Sodium-glucose cotransporter 2 inhibitor tofogliflozin ameliorates insulin signaling by improving mitochondrial function in the podocytes in DKD

Podocyte mitochondrial dysfunction may contribute to the progression and exacerbation of diabetic kidney disease (DKD). Sodium-glucose cotransporter-2 (SGLT2) inhibitors have been shown to slow DKD progression. However, the effects of SGLT2 inhibitors on renal mitochondria remain unknown. In this study, we sought to determine the effect of SGLT2 inhibitors on podocyte mitochondrial function. To determine whether tofogliflozin restores mitochondrial function, podocytes were exposed to low (5.5 mM) or high glucose (25 mM) in the absence or presence of tofogliflozin (0.1 µM). Expression of the mitophagy marker, PTEN induced putative kinase 1 (PINK1), was evaluated by real-time polymerase chain reaction. Mitochondrial membrane potential (MitoMP) was detected using a MitoMP assay kit. Podocytes growing in RPMI-1640 medium supplemented with 0.1% fetal calf serum were stimulated with insulin (10 nM) for 5 min to assess insulin signaling. Incubation of podocytes under high glucose conditions resulted in a significant decrease in PINK1 expression, suggestive of inhibition of mitophagy. Levels of BCL2 interacting protein 3 (BNIP3) and proliferator-activated receptor-γ co-activator-1α (PGC1α), mitochondrial function markers, also decreased, although the change was not significant. MitoMP assay showed decreased MitoMP in cells under high glucose conditions. In contrast, tofogliflozin significantly increased PINK1, BNIP3, and PGC1α expression and restored MitoMP. Finally, we analyzed the effects of tofogliflozin on insulin signaling. High glucose decreased insulin receptor substrate-1 (IRS1) and Akt phosphorylation, whereas treatment with tofogliflozin partially reversed this effect. Our results indicate that diabetic conditions might decrease mitochondrial function and inhibit insulin signaling in podocytes. Tofogliflozin could restore mitochondrial function and consequently restores insulin signaling resulting in anti-apoptotic effects in podocytes.