15 BEDREST Effects of bed rest on the circadian organisation of the human transcriptome as a model for temporal dysregulation in an ageing population

Circadian (about a day) rhythms in behaviour and physiology synchronise our activity to the outside world. The importance of robust, well-synchronised circadian rhythms is evident from the negative effects experienced during jet lag or sleep deprivation, and also disruption of sleep and circadian rhythms that occurs during spaceflight. The strength and the timing of circadian signals become reduced and disrupted during spaceflight and ageing and may account for many changes observed with sleep/wake activity in astronauts and the elderly. Circadian clocks around the body regulate most physiological processes such as metabolism, cardiovascular function, and the immune system and both long duration spaceflight and ageing may disrupt the circadian regulation of these processes and be associated with related negative health outcomes.

Circadian clocks also regulate hormones such as melatonin (which peaks in the night) and cortisol (which peaks on awakening). Cortisol is an important circulating signal that regulates the expression of many genes, including those that make proteins involved in immunity and inflammation. Cortisol secretion is also disrupted during spaceflight and ageing and could change the regulation of the expression of many genes.

Blood circulates around the body and is increasingly viewed as a 'window' on the whole-body state. For example, blood biomarkers are now used to diagnose and to monitor disease progression in many different diseases ranging from Alzheimer's to cancer. Temporal organisation in the expression of genes to make proteins is important - certain proteins need to be made at particular times of day or night - and in any given tissue around 6-10% of all genes are expressed with a circadian rhythm, including in blood. In two separate human studies, we have shown that one-week of insufficient sleep or mistimed sleep (as occurs in jet lag) leads to dramatic disruption (both timing and amplitude) to the circadian rhythms of blood gene expression. This included disruption to genes normally expressed during the day (immune response, inflammation, oxidative stress) and those normally expressed during the night (regulation of protein synthesis), as well as core clock genes central to the generation of circadian rhythmicity itself.

Spaceflight and its bed rest model result in circadian disruption to melatonin and cortisol. This circadian disruption likely extends to the temporal disruption of gene expression in blood, although nobody has investigated this to date. Thus, during bed rest there is disruption to circadian signals, elevated circulating cortisol, changes in blood circulation, changes to cardiovascular function, including suppressed immune function, all of which are also found in ageing. Therefore, many of the negative health effects found in astronauts and the elderly could be directly associated with temporal disruption to the circadian regulation of gene expression in blood. The main aim of the research proposed here is to perform a careful study of gene expression in blood of people who are undertaking a bed rest protocol. By comparing a series of blood samples collected through the day and night at different stages during the bed rest period with similar timed samples collected at baseline and during recovery, we will be able to identify networks of genes whose disruption affects specific biological processes, which may include the immune system and other processes not yet shown to be affected by bed rest. It is difficult to study these effects directly during long duration spaceflight or during ageing over extended time periods and the bed rest protocol provides a practical means to explore changes in defined laboratory conditions. It is assumed that bed rest models ageing and we will also use this model to assess the methodological aspects of whether blood sampling is a viable approach to monitor effects of temporal disruption in ageing and to assess the effects of countermeasures.

Circadian rhythms regulate gene expression and physiology. They are synchronised by external light-dark cycles and sleep/wake cycles, including posture changes. Biological processes are optimal when circadian rhythms are robust and synchronised with light-dark and behavioural cycles. Disruption of circadian rhythms is associated with obesity, diabetes and cardiovascular disease, and circadian signals become disrupted in ageing, which leads to altered sleep and related health problems.

We showed that disruption to sleep has large effects on the human blood transcriptome (Moller-Levet, PNAS, 2013; Archer, in revision PNAS). Overall expression was affected in genes associated with immunity, inflammation, and oxidative stress, while circadian rhythmicity was reduced in genes that regulate transcription and translation. Mistimed sleep reduced circadian transcripts by 97%. Genes that became arrhythmic included core clock genes. Thus, the overall expression levels and temporal organisation of the blood transcriptome is a 'window' into changes occurring to biological processes in response to sleep manipulation.

In bed rest the strength of the light-dark cycle and behavioural cycles (changes in posture) are reduced simulating the effects of spaceflight and ageing. Changes occur in blood composition and function, but changes to the blood transcriptome in bed rest have not been investigated. We will assess the effects on the overall expression levels and temporal organisation of the blood transcriptome of 1) a reduced light-dark cycle during baseline, 2) loss of postural changes during bed rest, and 3) regaining ambulation in recovery. Results will be compared with data collected in a second group that will receive an anti-inflammatory/anti-oxidant countermeasure. We will develop a model for the temporal disorganisation to the blood transcriptome that occur during spaceflight and ageing, and identify networks of disrupted genes and pathways that could impact upon health.

HEALTH AND WELLBEING. Many of the negative health effects that occur during spaceflight and bed rest simulations also occur during ageing. These include changes to blood functions, such as suppression of immune activity, which mimics the effects of immunosenescence that occurs in the elderly. Results from this study will provide essential data on the effects of bed rest on the temporal organisation of the blood transcriptome which can be used to model the negative effects of temporal dysregulation that occur during ageing. The results could also help to design countermeasures that could improve the health and wellbeing of the elderly.

ACADEMIC RESEARCH. Spaceflight and bed rest induce negative effects on the body that include muscle and bone loss, changes to blood circulation and cardiovascular function, and immunosuppression. Many of these effects centre on changes to the blood, which is increasingly recognised as a sentinel for changes occurring in other parts of the body. By monitoring changes that occur in the temporal organisation of the blood transcriptome during bed rest, we will provide data on changes occurring in biological processes in blood that can inform on the negative health effects experienced during spaceflight and ageing and indicate areas for possible countermeasures. These data could identify spaceflight biomarkers to monitor negative health impacts. Results from this study will be disseminated in publications, workshops, and conferences.

POLICY MAKING. The results from this study will inform on the negative health effects of spaceflight and potential areas for countermeasures, such as strengthening the light-dark cycle, and feedback from activity rest cycles. This will inform on policy decisions regarding future manned missions and recovery procedures after flight. Also using bed rest as a model for the negative effects on health seen during ageing will help health policy makers to understand better how to improve circadian signals in the elderly through environmental and behavioural alterations that can alleviate the effects of temporal dysregulation.

PUBLIC ENGAGEMENT. The applicants have experience in public engagement activities. Dr Archer was PI on a Wellcome Trust Public Engagement Award to raise public awareness of sleep and circadian research. We have experience with giving public lectures (e.g. British Science Festival, Café Scientifiques) and also with frequent interaction with the media. Our research on circadian disruption to the transcriptome and its health implications featured on the recent BBC documentary 'Trust me I'm a Doctor'. Professor Dijk holds a Wolfson Research merit award, of which public engagement is a key element. In addition, Professor Dijk already has experience of performing sleep and circadian research in ground-based studies and during spaceflight (Neurolab Space shuttle missions) in collaboration with NASA and the NSBRI. Finally, the University of Surrey is also well known for its space research (Surrey Satellite Technology, and the Surrey Space Centre). Thus, our track record in sleep research combined with our experience in public engagement and our existing links with space research (together with pro-active marketing and press offices) means that we will be able to promote the research and its results in an effective way that will have a positive impact on public awareness.

EDUCATION. The University of Surrey is research-focussed and understands the importance of integrating current research into teaching and research training. We are also active in outreach to local schools and organise interactive workshops for school visitors in many subject areas. Young people benefit from an awareness of cutting-edge topical research, which can inspire them to pursue studies and careers in science. Because of the topical and applied nature of the proposed research, we envisage that the study will feature highly in our portfolio of teaching and educational outreach.