Induction of Interleukin-37 Expression in Macrophages of Hyperlipidemic Mice to Attenuate Atherosclerosis

Abstract

Cardiovascular diseases (CVD) are the main cause of death worldwide, leading to massive medical and economic burdens on society. Atherosclerosis, the primary cause of CVD, is the progressive buildup of plaque within arterial blood vessels that can lead to fatal downstream events such as heart attack or stroke. A key event contributing to the pathogenesis of atherosclerosis is the infiltration of monocytes and the formation of lipid-laden macrophage foam cells within the vessel wall. This leads to inflammation and mass deposition of lipids within the artery wall, driving the disease progression. It is therefore extremely important to explore therapeutic options aimed at slowing the disease progression by preventing macrophage inflammatory signaling or controlling macrophage cholesterol homeostasis. I have investigated the role of macrophage-expressed Interleukin-37 (IL-37) in reducing the production and effects of pro-inflammatory cytokines and preventing foam cell formation. A retroviral vector with a region of the CD68 promoter upstream of my gene of interest was utilized to obtain robust, macrophage-specific expression of either IL-37 or EGFP. Experiments exploring the effect of IL-37 expression on macrophage inflammatory response, transmigration, and cholesterol homeostasis were performed in vitro. Macrophage IL-37 expression in vitro resulted in decreased mRNA and secreted protein production of key inflammatory cytokines, inhibited macrophage transmigration, as well as reduced lipid uptake compared to controls. The stable integration of the IL-37 or EGFP genes was necessary to execute a long-term atherosclerosis mouse study in vivo. The in vivo effects of macrophage-expressed IL-37 were investigated through bone marrow transplantation of transduced hematopoietic stem cells (HSC) into irradiated, atherosclerosis-prone Ldlr-/- mice. After 10 weeks on a high fat diet, I found that mice with IL-37-expressing macrophages showed reduced disease pathogenesis, which was demonstrated by significantly less arterial plaque development compared to control mice. The athero-protective effect of macrophage-expressed IL-37 has implications for development of future therapies to treat atherosclerosis as well as other chronic inflammatory diseases.