A growing family of collagens in articular cartilage: identification of 5 genetically distinct types.
Cartilage displays an extensive polymorphism of collagen types. All hyaline cartilages are known to contain type II collagen (90-95% of the collagen) and 2 other cartilage-specific minor collagens called types IX (or M) and XI (or 1 alpha 2 alpha 3 alpha). In the present work, the molecular heterogeneity of articular cartilage collagen was investigated in more detail. Two additional genetic types of collagen were found in the mature bovine tissue, types V and VI, each accounting for about 1-2% of the tissue dry weight. Type V, a close relative of type XI, apparently had accumulated after birth. Type VI is a short-helix, microfibrillar collagen of wide tissue distribution but unknown function. In understanding the physical changes in the collagen network of cartilage that are believed to herald the onset of cartilage degeneration in osteoarthrosis, all five of these collagen types deserve attention.