Mutations in ammonia transporter RhBG that impair NH3/NH4 + transport in patients with chronic kidney disease.

Chronic kidney disease (CKD) imposes a substantial health burden globally, with emerging evidence pointing to the significance of metabolic acidosis and low urinary NH4 + excretion resulting in poor CKD outcomes. The present study aims to identify in CKD patients, loss of function mutations in RhBG, one of the NH3/NH4 + transporters in the collecting duct, and to show that NH3/NH4 + transport is impaired by these mutations. Single nucleotide polymorphisms of RhBG associated with CKD occurrence were identified using ancestry-stratified data from the Chronic Renal Insufficiency Cohort (CRIC) study. Functional analysis of NH3/NH4 + transport was conducted in Xenopus oocytes expressing RhBG protein or mutants. NH3 and NH4 + transport was evaluated by electrophysiological measurements, including whole cell current, surface pH and intracellular pH. Our study identified six critical RhBG mutations associated with CKD. G86S and G86C inhibited the transport of NH3; mutations G148R and G148W completely blocked transport of NH3 and NH4 +, whereas T250A and T250S only inhibited NH3 transport. Mutation T250M completely inhibited transport of both NH3 and NH4 +. Our study identified critical rare non-synonymous single nucleotide polymorphisms in RhBG associated with CKD and elucidated the impact of these variants on NH3/NH4 + transport. These data are crucial to our understanding of how mutations can disrupt NH3/NH4 + transport, potentially affecting kidney function in CKD patients susceptible to acidosis. KEY POINTS: Acidosis and low urinary ammonium excretion contribute to poor outcomes in chronic kidney disease (CKD). This study investigates how the function of an ammonia transporter in renal collecting duct (RhBG) may contribute to CKD. Here, we report six rare RhBG mutations associated with CKD, identified using data from the Chronic Renal Insufficiency Cohort (CRIC) study. Using electrophysiological measurements, functional analysis in Xenopus oocytes showed that these RhBG mutations disrupt ammonia transport, with some mutations affecting only NH3 transport, whereas others affect both NH3 and NH4 + transport. The results suggest that impaired ammonia transport by RhBG contributes to CKD, highlighting the need to understand mechanisms that link function (NH3/NH4 + and acid-base regulation) and genetic predisposition to CKD.