Regeneration, Repair, and Wound Healing

Question 1

regeneration

Answer 1

• restoration of damaged or lost cells or tissues to their original state
• requires cell proliferation (parenchyma or stem cell pop) and an intact ECM scaffold
• eg normal/homeostatic replacement of skin cells

Question 2

repair

Answer 2

• involves a combination of regeneration and scar formation by collagen deposition
• requires cell proliferation; ECM is usually damaged and new ECM (collagen) is deposited
• eg burn healing

Question 3

regulation of cell cycle

Answer 3

• G1-S checkpoint
• cylicns (D) bind to cyclin dependent kinase ->form heterodimer -> phophorylate retinoblastoma protein -> release E2F -> protein transcripton
• CDK inhibited by growth inhibitors (TGF-B, p53), activated by growth factors (EGF, PDGF)

Question 4

growth factors

Answer 4

• polypeptides that bind cellular receptors and stimulate cell proliferation
• can also stimulate cytoskeletal rearrangement (alter cellular motility and contractility), cellular differentiation, angiogenesis

Question 5

Epidermal growth factor (EGF)

Answer 5

• includes EGF, TGF-a
• receptor EGRF1, tyrosine kinase, juxtacrine
• from macrophages, inflammatory cells, platelets
• acts on epithelial cells, fibroblasts
• effects cellular proliferation
• diseases: psoriasis (TGF-a), Her2 receptor + breast cancer

Question 6

Platelet derived growth factor (PDGF)

Answer 6

• secreted proteins
• PDGRF a and B, receptor tyrosine kinase
• from platelets, macrophages, endothelial cells, fibroblasts
• acts on mesenchymal cells (hematopoietic cells, fibroblasts)
• primary chemokine and mitogen for mesenchymal cells, stimulates fibroblasts to secrete ECM and collagenase, attract inflammatory cells-secrete growth factors
• chronic eosinophilic leukemia-receptor gene fusion-uncontrolled eosinophil proliferation

Question 7

Fibroblast growth factor (FGF)

Answer 7

• receptor tyrosine kinase; FGF must be bound to extracellular matrix to activate
• from macrophages, endothelial cells
• target fibroblasts, endothelial cells
• fibroblast chemotaxis and proliferation, ECM deposition, angiogenesis
• lots of diseases

Question 8

Vascular endothelial growth factor (VEG-F)

Answer 8

• polypeptide growth factors
• receptor tyrosine kinase
• from variety of mesenchymal cells (leukocytes and fibroblasts)
• target endothelial cells
• angiogenesis, endothelial cell proliferations and migration, increase vascular permeability

Question 9

Transforming growth factor B (TGF-B)

Answer 9

• polypeptide growth factors
• receptor serine/threonine kinase
• from platelets, endothelial cells, fibroblasts, macrophages, lymphocytes
• target fibroblasts, leukocytes
• multiple opposing effects: promotes fibrogenesis, stimulate fibroblast and smooth muscle proliferation, inhibit epithelial and mesenchymal cell growth, strong anti-inflammatory agent, attract neutrophils, fibroblasts, macrophages

Question 10

Interferon

Answer 10

• cytokine
• from T-cells
• target macrophages and fibroblasts
• role in wound healing: activates macrophages (major mediator of wound healing), down regulates collagen synthesis, inhibit fibroblast proliferation

Question 11

Interleukin-1

Answer 11

• cytokine
• from macrophages
• target inflammatory cells and fibroblasts
• wound healing: mediates inflammatory cell fxns in wound, neutrophil and fibroblast chemotaxis

Question 12

Tumor necrosis factor

Answer 12

• cytokine
• from macrophages and t-cells
• target macrophages and t-cells (autocrine)
• wound healing: activates macrophages, stimulate IL-1 production, activate t-cells, induce collagen production in fibroblasts, attract neutrophils

Question 13

Embryonic stem cells

Answer 13

• derived from inner cell mass of blastocyst
• each cell is pluripotent
• have self renewal capacity
• uses-treatment of ds where there is a loss of critical cell types (MI, Alzheimers, Parkinsons, spinal cord injury, DM type 1)
• challenges- ethical issues, transplant rejection, tumor formation (teratoma), persistence of underlying ds, making differentiated cells fxn normally

