Investigation of the role of calcium in circadian rhythms

Virtually all aspects of our physiology and behaviour display 24-hour variations, driven by a circadian clock, which can be found every cell of our body. In mammals, the master clock is present in the brain, which receives light information from the eye and relays it to other tissues in the body to synchronise biological processes with the 24h environmental light-dark cycle. Examples of processes regulated by the clock include the sleep-wake cycle, the regulation of hormone secretion and body temperature and also more complex processes such as cognition and memory formation. Given the importance of clock in regulating large swathes of physiological processes, it's not surprising that disruption of the circadian clock leads to various disorders ranging from diabetes to mood disorders.

Whilst there has been great progress in the identification of key proteins involved in the generation of circadian rhythms, we are much further behind in our understanding of how cellular signalling processes influence the circadian clock at the molecular level. Environmental information, such as the time of day are communicated to the molecular clock by signalling mechanisms and an understanding of these mechanisms holds the key to developing drugs that may be used to target the clock.

In this application we propose to explore the role of calcium, arguably the most ubiquitous cellular signalling messenger, in regulating circadian rhythms. Calcium signalling plays a major role in regulating how and when genes are turned on and off in response to environmental stimuli in nearly all systems including the heart and brain. Our preliminary work shows that calcium is likely to play a fundamentally important role in the regulatory networks underlying circadian rhythms, and by extension, biological rhythms in all cells. We propose to build upon these findings and conduct a detailed investigation on the role of calcium and the signalling pathways by which it modulates the core molecular clock.

In mammals, almost all cell types contain a functional molecular clock and these individual clocks are held in synchrony by a master clock in the suprachiasmatic nucleus (SCN), contained in the hypothalamus. The molecular circadian clock comprises of cell autonomous transcriptional networks with auto regulatory feedback loops, consisting of the transcriptional drivers CLOCK and BMAL1 and the repressors of transcription PER and CRY. While there has been remarkable progress in identifying core clock proteins and feedback loops regulating these proteins, research on how cellular signalling processes affect circadian rhythms is still in its infancy.

Here I propose to test the hypothesis that calcium, a ubiquitous signalling molecule, along with its signalling toolkit, forms a key component of the circadian machinery. This hypothesis builds upon the finding that messengers such as cAMP and calcium show a robust 24-h rhythm within the SCN and that modulating calcium in turn affects circadian rhythms. However, there exist no reports of a role for calcium in regulating circadian rhythms non-neuronal cells. Given that circadian rhythms are cell autonomous processes, if calcium were a key component of the circadian machinery, such regulation should be ubiquitous and not restricted to the SCN. My preliminary findings show that this is indeed the case, where we find robust 24-h calcium rhythms in quiescent human cell lines such as the U2OS osteosarcoma cell line. In this application I propose to conduct a detailed investigation on the role of calcium in modulating circadian rhythms in peripheral and cellular clocks and by extension, the consequences of modulating calcium signalling mechanisms on the molecular clock.

The findings from this proposal will significantly add to our understanding of the regulatory networks underlying biological rhythms and provide the mechanistic substrate with which clock-based interventions could be developed in the future.

The main deliverables from this work include 1) The mechanistic understanding of the role of calcium in regulating the molecular clock. This will provide the substrate with which to develop interventions targeting the circadian network. 2) The identification of specific signalling pathways that converge on the circadian clock. These findings will increase our understanding of the regulatory networks underlying biological rhythms, and provide tangible outputs that will find application in disease areas where circadian disruption is implicated. These include obesity, diabetes, cardiovascular disease, mental health disorders and cancer, which together cover the top 3 spending areas of the NHS and cost the economy over £100 billion. These disorders are also the major factors underlying a substantially shorter healthspan in comparison to lifespan.
This findings from this research will directly benefit
1) Academic labs researching disease mechanisms in the above areas as well as those interested in calcium and calcium signalling and circadian rhythms.
2) Pharmaceutical and biotech industries as well as academic drug discovery initiatives working on sectors where circadian disruption is implicated and where an understanding of the mechanisms regulating the clock could be translated. These include metabolic disease, oncology and mental health disorders.
3) The healthcare sector, as these findings can underpin the development of new therapeutics to treat chronic and debilitating conditions as discussed above. This information will be disseminated by dedicated outreach wings of the University, and also via workshops, roadshows, television and press releases, etc.

In terms of staff development, I will gain a platform to develop as a new PI. The Post-doctoral research assistant on this program will gain research skills and technical expertise, which would be applicable in the wider fields of pharmacology, cell and molecular biology research. In addition, they will gain skills in writing, presentation and project management, which would be of benefit in all employment sectors.