硫化氢对梗阻性肾病中尿液浓缩功能障碍的保护作用

Urinary tract obstruction is a serious disorder that may potentially result in irreversible kidney damage associated with impaired renal function, such as a compromised ability　to regulate urinary excretion of water and sodium. Release of a ureteral occlusion is characterized by a reduced urinary concentrating capacity, natriuresis and polyuria. Previously, we demonstrated that the abundance of renal aquaporins (AQPs), sodium and urea transporters was significantly reduced in response to ureteral obstruction, suggesting that these proteins at least partly contribute to the urinary concentrating defect in response to urinary tract obstruction. .Hydrogen sulfide (H2S), a gasotransmitter, is a key mediator in human physiology and pathophysiology. H2S is involved in maintainence of body homeostasis (e.g.blood pressure control, water and electrolyte balance), and oxidative stress and inflammation. The kidney plays a decisive role in many of these processes, indicating an interplay between H2S and renal (patho)physiology. Cystathionine-Ƴ-lyase or cystathionase (CSE), cystathionine-β-synthase (CBS) and 3-mercaptopyruvate sulphurtransferase (MST), which are responsible for the primary endogenous production of H2S, are abundantly expressed in the kidney. .Our preliminary data demonstrated that unilateral ureteral obstruction (UUO) for 7 days was associated with downregulation of CBS and CSE in the obstructed kidneys. H2S donor NaHS improved the polyuria and abolished the reduction of AQP1, 2, and 3 protein expressions in the obstructed kidney of 7UUO. NaHS also prevented the decreased mRNA expression of Na-K-2Cl cotransporter and Na-Cl cotransporter which are responsible for sodium reabsorption in the thick ascending limb and distal tubules. In the primary cultured inner medullary collecting duct cells, NaHS significantly increased AQP2 protein and mRNA expression, which was blocked by PKA inhibitor H89, indicating the involvement of cAMP-PKA pathways. The purpose of the present project was to investigate whether H2S prevents downregulation of renal aquaporins and sodium transporters in the obstructed kidneys and whether H2S improves the polyuria and sodium loss observed after release of ureteral obstruction. We will investigate 1) whether H2S prevents polyuria and sodium loss and downregulation of renal aquaporins and sodium transporters, as well as inflammatory　response in association with UUO, bilateral ureteral obstruction (BUO), and release of BUO; 2) whether reduced endogenous H2S in CBS knockout mice treated with CSE inhibitor PPG could cause an abnormal regulation of water and sodium in the kidney; 3) whether H2S directly regulates AQP2 expression in the primary cultured inner medullary collecting duct cells and what relevant cellular pathways are involved? The present project will provide us evidence that H2S, as a gasotransmitter, has a therapeutic potential in preventing urinary concentrating defect in association　with obstructive nephropathy.

梗阻性肾病可以诱发肾脏水钠代谢紊乱，损伤肾脏功能。我们已证明肾脏集合管水通道蛋白（AQP）和髓袢钠转运蛋白表达下降是梗阻性肾病缓解后尿液浓缩功能障碍的分子机制之一。气体分子硫化氢（H2S）通过血管效应、抗氧化、抗炎等参与多种肾脏病理生理过程，但是否参与肾脏水钠代谢的调节仍未有报道。我们的前期工作表明，H2S直接上调原代培养的肾脏集合管细胞AQP2的表达，给予外源性H2S能缓解输尿管梗阻后的尿液浓缩障碍，因此提出假设：H2S通过上调肾脏AQPs和钠转运蛋白进而改善尿液浓缩功能，保护肾脏损伤。本项目拟（1）利用H2S合成酶CBS基因敲除鼠，研究内源性H2S减少对尿液浓缩能力的影响；（2）利用输尿管梗阻模型，观察H2S上调肾脏AQPs和钠转运蛋白进而改善尿液浓缩功能的分子机制；（3）在细胞水平阐明H2S调节AQP2表达的信号通路。本研究成果将为临床治疗梗阻缓解后尿液浓缩功能障碍提供新的研究思路。

梗阻性肾病可以诱发肾脏水钠代谢紊乱，损伤肾脏功能。我们已证明肾脏集合管水通道蛋白（AQP）和髓袢钠转运蛋白表达下降是梗阻性肾病缓解后尿液浓缩功能障碍的分子机制之一。气体分子硫化氢（H2S）通过血管效应、抗氧化、抗炎等参与多种肾脏病理生理过程，但是否参与肾脏水钠代谢的调节仍未有报道。我们的研究结果一方面发现气体分子硫化氢可以弥散进入细胞内，通过AC-cAMP-PKA通路促进AQP2的迁移和蛋白合成增加，同时抑制内源性磷酸二酯酶，减少AC的降解，从而稳定增加AQP2的表达；AQP2的表达增加，进一步促进肾小管上皮细胞对水的重吸收，尿量减少，从而增加肾脏的浓缩能力。同时，在梗阻性肾脏损伤的模型中我们发现硫化氢供体NaHS可以增加硫化氢合成酶CBS和CSE的含量， 缓解了梗阻性肾病引起的肾脏AQP1、2、3、NKCC2和NCC的下降。NaHS处理明显改善了肾脏p-AKT的蛋白水平，提示AKT信号通路可能参与硫化氢对水通道2的调节过程。肾脏上皮细胞中发现牵拉可以引起细胞的纤维化指标Fibronectin和alpha-SMA的表达增加，减少肾脏上皮细胞水通道蛋白的表达，H2S供体GYY4137，可以缓解上述的变化。本研究发现气体分子硫化氢可以通过AC-cAMP-PKA通路调节AQP2的表达，同时改善牵拉作用下对细胞水通道蛋白的下调及纤维化的变化的程度，对梗阻性肾病的浓缩能力障碍具有一定的保护作用，该研究成果将为临床治疗梗阻缓解后尿液浓缩功能障碍提供新的研究思路。