Previous studies have revealed a phosphatase and tensin homolog (PTEN)–dependent interaction between the sphingolipid agonist dihydrosphingosine 1-phosphate (dhS1P) and the transforming growth factor β/Smad3 signaling pathway. This study was undertaken to examine responses of systemic sclerosis (SSc) fibroblasts to sphingosine 1-phosphate (S1P) and dhS1P and to gain further insight into the regulation of the S1P/dhS1P/PTEN pathway in SSc fibrosis.
Fibroblast cultures were established from skin biopsy samples obtained from patients with SSc and matched healthy controls. Western blotting and quantitative polymerase chain reaction were used to measure protein and messenger RNA levels, respectively. PTEN protein was examined in skin biopsy samples by immunohistochemistry.
PTEN protein levels were low in SSc fibroblasts and correlated with elevated levels of collagen and phospho-Smad3 and reduced levels of matrix metalloproteinase 1 (MMP-1). Treatment with dhS1P restored PTEN levels and normalized collagen and MMP-1 expression, as well as Smad3 phosphorylation status in SSc fibroblasts. S1P was strongly profibrotic in SSc and control fibroblasts. Distribution of S1P receptor isoforms was altered in SSc fibroblasts, which had reduced levels of S1P receptor 1 and S1P receptor 2 and elevated levels of S1P receptor 3. Only depletion of S1P receptor 1 abrogated the effects of dhS1P and S1P in control dermal fibroblasts. In contrast, depletion of either S1P receptor 1 or S1P receptor 2 prevented the effects of S1P and dhS1P in SSc fibroblasts.
Our findings demonstrate that PTEN deficiency is a critical determinant of the profibrotic phenotype of SSc fibroblasts. The antifibrotic effect of dhS1P is mediated through normalization of PTEN expression, suggesting that dhS1P or its derivatives may be effective as therapeutic antifibrotic agents. The distribution and function of S1P receptors differ in SSc and healthy fibroblasts, suggesting that alteration in the sphingolipid signaling pathway may contribute to SSc fibrosis.