RESUMO
BACKGROUND/PURPOSE: Photoaging of the skin is a result of chronic exposure to environmental ultraviolet radiation (UV). The milieu provided by the extracellular matrix, which significantly influences the behaviour of resident fibroblasts, depends critically on the supermolecular collagen structure. We ask whether direct photochemical treatment of type I collagen with solar wavelengths capable of reaching the dermis can modify the substrate's susceptibility to collagenase in a model in vitro system. METHODS: Acid- extracted Skh-1 hairless mouse collagen samples were irradiated with 0-140 J/cm2 of radiation from bank of filtered FS lamp (UVB/UVA = 0.33, fluence rate = 0.81 mW/cm2). Subsequent to UV irradiation, collagen samples were coupled with fluorescein isothiocyanate (FITC) and assayed for susceptibility to bacterial collagenase by monitoring the appearance of supernatant FITC fluorescence (a measure of lysed collagen) over time of incubation. As a 'reference', unirradiated commercial FITC-labelled citrate-soluble collagen (Elastin Products, Owensville, MO 65066, USA) was similarly analysed. RESULTS: Unirradiated mouse collagen had a lower rate of cleavage than did the calfskin sample. Irradiation of unlabelled mouse collagen for 0-48 h (0-140 J/cm2 total UV) rendered the sample more soluble, with concomitant chain degradation, cross-linking and loss of intrinsic collagen fluorescence. At irradiation time's >/= 4 h (>/=11.7 J/cm2), the irradiated collagen was significantly more susceptible to bacterial collagenase digestion. DISCUSSION: It appears that the rate of cleavage depends on the superstructure of the collagen, since the kinetics of collagen cleavage differ for two collagen samples having essentially the same primary structure. Cleavage kinetics may depend on the 'maturity' (solubility) of the collagen. The observation that UV-damaged mouse collagen is a better substrate for collagenase than the intact sample may be illustrative of a mechanism whereby damaged collagen targets itself for selective attack by collagenase.
