Joshua P. Thaler, Ph.D. - US grants

DESCRIPTION (provided by applicant): This proposal delineates a 5-year program to provide the training toward the development of an independent academic research career in the study of neuroimmune interactions that affect energy balance. The goal of this research program will be to determine brain mechanisms that govern dysregulation of energy balance in high-fat diet induced obesity in order to provide molecular targets for therapy. The candidate has been prepared for this pathway by completing MD and PhD degrees and clinical training in Internal Medicine and Endocrinology. This research will be conducted in the laboratory of Dr. Michael Schwartz, an expert in the field of hypothalamic regulation of energy balance and glucose homeostasis, and will involve collaboration with a large group of experts in metabolism and inflammatory biology at the University of Washington. It will be overseen by an expert mentoring committee with several members of the Endocrinology Division as well as three external advisors. The clinical problem of weight gain associated with dietary excess has been hampered by a limited understanding of the central nervous system (CNS) mechanisms that account for this disruption in energy homeostasis. Our preliminary data has uncovered a potential interaction between microglia, the immune cells of the brain, and neurons, the regulators of energy balance. At the onset of high-fat feeding, there is a period of early hyperphagia and a concomitant inflammatory response specifically in the hypothalamus. At the same time, an increase in microglial number and cell size occurs in the arcuate nucleus, a region of the hypothalamus containing leptin-responsive melanocortin (POMC) neurons. Blocking microglial activation results in enhanced susceptibility to high-fat diet-induced weight gain. This research will characterize the mechanisms by which high-fat diet-induced inflammation in the hypothalamus contributes to excess weight gain through two specific aims. In Aim 1, we will examine the energy balance, inflammatory, hormonal, and cellular mechanisms by which microglial inhibition confers increased susceptibility to weight gain on high-fat diets. Aim 2 focuses on the effect of preventing high-fat diet-induced inflammation in the POMC neuron on leptin sensitivity, energy balance, and glucose homeostasis. This research course will provide the training and expertise necessary for an independent investigative career while transitioning the PI toward translational research in the expanding field of neuroimmunology. The overarching goal of this proposal is to determine the mechanisms by which inflammatory signals alter energy homeostasis in order to generate better therapeutic options to improve patient care. PUBLIC HEALTH RELEVANCE: Obesity is the underlying cause of most cases of type 2 diabetes worldwide. Therapies that target obesity could reduce the incidence of diabetes, thereby greatly improving general health. This research focuses on the brain's role in high-fat diet-induced weight gain with an effort to develop therapies to reduce weight gain.

DESCRIPTION (provided by applicant): Obesity is among the most challenging health problems confronting developed countries due to its association with metabolic disorders such as type 2 diabetes, hypertension, and cardiovascular disease. Obesity is remarkably common, affecting >1/3rd of US adults, but is very challenging to treat due to the inexorable regain of los weight. Since body fat stores are subject to homeostatic regulation in both lean and obese subjects, the failure of obesity therapy over time likely represents the defense of an elevated level of body fat mass. Our recent findings implicate neuron injury and surrounding gliosis in key hypothalamic areas for body weight control as a significant contributory mechanism to obesity pathogenesis. Specifically, we observed a rapid accumulation of reactive astrocytes and microglia in the mediobasal hypothalamus during the initiation of high fat diet consumption in rodents concomitant with cellular stress responses in surrounding energy homeostasis- regulating neurons. Our K08 proposal focused on the contribution of hypothalamic microglia to obesity- associated inflammation and injury. In this proposal, we extend these ongoing investigations to focus on metabolic coupling between hypothalamic astrocytes and neurons. Astrocytes contain glycogen stores that are mobilized to provide lactate to surrounding neurons during times of increased synaptic activity. We have recently determined that acute blockade of hypothalamic astrocyte glycogenolysis promotes food intake, and that obese rodent models contain increased hypothalamic accumulations of astrocyte glycogen. These data support the premise that disruption of metabolic coupling between hypothalamic astrocytes and neurons contributes to obesity pathogenesis. We will investigate this hypothesis by determining the specific hypothalamic nuclei involved in food intake-triggered lactate utilization, whether diet composition and metabolic status affect hypothalamic lactate production, and the extent to which defective astrocyte glycogenolysis is necessary and sufficient for the development of obesity. The data obtained from these investigations will form the basis of a new line of research centered on glial-neuronal metabolic coupling as a novel obesity target.

