Extracellular matrix

Context

Cells in multicellular tissues do not exist in isolation. They sit embedded in the ECM, a scaffold of large structural proteins (collagens), adhesion proteins (fibronectin, laminin), and hydrated polysaccharide-protein complexes (proteoglycans, glycosaminoglycans). The composition and organization of the ECM varies dramatically by tissue: bone is heavily mineralized, skin is flexible and tough, cartilage is compressible and hydrated.

Cartilage ECM is about 60-80% water, held in place by proteoglycans (especially aggrecan) with hyaluronic acid as the backbone. The remaining dry mass is predominantly type II collagen (the scaffold) and proteoglycans (the water-binding filler). This composition is what gives cartilage its ability to resist compression and recover shape after load.

Why it matters for joint health

Cartilage aging and osteoarthritis are, at the tissue level, a process of ECM degradation. Collagenase enzymes (especially MMP-13) cleave type II collagen; aggrecanases (ADAMTS-4, ADAMTS-5) cleave aggrecan. As the ECM breaks down, cartilage loses its compressive strength and elasticity, and the joint function degrades. Supporting matrix synthesis (via glucosamine, HA, collagen peptides) and modulating the signaling that drives degradative enzymes (NF-kB, 5-LOX pathway) are the two sides of the ECM balance that joint supplements target.