The central hypothesis of this proposal is the circadian molecular clock is required for normal-cell function and its disruption leads to -cell failure . Circadian rhythm perturbations have been associated with human disease, such as metabolic syndrome and diabetes. It is, therefore, imperative to understand the interaction between the circadian clock and -cell function. The molecular machinery driving circadian rhythm (the circadian clock) is composed of a set of interlocking molecular feedback loops resulting in cascades of gene expression with 24 hour periodicity. At its core is the transcription factor complex of Bmal1 and Clock that activates expression of negative regulators that inhibit Bmal1/Clock activity, thus forming a feedback loop. The central clock in the suprachiasmatic nucleus (SCN) and peripheral clocks in each tissue regulate the circadian oscillations of many metabolic processes. Furthermore, disruption of various core clock components results in metabolic disturbances in mouse models. Though -cells express core clock genes, their role in the pathophysiology of -cell failure and diabetes is unknown. The rationale for our hypothesis stems from the metabolic phenotype of global Bmal1 Knockout (Bmal1 KO) mice which lack a functional clock and exhibit glucose intolerance without insulin resistance, but are hypoinsulinemic. This combination, confirmed and extended by our preliminary data demonstrating impaired glucose stimulated insulin secretion (GSIS) and progressive diabetes in global Bmal1 KO mice, strongly suggests disruption of the circadian clock causes - cell failure. The broad goal of this proposal is therefore to test the hypothesis that the molecular clock is necessary for normal -cell function by comprehensively analyzing glucose homeostasis and -cell function in Bmal1 KO mice.
The Specific Aims are: 1. Determine if disruption of the molecular clock in Bmal1 KO mice causes -cell failure in vivo by assessing whole body glucose homeostasis and -cell phenotype in Bmal1 KO mice in 12 hr light/dark and dark/dark cycles and testing -cell stimulus-secretion coupling. We will assess -cell mass, function and glucose homeostasis in HFD challenged Bmal1 KO mice to decipher the role of Bmal1 in -cell compensatory ability. 2. Determine the differential roles of the central and peripheral clocks in -cell function by creating -cell specific Bmal1 KO mice and compare their glucose homeostasis and -cell function with global Bmal1 KO mice. 3. Identify the molecular mechanisms that link circadian clock function with -cell function and test the proposed regulatory pathway: Bmal1-Nampt-NADSirt1- Ucp2. We will assess changes in expression of genes involved in stimulus-secretion coupling and perform ex vivo and in vitro rescue studies targeting glut2, glucokinase, Sirt1 and UCP2. In summary, we present data highlighting the novel role of the circadian clock in -cell function by demonstrating that disruption of the Bmal1 causes -cell failure and diabetes. Understanding the interaction between the molecular clock and -cell function will help develop novel strategies to prevent and treat -cell failure and diabetes.
Circadian rhythm perturbations in humans have been associated with metabolic syndrome and diabetes with recent genome-wide association studies specifically implicating circadian genes in -cell function and diabetes. With compelling data highlighting the novel role of the circadian clock in -cell function by demonstrating that disruption of the circadian clock in mice causes -cell failure and diabetes, we propose to identify and dissect the molecular mechanisms that link circadian clock function with -cell function. This understanding will help develop novel therapies that could prevent and reverse -cell failure and diabetes.
