Effects of UVA irradiation following treatment with 8-methoxypsoralen on type I and type III collagen synthesis in normal and scleroderma fibroblast cultures.

Recent studies have demonstrated the efficacy of PUVA (psoralen plus ultraviolet A irradiation) therapy against sclerotic skin lesions in scleroderma, although the mechanisms underlying the improvement of the skin sclerosis by this therapy remain unknown. We investigated the effects of ultraviolet A (UVA) irradiation following the treatment with 8-methoxypsoralen on types I and III collagen synthesis and the gene expression of collagenase in cultured normal and scleroderma fibroblasts. The treatment reduced types I and III collagen synthesis and consequently, the types I and III collagen mRNA levels, in a UVA dose-dependent manner in both the normal and SSc fibroblasts, whereas the mRNA levels of collagenase remained almost unaltered. These results suggest that reduction of collagen synthesis by the fibroblasts may be one of the mechanisms underlying the efficacy of PUVA therapy against the sclerotic skin lesions in scleroderma.