CAREER: Deciphering the Neural Network Orchestrating Sex Differences in Metabolic Circadian Rhythms

Circadian rhythms are critical for regulating energy balance. From flies to humans, disrupting metabolic circadian rhythms exacerbates metabolic risk. My long-term research goal is to elucidate the neural circuitry that regulates circadian rhythms of physiology and behavior to optimize metabolism. We recently discovered a sex difference in metabolic circadian rhythms. Our preliminary data show that estrogen signaling in female, but not in male, mice regulates eating behavior and liver circadian rhythms during a nutritional challenge. The research objective of this CAREER proposal is to leverage the sex difference we discovered as a novel approach to elucidate the neural circuitry that proximately controls eating and liver circadian rhythms in mice, and ultimately energy balance. To complement our studies in mice, the educational projects will develop course-based undergraduate research experiences (CUREs) to study sex differences in circadian rhythms in humans. The research goal of this CAREER project is to test the overarching hypothesis that estrogen regulates the neural circuitry controlling metabolic circadian rhythms resulting in sex differences in energy balance. Aim 1 will determine whether estrogen receptor á (ERá) signaling is necessary and sufficient to regulate the sex difference in the circadian eating behavior rhythm using whole-body ERá knockout mice and ERá-specific agonists. Aim 2 will determine which areas of the brain mediate estrogen regulation of eating circadian rhythms by targeting specific neurons with Cre-lox and AAV-mediated gene knockdown. Aim 3 will test the hypothesis that estrogen regulation of the eating rhythm controls the liver circadian clock using bioluminescence reporters to measure tissue circadian rhythms. The approach integrates the study of circadian regulation of energy balance across molecular, tissue, and behavioral levels, which is critical to understanding how the network of circadian clocks regulates metabolism. The educational goal of this CAREER project is to develop sustainable educational projects that provide instruction in scientific inquiry and analysis of sex differences in circadian rhythms, and that include students from diverse training, ethnic, and economic backgrounds. Circadian rhythms are ideal for engaging students because they are inherently intriguing and familiar. The educational approaches are to develop course-based undergraduate research courses (CUREs) for non-STEM and STEM students to study sex differences in human circadian rhythms, which will complement our studies in mice; to develop, implement, and disseminate a virtual lab activity that provides experimental training in the fundamental properties of circadian rhythms; and to integrate high school, undergraduate, and graduate students from disadvantaged backgrounds into the research project. Intellectual Merit: The mammalian circadian system is organized hierarchically, with the suprachiasmatic nucleus (SCN) as the master clock that coordinates the timing of other clocks in the brain and periphery that in turn regulate behavioral and physiological rhythms. This hierarchical organization of the circadian system was discovered almost 20 years in mammals and yet we still know very little about the circuits downstream from the SCN that proximally regulate circadian rhythms of behavior and physiology. This project will study the extra-SCN neural circuitry that regulates metabolic circadian rhythms and will expand our understanding of the circadian control of energy balance. We will also elucidate the anatomical substrate(s) and molecular signaling mechanisms underlying sex differences in circadian rhythms, which are understudied. Broader Impacts: The research and educational goals of the proposed project will have many broader impacts. First, the teaching projects will generate new courses for undergraduate students in non-STEM and STEM that will improve science literacy and dispel distrust in science. Second, the project will increase participation of women, minorities, and those from economically disadvantaged backgrounds in science. Third, the project will provide exceptional training for high school, undergraduate, and graduate students in science. Fourth, the proposed work will benefit society by bringing attention to sex differences in behavior and physiology, which are underappreciated and understudied, but are critically important for understanding neuroendocrinology and energy balance.