Role of SIK3 in PKA/mTORC1 regulation of adipose browning

Project Summary: . Obesity is at epidemic proportions in the US. Over 60% of the population is either overweight (Body Mass Index [BMI] ≥25 to <30 kg/m2) or obese (BMI ≥30 kg/m2), placing them at risk for a large number of chronic diseases, including insulin resistance, metabolic syndrome, and type 2 diabetes. The annual costs of obesity exceed $100 billion, making it one of the most significant public health and economic issues facing the country. Unfortunately, the treatment of obesity is unsatisfactory. Lifestyle and behavioral approaches have a modest, and often transient, effect while FDA-approved therapeutic options targeting appetite or fat absorption have poor tolerability and, in some cases, safety concerns. Thus, there is a critical need for novel approaches to treat obesity. Agents acting via peripheral mechanisms to increase energy expenditure would be valuable. The sympathetic nervous system (SNS) is well-known as an activator of brown adipose tissue (BAT) and the “browning” of cells in white adipose tissue (WAT) depots to increase uncoupled mitochondrial respiration and energy expenditure. Our earlier work established signaling cascades from β-adrenergic receptors (βARs)  cAMP  protein kinase A (PKA)  p38 MAP kinase (MAPK), and also from PKA to mTORC1. These downstream signaling modules are key to drive the transcription of brown adipocyte genes such as uncoupling protein-1 (UCP1), PPAR-gamma coativator-1α (PGC-1α), and the broader program of mitochondrial biogenesis. The Scientific Premise of this project is based upon our identification of substrates of PKA- activated mTORC1 that convey the brown-adipose promoting machinery, and we will determine their molecular mechanisms. Our long-term goal is to define signaling pathways that are critical to metabolic and cardiovascular disease and, using this knowledge, to target pivotal components of these signaling pathways to prevent or reverse the diseases.