The objective of this project is to define novel molecular mechanisms by which nuclear receptors modulate lipid homeostasis. Given the central roles that metabolism plays in diseases such as atherosclerosis and diabetes, elucidating novel lipid signaling pathways may uncover new opportunities for therapeutic intervention, and will advance our understanding of fundamental physiological and pathophysiological processes. For the past 15 years, this grant has focused on understanding the mechanism of action of LXR nuclear receptors. Work from this project has identified LXRs and several of their downstream genes as potential targets for the modulation of human lipid metabolism. In the current grant cycle, we characterized the structure and physiology of IDOL, an E3 ubiquitin ligase who activity is controlled by LXRs. The current application is centered on novel RNA mediators of LXR and their roles in the control of gene expression and systemic lipid homeostasis. We have identified two novel long non-coding (lnc) RNAs that are regulated by LXRs in a tissue-selective manner, suggesting that they perform context-specific functions in metabolism. LeXis (Liver-expressed LXR-induced sequence) is highly responsive to LXR activation in liver, whereas MeXis (Macrophage- expressed LXR-induced sequence) is selectively expressed in macrophages. Preliminary data show that LeXis lowers plasma cholesterol levels by selectively targeting SREBP-2 pathway genes involved in sterol synthesis, and that MeXis functions in cis to modulate Abca1 expression in a cell type- selective manner.
Aim 1 is to determine the function and mechanism of action of the lncRNA LeXis in hepatic lipid metabolism.
Aim 2 is to determine the function and mechanism of action of the lncRNA MeXis in macrophage biology.
Aim 3 is to test the impact of physiological and pharmacological lncRNA expression on atherosclerosis. We have developed knockout models for both LeXis and MeXis and have validated state-of-the art mechanistic approaches to deciphering their mechanisms of action. Understanding the mechanisms by which LXRs regulate lipid homeostasis through control of lncRNA expression will bring fundamental insights relevant for the treatment or prevention of metabolic disease.

Public Health Relevance

Statement Lipid metabolism and liver X receptor signaling are important determinants of metabolic diseases including atherosclerosis and diabetes. Elucidating novel lipid signaling pathways regulated by liver X receptors may uncover new opportunities for therapeutic intervention, and will advance our understanding of fundamental physiological and pathophysiological processes. The discovery that LXR controls two previously unknown lncRNA pathways for metabolic regulation could lead to new drug targets for cardiovascular disease.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL066088-18
Application #
9468400
Study Section
Atherosclerosis and Inflammation of the Cardiovascular System Study Section (AICS)
Program Officer
Srinivas, Pothur R
Project Start
2001-02-01
Project End
2019-04-30
Budget Start
2018-05-01
Budget End
2019-04-30
Support Year
18
Fiscal Year
2018
Total Cost
Indirect Cost
Name
University of California Los Angeles
Department
Pathology
Type
Schools of Medicine
DUNS #
092530369
City
Los Angeles
State
CA
Country
United States
Zip Code
90095
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Beceiro, Susana; Pap, Attila; Czimmerer, Zsolt et al. (2018) LXR nuclear receptors are transcriptional regulators of dendritic cell chemotaxis. Mol Cell Biol :
Sallam, Tamer; Jones, Marius; Thomas, Brandon J et al. (2018) Transcriptional regulation of macrophage cholesterol efflux and atherogenesis by a long noncoding RNA. Nat Med 24:304-312
Gao, Jie; Marosi, Mate; Choi, Jinkuk et al. (2017) The E3 ubiquitin ligase IDOL regulates synaptic ApoER2 levels and is important for plasticity and learning. Elife 6:
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Tontonoz, Peter; Wu, Xiaohui; Jones, Marius et al. (2017) Long Noncoding RNA Facilitated Gene Therapy Reduces Atherosclerosis in a Murine Model of Familial Hypercholesterolemia. Circulation 136:776-778
Sallam, Tamer; Jones, Marius C; Gilliland, Thomas et al. (2016) Feedback modulation of cholesterol metabolism by the lipid-responsive non-coding RNA LeXis. Nature 534:124-8
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Tian, Xiao Yu; Ganeshan, Kirthana; Hong, Cynthia et al. (2016) Thermoneutral Housing Accelerates Metabolic Inflammation to Potentiate Atherosclerosis but Not Insulin Resistance. Cell Metab 23:165-78

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