Invesigation on cellular mechanism of erythropoietin induced hypertension

维持性血液透析患者促红细胞生成素(EPO)引起的高血压是临床肾病研究的热点问题。尽管EPO诱发高血压的机制有多种可能，但我们特别参考了培养的大鼠血管平滑肌细胞(VSMC)的一氧化氮(NO)代谢来研究它。我们已经证实，EPO可以抑制IL-1β诱导的VSMC诱导型一氧化氮合酶基因和蛋白的表达以及NO的产生。最近的研究表明，几种细胞因子可以通过NO诱导VSMC的凋亡。此外，EPO还可以诱导细胞内游离钙的动员，还可以调节心血管系统对血管紧张素II(AGII)、去甲肾上腺素(NE)和内皮素(ET)等血管收缩物质的敏感性。因此，在本课题中，我们探讨了促红细胞生成素是否对IL-1β或NO供体硝普钠(SNP)诱导的VS…细胞凋亡具有调控作用。此外，我们还探讨了促红细胞生成素(EPO)诱导血管内皮细胞[Ca~(2+)]i动员的机制及其在MAPK激活和DNA合成中的作用，以及EPO对AgII、NE和ET诱导的VSMC[Ca~(2+)]i动员反应性的影响。我们的研究表明，重组人促红细胞生成素抑制IL-1β或硝普钠诱导的VSMC凋亡。促红细胞生成素对IL-1β和硝普钠诱导的血管内皮细胞凋亡的拮抗作用可能是通过TK依赖途径，尤其是PI3-激酶依赖途径来实现的。酪氨酸磷酸化在[Ca^&lt；2+&gt；]i的调节中起关键作用，但PKC的激活只在Ca^&lt；2+&gt；内流的调节中起重要作用。二氢吡啶敏感的L型钙通道可能参与了促红细胞生成素诱导的钙内流。此外，EPO还可促进VSMC内[Ca^&lt；2+&gt；]i的升高，刺激MAP激活和DNA合成。此外，EPO对AGII、NE或ET诱导的VSMC内[Ca^&lt；2+&gt；]i的动员有协同作用，尤其是对细胞内[Ca^&lt；2+&gt；]i的释放有协同作用，这可能是EPO治疗高血压的可能机制之一。然而，还需要进一步的研究来阐明较低浓度的EPO对[Ca^&lt；2+&gt；]i动力学的影响。

Erythropoietin (EPO)-induced hypertension in the patients on maintenance hemodialysis is a matter of paticular interest in clinical nephrology. Although various possibility is indicated on the mechanism of the EPO-induced hypertension, we have examined it with special reference to nitric oxide (NO) metabolism in cultured rat vascular smooth muscle cells (VSMC). We already demonstrated that EPO inhibited interleukin -1β induced iNOS mRNA and protein expression and NO production in VSMC.Recent studies have shown that several cytokines could induce apoptosis to VSMC via the induction of NO.In addition, EPO induces cytosolic free calcium ([Ca^<2+>]i) mobilization and also modulates the sensitivity of the cardiovascular system to vasoconsrictive substances such as angiotensin II (AgII), norepinephrine (NE) or endothelin (ET). Therefore, in the present project, we explored whether EPO has a modulatory effect of apoptosis on IL-1β or NO donor sodium nitroprusside (SNP) induced apoptosis in VS … More MC.Furthermore, we explored the mechanism of EPO induced [Ca^<2+>]i mobilization and its role in the activation of MAP kinase and DNA synthesis and explored the effect of EPO on the responsiveness of AgII, NE or ET induced [Ca^<2+>]i mobilization in VSMC.Our present study demonstrated that rHuEPO inhibited IL-1β or SNP induced VSMC apoptosis. The TK dependent pathway, particularly the PI 3-kinase dependent pathway seems to be critical to the countervailing effect of rHuEPO on IL- 1β and SNP induced VSMC apoptosis.Concerning the effects of EPO on [Ca^<2+>]i, (1) EPO increases [Ca^<2+>]i by both Ca^<2+> influx and Ca^<2+> release from intracellular stores. Tyrosine phosphorylation is critical in the regulation of [Ca^<2+>]i, but PKC activation is important only in the regulation of Ca^<2+> influx. Dihydoropyridine sensitive L-type Ca^<2+> channel seems to be involved in EPO induced Ca^<2+> influx. In addition, increase of [Ca^<2+>]i by EPO stimulates MAP kinase activation and DNA synthesis in VSMC.Furthermore, EPO has synergistic effects on AgII, NE or ET induced [Ca^<2+>]i mobilization, particularly on intracellular Ca^<2+> release, in VSMC.This may be one of the potential mechanisms that contribute to hypertension associated with EPO therapy. However, further investigations were needed to clarify the effect of lower concentaration of EPO on the dynamics of [Ca^<2+>]i. Less