EDG1 receptor stimulation leads to cardiac hypertrophy in rat neonatal myocytes

Sphingosine I phosphate (SIP), an aminophospholipid, acts extracellularly as a ligand via the specific G protein-coupled receptors of the endothelial differentiation gene (EDG) 1. 3. 5, 6 and 8 receptors family and intracellularly as a second messenger in various cellular types. The aim of this work was to investigate biological activity of SIP in cardiomyocytes with respect to related sphingolipids. SIP was applied for 48 h on rat neonatal cardiomyocytes at 10 nM, 100 nM and 1 mum. S1P induced a concentration-dependent cellular hypertrophy evidenced by an increase in cell size, [H-3]-phenylalanine incorporation, protein content and Brain Natriuretic Peptide (BNP) secretion. Among the lipids tested SIP exhibits the lower EC50 (67 nM) followed by dihydro-SIP (107 nM) and sphingosylphosphorylcholine (1.6 mum). The effect of SIP could be related to a stimulation of the EDG1 receptor since we showed that the EDG1 receptor is predominantly expressed at the mRNA and protein levels in rat cardiomyocytes and that specific anti-EDG1 antibodies inhibited the hypertrophic effect induced by S1P. Furthermore the expression level of most other EDG receptors for S1P appeared very low in cardiac myocytes. SIP (100 nm) increased the phosphorylation of p42/44MAPK, p38MAPK, JNK, Akt and p70(S6K), this effect being reversed by inhibitors of their respective phosphorylation which also rescue the hypertrophic phenotype. Finally, SIP stimulated actin stress fibre formation reverted by the Rho inhibitor, the C3 exoenzyme. Altogether. our results show that SIP induces cardiomyocyte hypertrophy mainly via the EDG1 receptor and subsequently via Gi through ERKs, p38 MAPK, JNK, P13K and via Rho pathway. (C) 2001 Academic Press.