Abstract
Adipose tissues fulfil functions of energy storage and hormone secretion, many of which exhibit daily variations. Literature showed that approximately 20% of the murine adipose transcriptome exhibits daily oscillations, with 2-4% of the transcriptome rhythmic in constant conditions; in humans and mice. A disruption of circadian rhythms is associated with metabolic disturbances such as obesity and metabolic syndrome, highlighting the importance of understanding mechanisms of circadian metabolism. Published work identified energy substrates as biomarkers of insulin resistance and glucose intolerance in humans; hallmarks of obesity and diabetes, with unknown utilisation dynamics in vitro within adipocytes. My thesis aimed to provide a clearer view on circadian adipose biology using molecular, electrophysiological and metabolic approaches. I tested the hypotheses that an endogenous oscillator within pre-adipocytes was driving rhythmic utilisation of carbon sources involved in key metabolic pathways, that electrophysiological parameters in pre-adipocytes exhibited biological variations, and that bioluminescence rhythms of clock genes showed a reduced amplitude and faster damping in adipocytes in comparison to pre-adipocytes. Using 3T3-L1 pre-adipocytes, circadian rhythms of glucose utilisation were confirmed, with an acrophase for the first time demonstrated as similar or anti-phasic to an array of other carbon-based sources utilised in a circadian fashion. Other substrates exhibited steady-state utilisation patterns. Dielectrophoresis potential enabled the determination of circadian rhythms in cellular membrane capacitance, whilst membrane conductance exhibited rhythms of a shorter period. Finally, persistent anti-phasic circadian rhythms of bioluminescence driven by the promoters of Per2 and Bmal1 were characterised in pre-adipocytes and adipocytes, with Per2 pre-adipocytes presenting a higher amplitude than their adipocyte counterpart. These data provide novel understanding of adipose circadian biology, especially revealing circadian rhythmicity of intermediates in key metabolic pathways strongly linked to the development of metabolic diseases. These findings could help explain metabolic pathways disruptions in obesity and related pathologies.