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.

Crystallin zeta (CRYZ) 是一种系统发育受限的水溶性蛋白质，可通过多种机制提供细胞保护以对抗氧化应激。越来越多的证据表明，CRYZ 在肾脏中大量表达，它在增加谷氨酰胺分解和 Na ⁺ /K ⁺ /2Cl ^{– 中}充当反式作用因子共转运蛋白 (BSC1/NKCC2) 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 CRYZ 的机制在很大程度上仍未得到表征。在这里，我们表明 CRYZ 是法尼醇 X 受体 (FXR) 的直接靶标，FXR 是一种对肾脏生理学很重要的核受体。我们发现 CRYZ 在小鼠肾脏中普遍表达，并在髓集合管细胞 (MCD) 的细胞质中组成型表达。在原代培养的小鼠 MCD 中，FXR 的激活和过表达显着上调了 CRYZ 的表达。FXR 诱导的 CRYZ 表达在 MCD 细胞中几乎完全消失，siRNA 介导的 FXR 敲低。一贯地，用 FXR 激动剂治疗未能在从具有全局和集合管特异性 FXR 缺陷的小鼠中分离的 MCD 中诱导 CRYZ 表达。我们在 CRYZ 基因启动子上确定了一个推定的 FXR 响应元件 (FXRE)。荧光素酶报告基因和 ChIP 分析表明，FXR 可以直接结合 FXRE 位点，FXR 激活进一步显着增强了这一点。此外，我们发现 MCD 中 CRYZ 过表达可能通过增加 Bcl-2 表达显着减轻高渗诱导的细胞死亡。总的来说，我们的研究结果表明 CRYZ 在肾髓质集合管细胞中组成型表达，在那里它由 FXR 转录控制。鉴于 FXR 在 MCD 中的关键作用，CRYZ 可能负责 FXR 在脱水期间高渗条件下对 MCD 存活的保护作用。