Bip/GRP78对肝脏和胰腺发育的影响及其病理生理学意义

Endoplasmic reticulum (ER) stress is triggered by accumulation of unfolded and misfolded proteins in the ER lumen resulting in activation of a set of signaling pathways collectively known as unfolded protein response (UPR). While there has been great progress in understanding ER stress and diseases, ER stress occurring during embryonic development is less well understood. We have found that BiP/GRP78, an important chaperone in ER, plays important roles in early embryonic development of Xenopus laevis, the African clawed frog. DNA microarray and in situ hybridization showed that knockout of BiP/GRP78 results in down-regulation of pancreas and liver specific genes and severe impairment of pancreas and liver development. In addition, it was found that low concentration of the ER stress inducer tunicamycin up-regulates mRNA expression of BiP/GRP78 in embryonic stem (ES) cells and promotes endoderm induction during ES cell differentiation. In this proposed study, we hypothesize that Bip/GIP78 is involved in ER stress mediated regulation of liver and pancreas development. Using Xenopus embryos, transgenic mice model and ES cells, we will investigate the roles of Bip/GIP78 during liver and pancreas development in the frog and mouse as well as differentiation of ES cells. We will also elucidate the molecular basis of phathophysiological functions of Bip/GIP78 in liver and pancreatic diseases. Our findings will reveal a new mechanism of liver and pancreas development, and provide scientific basis for identification of noval therapeutic targets for liver and pancreatic diseases.

胚胎发育是个体发育的基础，同时也与很多疾病密切相关。BiP/GRP78是内质网重要的伴侣分子，与内质网应激密切相关，但是其在胚胎和器官发育中的作用尚不清楚。前期研究发现，Bip/GRP78在胚胎的发育中的起着关键作用。基因芯片和原位杂交的结果显示，敲除Bip/GPR78特异性下调与胰腺和肝脏功能相关的基因。进一步的胚胎干细胞研究发现，低浓度的内质网应激诱导剂tunicamycin上调Bip/GIP78 mRNA并诱导干细胞向内胚层分化。我们首次提出Bip/GIP78通过内质网应激调控肝脏和胰腺发育的可能性。本项目拟采用胚胎肝细胞、非洲爪蛙以及转基因鼠为模型，采用基因芯片、原位杂交、疾病动物模型等方法，旨在获得Bip/GIP78调控肝脏和胰腺发育的可靠证据，并在分子水平上阐明其病理生理学作用机制。本项目有望揭示肝胰发育的新机制，并为确立BiP/GIP78作为肝脏胰腺疾病新靶标提供充科学依据。

BiP/GRP78(Hspa5)是内质网重要的伴侣分子，与内质网应激密切相关，但是其在胚胎和器官发育中的作用尚不清楚。本项目采用非洲爪蛙和胚胎干细胞，旨在获得内质网应急和Bip/GIP78(Hspa5)调控肝脏和胰腺发育的证据及其作用机制。研究发现，Bip/GRP78(Hspa5)在胚胎的发育中的起着关键作用。基因芯片和原位杂交的结果显示，非洲爪蛙中敲除Bip/GPR78下调与胰腺和肝脏功能相关的基因。此外，Bip/GRP78 (HSPA5) 调控Retinoic acid（RA）信号通路，而RA信号通路影响早期胚胎诸多器官。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，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。另一方面，我们发现在胚胎干细胞中，内质网应激引起的未折叠蛋白反应通过Smad2 和beta –catenin信号通路影响内胚层的诱导；低浓度的内质网应激诱导剂tunicamycin 和thapsigargin 上调Bip/GIP78 mRNA并诱导干细胞向内胚层分化。我们将结合爪蛙胚胎、小鼠ES 细胞和转基因小鼠三种研究系统，深入探索Bip/GRP78对胰腺、肝脏发育的影响及其分子机制，完善对发育生物学基本规律的认识，为治疗胰腺和肝脏相关疾病提供科学依据。