.....This study was designed to investigate the mechanisms by which 7-ketocholesterol (7-KC), a major component of oxidized lipoproteins, induces autophagy. This study was also designed to determine the effect of autophagy induction on apoptosis, a central event in the development of atherosclerosis. Exposure of human aortic smooth muscle cells to 7-KC promoted conversion of microtubule-associated protein light chain 3 (LC3)-I to LC3-II, enhanced accumulation of green fluorescent protein-tagged, LC3-positive intracellular vacuoles, and increased autophagic flux. Autophagy induction was suppressed by treating the cells with either a reactive oxygen species scavenger or an antioxidant. Administration of 7-KC concomitantly up-regulated Nox4 expression, increased intracellular hydrogen peroxide levels, and inhibited autophagy-related gene 4B activity. Catalase overexpression to remove hydrogen peroxide or Nox4 knockdown with siRNA reduced intracellular hydrogen peroxide levels, restored autophagy-related gene 4B activity, and consequently attenuated 7-KC-induced autophagy. Moreover, inhibition of autophagy aggravated both endoplasmic reticulum (ER) stress and cell death in response to 7-KC. In contrast, up-regulation of autophagic activity by rapamycin attenuated 7-KC-induced ER stress and cell death. Finally, activation of autophagy by chronic rapamycin treatment attenuated ER stress, apoptosis, and atherosclerosis in apolipoprotein E knockout (ApoE-/-) mouse aortas. In conclusion, we demonstrate that up-regulation of autophagy is a cellular protective response that attenuates 7-KC-induced cell death in human aortic smooth muscle cells.