Cellular Pathology (VPM 152) Lecture 1 (web) Paul Hanna Jan 2016 CELLULAR PATHOLOGY “All organ injuries start with structural or molecular alterations in cells” concept began by Virchow in 1800's • modern study of disease attempts to understand how cells react to injury, often at the subcellular or molecular level, and how this is manifested in the whole animal. J Clin Invest. 2006; 116(8): 2272–79 Podocyte cell body Primary process Foot processes Glomerular podocytes of normal mouse Degeneration / loss of podocyte foot processes in mouse with defective laminin in the glomerular basement membrane NORMAL CELLS • to understand the abnormal, you first have to understand the normal! © Pearson Education Inc. PLASMA MEMBRANES • phospholipid bilayer with embedded proteins / glycoproteins / glycolipids • semipermeable membrane with pumps (ionic/osmotic balance), receptors, adhesion molecules, etc Fig 1-3 (Zachary) A variety of functions are performed by different types of transmembrane proteins. NUCLEUS Robbins & Cotran, 9th ed • chromatin (euchromatin vs heterochromatin) • nucleolus (synthesis of rRNA) • transcription of genes to mRNA moves to cytoplasm for translation to protein MITOCHONDRIA • site of oxidative phosphorylation, the main source of ATP Intermembrane space Mitochondria are present in almost all mammalian cells; exceptions are erythrocytes, lens fibers and keratinocytes of the stratum corneum © Pearson Education Inc. MITOCHONDRIA • pyruvate & fatty acids enter mitochondria and broken down to acetyl CoA • acetyl CoA enters citric acid cycle and electrons are stripped off to reduce NAD to NADH. • high energy electrons passed from NADH to electron transport chain in inner membrane. • electron transport creates proton gradient across the inner membrane. • proton gradient drives the rotary enzyme ATP synthase to produce ATP Glycolysis = 2 ATP Ox-Phos = ~30 ATP [Molecular Biology of the Cell] RIBOSOMES, ENDOPLASMIC RETICULUM & GOLGI APPARATUS RER & Golgi • synthesis and packaging of proteins for export, membranes, lysosomes SER • lipid biosynthesis (eg membranes, steroids) • detoxification of harmful compounds (via P450’s) • sequestration of Ca2+ ions [Bloom & Fawcett: A textbook of Histology] PROTEIN PRODUCTION AND ASSEMBLY Robbins & Cotran, 9th ed In healthy cells, newly synthesized proteins are folded with the help of chaperones and are then incorporated into the cell or secreted. Cytosolic proteins destined for turnover, senescent proteins, or proteins that have become denatured due to extrinsic mechanical or chemical stresses can be tagged by multiple ubiquitin molecules which marks them for degradation by proteasomes. Robbins & Cotran, 9th ed Various external stresses or mutations induce a state called ER stress, in which the cell is unable to cope with the load of misfolded proteins. Accumulation of these proteins in the ER triggers the unfolded protein response, which tries to restore protein homeostasis; if this response is inadequate, the cell dies by apoptosis LYSOSOMES AND MEMBRANE TRAFFICING • autophagy vs heterophagy / endocytosis • phagocytosis vs pinocytosis vs receptor-mediated endocytosis • enzymatic (acid hydrolases) digestion of materials in the cell [Molecular Biology of the Cell] Macrophage phagocytosing two chemically altered red blood cells. Robbins & Cotran, 9th ed Figure 1-9 A, Lysosomal degradation. In heterophagy (right side), lysosomes fuse with endosomes or phagosomes to facilitate the degradation of their internalized contents. The end-products may be released into the cytosol for nutrition or discharged into the extracellular space (exocytosis). In autophagy (left side), senescent organelles or denatured proteins are targeted for lysosome-driven degradation by encircling them with a double membrane derived from the endoplasmic reticulum and marked by LC3 proteins (microtubule-associated protein 1A/1B-light chain 3). Cell stressors such as nutrient depletion or certain intracellular infections can also activate the autophagocytic pathway. CYTOSKELETON structure & movement of cells / organelles / molecules / phagocytosis Microfilaments = actin (~7 nm): in various arrangements → cell shape & movement [Molecular Biology of the Cell] Microtubules (~25 nm): organelle movement / flagella / cilia / mitotic spindle [Molecular Biology of the Cell] Basic Histology [Molecular Biology of the Cell] Intermediate filaments (~10 nm): cytokeratins, vimentin, desmin, GFAP, neurofilaments Molecular Biology of the Cell [Molecular Biology of the Cell] Cytokeratin in epidermal keratinocytes PEROXISOMES • enzymes (oxidases, catalase) for fatty acid metabolism / detoxification / antioxidation [Molecular Biology of the Cell] [Molecular Biology of the Cell] Figure 12–2 An electron micrograph of part of a liver cell Frida Kahlo (1907–1954) was a Mexican painter, who has achieved great international popularity. She painted using vibrant colors in a style that was influenced by indigenous cultures of Mexico as well as by European influences that include Realism, Symbolism, and Surrealism. CELL ADAPATION, INJURY & DEATH I. DEFINITIONS AND TERMINOLOGY II. CELLULAR ADAPTATIONS OF GROWTH III. CAUSES OF CELL INJURY IV. MECHANISMS OF CELL INJURY V. ISCHEMIC AND HYPOXIC CELL INJURY VI. FREE RADICAL - INDUCED CELL INJURY VII. CHEMICAL INJURY DEFINITIONS 1) Homeostasis • cells maintain normal structure & function in response to physiologic demands 2) Cellular Adaptation • as cells encounter some stresses they may undergo functional or structural adaptations to maintain viability / homeostasis • adapt to some stimuli by increasing or decreasing specific organelles • adaptive processes: atrophy, hypertrophy, hyperplasia and metaplasia DEFINITIONS 3) Cell Injury • if limits of the adaptive response are exceeded or if adaptation not possible, a sequence of events called cell injury occurs a) Reversible Cell Injury • removal of stress / injury complete restoration of structural & functional integrity Fig 2-1 (Robbins) Stages of the cellular response to stress and injurious stimuli. b) Irreversible Cell Injury / Cell Death • if stimulus persists (or severe enough from start) cell suffers irreversible cell injury & death • 2 main morphologic patterns: necrosis & apoptosis Myocardial hypertrophy Myocardial infarction (ischemic necrosis) Fig 2-2 (Robbins) The relationship between normal, adapted, reversibly injured, and dead myocardial cells. All three transverse sections of the heart have been stained with triphenyltetrazolium chloride, an enzyme substrate that colors viable myocardium magenta. The cellular adaptation shown here is myocardial hypertrophy (lower left), caused by increased blood pressure requiring greater mechanical effort by myocardial cells. This adaptation leads to thickening of the left ventricular wall (compare with the normal heart). In reversibly injured myocardium (illustrated schematically, right), there are functional alterations, usually without any gross or microscopic changes but sometimes with cytoplasmic changes such as cellular swelling and fat accumulation. In the specimen showing necrosis, a form of cell death (lower right), the light area in the posterolateral left ventricle represents an acute myocardial infarction caused by reduced blood flow (ischemia). CELLULAR ADAPTATIONS OF GROWTH & DIFFERENTIATION * * To be discussed in detail in * Disorders of Growth / Neoplasia ATROPHY • definition: decrease in the amount of a tissue or organ after normal growth has been attained • adaptive response where a tissue or organ undergoes a reduction in mass, due to a decrease in the size &/or number of cells Etiology of Atrophy • due to: decrease in work load loss of innervation loss of hormonal stimulation reduced blood supply / hypoxia inadequate nutrition compression aging • atrophic cells have a reduced functional capacity • still control their internal environment & produce enough energy to survive • in many cases return to ‘normal’ when causative stimulus is removed Mechanisms & Biochemistry of Atrophy • catabolic > anabolic processes; eg, muscle atrophy: ↓ myofilaments, ↓ mitoch., ↓ ER, ↓ metabolic activity • cell