Abstract 3622: Oxidized LDL-derived Reactive Aldehydes Induce ER Stress and Trigger the Unfolded Protein Response: Implications for Atherosclerotic Lesion Formation
All stages of atherosclerotic lesion formation are associated with the accumulation of proteins modified by aldehydes that are generated from the oxidation of membrane phospholipids and lipoproteins. Although aldehyde-adducted proteins elicit strong immunogenic responses, the role of lipid peroxidation products in promoting and sustaining atherogenesis remains unclear. To examine aldehyde-induced protein modification and to assess its contribution to vascular stress, vascular smooth muscle and endothelial cells (EC) were exposed to 4-hydroxy-trans-2-nonenal (HNE), one of the most abundant and reactive oxidized lipid-derived aldehyde (LDA). Exposure to HNE (25 μM, 2h) resulted in extensive modification of cellular proteins in both cell types. Majority of these proteins, identified by MALDI/MS analysis, were ER-resident protein chaperones that assist in protein folding. Confocal imaging of HNE treated EC showed that the modified proteins were associated with the ER. Exposure to HNE led to the splicing of the bZIP transcription factor, XBP-1, a characteristic feature of the alarm phase of ER stress, and an increase in the phosphorylation of eIF2α, which regulates the expression of multiple ER-stress dependent transcription factors. These transcription factors, ATF3, ATF4, and CHOP were also strongly (2–5-fold) induced by HNE. Treatment with HNE was associated with a 2–5 fold increase in the expression of ER chaperones, GRP78 and HERP, indicating that HNE triggers the adaptive phase of the response, which increases the protein folding capacity of the ER. Pretreatment with the chemical chaperone, phenylbutyric acid (PBA), to facilitate protein folding, completely abolished HNE-induced increase in the expression of ATF3. EC treated with HNE enhanced monocyte adhesion, which was attenuated by PBA, indicating that early stages of lesion formation may be ER-stress dependent. In intermediate arterial lesion of 20 week old apoE-null mice, HNE-adducted proteins were localized to areas immunopositive for ATF3, ATF4, and phospho-PERK. These results suggest that protein modifications by LDA induce ER stress and the alarm and adaptive responses to this stress may be significant determinants of lesion progression and stability.