MICA Cryo-chronobiology: how do cold-inducible chaperones maintain neural clock function under brain temperature fluctuation?

Biological clocks are fundamental to life, adapting us to predictable changes in our environment. Disruption of these clocks occurs in several brain disorders including dementia - a leading cause of death in the UK. Understanding how clocks work means that we can control them; a fresh strategy to tackle some of our most complex global health challenges. At the molecular level, feedback loops support daily 'circadian' rhythms in cell function throughout the body. The 24-hour cycle of these rhythms is resistant to temperature variation, ensuring that cellular clocks do not speed up or slow down at different body temperatures. Remarkably however, cellular clocks synchronize to daily changes in body temperature, which means they must sense and respond to temperature shift. This 'temperature paradox' of the clockwork remains unexplained, especially for the brain where nerve cell activity produces rapid changes in brain temperature. What then keeps our brain cell clocks ticking robustly as brain temperature changes? Circadian rhythms and responses to cold are critical cellular functions that have been retained throughout evolution. Cold-inducible chaperones (CICs) are highly active proteins at cold temperatures; they safeguard the manufacture of key cellular proteins under conditions that would normally halt protein production. CICs do this by binding to messages transcribed from the DNA in each of our cells so that these messages can be translated into proteins that are critical for cell survival, including components of the clockwork. CIC activity also cycles in a circadian manner, responding to daily changes in body temperature. I propose that CIC-clock protein interactions are critical to timekeeping in brain cells. I will test whether these interactions are required to maintain brain cell clock function as brain temperature changes. Data from patients with brain injury show that, like body temperature, human brain temperature cycles with a 24-hour rhythm. However, brain and body temperature are not the same, and we need to know what happens in the healthy brain. In collaboration with Edinburgh Imaging, I will use a non-invasive MRI scan technique to map brain temperature in healthy volunteers at different times of the day. In parallel, I will monitor brain temperature cycles in mice remotely using radio transmitters. These experiments will establish normal human brain temperature ranges, and separate the effects of circadian and sleep-wake cycles on brain temperature rhythms. Experiments in Cambridge will then determine the impact of CIC versus clock protein disruption on brain cell circadian rhythms under simulated brain temperature cycles. The brain cell clock will be characterized 'in a dish' by tagging CIC and clock proteins with luminescent reporters in brain cells grown from human stem cells. This will make it possible to monitor the cyclic abundance of CIC and clock proteins in real time over several days at different temperatures, and during transitions between them. CIC and clock proteins will then be manipulated so that they are trapped in different parts of the cell and can no longer interact with each other. This 'trapping' will be entirely reversible such that CIC-clock interactions can be switched on or off during temperature shifts, to see what effect this has on clock function. Finally, radio transmitter experiments will be repeated in mice carrying genetic mutations in CIC and clock proteins. This work will establish a basis for modulating CIC-clock interactions in human cellular models of dementia and other chronic brain disorders. I predict that boosting CIC activity will protect and restore clock function in vulnerable brain cells. The results could ultimately lead to new treatments for a range of disorders in which circadian rhythms are disrupted, and also new ways to manage our 'circadian health' in the modern world.