ECM Flashcards
ECM organisation Fibers
embedded in proteoglycan gel
Collagen (str, resists stretch and orgo ECM)
Elastin (elasticity) - fibrillin
ECM organisation Ground Substance
Hydrated gel, resists compression, permits rapid diffusion of nutrients, metabolites, Hormones between blood and tissue
Proteoglycans (protein and GAGs): resist comp and fill
Glycoproteins (sugars and prot): Adhesive = fibronectin, laminin, entactin
ECM determination of physical properties of tissue
Components secreted locally, assembled into meshwork with cell producing them (fibroblasts)
Function of ECM
- Scaffold to stabalize physical structure and resist forces
- Influence cell behavior, survival, development, migration, proliferation, shape, and function
Influence of ECM on structures
Bone/teeth (calcified), Corneal Stroma (transparent), tendons (ropelike), Cartilage (shock absorb)
Functions of fibrous proteins
- Fibrous proteins impart str and flex
- Simple repeat element of 2nd struc
- Water insoluble (Hphobic, packed center)
- EC, long lived proteins
- Construct CT, tendons, bone, matrix
Collagen general info
3x helix of alpha chains for tensile strength of tissue.
Components of tendons (increased tensile str, parallel bundles) skin (loose, flexible fibers) teeth/bone (contains hydroxyapoptic-Ca phosphate polymer), Cornea (nearly crystalline, transparent)
Made by fibroblasts (osteoblasts, chondroblasts) and epithelial cells (BL)
Collagen AA’s
Glycine every 3rd AA allows H bond between gly backbone with adjacent helix
Proline and hydroxyproline (25%) = kinks, fixed angles, helps helix formation
Lysines and hydroxylysines
Collagen organisation
3x helix = str - resists unwinding
Formed as long preprocollagen
Type 1 collagen: 2x alpha1 chains and 1xalpha2 chain. Prepro - sig seq - rER=formation - cleaves sig seq - procollagen= peptide domains enter helix formation and prevent premature fibril formation
Procoll processing in ER
Hydroxylation of prolyl and lysyl residues; important for interchain H-bonds. Glycosylation of H-lysins
Disulfide bond form (C term); aligns chain, intiates 3x helix form - zip C’ to N’’
H-bonds btwn 3 procoll - procoll 3x helix - golgi - secreted
Proline and lysine: post transL in ER
to hydroxy form (rqr ascorbic acid;vit C; and iron) hydroxyproline only in collagen (and elastin)
Lack H-proline destabilizes 3x helix
Hlysine - intra and intermolec collagen (crosslinking= site for sugar attachment and stable crosslink form)
Hproline= helix stability w/o = destab at >20 deg C
Post secretion Collagen fibril form
Peptidases remain N+C peptides: proc - coll= additional crosslinking
Self assembly to coll fibrils: fibril cross link by lysine mod, inter and intra molec crosslinks increase strength of collagen fiber
Covalent Intramolec and inter bonds btwn Lys and H-lys
Lys and Hlys deanimated by lysyl oxidase (ec) - reactive aldehyde (needs o2 and cooper)
Aldehydes react spontaneously to covalent bonds with each other or other lys/Hlys (usually at ends, stab side by side packing)
Collagen families
- Fibrillar - 1,2,3,4
- Fibrillar Associated (FACIT=connecting collagen): 6,9,12
- Sheet (network) forming coll: 4,10
- Anchoring fibrils: 7
* 6 bonds and link type 1 fibrils
* 9 bonds and links type 2 fibrils and bind chondrotin sulfide (GAG)
FACIT
Fibril associated Collagen (6,9,12) with interrupted triple helices
Organize fibrils in ECM: mediate interaction of coll fibrils with other fibrils and ECM proteins, proteoglycans, GAGs
FACIT Binding fibrillar coll surface
3 stranded structure interrupted by non-helical domains to increase flex than fibrillar coll. Retains propetides after secretion therefore ends not cleaved
FACIT binding fibrillar coll locations
Different fiber organization:
Tendons - org into parallel bundles along major axis of tension
Corneal Stroma: perpendicular angles
Degradation of Collagen: Matrix Metalloproteinases (MMPs)
MMP1 (coll1) MMP (coll4) remodel ECM
Zn dependent enzymes - degrade ECM: secreted as zymogen, function following activation by other proteins, increased MMP activation = cancer invasion and metastasis
Elastic Fibrils ECM provide Elasticity
Elastin = dom ECM protein in arts, skin, lungs, uterus, highly H-phobic, rich proline and glycine (not glycosylated and no H-lys)
Collagen often interwoven to limit stretch and prevent tearing
Elastic Fibril formation
Soluble tropoelastin secreted and assembled into elastic fibers close to PM = little 2nd struc (stretch). Covalently crosslinked to form fiber and sheet (tropo to elastin)
EF consists of Elastin microfibrils
Elastin core covered with microfibrils, composed of glycoproteins (fibrillin)
Fibrillin binds to elastin for assembly and integrity of EF
Microfibrils = scaffold for deposited elastin
Elastic Degradation
Elastase= serine proteases, secreted by neutrophils (increased flex= inhibit elastin)
alpha1-antitrypsin (a1-AT) binds to active site on elastase and trypsin (secreted by liver)
Glycasamoglycan (GAG) and proteoglycans
GAGs covalently linked to core protein to form proteoglycan = very long unbranched negative charged repeating disaccs. Amino sugar (NAcylglu/Nacyl galac::: usually sulfated) Sugar acid (glucuronic/iduronic). Neg charge attracts Na and therefore water
