Catabolism of intact type VI collagen microfibrils: Susceptibility to degradation by serine proteinases

We present the first direct biochemical evidence for the turnover of intact type VI collagen microfibrils. Matrix-degrading enzymes of the serine proteinase class, including rat mast cell chymases I and II, human mast cell tryptase, neutrophil elastase, cathepsin G and trypsin, were able to catabolize intact type VI collagen microfibrils isolated from foetal bovine skin and metabolically labelled intact type VI collagen immunoprecipitated from fibroblast culture medium. By contrast, intact type VI collagen was not degraded by the human matrix metalloproteinases, MMP-1, MMP-2, MMP-3 and MMP- 9. These data have important implications for the stability of type VI collagen in connective tissues and highlight the potential role of serine proteinases both in normal type VI collagen turnover and in inflammatory conditions characterized by matrix degradation.