Cardiovascular Research Advance Access [Accepted Manuscript] published online on January 31, 2008
Cardiovascular Research, doi:10.1093/cvr/cvn018
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Differential Effects of PARP Inhibition on Vascular Cell Survival and ACAT-1 Expression Favoring Atherosclerotic Plaque Stability
Department of Pharmacology and Experimental Therapeutics, LSU Health Sciences Center, New Orleans, LA
Corresponding Author: Hamid Boulares, Ph.D. LSUHSC, Department of Pharmacology and Experimental Therapeutics, 1901 Perdido St., New Orleans, LA 70112, U.S.A., Tel: (504) 568-2304; Fax: (504) 568-2361; E-mail: hboulr{at}lsuhsc.edu
Aim: The aim of this study was to take a combination of animal and cell culture approaches to examine the individual responses of vascular cells to varying inflammatory factors in order to gain insights on the mechanism(s) by which poly(ADP-ribose) polymerase (PARP) inhibition promotes factors of plaque stability.
Methods: Apolipoprotein (ApoE)-/- mice fed a high-fat diet were used as a model of atherosclerosis. Primary endothelial cells, smooth muscle cells (SMCs) and ex-vivo generated foam cells were used in our in vitro studies.
Results: PARP inhibition significantly decreased markers of oxidative stress and caspase-3 activation, and increased smooth muscle actin within plaques from ApoE-/- mice fed a high-fat diet. PARP inhibition protected against apoptosis and/or necrosis in SMCs and endothelial cells in response to H2O2 or tumour necrosis factor (TNF). Remarkably, PARP inhibition in foam cells resulted in significant sensitisation to 7-ketocholesterol (7-KC) by increasing cellular toxic free cholesterol, potentially through a down-regulation of acyl-CoA:cholesterol acyltransferase-1 (ACAT-1) expression. 7-KC induced exclusively necrosis in endothelial cells, which was, surprisingly, unaffected by PARP inhibition indicating that PARP inhibition does not prevent all forms of necrotic cell death. In SMCs, PARP-1 inhibition by gene deletion conferred protection against 7-KC or TNF, potentially by reducing caspase-3-like activation, preventing induction of c-Jun N-terminal protein kinase phosphorylation, and inducing extracellular signal-regulated kinase phosphorylation independently of PARP classical enzymatic activity.
Conclusions: These data present PARP-1 as an important player in the death of cells constituting atherosclerotic plaques contributing to plaque dynamics. PARP inhibition may be a protective, a neutral, or a sensitising factor. Additionally, PARP-1 may be a novel factor that can alter lipid metabolism. These novel functions of PARP not only challenge the current understanding of the role of the enzyme in cell death but also provide insights on the intricate contribution of PARP in cellular responses to predominant inflammatory factors within atherosclerotic plaques, presenting additional evidence for the viability of PARP inhibition as a therapeutic strategy for atherosclerosis.
KEYWORDS Atherosclerosis; Apoptosis; Necrosis; PARP-1; lipid metabolism
Time for primary review : 21
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Cardiovasc Res 2008 78: 407-408.
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