Abstract 18739: Autophagy Regulates Vascular Smooth Muscle Cell Synthetic Phenotype Transition and Resistance to Oxidative Stress
Arterial lesions due to atherosclerosis and restenosis are characterized by heightened oxidative stress and the transformation of vascular smooth muscle cells (VSMCs) to a synthetic phenotype. However, it is not known how synthetic VSMCs (sVSMCs) respond to the stress encountered in advanced vascular lesions. Our previous studies show that electrophilic stress caused by lipid peroxidation products promotes autophagy and endoplasmic reticulum stress. In this study, we tested the hypothesis that conversion to the synthetic phenotype primes VSMCs to survive under conditions of high oxidative stress. Synthetic VSMCs, elicited by exposure to platelet-derived growth factor-BB (PDGF-BB), maintained lower levels of endogenous protein-aldehyde adducts and demonstrated a heightened ability (2.5-fold; p<0.05) to remove proteins modified by the lipid peroxidation product 4-hydroxy-trans-2-nonenal (HNE) than contractile VSMC (cVSMC). Moreover, HNE detoxification in sVSMCs was enhanced; the primary pathway of HNE detoxification—aldehyde dehydrogenase-mediated oxidation to 4-hydroxynonenoic acid—was increased by 30% and glutathione conjugation was increased by 50% (p<0.05). The sVSMCs showed a 20% increase in viability compared with cVSMCs when challenged with HNE (p<0.05). This resistance to stress in sVSMCs was found to be due primarily to robust induction of the autophagic program. PDGF-BB exposure increased autophagic flux (>2-fold vs. untreated cells; p<0.05), as assessed by quantifying GFP-microtubule-associated protein 1 light chain 3 (LC3) puncta as well as electron microscopy and LC3II abundance. Blockade of autophagy by spautin-1 or 3-methyladenine prevented the PDGF-BB-induced decreases in expression and abundance of calponin and α-SM-actin, suggesting that autophagy is required for VSMC phenotype conversion. Inhibiting autophagy also prevented removal of HNE-damaged proteins and prevented PDGF-induced increases in NAD+- and glutathione-linked HNE detoxification (p<0.05). Collectively, these results show that PDGF-BB induces autophagy in VSMCs, which is required for conversion of VSMCs to the synthetic phenotype and for resistance to the oxidative stress characteristic of vascular lesions.
- © 2012 by American Heart Association, Inc.