Antiproliferative Properties of Sphingosine 1-Phosphate in Human Hepatic Myofibroblasts

Abstract

Proliferation of hepatic myofibroblasts (hMF) is central for the development of fibrosis during liver injury, and factors that may limit their growth are potential antifibrotic agents. Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid with growth-regulating properties, either via Edg receptors or through intracellular actions. In this study, we examined the effects of S1P on the proliferation of human hMF. Human hMF expressed mRNAs for the S1P receptors Edg1, Edg3, and Edg5. These receptors were functional at nanomolar concentrations and coupled to pertussis toxin-sensitive and -insensitive G proteins, as demonstrated in guanosine 5-3-O-(thio)triphosphate binding assays. S1P potently inhibited hMF growth (IC 50 ‫؍‬ 1 M), in a pertussis toxininsensitive manner. Analysis of the mechanisms involved in growth inhibition revealed that S1P rapidly increased prostaglandin E 2 production and in turn cAMP, two growth inhibitory messengers for hMF; C 2 -ceramide and sphingosine, which inhibited hMF proliferation, did not affect cAMP levels. Production of cAMP by S1P was abolished by NS-398, a selective inhibitor of COX-2. Also, S1P potently induced COX-2 protein expression. Blocking COX-2 by NS-398 blunted the antiproliferative effect of S1P. We conclude that S1P inhibits proliferation of hMF, probably via an intracellular mechanism, through early COX-2-dependent release of prostaglandin E 2 and cAMP, and delayed COX-2 induction. Our results shed light on a novel role for S1P as a growth inhibitory mediator and point out its potential involvement in the negative regulation of liver fibrogenesis.

Sphingosine 1-Phosphate Triggers Both Apoptotic and Survival Signals for Human Hepatic Myofibroblasts

“…We previously identified S1P receptors (Edg-1, -3, and -5) in human hepatic myofibroblasts and noted that they relay the antiproliferative effect of S1P (13). In the present study, we show that S1P modulates apoptosis of hepatic myofibroblasts with a dual effect.…”

“…S1P is a downstream metabolite of ceramide that is produced after phosphorylation of sphingosine by sphingosine kinase (10). In contrast to ceramide and sphingosine, S1P generally elicits mitogenic and antiapoptotic effects (12), although growth-inhibitory and apoptotic effects have occasionally been described (13)(14)(15)(16)(17)(18). S1P modulates cell function by two distinct mechanisms, either as an intracellular messenger or as a ligand of a family of G proteincoupled receptors, the Edg (endothelial differentiation gene) receptors, which includes Edg-1, -3, -5, -6, and -8 (10,19).…”

Roles of AKT and sphingosine kinase in the antiapoptotic effects of bile duct ligation in mouse liver

“…Sphingosine kinase (SphK) catalyzes the phosphorylation of sphingosine to sphingosine 1-phosphate, and this metabolite promotes liver fibrogenesis. 10,11 SphK1 is also involved in the regulation of tissue inhibitor of metalloproteinase 1 (TIMP-1) in fibroblasts. 12 TIMP-1 inhibits MMP-9 and MMP-2.…”

Enhancement of survival by LPA via Erk1/Erk2 and PI 3-kinase/Akt pathways in a murine hepatocyte cell line

“…It has been shown recently that the LPA counterpart sphin-gosine-1-phosphate (S1P) induced proliferation of hepatic stellate cells (23,48). Other authors reported growth inhibition by S1P in hepatic myofibroblasts (11) and in primary rat hepatocytes stimulated with hepatocyte growth factor (24). On the other hand, LPA was shown to increase motility and migration of a human hepatoma cell line (37).…”