lecture 8 Flashcards
What is the extracellular matrix?
- macromolecules outside cells, formed by local secretion and assembled into network surrounding cells
What are the functions of the ECM?
- reservoir for growth factors
- scaffolding within which cells adhere, migrate, and proliferate
- sequester H2O for turgor (physical pressure that ECM exerts on cells within the matrix); minerals for rigidity
What are the three stages of after wounding?
Inflammation (2-6days)
- clot formation
- chemotaxis
Proliferation (6-12 days)
- re-epithelialization
- angiogenesis and granulation tissue
- provisional matrix
Maturation (12-16 days)
- collagen deposition
- collagen matrix
- wound contraction
What is the importance of the matrix in regeneration and repair?
- ECM regulates proliferation, movement and differentiation of the cells living in it
- If the ECM is destroyed you can’t regenerate –> a scar forms instead
What are the two types of cellular-macromolecular organisation?
Interstitial matrix/a.k.a stroma
- spaces between epithelial, endothelial and smooth muscle cells and in connective tissue
Basement membrane
- associated with cell surfaces (epithelial and mesenchymal)
What are the three groups of molecules that form the matrix?
- fibrous structural proteins e.g. collagen, elastins
- adhesive glycoproteins e.g. fibronectin, laminin
- gelatinous-like molecules e.g. proteoglycans, hyaluronan
What is important to note about the ECM?
- not a layering
- there is an interaction between all aspects
- e.g. between epithelium and basement membrane via integrins
What is collagen?
most common protein in the animal world
- each molecule
- 3 right handed alpha (triple) helices
- gly-X-Y repeating sub-units
- mutations: collagens lose stability and vulnerable to proteinase digestion: bone structure can be affected, flexibility/elasticity, skin/hair/eye integrity
- 27 types: 41 genes, 14 chromosomes
- I, II, III, V, XI: fibrillar = extracellular structures
- IV non-fibrillar:amorphous - forms sheets - Basement membrane
- other collagens:
- meshworks/anchors at epidermis/epidermis junction, cartilage, blood-platelet activation; vessel wall
How is collagen synthesised?
- procollagen 3 strands put together
- enzymes cleave off terminal ends - forms tropocollagen
- lots of glycine residues
- cross-linking with other triple helices - collagen fibre formed
What is elastin/fibrillin?
- blood vessels, skin, uterus, lung - need elasticity
- elastic fibres: stretch to several times length - return after release of push/pull force
- elastic fibres = central core (elastin), surrounded by fibrillin
- 70 kD protein
- rich in amino acids: glycine, proline, alanine
- cross-links enable and regulate elasticity
associated with:
- fibrillin = microfibrillar network - surrounds core
- 350kD glycoprotein
- self-associating
- scaffolding for elastin/elastic fibres
What is marfan syndrome?
- connective tissue genetic disorder affecting the FBN1 gene that encodes Fibrillin-1
- tall stature and long limbs resulting in defects of the aorta and heart valves, lungs, eyes, skeleton
- affected individuals exhibit increased chronic inflammatory disease (e.g. severe RhA) since Fibrillin-1 regulates TGF-beta dependent inflammation
What are the 4 major families of adhesive glycoproteins/integrins?
- in membranes = receptors - homotypic or heterotypic binding OR
- in cytoplasm (stored
immunoglobulin cell adhesion molecules
- ICAMs
- hetero/homotypic
Cadherins
= Ca++ dependent adherence protein, homotypic
- connect plasma membranes of adjacent cells - regulate motility, proliferation and differentiation
Integrins
- cell adhesion
- bind to fibronectin and laminin
- bind cells/ECM and cell/cell
Selectins
- e.g. neutrophil margination and rolling (E and P selectin)
What is fibronectin?
- adhesive glycoprotein - stromal
- multifunctional - attaches cells to matrix
- 450 kD glycoprotein - 2 chains - disulphide bonds
- from: fibroblasts, monocytes, endothelial cells
- binds to: collagen, fibrin, proteoglycans - domains
- binds to: cells via receptors/membrane e.g. bone marrow stroma
- cell attachment and spreading, cell migration
- enhances sensitivity to growth factors
What is laminin?
- most abundant glycoprotein in basement membrane
- = family - 820kD, heterotrimeric, cross shaped
- bind with receptors on cell surface
- binds with matrix e.g. collagen type IV, heparan sulphate
- mediates attachment: cells to connective tissue substrate
- in vitro: growth, survival, morphology, motility cells e.g. alignment of endothelial cells - capillaries
- binds to integrins
What are integrins?
- major family of cell surface receptors
- transmembrane, 2 chains: alpha (14 types) Beta (8 types)
- at least 30 different heterodimers
attachment
- cell-ECM, cell-cell e.g. leukocytes
- via recognition of RGD sequence by extracellular domain
crucial in
- development
- leukocyte extravasation, platelet aggregation, wound healing
- lack of attachment via integrins leads to apoptosis
- transduction of signals: ECM -> cell interior
- organise actin cytoskeleton into focal adhesion complexes
- complexes - activate signal transduction pathways
- possible similar to growth factor pathways e.g. MAP kinase, PI3 kinase.
