levels.
Both strategies lead to formation of a gradient of protein X. In the former
scenario, cells with higher gene dosage produce greater amounts of the
product protein even though the expression level from each gene copy is
constant between cells. In the latter scenario, all cells have the same number
of gene copies; however, the expression levels of the gene are controlled
differentially (indicated by the thickness of the transcription arrow).
Spatially regulated genetic induction of fibroblasts within three-dimensional matrices.
A spatial distribution of Runx2 retrovirus (R2RV) was created by partially coating the
proximal portion (left) of collagen scaffolds with poly-L-lysine (PLL). (Top) Confocal
microscopy images demonstrating a graded distribution of a FITC-labeled PLL gradient
colocalized with uniformly distributed cell nuclei (DAPI) (blue). (Bottom)
Immunohistochemical staining for enhanced GFP (eGFP) (pink) counterstained with
hematoxylin (blue) revealed elevated eGFP expression on the proximal scaffold portion
coated with PLL+R2RV.
Gabriel Monteiro, 23-24
Annu. Rev. Biomed. Eng. 2016. 18:1–24
Effects of a nanoscale spatial arrangement of RGD on
dedifferentiation of chondrocytes
Schematic illustrating the experimental design. PEG hydrogel surfaces
were nanopatterned with RGD peptides and then cultured with
chondrocytes to explore the effect of material techniques of
nanopatterning on the dedifferentiation of chondrocytes. b Schematic
illustrating the effects of RGD nanopatterns on the dedifferentiation
of chondrocytes. RGD with a nanospacing greater than 70 nm is
beneficial for maintaining the chondrocyte phenotype.
Gabriel Monteiro, 23-24
Regenerative Medicine (2020) 5:14
Metabolism in mesenchymal stem cells (MSCs) under different
oxygen tension levels
Under “sufficient” oxygen, glucose molecules are
broken down in glycolysis for the production of ATP
molecules. By-products of glycolysis and other chemical
components enter the tricarboxylic acid (TCA) cycle in
mitochondria. In OXPHOS, electron byproducts of the
TCA cycle pass through the electron transport chain
(ETC) at the mitochondrial cristae and produce more
ATP molecules. Moreover, HIF-1α is degraded under
“sufficient” oxygen-level conditions by proteosomes.
1,3BPG, 1,3-bisphosphoglycerate; ADP, adenosine diphosphate; ATP, adenosine triphosphate; F-6-P,
fructose- 6 phosphate; G-6-P, glucose- 6-phosphate; GA3P, glyceraldehyde- 3-phosphate; GLUT,
glucose transporter; GPI, glucose-6-phosphate isomerase; HIF, hypoxia-inducible factor; HK,
hexokinase; LDHA, lactate dehydrogenase; MCT, Monocarboxylate transporter; NHE, Na+- H+exchanger; PDH, pyruvate dehydrogenase; PDK1, pyruvate dehydrogenase kinase; PEP, phosphoenolpyruvate; Pi, inorganic phosphate; PK, pyruvate kinase; PPP, pentose phosphate pathway; Ribose-5-P,
ribose- 5-phosphate; Ribulose-5-P, ribulose- 5-phosphate; TKTL1/2, transketolase1/2; Xylulose-5-P,
xylulose-5-phosphate
Gabriel Monteiro, 23-24
Stem Cells. 2020;38:22–33
Metabolism in mesenchymal stem cells (MSCs) under different
oxygen tension levels
In a near-anoxia environment (pO2 < 0.1%), however, (a)
HIF-1α escapes oxygen driven proteosomal degradation
and translocates to the nucleus, where it dimerizes with
HIF-1β. Accumulation of HIF-1 α/β activates (b) the
transcription of genes that increase expression of glucose
transporters and glycolytic enzymes, which (c) increase
glycolytic flux; and (d) decrease activity and eventually
block the OXPHOS pathway. Increased activity of the
glycolytic pathway yields a buildup of lactate, which (e)
increases intracellular pH.
