Loop‐Diuretics Increase Pendrin through alpha‐ketoglutarate receptor, Oxgr1

Abstract

IntroductionIt is well appreciated that loop diuretic resistance is governed by pendrin and activation of the thiazide‐sensitive sodium chloride cotransporter, NCC. Recently, our lab discovered pendrin increases as the natriuretic response wanes, coincident with the activation of a‐ketoglutarate (AKG) synthesis, secretion of a‐KG into the pro‐urine, and increased gene expression of the AKG GPCR, Oxgr1. Here we test the hypothesis that activation of Oxgr1 is necessary for the development of loop diuretic resistance.Methods10 week old male OXGR1 KO and WT (C57B6J) mice were challenged with furosemide (100 mg/kg) for 4 days. Urine was collected over 24 hours, daily, and urinary electrolytes were measured. Mice were euthanized at the end of the experiment and plasma electrolytes and aldosterone levels were measured using standard methods. Cortical protein and RNA abundances were measured using western blot and qRT‐PCR, respectively.ResultsWT and OXGR1 KO displayed distinguishing phenotypes only after furosemide administration. The loop‐diuretic challenge increased pendrin protein in WT mice but not in the OXGR1 KO mice despite identical increases in the chief pendrin stimulators, aldosterone and metabolic alkalosis. Pendrin transcript increased to the same extent in both genotypes, indicating OXGR1 augments pendrin via a post‐translational mechanism. Even with compromised upregulation of pendrin, OXGR1 KO mice exhibited the same diuretic response as WT mice. Upregulation of NCC was not compromised in the OXGR1 mice.ConclusionOXGR1 is required for post‐translational upregulation of pendrin protein post diuretic challenge, consistent with activation of a aKG‐OXGR1‐pendrin signaling axis. Upregulation of NCC and residual pendrin activity may be sufficient to brake the loop‐diuretic response.