Oxidized low-density lipoprotein induces autophagy in vascular endothelial cells via Akt/mTOR/p70S6K pathway

Abstract

Objective To investigate the effects of oxidized low density lipoprotein (oxLDL) on autophagy and its effect on Akt/mTOR/p70S6K signaling pathway in human umbilical vein endothelial cells (HUVECs). Methods The cultured HUVECs were divided into either an oxLDL or a control group, and treated with 100 μg/ml oxLDL and equal volume phosphate buffer solution respectively. The cells were collected after 6 h and 12 h. Transmission electron microscopy was used to observe the autophagosome. Real-time fluorescence quantitative polymerase chain reaction was used to detect expression levels of microtubule associated protein 1 light chain 3 (LC3) and p62 mRNA. Western blot was used to detect the expression levels of LC3, p62, P-Akt/Akt, P-mTOR/mTOR, and p-p70S6K/p70S6K. Results Compared with the control group, the number of intracellular autophagosome increased obviously (P<0.05), LC3 mRNA and protein expression levels increased significantly (all P<0.05), and p62 mRNA and protein expression levels decreased significantly (all P<0.05) in the oxLDL group. In addition, the phosphorylated protein expression levels of Akt, mTOR and p70S6K in the oxLDL group were significantly decreased than those in the control group (all P<0.01). However, total protein levels of Akt, mTOR, and p70S6K were not significantly different between the oxLDL group and the control group. Conclusion oxLDL may induce the autophagy of HUVECs via inhibiting the Akt/mTOR/p70S6K signaling pathway. Key words: Endothelial Cells; Endothelium, Vascular; Lipoproteins, LDL; Autophagy; Atherosclerosis; Signal Transduction; TOR Serine-Threonine Kinases; Proto-Oncogene Proteins c-akt; Ribosomal Protein S6 Kinases, 70-kDa; Microtubule-Associated Proteins