Daily organisation of cellular physiology by mTOR kinase
Circadian rhythms are self-sustained biological oscillations with a period of approximately 24 hours. They are observed across all levels of biological scale and organise physiology to accommodate the different environmental and energetic demands of day and night. In mammalian cells, the mechanistic target of rapamycin complex (mTORC) activity exhibits daily rhythms both in vivo and in cultured cells. Circadian rhythms are sensitive to changes in mTORC activity, moreover, many circadian-regulated process are directly or indirectly sensitive to changes in mTORC activity e.g., protein synthesis and macromolecular crowding. In my research I have sought to gain insight into the nature of the interaction between circadian regulation and mTORC signalling, in vitro and in vivo.
My lab previously observed reciprocal circadian rhythms in the abundance of soluble proteins and ions, which function to maintain cellular osmotic homeostasis and are dependent on mTORC activity. In the first part of this thesis, I explore the consequences of osmotic perturbation on circadian rhythms, and find that acute osmotic perturbations modulate circadian rhythms via mTORC. Next, I sought to understand the generation and function of cell-autonomous soluble protein, and functionally characterise them by quantitative proteomics and phosphoproteomics. I find that, in both cultured cells and in mouse liver, soluble protein rhythms are modulated by mTORC activity.
Through pharmacological inhibition of mTORC1 and 2 I explore how circadian regulation of physiological outputs, such as wound healing, is mediated by mTORC activity, as well as the effect of mTORC inhibition on circadian timing in vitro and in vivo. Taken together, this work points to a model where rhythmic mTORC may be sufficient to modulate signalling to and from the circadian timekeeping machinery to drive most rhythmic physiological outputs, both in vitro and in vivo.