Objectives: For fat to be utilized for energy, it is necessary for the triacylglycerols (TAG) in adipose tissue to be mobilized to free fatty acids (FFA) and then released into the circulation, i.e., lipolysis. The control of lipolysis is complex and involves multiple mechanisms. The counterpoint to lipolysis is lipid droplet formation, a process that is also not fully understood. The objective of this proposal is to understand the cellular and molecular mechanisms regulating lipolysis and lipid droplet metabolism. We will test 2 hypotheses: 1) A physical interaction between hormone sensitive lipase (HSL) and vimentin participates in the translocation of HSL to the lipid droplet, thus facilitating lipolysis. 2) Vimentin has a dual function in adipose lipid metabolism, facilitating lipid droplet formation by allowing droplets to enlarge via the fusion of small droplets, while also facilitating the hydrolysis of lipid droplets. Research Plan and Methods: To test the first hypothesis, the location of the cellular compartment where the interaction between HSL and vimentin occurs will be determined using microscopy and biophysical techniques, the physiological importance of the HSL-vimentin interaction will be examined using vimentin knockout mice and in vitro knockdown, and the determinants of the HSL-vimentin interaction will be identified using mutational analyses. To test the second hypothesis, the dynamics of lipid droplet formation will be compared by microscopy in wild-type cells and cells lacking vimentin, and the interaction of droplet-associated proteins with vimentin will be examined by biophysical techniques. In addition, wild-type and vimentin null mice will be fed normal or high fat diets and the effects on adiposity, carbohydrate and lipid metabolism and adipose gene expression will be determined. Potential Impact on Veterans Health Care: A large proportion of patients for whom care is provided by the VA are obese. These obese veterans tend to have more complicated medical courses, and to have worse medical outcomes than nonobese patients. The obese patients within the VA have multiple medical problems, including hypertension, diabetes mellitus, hyperlipidemia, pulmonary disease, osteoarthritis, gout, and cancer. These conditions contribute to the development of atherosclerosis, with coronary artery disease (angina, myocardial infarction or cardiac failure), peripheral vascular disease and cerebrovascular disease (stroke) being extremely prevalent. Patients with all of these conditions are characterized by abnormal regulation of FFA flux. Understanding the basic mechanisms regulating FFA release and how lipolysis impacts the overall biology of adipose cells will have implications for delineating the abnormalities contributing to the accelerated atherosclerosis seen in obesity and in other conditions characterized by abnormal levels of circulating FFA.
7. Project Narrative Just as observed in the general population, a large proportion of patients who are medically evaluated and for whom care is provided by the VA are obese. These obese veterans tend to have more complicated medical courses, and to have worse medical outcomes than nonobese patients. The obese patients within the VA have multiple medical problems, including hypertension, diabetes mellitus, hyperlipidemia, pulmonary disease, osteoarthritis, gout, and cancer. These conditions contribute to the development of atherosclerosis, with coronary artery disease (angina, myocardial infarction or cardiac failure), peripheral vascular disease and cerebrovascular disease (stroke) being extremely prevalent. Patients with all of these conditions are characterized by abnormal regulation of free fatty acids (FFA). Understanding the basic mechanisms regulating FFA release and how this impacts the overall biology of adipose cells will have implications for delineating the abnormalities contributing to the accelerated atherosclerosis seen in obesity and in other conditions characterized by abnormal levels of circulating FFA.
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