Fibroblast matrix gene expression and connective tissue remodeling: Role of endothelin-1

This study examines endothelin-induced modulation of extracellular matrix s ynthesis and remodeling by fibroblasts, and its potential role in the patho genesis of systemic sclerosis (scleroderma). Endothelin-1 promoted fibrobla st synthesis of collagen types I and III, but not fibronectin, by a mechani sm dependent upon both ETA and ETB receptors. Conversely, endothelin-1 inhi bited both protein expression of matrix metalloproteinase 1 and zymographic activity exclusively via ETA receptors. A dual regulatory role for endothe lin-1 in transcriptional regulation was suggested by the ability of endothe lin-1 to enhance steady-state levels of collagen mRNA and activate the pro alpha2(I) collagen (Col1a2) promoter, but in contrast to reduce matrix meta lloproteinase 1 transcript expression and suppress transcription of a human matrix metalloproteinase 1 promoter reporter construct in transient transf ection assays. Although endothelin-1 significantly enhanced remodeling of t hree-dimensional collagen lattices populated by normal fibroblasts, this wa s not observed for lattices populated by systemic sclerosis fibroblasts. Pr omotion of matrix remodeling was dependent upon ETA receptor expression and was blocked by specific inhibitors of tyrosine kinases or protein kinase C . Reverse transcriptase polymerase chain reaction, S1 nuclease, and functio nal cell surface binding studies showed that normal and systemic sclerosis fibroblasts express both ETA and ETB receptors (predominantly ETA), but tha t ETA receptor mRNA levels and ETA binding sites on fibroblasts cultured fr om systemic sclerosis skin biopsies are reduced by almost 50%. Endothelin-1 is thus able to induce a fibrogenic phenotype in normal fibroblasts that i s similar to that of lesional systemic sclerosis fibroblasts. Moreover, red uced responsiveness to exogenous endothelin-1 in systemic sclerosis suggest s that downstream pathways may have already been activated in vivo. These d ata further implicate dysregulated endothelin-receptor pathways in fibrobla sts in the pathogenesis of connective tissue fibrosis.