Molecular control of BAT functions by adrenergic/purinergic signaling

ABSTRACT Epidemiological evidence demonstrates that obesity is rising exponentially to pandemic levels in the United States. The need of new therapeutic strategies is highlighted by the failure of current pharmacological approaches to treat obesity. New strategies require new knowledge. The brown adipose tissue (BAT) is an organ likely to play a major role in energy balance, obesity, and diabetes due to a potent glucose and lipid clearance to fuel its thermogenic function. The best characterized mechanism for BAT activation is cold-induced, sympathetic nervous system-secretion of norepinephrine (NE) activating b-adrenergic receptors (b-ARs) and resulting in tissue differentiation and uncoupling protein 1 (UCP1)-mediated thermogenesis. Notwithstanding, recent work from our lab demonstrated that b-ARs are dispensable for mild, cold acclimation-induced or chronic subordination stress-induced BAT recruitment. Other published and preliminary data demonstrate that sympathetic nerves are necessary for BAT browning while excluding a major contribution of NE-activating aARs in absence of b-ARs expression. These data suggest that other sympathetic nerve-derived factors are critical for BAT functions in addition to NE. This project will test the hypothesis that adrenergic and purinergic signaling act as parallel and synergistic modulators of BAT functions, required for optimal tissue recruitment and activation. This hypothesis will be tested in three specific aims. Specific Aim 1 is to functionally dissect the mechanisms of BAT recruitment and functions by isolating the independent and synergistic contribution of the purinergic pathway, in the context of the pivotal role, exerted by noradrenergic signaling using innovative cre-lox approaches in vivo and in vitro. Specific Aim 2 is to identify the receptor-mediated mechanism of ATP-induced browning in mouse and human brown adipocytes. Specific Aim 3 is to test, in vivo, the hypothesis that the synergistic adrenergic/purinergic mechanism can be engaged to recruit and activate the BAT in conditions of low adaptive thermogenesis requirements in which BAT functions are normally minimal, e.g., thermoneutrality housing, thereby, exerting beneficial anti-obesity effects. Our innovative proposal is based on solid preliminary data and is translationally relevant because preliminary data demonstrate that the purinergic signaling pathway is conserved in human brown adipose tissue. Successful completion of our project will develop novel innovative tools to manipulate the purinergic pathway in rodent and human cellular models, will identify a novel mechanism of BAT regulation and finally, will offer proof of concept for the development of novel pharmacotherapies for obesity and obesity-associated metabolic diseases.