E4BP4在糖皮质激素诱导胰岛β细胞凋亡中的作用及其分子机制研究

Steroid diabetes is the most frequent side effect of glucocorticoid treatment. The apoptosis of pancreatic β cells is the main reason, but the underlying molecular mechanisms remain to be elucidated. In our previous work, we established in vitro cell model to mimic the pancreatic β cell apoptosis under glucocorticoid treatment. Genes that related to glucocorticoid-induced β cell apoptosis were screened by microarray, and the candidate gene E4BP4 was first confirmed to have an important role in glucocorticoid-induced β cell apoptosis by E4BP4 knockdown experiment. Further in vivo studies in mice showed that elevated blood glucose and serum lipid evoked by glucocorticoid may be another important factors that can lead to β cell apoptosis. In addition, glucolipotoxicity also can significantly increased the expression of E4BP4. Based on these results, we speculate that E4BP4 not only mediates glucocorticoid directly induced β cell apoptosis，but also mediates glucolipotoxicity induced β cell apoptosis. In this study, we want to investigate the role of E4BP4 in glucocorticoid-induced β cell apoptosis by using established E4BP4 stable knockdown MIN6 cells, E4BP4 inducible MIN6 cells, dexamethasone-induced diabetic mice model, β cell specific E4BP4 knockout mice, and elucidate its molecular mechanism. This study will provide new experimental data for unraveling the underlying mechanisms of steroid diabetes.

类固醇性糖尿病是糖皮质激素临床应用中常见的副作用，胰岛β细胞凋亡是其重要原因，但确切分子机制尚不清楚。我们前期建立了糖皮质激素诱导β细胞凋亡的细胞模型，通过基因芯片差异、基因沉默实验首次发现E4BP4参与了糖皮质激素直接诱导的β细胞凋亡。随后动物实验发现糖皮质激素除了直接引起β细胞凋亡外，其引起的动物血糖血脂升高是引起β细胞凋亡的另一重要因素，而糖脂毒性同样也能显著诱导β细胞E4BP4的表达。据此我们推测E4BP4可能介导了糖皮质激素直接诱导的β细胞凋亡以及糖皮质激素通过糖脂毒性间接诱导的β细胞凋亡，在类固醇性糖尿病发病过程中发挥重要作用。本研究拟应用已建立的稳定敲降或可诱导表达E4BP4的β细胞系、类固醇性糖尿病动物模型、β细胞特异性E4BP4敲除小鼠，阐明E4BP4介导糖皮质激素诱导胰岛β细胞凋亡的分子机制，并筛选保护药物，为阐明类固醇性糖尿病的发病机制和药物防治提供实验依据。

由于糖皮质激素在临床的应用相当广泛，而且继发类固醇性糖尿病的比例又很高，目前临床除了停药或减少剂量外尚无特殊有效的治疗手段。因此，深入研究其发病机制对类固醇性糖尿病的防治具有重要意义。近年来认为保护胰岛β功能、防止胰岛β细胞功能衰竭是重要的治疗目标。项目负责人首先发现糖皮质激素体外可以剂量依赖地诱导胰岛β细胞发生凋亡，并且通过基因芯片、qPCR和Western blot发现糖皮质激素可与此同时诱导E4BP4的上调表达；利用构建的稳定敲降E4BP4和可诱导表达E4BP4的胰岛β细胞系、E4BP4胰岛β细胞特异性敲除小鼠以及糖皮质激素受体GR胰岛β细胞特异性敲除小鼠，通过体内外研究充分证明了E4BP4在糖皮质激素诱导的胰岛β细胞凋亡中发挥重要的介导作用；机制研究发现糖皮质激素通过其受体GR诱导E4BP4上调，而E4BP4可诱导内质网应激的发生诱导胰岛β细胞凋亡。该研究有望阐明固醇性糖尿病新的发病机制，并为临床中固醇性糖尿病的防治提供潜在的治疗靶点，具有很好的创新性和应用前景。