Berberine attenuates diabetic kidney injury via FOXO1/SP1-associated regulation of renal SGLT-2 expression

Abstract Background Berberine (BBR), a plant-derived isoquinoline alkaloid, has been reported to exert anti-hyperglycemic and renoprotective effects. However, the mechanism by which BBR regulates renal glucose transport under diabetic conditions remains unclear. Sodium-glucose cotransporter-2 (SGLT-2), mainly expressed in renal proximal tubular epithelial cells, plays a key role in renal glucose reabsorption. This study investigated whether BBR attenuates diabetic kidney injury by regulating SGLT-2 expression and examined the potential involvement of FOXO1 and SP1 in this regulation. Methods Db/db mice and high-glucose-exposed human kidney-2 (HK-2) cells were used to evaluate the effects of BBR, empagliflozin (EM), and their combination. Metabolic and renal phenotypes were assessed by biochemical, histological, and ultrastructural analyses. Network pharmacology, public transcriptomic data mining, molecular docking, cellular thermal shift assay (CETSA), quantitative real-time PCR, western blotting, immunofluorescence, nuclear-cytoplasmic fractionation, co-immunoprecipitation, 2-NBDG uptake, dual-luciferase reporter assays, FOXO1 overexpression, and pharmacological interference with SP1-associated regulation were performed to investigate the regulatory mechanism. Results Both BBR and EM improved metabolic abnormalities and renal injury in db/db mice, whereas combined treatment produced marked metabolic and renal improvements but was accompanied by an increasing trend in AST. BBR reduced hyperglycemia, improved glucose tolerance and enhanced the glucose-lowering response to exogenous insulin during the ITT, suppressed urinary albumin excretion, and alleviated renal histopathological and ultrastructural damage. Molecular docking and qualitative CETSA findings suggested that FOXO1 may represent a potential molecular target of BBR. In HK-2 cells, high-glucose stimulation increased SGLT-2 expression and glucose uptake, accompanied by dysregulation of FOXO1 and SP1 signaling. BBR downregulated FOXO1 and SGLT-2, restored SP1 and phosphorylated FOXO1 levels, and reduced glucose uptake under high-glucose conditions. FOXO1 overexpression attenuated the BBR-induced reduction in SGLT-2 expression, whereas pharmacological interference with SP1-associated regulation further supported the functional involvement of SP1 in SGLT-2 regulation. Conclusion BBR attenuates diabetic kidney injury, at least in part, through FOXO1/SP1-associated regulation of renal SGLT-2 expression. These findings support the involvement of a FOXO1/SP1-associated regulatory axis in renal tubular glucose handling under diabetic conditions.