1,3BPG, 1,3-bisphosphoglycerate; ADP, adenosine diphosphate; ATP, adenosine triphosphate; F-6-P,
fructose- 6 phosphate; G-6-P, glucose- 6-phosphate; GA3P, glyceraldehyde- 3-phosphate; GLUT, glucose
transporter; GPI, glucose-6-phosphate isomerase; HIF, hypoxia-inducible factor; HK, hexokinase; LDHA,
lactate dehydrogenase; MCT, Monocarboxylate transporter; NHE, Na+- H+-exchanger; PDH, pyruvate
dehydrogenase; PDK1, pyruvate dehydrogenase kinase; PEP, phosphoenol- pyruvate; Pi, inorganic
phosphate; PK, pyruvate kinase; PPP, pentose phosphate pathway; Ribose-5-P, ribose- 5-phosphate;
Ribulose-5-P, ribulose- 5-phosphate; TKTL1/2, transketolase1/2; Xylulose-5-P, xylulose-5-phosphate
Gabriel Monteiro, 23-24
Stem Cells. 2020;38:22–33
Envisioned timeline of bioenergetic metabolic activity of cells
upon implantation
Before implantation, mesenchymal stem cells (MSCs)
are generally cultured under standard conditions of
21% pO2 and with “sufficient” glucose. Upon
implantation in an ischemic site, MSCs experience
insufficient levels of oxygen tension, which triggers a
switch to glycolysis only and represses, eventually
inhibiting, anabolic activities. Upon glucose
exhaustion, MSCs begin to experience metabolic
stresses, which are, in part, counteracted by the
activation of autophagy. Autophagy, or selfcatabolism, reduces sources of stress and provides
nutrients during times of nutrient withdrawal.
Eventually, the glycolytic reserves are exhausted, and
autophagy is unable to either provide MSCs additional
cell nutrients or mitigate cell stress. Ultimately, cell
death occurs when cells do not meet their minimal
bioenergetic demands. The time points indicated may
vary according to different culture conditions, such as
cell density and mass transport parameters.
Gabriel Monteiro, 23-24
Stem Cells. 2020;38:22–33
Design of the microfluidic platform developed to investigate the
biological cell responses to various stimuli
A) Schematic view of the device for applying electrical,
mechanical and chemical stimulations. The central channel (in
red) is the media channel to provide nutrients and soluble
factors to cells. The pneumatic channels (in light blue) perform
mechanical stimulation by stretching the PDMS membrane
(yellow arrows) where the cells are cultured. The electrical
layer contains two conductive regions composed of a mixture
of CNTs and PDMS (in light gray), which are connected to the
stimulator through two external gold-coated connectors (in red
and black). The uniform electric field across the cell culture
region is represented by the red arrows.
(B) Cross section of the device in the unstimulated
configuration.
(C) Cross section of the device in the electromechanical
stimulated configuration. Applying vacuum in the two lateral
pneumatic channels (in light blue) allows stretching of the cells
on the deformable membrane (in yellow).
Gabriel Monteiro, 23-24
Scientific Reports 5:11800 (2015)
Constraints in experimental design or system optimization in cell
culture and tissue engineering
Gabriel Monteiro, 23-24
Regenerative Medicine (2022) 7:44
A Verger's Dream
Saints Cosmas and Damian performing a miraculous cure by
transplantation of a leg. Master of Los Balbases, 1495
Gabriel Monteiro, 23-24
“Saints Cosmas and Damian were early Christian martyrs who, according to legend,
practiced medicine without payment and therefore were represented to the public
as medical ideals. In this Spanish altarpiece, the saints appear in a vision, dressed in
the full finery of academic doctors as they perform the miracle of transplanting a
leg. The vision is described in a book of 1275 by Jacobus de Voragine, Legenda aurea
(The golden legend). The vision was received in the Church of Saints Cosmas and
Damian, in Rome, by a verger who had a disease that was eating away the flesh of
his leg. One night he dreamed that the two saints came and cut off his bad limb, and
in its place transplanted the leg of a dead African who had just been buried in a
nearby churchyard. When he awoke, the verger found that he had a healthy black
leg, while it was discovered that the African's body now lacked a limb. The
conclusion: "Then let us pray unto these holy martyrs to be our succor and help in all
our hurts, wounds and sores, and that by their merits after this life we may come to
everlasting bliss in heaven. Amen." The painting was probably once in the Church of
Saints Cosmas and Damian in Burgos, in northern Spain. The painter is called the
Master of Los Balbases after a nearby town in which there is an altarpiece by him in
the Church of Saint Stephen.” From https://www.loc.gov/item/2021669915/
Trachea transplantation
http://news.bbc.co.uk/2/hi/7735696.stm
1 Trachea is removed from dead donor patient
2 It is flushed with chemicals to remove all existing cells
3 Donor trachea "scaffold" coated with stem cells from the patient's hip bone marrow. Cells from the airway lining added
4 Once cells have grown (after about four days) donor trachea is inserted into patient's bronchus
Gabriel Monteiro, 23-24
Tissue engineering
- Organ printing, or computer-aided layer-by-layer assembly of biological tissues and organs
- A cell printer that can print gels, single cells and cell aggregates has been developed.
