Sphingosine Kinase-1 Pathway Mediates High Glucose-Induced Fibronectin Expression in Glomerular Mesangial Cells

Diabetic nephropathy is characterized by accumulation of glomerular extracellular matrix proteins, such as fibronectin (FN). Here, we investigated whether sphingosine kinase (SphK) 1 pathway is responsible for the elevated FN expression in diabetic nephropathy. The SphK1 pathway and FN expression were examined in streptozotocin-induced diabetic rat kidney and glomerular mesangial cells (GMC) exposed to high glucose (HG). FN up-regulation was concomitant with activation of the SphK1 pathway as reflected in an increase in the expression and activity of SphK1 and sphingosine 1-phosphate (S1P) production in both diabetic kidney and HG-treated GMC. Overexpression of wild-type SphK1 (SphK(WT)) significantly induced FN expression, whereas treatment with a SphK inhibitor, N,N-dimethylsphingosine, or transfection of SphK1 small interference RNA or dominant-negative SphK1 (SphK(G82D)) abolished HG-induced FN expression. Furthermore, addition of exogenous S1P significantly induced FN expression in GMC with an induction of activator protein 1 (AP-1) activity. Inhibition of AP-1 activity by curcumin attenuated the S1P-nduced FN expression. Finally, by inhibiting SphK1 activity, both N, N-dimethylsphingosine and SphKG82D markedly attenuated the HG-induced AP-1 activity. Taken together, these results demonstrated that the SphK1 pathway plays a critical role in matrix accumulation in GMC under diabetic condition, suggesting that the SphK1 pathway could be a potential therapeutic target for diabetic nephropathy. (Molecular Endocrinology 25:2094-2105, 2011)