Department of Physiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
FASEB J. 2018 Apr;32(4):2046-2059. doi: 10.1096/fj.201700610RR. Epub 2018 Jan 5.
The investigation of orphan GPCRs (GPRs) has the potential to uncover novel insights into whole animal physiology. In this study, our goal was to determine the renal localization of Gprc5c, a receptor that we previously reported to be highly expressed in murine whole kidney, and to examine physiologic parameters in Gprc5c knockout (KO) mice to gain insight into function. Gprc5c localized to the apical membrane of renal proximal tubules (PTs) in mice, rats, and humans. With the comparison of Gprc5c wild-type (WT) and KO mice, we found that Gprc5c KO mice have altered acid-base homeostasis. Specifically, Gprc5c KO mice have lower blood pH and higher urine pH compared with WT mice, with a reduced level of titratable acids in their urine. In an in vitro GPCR internalization assay, we observed that Gprc5c internalization (an index of activation) was triggered by alkaline extracellular pH. Furthermore, with the use of an in vitro BCECF assay, we observed that Gprc5c increases Na/H exchanger 3 (NHE3) activity at alkaline pH. We also find that the NHE3 activity is reduced in Gprc5c KO mice by 2 photon imaging in seminaphthorhodafluors (SNARF)-4F-loaded kidney sections. NHE3 is a primary contributor to apical transport of H in the renal PT. Together, these data imply that Gprc5c modulates the renal contribution to systemic pH homeostasis, at least in part, by taking part in the regulation of NHE3.-Rajkumar, P., Cha, B., Yin, J., Arend, L. J., Păunescu, T. G., Hirabayashi, Y., Donowitz, M., Pluznick, J. L. Identifying the localization and exploring a functional role for Gprc5c in the kidney.
孤儿 G 蛋白偶联受体（GPCRs）的研究有可能揭示整个动物生理学的新见解。在这项研究中，我们的目标是确定 Gprc5c 的肾脏定位，我们之前曾报道 Gprc5c 在整个鼠肾中高度表达，并检查 Gprc5c 敲除（KO）小鼠的生理参数，以深入了解其功能。Gprc5c 在小鼠、大鼠和人类的肾近端小管（PT）的顶膜上定位。通过比较 Gprc5c 野生型（WT）和 KO 小鼠，我们发现 Gprc5c KO 小鼠的酸碱平衡发生了改变。具体来说，与 WT 小鼠相比，Gprc5c KO 小鼠的血液 pH 值较低，尿液 pH 值较高，尿液中的可滴定酸水平降低。在体外 GPCR 内化测定中，我们观察到碱性细胞外 pH 值触发了 Gprc5c 的内化（激活指标）。此外，使用体外 BCECF 测定，我们观察到 Gprc5c 在碱性 pH 值下增加了 Na/H 交换器 3（NHE3）的活性。我们还发现，通过 SNARF-4F 负载的肾切片的 2 光子成像，Gprc5c KO 小鼠的 NHE3 活性降低。NHE3 是肾 PT 中 H 顶端转运的主要贡献者。综上所述，这些数据表明，Gprc5c 通过参与 NHE3 的调节，至少部分地调节肾脏对全身 pH 稳态的贡献。-Rajkumar，P.，Cha，B.，Yin，J.，Arend，L. J.，Păunescu，T. G.，Hirabayashi，Y.，Donowitz，M.，Pluznick，J. L. 鉴定 Gprc5c 在肾脏中的定位并探索其功能作用。
