Regulation of glucose homeostasis by prokineticin 2 signaling

描述(申请人提供)：尽管取得了巨大的进展，但长期控制2型糖尿病的高血糖仍然是一个主要的挑战。现有的控制高血糖的药理选择包括双胍类、磺脲类、噻唑烷二酮类、α-葡萄糖苷酶抑制剂、胰岛素和胰岛素类药物。这些目前的治疗方法通常与低血糖、体重增加或其他不良事件有关，如胃肠道不适、水肿、心力衰竭或骨折。新的治疗方法可以长期纠正高血糖，而不会引起不良反应，这是非常可取的。胰岛素类药物的成功支持了G蛋白偶联受体在胰岛素释放和血糖稳态中的重要性。最近，我们积累了大量证据支持原激动素2(PK2)的胰岛素抑制作用。PK2作为一种分泌型调节肽，通过激活两个同源的G蛋白偶联受体，原激动素受体1(PKR1)和原激动素受体2(PKR2)来调节多种生物学过程。PK2、PKR1和PKR2在胰岛β细胞中表达。PK2基因缺陷的小鼠降低了循环血糖水平，提高了空腹胰岛素水平，并在糖耐量试验中表现出增强的表现。给予外源性PK2可降低小鼠的葡萄糖清除能力。相反，给予小分子PK2受体拮抗剂可增强小鼠体内的葡萄糖清除。在急性分离的胰岛和类似β细胞的MIN6细胞中，PK2减少了葡萄糖刺激的胰岛素分泌，可能是通过Gi偶联途径。我们还发现，高糖处理可以诱导MIN6细胞将PK2释放到条件培养液中。我们进一步表明，高脂饮食诱导的高血糖上调了胰岛PK2的表达，表明慢性高血糖对PK2表达的动态上调可能会扰乱随后对葡萄糖负荷的胰岛素释放。综上所述，我们的初步发现表明，PK2在胰岛β细胞的功能中起到反馈的胰岛素抑制作用。我们建议进一步研究PK2信号在葡萄糖动态平衡中的作用。特别是，我们将进一步研究PK2拮抗剂对瘦小鼠和db/db小鼠口服葡萄糖的降糖作用。我们将在体外和体内研究高糖对胰岛β细胞PK2表达的动态变化。我们将进一步研究PK2信号在胰岛胰岛素释放中的作用和信号机制。最后，我们试图用PK2信号缺陷的人类受试者来验证我们的发现。这些研究的成功完成将导致验证一种新的胰岛素释放和葡萄糖稳态的信号机制。由于2型糖尿病的一个重要病理生理特征是葡萄糖对胰岛β细胞的胰岛素释放不足，因此通过小分子拮抗剂拮抗PK2来缓解PK2的胰岛素抑制作用可能为控制高血糖提供一种新的治疗途径。

DESCRIPTION (provided by applicant): Despite enormous advances, long term control of hyperglycemia for type 2 diabetes remains a major challenge. Existing pharmacological options of hyperglycemia control include biguanides, sulfonylureas, thiazolidinediones, alpha-glucosidase inhibitors, insulin and incretin agents. These current therapies are often associated with hypoglycemia, weight gain or other adverse events such as gastrointestinal discomfort, edema, cardiac failure or fractures. New therapies that can correct hyperglycemia on a long-term basis without causing adverse events are highly desirable. The success of incretin agents has supported the importance of G-protein coupled receptors on insulin release and therefore glucose homeostasis. Recently, we have accumulated substantial evidence that supports the insulinostatic effect of prokineticin 2 (PK2). PK2, as a secreted regulatory peptide, has previously been shown to regulate diverse biological processes via the activation of two cognate G protein-coupled receptors, prokineticin receptor 1 (PKR1) and prokineticin receptor 2 (PKR2). PK2 as well as PKR1 and PKR2 are expressed in pancreatic beta-cells. PK2-deficient mice have reduced circulating glucose levels, elevated fasting insulin levels, and exhibit enhanced performance in a glucose tolerance assay. Administration of exogenous PK2 was shown to diminish capabilities of glucose clearance in mice. Conversely, administration of a small molecule PK2 receptor antagonist enhances glucose clearance in mice. PK2 decreases glucose-stimulated insulin secretion in acutely isolated pancreatic islets as well as in beta-cell-like MIN6 cells, likely via Gi-coupled pathway. We have also shown that high glucose treatment induces the release of PK2 into conditioned media from MIN6 cells. We have further shown that high fat diet-induced hyperglycemia up-regulates PK2 expression in pancreas islets, indicating dynamic up-regulation of PK2 expression in response to chronic hyperglycemia may disrupt subsequent insulin release in response to glucose load. Taken together, our preliminary findings have indicated that PK2 plays a feedback insulinostatic role on the function of pancreatic beta-cells. We propose to further investigate the role of PK2 signaling on glucose homeostasis. Particularly, we will further examine the glucose-lowering effect of PK2 antagonists in response to oral glucose in lean mice as well as in db/db mice. We will investigate the dynamic change of PK2 expression in pancreas beta-cells in response to high glucose in vitro and in vivo. We will further investigate the role and signaling mechanism of PK2 signaling on insulin release with isolated pancreas islets. Finally, we seek to validate our findings with human subjects that are deficient in PK2 signaling. The successful completion of these studies will lead to the validation of a novel signaling mechanism for insulin release and glucose homeostasis. As one characteristic pathophysiological feature of type 2 diabetes is the inadequate release of insulin from pancreatic beta-cells by glucose, PK2 antagonism via small molecule antagonists to relieve the insulinostatic effect of PK2 may provide a potential novel therapeutic avenue for controlling hyperglycemia.