A potential role for protease nexin 1 overexpression in the pathogenesis of scleroderma

Scleroderma currently affects approximately 75,000-100,000 individuals in t he United States. Fibroblasts isolated from lesional skin of scleroderma pa tients overexpress collagens and other matrix components, and this abnormal ity is maintained for multiple passages in culture. To understand the molec ular basis for matrix gene overexpression, we performed a differential disp lay comparison of fibroblasts from clinically lesional and nonlesional scle roderma skin. The results suggested that protease nexin 1 (PN1), a protease inhibitor, is overexpressed in scleroderma fibroblasts. Northern blot veri fication showed that lesional and nonlesional scleroderma fibroblasts had t hree- to five-fold increased levels of PN1 mRNA compared with healthy fibro blasts. Western analysis showed that scleroderma fibroblasts also secreted more PN1. In situ hybridization of skin biopsy specimens demonstrated PN1 e xpression in the dermis of four out of six scleroderma patients but no PN1 expression in the dermis of six healthy volunteers. Transient or stable ove rexpression of PN1 in mouse 3T3 fibroblasts increased collagen promoter act ivity or endogenous collagen transcript levels, respectively. PN1 mutageniz ed at its active site and antisense PN1 both failed to increase collagen pr omoter activity. These results suggest that overexpression of enzymatically active PN1 may play a pathogenic role in the development of the scleroderm a phenotype.