Circadian Clock and Beta Cell Stress Adaptation

描述(申请人提供)：昼夜节律紊乱，现代生活方式的祸害，一直与糖尿病和代谢综合征密切相关。最近的人类研究还表明，b细胞功能障碍是代谢异常的一个重要组成部分。因此，有必要了解生物钟和细胞功能调节之间的相互作用，以保存胰岛素分泌，预防糖尿病。我们之前已经证明，在小鼠中，生物钟的遗传破坏，通过缺失一个非冗余的核心时钟基因BMal1，会导致？细胞衰竭和糖尿病，继而导致葡萄糖刺激的ATP产生受损、OXPHOS解偶联和葡萄糖刺激的胰岛素分泌受损(GSIS)。然而，细胞的适应性应激反应是否需要内在的细胞时钟尚不清楚。在初步研究中，我们证明了轮班工作模拟引起的中枢时钟干扰，BMal1基因的表型破坏在引起未折叠蛋白反应(UPR)，促凋亡基因CHOP上调，提示不可修复的内质网应激 -细胞，并伴有GSIS受损。重要的是，B细胞中BMal1基因缺失的小鼠会因为B细胞功能衰竭而患上糖尿病。令人惊讶的是，缺失REV-ERBα，一个时钟功能的负调节基因和一个BMAL1靶基因，会导致类似的未折叠蛋白反应(UPR)的诱导。我们还发现，参与UPR的关键转录因子ATF4在表达上表现出昼夜节律性，是BMal1的直接转录靶点。因此，我们假设内在的？细胞时钟调节因子BMAL1和REV-ERBα通过对其关键成分的转录控制来协调适应性UPR通路，以减轻内质网应激。我们的主要目标是通过分子时钟的遗传、环境和药物调节来描绘内质网应激诱导的ç细胞功能障碍中关键的昼夜节律时钟调节通路。我们将具体地1.测试昼夜节律的干扰是否足以引起内质网应激和？细胞衰竭b解剖中枢和外周时钟对内质网应激和？细胞功能的不同作用。我们还将确定分子时钟在ER应激中的细胞自主作用2.确定BmAL1和REV-ERBα在UPR和ER应激中的转录靶点；3.测试生物钟是否调节人胰岛的ER应激适应反应和胰岛素分泌反应。我们还将测试分子时钟的药物调节是否可以挽救糖尿病患者胰岛的适应性应激信号。总之，拟议的研究将关键地解决分子时钟如何调节内质网应激和？细胞内稳态，并将导致对？细胞中昼夜节律调节的适应性应激途径的新见解。我们预计，这项研究的结果将导致发现有针对性的治疗方法，以调节生物钟功能，从而在抗击糖尿病的过程中保持？细胞功能。

DESCRIPTION (provided by applicant): Circadian disruption, the bane of modern lifestyle, has been strongly associated with diabetes and metabolic syndrome. Recent human studies also implicate b-cell dysfunction as a significant component of the metabolic abnormalities. It is, therefore, imperative to understand the interaction between the circadian clock and regulation of ß-cell function for the preservation of insulin secretion to prevent diabetes. We have shown previously that genetic disruption of the circadian clock, by deletion of Bmal1, a non-redundant core clock gene, in mice, leads to ß-cell failure and diabetes, secondary to impaired glucose-stimulated ATP production, uncoupling of OXPHOS and impaired glucose-stimulated insulin secretion (GSIS). However, whether the intrinsic ß-cell clock is required for adaptive stress responses in ß-cells is unknown. In preliminary studies, we demonstrate that central clock disruption induced by shift work simulation, phenocopies genetic disruption of Bmal1 in ß-cells in inducing Unfolded Protein Response (UPR), upregulation of the pro-apoptotic gene CHOP, suggestive of irremediable ER stress in ß-cells, and is accompanied by impaired GSIS. Importantly, mice with a deletion of Bmal1 in ß-cells become diabetic due to ß-cell failure. Surprisingly, deletion of Rev-erbα, a negative regulator of clock function and a Bmal1 target gene, leads to similar induction of unfolded protein response (UPR) in ß-cells. We also show that ATF4, a key transcription factor involved in UPR, displays circadian rhythmicity in expression and is a direct transcriptional target of Bmal1. We, hence, hypothesized that intrinsic ß-cell clock regulators, Bmal1 and Rev-erbα, coordinate the adaptive UPR pathway, through transcriptional control of its key components, to mitigate ER stress. The broad goal is to delineate key circadian clock-regulated pathways in ER stress-induced ß-cell dysfunction through genetic, environmental and pharmacological modulation of the molecular clock. We will specifically 1. Test if circadian disruption is sufficient to induce ER stress and ß-cell failure b dissecting the differential role of the central and peripheral clocks on ER stress and ß-cell function. We will also determine the cell-autonomous role of the molecular clock in ER stress in ß-cells 2. Define the transcriptional targets of Bmal1 and Rev-erbα in UPR and ER stress in ß-cells and 3. Test if the circadian clock regulates ER stress adaptive responses and insulin secretory response in human islets. We will also test if pharmacological modulation of the molecular clock can rescue adaptive stress signaling in diabetic patient islets. Collectively, the proposed studies will critically address how the molecular clock regulates ER stress and ß-cell homeostasis and will lead to novel insights into circadian clock regulated adaptive stress pathways in ß-cells. We envision that the results from this study will lead to discovery of targeted therapies to modulate circadian clock function for the preservation of ß-cell function in combating diabetes.