S1PR1抑制肾脏集合管上皮钠通道改善盐敏感高血压的分子机制

Impaired renal sodium excretion in the renal medulla may represent a novel mechanism for salt-sensitive hypertension.Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid metabolite, we have recently shown that renal medullary infusion of S1P agonist increases sodium excretion possibly through inhibition of epithelial sodium channel (ENaC) activity via S1P receptor 1 (S1PR1), which is prominently localized in the collecting ducts. We generated conditional knocked-out (CKO) mice with collecting duct-specific ablation of S1PR1. Functionally, in S1PR1 CKO mice，the pressure natriuresis was severely impaired, urinary sodium excretion was significantly decreased. Furthermore, chronic high salt-induced sodium retention was remarkably enhanced in S1PR1 CKO mice comparing to the control animals. We therefore hypothesize that the S1PR1 in collecting duct plays a pivotal role in the regulation of renal sodium handling and salt-sensitive hypertension via regulating ENaC. In the current project, we are going to investigate 1) whether S1PR1 in collecting duct plays an important role in the regulation of ENaC and renal sodium handling in S1PR1 gene knockout mice; 2) whether S1PR1 inhibits ENaC in cultured inner medulla collecting ducts cells as well as relevant signaling pathways; The current project is expected to provide evidence for therapeutic approach of salt-sensitive hypertension by modulation of S1PR1 function in the renal medulla.

肾脏排钠障碍是盐敏感高血压发生的病理机制之一。我们研究报道，1-磷酸鞘氨醇（S1P）是肾髓质利钠因子，通过抑制上皮钠通道（ENaC）促进肾脏排钠，且S1P的利钠作用可能由其受体S1PR1介导。S1PR1在肾集合管表达较多且受到高盐饮食上调。那么，集合管S1PR1是否能抑制ENaC并改善盐敏感高血压？其机制是什么?我们在肾脏集合管S1PR1基因特异性敲除小鼠模型发现，敲除SIPR1显著抑制小鼠肾脏的压力利钠功能，降低肾脏处理盐负荷能力，引起钠潴留并导致盐敏感高血压。据此我们提出假设：肾脏集合管S1PR1抑制ENaC，促进肾脏排钠，改善盐敏感高血压。本项目拟：1）利用基因特异敲除小鼠，明确肾集合管S1PR1抑制ENaC调控盐敏感高血压的作用及机制；2）利用体外培养肾脏集合管细胞，从细胞水平阐明S1PR1抑制ENaC的信号通路；本课题将为阐明盐敏感高血压的发病机制和治疗提供新点。

肾脏排钠障碍是盐敏感高血压发生的重要机制。我们前期发现，1-磷酸鞘氨醇S1P可抑制ENaC并促进肾脏排钠，其作用可能由受体S1PR1介导。在此基础上，本研究进一步研究集合管S1PR1是否通过调控ENaC调节盐敏感高血压? 利用基因敲除小鼠和细胞模型，我们研究了S1PR1、SphK-S1P信号通路对肾脏排钠功能和ENaC的调控。结果发现，①集合管S1PR1敲除减弱肾脏排尿和尿钠排泄功能，损害机体盐平衡和急性盐负荷处理能力，促进水钠潴留并升高血压，表明S1PR1的确参与小鼠肾脏排钠和血压调控。在集合管细胞中，S1PR1和ENaC对高盐处理呈现不同的时空表达模式，提示S1PR1参与调控肾脏排钠和高血压的作用可能并不直接通过调节ENaC实现；② S1P合成酶SphK1或SphK2敲除，均能下调ENaC的表达和活性，增强肾脏急性盐负荷处理能力，促进肾脏排钠。不同的是SphK2的作用较快，而SphK1的作用相对滞后。Sphk1和Sphk2的敲除，对细胞内S1P的调节也存在差异，敲除Sphk2显著升高细胞S1P水平。本研究为揭示SphK/S1PR1/S1P信号调节盐敏感高血压的发病机制奠定重要基础。