Generation and characterization of collecting duct specific GPR56 knockout mice
Authors: Xue Jianxiang , Steichen Hailey , Eaton Krystin , Yan Teagan , Tall Gregory G. , Zaidman Nathan 
Published: May 2024

GPR56 is a multifunctional adhesin G protein-coupled receptor involved in diverse biological processes, including neurodevelopment and disease, immune regulation, reproduction, hemostasis, and tumorigenesis. The role of GPR56 in the kidneys has been understudied. A recent study demonstrated that GPR56 in the glomerular endothelial cells promoted diabetic kidney disease progression via regulation of eNOS. Using RNAscope in situ hybridization (ISH) for GPR56 and aquaporin 2 (AQP2) followed by immunofluorescent labeling with NKCC2 (thick ascending limb, TAL marker), we detected GPR56 mRNA highly expressed in the collecting duct (both AQP2 positive principal cells and AQP2 negative intercalated cells) and TAL of the loop of Henle. In contrast, GPR56 mRNA is not detected in the proximal tubule or glomeruli. This expression pattern is further confirmed by quantitative RT-qPCR for GPR56 in microdissected inner medulla/inner stripe outer medulla and renal cortex. Of note, inner medulla/ inner stripe outer medulla is primarily composed of the collecting duct and the loop of Henle. GPR56 mRNA exhibited over a 6-fold higher expression levels in the inner medulla/inner stripe outer medulla compared to renal cortex, which is consistent with limited expression in the proximal tubule. To determine the physiological role of GPR56 in the collecting duct, we generated a collecting duct-specific GPR56 knockout (GPR56CD-KO) mouse model by crossing GPR56flox (Control, Con) with cadherin 16 Cre (Ksp-Cre) mice. The deletion of GPR56 in the collecting duct was confirmed by RNAscope ISH for GPR56 and AQP2 followed by fluorescent labeling with NKCC2. GPR56CD-KO mice were born at predicted Mendelian frequencies, appeared grossly indistinguishable from Con mice, and developed normally. For baseline phenotypic characterization, we found no differences in blood pH (7.21±0.01 vs 7.19±0.01, NS), blood HCO3− (17.4±0.5 vs 16.8±1.1 mmol/L, NS), blood Na+ (143±0 vs 144±0 mmol/L, NS), or blood K+ (4.3±0.1 vs 4.3±0.1 mmol/L, NS) between GPR56CD-KO (n=5, males) and Con mice (n=6, males). We also conducted metabolic cage experiments. No differences were observed for fluid intake (4.7±0.5 vs 4.5±0.2 mL/(day*30 g bodyweight), NS), urine volume (629±87 vs 662±108 mL/day, NS), urinary pH (5.75±0.03 vs 5.69±0.03, NS) or urine osmolality (2456±151 vs 2776±253 mOsm/kg, NS) between genotypes in baseline. After 24hr water deprivation, urine osmolality in both mice groups had significantly increased compared to that in baseline, however, no difference (Δ change: 558±82 vs 583±60 mOsm/kg, NS) was found between GPR56CD-KO and Con mice. In conclusion, we successfully generated collecting duct-specific GPR56 knockout mouse and found no defective urine concentrating ability in GPR56CD-KO mice. This mouse model will be useful to delineate the collecting duct-specific role of GPR56 for renal function, including acid-base regulation. We will also generate whole kidney GPR56 knockout mice to determine the isolated role of GPR56 in the loop of Henle compared to that in the collecting duct. This study is supported by the National Institute of Diabetes and Digestive and Kidney Diseases (4R00DK127215). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.