ROLE OF TGF-B INDUCIBLE EARLY GENE IN OSTEOCLASTOGENESIS

描述(申请人提供)：在病理性骨丢失和正常骨代谢期间，破骨细胞数量的调节对破骨细胞介导的骨降解都有深远的影响。转化生长因子-β在骨环境中含量丰富，并参与破骨细胞分化的调节。我们发现了TIEG1(TIEG)，这是一种转录因子，经转化生长因子-1处理后，其在人成骨细胞中的表达迅速增加。为了更好地了解TIEG(S)在骨代谢中的作用，我们产生了TIEG缺失的小鼠。与年龄匹配的野生型小鼠相比，这些小鼠的骨骼更弱、更小，股骨头中的骨小梁间距增加。来自TIEG-/-小鼠的骨髓和脾来源的破骨细胞前体在体外具有增强的分化为破骨细胞的能力，并增强了NFkB的激活。此外，与野生型小鼠的破骨细胞前体不同，在分化过程中进行的转化生长因子-1治疗不会刺激分化。颅骨来源的TIEG-/-成骨细胞支持破骨细胞分化的能力降低，部分原因是OPG增加和RANKL表达减少。这些观察结果和已发表的文献引出了我们的中心假设，即TIEG在破骨细胞前体和成骨支持细胞中的表达在调节破骨细胞分化中起重要作用，而破骨细胞前体TIEG的表达对于促进分化是必不可少的。为了验证这一假说，本建议的具体目的是：1.阐明TIEG-/-破骨细胞前体中NFkB通路激活的机制。2.阐明NFkB信号增强在TIEG-/-破骨细胞前体细胞分化增强中的作用。3.确定TIEG在体外促进破骨细胞前体分化中的作用。4.探讨体外培养的TIEG-/-颅骨细胞OPG基因和蛋白表达增加的分子机制。5.明确TIEG刺激成骨细胞RANKL基因表达的机制。由于骨丢失的速度主要取决于破骨细胞的数量，了解破骨细胞分化的规律可能会为治疗病理性骨丢失时减缓骨降解提供重要途径。这些研究将增加这方面的知识，并增加我们对破骨细胞介导的骨丢失的理解。此外，这些研究应该为破骨细胞分化的分子机制提供关键信息。

DESCRIPTION (provided by applicant): Modulation of osteoclast numbers has a profound influence on osteoclast-mediated bone degradation in both pathological bone loss and during normal bone metabolism. TGF-( is abundant in the bone environment and has been implicated in regulation of osteoclast differentiation. We have discovered TIEG1 (TIEG), a transcription factor whose expression is rapidly increased in human osteoblasts following TGF-( treatment. To better understand TIEG's role(s) in bone metabolism, we have generated mice lacking TIEG. Bones from these mice are weaker and smaller with increased trabecular spacing in the femoral head compared to age matched wildtype littermates. Marrow- and spleen-derived osteoclast precursors from the TIEG-/- mice have an amplified ability to differentiate into osteoclasts in vitro and enhanced NFkB activation. Moreover, TGF-( treatment during differentiation did not stimulate differentiation, unlike osteoclast precursors from wildtype mice. Calvarial-derived TIEG-/- osteoblasts have a reduced capactiy to support osteoclast differentiation, in part due to increased OPG and decreased RANKL expression. These observations and the published literature lead to our central hypothesis that TIEG expression in both osteoclast precursors and osteoblastic support cells is important in modulating osteoclast differentiation and that osteoclast precursor TIEG expression is essential for TGF-( stimulation of differentiation. To test this hypothesis, the Specific Aims of this proposal are to 1. Elucidate the mechanisms by which NFkB pathway activation is enhanced in TIEG-/- osteoclast precursors. 2. Resolve the role of enhanced NFkB signaling in the increased differentiation of TIEG-/- osteoclast precursors. 3. Determine the roles of TIEG in TGF-( stimulation of osteoclast precursor differentiation in vitro. 4. Discover the molecular mechanisms involved in the increased expression of OPG mRNA and protein in TIEG-/- calvarial cells cultured in vitro. 5. Ascertain the mechanism of TIEG stimulation of RANKL gene expression in osteoblasts. Since the rate of bone loss is mainly determined by the number of osteoclasts, understanding regulation of osteoclast differentiation is likely to provide important avenues for therapies to slow bone degradation during pathological bone loss. These studies will add to this knowledge and increase our understanding of osteoclast-mediated bone loss. Further, these studies should provide key information on the molecular mechanisms of osteoclast differentiation.