This 2002 review describes the collagen in adult joint cartilage. Collagen forms the extracellular framework and two-thirds of the dry mass. Type II collagen is the main molecule, built into a cross-linked network with collagens IX and XI, and collagens III, VI, X, XII and XIV also have roles.
This is a review, not a new experiment. The author summarised what was known about the different collagen types in articular cartilage, how they fit together into a network, and what each appears to do.
Polymeric collagen makes up the extracellular framework and two-thirds of the dry mass of adult articular cartilage. Type II collagen is the principal molecule in mammals, but collagens III, VI, IX, X, XI, XII and XIV all contribute to the mature matrix. In developing cartilage, the core fibre network is a cross-linked copolymer of collagens II, IX and XI. The roles of IX and XI are not fully defined, but mutations in their genes cause skeletal growth disorders (chondrodysplasias) that include early joint degeneration, so they clearly matter. Collagens XII and XIV sit on the fibre surfaces without being chemically bonded to them. Collagen VI forms its own filament network with many attachment points for cells and other matrix parts, and collagen X is normally limited to the thin calcified layer where cartilage meets bone.
A review adds no new data, and the abstract does not cite the studies behind each statement. It describes the structure of cartilage collagen, not how it is broken down, and it does not mention MMP13 or any other enzyme.
To understand what MMP13 destroys, it helps to know what cartilage is built from. Type II collagen is the main structural molecule of joint cartilage, which is why the enzyme with the highest activity against type II collagen draws so much attention. The review also shows the collagen network is a mix of types, not one.
Type II collagen is the main collagen in joint cartilage. Collagen makes up about two-thirds of adult cartilage's dry mass, and type II is its principal molecule, woven...
MMP13 cuts type II collagen, the rope-like fibre that gives cartilage its strength. It cleaves each three-stranded collagen molecule at one spot, leaving a three-quarter...