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Growth Factors in Wound
Healing
Sashwati Roy, PhD
Associate Professor
Department of Surgery
Learning Objectives
Determine
Recognize
Identify
Understand
At the end of this module,
you will learn:
• what are growth factors, their origin and major types
• the role of growth factors in wound healing.
• Major receptors and pathways of growth factor
signaling
• Clinical implication of growth factors in tissue repair
Learning Resources
• Reading: Werner S, Grose R. Regulation of
wound healing by growth factors and
cytokines. Physiol Rev. 2003 Jul;83(3):83570.
Growth Factors
• proteins and polypeptides that are
important to growing of eukaryotic cells
• can cause growth or inhibition of growth in
cells
• mitogenic effect - promotes cell growth
• various classes
– cytokines- Ils, TGF-ß, and CSFs
WOUND HEALING
Wound healing is a dynamic pathway
that optimally leads to restoration of
tissue integrity and function.
This complex process organized into
several overlapping phases:
Hemostasis
inflammatory phase
proliferative phase
(angiogenesis & fibroplasia)
maturation phase
(matrix deposition and remodeling)
Martin P: Wound healing
– aiming for perfect skin
regeneration.
Science 1997, 276:75-81
Martin, 1997 Science: Vol. 276 no. 5309 pp. 75-81
PLATELET-DERIVED GROWTH FACTOR
(PDGF)
• PDGFs comprise a family of homo- or
heterodimeric growth factors, including
PDGF-AA, PDGF-AB, PDGF-BB, PDGF-CC,
and PDGF-DD.
The PDGF family in mammals
PDGF–PDGFR interactions.
• PDGF exert their
functions by binding
to three different
transmembrane
tyrosine kinase
receptors, which
are homo- or
heterodimers of an
α- and a β-chain
Andrae J et al. Genes Dev. 2008;22:1276-1312
PDGF at the Wound Site
• Upon injury, PDGF is released in large amounts from degranulating
platelets at wound site
• The expression of PDGFR has been demonstrated in various cells of
murine, pig, and human wounds
• The expression patterns of PDGF and PDGFR at wound site suggest a
paracrine mechanism of action, the ligands are predominantly
expressed in the epidermis, whereas the receptors are found in the
dermis and the granulation tissue.
• The expression of PDGFs and their receptors are decreased in wounds
of healing-impaired genetically diabetic db/db mice and glucocorticoidtreated mice
• Augmented PDGF production might be involved in the pathogenesis of
hypertrophic scars and keloids as suggested by the potent effect of
PDGF on fibroblast proliferation and extracellular matrix production.
PDGF in Wound Therapy
Brand Names: Regranex
Generic Name: becaplermin topical
REGRANEX Gel contains becaplermin, a
recombinant human platelet-derived
growth factor for topical administration
The ONLY currently
available commercial
product based on
growth factor therapy
for chronic wounds
REGRANEX: WARNINGS AND PRECAUTIONS
• Becaplermin should be used with caution in patients with a known
malignancy
• Malignancies distant from the site of application have occurred in
becaplermin users in both a clinical study and postmarketing use, and
an increased rate of death from systemic malignancies was seen in
patients who have received 3 or more tubes of REGRANEX Gel.
• In a follow-up study, 491 (75%) of 651 subjects from two randomized,
controlled trials of becaplermin gel 0.01% were followed for a median
of approximately 20 months to identify malignancies diagnosed after
the end of the trials. Eight of 291 subjects (3%) from the becaplermin
group and two of 200 subjects (1%) from the vehicle/standard of care
group were diagnosed with cancers during the follow-up period, a
relative risk of 2.7 (95% confidence interval 0.6–12.8). The types of
cancers varied and all were remote from the treatment site.
http://dailymed.nlm.nih.gov/dailymed/drugInfo
PDGF in Wound Therapy
Platelet Rich Plasma (PRP)
Platelet Rich Plasma (PRP)
•Concentration of autologous platelets greater than
the peripheral blood concentration suspended in a
solution of autologous plasma.
•Synonyms:
•Platelet Concentrates (PC)
•Plasma Very Rich in Platelets (PVRP)
Platelet Granule Content
Alpha granule
(200-500 proteins)
•PDGF: Platelet-derived growth factor
•TGF-Beta: Transforming growth factor
•FGF: Fibroblast growth factor
•PDEGF: Platelet-derived epidermal
Growth factor
•PDAF: Platelet-derived angiogenesis
Factor
•PF-4: Platelet factor 4 (anti-heparin)
•PAF: Platelet activating factor
•IGF: Insulin-like growth factor
• CTGF: connective tissue growth factor
Dense granules
•Ionized calcium
•ADP (stimulates aggregation)
•Histamine
•Epinephrine
•Serotonin
TRANSFORMING GROWTH FACTOR-β
• The TGF-β superfamily encompasses a diverse range of
proteins, many of which play important roles during
development, homeostasis, disease, and repair.
