Triptolide protects podocytes from TGF-β-induced injury by preventing miR-30 downregulation

Triptolide is known to have a strong anti-proteinuric effect through direct protection of podocytes from injury and is used to treat glomerular diseases. However, the mechanism underlying its protective effect on podocytes remains elusive. MiR-30 family has recently been shown to be essential for structural and functional homeostasis of podocytes but is downregulated by injurious factors, leading to podocyte injury. In the present study, we explore whether Triptolide protects podocytes through preventing miR-30 downregulation. Since TGF-β signaling is a critical mediator in various podocyte injuries and we previously found that TGF-β induces podocyte injury through downregulating miR-30s, we thus used TGF-β-induced podocyte injury model to address the issue. We found that Triptolide is capable of protecting cultured podocytes from TGF-β-induced cytoskeletal injury and apoptosis, as expected. Consistently, Triptolide also prevented TGF-β-induced signaling activation of MAPK p38, NFkB (p65) and calcineurin/NFATC3, which are known to be downstream mediators of podocyte injury. Meanwhile, Triptolide was found to completely prevent TGF-β-induced miR-30 downregulation, indicating that Triptolide protects podocytes by sustaining miR-30 expression. Mechanistically, we found that Triptolide can prevent TGF-β-induced Smad2/3 phosphorylation/activation, which likely underlies miR-30 restoration by Triptolide. We also performed ex vivo study and found that Triptolide prevented TGF-β-induced miR-30 downregulation and Smad2/3 phosphorylation in the isolated glomeruli of mice or rats. Thus, our study has provided novel insights into the mechanism underlying the therapeutic effectiveness of Triptolide on podocytopathies.