Daily rhythmicity in rat white adipose tissue

The circadian timing system is of key importance to metabolic health. Circadian disruption by shift work or (social) jetlag is correlated with an increased prevalence of obesity and related metabolic disturbances like diabetes mellitus type 2. White adipose tissue (WAT) plays a central role in regulation of energy homeostasis, however it was largely unknown how daily gene expression rhythms are regulated in WAT.
The studies described in this thesis improve our understanding of how daily gene expression rhythms in rat white adipose tissue are regulated. We found that clock gene rhythms in WAT do not fully depend on the central brain clock (suprachiasmatic nuclei; SCN), although the SCN do contribute to phase synchronization and increases the amplitude of its daily rhythmicity. Furthermore, clock gene rhythms in WAT do not solely depend on adrenal hormones or the daily feeding rhythm, but at least one of these signals should be present to maintain WAT gene expression rhythmicity.
We discussed that light could influence clock gene rhythms in WAT via multiple pathways; the SCN, central pathways not involving the SCN, via the skin or even directly at the level of the adipocyte. However, in absence of a rhythm in adrenal hormones and food intake, the light dark cycle cannot maintain rhythmicity in WAT. Furthermore, we discussed autonomous clocks may sustain a degree of tissue rhythmicity in absence of the SCN. However, in absence of both adrenal hormones and the daily rhythm in food intake, autonomous clocks in WAT cannot maintain rhythmicity for extended periods.