PROTECTIVE EFFECT OF SPHINGOSINE 1-PHOSPHATE ON LIVER SINUSOIDAL ENDOTHELIAL CELLS AGAINST ETHANOL-INDUCED APOPTOSIS

酒精性肝病的发病机制主要是在肝实质细胞中进行研究。然而，很少有人知道的机制，保护窦内皮细胞（SECs）对乙醇诱导的损伤。1-磷酸鞘氨醇（sphingosine 1-phosphate，S1 P）是一种由血小板活化释放的生物活性脂质，具有调节细胞增殖、迁移、创伤愈合和抑制细胞凋亡等多种生物学功能。为了验证S1 P是否影响乙醇诱导的肝损伤中SECs的生物学功能，我们检测了细胞外S1 P对原代培养的SEC的影响，结果表明，S1 P对原代培养的大鼠肝SEC具有保护作用，其保护作用可能是通过激活Ca^<2+>敏感的eNOS和随后的NO生成来介导的。这与以前的报道一致，即eNOS产生的NO对于保护几种细胞类型的凋亡是重要的，并且进一步得到我们目前的发现的支持，即抑制钙调蛋白（一种Ca^2+结合蛋白）减弱S1 P诱导的SEC中eNOS活性。S1 P还能改善乙醇引起的细胞DNA合成减少。因此，我们认为，S1 P可能在酒精性肝损伤中参与了肝窦的保护和重塑，尽管Ca^2+、CaM和eNOS活性之间的分子相互作用还需要进一步的研究，但我们的研究结果提示了S1 P调节酒精诱导的SEC凋亡的可能机制。S1 P的生理重要性是不确定的。然而，我们的研究结果可能会导致更好地理解S1 P作为酒精性肝损伤新治疗策略的靶点。

The mechanism of alcoholic liver disease has been largely investigated in parenchymal hepatocyte. However, little is known about the mechanisms underlying the protection of sinusoidal endothelial cells (SECs) against ethanol-induced injury. Recently, sphingosine 1-phosphate (S1P), a serum-borne bioactive lipid released from activated platelets, has been reported to regulate diverse biological processes, such as cell proliferation, migration, wound healing and inhibition of apoptosis. To test whether S1P may affect biological function of SECs in ethanol-induced liver injury, we examined the effect of extracellular S1P on SECs in primary culture.Our results show that S1P protects SECs against ethanol-induced injury in primary culture of rat liver, and that the protective effect of S1P may be mediated by activation of Ca^<2+>-sensitive eNOS and subsequent NO formation. This is consistent with previous report that NO generated by eNOS is important for protection of apoptosis in several cell types, and further supported by our present finding that inhibition of calmodulin, a Ca^<2+> binding protein, attenuates S1P-induced eNOS activity in SECs. S1P also ameliorated the decreased DNA synthesis of cells caused by ethanol. We thus propose that S1P, which is possibly released from activated platelets in response to ethanol consumption, could contribute to sinusoidal protection and remodeling in alcoholic liver injury.Although further research is required to elucidate the molecular interaction between Ca^<2+>, CaM and eNOS activity, our results suggest a possible mechanism for the regulation of ethanol-induced apoptosis in SECs by S1P. Physiological importance of S1P is uncertain. However, our findings may lead to a better understanding of S1P as a target for novel therapeutic strategies in alcoholic liver injury.