Role of Histone Deacetylase 9 (HDAC9) in adipose tissue aging: mitochondrial function, oxidative stress and senescence

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PROJECT SUMMARY Adipose tissue is a major depot for senescent cell accumulation and sterile inflammation in aging. While adipose tissue senescence in aging is causally linked to mitochondrial dysfunction and oxidative stress, the underlying mechanisms are undefined. Here, we propose the novel hypothesis that histone deacetylase 9 (HDAC9), a class II histone deacetylase, plays a key role in promoting adipose tissue senescence in aging by promoting mitochondrial dysfunction. Our preliminary data demonstrate that HDAC9 expression is increased in adipose tissues of aged mice and humans. Moreover, HDAC9 gene deletion improves adipose tissue mitochondrial energy expenditure and reduces adipose stem cell (ASC) senescence in 1-year-old chow diet fed mice, while protecting ASCs against senescence in vitro. Our hypothesis will be tested with two specific aims. Aim 1 will test the hypothesis that increased HDAC9 expression in aged adipose tissues contributes to mitochondrial dysfunction and oxidative stress by disrupting mitochondrial dynamics. Our preliminary data suggest that HDAC9 is strongly upregulated in the mature adipocytes of aged mice. Therefore, we will employ two novel mouse models to test our hypothesis: adipocyte-specific HDAC9 knockout (A-KO; HDAC9flox/flox adiponectin-Cre) and adipocyte-specific transgenic (A-Tg, HDAC9Tg-flox-STOP-flox adiponectin-Cre) mice. Primary ASCs will be cultured and differentiated to mature adipocytes. Mitochondrial function and dynamics will be measured in adipose tissue explants and mature adipocytes using the Seahorse analyzer, Western blot, immunofluorescence, transmission electron microscopy and confocal imaging. Aim 2 will test the hypothesis that HDAC9 gene deletion represses the development of adipose tissue senescence and promotes healthy adipose tissue aging, while overexpression of HDAC9 accelerates adipose tissue aging and augments senescence. We will quantify senescent cell accumulation in adipose tissue and metabolic health through glucose and insulin tolerance testing. ASC cultures from global HDAC9 knockout mice will be used to assess susceptibility to UV-induced senescence. Additionally, senescent cell accumulation in A-KO and A-Tg mice will be assessed by senescence-associated β-galactosidase staining, qRT-PCR and Western blot. This project will allow me to acquire deep knowledge of mitochondrial biology while developing new technical skills, including primary cell culture, tissue staining and imaging. Most importantly, it will allow me to gain expertise in conducting rigorous, hypothesis-driven research, thus setting the stage for a career as a physician-scientist. The project will be conducted under the mentorship of Dr. Neal Weintraub and co-mentorship of Dr. Masuko Ushio-Fukai in the Vascular Biology Center at the Medical College of Georgia at Augusta University, which has a rich history of successful pre- and post-doctoral training. We anticipate that findings from this proposal will identify elevated HDAC9 expression in adipose tissue aging as a key mediator of mitochondrial dysfunction and senescence and will provide insight into potential therapeutic approaches to improve adipose tissue health in aging.