Renal sphingosine-1-phosphate receptor 1 in salt-sensitive hypertension

鞘脂最初被认为是细胞膜的沉默结构元件。最近， 鞘脂代谢物正成为重要的脂质信号分子。其中鞘氨醇-1- 已知磷酸盐（S1 P）在各种器官系统中的细胞过程中起重要作用， 心血管系统和肾脏。S1 P受体家族的五个成员（S1 P1-S1 P5）已被发现。 鉴定S1 P1 -3受体广泛表达，而S1 P4在肺和淋巴系统中表达， S1 P5主要分布于脑组织。S1 P1 -3受体存在于肾脏中。结果表明，S1 P 该系统在许多疾病的发病机制中起着重要作用，包括心血管和肾脏 疾病值得注意的是，肾脏中三种S1 P受体的功能不同。S1 P1介导保护性 S1 P2和S1 P3介导肾脏的损伤作用。尽管许多报告显示， S1 P通路参与肾脏生理和病理过程，但对肾脏S1 P的作用知之甚少 Na+排泄系统。我们最近发现，S1 P1 -3受体显著表达于 肾髓质，主要位于集合管中，并且肾髓质中的S1 P1受体介导 通过抑制上皮Na+通道（ENaC）产生强的利钠利尿作用。我们的初步数据显示， 盐的摄入上调了肾髓质中S1 P1的水平，有趣的是，醋酸脱氧皮质酮 （DOCA）治疗显著降低了肾髓质中S1 P1的水平。在有集合管的小鼠中 （CD）特异性S1 P1基因敲除（KO），压力性尿钠排泄减弱，高盐摄入促进更多 与对照小鼠相比，Na+潴留。此外，高盐摄入产生盐敏感性高血压 在CD特异性S1 P1 KO小鼠中，但在对照小鼠中，当用DOCA的降压剂量处理时，没有。上 另一方面，将选择性S1 P1激动剂BAF 312局部注入肾髓质， DOCA盐性高血压基于这些发现，我们假设肾髓质S1 P1通路是一个神经系统的信号通路。 关键的平衡机制，以抑制过度的Na+重吸收和抑制肾 延髓S1 P1通路参与盐敏感性高血压的发生。三个具体目标是 来检验我们的假设目的1：确定肾组织中S1 P1通路的抑制是否与肾组织中的S1 P1通路有关。 髓质有助于盐敏感性高血压的发病机制。CD特异性S1 P1缺失小鼠 或CD特异性过表达S1 P1转基因。目的2：确定S1 P1通路是否 抑制ENaC活性，从而增加Na+排泄，发挥抗高血压作用。膜片钳 在新鲜分离的集合管中进行ENaC通道活性的研究。目标3：探索 S1 P1激活抑制ENaC活性以通过Gi发挥抗高血压作用的机制 蛋白质/cAMP偶联信号传导。这些研究将揭示肾脏Na+损伤的新分子机制 处理和盐敏感性高血压的发病机制提供了新的见解。

Sphingolipids were originally thought to serve as silent structural elements of the cell membrane. Recently, sphingolipid metabolites are emerging as important lipid signaling molecules. Among them, sphingosine-1- phosphate (S1P) is known to play important roles in cellular processes in various organ systems including the cardiovascular system and kidney. Five members of the S1P receptor family (S1P1–S1P5) have been identified. The S1P1-3 receptors are ubiquitously expressed, while S1P4 is in the lung and lymphoid system, and S1P5 mainly in brain tissue. The S1P1-3 receptors are present in the kidneys. It has been shown that S1P system plays a significant role in the pathogenesis of many diseases, including cardiovascular and kidney diseases. Notably, the functions of three S1P receptors in the kidneys are different. S1P1 mediates protective effects, whereas S1P2 and S1P3 mediate injurious effect in the kidneys. Despite many reports showing the involvement of S1P pathway in renal physiology and pathology, little is known about the role of renal S1P system in Na+ excretion. We have recently demonstrated that S1P1-3 receptors are prominently expressed in the renal medulla, mainly located in the collecting ducts, and that S1P1 receptor in the renal medulla mediates a strong natriuretic effect via inhibiting epithelial Na+ channel (ENaC). Our preliminary data showed that high salt intake upregulated the level of S1P1 in the renal medulla, and interestingly, deoxycorticosterone acetate (DOCA) treatment significantly reduced the level of S1P1 in the renal medulla. In mice with collecting duct (CD)-specific S1P1 knockout (KO), the pressure natriuresis was blunted and high salt intake promoted more Na+ retention compared with control mice. Furthermore, high salt intake produced a salt-sensitive hypertension in CD-specific S1P1 KO mice but not in control mice when treated with a subpressor dose of DOCA. On the other hand, infusion of BAF312, a selective S1P1 agonist, locally into the renal medulla remarkably attenuated DOCA-salt hypertension. Based on these findings, we hypothesize that the renal medullary S1P1 pathway is a critical counterbalancing mechanism to inhibit the excessive Na+ reabsorption and that suppression of renal medullary S1P1 pathway contributes to the development of salt-sensitive hypertension. Three specific aims are proposed to test our hypothesis. Aim 1: To determine whether the suppression of S1P1 pathway in the renal medulla contributes to the pathogenesis of salt-sensitive hypertension. Mice with CD-specific deletion of S1P1 or CD-specific overexpression of S1P1 transgene will be used. Aim 2: To determine whether S1P1 pathway inhibits ENaC activity and thereby increases Na+ excretion, exerting the antihypertensive action. Patch clamp studies of ENaC channel activity in freshly isolated collecting ducts will be performed. Aim 3: To explore the mechanism by which S1P1 activation inhibits ENaC activity to exert antihypertensive action via Gi protein/cAMP-coupled signaling. The proposed studies will reveal a novel molecular mechanism in renal Na+ handling and provide new insights into the pathogenesis of salt-sensitive hypertension.