Question 14

induced pluripotent stem cells

Answer 14

-skin cells -> transduce in certain genes -> proteins -> induce cells back to pluripotent state

Question 15

Adult stem cells

Answer 15

• small reservoirs of self-renewing cells in multiple tissues
• restricted in their differentiation potential
• fxn is to regenerate cells lost by normal wear and tear (hair follicle, GI crypts, liver, eye)
• if moved to different tissue, can transdifferentiate in vitro; otherwise restricted niches

Question 16

ECM fxns

Answer 16

• provide turgor by sequestering water or rigidity by sequestering minerals
• reservoir for secreted growth factors
• framework for cells to adhere, migrate and proliferate in
• mediates cell-cell interactions
• site of remodeling during wound healing

Question 17

ECM composition

Answer 17

• fibrous structural proteins
• adhesive glycoproteins
• proteoglycans and hyaluronic acid

Question 18

Col I

Answer 18

most common type in mammals
bone, tendon, mature scars
fibrillar

Question 19

Col II

Answer 19

articular and hyaline cartilage

fibrillar

Question 20

Col III

Answer 20

• embryonic collagen
• in adults, found in bv, uterus, and GI tract
• 1st collagen deposited in wound healing; eventually degraded and replaced by Col I
• fibrillar

Question 21

Col IV

Answer 21

Basement membrane

Non-fibrillar (sheet)

Question 22

Elastic fibers

Answer 22

• core of elastin surrounded by fibrillin
• specialized fiber that allows for recoil after stretching
• found in arteries, skin, uterus, lung
• Marfans-mutation in fibrillin-aortic dissection, corneal dislocation, tall stature

Question 23

fibronectin

Answer 23

• secreted cell adhesion protein
• in plasma-stabilizes early clot (fibrin plug)
• in cells (secreted from fibroblasts, macrophages, endothelial cells)
• binds numerous molecules
• first ECM deposited in wound healing

Question 24

functions of fibronectin

Answer 24

• adds structural integrity to clot
• chemotactic for many cells
• substrate for cellular adhesion (RGD dominant)
• substrate for other ECM protein attachment and assembly

Question 25

laminin

Answer 25

• secreted cell adhesion protein
• found primarily in BM-forms tight polymer networks w/ Col IV to maintain BM integrity
• similar fxns to fibronectin: substrate for ECM protein binding and cell adhesion

Question 26

Integrins

Answer 26

• cell surface bound adhesion protein
• transmembrane receptors
• facilitate cell-cell interaction
• facilitate cellular interaction w/ ECM by binding collagen, fibronectin, and laminin
• links cell surface to cytoskeleton-conformation changes may -> cell proliferation, apoptosis, differentiation, etc

Question 27

cadherins

Answer 27

• cell surface bound adhesion protein
• facilitate cell-cell interactions between similar cell types
• facilitate formation of cell jxns
• linked to cytoskeleton through catenins to regulate cell motility, proliferation, and differentiation

Question 28

proteoglycans

Answer 28

• repeating polymers of disaccharides bound to a protein core
• forms an ECM scaffold for tissue structure and permeability

Question 29

Hyaluronic acid

Answer 29

• huge molecule of long repeating polysaccharides w/o a protein core
• can bind large amount of H20-forms viscous hydrated gel; allows ECM to resist compressive forces, deposited early during wound healing to facilitate cell migration and proliferation

Question 30

Hemostasis phase of wound healing

Answer 30

• 1st phase
• stop bleeding and facilitate inflammation
• platelets activated by exposed collagen
• serum fibrin/fibronectin forms plug
• platelets release thromboxane
• vasodilation and increased permeability

Question 31

Inflammatory phase of wound healing

Answer 31

• 2nd phase

- stop infection, clear debris, induce repair

Question 32

early inflammatory phase

Answer 32

• neutrophils come (attracted by chemokines) -> phagocytosis

- Macrophages come -> predominate, secrete stuff, phagocytosis; orchestrate wound healing

