Emodin Ameliorates High Glucose-Induced Podocyte Apoptosis via Regulating AMPK/mTOR-Mediated Autophagy Signaling Pathway

Objective: To investigate the effect of emodin on high glucose(HG)-induced podocyte apoptosis and whether the potential anti-apoptotic mechanism of emodin is related to induction of adenosinemonophosphate-activated protein kinase(AMPK)/mammalian target of rapamycin(mTOR)-mediated autophagy in podocytes(MPC5 cells) in vitro. Methods: MPC5 cells were treated with different concentrations of HG(2.5,5, 10, 20, 40, 80 and 160 mmol/L), emodin(2, 4, 8 μmol/L), or HG(40 mmol/L) and emodin(4 μmol/L) with or without rapamycin(Rap, 100 nmol/L) and compound C(10 μmol/L). The viability and apoptosis of MPC5 cells were detected using cell counting kit-8(CCK-8) assay and flow cytometry analysis, respectively. The expression levels of cleaved caspase-3, autophagy marker light chain 3(LC3) Ⅰ/Ⅱ, and AMPK/mTOR signaling pathwayrelated proteins were determined by Western blot. The changes of morphology and RFP-LC3 fluorescence were observed under microscopy. Results: HG at 20, 40, 80 and 160 mmol/L dose-dependently induced cell apoptosis in MPC5 cells, whereas emodin(4 μmol/L) significantly ameliorated HG-induced cell apoptosis and caspase-3 cleavage(P<0.01). Emodin(4 μmol/L) significantly increased LC3-Ⅱ protein expression levels and induced RFP-LC3-containing punctate structures in MPC5 cells(P<0.01). Furthermore, the protective effects of emodin were mimicked by rapamycin(100 nmol/L). Moreover, emodin increased the phosphorylation of AMPK and suppressed the phosphorylation of mTOR. The AMPK inhibitor compound C(10 μmol/L) reversed emodininduced autophagy activation. Conclusion: Emodin ameliorated HG-induced apoptosis of MPC5 cells in vitro that involved induction of autophagy through the AMPK/mTOR signaling pathway, which might provide a potential therapeutic option for diabetic nephropathy.