The effect of macrophage sphingomyelin synthase (SMS) on atherosclerosis

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DESCRIPTION (provided by applicant): Macrophages are the most prominent cell type in atherosclerotic lesions, and are associated with three hallmarks of the disease:lipid deposition, inflammation, and macrophage-derived foam cell disordered apoptosis. The ability to regulate SMS activity could become a promising approach for regulating these macrophage functions, thus influencing the atherosclerosis. SMS utilizes ceramide and phosphatidylcholine (PC) as substrates to produce sphingomyelin (SM) and diacylglycerol. SM is one of the major lipid components of cell membranes, including macrophages. SM-enriched lipid rafts in these plasma membranes provide a platform for many important cellular processes, such as cholesterol efflux and signal transduction. The SMS activity-related events listed above may well have an impact on the development of atherosclerosis. SMS has two isoforms: SMS1 and SMS2. We have evidence demonstrating that SMS activity is closely related to macrophage plasma membrane structure and function. Such findings emphasize the need for better understanding of these SMS functions in our exploration of the relationship between macrophage SMS (SMS1 and SMS2) and atherosclerosis. We now hypothesize that both SMS1 and -2 deficiencies decrease macrophage SM levels, promote cholesterol efflux, diminish the production of inflammatory cytokines and chemokines, and reduce apoptosis. They thus prevent the development of atherosclerosis, while SMS1 and -2 overproduction have the opposite effect. The major focus of this project will be to manipulate SMS activity using SMS1 and -2 gene knockout or over expression approaches to manipulate SM levels. It should be mentioned that the gene knockout mice and adenovirus-mediated expression system necessary for this work are already available in our laboratory. Our Specific Aims are to: 1) determine the role of SMS1 and SMS2 deficiencies in macrophage cholesterol efflux, 2) explore the impact of SMS1 and -2 deficiencies and over expression on inflammatory response and apoptosis in macrophages, and 3) investigate the role of macrophage SMS1 and -2 deficiencies in atherosclerosis. Success with this proposal will help us elucidate the distinctive functions of macrophage SMS relative to atherosclerosis, determine the differences and similarities between macrophage SMS1 and macrophage SMS2 in the process of atherosclerosis, and evaluate SMS as a therapeutic target for treatment of it. PUBLIC HEALTH RELEVANCE: The success of this proposal will help us to elucidate the distinctive function of macrophage SMS relative to atherosclerosis; disclose the difference and similarity between macrophage SMS1 and SMS2, in the process of atherosclerosis; and evaluate SMS as a therapeutic target for atherosclerosis treatment.