Ganoderic acid A attenuates streptozotocin-induced diabetic kidney injury: associations with mitochondrial oxidative stress and TGF-β/Smad signaling.

Background

Diabetic kidney disease (DKD) involves renal tubular epithelial injury, mitochondrial oxidative stress, and progressive fibrosis. Ganoderic acid A (GAA) has antioxidant and anti-inflammatory activities, but its potential renoprotective effects have not been fully explored in the context of DKD. This study investigated whether GAA affects high glucose (HG)-induced tubular epithelial injury in vitro and streptozotocin-induced diabetic kidney injury (STZ-DKI) in vivo, focusing on TGF-β/Smad signaling and mitochondrial impairment.

Methods

HK-2 cells were pretreated with GAA before HG exposure. Cell viability, LDH release, apoptosis, oxidative stress, mitochondrial superoxide, membrane potential, ATP levels, mtDNA copy number, complex I activity, and MitoTracker Red CMXRos fluorescence were assessed. Fibrotic responses and TGF-β/Smad signaling were examined by immunoblotting and immunofluorescence, and TGF-β1 overexpression was used for mechanistic validation. Mice with STZ-DKI received GAA for 8 weeks, followed by assessments of renal function, histopathology, tubular injury, and protein expression.

Results

GAA improved HK-2 cell viability and reduced LDH release and apoptosis under HG conditions. It decreased intracellular and mitochondrial ROS, improved mitochondrial-associated parameters, and reduced NOX1/2 while increasing SOD1/2 and COX4 expression. GAA also suppressed EMT and fibrotic markers, including α-SMA, fibronectin, and collagen IV, together with reduced TGF-β1/Smad2/3 activation. TGF-β1 overexpression partially reversed these effects. In vivo, GAA-treated mice showed improved renal functional parameters and reduced histopathological injury, tubular damage, apoptosis, and fibrosis, along with lower fasting blood glucose levels.

Conclusion

GAA attenuates HG-induced renal tubular epithelial injury in vitro and ameliorates renal injury in STZ-induced diabetic mice, accompanied by decreased TGF-β/Smad signaling and mitochondrial oxidative stress in both models.