The heart forms early in development and delivers oxygenated blood to the rest of the embryo. After birth, the heart requires kilograms of ATP each day to support contractility for the circulation. Cardiac metabolism is omnivorous, utilizing multiple substrates and metabolic pathways to produce this energy. Cardiac development, metabolic tuning, and the response to ischemia are all regulated in part by the hypoxia-inducible factors (HIFs), central components of essential signaling pathways that respond to hypoxia. Here we review the actions of HIF1, HIF2, and HIF3 in the heart, from their roles in development and metabolism to their activity in regeneration and preconditioning strategies. We also discuss recent work on the role of HIFs in atherosclerosis, the precipitating cause of myocardial ischemia and the leading cause of death in the developed world.

Endothelial cells (EC) play a key role in atherosclerosis. Although EC are in constant contact with low density lipoproteins (LDL), how EC process LDL and whether this influences atherogenesis, is unclear. Here we show that EC take up and metabolize LDL, and when overburdened with intracellular cholesterol, generate cholesterol crystals (CC). The CC are deposited on the basolateral side, and compromise endothelial function. When hyperlipidemic mice are given a high fat diet, CC appear in aortic sinus within 1 week. Treatment with cAMP-enhancing agents, forskolin/rolipram (F/R), mitigates effects of CC on endothelial function by not only improving barrier function, but also inhibiting CC formation both in vitro and in vivo. A proof of principle study using F/R incorporated into liposomes, designed to target inflamed endothelium, shows reduced atherosclerosis and CC formation in ApoE ^−/− mice. Our findings highlight an important mechanism by which EC contribute to atherogenesis under hyperlipidemic conditions.

Summary: Atherosclerosis is primarily a disorder of lipid metabolism, but there is also a prominent chronic inflammatory component that drives the atherosclerotic lesion progression in the artery wall. During hyperlipidaemic conditions, there is a rapid influx of circulating monocytes into the atherosclerosis-prone areas of the arterial intima. These infiltrated monocytes differentiate into macrophages and take up the atherogenic lipoproteins in the intima of the vessel wall that have been modified within the lesion environment. Interleukin (IL)-10 is a prototypic anti-inflammatory cytokine made primarily by the macrophages and Th2 subtype T lymphocytes. In terms of atherosclerosis its major roles include inhibition of macrophage activation as well as inhibition of matrix metalloproteinase, pro-inflammatory cytokines and cyclooxygenase- 2 expression in lipid-loaded and activated macrophage foam cells. Recent discoveries suggest another important role of IL-10 in atherosclerosis: its ability to alter lipid metabolism in macrophages. The current review will highlight the present knowledge on multiple ways in which IL-10 mediates atherosclerosis. As macrophages play a critical role in all stages of atherosclerosis, the review will concentrate on how IL-10 regulates the activities of macrophages that are especially important in the development of atherosclerosis.

In atherogenesis, macrophage foam cell formation is modulated by pathways involving both the uptake and efflux of cholesterol. We recently showed that interleukin‐10 (IL‐10) modulates lipid metabolism by enhancing both uptake and efflux of cholesterol in macrophages. However, the mechanistic details of these properties in vivo have been unclear. Thus, the purpose of this study was to determine whether expression of IL‐10 in macrophages would alter susceptibility to atherosclerosis and whether IL‐10 exerts its antiatherosclerotic properties by modulating lipid metabolism in macrophages. We utilized a macrophage‐specific retroviral vector that allows long‐term in vivo expression of IL‐10 in macrophages through transplantation of retrovirally transduced bone marrow cells (BMCs). IL‐10 expressed by macrophages derived from transduced BMCs inhibited atherosclerosis in LDLR ^−/− mice by reducing cholesteryl ester accumulation in atherosclerotic sites. Experiments with primary macrophages indicated that macrophage source of IL‐10 stimulated both the uptake (by up‐regulating scavenger receptors) and efflux of cholesterol (by activating the PPARγ‐LXR‐ABCA1/ABCG1 pathway), thereby reducing inflammation and apoptosis in atherosclerosis. These findings indicate that BMC‐transduced macrophage IL‐10 production can act as a strong antiatherogenic agent, and they highlight a novel antiatherosclerotic therapy using a simple, yet effective, stem cell transduction system that facilitates long‐term expression of IL‐10 in macrophages.—Han, X., Kitamoto, S., Wang, H., Boisvert, W. A. Interleukin‐10 overexpression in macrophages suppresses atherosclerosis in hyperlipidemic mice. FASEB J . 24, 2869–2880 (2010). www.fasebj.org

Objective—: Macrophage foam cell formation is a key feature of atherosclerosis. Recent studies have shown that specific microRNAs (miRs) are regulated in modified low-density lipoprotein–treated macrophages, which can affect the cellular cholesterol homeostasis. Undertaking a genome-wide screen of miRs regulated in primary macrophages by modified low-density lipoprotein, miR-302a emerged as a potential candidate that may play a key role in macrophage cholesterol homeostasis.Approach and Results—: The objective of this study was to assess the involvement of miR-302a in macrophage lipid homeostasis and if it can influence circulating lipid levels and atherosclerotic development when it is inhibited in a murine atherosclerosis model. We found that transfection of primary macrophages with either miR-302a or anti–miR-302a regulated the expression of ATP-binding cassette (ABC) transporter ABCA1 mRNA and protein. Luciferase reporter assays showed that miR-302a repressed the 3′ untranslated regions (UTR) activity of mouse Abca1 by 48% and human ABCA1 by 45%. In addition, transfection of murine macrophages with miR-302a attenuated cholesterol efflux to apolipoprotein A-1 (apoA-1) by 38%. Long-term in vivo administration of anti–miR-302a to mice with low-density lipoprotein receptor deficiency (Ldlr^−/−) fed an atherogenic diet led to an increase in ABCA1 in the liver and aorta as well as an increase in circulating plasma high-density lipoprotein levels by 35% compared with that of control mice. The anti–miR-302a–treated mice also displayed reduced atherosclerotic plaque size by ≈25% and a more stable plaque morphology with reduced signs of inflammation.Conclusions—: These studies identify miR-302a as a novel modulator of cholesterol efflux and a potential therapeutic target for suppressing atherosclerosis.