L3 07 Mar 2019 Flashcards
Cells and Molecules in Healing
labile tissues
constant proliferation for high cell turnover (e.g. haematopoietic cells, surface epithelia)
stable tissues
quiescent, but can be activated for proliferation (e.g. parenchyma of most solid organs, endothelial cells, fibroblasts, smooth muscle cells)
permanent tissues
no proliferation, irreversible injury and repair leads to scar formation (e.g. majority of neurons, cardiac muscle cells)
functions of biochemical factors released in response to cell injury, cell death or trauma
- MOST IMPORTANT: induce resting cells to enter cell cycle
- balance of stimulatory and inhibitory factors - regulation
- shorten cell cycle - faster cell division inhibit apoptosis - decrease rate of cell losee
the two main types of healing
regeneration and connective tissue deposition (scar formation)
regeneration
proliferation of cells, survives injury, maintains function, and still has ability to proliferate and maintain stem cells
connective tissue deposition (scar formation)
deposition of new connective tissue (structural stability)
Repair is a balance of regeneration and connective tissue deposition. TRUE or FALSE
TRUE, they work together to achieve varying degrees of repair involving proliferation, differentiation, migration and communication of various cells and extensive interaction with the ECM
What is the purpose of remodelling scar tissue?
to return to homeostasis
methods to regulate/activate cell proliferation
- cell-cell contact
- cell-ECM interaction
- paracrine or autocrine factors
PI3 pathway
growth factor attaches to receptor with intrinsic tyrosine kinase activity –> PI3 kinase attaches to receptor and PI3 pathway is activated with the Akt (PKB) ligand –> affects transcription factor –> proliferation
MAP-kinase pathway
growth factor attaches to receptor –> activation by phosphorylation via extracellular kinases –> activates MAP kinas cascade –> RAS compound attaches to RAF –> MEK –> ERK –> ERK breaks into nucleus and affects transcription factors –> multiple functional effects
cAMP pathway
GPCR attaches to intracellular proteins (including G-proteins) –> cAMP pathway –> cAMP –> multiple effects
JAK/STAT pathway
cytokines attach to receptors w/o intrinsic tyrosine kinase activity –> JAKs interact with receptor –> JAK/STAT pathway –> STATs directly bind to DNA –> multiple effects
EGF
epidermal growth factor: from activated macrophages mitogenic for keratinocytes & fibroblasts, stimulates keratinocyte migration; stimulates formation of granulation tissue important for first stages of healing
TGF-α
transforming growth factor-α: from activated macrophages and keratinocytes stimulates proliferation of hepatocytes and other epithelial cells
HGF
hepatocyte growth factor (scatter factor): from fibroblasts mitogenic for epithelial cells (not just hepatocytes) causes cell migration (therefore scatter factor) required for survival during embryogenesis
VEGF
vascular endothelial growth factor: from mesenchymal cells angiogenesis, VEGF-A for neoangiogenesis, bind to receptors on endothelial cells
PDGF
platelet derived growth factor: from platelets, macrophages, endothelial cells. smooth muscle cells, keratinocytes regulate inflammation, activation of fibroblast in first steps of healing
FGF
fibroblast growth factors (including acidic, FGF-1, and basic, FGF-2): activation of fibroblasts
what is the significance of GFs that activate fibroblasts?
they have the ability to regulate formation of ECM and healing of tissues
what are the two components of the ECM?
interstitial matrix and basement membrane
interstitial matrix
in connective tissue, synthesised by mesenchymal cells, forms amorphous 3D gel contains: collagens, fibronectin, elastin, proteoglycans, hyaluronate
basement membrane
highly organised, support and holds up epithelial cells, endothelial cells and smooth muscle cells contains: non-fibrillar type IV collagen and laminin
what kind of thing creates the ECM
fibroblasts or mesenchymal cells
structural fibers of the ECM
elastin, fibrillin, elastic fibres: provides elasticity
functions of ECM in tissue repair
- ECM regulates cell proliferation, locomotion, differentiation
- provides: mechanical support, control of cell proliferation and scaffolding
ECM maintains cell polarity. What is the importance of this?
Cell polarity is used in differentiation in cells (sometimes or always? idk?) and loss of polarity may (or will) trigger carcinogenesis
adhesive proteins in ECM and cell-matrix interactions
- Cell surface integrins interact with cytoskeleton at focal adhesion complexes
- Can initiate production of intracellular messengers or can directly transduce signals to nucleus
- Cell surface receptors for growth factors can activate signal transduction pathways that overlap with those mediated through integrins
- Signals from ECM components and growth factors can be integrated by cells to produce a given response, including changes in proliferation, locomotion, and/or differentiation.
