Metformin reduces TRPC6 expression through AMPK activation and modulates cytoskeleton dynamics in podocytes under diabetic conditions

Podocytes have foot processes that comprise an important cellular layer of the glomerular barrier involved in regulating glomerular permeability. The disturbance of podocyte function plays a central role in the development of proteinuria in diabetic nephropathy. AMP-activated protein kinase (AMPK), a key regulator of glucose and fatty acid metabolism, plays a major role in obesity and type 2 diabetes. Accumulating evidence suggests that TRPC6 channels are crucial mediators of calcium transport in podocytes, and these channels are involved in disturbing the glomerular filtration barrier in diabetes. Metformin is an anti-diabetic drug widely used for treating patients with type 2 diabetes. Recent studies have suggested that the therapeutic effect of metformin might be mediated by AMPK. The precise function of metformin on cellular function and intracellular signaling in podocytes under diabetic conditions is not fully understood. In this study, we demonstrated that metformin normalized TRPC6 expression via AMPK alpha 1 activation in podocytes exposed to high glucose concentrations. A quantitative analysis showed that metformin increased the colocalization of TRPC6 and AMPK alpha 1 subunits from 42% to 61% in standard glucose (SG) medium and from 29% to 52% in high glucose (HG) medium. AMPK activation was also necessary for maintaining appropriate levels of Rho-family small GTPase activity in FIG conditions. Moreover, metformin through AMPK activation remodeled cytoskeleton dynamics, and consequently, reduced filtration barrier permeability in diabetic conditions.