Bip/GRP78对胰淀素引起胰岛beta细胞损伤的保护作用

The islet in type 2 diabetes (T2DM) is characterized by reduced beta cell mass, impaired insulin secretion, and accumulated human islet amyloid polypeptide (hIAPP). It has been suggested that formation of intracellular hIAPP oligomers might contribute to insulin-producing beta cell loss in T2DM. We and others previously reported that treatment with human hIAPP in INS-lE beta cells triggered apoptosis through MAPK, AKT, mitochondrial and ER stress pathways. It has also been reported that BIP/GRP78, an ER chaperone, prevented free fatty acid-induced cell apoptosis in liver and beta cells through attenuation of the ER stress. In this proposed study, we hypothesize that BIP/GRP78 may also prevent hIAPP-induced cell apoptosis though the same mechanism. Instead of using synthesized hIAPP, we would overexpress hIAPP in pancreatic beta ?cells by adenoviral gene transfer and examine the cytotoxic effects of overexpression of hIAPP and further elucidate whether BIP/GRP78 could attenuate the effects induced by hIAPP overexpression both in the cell and in islet transplanted mice models. The finding will provide a novel approach for the treatment of the T2DM subgroup that shows high risk of developing amyloidogenesis.

人胰岛素淀粉样多肽（hIAPP）沉淀是2型糖尿病的一个重要病理特征。我们的前期研究证明，hIAPP处理胰岛细胞可激活MAPK、抑制AKT信号通路，并触发线粒体和内质网应激，从而导致细胞凋亡。BIP/GRP78是内质网应激中改善应激的关键分子伴侣。那么BIP/GRP78是否可以抑制hIAPP引起的胰岛细胞损伤和凋亡？为此，我们构建了Bip/GRP78和hIAPP的腺病毒，进一步实验显示，Bip/GRP78可以抑制游离脂肪酸引起的beta细胞凋亡。由此，我们首次提出：Bip/GRP78可能对hIAPP引起胰岛beta细胞损伤和凋亡有保护作用。本项目拟进一步采用腺病毒、转基因鼠、活细胞成像、胰岛移植和动物模型等方法，旨在获得hIAPP诱导内质网应激和胰岛细胞损伤凋亡的可靠证据，明确Bip/GRP78是否有保护胰岛细胞的作用并揭示其调控机制，为确立其为2型糖尿病治疗的新靶标提供科学依据。

Bip/GRP78（HSPA5）是内质网应激中改善应激的关键分子伴侣。本研究课题旨在获得hIAPP诱导内质网应激和胰岛细胞损伤凋亡的可靠证据，明确Bip/GRP78是否有保护胰岛细胞的作用并揭示其调控机制，为确立其为2型糖尿病治疗的新靶标提供科学依据。我们发现，hIAPP通过CHOP-介导的信号通路诱导INS-1E细胞凋亡，INS-1E细胞中过表达hIAPP的同时内质网应激标记基因的表达也升高。这些结果表明，hIAPP通过诱导内质网应激而至胰岛细胞损伤凋亡。此外，在研究计划进行过程中，我们还发现Bip/GRP78 (HSPA5) 调控Retinoic acid（RA）信号通路，而RA信号通路影响早期胚胎很多器官包括胰腺等的发育。另外，也有研究报道，肾损伤小鼠模型中Bip/GRP78表达上升，对肾起到保护作用。于是我们采用非洲爪蛙为模型，深入研究了Bip/GRP78（HSPA5）在胚胎发育中的作用，我们发现敲低Bip/GRP78（HSPA5）明显抑制pronephros的发育,这种抑制作用可以被过表达受RA-调控的转录因子lhx1（lhx1是发育过程中的关键因子）一定程度上拯救。我们的工作表明Bip/GRP78（HSPA5）在胚胎早期pronephros发育中发挥重要作用，具体的分子机制是通过RA-lhx1信号途径实现对pronephros的发育的调控。