PTH-Induced NGFI-B Proteins Regulate Osteoblast Function

描述（由申请人提供）：恢复骨骼健康的合成代谢治疗可以改善牙科和医学的临床结果。甲状旁腺激素（PTH）在骨代谢中具有显著的合成代谢作用。然而，PTH的合成代谢作用的分子介质仍不清楚。我们的研究重点是pth诱导的原代基因作为转录因子靶向晚期基因表达并传播成骨细胞功能的变化。我们已经鉴定出NGFI-B核孤儿受体（Nurr1, Nur77, NOR-1）是成骨细胞中pth诱导的原代基因。NGFI-B蛋白通过靶基因启动子中的NGFI-B应答元件（NBREs）调控转录和细胞分化。Nurr1蛋白通过野生型（WT）而非突变型（mut） NBRE反激活大鼠骨钙素启动子。PTH诱导PPARgamma共激活因子pgc -1 α。反过来，PGC-1alpha强烈增强了Nurr1诱导的WT的转激活，但没有改变OCN启动子，这表明Nurr1与NBRE的结合对于NGFI-B靶启动子上转录体的组装至关重要。我们观察到共识PPARgamma反应元素（PPRE）包含一个NBRE。事实上，重组蛋白与pth诱导的Nurr1蛋白结合一致。有趣的是，除了与pgc1 α协同作用外，Nurr1和Nur77还与PPARgamma的必需伙伴RXR异二聚化。这些数据表明NGFI-B和PPARgamma信号可能会聚在含有ppre的启动子上。我们提出NGFI-B蛋白下调ppargamma反应基因，从而促进成骨而不是脂肪形成。为此，PTH抑制了原代成骨细胞中PPARg靶基因CD36。我们假设NGFI-B基因通过靶启动子调控和选择性辅因子募集是成骨细胞分化和功能的关键介质。我们的具体目标是：1)研究NGFI-B核孤儿受体在成骨细胞中的转录调控，2)研究pth诱导NGFI-B和pgc -1 α的相互作用，3)研究NGFI-B靶向过表达对体内骨的影响。

DESCRIPTION (provided by applicant): Anabolic treatments that restore bone health improve clinical outcomes in dentistry and medicine. Parathyroid hormone (PTH) has significant anabolic effects on bone metabolism. However, the molecular mediators of PTH's anabolic effects remain unclear. Our research focuses on PTH-induced primary genes that act as transcription factors to target late gene expression and propagate changes in osteoblastic function. We have identified NGFI-B nuclear orphan receptors (Nurr1, Nur77, NOR-1) as PTH-induced primary genes in osteoblasts. NGFI-B proteins regulate transcription and cellular differentiation through NGFI-B response elements (NBREs) in target gene promoters. Nurr1 protein transactivated the rat osteocalcin promoter through a wild type (WT), but not mutant (mut), NBRE. PTH induced the PPARgamma coactivator PGC-1alpha. PGC-1alpha, in turn, strongly enhanced Nurr1-induced transactivation of the WT, but no mut, OCN promoter, suggesting that Nurr1 binding to the NBRE is critical in transcriptosome assembly on NGFI-B target promoters. We observed that the consensus PPARgamma response element (PPRE) contains an NBRE. Indeed, recombinant and PTH-induced Nurr1 protein bound to a consensus PPRE. Intriguingly, in addition to synergizing with PGC1alpha, Nurr1 and Nur77 also heterodimerize with PPARgamma's obligatory partner, RXR. These data suggest that NGFI-B and PPARgamma, signaling may converge on PPRE-containing promoters. We propose that NGFI-B proteins downregulate PPARgamma-responsive genes thereby promoting osteogenesis over adipogenesis. To that effect, PTH inhibited the PPARg, target gene CD36 in primary osteoblasts. We hypothesize that NGFI-B genes are critical mediators of osteoblast differentiation and function through target promoter regulation and selective cofactor recruitment. Our Specific Aims are to: 1) study transcription regulation by NGFI-B nuclear orphan receptors in osteoblasts, 2) examine PTH-induction of and NGFI-B interactions with PGC-1alpha, 3) investigate the effect of targeted NGFI-B overexpression on bone in vivo.