Linking stress-associated brain and adipose functions

PROJECT SUMMARY/ABSTRACT The fundamental mechanisms by which acute intense stress affects energy homeostasis via brain substrates and sexual dimorphism of these processes are poorly understood. Environmental stressors induce fight-or- flight-or-freeze response via the locus coeruleus (LC) in the brainstem, a major sympathetic regulator in humans and animals that triggers energy metabolism. LC innervates the brown adipose tissue (BAT) and expresses high levels of PAC1 receptor for the neuropeptide PACAP (pituitary adenylate cyclase activating peptide). PACAP/PAC1 are critical regulators of stressors of all kinds, fear, appetite, feeding, and energy metabolism and genetically linked to stress-related disorders like post-traumatic stress (PTSD) in humans. Intriguingly, women with PTSD showing high blood levels of this neuropeptide and brain PAC1 receptors regulate fear in a sexually dimorphic manner in animals. To test the importance of PAC1 in acute intense stress and energy homeostasis, we used the stress-enhanced fear learning (SEFL) behavioral model in mice. Our preliminary data show that ablation of PAC1 receptors from the LC enhances SEFL expression, energy metabolism as assessed by indirect calorimetry measurement, and increases metabolic genes like uncoupling protein 1 in BAT in females than males. Thus, harnessing on the biology of PAC1 receptors, we aim to lay a mechanistic framework linking acute intense stress and energy metabolism in a systematic and sex-dependent manner via the LC. We hypothesize that PAC1 receptors in the LC are important for gating stress-associated metabolic information and BAT functions in a sexually dimorphic manner. Aim 1 will test a SEFL mediated loss of function of LC-PAC1 on whole body energy expenditure and on BAT functions. For this, we will test if viral cre-recombinase mediated PAC1 deletion from LC in mice with floxed PAC1 regulates SEFL-associated energy expenditure and induction of thermogenic genes in BAT in a sex-dependent manner (via transcript analysis, mitochondrial bioenergetics, and tissue lipolysis). Aim 2 will test if PAC1 expressing LC neurons project directly to BAT in a sexually dimorphic manner under SEFL. For this, we will use retrograde viral tracing to determine LC to BAT projecting cell populations combined with in situ hybridization for PAC1 in LC. We predict that female mice will show enhanced energy expenditure, BAT thermogenesis and increased LC projection to BAT. Overall, using state-of-the-art tools and techniques and rigorous systems biology approach of linking acute intense stress and energy metabolism, our studies will lay crucial groundwork for several future work. This will serve as a premise for studying central sympathetic control of metabolism in chronic stress- related conditions such as PTSD that are comorbid with metabolic diseases and increasingly prevalent in the US populations.