Regulation of insulin sensitivity by TUG acetylation

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DESCRIPTION (provided by applicant): Aging is associated with a marked increase in the prevalence of metabolic disease, including insulin resistance and type 2 diabetes, which contributes to cardiovascular risk, kidney disease, retinopathy, and other comorbidities. How aging affects insulin action in fat and muscle is not well understood. Sirtuins comprise a family of NAD+-dependent lysine deacetylases, which are implicated in various aspects of aging and longevity. These proteins couple cellular energy status to distinct outputs by controlling the acetylation of various target proteins. This proposal will test the overall hypothesis that acetylation regulates insulin sensitivity directly, by controlling the number of GLUT4 glucose transporters that reside in an intracellular, insulin-responsive pool. Data support a model in which GLUT4 is sequestered intracellularly in fat and muscle cells by TUG, which links GLUT4-containing vesicles to the Golgi matrix in the absence of insulin. Insulin then causes site-specifi cleavage of TUG to mobilize these vesicles to the cell surface and to promote glucose uptake. Aim 1 of the present proposal will test the hypothesis that TUG is acetylated near its carboxyl terminus, and that this acetylation prevents the sequestration of GLUT4-containing vesicles in an insulin-responsive pool. It will be tested if TUG acetylation is increased in aged rodents. Aim 2 will study how acetylation of TUG controls its interaction with specific Golgi matrix proteins. The hypothesis that will be tested is that, by altering the interaction of TUG with the Golgi matrix, acetylation prevents the trapping of GLUT4-containing vesicles in a pool that can be mobilized in response to an insulin signal. Aim 3 will test the hypothesis that a particular sirtui binds TUG and reduces its acetylation in response to cellular NAD+ concentrations, thus enhancing insulin sensitivity. It is anticipated that accomplishment of these Aims will provide new understanding of how aging is linked directly to reductions in insulin sensitivity, through effects on cellular energy status and protein acetylation. This understanding will shed light on the pathogenesis of age-related metabolic diseases, with potential implications for prevention and treatment. Public Health Significance: Almost one-third of elderly individuals have diabetes, and three-quarters have insulin resistance or diabetes. These metabolic abnormalities are an enormous public health burden, which contribute to substantial morbidity and mortality. The research proposed here will investigate how aging contributes to the development of insulin resistance in fat and muscle, which is a critical component in the pathogenesis of diabetes in the elderly population.