Department of Physiology, The Johns Hopkins University School of Medicine, Baltimore, MD 21205.
Department of Integrative Biology and Pharmacology, The University of Texas Health Science Center at Houston, Houston, TX 77030.
Proc Natl Acad Sci U S A. 2020 Oct 20;117(42):26470-26481. doi: 10.1073/pnas.2007620117. Epub 2020 Oct 1.
The diversity and near universal expression of G protein-coupled receptors (GPCR) reflects their involvement in most physiological processes. The GPCR superfamily is the largest in the human genome, and GPCRs are common pharmaceutical targets. Therefore, uncovering the function of understudied GPCRs provides a wealth of untapped therapeutic potential. We previously identified an adhesion-class GPCR, Gpr116, as one of the most abundant GPCRs in the kidney. Here, we show that Gpr116 is highly expressed in specialized acid-secreting A-intercalated cells (A-ICs) in the kidney using both imaging and functional studies, and we demonstrate in situ receptor activation using a synthetic agonist peptide unique to Gpr116. Kidney-specific knockout (KO) of Gpr116 caused a significant reduction in urine pH (i.e., acidification) accompanied by an increase in blood pH and a decrease in pCO compared to WT littermates. Additionally, immunogold electron microscopy shows a greater accumulation of V-ATPase proton pumps at the apical surface of A-ICs in KO mice compared to controls. Furthermore, pretreatment of split-open collecting ducts with the synthetic agonist peptide significantly inhibits proton flux in ICs. These data suggest a tonic inhibitory role for Gpr116 in the regulation of V-ATPase trafficking and urinary acidification. Thus, the absence of Gpr116 results in a primary excretion of acid in KO mouse urine, leading to mild metabolic alkalosis ("renal tubular alkalosis"). In conclusion, we have uncovered a significant role for Gpr116 in kidney physiology, which may further inform studies in other organ systems that express this GPCR, such as the lung, testes, and small intestine.
G 蛋白偶联受体 (GPCR) 的多样性和近乎普遍的表达反映了它们在大多数生理过程中的参与。GPCR 超家族是人类基因组中最大的家族，GPCR 是常见的药物靶点。因此，揭示研究较少的 GPCR 的功能提供了丰富的未开发的治疗潜力。我们之前鉴定了一种粘附类 GPCR，Gpr116，它是肾脏中最丰富的 GPCR 之一。在这里，我们通过成像和功能研究表明，Gpr116 在肾脏中专门分泌酸的 A 闰细胞 (A-ICs) 中高度表达，并且我们使用独特的 Gpr116 合成激动肽证明了原位受体激活。Gpr116 的肾脏特异性敲除 (KO) 导致尿液 pH 值显著降低（即酸化），同时血液 pH 值升高，pCO 降低与 WT 同窝仔相比。此外，免疫金电子显微镜显示，与对照组相比，KO 小鼠的 A-ICs 顶表面的 V-ATPase 质子泵积累更多。此外，用合成激动肽预处理分离的收集管可显著抑制 ICs 中的质子通量。这些数据表明 Gpr116 在调节 V-ATPase 运输和尿液酸化方面具有紧张抑制作用。因此，Gpr116 的缺失导致 KO 小鼠尿液中主要排泄酸，导致轻度代谢性碱中毒（“肾小管性碱中毒”）。总之，我们已经揭示了 Gpr116 在肾脏生理学中的重要作用，这可能会进一步为其他表达这种 GPCR 的器官系统（如肺、睾丸和小肠）的研究提供信息。
