The long-term goal of our research is to understand the metabolic regulation of plasma triglyceride (TG). Whereas factors such as lipoprotein lipase and apolipoproteins C-II / C-III are known to modulate plasma TG levels, accumulating evidence suggests the recently discovered apolipoprotein A-V (apoA-V) functions in lipid transport and maintenance of plasma TG homeostasis. To elucidate the molecular basis of apoA-V's physiological effects on plasma TG a combination of in vitro and in vivo studies will be performed. Adenovirus mediated gene transfer into apoa5 (-/-) mice will be performed to evaluate in vivo the ability of specific apoA-V variants to influence plasma TG levels and lipoprotein metabolism. Evidence indicates apoA-V binds heparan sulfate proteoglycans, low-density lipoprotein receptor family members and the endothelial cell surface protein glycosylphosphatidylinositol high-density lipoprotein binding protein 1 via a positively charged sequence motif (residues 186-227).
Aim 1 will test the hypothesis that this region of the protein is critical for manifestation of the TG modulation properties of apoA-V in vivo.
In Aim 2 a variant form of apoA-V correlated with hypertriglcyeridemia (HTG) that results from a c.553G>T SNP will be characterized for intra- molecular disulfide bond formation, heparin / receptor binding interactions and in vivo TG modulation capability.
In Aim 3 the hypothesis that the C-terminal domain of apoA-V is necessary and sufficient for TG modulation in vivo will be tested. In addition, in APOA5 transgenic mice, the ability of the NT domain to mimic effects on lipoprotein metabolism seen in human subjects harboring similar truncated forms of apoA-V will be assessed.
In Aim 4 the effect of apoA-V lipid droplet association on TG metabolism will be studied in stably transfected hepatoma cells. Knowledge gained will provide a molecular explanation for the relationship between apoA-V and plasma TG levels and will be useful in the design of strategies to diagnose, treat and/or prevent HTG and related disorders.
Statement of Relevance Hypertriglyceridemia is an independent risk factor for cardiovascular disease and is a recognized contributor to development of the metabolic syndrome. Increased understanding of factors that regulate plasma triglyceride levels should provide new opportunities for intervention. Improvements in diagnosis, prevention and/or treatment could have a major impact on the large population of Americans at risk for heart disease, obesity and Type 2 diabetes.
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