Molecular mechanism of emodin on inhibiting autophagy induced by HBSS in renal tubular cells

Abstract

To explore the regulative effects and possible mechanisms of emodin on autophagy induced by starvation in rat's renal tubular epithelial cells (NRK-52E). Firstly, Hank's balanced salt solution (HBSS) was used to induce starvation and the protein expression of microtubule-associated protein 1 light chain 3 (LC3) I/II, an autophagic marker of mammalian congener, was detected by Western blot with or without the treatment of emodin. Secondly, the changes of red fluorescent protein-microtubule associated protein light chain3 (RFP-LC3) fluorescent particles, treated by HBSS (1 mL) and bafilomycin A1 (10 nmol x L(-1)) with or without emodin, were observed through fluorescence microscopy in NRK-52E cells transient transfected by RFP-LC3 plasmid. With the intervention of mammalian target of rapamycin mTOR inhibitor rapamycin (100 nmol x L(-1)) , the effect of blocking mTOR signaling pathway on autophagic inhibition of emodin was observed. Finally, the effect of mTOR signaling pathway on autophagic inhibition of emodin was further evaluated through the over-expression of endogenous mTOR inhibitory protein DEP domain-containing mTOR-interacting protein-(DEPTOR). HBSS hunger could induce high protein expression of LC3 II in NRK-52E cells, and the intervention of emodin could reverse the unregulated protein expression of LC3 II induced by HBSS. The number of RFP-LC3 fluorescent particles was increased after the co-treatment of HBSS and bafilomycin A1, and this increase was inhibited by emodin. After the co-treatment of rapamycin, emodin and HBSS, the LC3 II protein expression restored in NRK-52E cells, compared with the treatment of HBSS. Over-expression of DEPTOR could also block the inhibitive effect of emodin on LC3 II protein expression. Emodin could inhibit HBSS-induced LC3 II protein expression and the activation of autophagy in NRK-52E cells, and the effect of blocking autophagy may be mediated through mTOR signaling pathway.