(a) Computer aided design-based presentation of model of cell printer. (b) Bovine aortic endothelial cells were printed in 50 µm size drops in a line. (c) Crosssection of the matrix gel showing the thickness of each sequentially placed layer. (d) Picture of the real cell printer and part of the print head with nine nozzles.
(e). The printer is connected to a bidirectional parallel cable together with 9 jets extent of mixing. Endothelial cell aggregates ‘printed’ on collagen before (f) and
after their fusion (g). Trends Biotech. 21, 157-161 (2003)
Gabriel Monteiro, 23-24
Cultured meat
Dr Mark Post shows the hamburger to the world's press. Photograph: David Parry/EPA
5 August 2013
http://www.dailymail.co.uk/sciencetech/article-2384715/At-tastes-meat--Worlds-test-tube-artificial-beef-Googleburger-gets-GOOD-review-eaten-time.html
Gabriel Monteiro, 23-24
Cultured meat
Currently, technoeconomic analysis estimates to produce one kg of
cultivated meat for $37-$51
Gabriel Monteiro, 23-24
Biotechnol Bioeng. 2021;118:3239–3250
Cultured meat
Companies and start-ups in the cultured meat industry
Consumer acceptance
Gabriel Monteiro, 23-24
Food Bioscience 53 (2023) 102614
Take home message
Cells sense their environment responding with several stress responses. RONS, which vary with metabolism/environment,
mediated stress response (from differentiation to cell death).
Cells under low stress signals may enter senescence or under acute stresses enter autophagy, which enables cells to cope
with periods of starvation. Under high stresses cell die either by necrosis (uncontrolled) leading to inflammation or through
apoptosis (controlled process).
Senescence occurs by telomer loss (replicative senescence) or induced by stress (inactivation of the tumour suppressors as
p16 or p53).
Autophagy (induced by amino starvation, glucose depletion) is regulated by mTORC1 inactivation and consequent formation
of autophagosome and organelle lysis.
Apoptosis depends on several pathways (intrinsic – ER/mitochondria and extrinsic - FasL and TNFα). Both pathways induce
cell death by activating initiator caspases, which then activate executioner caspases, which then kill the cell by degrading
proteins indiscriminately.
Gabriel Monteiro, 23-24
Take home message
The survival of a tissue graft depends on vascularization (not so relevant for cartilage, cornea, bladder, skin), which is
mandatory for clinical purposes. Neovascularization occurs through angiogenesis (formation of new vessels from preexisting ones) or by vasculogenesis (new blood vessels from endothelial progenitor cells).
To vascularize tissues, strategies that include soluble factors, vascular and proangiogenic cells, scaffolds/ECM can be
performed alone or combined.
The metabolism of the more specialized cells relies on energy high-yield and efficient oxidative phosphorylation from
different substrates (lipids, short-chain fatty acids, carbohydrates, amino acids, lactate, and/or ketones) depending on the
tissue. Metabolic supply is provided by increased perfusion (vascularization) and spatial zonation.
The maturation of a specific tissue (e.g. myocardial, neural, hepatic, bone and MSCs) is dependent on a set of specific cues.
These also includes the regulation of the level of gene expression (either by varying gene copy number and/or by varying
promoter strength), and modulation of the characteristics of the scaffold/ECM where cells are layered.
Microfluidic platforms are very useful for studying the cell responses to various stimuli. The development of a platform to
produce tissues for transplantation should also consider other factors (e.g., costs, process robustness)
Tissue engineering and organ printing may assist the assembly of biological tissues and organs for regenerative medicine
applications. As a side note, similar technologies are being employed to generate animal meat alternatives for human diet.
Gabriel Monteiro, 23-24