• The structurally related but functionally distinct mammalian
members include TGF-β1–3, bone morphogenetic proteins
(BMPs), Mullerian inhibiting substance, nodals, inhibins, and
activins.
• The biological effects of TGF-β superfamily members are
mediated by heteromeric receptor complexes, which activate
intracellular signaling cascades.
TRANSFORMING GROWTH FACTOR-β
• The three mammalian TGF-β isoforms (TGF-β1, -β2, and -β3) are
synthesized as latent precursors, usually being secreted as a
complex with latent TGF-β-binding protein, which is then removed
extracellularly via proteolytic cleavage.
• Active TGF-βs then exert their biological functions via binding to a
heteromeric receptor complex, consisting of one type I and one
type II receptor, both of which are serine-threonine kinases.
• In addition, they bind with high affinity to a nonsignaling type III
receptor, which functions mainly to present TGF-β to the type II
receptor.
• The three TGF-β isoforms have both distinct and overlapping
functions.
TRANSFORMING GROWTH FACTOR-β
ACTIVITY
• In vitro, they have been shown to be mitogenic for
fibroblasts, but they inhibit proliferation of most
other cells, including keratinocytes.
• TGF-βs are very potent stimulators of the
expression of extracellular matrix proteins and
integrins.
Multiple functions of TGF-β during wound healing
• Upon local hemorrhage, TGF-β is released in large amounts from platelets.
• In the healing wound, it is produced by leukocytes, macrophages, fibroblasts,
and keratinocytes and acts on these cells to stimulate infiltration of
inflammatory cells, fibroplasia, matrix deposition, and angiogenesis.
• In contrast, endogenous TGF-β has been shown to inhibit re-epithelialization.
• TGF-β1-Deficient Mice Show Severely Impaired Late-Stage Wound Repair
WERNER S , GROSE R Physiol Rev 2003;83:835-870
Activation of Smad proteins by transforming growth factor
receptors
•
•
•
•
•
TGF-β is first produced as an inactive precursor
that binds to latency-associated protein (LAP).
Upon activation, TGF-β is either sequestered by
extracellular binding proteins (decorin,
fibromodulin)
or it binds to a type III receptor that presents it to
the signal-transducing receptors (type II and type
I).
Upon ligand binding, TGF-β type II receptor
recruits and phosphorylates the type I receptor.
The latter subsequently binds and phosphorylates
Smad2 and Smad3. Phosphorylated Smad2 and
Smad3 bind to Smad4 and translocate to the
nucleus where they bind to other transcription
factors that confer specificity, leading to activation
of target genes.
WERNER S , GROSE R Physiol Rev 2003;83:835-870
©2003 by American Physiological Society
TRANSFORMING GROWTH FACTOR-β
ACTIVITY IN WOUND REPAIR
• TGF-a: Mitogenic and chemotactic for keratinocytes
and fibroblasts
• TGF-b1 and TGF-b2: Promotes angiogenesis, upregulates collagen production and inhibits
degradation, promotes chemoattraction of
inflammatory cells.
• TGF-b3 (antagonist to TGF-b1 and b2): Has been
found in high levels in fetal scarless wound healing
and has promoted scarless healing in adults
experimentally when TGF-b1 and TGF-b2 are
suppressed.
Prevention and reduction of scarring in the skin by
Transforming Growth Factor beta 3 (TGFbeta3)
(avotermin (by Renovo) – a recombinant human transforming
growth factor beta 3 for scar treatments)
avotermin
placebo
1.
Occleston et al., Discovery and development of avotermin (recombinant human transforming
growth factor beta 3): a new class of prophylactic therapeutic for the improvement of scarring.
Wound Repair Regen. 2011 Sep;19 Suppl 1:s38-48.
2.
Occleston et al.,Prevention and reduction of scarring in the skin by Transforming Growth Factor
beta 3 (TGFbeta3): from laboratory discovery to clinical pharmaceutical. J Biomater Sci Polym
Ed. 2008;19(8):1047-63.
Avotermin (planned trade name
Juvista) failed in Phase III trials
14 February 2011: Renovo shares
plummet 75% as scar revision product
Juvista fails to meet study endpoints
- The Pharma Letter
VASCULAR ENDOTHELIAL GROWTH FACTOR
VEGF family currently includes VEGF-A, VEGF-B,
VEGF-C, VEGF-D, VEGF-E, and placenta growth
factor (PLGF).
