Individuals with apolipoprotein (Apo) E deficiency develop hypercholesterolemia and atherosclerosis. Similarly, ApoE-deficient (ApoE-/-) mice elevate plasma ApoB48-carrying lipoproteins and develop atherosclerosis in a manner that resembles the human disease. The primary cause of atherosclerosis in ApoE-deficient patients and mouse models is the deposition of ApoE-deficient, ApoB48-carrying (E-/B48) lipoproteins in the arterial wall. The deposited lipoproteins recruit monocytes into the arterial intima and transform them into macrophages, which participate in the pathogenesis of atherosclerosis mainly through two mechanisms: 1) releasing inflammatory mediators, and 2) forming foam cells. An uncontrolled macrophage uptake of E-/B48 lipoproteins could be a mechanism underlying foam cell formation in ApoE-/- mice. Our laboratory recently demonstrated that E-/B48 lipoproteins reduce cellular cholesterol efflux from macrophages and down-regulates lysosomal hydrolase expression. In addition, the degradation of E-/B48 lipoproteins by macrophages declined over time. These novel findings indicate that both reduced cholesterol efflux and decreased degradation of E-/B48 lipoproteins could contribute to foam cell formation. Our preliminary studies also revealed that incubation of macrophages with E-/B48 lipoproteins enhanced eukaryotic translation initiationfactor 21 (eIF-2a) phosphorylation, which is linked to one of the unfolded protein response (UPR) signaling pathways. Thus, interaction of E-/B48 lipoproteins with macrophages may activate UPR signaling pathways, which in turn regulate gene expression and induce atherogenic events, such as triggering foam cell formation. In the proposed studies, we will test the hypothesis that activation of UPR signaling pathways is a mechanism by which E-/B48 lipoproteins regulate gene expression, induce foam cell formation and promote atherosclerosis. This project includes four specific aims: 1) to determine whether E-/B48 lipoprotein-induced changes in gene expression result from altered transcription or translation or both in mouse macrophages;2) to determine whether activation of UPR signaling pathways is a mechanism underlying E-/B48 lipoprotein-induced gene expression changes;3) to determine whether activation of UPR pathways is a mechanism underlying E-/B48 lipoprotein-induced foam cell formation;and 4) to determine the effect of inhibiting eIF-2a phosphorylation on atherosclerosis in ApoE-/- mice. If our hypothesis is correct, inactivation of UPR signaling pathways will attenuate E-/B48 lipoprotein-induced gene expression, and suppress foam cell formation and atherosclerosis development.

Public Health Relevance

Myocardial infarction and stroke are the leading caused of death in the United Sates. Atherosclerosis is the primary cause of myocardial infarction and stroke. Formation of lipid-laden foam cells in the vessel wall is the early stage of atherosclerosis. The goal of this proposal is to determine the involvement of endoplasmic reticulum stress in foam cell formation. Endoplasmic reticulum stress is a cellular event that reduces the level of some proteins but increases the level of other proteins in cells. Our preliminary studies indicate that lipoproteins obtained from mice deficient in apolipoprotein E can cause endoplasmic reticulum stress and induce foam cell formation. The experiments designed in this proposal will study whether endoplasmic reticulum stress is the cause of foam cell formation. Finding from this work should contribute to understanding of the molecular mechanism of foam cell formation, and provide strategies for treatment or prevention of atherosclerosis by inhibition of endoplasmic reticulum stress.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL089382-02
Application #
7878595
Study Section
Atherosclerosis and Inflammation of the Cardiovascular System Study Section (AICS)
Program Officer
Hasan, Ahmed AK
Project Start
2009-07-01
Project End
2012-06-30
Budget Start
2010-07-01
Budget End
2012-06-30
Support Year
2
Fiscal Year
2010
Total Cost
$436,840
Indirect Cost
Name
Meharry Medical College
Department
Other Basic Sciences
Type
Schools of Medicine
DUNS #
041438185
City
Nashville
State
TN
Country
United States
Zip Code
37208
Zhou, LiChun; Yang, Hong; Okoro, Emmanuel U et al. (2014) Up-regulation of cholesterol absorption is a mechanism for cholecystokinin-induced hypercholesterolemia. J Biol Chem 289:12989-99
Zhou, Lichun; Yang, Dezhi; Wu, Dong Fang et al. (2013) Inhibition of endoplasmic reticulum stress and atherosclerosis by 2-aminopurine in apolipoprotein e-deficient mice. ISRN Pharmacol 2013:847310
Lin, Xinghua; Yang, Hong; Zhang, Hongfeng et al. (2013) A novel transcription mechanism activated by ethanol: induction of Slc7a11 gene expression via inhibition of the DNA-binding activity of transcriptional repressor octamer-binding transcription factor 1 (OCT-1). J Biol Chem 288:14815-23
Okoro, Emmanuel Ugochukwu; Zhao, Yanfeng; Guo, ZhongMao et al. (2012) Apolipoprotein E4 is deficient in inducing macrophage ABCA1 expression and stimulating the Sp1 signaling pathway. PLoS One 7:e44430
Chen, Xinping; Guo, Zhongmao; Okoro, Emmanuel U et al. (2012) Up-regulation of ATP binding cassette transporter A1 expression by very low density lipoprotein receptor and apolipoprotein E receptor 2. J Biol Chem 287:3751-9
Zhang, Hong Feng; Lin, Xing Hua; Yang, Hong et al. (2012) Regulation of the Activity and Expression of Aryl Hydrocarbon Receptor by Ethanol in Mouse Hepatic Stellate Cells. Alcohol Clin Exp Res :
Zhou, Lichun; Yang, Hong; Lin, Xinghua et al. (2012) Cholecystokinin elevates mouse plasma lipids. PLoS One 7:e51011
Lin, Xinghua; Yang, Hong; Zhou, LiChun et al. (2011) Nrf2-dependent induction of NQO1 in mouse aortic endothelial cells overexpressing catalase. Free Radic Biol Med 51:97-106
Zhao, Yanfeng; Chen, Xinping; Yang, Hong et al. (2011) A novel function of apolipoprotein E: upregulation of ATP-binding cassette transporter A1 expression. PLoS One 6:e21453
Chen, Xinping; Zhao, Yanfeng; Guo, Zhongmao et al. (2011) Transcriptional regulation of ATP-binding cassette transporter A1 expression by a novel signaling pathway. J Biol Chem 286:8917-23

Showing the most recent 10 out of 13 publications