Extracellular matrix metabolism lecture[1]

ExtracellularMatrixMetabolism : 

ExtracellularMatrixMetabolism

Wound healing : 

Wound healing Biological mechanisms Contraction Epithelialisation Connective tissue matrix deposition Function: Mechanical support for cells and tissues. Integrates cells into tissues. Influences cell shape and cell movement. Influences cell development and differentiation. Coordinates cellular functions through signaling with cellular adhesion receptors. Reservoir for extracellular signaling molecules.

Extracellular matrix : 

Extracellular matrix 4 cell types Fibroblasts Macrophages Mast cells Fat cells Other components Ground substance Glycosaminoglycans Proteoglycans Hyaluronic acid Laminin Fibronectin Elastin Collagen

ECM components & function : 

ECM components & function

Ground substance:Glycosaminoglycans : 

Ground substance:Glycosaminoglycans Hydrophilic polymers of disaccharides that form a gelatinous matrix Highly negatively charged Attract osmotically active cations GAGs differ in the type of sugars in the disaccharide in their chemical bond. The most common GAGs are: Hyaluronic acid (HA) – glucuronate + N-acetyl-glucosamine Chondrotin sulfate – glucuronate + N-acetyl-galactosamine Heparan sulfate – glucuronate + N-sulfo-glucosamine Keratan sulfate – galactose + N-acetyl-glucosamine

Slide 6: 

Consist of a core protein to which GAGs are covalently coupled The protein-GAG linkage is always made between Ser and the 3-sugar ‘linker’ Xyl-Gal-Gal, followed by Glucuronic acid. Proteoglycans are found both in ECM and attached to the plasma membrane Ground substance : Proteoglycans

Slide 7: 

HA is a large, unbranched and negatively charged polymer of repeating (2-25K) disaccharides. Found in large quantities in in damaged/growing tissue  cytokine production by macrophages  angiogenesis Function Provides fluid environment to facilitate cell movement and differentiation Ground substance : Hyaluronic acid

Fibronectin : 

Fibronectin Dimer of two identical 250 kDa subunits joined by 2 disulfide bridges. Mediates the connection between the ECM and the cell membrane. Cell-binding domain made up of Arg, Gly, Asp (RGD sequence). Also binds a variety of other proteins like integrins, heparin, collagen, fibrin. It also self-interacts.

Laminin : 

Laminin Cross-shaped proteins. Contain α, β1 and β2 chains that are connected by disulfide bonds. Binds to membrane receptors (integrins) of the overlying cells. Also contains binding sites for other components of the basal lamina: type IV collagen, heparin, heparan sulfate and entactin. Miner, J.H. 2004. Annu Rev Cell Dev Biol.

Elastin : 

Elastin Elastic fibers permit long-range deformability and passive recoil. This function is crucial for arteries, lung, skin and other dynamic connective tissues that undergo cycles of extension and recoil. The major component of elastic fibers is the thread-like protein elastin Synthesised by fibroblasts  tropoelastin Assembled into elastin ECM

COLLAGEN : 

COLLAGEN Collagens make up ~25% of total protein mass in mammals Exists in large quantity in ECM of skin, bone, tendon, cartilage and other connective tissues for support and protection. Collagen comprises 25 isoforms. Collagen fibers withstand high pulling forces. How is a fiber of this strength produced???

Collagen Structure : 

Collagen Structure

Collagen Synthesis : 

Collagen Synthesis Nucleus: mRNA is produced. ER/Golgi: Pro-a-chains are produced Post-translational modifications hydroxylated and glycosylated at selected Lys and Pro residues. The lack of vitamin C prevents hydroxylation → impaired fibril formation (scurvy). Processed pro-peptides assemble into triple-helical pro-collagen. Golgi: Disulphide bonds form between the N- and C-termini of procollagen. After exocytosis, N- and C-termini are trimmed, allowing fibril assembly

Slide 16: 

Types of collagen

Role of Collagen in WH : 

Role of Collagen in WH Haemostasis  fluid exudate  cellular component  growth factors Support

Collagen & wound breaking strength : 

Collagen & wound breaking strength

Collagen degradation : 

Collagen degradation Mammalian collagenase Inactive zymogen  plasmin  α-2 macroglobulin TIMP Splits collagen into TCA & TCB fragments Further degradation by non-specific proteases Gelatinases Stromelysin

Regulation of collagen synthesis : 

Regulation of collagen synthesis  NAD+ Hypoxia  respiratory enzymes  lactate TGF- and IGF-1 Feedback by extension peptides

Genetic Disorders : 

Genetic Disorders Osteogenesis imperfecta Abnormal Type I collagen Characterised by Bones break easily Thin dermis Increased bruising Normal scarring Normal skin extensibility Marfans syndrome Collagen & elastin defects Characterised by Tall stature Lax ligaments Myopia Scoliosis Dissecting aneurysms of root & ascending portions of aorta Erlers-Danlos syndrome IV  abnormal Type III collagen VI  lysyl hydroxylase deficiency VII  abnormal Type I collagen IX  lysyl oxidase defect X  fibronectin defect Characterised by Joint laxity Hyperextensible & fragile skin Vascular rupture Poor wound healing Epidermolysis bullosa Increased collagenase Characterised by Blistering Ulceration