VEGF family members exert their biological functions
by binding to three different transmembrane tyrosine
kinase receptors, designated VEGFR-1, VEGFR-2,
and VEGFR-3.
vascular endothelial growth factor (VEGF)
family members and their receptors
VEGF in therapeutics
• anti-VEGF antibody bevacizumab (Avastin,
Macugen, Lucentis) is increasingly used to treat
advanced malignancy and Macular Degeneration.
• Because of essential role of VEGF in wound
healing, anti-VEGF therapies have been suggested
to potentially lead to wound-healing complications
(WHCs).
• These risk seems higher with neoadjuvant than
adjuvant bevacizumab use and may be decreased
by extending the bevacizumab-surgery interval.
Topical VEGF therapy accelerates wound healing in experimental diabetic wounds
Depicted are the gross appearance of wounds treated with either VEGF (left wounds) or PBS vehicle (right
wounds). A: Wounds at day 5. The wound on the left treated with VEGF has developed a hyperemic wound bed
that contains abundantly vascularized newly formed granulating tissue. It has not yet begun to significantly close
at this time. The wound on the right treated with PBS exhibits scant healing. B: Wounds at day 12 after
wounding. The VEGF-treated wound (left) has completely resurfaced, while the wound treated with PBS (right) is
only beginning to heal. There is a granulation tissue forming in the PBS-treated wound, but unlike the granulation
bed present in VEGF-treated wounds in A, there is no evidence of excessive hyperemia. C: This graph
demonstrates the kinetics of closure in VEGF-treated wounds (•), PBS-treated contralateral wounds (red), and
wounds made in control db/db mice in which neither wound was treated with VEGF (green). VEGF normalizes
the impairment in repair seen in this model of diabetic wound healing. Note that wounds made in animals in
which neither wound was treated with VEGF have the most delayed healing.
Galiano et al.,Topical vascular endothelial growth factor accelerates diabetic wound healing through increased angiogenesis and by mobilizing
and recruiting bone marrow-derived cells. Am J Pathol. 2004 Jun;164(6):1935-47.
FIBROBLAST GROWTH FACTOR (FGF)
• FGFs comprise a growing family of structurally related polypeptide growth
factors, currently consisting of 22 members.
• They transduce their signals through four high-affinity transmembrane protein
tyrosine kinases, FGF receptors 1–4 (FGFR1–4), which bind the different
FGFs with different affinities.
• Additional complexity is achieved by alternative splicing in the extracellular
domains of FGFR1–3, which dramatically affects their ligand binding
specificities.
• FGF1, however, binds to all known receptors, and FGF7 specifically interacts
with a splice variant of FGFR2, designated FGFR2IIIb.
• A characteristic feature of FGFs is their interaction with heparin or heparan
sulfate proteoglycans, which stabilizes FGFs to thermal denaturation and
proteolysis, and which strongly limits their diffusibility. Most importantly, the
interaction with heparin or heparan sulfate proteoglycans is essential for the
activation of the signaling receptors.
FIBROBLAST GROWTH FACTOR (FGF) FUNCTIONS
• FGF family are known to stimulate proliferation of various
cells of mesodermal, ectodermal, and also endodermal
origin.
• The only exception is FGF7 ( aka. keratinocyte growth factor,
KGF), which seems to be specific for epithelial cells, at least
in the adult organism.
• FGFs also regulate migration and differentiation of their
target cells, and some FGFs have been shown to be cytoprotective and to support cell survival under stress
conditions.
EPIDERMAL GROWTH FACTOR (EGF) FAMILY
• Epidermal growth factor (EGF) family of mitogens comprises several
members, including EGF, transforming growth factor-α (TGF-α),
heparin-binding EGF (HB-EGF), amphiregulin, epiregulin, betacellulin,
neuregulins, the recently discovered epigen.
• All these growth factors exert their functions by binding to four different
high-affinity receptors, EGFR/ErbB1, HER2/ErbB2, HER3/ErbB3, and
HER4/ErbB4
Epidermal growth factor (EGF) family members and
their receptors
EGF FUNCTIONS AND ROLE IN
WOUND HEALING
• EGF has been implicated in keratinocyte migration,
fibroblast function and the formation of granulation
tissue during wound healing.
• HB-EGF shedding can be inhibited by compound
OSU8–1. Interestingly, the application of this
compound to full-thickness mouse wounds caused a
strong retardation of reepithelialization as a result of
impaired keratinocyte migration suggesting a role of
HB-EGF in wound re-epithelialization.
Growth factors in the treatment of diabetic foot ulcers. Br J Surg. 2003
Feb;90(2):133-46.
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