Integration of Feeding Time and Glucose Metabolism by the Circadian Gene Network

点击翻译按钮获取中文摘要

 DESCRIPTION (provided by applicant): The escalation in the linked epidemics of obesity and diabetes mellitus has led to intensive investigation into environmental and genetic factors that contribute to the spread of these diseases. In addition to sedentary lifestyle and overnutrition, several environmental factors associated with industrialization are now believed to be linked to the development of obesity and metabolic dysfunction, including an increase in night-time shiftwork, jetlag, sleep restriction, and late-night eating, all of which can be traced to the spred of electric light. More recently, the overuse of illuminated screens that emit blue light in eReaders are also believed to induce a persistent jetlag state. While epidemiologic studies have provided mounting evidence for circadian disruption as a risk factor for metabolic disease, this work is limited as it is primarily correlative and the mechanistic basis linking circadian disorder to metabolic pathophysiology are not well established. Transformative discoveries have been that the core clock transcription factors CLOCK/BMAL1 are present not only in master pacemaker neurons of the hypothalamus, but also with within peripheral metabolic tissues, and that mutation of the mammalian Clock gene leads to obesity and metabolic syndrome, characterized by alterations in feeding time and intake, sleep, and energy expenditure. Further, during our previous grant cycle, we established that CLOCK/BMAL1 dysfunction specifically in pancreas leads to hypoinsulinemic diabetes mellitus independently of effects of the mutation on early growth and development. With analysis of the interplay between the β-cell and brain clock as the centerpiece of our grant, we have now developed inducible genetic and genomic approaches to define the molecular regulatory mechanisms through which (i) the β-cell clock controls rhythms of endogenous glucose-stimulated insulin secretion, nutrient signaling, and triggering of vesicle release through pathways involving protein kinase C and phosphoinositide, and (ii) the brain clock coordinates feeding time with activity of hypothalamic neurons regulating energy homeostasis. Our long-term objective is to test the hypothesis that circadian disruption, and the corresponding misalignment of rhythmic genomic cycles in peripheral β-cells and liver with those of brain, contributes to metabolic disorders by impairing glucose- responsive insulin secretion and desynchronizing hepatic gluconeogenesis with the sleep/wake-fasting/feeding cycle. An innovation of our work is the integration of studies of cellular and brain clock with genomic analyses to dissect the impact of clock time on glucose metabolism. Ultimately we are now poised to uncover new insight into how the central and peripheral clocks synchronize behavioral and transcriptional rhythms to impact physiology, findings which have broad implications for the treatment and prevention of obesity, metabolic syndrome, and type 2 diabetes mellitus.