Shift work cycle-induced alterations of circadian rhythms potentiate the effects of high-fat diet on inflammation and metabolism.

Based on genetic models with mutation or deletion of core clock genes, circadian disruption has been implicated in the pathophysiology of metabolic disorders. Thus, we examined whether circadian desynchronization in response to shift work-type schedules is sufficient to compromise metabolic homeostasis and whether inflammatory mediators provide a key link in the mechanism by which alterations of circadian timekeeping contribute to diet-induced metabolic dysregulation. In high-fat diet (HFD)-fed mice, exposure to chronic shifts of the light-dark cycle (12 h advance every 5 d): 1) disrupts photoentrainment of circadian behavior and modulates the period of spleen and macrophage clock gene rhythms; 2) potentiates HFD-induced adipose tissue infiltration and activation of proinflammatory M1 macrophages; 3) amplifies macrophage proinflammatory cytokine expression in adipose tissue and bone marrow-derived macrophages; and 4) exacerbates diet-induced increases in body weight, insulin resistance, and glucose intolerance in the absence of changes in total daily food intake. Thus, complete disruption of circadian rhythmicity or clock gene function as transcription factors is not requisite to the link between circadian and metabolic phenotypes. These findings suggest that macrophage proinflammatory activation and inflammatory signaling are key processes in the physiologic cascade by which dysregulation of circadian rhythmicity exacerbates diet-induced systemic insulin resistance and glucose intolerance.-Kim, S.-M., Neuendorff, N., Alaniz, R. C., Sun, Y., Chapkin, R. S., Earnest, D. J. Shift work cycle-induced alterations of circadian rhythms potentiate the effects of high-fat diet on inflammation and metabolism.