Sphingosine 1-phosphate protects rat liver sinusoidal endothelial cells from ethanol-induced apoptosis: Role of intracellular calcium and nitric oxide

Abstract

In alcoholic liver disease, ethanol-induced damage to sinusoidal endothelial cells (SECs) appears to be important in the progression of liver damage. However, little is known about the mechanisms responsible for protection of SECs against ethanol-induced injury. To elucidate the role of sphingosine 1-phosphate (S1P), which is stored in platelets and may be released from them on their activation, we investigated the effect of S1P on rat liver SECs in primary culture. Pretreatment of cells with 1 mol/L S1P attenuated ethanol-induced apoptosis. Electron microscopy confirmed this protective effect of S1P on damaged SECs in liver tissues after perfusion of ethanol. In the absence of ethanol, S1P increased DNA synthesis as determined via incorporation of bromodeoxyuridine. S1P also ameliorated the decreased DNA synthesis of cells induced by ethanol. Addition of S1P to cells induced an increase in intracellular calcium concentrations and NO production in cells. Western blotting revealed that S1P significantly induced the activation of endothelial NO synthase (eNOS), but not Akt, and that S1P-induced activation of eNOS was blocked by trifluoperazine, a calmodulin inhibitor. Furthermore, N G -nitro-L-arginine methyl ester, a NO synthase inhibitor, cancelled the effect of S1P on DNA synthesis, apoptosis, and NO production in vitro as well as the protective effect of S1P on cell damage in situ. In conclusion, the biological effect of S1P is at least partially mediated by Ca 2؉ -sensitive eNOS activation and subsequent NO formation; extracellular S1P could contribute to sinusoidal protection and remodeling in alcoholic liver injury. Supplementary material for this article can be found on the HEPATOLOGY website (http://interscience.wiley.com/jpages/0270-9139/suppmat/index.html).

Sphingolipids and cell death

“…Thus, the modulation of ceramide generation through ASMase mediating TNF/Fasinduced hepatocellular death may be a promising therapeutic approach to steatohepatitis [143], hepatic I/R damage [24] or alcohol-induced liver injury, in part, through activation of GCS and subsequent ganglioside generation that may target mitochondria weaken by depletion of mGSH [see 8 and references therein]. Finally, S1P has been shown to protect liver sinusoidal endothelial cells from ethanol-induced apoptosis, while the antiapoptotic role of SK through S1P formation has been involved in the protection of stellate cells in bile duct ligation-induced hepatic fibrosis [149,150]. Hence not only the generation of ceramide but its metabolism into antiapoptotic S1P derivative through concerted action of CDases and SK may have an important role in nonparenchymal cell fate and hence fibrogenesis.…”

Sphingosine-1-Phosphate Activates the AKT Pathway to Protect Small Intestines from Radiation-Induced Endothelial Apoptosis

“…S1P is already known to modulate endothelial functions, such as attenuate increase in vascular permeability by regulating junctional complexes (13). It has also been shown to block in vitro endothelial cell death induced by H 2 O 2 (14), ethanol (15), and serum deprivation (16). We recently showed that S1P protects human microvascular endothelial cells (HMEC-1) from radiation-induced apoptosis (17).…”

Sphingosine 1-Phosphate Has Dual Functions in the Regulation of Endothelial Cell Permeability and Ca2+Metabolism

“…In recent years, the endogenous lipid derivative, sphingosine-1-phosphate (S1P), has emerged as a potentially im-portant regulator of EC barrier function (Itagaki and Hauser, 2003;McVerry and Garcia, 2004;Finigan et al, 2005;Seol et al, 2005;Zheng et al, 2006). Upon a variety of stimuli leading to protein C activation, S1P is generated from sphingosine through the action of ubiquitous sphingosine kinase (SK).…”