Collagen Degradation in Aged/Photodamaged Skin in Vivo and after Exposure to Matrix Metalloproteinase-1 in Vitro

Biochemical and ultrastructural approaches were used to assess collagen changes in photodamaged skin. Extensive collagen fragmentation, clumping of the fragmented collagen, and interaction of fibroblasts with the damaged matrix were observed. Similar, though less extensive, collagen damage was also observed in sun-protected skin-individuals aged 80 y or older (naturally aged skin). In comparison, sun-protected skin from young individuals (18-29 y of age) demonstrated little damage. A uniform distribution of collagen fibrils was seen. Interstitial fibroblasts were embedded in the collagen matrix and in close apposition with intact collagen fibrils. In additional studies, three-dimensional lattices of type I collagen were exposed in vitro to matrix metalloproteinase-1 (interstitial collagenase), and examined for biochemical and ultrastructural alterations. Under conditions in which enzyme treatment produced fragmentation in 30-40% of the collagen molecules, the lattices demonstrated collagen fragmentation and clumping of the damaged matrix. Recent studies have demonstrated a loss of procollagen production by fibroblasts in contact with collagen fragments in vitro. This study demonstrates similar changes in collagen structure in vivo in aged and photodamaged skin. We suggest that collagen fragmentation in vivo could underlie the loss of collagen synthesis in photodamaged skin and, to a lesser extent perhaps, in aged skin.