[Down-regulation of PHLPP1 expression ameliorates high glucose-induced autophagy inhibition and apoptosis promotion of podocytes by activating PI3K/AKT/mTOR pathway].

Objective To investigate the expression of pleckstrin homology(PH) domain leucine-rich repeats protein phosphatase 1 (PHLPP1) in renal tissue of patients with diabetic nephropathy (DN) and its effect on podocyte autophagy and apoptosis, and to explore its related mechanism. Methods Immunohistochemistry was used to detect PHLPP1 expression in renal tissue of patients with DN and non-diabetes, and immunofluorescence histochemical staining was used to detect the co-expression of nephrin and PHLPP1 to determine the localization of PHLPP1 in podocytes. Human glomerular podocyte cell line was cultured in normal glucose (NG) and high glucose (HG) media. The expression of PHLPP1 mRNA was detected by real-time quantitative PCR. Small interfering RNA of PHLPP1 (si-PHLPP1) targeting down-regulation of PHLPP1 was transfected into podocytes by Lipofectamine transient transfection technology, and the transfection efficiency was assessed by real-time PCR. According to the different treatment of podocytes, the cells were divided into NG group (podocytes cultured with normal glucose media), HG group (podocytes cultured with high glucose medium), HG combined with si-PHLPP1 group (podocytes transfected with si-PHLPP1 were cultured in high glucose medium), and HG combined with HCQ group (podocytes treated with hydroxychloroquine and high glucose medium). The formation of autophagic vesicles was observed by transmission electron microscope, and the protein expression levels of LC3, P62, PI3K, mTOR, p-mTOR, cleaved caspase 3 (c-caspase-3), AKT, p-AKT were detected by Western blotting. Annexin V-FITC/PI staining combined with flow cytometry was used to detect apoptosis. Results PHLPP1 was highly expressed in the renal tissue of patients with DN, and it was mainly expressed in the glomerular podocyte. The HG culture medium could promote the expression of PHLPP1 mRNA in podocytes in a time-dependent manner. Compared with NG group, the autophagy level of podocytes, the expression of PI3K and the phosphorylation level of mTOR in the HG group, HG combined with si-PHLPP1 group and HG combined with HCQ group were significantly reduced; the apoptosis rate and c-caspase-3 protein expression level were significantly enhanced; the phosphorylation level of AKT in the HG combined with si-PHLPP1 group significantly increased, but it in the other two groups significantly decreased. Compared with HG group, the apoptosis rate and c-caspase-3 protein expression in the HG combined with si-PHLPP1 group were significantly reduced, while autophagy level, PI3K protein expression and phosphorylation level of mTOR and Akt protein were significantly elevated. The autophagy level of HG combined with HCQ group was significantly inhibited, the apoptosis rate and c-caspase-3 protein expression were significantly raised, and other indicators showed no significant changes. Conclusion PHLPP1 is highly expressed in renal tissue of patients with DN, and the down-regulated expression of PHLPP1 in podocytes can promote the autophagy of podocytes and reduced the apoptosis of podocytes by activating PI3K/AKT/mTOR pathway.