Background:How signals from activated angiotensin type-2 receptors (AT₂R) mediate inhibition of sodium ion (Na⁺) reabsorption in renal proximal tubule cells is currently unknown. Protein phosphatases including PP2A (protein phosphatase 2A) have been implicated in AT₂R signaling in tissues other than kidney. We investigated whether inhibition of protein phosphatase PP2A reduced AT₂R-mediated natriuresis and evaluated changes in PP2A activity and localization after renal AT₂R activation in normal 4- and 10-week-old control Wistar-Kyoto rats and 4-week-old prehypertensive and 10-week-old hypertensive spontaneously hypertensive rats.Methods and Results:In Wistar-Kyoto rats, direct renal interstitial administration of selective AT₂R nonpeptide agonist Compound-21 (C-21) increased renal interstitial cyclic GMP (cGMP) levels, urine Na⁺ excretion, and simultaneously increased PP2A activity ≈2-fold in homogenates of renal cortical tubules. The cyclic GMP and natriuretic responses were abolished by concurrent renal interstitial administration of protein phosphatase inhibitor calyculin A. In renal proximal tubule cells in response to C-21, PP2A subunits A, B55α and C, but not B56γ, were recruited to apical plasma membranes together with AT₂Rs. Calyculin A treatment abolished C-21-induced translocation of both AT₂R and PP2A regulatory subunit B55α to apical plasma membranes. Immunoprecipitation of AT₂R solubilized from renal cortical homogenates demonstrated physical association of AT₂R with PP2A A, B55α, and C but not B56γ subunits. In contrast, in spontaneously hypertensive rats, administration of C-21 did not alter urine Na⁺ excretion or PP2A activity and failed to translocate AT₂Rs and PP2A subunits to apical plasma membranes.Conclusions:In renal proximal tubule cells of Wistar-Kyoto rats, PP2A is activated and PP2A subunits AB55αC are recruited to C-21-activated AT₂Rs during induction of natriuresis. This response is defective in prehypertensive and hypertensive spontaneously hypertensive rats, presenting a potential novel therapeutic target for treating renal Na⁺ retention and hypertension.

中文翻译：

---

肾 AT2 受体通过蛋白磷酸酶 PP2A 介导尿钠排泄

背景：来自活化的血管紧张素 2 型受体 (AT ₂ R) 的信号如何介导肾近端小管细胞中钠离子 (Na ⁺ ) 重吸收的抑制目前尚不清楚。包括 PP2A（蛋白磷酸酶 2A）在内的蛋白磷酸酶与肾脏以外组织中的 AT _{2 R 信号传导有关。}我们研究了蛋白磷酸酶 PP2A 的抑制是否减少了 AT _{2 R 介导的尿钠排泄，并评估了肾 AT 2}后 PP2A 活性和定位的变化正常 4 周龄和 10 周龄对照 Wistar-Kyoto 大鼠和 4 周龄高血压前期和 10 周龄高血压自发性高血压大鼠的 R 激活。方法和结果：在 Wistar-Kyoto 大鼠中，直接肾间质给药选择性 AT ₂ R 非肽激动剂 Compound-21 (C-21) 增加肾间质循环 GMP (cGMP) 水平、尿液 Na ⁺排泄，同时增加肾皮质小管匀浆中的 PP2A 活性≈2 倍。循环 GMP 和利尿钠反应被同时肾间质给予蛋白磷酸酶抑制剂 calyculin A 消除。在响应 C-21 的肾近端小管细胞中，PP2A 亚基 A、B55α 和 C 而不是 B56γ 被募集到顶端质膜连同 AT ₂卢比 Calyculin A 处理消除了 C-21 诱导的 AT ₂ R 和 PP2A 调节亚基 B55α 向顶端质膜的易位。从肾皮质匀浆中溶解的 AT ₂ R的免疫沉淀表明 AT ₂ R 与 PP2A A、B55α 和 C 但不是 B56γ 亚基的物理关联。相比之下，在自发性高血压大鼠中，给予 C-21 不会改变尿液 Na ⁺排泄或 PP2A 活性，并且无法将 AT ₂ Rs 和 PP2A 亚基转移到顶端质膜。结论：在 Wistar-Kyoto 大鼠的肾近端小管细胞中, PP2A 被激活并且 PP2A 亚基 AB55αC 被招募到 C-21 激活的 AT ₂尿钠排泄诱导期间的 Rs。这种反应在高血压前期和高血压自发性高血压大鼠中是有缺陷的，为治疗肾 Na ⁺潴留和高血压提供了一个潜在的新治疗靶点。