AMPK-OXSR1 signaling coordinates proximal tubular sodium transport and is modulated by canagliflozin.

INTRODUCTION: The with-no-lysine kinase (WNK)/oxidative stress-responsive kinase 1 (OXSR1) pathway is vital for renal sodium transport in the distal nephrons as it regulates chloride cotransporters. However, its role in proximal tubule (PT) sodium transport remains unclear. We aimed to investigate whether this pathway acts as signaling convergence point involved in coordinating transepithelial sodium reabsorption using isolated human and rat PTs. METHODS: Freshly isolated human and rat PTs were treated with WNK or OXSR1 inhibitors to evaluate their effects on sodium reabsorption stimulated by insulin, a peroxisome proliferator-activated receptor gamma agonist, and angiotensin II (AngII). RESULTS: Inhibition of WNK or OXSR1 suppressed the stimulatory effects of insulin and AngII on sodium reabsorption in human and rat PTs. The sodium-glucose cotransporter 2 (SGLT2) inhibitor canagliflozin inhibited OXSR1 phosphorylation via AMP-activated protein kinase (AMPK)α1/2, thereby attenuating insulin- and AngII-induced PT Na+ transport, blood pressure elevation, and renal injury. Moreover, canagliflozin administration improved kidney function and increased AMPKα1/2 phosphorylation, suggesting that SGLT2-regulated OXSR1 is integral to Na+ transport stimulation. Incubation of PTs with different glucose concentrations and gene silencing of SGLT2 revealed that canagliflozin may activate AMPK by suppressing the transcellular glucose flux but not by reducing intracellular glucose in PTs. DISCUSSION: These findings identify OXSR1 as a crucial signaling convergence point involved in coordinating transepithelial sodium reabsorption and demonstrate that SGLT2 regulates OXSR1 activity via AMPKα1/2.