The Circadian System as a Neuronal Regulator of Feeding Time and Body Weight Setpoint

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Project Summary The escalating prevalence of obesity and metabolic syndrome suggest that both underlying genetic and environmental factors contribute to this epidemic. We have made the exciting discoveries that genetic ablation of the clock leads to obesity and metabolic syndrome, and high-fat feeding to wild-type mice induces circadian disruption and increases food intake during the incorrect circadian time (i.e., their normal rest period) that is directly linked to obesity and insulin resistance. While these observations suggest a fundamental role for the “timing” of food intake in energy balance, the underlying central nervous system clock mechanisms coordinating behavioral and metabolic rhythms remain poorly understood. A springboard for our studies has been the transformative discovery of the core molecular components of the clock, a negative transcription feedback loop that cycles in both pacemaker neurons of the suprachiasmatic nucleus (SCN) and nearly all peripheral metabolic cells. However, how the brain pacemaker cells entrain extra-SCN clocks to the light cycle, and the role of clocks within genetically distinct cells of the SCN in the regulation of energy balance, remains unknown. Given the mounting evidence that circadian and sleep cycle disruption lead to metabolic disorders through impeding signaling at the level of brain, a primary challenge is now to define the function of pacemaker neurons and clocks within energy-sensing neurons in establishing body weight setpoint. Our approach herein is to exploit powerful new genetic models in the mouse, with the ability to cause adult-onset ablation of the core clock machinery, and to do so within specific region of the hypothalamus, focusing on the master pacemaker, the SCN. We also implement stereotactically-guided DREADD technology (Designer Receptors Exclusively Activated by Designer Drugs) to pharmacologically manipulate the phase of SCN firing in distinct subpopulations, thus causing genetic jetlag, and to then probe the impact of this “on/off” switch of the central clock on behavior and energy balance. We seek to integrate behavioral, physiological, and molecular analyses to dissect actions of the clock within SCN and appetitive neurons in feeding and glucose metabolism. Our work has direct translation to human health since we will elucidate how the clock system contributes to weight loss with hypocaloric diets and maintenance of weight loss following cessation of dieting. In summary, our proposed research will provide detailed mechanistic insight into how disruption of pacemaker neuron activity and clock transcription factor regulation of neuronal gene transcription impacts the coordination of hunger, energy balance, and health. In summary, our proposed research will provide detailed mechanistic insight into how disruption of pacemaker neuron activity and clock-regulated neuronal gene transcription in both SCN and extra-SCN regions impact the coordination of hunger, energy balance and metabolic health.