Delineation of the role of brainstem pro-opiomelanocorin neurons in energy balance

Obesity and type 2 diabetes represent major medical and economic challenges of the 21st century. An understanding of the biological mechanisms regulating food consumption is essential to both the successful treatment and prevention of obesity and type 2 diabetes. The brain represents the master co-coordinator of energy balance, employing a number of interwoven neurological circuits to continually appraise and respond to changes in nutritional state. The brain melanocortin network is a fundamental regulator of energy homeostasis and serves as a gateway for many of these signals. Therefore, a clear understanding of the precise mechanism through which pro-opiomelanocortin (POMC) modulates appetite, food preference, body weight, and blood glucose is of intense interest. The aim of this application is to identify specific POMC neurons responsible for communicating energy balance information and to demonstrate that their manipulation, through state of the art pharmacogenetic and genetic techniques, is of direct relevance to metabolic fitness. We will also examine the impact of diet and adiposity on POMC energy balance circuitry function. Through the identification of primary, critical cells in the brain regulating energy balance, we anticipate that these data will ultimately have translational benefit for the treatment of global metabolic disease.

The rapid rise in the prevalence of obesity emphasizes the need for a greater understanding of the physiological mechanisms underlying energy homeostasis. Whilst traditional Cre-lox technology has demonstrated pro-opiomelanocortin (POMC) neurons to be a critical nexus for the integration of multiple energy balance circuits and fundamental to the physiological control of metabolic health, this approach does not permit functional and temporal dissociation of discrete populations of POMC neurons. Thus, the aim of this project is to establish the distinct role of NTS POMC neurons in the regulation of energy and glucose homeostasis. On the basis of our preliminary data, we hypothesise this population to be a critical component of the central metabolic network. Targeted manipulation of NTS POMC neurons will be facilitated by the use of cutting-edge pharmacogenetic technology (Designer receptor exclusively activated by designer drug - DREADD). This technique affords real-time control of neuronal activity and subsequent insight into their physiological function. Sterotaxic delivery of viral constructs into the NTS of a POMC-Cre mouse line promotes selective expression of DREADD receptors on NTS POMC neurons. Targeted activation/inhibition of these cells in freely behaving mice is induced by the administration of an inert ligand. The cell specific pharmacogenetic manipulation, together with comprehensive metabolic phenotyping (including food intake, diet preference, energy expenditure and glucose homeostasis), affords the opportunity for greater understanding of the physiological salience of brainstem POMC neurons. These data will offer important insight into the discrete neuronal circuits governing energy and glucose homeostasis. Given the pervasiveness of metabolic disease within the global community and the resulting socio-medical ramifications, unravelling the neuronal microcircuits governing the physiological control of energy balance is essential.

Academic impact
Metabolic health and disease is a continually expanding area of research, in which the UK has arguably been at the forefront. It is a multi-disciplinary field that encompasses neurobiology, physiology, pharmacology, genetics, nutrition and public health. This proposal therefore, has the potential to make a major academic impact, both within the UK and internationally, by furthering our understanding of the molecular mechanisms underlying metabolic health and disease. In addition to advancing knowledge, the proposed research will provide substantial capacity building by training the field's scientific leaders of tomorrow to encourage the maintenance of the UK's position in this area of scientific research. This will provide the potential for expansion of our research findings into other relevant animal models and incorporation in broader neuroscience, pharmacogenetic, pharmacological and genetic approaches. The research will also provide opportunities for improving teaching and learning of undergraduate and postgraduate students through seminars and research projects.

Economic and societal impacts
Obesity is a major health problem in the UK, both accelerating death and incurring a cost of a half billion a year in direct costs by the government. Obesity is the second largest cause of cancer, substantially increases the risk of heart disease, type 2 diabetes, and many other medical complications. Currently, only one drug is approved for obesity treatment, Ali, which is a lipase inhibitor. Given the prevalence of obesity worldwide and its health, societal, and economic implications, new treatments are a clinical imperative. In previous research, we addressed this conundrum by investigating a class of compounds, those augmenting 5-HT bioavailability, that have been effective in the clinic for weight loss for approximately the past 15 years. However, these drugs have been withdrawn from clinical use due to off-target effects. We previously determined that the anorectic therapeutic mechanism is via 5-HT activation of a discrete class of receptors 5-HT2Cs, expressed on a chemically defined population of neurons, pro-opiomelanocortin (POMC) (e.g. Heisler et al., Science 2002; Xu et al., Neuron 2008; Xu et al., J. Neuroscience 2010). This work further stimulated and supported drug discovery efforts for 5-HT2C receptor agonists at multiple pharmaceutical companies, including Arena. Arena's compound, lorcaserin, went through phase 3 clinical trials, effectively reduced body weight and was reviewed by the FDA, but not approved last year. This drug activates all 5-HT2C receptors, not just those discretely expressed on POMC neurons. Here we propose to evaluate the role of activation or inhibition of a specific population of POMC neurons in energy balance in real-time. An advantage of the new pharmacogenetic technology that we are employing over the traditional Cre-lox system is regional and temporal refinement. We speculate that directly targeting brainstem POMC cells will provide an effective new pharmacological target for the treatment of metabolic disease. In fact, we have already observed unique characteristics that distinguish this population of POMC neurons from those expressed elsewhere in the brain. Therefore, there may be opportunities for the commercialisation of new diagnostics (identifying individuals at risk of metabolic disease) and therapeutics (targeting specific POMC neurons). The proposed research may inform and benefit the pharmaceutical sector through access to new knowledge, technology development and databases. Thus it has the potential to enhance the knowledge economy and economic competitiveness of the UK. The research is also readily accessible to the general public, because of its immediate relevance to improving health and well being and enhancing quality of life. The project therefore provides an excellent vehicle for increasing public engagement and understanding.