Insm1调节胰岛β／δ／Pp细胞发育和分化的表观遗传机制

Epigenetic modifications play an essential role in the regulation of pancreatic endocrine cells development and differentiation. Our preliminary data showed that Insm1 interacts with histone modification factors Lsd1 and HDAC1/2 through its SNAG domain. Mutation of Insm1 resulted in alteration of H3K4me2 levels on TSS sites genome widely, a histone modification changes that catalyzed by Lsd1. When the SNAG motif was deleted in Insm1 gene, the final differentiation of β,δ and Pp cells altered with different patterns as that observed in Insm1 null mutation. Thus, the SNAG mediated epigenetic modification contributed to the phenotypes observed in Insm1-delSNAG mice. In this project, we will use both Insm1-SNAG mutated mice and β-cell specific Insm1-SNAG mutated mice to investigate the molecular mechanisms in the development, differentiation and trans-differentiation of β, δ and Pp cells mediated by Insm1-SNAG, particularly we will focus on the epigenetic modifications on the lineage-specific genes regulated by Insm1-SNAG. We will also investigate the epigenetic modifications regulated by Insm1-SNAG in islets of db/db mice. The results of our study will provide new knowledge in the pancreatic endocrine lineages differentiation that regulated by transcription factor mediated site-specific epigenetic modification. The results will further provide novel targets for beta cell regeneration from trans-differentiation in diabetic islets.

表观遗传修饰在细胞发育和分化中起重要作用，但胰岛内分泌细胞谱系分化的表观遗传调节还不完全清楚。前期工作中，我们发现转录因子Insm1的SNAG结构域可以募集Lsd1，HDACs等组蛋白修饰因子，进而调节Insm1结合区域染色质组蛋白甲基化／乙酰化修饰；Insm1基因SNAG结构域突变小鼠胰岛β／δ／Pp细胞发育分化表型不同于Insm1全突变，显示了SNAG介导的表观遗传修饰的特异性调节作用。本项目拟采用突变和β细胞特异性突变Insm1-SNAG结构域的小鼠,分析细胞谱系特异性基因表达和SNAG在这些基因区域介导的的组蛋白修饰，从而鉴定Insm1-SNAG调节胰岛细胞谱系分化的分子机制；在db/db糖尿病小鼠胰岛中分析这一调节作用的病理相关性。研究结果将拓展对胰岛内分泌细胞发育和分化过程中转录因子介导的位点特异性表观遗传调节机制的认识,为调节糖尿病病理条件下在体β细胞再生提供新知识和新靶点。

实验室前期对Insm1基因调控胰岛β细胞功能和增殖进行了一系列研究，基于这些研究基础，本课题分析了Insm1基因SNAG结构域对胰腺内分泌细胞发育的调控作用。课题采用Insm1-SNAG结构域特异性突变小鼠，在发育表型方面与Insm1-null突变小鼠进行了对比分析，发现了SNAG结构域特异性调控的细胞表型：SNAG结构域抑制β细胞向δ细胞转分化。突变SNAG结构域，导致δ细胞数量增加。通过细胞示踪分析、在条件性Insm1-SNAG突变小鼠中的验证分析，进一步证实了这一转分化表型。在机制方面，分析并证实了SNAG结构域可以募集Lsd1至δ细胞特异性调控基因Hhex基因启动子和内含子区域，并对该区域的H3K4me2组蛋白修饰水平进行调控，进而调控Hhex基因表达水平。.课题研究结果揭示了胰岛内分泌细胞之间进行转分化调节的新机制，为理解胰岛β细胞调控提供了新知识，为糖尿病状态下，维持β细胞稳态提供了新的调控靶点。