The role of SETDB1 in intestinal homeostasis and inflammation

炎症性肠病（IBD）是一组肠道慢性炎症性疾病，其易感性受宿主遗传调节。我们和其他人已经描述了孟德尔形式的IBD，其中单个基因的有害变异可以以单基因方式引起IBD。这些孟德尔形式的IBD为慢性肠道炎症的发病机制提供了巨大的见解，并强调了IBD个性化治疗的新途径。在这项工作中，我们已经确定了一位患有严重的，非常早发的，狭窄和瘘管性克罗恩病的女性患者。该患者的外显子组测序显示，预计SETDB1中存在一种错义变体，该变体编码SET结构域分叉组蛋白赖氨酸甲基转移酶1。SETDB1是一种甲基转移酶，对组蛋白H3的赖氨酸9残基具有高特异性，对异染色质的形成至关重要。我们发现SETDB1在肠道中的表达主要局限于肠上皮，在培养的人肠上皮细胞中删除SETDB1或设计ibd相关遗传变异的尝试与细胞死亡和上皮生长抑制相关。因此，我们培养了具有他莫昔芬诱导的肠上皮细胞SETDB1缺失的小鼠。SETDB1的上皮缺失与肠上皮结构改变、分化的分泌型和吸收型肠细胞缺失、低血糖和SETDB1缺失后10天内死亡相关。总之，这些数据揭示了SETDB1在肠道稳态和上皮分化中意想不到的关键作用。基于这些发现，我们提出(i)表征SETDB1在肠上皮谱系规范中的作用，并研究上皮SETDB1缺失的代谢和免疫学后果。此外，我们建议（ii）描述SETDB1依赖的上皮分化调控的分子途径，（iii）研究SETDB1在人类肠道稳态和IBD中的作用。拟议的研究将描述肠道内稳态的一种新的关键调节因子，并将描述SETDB1变异对IBD的潜在贡献。

Inflammatory bowel diseases (IBD) are a group of chronic inflammatory diseases of the intestine, the susceptibility to which is regulated by host genetics. We and others have described Mendelian forms of IBD in which deleterious variants in individual genes can give rise to IBD in a monogenic manner. These Mendelian forms of IBD have provided tremendous insight into the pathogenesis of chronic intestinal inflammation and have highlighted novel pathways to personalized treatment of IBD. In the work leading to this proposal, we have identified a female patient with severe, very early-onset, stricturing and fistulizing Crohn’s disease. Exome sequencing in this patient revealed a missense variant predicted to be deleterious in SETDB1, which encodes SET Domain Bifurcated Histone Lysine Methyltransferase 1. SETDB1 is a methyltransferase with high specificity for the lysine 9 residue of histone H3 and is critical for heterochromatin formation. We found that SETDB1 expression in the intestine was largely confined to the intestinal epithelium and attempts to delete SETDB1 or engineer the IBD-associated genetic variant in cultured human intestinal epithelial cells were associated with cell death and inhibition of epithelial growth. We therefore developed mice with tamoxifen-inducible intestinal epithelial deletion of SETDB1. Epithelial deletion of SETDB1 was associated with structural alterations in the intestinal epithelium, loss of differentiated secretory and absorptive enterocytes, hypoglycemia and death within 10 days of Setdb1 deletion. Together, these data reveal an unanticipated, critical role of SETDB1 in intestinal homeostasis and epithelial differentiation. Based on these findings, we propose to (i) characterize the role of SETDB1 in intestinal epithelial lineage specification and to study the metabolic and immunological consequences of loss of epithelial SETDB1. In addition, we propose (ii) to delineate the molecular pathways of SETDB1-dependent regulation of epithelial differentiation and (iii) to study the role of SETDB1 in human intestinal homeostasis and IBD. The proposed studies will characterize a novel and critical regulator of intestinal homeostasis and will delineate a potential contribution of SETDB1 variants to IBD.