Activation of farnesoid X receptor (FXR) induces crystallin zeta expression in mouse medullary collecting duct cells
Activation of farnesoid X receptor (FXR) induces crystallin zeta expression in mouse medullary collecting duct cells
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DOI：
10.1007/s00424-020-02456-4
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发表时间：
2020-09-10
影响因子：
4.5
通讯作者：
Zhang, Xiaoyan
中科院分区：
文献类型：
--
作者：
Alam, Gulzar;Luan, Zhilin;Zhang, Xiaoyan
晶体蛋白zeta（Crystallin zeta，ZHZ）是一种遗传学限制的水溶性蛋白质，通过多种机制提供抗氧化应激的细胞保护作用。越来越多的证据表明，在肾脏中高丰度地表达，在那里它作为一种反式作用因子，在增加多巴胺的分解和Na+/K+/2Cl（-）共转运蛋白（BSC 1/NKCC 2）的表达，以帮助维持酸碱平衡和髓质高渗梯度。然而，在肾脏中调节β-内酰胺酶的机制在很大程度上仍不清楚。在这里，我们表明，FXR Z是法尼醇X受体（FXR）的直接靶点，FXR是一种对肾脏生理学很重要的核受体。我们发现，在小鼠肾脏中广泛表达，并在髓质集合管细胞（MCDs）的细胞质中组成性表达。在原代培养的小鼠MCDs中，FXR的激活和过表达显著上调了FXR Z的表达。在siRNA介导的FXR敲低的MCD细胞中，FXR诱导的FXR Z表达几乎完全消失。一致地，用FXR激动剂治疗未能诱导从具有全局和集合管特异性FXR缺陷的小鼠中分离的MCDs中的FXR Z表达。我们确定了一个假定的FXR反应元件（FXRE）的ESTZ基因启动子。荧光素酶报告基因和ChIP分析显示，FXR可以直接结合到FXRE位点，这通过FXR活化进一步显著增强。此外，我们还发现MCDs中的BclZ过表达可能通过增加Bcl-2表达而显著减弱高渗诱导的细胞死亡。总的来说，我们的研究结果表明，FXR在肾髓质集合管细胞中组成型表达，在那里它是由FXR转录控制的。鉴于FXR在MCDs中的关键作用，在脱水期间，FXR对MCDs在高渗条件下的存活具有保护作用，因此，FXR可能是负责的。
Crystallin zeta (CRYZ) is a phylogenetically restricted water-soluble protein and provides cytoprotection against oxidative stress via multiple mechanisms. Increasing evidence suggests that CRYZ is high abundantly expressed in the kidney where it acts as a transacting factor in increasing glutaminolysis and the Na+/K+/2Cl(-)cotransporter (BSC1/NKCC2) expression to help maintain acid-base balance and medullary hyperosmotic gradient. However, the mechanism by which CRYZ is regulated in the kidney remains largely uncharacterized. Here, we show that CRYZ is a direct target of farnesoid X receptor (FXR), a nuclear receptor important for renal physiology. We found that CRYZ was ubiquitously expressed in mouse kidney and constitutively expressed in the cytoplasm of medullary collecting duct cells (MCDs). In primary cultured mouse MCDs, CRYZ expression was significantly upregulated by the activation and overexpression of FXR. FXR-induced CRYZ expression was almost completely abolished in the MCD cells with siRNA-mediated FXR knockdown. Consistently, treatment with FXR agonists failed to induce CRYZ expression in the MCDs isolated from mice with global and collecting duct-specific FXR deficiency. We identified a putative FXR response element (FXRE) on the CRYZ gene promoter. The luciferase reporter and ChIP assays revealed that FXR can bind directly to the FXRE site, which was further markedly enhanced by FXR activation. Furthermore, we found CRYZ overexpression in MCDs significantly attenuated hypertonicity-induced cell death possibly via increasing Bcl-2 expression. Collectively, our findings demonstrate that CRYZ is constitutively expressed in renal medullary collecting duct cells, where it is transcriptionally controlled by FXR. Given a critical role of FXR in MCDs, CRYZ may be responsible for protective effect of FXR on the survival of MCDs under hypertonic condition during dehydration.