A key pathogenic event in the clinical progression of atherosclerosis is plaque necrosis, which triggers plaque disruption and acute thrombosis. A major process in necrotic plaque formation is endoplasmic reticulum (ER) stress-induced macrophage (Mf) apoptosis coupled with defective phagocytic clearance of these apoptotic Mfs ("efferocytosis"). Another fundamental cell process that occurs in lesional Mfs is autophagy, whereby cells degrade proteins or organelles for protective purposes. Although autophagy is known to be activated during atherosclerosis, studies in this area have been largely descriptive and have lacked clear-cut hypotheses, mechanistic insight, and molecular-genetic causal proof in vivo. Based on published studies with other cell types and our own preliminary data, we hypothesize that autophagy is a compensatory cell-survival pathway that goes awry in advanced atherosclerosis. Intriguingly, autophagy may affect both ER stress- induced apoptosis and defective efferocytosis. We therefore propose to test the molecular-cellular mechanisms related to these ideas as well as relevance to advanced atherosclerosis in vivo.
In Aim I, we will explore the hypothesis that ER stress-induced autophagy is initially protective through a mechanism that modulates NADPH oxidase-induced reactive oxygen species (ROS). We will test this hypothesis and related ones, and study mechanism, using a variety of tools, including Mfs from conditionally gene-targeted mice lacking the key autophagy mediator ATG5. We will also investigate the mechanisms of ER stress-induced autophagy and whether failure of autophagy precedes eventual apoptosis.
In Aim II, we will test the hypothesis that inhibition of autophagy in apoptotic Mfs inhibits their efferocytic clearance. We will use various models of autophagy-inhibited apoptotic cells to monitor their ability to be recognized and engulfed by Mf efferocytes and then to study mechanism.
In Aim III, we will test these ideas in vivo by using Atg5flox/flox mice crossed with LysMCre and Ldlr-/- mice. In other models, LysMCre leads to very effective deletion of floxed genes in lesional Mfs, and in preliminary studies we have shown that the Mfs from Atg5flox/flox;Lysmcre+/- mice have inhibited autophagy, increased ROS, and accelerated apoptosis. We will investigate plaque parameters and molecules relevant to advanced atherosclerosis progression and autophagy in control vs. Mf-ATGF5- deficient mice on the Ldlr-/- background. We hypothesize that Mf-ATG5 deficiency will lead to lesions with inhibited Mf autophagy, enhanced ROS and apoptosis, possibly defective efferocytosis and increased inflammation, and accelerated plaque necrosis. Conversely, in mice whose Mfs have enhanced autophagy through genetic overexpression of Bcn1 (Beclin-1), we predict improvement in these parameters and decreased plaque necrosis. Upon the completing of these studies, we hope to have mechanistic and in-vivo causation data supporting a protective role of autophagy in atherosclerosis which, in turn, may suggest novel therapeutic strategies to prevent the clinical progression of atheromata.

Public Health Relevance

Heart attacks, strokes, and sudden death due to heart disease-the leading cause of death in our society-are triggered by a sudden cutting off of the blood supply feeding these organs by platelet plugs, which form because the vessel in that area has a disease process called atherosclerosis (hardening of the arteries). In view of the fact that only certain types of atherosclerotic lesions trigger platelet plugs, the overall objective of this proposal is to add to our knowledge of what processes influence the formation of these dangerous atherosclerotic lesions. In this context, we will study a fundamental process that occurs in macrophages in atherosclerosis, called autophagy, which can help protect the vessel from developing these dangerous lesions and thus may suggest new ways to prevent dangerous atherosclerotic lesions from forming.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL106019-02
Application #
8208979
Study Section
Atherosclerosis and Inflammation of the Cardiovascular System Study Section (AICS)
Program Officer
Hasan, Ahmed AK
Project Start
2011-01-01
Project End
2014-11-30
Budget Start
2011-12-01
Budget End
2012-11-30
Support Year
2
Fiscal Year
2012
Total Cost
$465,077
Indirect Cost
$176,209
Name
Columbia University (N.Y.)
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
621889815
City
New York
State
NY
Country
United States
Zip Code
10032
Wang, Ying; Wang, Gary Z; Rabinovitch, Peter S et al. (2014) Macrophage mitochondrial oxidative stress promotes atherosclerosis and nuclear factor-*B-mediated inflammation in macrophages. Circ Res 114:421-33
Subramanian, Manikandan; Tabas, Ira (2014) Dendritic cells in atherosclerosis. Semin Immunopathol 36:93-102
Wang, Ying; Tabas, Ira (2014) Emerging roles of mitochondria ROS in atherosclerotic lesions: causation or association? J Atheroscler Thromb 21:381-90
Subramanian, Manikandan; Hayes, Crystal D; Thome, Joseph J et al. (2014) An AXL/LRP-1/RANBP9 complex mediates DC efferocytosis and antigen cross-presentation in vivo. J Clin Invest 124:1296-308
Libby, Peter; Tabas, Ira; Fredman, Gabrielle et al. (2014) Inflammation and its resolution as determinants of acute coronary syndromes. Circ Res 114:1867-79
Tabas, Ira (2013) Making things stick in the fight against atherosclerosis. Circ Res 112:1094-6
Tabas, Ira; Glass, Christopher K (2013) Anti-inflammatory therapy in chronic disease: challenges and opportunities. Science 339:166-72
Subramanian, Manikandan; Thorp, Edward; Hansson, Goran K et al. (2013) Treg-mediated suppression of atherosclerosis requires MYD88 signaling in DCs. J Clin Invest 123:179-88
Ouimet, Mireille; Franklin, Vivian; Mak, Esther et al. (2011) Autophagy regulates cholesterol efflux from macrophage foam cells via lysosomal acid lipase. Cell Metab 13:655-67
Moore, Kathryn J; Tabas, Ira (2011) Macrophages in the pathogenesis of atherosclerosis. Cell 145:341-55

Showing the most recent 10 out of 11 publications