Systemic Succinate Homeostasis and Local Succinate Signaling Affect Blood Pressure and Modify Risks for Calcium Oxalate Lithogenesis

Abstract

Background In the kidney, low urinary citrate increases the risk for developing kidney stones, and elevation of luminal succinate in the juxtaglomerular apparatus increases renin secretion, causing hypertension. Although the association between stone formation and hypertension is well established, the molecular mechanism linking these pathophysiologies has been elusive. Methods To investigate the relationship between succinate and citrate/oxalate levels, we assessed blood and urine levels of metabolites, renal protein expression, and BP (using 24-hour telemetric monitoring) in male mice lacking slc26a6 (a transporter that inhibits the succinate transporter NaDC-1 to control citrate absorption from the urinary lumen). We also explored the mechanism underlying this metabolic association, using coimmunoprecipitation, electrophysiologic measurements, and flux assays to study protein interaction and transport activity. Results Compared with control mice, slc26a6 2/2 mice (previously shown to have low urinary citrate and to develop calcium oxalate stones) had a 40% decrease in urinary excretion of succinate, a 35% increase in serum succinate, and elevated plasma renin. Slc26a6 2/2 mice also showed activity-dependent hypertension that was unaffected by dietary salt intake. Structural modeling, confirmed by mutational analysis, identified slc26a6 and NaDC-1 residues that interact and mediate slc26a6's inhibition of NaDC-1. This interaction is regulated by the scaffolding protein IRBIT, which is released by stimulation of the succinate receptor SUCNR1 and interacts with the NaDC-1/slc26a6 complex to inhibit succinate transport by NaDC-1. Conclusions These findings reveal a succinate/citrate homeostatic pathway regulated by IRBIT that affects BP and biochemical risk of calcium oxalate stone formation, thus providing a potential molecular link between hypertension and lithogenesis.

A dynamic anchor domain in slc13 transporters controls metabolite transport

“…As control, we also monitored the interaction between hNaCT and mA6(E613A), which showed lower interaction with hNaCT ( Fig. 3C) in agreement with previous results (6). The results in Fig.…”

“…As we have previously shown, the H4c domain of slc13s mediates intracellular interaction with slc26a6 which results in inhibition of two slc13 transporters, NaDC-1 and, as we show in the current study, hNaCT (6). The functional and in silico analyses of mutations in H4c basic residues suggest that R108 is essential due to its positive charge and other exclusive attributes such as hydrophilicity, the size and optional rotamers of the residue.…”

“…The major succinate and citrate transporters expressed on the plasma membrane of mammalian cells are members of the slc13 family (1)(2)(3), which is part of the larger divalent anion:sodium symporter family (4). The physiological importance of slc13 transporters and, among them, the citrate transporter slc13a5 (NaCT), is underscored by numerous pathologies that are associated with these genes including hypertension, kidney stones and epilepsy (5)(6)(7)(8). Being the major citrate transporter, NaCT deletion mimics caloric restriction which promotes prolonged life span in Drosophila Melanogaster (9).…”

“…Interaction between the oxalate transporter and the succinate/citrate transporter results in inhibition of succinate transport (6,7), and is associated with protection from kidney stone formation and hypertension (6,7). However, the molecular mechanism that mediates the interaction with slc13 transporters to regulate their activity is unknown.…”

“…Specifically, TMD 4 consists of three segments, two of which, 4a and 4b, are involved in forming the dimerization interface; while the third segment, TM 4c or the H4c domain, is located near the surface of the inner membrane. We have previously reported that the putative H4c domain of the slc13 family member, NaDC-1, mediates interaction with partner proteins (6,7). We showed that a positively charged residue, K107, on the H4c domain of NaDC-1 mediates interaction with a Glu residue (E613) in the intracellular C terminal domain (STAS domain) of slc26 transporters.…”