Role of a TGF-B Regulated Gene in Human and Mouse Osteoblasts and Skeleton

描述（由申请人提供）：雌激素（E2）和TGF β在骨骼生长、成骨细胞（OB）分化和骨质疏松症等骨骼疾病中起关键作用。尽管它们在成骨细胞分化和骨重建中的作用，但E2和TGF β在骨组织中作用的分子机制尚未完全了解。在本实验室的调查E2和TGF β的行动OBs，我们发现和特点的新TGF β诱导早期基因-1（TIEG）的Kruppel家族的转录因子（KLF-10）的成员。OBs中的TIEG表达显示由E2、TGF β和BMP诱导。在过去的资助期间，我们确定了TIEG在介导TGF β信号传导中的重要作用，因为它抑制Smad 7的表达并诱导Smad 2的表达。为了更好地理解TIEG在骨中的功能，我们已经产生了TIEG-缺失（TIEG-/-）小鼠，并且已经发现雌性而不是雄性具有较小和较弱的骨，其特征在于相对于野生型同窝仔的骨质减少。我们已经报道了从TIEG-/-小鼠分离的颅骨OB具有显著降低的矿化骨和支持破骨细胞生成的能力。这些OB的进一步表征显示Runx 2、osterix、碱性磷酸酶和其他重要OB标记基因的表达水平降低。最近，我们已经证明，TIEG是能够直接调节Runx 2的转录，Runx 2似乎是，至少部分，负责TIEG-/- OB矿化中观察到的缺陷。我们的初步研究表明，E2诱导TIEG的表达在雌激素受体（ER）亚型特异性的方式。最后，E2还诱导Runx 2在野生型OB中的表达，但在TIEG-/-OB中不诱导Runx 2的表达，这表明TIEG在介导E2在骨中的作用中具有重要作用。基于这些数据，我们假设TIEG的E2调节和Runx 2的后续TIEG调节至少部分地导致观察到的OB缺陷，这反过来导致TIEG-/-小鼠中的性别特异性骨质减少表型。为了验证这一假设，我们计划确定：1）TIEG对Runx 2表达的调节对观察到的TIEG-/-OB缺陷的作用，2）E2对TIEG表达的调节对TIEG-/- OB表型的贡献，3）TIEG在介导E2激活OB中Runx 2表达中的作用，（4）TIEG-/-小鼠性腺切除对骨骼表型的影响。这些研究的完成将有助于确定TIEG在OB功能以及骨骼发育和维护中的生物学作用。此外，这些研究将为E2和TIEG调节Runx 2表达的机制及其对骨疾病（包括骨质疏松症）的贡献提供新的见解。

DESCRIPTION (provided by applicant): Estrogen (E2) and TGFb play pivotal roles in skeletal growth, osteoblast (OB) differentiation, and bone diseases such as osteoporosis. In spite of their role in OB differentiation and bone remodeling, the molecular mechanisms of E2 and TGFb action in bone tissue are not fully understood. During this laboratory's investigations of E2 and TGFb actions in OBs, we discovered and characterized the novel TGFb Inducible Early Gene-1 (TIEG) as a member of the Kruppel family of transcription factors (KLF-10). TIEG expression in OBs was shown to be induced by E2, TGFb, and BMPs. During the past funding period, we identified an important role for TIEG in mediating TGFb siganling as it represses Smad 7 expression and induces the expression of Smad 2. In order to better understand the function of TIEG in bone, we have generated TIEG-null (TIEG-/-) mice and have found that females, but not males, have smaller and weaker bones, characterized as osteopenic, relative to wild-type littermates. We have reported that calvarial OBs isolated from TIEG-/- mice have a markedly reduced capacity to mineralize bone and to support osteoclastogenesis. Further characterization of these OBs revealed decreased expression levels of Runx2, osterix, alkaline phosphatase, and other important OB marker genes. Recently, we have demonstrated that TIEG is capable of directly regulating the transcription of Runx2 and that Runx2 appears to be, at least in part, responsible for the observed defects in TIEG-/- OB mineralization. Our preliminary studies have shown that E2 induces the expression of TIEG in an estrogen receptor (ER) isoform specific manner. Finally, E2 also induces the expression of Runx2 in wild-type OBs, but not in TIEG-/- OBs, suggesting an important role for TIEG in mediating E2 action in bone. Based on these data, it is our hypothesis that the E2 regulation of TIEG, and the subsequent TIEG regulation of Runx2, is at least in part responsible for the observed defects in OBs which, in turn, leads to a gender-specific osteopenic phenotype in TIEG-/- mice. In order to test this hypothesis, we plan to determine: 1) the role that TIEG regulation of Runx2 expression has on the observed defects in TIEG-/- OBs, 2) the contribution of E2 regulation of TIEG expression to the TIEG-/- OB phenotype, 3) the role of TIEG in mediating E2 activation of Runx2 expression in OBs, and 4) the effects of gonadectomy of male and female TIEG-/- mice on the skeletal phenotype. The completion of these studies will help determine the biological role of TIEG in OB functions as well as skeletal development and maintenance. In addition, these studies will provide new insights into the mechanisms of E2 and TIEG regulation of Runx2 expression and their contribution to bone disease, including osteoporosis.