A TARGETED MUTATION AT THE KNOWN COLLAGENASE CLEAVAGE SITE IN MOUSE TYPE-I COLLAGEN IMPAIRS TISSUE REMODELING

Degradation of type I collagen, the most abundant collagen, is initiat ed by collagenase cleavage at a highly conserved site between Gly(775) and Ile(776) of the alpha 1(I) chain. Mutations at or around this sit e render type I collagen resistant to collagenase digestion in vitro. We show here that mice carrying a collagenase-resistant mutant Colla-1 transgene die late in embryogenesis, ascribable to overexpression of the transgene, since the same mutation introduced into the endogenous Colla-1 gene by gene targeting permitted normal development of mutant mice to young adulthood. With increasing age, animals carrying the tar geted mutation developed marked fibrosis of the dermis similar to that in human scleroderma. Postpartum involution of the uterus in the muta nt mice was also impaired, with persistence of collagenous nodules in the uterine wall. Although type I collagen from the homozygous mutant mice was resistant to cleavage by human or rat fibroblast collagenases at the helical site, only the rat collagenase cleaved collagen trimer s at an additional, novel site in the nonhelical N-telopeptide domain. Our results suggest that cleavage by murine collagenase at the N-telo peptide site could account for resorption of type I collagen during em bryonic and early adult life. During intense collagen resorption, howe ver, such as in the immediate postpartum uterus and in the dermis late r in life, cleavage at the helical site is essential for normal collag en turnover. Thus, type I collagen is degraded by at least two differe ntially controlled mechanisms involving collagenases with distinct, bu t overlapping, substrate specificities.