Marcelo O. Dietrich - US grants

? DESCRIPTION (provided by applicant): The maintenance of energy metabolism is a fundamental homeostatic function found in all organisms from humans to simple cells. Disruption of energy metabolism can lead to life-threatening conditions, including chronic metabolic disorders such as obesity and diabetes. Understanding the regulatory principles that control energy metabolism is of the utmost importance in helping to design better treatments for metabolic disorders. AGRP neurons in the hypothalamus participate in the regulation of energy metabolism and are activated during times of food deprivation. Paradoxically, we showed that AGRP neuronal activity is also elevated in diet- induced obese mice. We have recently found that mitochondria in AGRP neurons undergo fusion when mice switch from negative to positive energy balance (i.e., from food deprived to high-fat fed). When we blocked mitochondria fusion in AGRP neurons (by knocking down Mfn2) in mice fed a high-fat diet, AGRP neuron activity decreased due to reduced intracellular levels of ATP, and the mice became resistant to diet-induced obesity. Because in both food deprived and high-fat diet fed mice the activity of AGRP neurons is high, we hypothesize that AGRP neuron activity is supported by different mechanisms in these two conditions. This is illustrated by the fission state of mitochondria in AGRP neurons during food deprivation, and the fused state in high-fat fed mice. The goal of this application is to provide mechanistic insight into the complexity of the biology involved in the adaptations of AGRP neurons to different metabolic conditions. In Aim 1, we will use cell-specific ribosome profiling of AGRP neurons combined with RNA-sequencing to identify changes in the translational landscape of AGRP neurons. In Sub-Aim 1.1 we will characterize the ribosome-associated transcriptome (translatome) involved in AGRP neuron function in food deprived, fed and high-fat diet fed mice. In Sub-Aim 1.2 we will characterize how the translatome of AGRP neurons is modified in the absence of mitochondria fusion during diet-induced obesity in AGRP-Mfn2KO mice. These experiments will identify the putative intracellular mechanisms that allow AGRP neurons to adapt to the changing metabolic milieu. In Aim 2, we will tackle a very important mechanistic question that is whether mitochondrial dynamics in AGRP neurons is controlled by the electrical activity of the cells. We will use a multi-faceted approach to selectively and acutely activate/inhibit Agrp neurons utilizing transgenic and AAV-mediated mouse models with the goal of identifying dynamic morphological changes in mitochondria through electron microscopic analyses. This proposal will deliver novel insights into the central regulation of metabolism and offer new candidates to pursue as drug targets for obesity and related metabolic disorders.

PROJECT SUMMARY Vocalization (i.e., cry) is the first and most intense behavior manifestation in the life of a neonate. Neonates vocalize when isolated from their primary caregivers, attracting their attention to receive comfort, care, and nutrition. In humans, atypical cry behavior is symptomatic of neurodevelopmental disorders, such as autism and Angelman syndrome. However, how the immature neonatal brain controls vocal behavior is a fascinating question in developmental neurobiology that remains unsolved. The goal of this proposal is to elucidate neural circuits that transiently modulate the emission of vocalizations in neonatal mammals. The hypothalamus is a region in the bottom of the mammalian brain suggested to mediate vocalization based on experiments using electric stimulation of this brain region. In the hypothalamus, there is a region called the arcuate nucleus, which contains two populations of neurons that produce either Agouti-related peptide (Agrp) or Proopiomelanocortin (POMC). Our preliminary experiments suggest these two populations of neurons exert a modulatory role in the emission of neonatal vocalizations. Thus, in this proposal, we will use state-of-the-art approaches in circuit neurosciences applied to the neonatal brain to investigate the mechanistic details involved in the control of neonatal vocal behavior by Agrp and POMC neurons. At its conclusion, this project will reveal novel neuronal circuits that control precise behavior outputs in the developing mammalian brain. This project will also shed new light on how vocal behavior dynamically changes during early postnatal life. In addition to illuminating fundamental principles of behavior control early in life, the mechanistic insights revealed in this project might also aid the understanding of impaired vocal behavior in several neurodevelopmental diseases.