Simultaneous analysis of [³H]-thymidine uptake and α1(I) procollagen mRNA expression in systemic sclerosis skin fibroblasts – an in situ hybridization study

Abstract Heterogeneity of DNA synthesis and collagen synthesis has been reported in skin fibroblasts from systemic sclerosis (SSc) patients. The uptake of [³H]-thymidine and expression of α1(I) procollagen mRNA by cultured skin fibroblasts from four normal controls and four SSc patients was analyzed simultaneously. The grains overlying the cytoplasm representing α1(I) procollagen mRNA and overlying the nucleus representing [³H]-thymidine uptake were counted using computer-aided image analysis. The results were analyzed statistically. Procollagen mRNA expression by SSc fibroblasts was significantly greater than by control fibroblasts (P < 0.01). The distribution curve of [³H]-thymidine uptake showed two peaks representing low- and high-uptake cells. Significantly more SSc fibroblasts than control fibroblasts showed high [³H]-thymidine uptake (P < 0.05). The number of SSc fibroblasts expressing low amounts of α1(I) procollagen mRNA was significantly lower than the number of control fibroblasts (P < 0.05). [³H]-thymidine uptake by SSc fibroblasts expressing high amounts of α1(I) procollagen mRNA was significantly lower than by those expressing low amounts (P < 0.05). These results indicate that elevated DNA synthesis and elevated collagen mRNA synthesis in SSc skin fibroblasts are due to different clones with high DNA-synthesizing ability and high collagen-producing ability.