高尿酸血症通过调控肾上皮钠通道(ENaC)介导盐敏感性高血压的机制研究

It is evident that hyperuricemia is closely associate with high prevalence of hypertension. Approximately 50% of hypertensive individals are salt-sensitive hypertension. The interaction of hyperuricemia with salt-sensitive hypertension is still unclear. The kidney has a central role in the regulation of blood pressure, in large part through its role in the regulated resorbstion of filtered Na+. The epithelial Na+ channel (ENaC) is a key Na+ transporter in this segment of the nephron. Our preliminary data has shown the mice and rat with hyperuricemia demonstrate a significant high blood pressure and obviously incresed ENaC expression. The results from in vitro study have shown that uric acid elicited significant, dose-dependent increases in the expression of ENaC, SGK1 as well as GILZ1 which is central player of ENaC regulatory complex (ERC). Those findings implicated that hyperuricemia is key factor on hypertension, and its regulation of ENaC is potential mechanism pathway which Uric acid contributes to high blood pressure with. In the future work of this project, we will further explore the potential mechanism of high uric acid on hypertension, especailly salt-sensitive hypertension. The studies (in vivo) will be performed to examine whether hyperuricemia plays a important role in salt-sensitive hypertension using rat model. We will test other three specific aims in mouse cortical collecting duct (mCCD) cells (in vitro): (1) to define the role of uric acid in ENaC expression and function; (2) to examine whether uric acid has effect on ENaC regulatory complex (ERC); and (3) to evaluate the interactions among ERC components with uric acid stimulation in mCCDs. Successful completion of this proposal will advance our understanding of molecular mechanism of uric acid on ENaC regulation and provide a roadmap for identifying novel potential therapeutic targets to hyperuricemia and salt-sensitive hypertension.

大量的临床证据表明，高尿酸血症与高血压，尤其是盐敏感性高血压的发生发展密切相关；但是二者之间内在的联系至今尚未阐明。肾脏上皮细胞钠离子通道(Epithelial Na+ channel,ENaC)的过度激活(gain-of-function)是多种类型高血压发病的重要因素之一。本课题的前期结果提示，高尿酸血症诱发大鼠高血压；明显的增加肾组织ENaC的表达；肾脏集合管上皮细胞ENaC的表达也对尿酸刺激呈浓度依赖性的上调；此外尿酸可诱发ENaC调控复合体 (ERC) 中SGK1和GILZ1的激活；抑制ERK和p38的磷酸化。这些结果均提示尿酸诱发高血压可能的机制是尿酸参与调控ENaC的表达和功能。本课题将利用在体实验和体外实验两个模型，动态观察高尿酸血症大鼠与盐敏感性高血压发生发展的内在联系；也深入探讨尿酸调控ENaC的表达及其可能的分子机制，为今后有效防治高尿酸血症及其并发症奠定理论基础。

肾脏通过调节远曲小管以及集合管上皮细胞膜上的钠离子通道 (ENaC) 调节人体内的水、钠平衡，维持机体的血压稳定。肾小管上皮细胞ENaC的过度激活是多种类型高血压发病的重要因素之一。高尿酸血症与高血压的发生发展密切相关，但是二者之间内在的联系至今尚未阐明。本研究的目的是探讨高尿酸血症引起盐敏感性高血压的过程中，对肾脏上皮钠离子通道表达的影响及其相关机制。大鼠被随机分成4组每组：对照组 (Con)；氧嗪酸组 (OA)；苯溴马隆组(OA+Ben)；阿米洛利组 (OA+Ami)。检测各组大鼠血生化指标、血压、肾脏形态学、 肾脏α-、β-、γ-ENaC的表达。体外培养肾脏集合管上皮细胞 (mCCD) 给予尿酸刺激并检测α-、β-、γ-ENaC表达以及ENaC调节复合物 (ERC) 的表达来揭示尿酸对ENaC调控的分子机制。使用Ussing chamber电生理检测尿酸处理mCCD细胞ENaC介导的短路电流 (Isc) 的影响。与Con组比较，OA组大鼠的血压、血UA、BUN、Cr 及ALD有显著的升高，尿Na+排泄显著降低，尿Na+/K+显著降低，血Na+、K+、Cl-及尿K+无显著差异。肾脏病理提示肾小球基本正常，局灶肾小管萎缩和肾间质纤维化。与OA组比较，OA+Ben组大鼠血压有显著的降低，血UA、ALD、BUN、血Cr有显著的降低，尿Na+、尿Na+/K+有显著的升高，肾脏病理提示肾间质病变减轻。与OA组比较，OA+Ami组大鼠血压、 BUN及血Cr有显著的降低，尿Na+和尿Na+/K+有显著的增加，血UA及 ALD无显著差异，肾脏病理提示肾间质病变减轻。免疫组化及Western blot分析提示，OA组大鼠的肾集合管ENaC的表达显著增加。Ben能显著降低高尿酸诱导的肾集合管ENaC表达。Ami不能显著降低高尿酸诱导的肾集合管ENaC表达。在mCCD细胞中尿酸剂量依赖性增加α-、β-、γ-ENaC的表达。电生理检测尿酸刺激mCCD细胞的Isc增加。在高尿酸刺激的mCCD细胞中，ENaC调节复合物成分SGK-1、GILZ1的表达增加，P-ERK1/2表达下调。高尿酸血症可诱导高血压的发生和肾间质的损伤。高尿酸诱导高血压的发生与肾脏ENaC表达和活性增加以及高尿酸刺激ENaC调节复合物成分GILZ1，SGK1的表达和抑制p-ERK1/2的表达相关。