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

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-beta (TGF-beta) using mouse CF were examined. S1P increased alpha-smooth muscle actin (a myofibroblast marker) and collagen expression in a S1P(2) receptor- and Rho kinase-dependent manner. TGF-beta increased sphingosine kinase 1 (SphK1; the enzyme responsible for S1P production) expression and activity. TGF-beta-stimulated collagen production was inhibited by SphK1 or S1P(2) siRNA, a SphK inhibitor, and an anti-S1P monoclonal antibody. These findings suggest that TGF-beta-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 S1P(2) and increase collagen production.