Novel Posttranslational Modifications in Adipose Biology

Project Summary Metabolic health depends on the maintenance of 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 AT (WAT) and brown AT (BAT) act together to maintain a balance between fat accumulation and energy expenditure. Upstream players that regulate WAT and BAT 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 that has the highest homology with Ub, remains poorly understood in the 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 NEDD8 E1 enzyme) in mice resulted in loss of adipose tissue potentially through mitochondrial dysfunction and inflammation. Pharmacological inhibition of neddylation promoted mitochondrial ROS production and impaired mitochondrial function in mature adipocytes. Interestingly, AT-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. In BAT, neddylation deficiency causes BAT atrophy and activation of non-canonical NF-κB signaling. These compelling preliminary data form the basis of our central hypothesis that neddylation is required for mature white and brown adipose tissue maintenance through regulation of CUL3-mediated mitochondrial function and/or non-canonical NF-κB pro-inflammatory signaling. Aim 1 will establish the significance and identify the proteome of neddylation in regulating mitochondrial dysfunction, adipose tissue remodeling and thus energy balance and adaptive thermogenesis. Aim 2 will dissect the molecular basis by which neddylation targets a novel mitochondrial targeted CUL3 E3 Ub ligase to mediate adipocyte mitochondrial activity and turnover thus energy balance. Aim 3 will elucidate a newly identified neddylation target in mediating non-canonical NF-κB signaling to accelerate brown adipocyte inflammation and turnover. Our proposed study will provide the most in-depth analysis of neddylation as a hitherto novel post-translational modification essential for both mature white and brown adipose tissue maintenance. We expect that new findings from this proposal will provide novel insights into our understanding of the pathophysiology of adipose tissue and its implications on obesity/ lipodystrophy and its associated metabolic disorders.