shrinks in volume & decreases functions ↓ energy requirements • autophagic vacuoles increase and some cells may die Gross Appearance of Atrophy • tissue/organ is decreased in size Microscopic Appearance of Atrophy • cells are smaller &/or fewer than normal Fig 2-5 (Robbins) Atrophy as seen in the brain. A, Normal brain of a young adult. B, Atrophy of the brain in an 82-year-old man with atherosclerotic cerebrovascular disease, resulting in reduced blood supply. Note that loss of brain substance narrows the gyri and widens the sulci. The meninges have been stripped from the right half of each specimen to reveal the surface of the brain. Normal Normal pectoral muscle bird (top) compared to marked bilateral pectoral muscle atrophy (bottom) due to malnutrition / starvation, ie muscle proteins broken down and used for basic energy requirements Horse with atrophy of the muscles of the left upper hindlimb; could be due to nerve damage or disuse secondary to a local injury Great horned owl, unilateral atrophy of pectoral muscles. Illustration showing what the pectoral muscles in this bird would look like in cross-section; note “shrinkage” of the birds right pectoral muscle indicating atrophy Great horned owl, further dissection shows cause of the unilateral pectoral muscle atrophy; ie tearing / damage (avulsion) of right brachial plexus (see arrow) resulting in denervation atrophy. Great horned owl, atrophic muscle on left of screen, normal muscle on right Close-up of atrophic muscle (cross-section), showing reduced diameter of most myocytes. Bovine, normal solid epicardial fat in coronary sulcus (coronary groove) and interventricular grooves. Ovine, serous atrophy of epicardial fat. Bovine, perirenal fat – normal control animal (left); serous atrophy of perirenal fat from emaciated animal (right) Control animal showing normal marrow fat (top). Serous atrophy of marrow fat from an emaciated sheep (bottom), which appears gelatinous / transparent. HYPERTROPHY • definition: adaptive response by which organs are increased in size due to an increase in cell size Etiology of Hypertrophy • a response to increased work load: physiological - eg, with exercise see increase in muscle cell size pathological - eg, heart failure see enlargement of cardiac myocytes • a response to trophic signals: physiologic hypertrophy (& hyperplasia) eg: uterus and mammary gland in pregnancy, lactation pathological hypertrophy eg: myocardial hypertrophy in hyperthyroid cats Mechanisms & Biochemistry of Hypertrophy Fig 2-4 (Robbins) Biochemical mechanisms of myocardial hypertrophy. The major known signaling pathways and their functional effects are shown. Mechanical sensors appear to be the major triggers for physiologic hypertrophy, and agonists and growth factors may be more important in pathologic states. ANF, Atrial natriuretic factor; GATA4, transcription factor that binds to DNA sequence GATA; IGF1, insulin-like growth factor; NFAT, nuclear factor activated T cells; MEF2, myocardial enhancing factor 2. Mechanisms & Biochemistry of Hypertrophy • anabolic processes > catabolic ones. • increase in organelles / cellular proteins: eg, mitochondria, ER, myofibrils Gross Appearance of Hypertrophy • tissue/organ is increased in size Microscopy of Hypertrophy • cells are larger than normal Marked muscle hypertrophy due to increased work load (weight lifting) and probable hormonal stimulation (ie injecting anabolic steroids - just a wild guess!) HYPERTROPHY Canine, normal heart Canine, left ventricular hypertrophy (in this case due to hypertension) Canine, normal myocardium Canine, left ventricle, cardiac myocyte hypertrophy; (same magnification as normal slide to left) note enlargement of individual myocytes Hyperplasia • increased organ/tissue mass caused by an increase in the number of constituent cells • hypertrophy and hyperplasia occur together in many tissues Canine, functional pituitary adenoma secreting excess ACTH causing marked diffuse bilateral adrenal cortical hyperplasia (& hypertrophy). Canine, normal adrenals, note ratio of cortex to medulla.