Circadian contol of metabolism: implications for health and disease

Daily 24-hour rhythms are present in virtually all aspects of our behaviour and physiology such as sleep/wake, feeding and body temperature cycles. These rhythms are underpinned by inherent timing systems (circadian clocks) which run throughout the body, and act within each tissue to orchestrate many organ functions and rhythmic activities (e.g. glucose homeostasis in the liver). In mammals, circadian timing is headed by a 'master clock' located in a small area of the brain called the suprachiasmatic nucleus (SCN). The SCN synchronises clocks in the rest of the body, so that functioning of different organ systems are coordinated with each other, as well as overriding behavioural cycles (e.g. feeding, sleeping). It has recently become clear that our circadian clocks are intimately linked to energy metabolism, and diminished circadian rhythmicity is now considered a hallmark feature of metabolic diseases such as obesity and diabetes. It is therefore critical that we understand how our internal clocks regulate energy metabolism, and how a disruption of circadian timing may contribute to metabolic disease. In many tissues, circadian clock genes (the machinery that drives the clock) are closely connected to metabolic pathways. Importantly this connection is reciprocal, meaning that the clock not only drives the rhythmic activity of key metabolic genes, but is itself strongly influenced by metabolism and cellular energy status. For example, when nocturnal laboratory mice are forced to feed only during the day, many aspects of their physiology (and the clocks that underlie these physiologies) become desynchronised and disconnected from the SCN, which remains locked to environmental light cycles. Thus, the strong influence of diet and eating behaviour on circadian clocks suggests that abnormal energy supply (over consumption of high-calorie foods, or eating habits that are out of synchrony with normal patterns of behaviour) will be effective at dampening or even blocking circadian control of metabolism. This raises three important questions: 1) are some of our body clocks particularly susceptible to diet-induced disruption; 2) how does the loss of clock function within these 'susceptible' clocks impact on overall metabolic or behavioural rhythms; 3) what critical components form the clock-metabolic interface in such tissues. My research proposal aims to address these questions. Specifically, I will investigate how diet-induced obesity impacts on behavioural (sleep, feeding) and physiological processes (metabolic rate, body temperature, blood glucose) across the day, using state-of-the-art monitoring equipment. Genetic mapping of clock genes in different regions of the brain and peripheral organs will be used to identify clocks that are most affected during obesity, so that these clock structure may be directly targeted in vivo (in animal) or in vitro (excised tissue cultures). In vivo targeting will employ elegant genetic modification of mice, such that the clock has been removed or accelerated (20hr vs 24hr) selectively within the brain, specific regions of the brain, or in peripheral organs. This will allow me to investigate how tissue clocks interact with each other to dictate metabolic rhythms. In vitro studies will target the mechanisms by which the clock is connected to and regulates metabolic functions within a model tissue (e.g. fat storage/breakdown in white adipose tissue) by manipulating specific components (e.g. REV-ERBa) or properties (e.g. speed) of the clock pharmacologically. My preliminary data suggests that the circadian clock gene REV-ERBa represents a critical connection point between the clock and metabolic pathways. Mice lacking this gene are obese, exhibit dampened metabolic rhythms, and remarkably show no clock gene rhythms in white adipose tissue. Finally, I will examine whether pharmacological strengthening of the circadian system can improve the metabolic consequences of obesity.

This application investigates the coupling of metabolism to the circadian clock, and will define how central brain timers and peripheral body clocks interact to govern overall energy homeostasis. We now know that the circadian clock is tightly coupled to cellular metabolism and energy supply, and that dysfunction of our circadian timing systems contributes to many disease states, including metabolic disease. However, we do not know how the clock orchestrates metabolic processes on a whole organism level or how the circadian control over metabolism is lost in metabolic disease. The overall hypothesis of this proposal is that the disconnection of central and peripheral clocks is a critical factor in the development of obesity and metabolic disease. Preliminary data suggest that the clock gene REV-ERBa is a key interface point of the clock and energy metabolism, and is critical to white adipose tissue (WAT) rhythmicity. I will therefore use elegant transgenic mouse models to desynchronise brain and peripheral clocks, knockout REV-ERBa globally, and remove the clock specifically in WAT. These mice will be challenged with high fat diet, and subject to comprehensive in vivo behavioural and physiological analysis. I will then use primary adipocyte cultures to dissect the interconnection of clock and metabolic (lipogenic/lipolytic) pathways by modulating the inherent properties of the clock and specifically targeting Rev-erb. Finally, I will examine whether pharmacological entrainment of circadian clocks is effective at attenuating circadian and metabolic disruption in obesity.

The research questions posed within this proposal are of major interest to ACADEMIC GROUPINGS in Biological and BioMedical Sciences. The academic community will benefit from elucidation of novel mechanisms whereby metabolic factors interact with the circadian clockwork on a molecular and anatomical level. Examination of the adverse effects of disrupted clock function on metabolism, and whether targeting the clock represents a potential avenue for treatment of obesity and related disorders presents clear translational application to human health and welfare. As such, research findings will impact greatly on the HEALTH CARE COMMUNITY. I will disseminate findings by publishing primary papers and reviews in high impact journals, and presenting work at national and international meetings. I have published regularly (15 papers since 2005) and spoken at numerous national and international meetings (11 selected or invited seminars since 2005). I anticipate that the proposed work will produce 3-6 high-quality primary research papers. All findings will be of high interest to the GENERAL PUBLIC due to the prevalence of obesity and 24hr lifestyles in our modern society. At its most basic, the work will engage sections of the populous who wish to learn about their health and human physiology. My research also has realistic potential to inform the general public about how dietary habits (what you eat and when you eat it) may detrimentally affect health. My research findings will be delivered to the general public through public engagement activities (e.g. brain awareness week), as well as through mass media. For example, my recent (joint first author) article in PNAS (re-entrainment of disrupted clocks) was reported widely in national and international newspapers, on local radio, and on the intranet following press releases issued by the University of Manchester and BBSRC. The proposed research is of major interest to PHARMACEUTICAL COMPANIES due to direct implications for human metabolic disease. Pharmaceutical industry investment into circadian biology is rapidly growing due to the fact that circadian dysfunction has been linked to sleep disorders, mental health disorders, cancer, inflammation, and aging. I am already involved in collaborations with Pfizer and GSK on circadian-related projects, and regular communication with these companies will ensure research findings are taken-up by and impact upon industrial beneficiaries. The Faculty of Life Science at Manchester has taken a strong proactive role in developing links with major pharmaceutical companies, enhancing public communication of science, as well as identification and development of commercialisation opportunities. There are dedicated members of staff employed within the Faculty to assist in these areas. Benefits of this research to the UK ECONOMY are neither immediate nor guaranteed. However, obesity and related disorders (cardiovascular disease, diabetes etc) are, and will continue to be, a massive burden on the national health care service. This will only increase with the aging population, in which circadian and metabolic disturbance is common. Thus, future economic benefits may be substantial. This proposal also offers a unique and significant opportunity for high level in vivo training of the associated post-doctoral scientist, and any PhD students joining for related work. This is a significant benefit as a lack of in vivo research training has been highlighted as a weakness in UK bioscience. Numerous undergraduate and Master's degree students will be exposed to my research and gain valuable research skills through lab based projects. Finally, I will be a primary beneficiary of the proposed funding. The line of work and techniques that I have set out for this fellowship will elevate my research to the highest level, and facilitate my development into an internationally recognised leader in the field of circadian biology.