Rapamycin Promotes the Autophagic Degradation of Oxidized Low-Density Lipoprotein in Human Umbilical Vein Endothelial Cells.

BACKGROUND/AIMS: Oxidized low-density lipoprotein (ox-LDL) has been extensively implicated in the initiation of atherosclerosis. Our previous studies reported that ox-LDL could activate autophagy in human umbilical vein endothelial cells (HUVECs). Because of this, subsequent studies were designed to elucidate the possible role of the autophagic inducer, rapamycin, on ox-LDL degradation in endothelial cells.

METHODS

Intracellular cholesterol content was measured using a tissue total cholesterol assay kit. ox-LDL trafficking within endothelial cells was analyzed by flow cytometry. Levels of proteins involved in the autophagic process, microtubule-associated protein 1 light chain 3 (MAP1-LC3), lysosome-associated membrane protein 1 (LAMP1), Beclin 1 and p62, were assessed by Western blot analysis.

RESULTS

We discovered that rapamycin could decrease the ox-LDL content in HUVECs at the 3-hour time point. Rapamycin also mediated an obvious increase in Dil-labeled ox-LDL (Dil-ox-LDL)/LC3 and Dil-ox-LDL/LAMP1 co-localization, which was inhibited by 3-methyladenine (3-MA), an autophagic inhibitor. In addition, significant co-localization of LC3 and LAMP1 occurred in cells pretreated with rapamycin. In the presence of rapamycin, p62 levels were reduced, and autophagic flux was enhanced.

CONCLUSION

These data demonstrate that the activation of the autophagy-lysosome pathway by rapamycin may accelerate ox-LDL degradation.