Elucidation of the mechanism of the inhibitory effect of sphingosine 1-phosphate on hepatocyte proliferation and the significance in liver regeneration

背景与目的：鞘氨醇1-磷酸（S1P）是G蛋白偶联内皮分化基因-1 （Edg-1）、Edg-3、Edg-S、Edg-6和Edg-8的配体，可引起细胞的多种反应，其中最突出的是细胞增殖。S1P在血小板中大量储存，激活后释放，提示S1P在体内发挥病理生理作用。由于注射的S1P大部分分布在小鼠的肝脏中，我们想知道肝脏是否会成为其靶点之一。研究了S1P对肝脏主要组成细胞肝细胞的影响。方法与结果：Northern blot分析显示，培养的大鼠肝细胞中Edg-1和Edg-5 mrna的表达，其中S1P减少HGF或EGF诱导的DNA合成，但不影响总蛋白的合成。用03外毒素灭活小GTPase Rho可以减弱这种抑制作用，而百日咳毒素灭活G1则不能。此外，在新开发的Edg-5特异性结合拮抗剂JTE-013的存在下，抑制作用也被取消。最后，大鼠部分肝切除70%后给予S1P降低了肝细胞DNA合成峰值，Rho活性升高，并且部分肝切除后24-72小时肝细胞中Edg-5 mRNA表达增强，但Edg-i mRNA表达不增强，这与肝细胞减少相一致。扩散。结论：S1P通过Edg-5激活Rho对大鼠肝细胞具有抗增殖作用。我们的结果提出了S1P在肝脏再生中是负调节因子的可能性。

Background & Aims: Sphingosine 1-phosphate (S1P), a ligand for G protein-coupled endothelial differentiation gene-I1(Edg-1), Edg-3, Edg-S, Edg-6 and Edg-8, elicits a variety of responses by cells: prominent among these is cell proliferation. S1P is abundantly stored in platelets and released upon their activation, suggesting that S1P plays a pathophysiological role in vivo. Because the major part of injected S1P was distributed into the liver in mice, we wondered whether the liver would be one of its targets. The effects of S1P on hepatocytes, the major constituent cells in the liver, were examined. Methods & Results: Northern blot analysis revealed the expression of Edg-1 and Edg-5 mRNAs in cultured rat hepatocytes, where S1P decreased DNA synthesis induced by HGF or EGF without affecting total protein synthesis. This inhibitory effect was attenuated by inactivation of small GTPase Rho with 03 exotoxin, but not by inactivation of G1 with pertussis toxin. Moreover, in the presence of JTE-013, a newly developed and specific binding antagonist for Edg-5, the inhibitory effect was also cancelled. Finally, the administration of S1P after 70% partial hepatectomy in rats reduced the peak of DNA synthesis in hepatocytes with increased Rho activity Furthermore, Edg-5 but not Edg-i mRNA expression was enhanced in hepatocytes 24-72 hours after partial hepatectomy, which coincides with decreasing hepatocyte. proliferation. Conclusions: S1P has an antiproliferative property in rat hepatocytes by activating Rho via Edg-5. Our results raise the possibility that S1P is a negative regulator in liver regeneration.