Central and peripheral actions of FGF21 in promoting fat catabolism (invited resubmission)

The purpose of this research is to understand how and where in the body the novel hormone fibroblast growth factor 21 (FGF21) acts to reduce food intake, decrease body weight and regulate body fat. This hormone was first discovered over ten years ago, but we are uncertain about which tissues in the body produce it, where it acts, and what its normal role in our biology is. Our previous research has exploited seasonal cycles in body weight in the Siberian hamster, as this provides a natural animal model of body weight gain in summer (fat state) and loss in winter (lean state).

Using this model, we have already found that FGF21 is more effective at reducing appetite and causing weight loss in seasonally fat hamsters. This is a hugely important finding, because responses to other major metabolic hormones are often decreased in states of high body fat. The fact that obesity is an insulin- and leptin-resistant state presents challenges for using these pathways to manage body weight disorders. Understanding the natural biology of FGF21 should therefore have important implications for pharmaceutical and/or nutritional treatment of obesity as this pathway is likely to be amenable to manipulation.

The first objective is to determine which tissues respond to FGF21 treatment by changing their uptake of glucose and fatty acids. This will be achieved using a small animal positron emission tomography (PET) scanner, which allows uptake of these metabolites to be observed non-invasively in living animals. We will also test in vitro whether FGF21 can promote fat breakdown. These studies will identify which tissues are the primary targets of FGF21 action, and confirm whether actions on glucose and fatty acid uptake underlie the whole body effects on fat depots and body weight.

The second objective is to investigate the hypothesis that FGF21 also acts in the brain to reduce food intake and to increase energy expenditure. Other metabolic hormones such as leptin and ghrelin are known to signal from fat and the stomach respectively to the brain to regulate our appetite. Our preliminary studies also provide evidence that FGF21 can act in the brain. We are particularly interested in actions on a layer of glial cells in the hypothalamus known as tanycytes, as these cells express a receptor for FGF21 known as FGFR1c, and show changes in gene expression and glucose-stimulated calcium signalling in response to stimulation of these receptors. We will test the hypothesis by determining whether administration directly into the brain of FGF21 itself or a closely related compound developed by the pharmaceutical company Eli Lilly changes appetite, energy expenditure and body weight. We will also use imaging of slices of brain derived from rodents to determine whether FGF21 directly affects neurons and glial cells.

The overall outcome of this project is that we will understand how the hormone FGF21 is able to produce its beneficial effects of improved glucose dispersal and loss of body fat. We will have identified which tissues respond to FGF21, and will determine if part of its action is in the brain via the control of behaviour and the autonomic nervous system. There are many beneficiaries of this project. The information gained will be important for other academic researchers in universities and in research institutes, and for researchers in the pharmaceutical industry working on obesity. In addition, the project will provide training in advanced imaging and experimental physiology, and the researchers will promote public understanding of research into appetite control and obesity.

The overall aim of this project is to determine the sites and mechanisms of action by which FGF21 regulates body fat depots. This will be achieved by exploiting a natural animal model of body weight gain in long summer photoperiods, and weight loss in short winter photoperiods, where the body weight changes predominantly reflect changes in visceral adiposity: the Siberian hamster. Our pilot studies reveal that FGF21 and a monoclonal antibody (H7) which targets its likely receptor (FGFR1c) are more effective at reducing appetite and causing weight loss in seasonally fat hamsters as compared to those in the winter lean state, hence the importance of identifying where and how FGF21 exerts its effects. The first objective is to identify which tissues respond to FGF21. We will use 18F-2-deoxy-D-glucose and 16-18F-4-thia-palmitate tracers in a small animal quantitative positron emission tomography (PET)/nanoCT scanner to identify potential sites of action. Fat (long day) and lean (short day) hamsters will be tested, in the presence and absence of an insulin challenge. These in vivo studies will be complemented by ex vivo biochemical and molecular analysis of signal transduction pathways in tissues removed from the scanned animals, and by in vitro analyses of the effects of FGF21 on lipolysis and insulin secretion using isolated adipose tissue and beta cell islets, respectively. The second objective is to investigate the hypothesis that FGF21 also acts centrally to reduce food intake and to increase energy expenditure. We will determine whether administration of FGF21 directly into the brain (or a mimetic, LY2405319) changes appetite, metabolic rate, fat oxidation and body weight. We will also determine whether these central treatments alter gene expression and signalling in hypothalamic tanycytes, glial cell known to express FGFr1c which we have previously shown to mediate seasonal regulation of body weight via their regulation of the local thyroid hormone availability.

The proposed research will benefit the biomedical research community, the pharmaceutical industry, and the public sector and society in general. The results generated from this project will lead to a significant advance in our knowledge about how the recently identified novel hormone FGF21 affects appetite, energy metabolism and ultimately body weight. Obesity and related diseases are estimated to reduce lifespan by an average of 9 years and cost the UK economy more than £7bn, of which more than £1bn is directly attributable to money spent by the NHS on treatment. The information generated from the proposed project is likely to be of direct interest to the pharmaceutical industry in their attempts to target drugs at modifying food intake and fat deposition to counter the rise in worldwide obesity rates. Indeed, to our knowledge three major companies, Eli Lilly, Amgen and NovoNordisk have research programmes on FGF21. We have an existing collaboration with Lilly that will provide recombinant FGF21 and its analogue LY2405319 for the proposed studies in our unique animal model of natural weight gain and loss. Current approaches to targeting mechanisms of appetite control by pharmaceutical intervention have not been successful. The proposed project offers insight into a novel mechanism regulating appetite and energy balance. The information generated in this project may help expedite drug discovery or alternatively may reveal nutrient sensing pathways that could be targeted with a food based solution. Any impact on reducing weight gain or inducing weight loss will also have very beneficial consequences on healthy ageing, a key strategic area of BBSRC interest, and would ultimately benefit individuals and the economy. The project may give rise to commercially exploitable results which will be reviewed in conjunction with the Research Innovation services at the University of Nottingham, Research and Innovation centre at the University of Aberdeen and Eli Lilly for potential patent applications and development.
The researchers who will carry out this research are committed to promoting public awareness and understanding of this fundamental research into the control of body weight. For example, in the forthcoming year they will participate in the Mayfest event in Nottingham (May 2014) and in Aberdeen's Techfest (Sep 2014), and during the course of the project they will participate in subsequent Mayfest events at Nottingham and Techfest and Café Scientifique events at Aberdeen. Such events not only highlight advances made in pharmaceutical management of body weight, but highlight the importance of healthy lifestyle and dietary choices. Finally, the research will benefit both the public and private sector by providing integrated and multidisciplinary training for individuals in advanced experimental skills and methodologies for understanding metabolic function. A strategic objective of the BBSRC is to train researchers with 'high class skills'. The proposed project will train a post-doctoral research assistant (PDRA) in cutting edge nanoCT/PET imaging and in vivo and laboratory-based metabolic physiology techniques. These activities will have a societal and economic impact by providing a highly-skilled a scientist to the employment pool at the end of the award period. This impact is amplified because by conducting the research in a University environment other individuals, including PhD, Masters and undergraduate students, will be exposed to this work, thus enhancing the skills of multiple individuals who will enter the employment market at the end of their university studies.