What are the potential consequences of circadian rhythm disruption during pregnancy? (#169)
In Australia, 17% of the working population, or 1.4 million Australians, are working some form of shift work. There is strong evidence implicating shift work in the development of many chronic diseases including coronary heart disease, obesity, diabetes and other metabolic disturbances. Additionally, shift work during pregnancy has been associated with poor pregnancy outcomes including preterm birth, low birth weight and spontaneous abortion. Shift work is characterised by forced disruptions in the timing of activity, sleep and light exposure, leading to disordered endocrine, metabolic and behavioural circadian rhythms. Using animal models, we and others have examined the effect of disrupted circadian rhythmicity on reproduction. Mice that have had key circadian clock genes knocked out or mutated, leading to circadian disruption have perturbed fertility and poor pregnancy outcomes. Furthermore, exposure of pregnant rats to rapidly changing photoperiods during gestation programs disrupted metabolic homeostasis in the adult offspring. A comprehensive examination of maternal and fetal circadian rhythms during pregnancy demonstrated that exposure to changing photoperiods profoundly alters the normal circadian patterns of plasma endocrine and metabolite concentration, as well as metabolic and circadian gene expression in the mother and fetus. Furthermore, photoperiod shifts induced disruptions in the timing of food consumption and the downstream metabolic processes required to utilise that food, leading to poor maternal weight gain during early embryonic development. If these effects observed in our animal experiments also occur in humans, then exposure to altered lighting conditions and the timing of food consumption, as occurs during shift work, may have lasting impacts upon the developing baby, and predispose offspring to the development of metabolic disorders as adults.