Unsaturated lipid peroxidation-derived aldehydes activate autophagy in vascular smooth-muscle cells

Abstract

Proteins modified by aldehydes generated from oxidized lipids accumulate in cells during oxidative stress and are commonly detected in diseased or aged tissue. The mechanisms by which cells remove aldehyde-adducted proteins, however, remain unclear. Here, we report that products of lipid peroxidation such as 4-HNE (4-hydroxynonenal) and acrolein activate autophagy in rat aortic smooth-muscle cells in culture. Exposure to 4-HNE led to the modification of several proteins, as detected by anti-protein–4-HNE antibodies or protein-bound radioactivity in [3H]4-HNE-treated cells. The 4-HNE-modified proteins were gradually removed from cells. The removal of 4-HNE-modified proteins was not affected by the oxidized protein hydrolase inhibitor, acetyl leucine chloromethyl ketone, or lactacystin, although it was significantly decreased by PSI (proteasome inhibitor I), the lysosome/proteasome inhibitor MG-132 (carbobenzoxy-L-leucyl-L-leucyl-leucinal), insulin or the autophagy inhibitor 3-MA (3-methyladenine). Pre-incubation of cells with rapamycin accelerated the removal of 4-HNE-modified proteins. Treatment with 4-HNE, nonenal and acrolein, but not nonanal or POVPC (1-palmitoyl-2-oxovaleroyl phosphatidyl choline), caused a robust increase in LC3-II (microtubule-associated protein 1 light chain 3-II) formation, which was increased also by rapamycin, but prevented by insulin. Electron micrographs of 4-HNE-treated cells showed extensive vacuolization, pinocytic body formation, crescent-shaped phagophores, and multilamellar vesicles. Treatment with 3-MA and MG-132, but not proteasome-specific inhibitors, induced cell death in 4-HNE-treated cells. Collectively, these results show that lipid peroxidation-derived aldehydes stimulate autophagy, which removes aldehyde-modified proteins, and that inhibition of autophagy precipitates cell death in aldehyde-treated cells. Autophagy may be an important mechanism for the survival of arterial smooth-muscle cells under conditions associated with excessive lipid peroxidation.