IKK2调控胰岛素分泌的机制研究

Glucose-induced insulin secretion (GIIS) of pancreatic β cells is a cornerstone of glucose homeostasis. Its impairment is requisite for occurrence of diabetes. With a focused scientific effort in the last few decades, a central dogma of GIIS has been established: Glucose metabolism produces adenosine triphosphate (ATP) and opens ATP-sensitive K+ channels (KATP channels), resulting in depolarization of plasma membrane and activation of L-type voltage-dependent Ca2+ channels (VDCC), which leads to Ca2+ influx and subsequently promotes insulin exocytosis. Recent studies, particularly those related to actions of glucagon-like peptide-1 (GLP-1), suggested that additional mechanisms may also play an important role in GIIS. Consistent with this, our preliminary data revealed that inhibitor-kB kinase 2 (IKK2), a kinase essential for nuclear factor-kB (NF-kB) activation, was also essential for GIIS, as evidenced by impaired GIIS in IKK2-deficient mice and IKK2 inhibitor-treated Min6 cells. IKK2 up-regulates exocytosis in some cells through direct phosphorylation of synaptosomal-associated protein, 23kDa (SNAP23), and the latter is expressed in β cells. In agreement with the existence of this IKK2/SNAP23 pathway in β cells, our data showed that inhibition of IKK2 reduced SNAP23 phosphorylation and knockdown of SNAP23 decreased GIIS in Min6 cells, warranting further studies to confirm this novel mechanism of GIIS. Given the essential role of GIIS impairment in the development of diabetes, these data also warrant further studies to investigate the pathophysiological role of this novel mechanism of GIIS. Therefore, in the present study, we hypothesize that IKK2 mediates GIIS through phosphorylation of SNAP23 and thus is implicated in the development of diabetes, and pursue 2 discrete yet linked aims: 1) To confirm that IKK2/SNAP23 pathway mediates GIIS in pancreatic β cells; 2) To determine if IKK2/SNAP23-mediated GIIS is implicated in the development of diabetes.

胰岛β细胞的葡萄糖引起的胰岛素分泌反应（GIIS）异常是糖尿病发病的主要病理基础。研究显示该反应主要由钙信号介导，也受其它信号调控。但有关后者的具体性质目前却还不清楚。我们前期研究发现，敲除或抑制IKK2 （一个以介导炎症反应而为人熟知的激酶）显著降低小鼠糖耐量，却不影响全身的胰岛素敏感性，从而提示了一个可能是非钙依赖的GIIS调控新机制。我们进一步在β细胞系Min6的研究中发现，抑制NF-kB激活（IKK2最著名的下游通路，主要介导炎症反应）并不影响GIIS，而敲低IKK2的另一个底物SNAP23却显著降低GIIS，表明IKK2很可能通过磷酸化SNAP23来调控GIIS。因此，本项目拟运用多种技术手段确定IKK2/SNAP23通路是否调控GIIS，并利用高脂饮食引起的糖尿病小鼠模型探讨该新机制在糖尿病发病过程中具体作用。

胰岛β细胞的葡萄糖引起的胰岛素分泌反应（GIIS）异常是糖尿病发病的主要病理基础。研究显示该反应主要由钙信号介导，也受其它信号调控。但有关后者的具体性质目前却还不清楚。我们前期研究发现，敲除或抑制IKK2 （一个以介导炎症反应而为人熟知的激酶）可显著降低小鼠糖耐量，却不影响全身的胰岛素敏感性，从而提示了一个可能是非钙依赖的GIIS调控新机制。本项目拟运用多种技术手段确定IKK2/SNAP23通路是否调控GIIS，并利用多种组织特异性基因敲除小鼠模型探讨该新机制在糖尿病病程中的具体作用。.在本项目的执行期间，我们首先通过IKK2全身敲除、全身抑制及中枢IKK2抑制等体内动物模型，证实了IKK2/SNAP23信号通路可影响GIIS。此外，我们结合了体外MIN6细胞系，利用IKK2特异性抑制剂及定点突变等技术，明确了IKK2/SNAP23信号通路在GIIS中的作用。更重要的是，我们成功培育了肺上皮细胞IKK2特异性敲除和神经元IKK2特异性敲除小鼠模型，利用课题组已有的大气细颗粒物动物全身实时暴露染毒系统进行过滤空气或大气细颗粒物暴露，深入解析了IKK2/SNAP23信号通路在空气污染引发的糖代谢紊乱中的作用，初步阐明了其对糖尿病病程的影响。我们的初步结果显示上述研究具有潜在的临床及预防干预意义，为今后相关药物及干预新策略的提出打下了一定基础。