Division of Nephrology, Department of Internal Medicine, Teikyo University School of Medicine, Tokyo, 173-8605, Japan.
Division of Nephrology, Department of Internal Medicine, Teikyo University School of Medicine, Tokyo, 173-8605, Japan; Department of Nephrology, The Second Affiliated Hospital of Harbin Medical University, Harbin, 150081, China.
Biochem Biophys Res Commun. 2020 Apr 9;524(3):710-715. doi: 10.1016/j.bbrc.2020.01.142. Epub 2020 Feb 5.
Na-K-2Cl cotransporter 2 (NKCC2) in thick ascending limb (TAL) in the kidney plays a central role in tubuloglomerular feedback (TGF) system by sensing NaCl delivery to the distal tubules. Although accumulating data indicate that dysregulated TGF contributes to the progression of diabetic complications, the regulation of NKCC2 in diabetes mellitus (DM) remains unclear. We here show that NKCC2 is overactivated via a vasopressin receptor 2 (V2R)-dependent mechanism in db/db mice, a mouse model of obese DM. Compared with db/+ mice, we found that both aquaporin 2 and NKCC2 levels were significantly increased in the kidney in db/db mice. Immunohistochemical analysis of V2R and NKCC2 in the kidney demonstrated that V2R is present in the TAL, as well as in the collecting duct. Moreover, the administration of tolvaptan, a selective V2R antagonist, sharply decreased aquaporin 2 and NKCC2 in db/db mice, confirming the causal role of V2R signaling in NKCC2 induction in this model. Although tolvaptan reduced aquaporin 2 abundance also in db/+ mice, its effect on NKCC2 was modest compared with db/db mice. In total kidney lysates, uromodulin expression was not altered between db/+ and db/db mice, suggesting that V2R signaling alters NKCC2 without altering uromodulin levels. These data implicate the dysregulation of NKCC2 in the pathophysiology of type 2 DM, and underscore the complex nature of fluid volume disorders in diabetic kidney disease.
肾脏中的升支粗段（TAL）中的钠钾 2 氯协同转运蛋白 2（NKCC2）通过感知 NaCl 递送至远端小管，在管球反馈（TGF）系统中发挥核心作用。尽管越来越多的数据表明失调的 TGF 有助于糖尿病并发症的进展，但糖尿病中 NKCC2 的调节仍不清楚。我们在此表明，db/db 小鼠（肥胖型糖尿病的小鼠模型）中，通过血管加压素受体 2（V2R）依赖性机制，NKCC2 过度激活。与 db/+ 小鼠相比，我们发现 db/db 小鼠肾脏中的水通道蛋白 2 和 NKCC2 水平均显著升高。肾脏中 V2R 和 NKCC2 的免疫组织化学分析表明，V2R 存在于 TAL 以及集合管中。此外，选择性 V2R 拮抗剂托伐普坦的给药可显著降低 db/db 小鼠中的水通道蛋白 2 和 NKCC2，证实了 V2R 信号在该模型中诱导 NKCC2 的因果作用。尽管托伐普坦也降低了 db/+ 小鼠中的水通道蛋白 2 丰度，但与 db/db 小鼠相比，其对 NKCC2 的作用不大。在总肾裂解物中，db/+ 和 db/db 小鼠之间的尿调蛋白表达没有改变，这表明 V2R 信号改变 NKCC2 而不改变尿调蛋白水平。这些数据提示 NKCC2 的失调参与了 2 型糖尿病的病理生理学，并强调了糖尿病肾病中液体体积紊乱的复杂性。
