利用条件性基因敲除小鼠研究KLF4在破骨细胞发生、功能中的作用机制。

Kruppel样因子4（Kruppel-like factor 4，KLF4）通过激活CD14转录等促进单核细胞发生，下调NF-κB活性等机制调节巨噬细胞功能。破骨细胞属于单核巨噬细胞系统。申请人发现，在能分化为破骨细胞的HL60、U937细胞系中，KLF4上调PU.1、下调RANK表达和NF-κB活性；提示KLF4可能抑制破骨细胞的发生及功能。申请人拟利用两种遗传变异小鼠，杂交后能实现在巨噬细胞、破骨细胞中特异性敲除KLF4。基于该小鼠模型，本课题拟阐明KLF4在破骨细胞中的基因功能：通过骨组织形态计量、显微CT、ELISA等方法检测KLF4敲除对小鼠骨量、骨结构、破骨细胞活性的影响；培养原代细胞研究KLF4对破骨细胞发生、功能的调控。本课题成果不仅有助于揭示破骨细胞发生、功能的调控机制，而且对骨质疏松、骨肿瘤等病理过程的研究提供参考。

In monocyte phagocytic system, Kruppel-like factor 4 (KLF4) is regulated by PU.1 and STAT6, thereby expresses at a high level. KLF4 promotes the differentiation of monocytes by activating the monocytic-specific CD14 promoter. Moreover, KLF4 regulates polarization of macrophage partly by downregulation of NF-κB activity. Osteoclasts belong to the monocyte phagocytic system, roles played by KLF4 in osteoclast have yet to be revealed. In HL60 and U937, two cell lines can be induced to differentiate into osteoclasts, we found that KLF4 upregulated PU.1, repressed RANK expression and NF-κB activity. We hypothesized that KLF4 might repress osteoclastogenesis and function. To this end, we acquired two genetically modified mice, CD11b-Cre and KLF4loxp mice. Breeding between the two mouse lines can give rise to mice with KLF4 deleted specifically in macrophages and osteoclasts. We propose to determine whether deletion of KLF4 in osteoclastic lineage affect osteoclastogenesis and bone resorption in vivo. We will culture primary monocytes from the knockout mice and induce differentiation to osteoclasts; thereby impact of KLF4 deletion on osteoclastogenesis and function can be elucidated. Our study will elucidate the regulation of osteoclastogenesis and bone resorption by KLF4. Moreover, it will provide insight into mechanisms of osteoporosis, bone tumors and etc.