Novel Posttranslational Modifications in Adipose Biology

Project Summary Metabolic health depends on maintaining normal mass and function of adipose tissue (AT). Accumulation of excess body fat or pathological loss of AT is associated with insulin resistance and cardiometabolic diseases. White and brown adipose tissues act together to maintain a balance between fat accumulation and energy expenditure. Upstream players that regulate AT maintenance remain less characterized. Ubiquitin (Ub) and Ub- like proteins modify diverse protein substrates and expand the functional diversity of the proteome. However, the functional role of NEDD8, a novel Ub-like protein with the highest homology with Ub, remains poorly understood in adipose tissue. Neddylation covalently attaches NEDD8 to target proteins via NEDD8-specific E1- E2-E3 enzymes. Induced adipose deletion of NAE1 (a regulatory subunit of the only NEDD8 E1 enzyme) in mice resulted in the loss of adipose tissue potentially through mitochondrial dysfunction. Pharmacological inhibition of neddylation promoted mitochondrial ROS production and impaired mitochondrial function in mature adipocytes. Interestingly, adipocyte-specific loss of CUL3 (a bona fide neddylation target) largely phenocopied neddylation deficiency-induced AT loss, and neddylation dominantly targets CUL3 to modulate mitochondrial function and adipocyte turnover. These compelling preliminary data form the basis of our central hypothesis that neddylation is required for mature adipose tissue maintenance through regulating CUL3-mediated mitochondrial function. Aim 1 will establish the significance and identify the proteome of neddylation in regulating mitochondrial dysfunction, adipose tissue remodeling, and thus energy homeostasis. Aim 2 will dissect the molecular basis by which neddylation targets a novel mitochondrial targeted CUL3 E3 Ub ligase to mediate adipocyte mitochondrial function and turnover, thus energy balance. Our proposed study will provide the most in-depth analysis of neddylation as a novel post-translational modification essential for adipose tissue maintenance. We expect that new findings from this proposal will provide fundamental insights into our understanding of the role of posttranslational modifications in the pathophysiology of adipose tissue and its implications on obesity/lipodystrophy and its associated metabolic disorders.