Alessandro Bartolomucci, Ph.D. - US grants

DESCRIPTION (provided by applicant): Epidemiological evidence demonstrates that obesity is rising exponentially to pandemic levels in the USA. The failure of current pharmacological approaches to treat obesity strongly indicates that new therapeutic strategies are required. New strategies require new knowledge. We recently identified a peptide named TLQP-21 which is encoded by the VGF gene. TLQP-21 binds the G-protein coupled receptor Complement 3a receptor1 (C3aR1), potentiates ¿-adrenergic receptors (¿AR)-induced lipolysis and, reduces fat mass in obese mice. TLQP-21 also improves diabetes and has a very safe cardiovascular profile. Much remains to be established on it molecular mechanism of action. Similarly, the role of C3aR1 is well established in immunity but its functional role in adipocytes and obesity is poorly understood. We propose a project in which the Central Hypothesis will be tested that TLQP-21 opposes obesity by enhancing lipolysis with a mechanism requiring priming by cAMP and mediated by increased intracellular calcium concentration. The Specific Aim (SA)1 will determine the role of cAMP on priming TLQP-21-induced activation of C3aR1 in adipocytes and the role of increased [Ca2+]i on its pro-lipolytic effect. The SA2 will investigate the physiologicl consequence of introducing an inactive TLQP-21 mutant on the development of obesity in mice and the behavior of the peptide in a C3aR1 ko mouse. Finally, SA3 will focus on the pro-lipolytic effect of TLQP-21 in human adipocytes. The impact of successful achievement of the aims of this project will be significant on the field. After the failure of sympathomimetic drugs and other pro-lipolytic agents to cure obesity, current therapeutic approaches primarily target feeding or nutrient absorption through the gastro-enteric tract. These more recent approaches are not devoid of adverse effects. The mechanism of action of TLQP-21 has the potential to cure obesity by selectively and safely reducing the excessive adipose fat mass.

Body weight is controlled in large part by communication between the brain and peripheral metabolic tissues, including white and brown adipose tissue, via the sympathetic nervous system to regulate energy expenditure and lipolysis. Pharmacotherapeutic intervention to reduce adiposity, however, has been relatively unsuccessful. We have identified the neurotrophin-inducible neuronal protein VGF (non-acronymic), and one of its processed C-terminal peptides TLQP-21, as central and peripheral regulators of energy expenditure and lipolysis. TLQP-21 activates the Complement C3a Receptor 1 (C3aR1), an integral component of the innate immune system, and in adipocytes, enhances lipolysis mediated by the beta-adrenergic agonist isoproterenol. Mice with VGF ablated in the adult ventromedial hypothalamus (VMH) and arcuate (ARC) have increased adiposity and decreased energy expenditure, a phenotype that is consistent with a key physiological role for TLQP-21 in the adult CNS, one that is also congruent with many actions of brain-derived neurotrophic factor (BDNF) in the hypothalamus. Utilizing floxed (lox-p flanked) VGF and C3aR1 mouse models together with established transgenic Cre-driver lines and targeted AAV-Cre administration, we will test the hypothesis that in adults, VGF and its peptides, particularly TLQP-21, regulate energy expenditure, lipolysis, and glucose homeostasis via central modulation of sympathetic outflow from the VMH and paraventricular hypothalamus (PVH), which receives extensive VGF-containing projections from ARC/VMH, and provides essential BDNF- and VGF-containing sympathetic outflow pathways to brown adipose tissue (BAT). Two specific aims are proposed. Aim 1 will probe the roles of VGF in the CNS pathways that originate in the PVH and VMH, which can be activated by `designer receptors exclusively activated by designer drugs' (DREADD), and regulate energy expenditure, glucose metabolism and lipolysis via sympathetic outflow from hypothalamus. Aim 2 will define the site(s) of action and function(s) of the pivotal VGF-derived peptide TLQP-21, determining whether its actions in the adult CNS are dependent on C3aR1 that is expressed on neurons, microglia, and/or astrocytes. The complementary research expertise of the PIs will be essential for successful completion of our aims, providing fundamental insight into the mechanisms by which VGF, its peptide TLQP-21, and the TLQP-21 receptor C3aR1, contribute to hypothalamic-sympathetic circuits that control energy and glucose homeostasis, potentially identifying promising new drug targets for the treatment of obesity and diabetes.

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.

Project Summary As the population of the United States ages, the health burden imposed by diseases of aging is expected to increase concomitantly. Social factors, including low socioeconomic status, social isolation, and low social support, are among the best predictors of susceptibility to diseases of aging, as well as lifespan itself. Nevertheless, key questions about the causal relationship and the biological mechanisms that link social experiences to health and aging remain unanswered. Animal models are a powerful tool to address these questions. Like humans, other social mammals exhibit strong associations between social adversity, health, and mortality. Unlike humans, though, they experience less complex environments, have shorter generation times, and can be subjected to experimental manipulation in controlled environments. The goal of this proposal is to build a Research Network on Animal Models to Understand Social Dimensions of Aging. By supporting interdisciplinary communication and pilot research from both human and nonhuman animal researchers, we aim to maximize the impact of animal model research on understanding the social determinants of health and aging. A Research Network is essential because current research in this area is distributed across many different disciplines, there is no standard set of conferences or publication venues where researchers with related interests overlap, and there are high barriers to entry for animal model work. The proposed network will overcome these challenges by supporting scientific meetings and workshops that build contacts across disciplines and among researchers at all career levels. It will also recruit new, diverse investigators into the field by providing opportunities for pilot project support, travel fellowships, and mentorship by experienced senior investigators. As part of these activities, the network will provide hands-on training for animal model research in rodents and nonhuman primates and for comparative research that leverages human and animal data sets. To build visibility, it will support targeted symposia at meetings where animal model work on the social dimensions of aging has not traditionally been represented. Finally, it will identify priority areas for animal model research and promote data and protocol dissemination. These activities will help set a research agenda that extends beyond the network?s immediate activities. Thus, the proposed network will transform a weakly connected community into a self-sustaining field of researchers equipped to conduct impactful research on the social dimensions of aging. Areas of particular interest include models to test the causal effects of social interactions on health; methods that can be flexibly deployed in both nonhuman animals and human populations; and research that investigates the benefits of behavioral interventions for alleviating the costs of social adversity. Advances in these areas will have direct translational application to human health and well-being during aging.