Question 33

late inflammatory phase

Answer 33

• macrophage secretion peaks
• secreted factors attract and activate cells needed for proliferative phase
• neutrophils and macrophages decrease
• fibroblasts predominate
• early wound ECM consists of fibrin, fibronectin, and HA-anchor for cell adhesion and collagen deposition

Question 34

Proliferative phase of wound healing

Answer 34

• 3rd phase
• replacement of lost tissue with scar
• provides structural support
• consists of: angiogenesis, formulation of granulation tissue, fibroplasia, epithelialization, wound contraction
• fibroblast activity, ECM deposition, tissue remodeling

Question 35

Angiogenesis

Answer 35

• restore perfusion to wound
• VEGF -> increase vascular permeability, endothelial cell migration, promote angiogenesis
• fibronectin/fibrin in ECM facilitate endothelial cell migration; proteases degrade existing ECM
• new thin walled vessels in wound site
• most vessels regress

Question 36

Granulation tissue

Answer 36

• fills defects left by injury prior to vigorous collagen deposition
• 2-5 days after injury
• highly vascular loose fibrous tissue w/ scattered inflammatory cells and fibroblasts
• ECM-fibronectin, Col III, HA
• growth factors- PDGF and TGF-B

Question 37

Fibroplasia

Answer 37

• influx and proliferation of fibroblasts w/ subsequent collagen deposition
• fibroblasts attracted and activated by TFG-B, PDGF, EGF, FGF, and cytokines
• 2-4 weeks

Question 38

TGF-B in fibrogenesis

Answer 38

• increase fibroblast proliferation/migration
• increase Col and fibronectin synthesis
• decrease ECM degradation
• chemotactic for monocytes

Question 39

Epithelialization

Answer 39

• restoration of injured epithelium
• basal keratinocytes proliferate from edges of wound-migrate in
• stimulated by EGF, KGF, FGF
• migration facilitated by interaction w/ fibronectin/fibrin in provisional ECM of granulation tissue (migrate over gran tissue and under scab)

Question 40

Contraction

Answer 40

• pulls edges of wound together to reduce the wound surface area
• decrease wound size by 40-80%
• mediated by myofibroblasts
• TGF-B induces differentiation of fibroblasts and myofibroblasts
• myofibroblasts contain actin filaments that are linked to ECM and facilitate contraction

Question 41

Maturatoin phase

Answer 41

• remodeling of ECM w/ mature scar formation to increase tensile strength
• collagen production = degradation
• can last over a year
• matrix metalloproteinase degrade collagen and ECM
• replace Col III w/ Col I -organized, cross linked, aligned along lines of tension (final strength 80%)
• replace HA w/ proteoglycans
• mature scar- dense Col I, elastic fibers, proteoglycans, scattered fibroblasts

Question 42

Local factors that affect wound healing

Answer 42

• size, type, location of wound
• vascular supply
• oxygen supply
• infection
• necrosis-lowers tissue pH, causes inflammation, prevents healing
• foreign material
• movement
• radiation

Question 43

Systemic factors that affect wound healing

Answer 43

• circulatory compromise
• nutritional status (protein, zinc, vit C, A, thiamine and riboflavin)
• diabetes
• obesity
• hormones
• chemotherapy

Question 44

Fibrosis

Answer 44

• persistent stimulus (chronic inflammation) -> chronic activation of macrophages and lymphocytes
• proliferation of fibroblasts, endothelial cells, and specialized fibrogenic cells; increase collagen synthesis, decrease collagen degradation

Question 45

healing by primary intention

Answer 45

-clean edges, close w/ stitches, glue, staples, etc

Question 46

healing by delayed primary intention

Answer 46

-wound is initially left open, when granulation tissue is judged clean and viable wound is closed by primary intention

Question 47

secondary intention

Answer 47

• considered for contaminated or necrotic wounds, left open to scar in from below
• greater inflammatory response, more granulation tissue, increased wound contraction, often larger scar