Project Summary Obesity is a significant public health concern worldwide, and the incomplete understanding of its pathogenesis has limited the development of effective treatments. Overnutrition triggers immune cell activation in peripheral tissues and the brain, suggesting that strategies to target the inflammatory response have theoretical therapeutic potential. However, these approaches remain largely untested. We recently demonstrated that mice lacking IKK? in brain glia (astrocytes and microglia) show reduced susceptibility to diet-induced obesity (DIO) and hyperphagia, but with different kinetics. Microglial activation occurs earlier and is required for DIO susceptibility from the onset of HFD feeding whereas astrocyte protection from DIO only occurs after weeks of HFD exposure. Consistent with the known role of microglia to induce reactive astrocytosis in CNS inflammatory diseases, these data suggest a cascade of inflammatory activation beginning with microglia that subsequently triggers astrocytes to promote DIO. Another stark difference between the mouse models is a paradoxical impairment of glucose tolerance in the lean microglial IKK? knockout, suggesting dissociation between the regulation of energy balance and glucose homeostasis by microglia. However, the molecular mediators responsible for this phenotype remain unknown. We have now developed a diet-independent inducible model of microglial activation using the Designer Receptor Activated by Designer Drugs (DREADD) approach. Microglia expressing the Gq-coupled DREADD receptor hM3D are rapidly activated by CNO treatment with marked upregulation of TNFa expression. Nevertheless, the CNO treatment causes an immediate improvement in glucose tolerance even in HFD-fed mice. Unexpectedly, this effect can be blocked using icv pretreatment with either a specific TNF receptor antagonist or a melanocortin 3/4 receptor antagonist. While TNF signaling can disrupt leptin sensitivity in hypothalamic neurons, it also increases POMC neuron firing, promotes synaptic plasticity and activates the melanocortin pathway. Therefore, we hypothesize that HFD feeding acts through microglial TLR4 to triggers DIO susceptibility but improve glucose tolerance through the melanocortin pathway. To investigate these premises further, in Aim 1 we will determine whether astrocyte activation is dependent on microglial inflammatory signaling and required for microglia-induced DIO. Aim2 will determine whether microglial TNF and melanocortin signaling are required for the improved glucose tolerance induced by microglial activation. Finally, Aim 3 investigates the peripheral mechanisms of improved glucose tolerance and includes a transcriptomic screen for additional microglial mediators of glucose homeostasis regulation. Together, these studies will help identify the cellular and molecular components of microglial activation that mediate its impact on obesity and diabetes pathogenesis.

The well-established Enrichment Program is an integral component of the Nutrition and Obesity Research Center (NORC) and supports its mission to foster collaboration within, and the educational enrichment of, the local nutrition and obesity research community. The Enrichment Program fulfills these goals by hosting symposia on nutrition, obesity, diabetes and metabolism research of interest to NORC Affiliate Investigators (AIs) and the greater community, facilitating interdisciplinary exchange and collaboration, and providing training opportunities to enhance the educational experience and research competitiveness of NORC AIs. We propose two aims that elaborate our programmatic offerings. In Aim 1, we will continue our joint program with the UW Diabetes Research Center (DRC), the UW Medicine Diabetes Institute (UWMDI), Benaroya Research Institute (BRI), Pacific Northwest Research Institute (PNRI), and the Cystic Fibrosis Research and Translation Center (CFRTC) to provide a broad-based education and enrichment program involving top-level local and invited speakers for full- and half-day symposia, round table presentations, and annual research retreats featuring trainee/junior faculty presentations. In addition, we will provide two new NORC-specific offerings: a joint symposium with the UW Collaborative on Obesity Research and Action (CORA) to increase cross-exposure of the basic/translational and community health/epidemiology/public policy research communities and a training workshop on grant writing and presentation skills delivered by key faculty within the NORC organizational structure. Aim 2 continues our collaboration with the T32 Fellowship Training programs awarded to the Division of Metabolism, Endocrinology and Nutrition to provide trainees direct interaction with visiting faculty, education and career development sessions, and skills workshops in the areas of nutrition, obesity, metabolism, and diabetes research.