Metformin modulates apoptosis and cell signaling of human podocytes under high glucose conditions

Diabetic nephropathy, which is associated with loss of human (h) podocytes (PC), is a major complication in diabetes mellitus. High-glucose modulates AMP-activated protein kinase (AMPK) signaling and cell apoptosis. Metformin has been demonstrated to reduce apoptosis and albuminuria in type 2 diabetes. Here, we examined the effect of metformin on cell apoptosis and on pro-/anti-apoptotic signaling in hPC. Expression analyses were done by real-time polymerase chain reaction and western blotting. Moreover, a functional apoptosis assay was performed in hPC. Determination of kinase activation by phosphorylation was done via immunodetection analyses and digital quantification. We found that hPC express organic cation transporter 1 which is the major uptake transporter of metformin. High-glucose reduced AMPK phosphorylation and induced mammalian target of rapamycin (mTOR) activation in podocytes, which was abolished and reversed by pre-treatment with metformin. Furthermore, metformin reduced high-glucose-induced podocytes apoptosis in a concentration-dependent manner. In summary, metformin exhibits an anti-apoptotic impact on podocytes under high-glucose conditions via activation of AMPK and inhibition of mTOR signaling. These data support a beneficial effect of metformin in diabetic nephropathy.