Sphingosine-1-phosphate and sphingosine kinase are critical for transforming growth factor- -stimulated collagen production by cardiac fibroblasts

Abstract

Following injury, fibroblasts transform into myofibroblasts and produce extracellular matrix (ECM). Excess production of ECM associated with cardiac fibrosis severely inhibits cardiac function. Sphingosine-1-phosphate (S1P), a bioactive lysophospholipid, regulates the function of numerous cell types. In this study, we determined the role of S1P in promoting pro-fibrotic actions of cardiac fibroblasts (CFs). S1P-mediated effects on myofibroblast transformation, collagen production, and cross-talk with transforming growth factor-β (TGF-β) using mouse CF were examined. S1P increased α-smooth muscle actin (a myofibroblast marker) and collagen expression in a S1P₂ receptor- and Rho kinase-dependent manner. TGF-β increased sphingosine kinase 1 (SphK1; the enzyme responsible for S1P production) expression and activity. TGF-β-stimulated collagen production was inhibited by SphK1 or S1P₂ siRNA, a SphK inhibitor, and an anti-S1P monoclonal antibody. These findings suggest that TGF-β-stimulated collagen production in CF involves ‘inside-out’ S1P signalling whereby S1P produced intracellularly by SphK1 can be released and act in an autocrine/paracrine fashion to activate S1P₂ and increase collagen production.