Role of bile acid-dependent Takeda G-coupled protein receptor 5 (TGR5) in regulating AMPK expression in human podocytes

Bile acids affect podocyte function by stimulating membrane-bound Takeda G protein-coupled receptor 5 (TGR5), the activity of which is linked to the regulation of glucose and lipid metabolism. In podocytes, adenosine monophosphate-dependent protein kinase (AMPK) is critical for maintaining energy balance, suggesting that the bile acid-dependent stimulation of TGR5 may impact AMPK activity to regulate metabolic processes in podocytes. Despite the beneficial effect of TGR5 activation on AMPK activity in podocytes that are exposed to hyperglycemic conditions, the effect of TGR5 signaling on AMPK alpha expression and phosphorylation state under control conditions have not been studied in podocytes. Our studies confirmed TGR5 expression in podocytes at both the mRNA and protein levels. Moreover, TGR5 inhibition decreased the protein expression of both AMPK alpha 1 and AMPK alpha 2 isoforms, which correlated with significantly lower levels of AMPK alpha phosphorylation at Thr172 in podocytes. Additionally, the immunofluorescent staining of podocytes with pharmacologically inhibited TGR5 activity were characterized by a lower mean intensity of the AMPK alpha fluorescence signal. TGR5 stimulation decreased the mRNA expression of AMPK alpha 1 and AMPK alpha 2 but did not change the degree of AMPK alpha phosphorylation at Thr172. These data suggest that TGR5 inactivation significantly downregulates AMPK activity. This may shed new light on the bile acid-dependent regulation of glucose and lipid metabolism in podocytes, especially under pathological conditions.