MATRICE EXTRACELLULARE - ECM E’ un complesso miscuglio di Proteine Glicoproteine proteoglicani strutturali e funzionali, organizzati in un’unica ultrastruttura tri-dimensionale tessuto-specifica. variazioni della quantità relativa dei vari tipi di macromolecole modo in cui esse si organizzano Diversità di forme e funzioni, adatte ai requisiti di ciascun tessuto

Distinguiamo due tipi di ECM • La matrice extracellulare (interstiziale) dei tessuti connettivi • La lamina basale Nelle lamine basali le molecole di ECM sono deposte solo sulla superficie basale su cui sono si adagiano le cellule Nella matrice extracellulare le molecole dell’ECM circondano le cellule riempiendo gli spazi interstiziali intercellulari Mentre nella matrice interstiziale le molecole tendono a formare un lattice tridimensionale, la membrana basale si organizza invece in un piano

Types of ECMs Basement membrane (basal lamina) Epithelia, endothelia, muscle, fat, nerves Elastic fibers Skin, lung, large blood vessels Stromal or interstitial matrix Bone, tooth, and cartilage Tendon and ligament

Funzioni dell’ ECM (attive) Ruolo strutturale: supporto per le cellule Regolazione divisione cellulare adesione motilità Sviluppo migrazione differenziamento Riserva di fattori di crescita Trasduzione del segnale molecole dell’ECM -> recettori di superficie -> espressione genica

Why do all multicellular animals have ECM? Act as structural support to maintain cell organization and integrity (epithelial tubes; mucosal lining of gut; skeletal muscle fiber integrity) Compartmentalize tissues (pancreas: islets vs. exocrine component; skin: epidermis vs. dermis) Provide hardness to bone and teeth (collagen fibrils become mineralized) Present information to adjacent cells: Inherent signals (e.g., RGD motif in fibronectin) Bound signals (BMP7, TGFβ, FGF, SHH) Serve as a highway for cell migration during development (neural crest migration), in normal tissue maintenance (intestinal mucosa), and in injury or disease (wound healing; cancer)

Nella maggior parte dei tessuti connettivi le macromolecole della matrice sono secrete in gran parte dai fibroblasti Altre proteine della famiglia dei fibroblasti: Condroblasti -> formano la cartilagine Osteoclasti -> formano l’osso

Types of ECM Components Proteoglycans Perlecan, aggrecan, agrin, collagen XVIII Hyaluronan (no protein core) Collagens Fibrillins, elastin, LTBPs, MAGPs, fibulins Large Glycoproteins Laminins, nidogens, fibronectin, vitronectin “Matricellular” Proteins SPARC, Thrombospondins, Osteopontin, tenascins

GLYCOSAMINOGLYCANs - GAGs Glycosaminoglycans (GAGs) are unbranched polysaccharide chains composed of repeating disaccharide units. One of the two sugars in the repeating disaccharide is always an amino sugar (N-acetylglucosamine or N-acetylgalactosamine), which in most cases is sulfated (----). The second sugar is usually a uronic acid (glucuronic or iduronic).

Hyaluronan (also called hyaluronic acid or hyaluronate) is the simplest of the GAGs. It consists of a regular repeating sequence of up to 25,000 disaccharide units, is found in variable amounts in all tissues and fluids in adult Funzioni: Resistenza a forze di compressione (tessuti/cartilagini) Riempitore (sviluppo embrionale) Presente nel fluido articolare (lubrificante)

FDA approved HA for cosmetic use in humans – 2003:

Role of HA in morphogenesis: • Acts as space filler and facilitator of cell migration – If synthesized on the basal side of an epithelium, creates a cell-free space into which other cells can migrate The role of HA in atrioventricular canal morphogenesis:

Functions of hyaluronan: • Resists compressive forces in joints and tissues – Important constituent of joint fluid • In osteoarthritis, decreased concentration and decreased molecular weight of intra-articular HA

Proteoglycans are composed of GAG chains covalently linked to a core protein Classified by sugar composition – Keratan sulfate, chondroitin sulfate, dermatan sulfate, heparan sulfate • Modification of sugar residues allows for enormous diversity • Associate with each other and with other ECM components to make complex meshworks

Proteoglycans Are Composed of GAG Chains Covalently Linked to a Core Protein proteoglycans can contain as much as 95% carbohydrate by weight, mostly in the form of long, unbranched GAG chains, each typically about 80 sugars long

Funzione dei proteoglicani Intrappolamento dell’acqua Resistenza alla compressione Ritorno alla forma originale Creazione di spazi Legame alle fibre di collagene Formano una rete Nell’osso, si combinano con l’idrossiapatite di calcio e carbonato di calcio. Adesione cellulare Migrazione cellulare durante lo sviluppo embrionale Possono regolare l’attività di fattori di crescita (quali FGF)

Aggrecan is the major glycoprotein of articular cartilage: • Provides hydrated gel structure that endows cartilage with load-bearing properties • Chondroskeletal morphogenesis during development

Signaling roles of proteoglycans: • Proteoglycans can regulate the activities of secreted proteins – Gels formed by GAG chains act as “sieves” that regulate passage of molecules by size and charge – Bind secreted signaling molecules • Control diffusion, range of action, lifetime, modify signaling activity – e.g.,heparan sulfate immobilizes chemokines on the endothelial surface of a blood vessel at a site of inflammation • Cell-surface proteoglycans act as co-receptors