#3347 Renal magnesium handling in mouse model of Fanconi–Bickel syndrome

Abstract Background and Aims Kidney plays a central role on the homeostasis of magnesium. The thick ascending limb (TAL) uptakes 40%–70% of Mg2+ via claudin-16 and claudin-19 complex, id the major segment for renal magnesium absorption. The DCT, reabsorb about 5% of the filtered Mg2+, but is the main regulatory site for serum Mg2+ concentration. The proximal tubule of the nephron reabsorbs approximately 10-20% of filtered amount of Mg2+ likely mediated by tight-junction proteins claudin-2 and claudin-12 driven by Na+/H+ exchanger 3 (NHE3)-mediated Na+ reabsorption. We have recently generated and characterized a mouse model with kidney-specific ablation of GLUT2 (Glut2Pax8Cre +), which recapitulate the renal phenotype of Glycogen storage disease XI, also known as Fanconi–Bickel syndrome. In the current study, we aimed at investigating the Mg2+ homeostasis in Glut2Pax8Cre + mice to unveil the molecular mechanisms on renal Mg handling associated with glycogen accumulation in PT and the effect of the SGLT2-inhibitors on renal Mg2+ handling. Method Urine samples were collected from male control mice (Glut2lox/lox; Pax8Cre/−) and GLUT2 cko (Glut2Pax8Cre +) mice with or without treatment with Dapaglifozin (DAPA) to evaluate the Mg2+ levels. Kidney tissues from control and cko mice were utilized for RNA extraction to perform RT-PCR analyses on CLDN16, CLDN19, TRPM6, TRPM7, SLC41A1, and CNNM2. To verify the expression of Claudin 16, immunofluorescence was performed on kidney tissues. Results Glut2 cKO mice exhibit a larger urinary Mg2+ loss compared to control mice. RT-PCR revealed that mRNA expression of CLDN16 were significantly increased in Glut2 cKO mice compared to controls. Immunofluorescence on renal tissues from ctr and Glut2 cKO mice further confirmed a similar localization of CLDN16 on the TAL. In addition, the Mg2+ transporters TRPM6 and TRPM7 expressed along the DCT did not present significant in mRNA abundance between the two groups. Since we have previously demonstrated that the treatment with dapagliflozin, a SGLT2-inhibitor, is able to rescue the phenotype of Glut2 cKO mice regarding, metabolic acidosis, albuminuria, phosphaturia and glycogen accumulation. We tested whether dapagliflozin could limit urinary Mg2+ loss in these mice. Dapagliflozin, effectively restored urinary Mg2+ loss at the control level. Conclusion Glut2 cKO mice could serve as a valid model to investigate the mechanisms behind the ability of SGLT2-inhibitors of increasing serum Mg2+ concentration. Here by showing an effect on magnesium excretion of dapagliflozin we could hypothesize that the SGLT2-inhibitors could act directly on proximal tubule Mg2+ transport. However, additional experiments are required to further elucidate the molecular mechanism.