Astragaloside IV reduces diabetic kidney injury by inhibiting the PKC/NOX4/MAPK pathway

Diabetic nephropathy (DN) is a major complication of diabetes and a leading cause of end-stage renal disease. This study investigated the renoprotective effects and underlying mechanisms of Astragaloside IV (AS) in a rat model of type 2 diabetes induced by a high-fat diet and low-dose streptozotocin. The rats received AS treatment (20, 40, or 80 mg/kg) for 13 weeks. AS significantly improved blood glucose and lipid profiles, enhanced the glomerular filtration rate, and reduced kidney injury without inducing hepatic toxicity. Histological staining, including hematoxylin and eosin, Masson's trichrome, and periodic acid-Schiff staining, revealed attenuation of glomerular hypertrophy, mesangial expansion, and interstitial fibrosis. These improvements were corroborated by molecular analyses showing the downregulation of kidney injury molecule-1 and fibronectin, along with the restoration of nephrin expression at both the mRNA and protein levels. AS also attenuated high glucose-induced oxidative stress both in vivo and in vitro, as indicated by reduced reactive oxygen species and malondialdehyde levels and enhanced antioxidant enzyme activities, including superoxide dismutase and glutathione peroxidase in diabetic renal tissues and high glucose-stimulated HBZY-1 cells. Mechanistically, AS inhibited protein pinase C (PKC) beta expression and downstream NADPH Oxidase 4 activation, leading to suppression of mitogen-activated protein kinase (MAPK) signaling (ERK, p38, JNK) and NF-κB phosphorylation, thereby reducing inflammatory cytokine production. siRNA-based knockdown experiments further validated the PKC-β/NOX4 axis in mediating these protective effects. Collectively, AS alleviates diabetic renal injury by modulating the PKC-β/NOX4/MAPK pathway to reduce oxidative stress and inflammation, supporting its potential as a therapeutic candidate for DN.