The role of circadian mechanisms in migraine-related pain

Migraine is a complex condition of uncertain cause that typically intensifies during the mid-20 to 60's, significantly impacting sufferers during their most productive years. With an incidence of up to 1 in 5, especially in females for whom it is three times more likely, migraine is the 6th most disabling disorder globally. Many sufferers report specific attack timing, most commonly in the early morning, highlighting the importance of our body's daily (circadian) rhythms. We do not have the medications to prevent migraine as current therapies are either ineffective or poorly tolerated in the majority of cases. Finding more effective drugs is complicated by the lack of knowledge of the underlying brain mechanisms that lead to this enhanced migraine susceptibility. By generating this information we could enhance treatment options and identify basic lifestyle interventions to lighten the burden of migraine with potential impact across several pain disorders.
Increasing evidence from clinical and basic scientific research suggests that disruption of our internal body clocks, for example during jetlag, shift work or sleep disruption, plays a significant role in migraine triggering. There is much enthusiasm for the idea that proteins in our brains that help to set our circadian rhythms, including sleep-wake cycles, are linked to our lifelong health and wellbeing. Much of this interest in migraine comes from a circadian disorder where sufferers feel excessively sleepy and go to bed early and awaken very early in the morning (03.00). Remarkably, the majority of these extreme morning larks suffer from migraine with aura: repeated bouts of severe pain and associated symptoms including visual flashing lights. However, to really know the reason behind this association and the impact of disrupted circadian rhythms we need to enhance our basic knowledge of the underlying mechanisms. It is possible to measure and modulate these circadian rhythms in mice and thus we have developed several techniques to measure the migraine-related susceptibility and pain sensitivity of mice. We will use these detailed methods to give a decisive yes or no to the question of whether disrupted circadian rhythms impact on migraine-related pain and further identify their relevance in chronic pain states. The combination of these factors has never been applied to preclinical migraine models.
We also want to know what the underlying mechanisms are that might cause this association between circadian disruption and migraine. There is a good case that some form of the association results from abnormal pain processing in the brain. Chemical messengers signalling head pain to the brain (neurotransmitters) activate specific brain regions. These regions are abnormally active in the mice generated to carry the human cause of this combined circadian disruption and migraine. We will further test this using sensitive pain threshold techniques and by measuring the levels of specific proteins that respond to these neurotransmitters (glutamate). We will detect if there are problems in how the brain releases and responds to glutamate, identifying potential therapeutic targets for future research.
Finally, we want to know if acute alterations in our daily rhythms can predispose individuals to attack triggering, either directly or by indirectly reducing the thresholds for other factors to have their effect. For example we can use modulation of light-dark cycles to model jetlag in mice and measure if this renders them more susceptible to migraine-related pain. We can further measure how changes in localised circadian clocks can impact on local physiology and therefore may provide targeted opportunities for future research and therapeutic development.
The results are potentially game-changing and could point the way for lifestyle changes and new drug treatments for migraine while re-invigorating the interest of industry in developing new treatments for migraine and chronic pain.

This proposal will identify if dysregulation of circadian regulation impacts directly or indirectly on migraine susceptibility specifically, and chronic pain more generally. The role of circadian genes, their respective proteins, and downstream mechanism including altered glutamatergic signalling, will be investigated. Regional brain measurements will identify if local clocks influence migraine-related pain and cortical excitability leading to enhanced cortical spreading depression (CSD), the experimental correlate of migraine aura. CSD thresholds, head pain trigeminal nociceptive thresholds and trigeminal nociceptive activity (c-Fos) will measure migraine susceptibility. These results will indicate how the underlying pain processing trigeminovascular system is altered in transgenic mice harbouring a human circadian sleep disorder mutation that is comorbid with migraine with aura and the impact of experimental alteration of light-dark cycles as a model of jetlag. Specific mechanisms will be investigated using immunocytochemistry and biochemistry to detect alterations in clock genes (e.g., Per2, Clock & Bmal1), their respective protein products, glutamatergic signalling (e.g., phosphorylated NR1/NR2B NMDA receptor subunits & Eaat1) and important kinases (Casein kinase 1delta/epsilon). This proposal will identify novel knowledge regarding the circadian rhythm of migraine biology and will confirm or refute the role for altered circadian regulation in migraine triggering and other pain disorders. If refuted, efforts will be concentrated on the underlying mechanisms of disruption leading to the comorbidity of familial advanced sleep phases and migraine. Either way, this will open up new avenues for the development of targeted lifestyle interventions and pharmacological therapy to treat this disabling neurological disorder.

This proposal focuses on understanding the relevance and underlying mechanisms of circadian rhythms and their disruption in migraine and other pain disorders. The generation of new knowledge identifying key mechanistic targets is critical and as such the work outlined in this proposal will directly impact a number of key groups.

1) The Public. Migraine is the 6th most disabling condition in the world affecting up to 20% of the population. Because of its complexity current therapies are either ineffective or poorly tolerated in the majority of cases, thus highlighting the urgent need to develop new therapeutic targets. This will only be realised through increased knowledge of the fundamental mechanisms leading to attack triggering that will be identified in this proposal. Through public dissemination, including biannual involvement in patient awareness days via the Migraine Trust and British Association for the Study of Headache (BASH), this work will provide the public with fundamental knowledge and lifestyle information. Moreover, upon completion of this work researchers and pharmaceutical companies will be able to identify novel therapeutic targets. The development of which will directly impact patients and their families by significantly improving their quality of life.

2) Clinical practitioners. Whilst this work is a basic, preclinical study, results from the project will help to guide clinicians in the potential therapeutic value of circadian regulation, including lifestyle factors. Upon completion of these studies we will have a greater understanding of the impact of disrupted circadian rhythms (e.g., shift work and jetlag) on disease mechanisms. Moreover, as these studies are largely based on human mutations known to impact migraine, the studies will provide a solid basis from which translational studies can be proposed. This impact will be optimised via targeted dissemination through existing and relevant new networks: The PI regularly presents at educational days for GP's and Neurologists, including recently in London and Newcastle for BASH and has direct access to local and International clinical collaborators (e.g., involvement in European consortia, EUROHEADPAIN).

3) Pharmaceutical companies. The PI has long standing collaborations and interactions with the pharmaceutical companies interested in migraine and other disorders. Current collaborations include Eli Lilly, Amgen and Allergan for which the PI regularly conducts educational talks and participates in discussion forums. Specifically, the proposal will benefit from the well characterised mechanisms of circadian regulation to identify specific circadian-related molecules that can be targeted for translational research in migraine and other pain disorders.

4) Government and policy makers. Treatment of migraine disorders alone costs in excess of £150 million per annum in the UK with 25 million lost work and school days. Results from this study will generate increased knowledge that will direct strategies for novel therapeutic targets to reduce the burden of disease. This increased understanding will enable improved strategies allowing sufferers to return to and engage more effectively in work and school, with resultant economic and educational impact. Specific avenues to realise this impact already exist via the PI's involvement in the All Party cross Parliamentary Group on Primary Headaches and council membership of BASH with regular input to the National Institute of Clinical Excellence guidelines.

5) Staff development. As part of the proposal the named research assistant will be enrolled as a part-time PhD student, enhancing her academic and non-academic employment opportunities.