Hyaluronic- unique GAGs
Repeat around 25k nonsulfated disaccs (GLCNAc-Glucorunic Acid), not covalently bound to core protien, synth by enzyme on basal epi surface and intracell to be secreted
Function of Hyal GAGs
Produced during wound healing to cell free space allowing easy cell migration
Lubes joints (attracts H2O)
Resists compression
Backbone for large proteoglycan complexes (Aggrecan)
Hyal in eye (Vitrous humor)
Noncompress, increased viscoelasticity
Struc: proteoglycans cross link coll fibrils (2,9) via specific binding sites on coll fibrils. Proteogly-coll structure held by Hyal network
Proteoglycan Structure
Sugar groups to core protein = large complexes with Hyal
Aggrecan Proteoglycan in cartilage
Hyal acid forms central core but not covalent bound to proteins. Core proteins associated with Hyal Acid through link proteins
Functions of Proteoglycans in ECM
- Forms porous hydrated gel - fills spaces and resists compression
- Structural - associated with each other, coll and basal lamina
- Cell signaling - binds growth factors, increases cell surface receptor binding affinity for growth factors
- Cell migration - free space, bind and regulate of proteases and inhibitors, immobilize chemokines
Basal Lamina
Specialized ECM, flexible, thin. Underlies epi, surrounds individual cells, skl muscle cells, adipocytes, schwann cells. Interposed between 2 cell sheets (kid glom)
Basal Lamina Network
Produced by adjacent cells: Type 4 collagen (sheer formation), Laminin, entactin/Nidogen, HSPGs = Perlecan
Adhesive glycoprotein: Laminin
Anchors epi cells to BL: Laminin and type 4 coll bind = scaffold, also binds HSPG, entactin, integrins
Org assembly of BL by binding cell membrane laminin receptors (integrins, dystroglycans)
Laminin receptor binding (adhesion) increases cell growth and differentiation
Most prevalent constituent of all Basal Lamina
Perlecan Function in BL
(Heparin Sulphate proteoglycan, HSPG) is found in all cell BM. Mediates cell attachment to BL for endothelial cells and fibroblasts:
Binds enactin, laminin, coll 4 and fibronectin. Interactions with other proteoglycans in matrix increase strength
ECM proteoglycans bind to Mitogens
HSPGs perlecan and Syndecin function in angiogenesis and mitogenesis. Perl and Syn bind and sequester Growth factors - bind to R on cell surface with increased affinity
GAGs function as charge and size filter
HSPG perlecan rich in BL of kid glom, prevents macromolec passing to urine
GAGs=size and charge filer as most proteins are neg charge similar to GAG
Diabetes induced changes in renal BM changes renal selectivity
BL functions
- Structural support for cells (transmembrane integrin receptor bind coll 4 and laminin= organizes cells and tissue)
- Scaffold for tissue regen
- Filter in glom, selective barriers
- Determines cell polarity
- Cell survival, proliferation, differentiation
Fibronectin
Org ECM and cell attachment: all ECM (except coll 4, BL, mod’d by laminin), as a Dimer
- Binding site for ECM components: Coll (fibrillar), proteoglycans, fibrin
- Binding site for cell surface receptors (integrins): RGD (Arg, Gly, Asp) sequences
- Soluble plasma fibronectin = plasma glycoprotein, made by liver, circulates in blood, enchances blood clot
- Insoluble on cell surface and deposited in ECM
* Necessary for embryogenesis as it guides cell migration
Fibronectin secretion
Secreted by fibroblasts: fibronectin dimers crosslink and assemble into fibrils by binding to integrins at cell surface - stims fibril formation with other fibronectins via disulfide bonds
Deficiency of Vit C (Asorbic Acid)
Scurvy - fewer coll bonds formed, weak CT, def for 20-40 days, bleeding gums, loose teeth, eccymoses, poor wound healing, bone develop anemia and fatigue
Risk in elderly, alch, smokers, lost through cooking
Ehlers Darlos Syndrome
Defect in coll (fibrillar) synth - improper assembly of coll therefore CT weak leading to hyperextensible skin and joints
Collagen Defects: Disorders
Coll Mutation - CT defects Osteogenesis imperfecta: 1 Ehlers Dalos: 1,3,5 Alport Syndrome: 4 Good posture syn: 4 Epidemolysis Bullosa: 7
Marfan Syndrome
Fibrillin gene mutation - weak elastic tissue, Heart (aortic root dilation, dissection, aortic/mitril regurgitation) Eye (lens subflexion, retina detach) Skeleton (tall thin, arachnodactyly and pectus involvement)
Defect in a1-AT
Uninhib destruction of elastic fibers by elastase
COPD (emphysema) - AR, by 30-50, early=smoking
Destruction of alveolar tissue by neutrophil elastase
Smoke = irritant and inhib a1-AT (oxidizes Methionine) so smoking recruits neutrophiles which release elastase leading to lung (paranchymal) tissue non regen - elastic loss - decreased flex of alveolus - stagnant alveolar air, resp insufficiency, resp distress
Tx=a1-AT
Diabetic Nephropathy: BM dysfx
HSPGs detect sieving properties and inhibit uncontrolled replication of cells on BM
Hyperglycemia - decreased HSPG, coll glycosylation, crosslinking - GBM thickening due to increased coll and decreased HSPG - expansion of mesangial matrix leading to kidney failure (#1 cause)
