MicroRNA21/HDAC4 mediates podocyte apoptosis under high glucose conditions by regulating the activation of FoxO1

Diabetic kidney disease (DKD), which lacks effective treatment, has become the leading cause of end-stage renal disease. Apoptosis of podocytes, as a vital mode of cell injury, plays an important role in the progression of DKD. MicroRNA-21 (miR-21) and Forkhead transcription Factor O1 (FoxO1) have been revealed to act in DKD, but the mechanisms remain elusive. Here, we investigated the special regulatory mechanism by which miR-21 activates FoxO1 in mouse podocytes induced by high glucose (HG). In vitro, after exposure to HG, podocyte apoptosis, miR-21, HDAC4, FoxO1/acetylate-FoxO1/phosphorylate-FoxO1, Bcl-2, and nephrin were examined. Then, we evaluated the vital effect of miR-21 in regulating podocyte apoptosis and identified the critical activator of FoxO1 by overexpression or inhibition of miR-21/HDAC4 via adenoviral transfer. The results showed that HG increased podocyte apoptosis, elevated the expression of miR-21, HDAC4, acetylate-FoxO1, and FoxO1, and reduced the expression of Bcl-2 and nephrin. In addition, overexpression or inhibition of miR-21 could affect the levels of HDAC4, acetylated FoxO1, FoxO1, Bcl-2, and nephrin. Finally, overexpression of HDAC4 decreased the acetylation of FoxO1 while increasing the phosphorylation of FoxO1, which resulted in a decline in Bcl-2 and nephrin. Therefore, these data indicated that miR-21/FoxO1 was a key pathway in regulating podocyte apoptosis under HG conditions. Furthermore, phosphorylation rather than acetylation was the critical activator of FoxO1.