proteoglycans
- made up of core protein + polysaccharides (GAGs)
- negative charge, large volume, hydrophilic
- in all ECM, on cell surfaces and in biological fluids
- regulates connective tissue structure and permeability
- modulates cell growth and differentiation (esp. fibroblasts)
examples of proteoglycans
heparan sulphate and chondroitin sulphate - molecules for skin hydration
regulation of neoangiogenesis
- other endothelial cells (VDGFs, PDGF, NO, prostaglandins (PGs))
- ECM (once broken) - integrins and collagen debris
- Inflammatory cells (PGs, angiopoietins (ang), COX, NO, inflammatory cytokines)
- GF from activated cells
fibroplasia
deposition of collagen by activated fibroblasts to regenerate structure of the tissue
granulation tissue
has neoangiogenesis occuring, there is a new ECM and provides scaffolding for healing
maturation of wounds
- vascular granulation tissue leads to avascular scar, via growth factors
- a new ECM is synthesised and old ECM (used during granulation tissue) is destroyed in favour of a more mature ECM - important because repair is about return to homeostasis
Liver regeneration phases
- priming phase: cytokines (IL-6 and Kupffer cells) act on hepatocytes to make them more receptive of GFs
- growth factor phase: HGF and TGF-α act on primed hepatocytes, during this phase more than 70 genes are activated
- termination phase: cells return to quiescence
During liver regeneration all cells can be regenerated. TRUE or FALSE
FALSE. but is a high percent (much higher when compared to other organisms) 90%
healing molecular mechanisms
- wounding-proliferation-migration-synthesis-remodelling
- ligand+receptor (cell membrane)-2nd messenger cascade (cytoplasm)-transcription factor activation (nucleus)-gene expression (nucleus)-healing
What is the importance of the 2nd messenger cascades?
part of proliferation; signal transduction = MAP-kinase also includes PI3Km JAK/STAT and cAMP
cellular environment in healing
- non-cellular interstitium/matrix (ECM)
- inflammatory cells: fibroblasts, endothelial cells, epithelial cells and stem cells
why are cell interactions with ECM important for healing?
regulates cell proliferation, migration and differentiation
steps of cutaneous wound healing
- INFLAMMATION: wounding activates coagulation pathway, clot stops bleeding plus protects wounded area; macrophagesrelease proteolytic enzymes and begin to clear debris
- PROLIFERATION: neutrophils replaced by macrophages, granulation tissue is synthesised by activated fibroblasts (ECM), neoangiogenesis, epithelial cells proliferate and migrate over granulation tissue
- MATURATION: leukocytes, oedema and angiogenesis diminishes, scar formation
haemostasis in inflammatory phase
- platelet aggregation + release of fibrin
- cytokines, chemokines, and hormones
- vasoconstriction
- platelet aggregation+vascular leaking=clot formation
- platelet activation=degranulation
- release of chemotactic and growth factors (PDGF, proteases, vasoactive agents, serotonin and proinflammatory cytokines e.g. histamine)
- chemokines attract inflammatory cells
acute inflammation in inflammatory phase
- injured blood cells leak transudate = oedema
- increased porosity of blood vessels= entry of inflammatory cells into wound site
- inflammation prevents infetion - things are removed from wound area
- leukocytes, GF, and enzymes create swelling, heat, pain, and redness
proliferation phase and deposition of connective tissue (wound healing)
- fibroblasts: migrate from surrounding edges, proliferate and some differentiate
- synthesise and depose immature ECM (type III collagen, fibronectin) = granulation tissue = scaffold
- secrete factors (FGFs and TGF-β) + ECM factors (integrins) + angiogenetic factors (VEGF) that regulate cell proliferation and neo-angiogenesis
- start of wound contraction: myofibroblasts pull collagen fibres together. synthesis of type I collagen reinforces contraction
during proliferation phase, acute inflammation is still occuring. TRUE or FALSE?
TRUE. acute inflammation still on: M2 macrophages (TGF-β stimulates fibroblasts + epithelial cells + endothelial cells)
re-epithelialisation in proliferation phase
- GT established - transformation (epithelial cells become less differentiated - more stem cell like)
- proliferation
- migration: newly formed cells migrate along newly synthesised basement membrane
- epithelial migration stops with contact inhibition with other wound edge
- epitheilal cells differentiate (keratinisation, squames)
angiogenesis in proliferation phase
- endothelial activation
- separation of pericytes
- M2 macrophages and endothelial cells secrete proteases (collagenases, MMPs) - break down existing vascular basement membrane
- endothelial cells proliferate and detach from vascular wall, degrade and invade ECM, guided by FGFs
- sprouting - extends in length until they encounter another cell: vascular loops then capillary tubes
- maturation: endothelial proliferation and migration stops - new basement membrane and pericytes
remodelling and contraction in maturation phase
- remodelling: cells organise surrounding connective tissue and lead to formation of scar
- fibroblasts replace type III collagen with type I = tensile strength
- fibroblasts become less proliferate
- myofibroblasts provides force for contraction
- vascular regression - avascular scar
- in skin: new continous basement membrane under regenerated epithelium
