组蛋白甲基转移酶Ash1l通过调节Stac2基因表达影响破骨分化的作用及机制研究

组蛋白甲基转移酶Ash1l具有调节免疫和炎症等多种功能，但Ash1l在破骨分化中可能的调控作用国内外尚无报道。我们前期实验利用所构建的髓系细胞特异性敲除Ash1l基因的小鼠（Ash1l-cKO）发现，Ash1l缺失导致该动物出现骨质疏松样表型；Ash1l还可抑制骨髓巨噬细胞（BMMs）向破骨细胞分化。前期数据还发现Ash1l缺失后Stac2基因表达降低且Ash1l可富集至Stac2启动子区。由于Stac2是已知的破骨分化负调控因子，我们推测Ash1l可能通过调节Stac2基因表达水平而影响破骨分化和骨代谢。本项目拟利用Ash1l-cKO小鼠及其BMMs为主要研究对象，阐明Ash1l调节Stac2基因表达而影响破骨分化的作用及机制。本项目立意新颖，属于国内外首次利用条件性敲除小鼠对Ash1l在破骨分化中的可能作用机制进行深入研究，将为理解骨代谢的表观调控机制提供全新视角。

Absent, small, or homeotic-like (Ash1l), a histone 3 lysine 4 (H3K4) trimethyltransferase, is known to be involved in the regulation of several processes including innate immunity response and inflammation. However, little is known with regard to its functional role in osteoclastogenesis. In this study, we generated a mouse model with specific deletion of Ash1l (Ash1l-cKO) in osteoclast precursor cells using Cre-loxP system. Osteoporosis-like phenotypes were observed in 3-month-old male Ash1l-cKO mice when compared with the wild type littermates. Our preliminary data also demonstrated that Ash1l significantly inhibited the differentiation of bone marrow-derived macrophages (BMMs) into osteoclasts upon receptor activator of nuclear factor-κB ligand (RANKL) induction in vitro. Moreover, RNA-seq and qRT-PCR analysis indicated Ash1l deficiency greatly reduced Stac2 gene expression, and Ash1l were found to be enriched in the promoter of Stac2 gene by chromatin immunoprecipitation. As Stac2 has been reported to be a negative regulator of osteoclastogenesis, we hypothesize that Ash1l could negatively regulate osteoclastogenesis by regulating Stac2 gene expression. In this project, we aim to thoroughly study the effect and potential mechanisms of Ash1l on osteoclastogenesis using the Ash1l-cKO mice in vivo and BMMs in vitro. This novel project will provide first evidences to demonstrate the function of Ash1l in osteoclastogenesis as well as a new perspective for understanding the epigenetic regulatory mechanisms in bone metabolism.