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改善牙科和医学的临床结果。甲状旁腺激素（PTH）对骨代谢具有重要的合成代谢作用。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诱导的主要基因，作为转录因子，以靶向晚期基因表达和传播成骨细胞功能的变化。我们已经确定NGFI-B核孤儿受体（Nurr 1，Nur 77，NOR-1）作为PTH诱导的成骨细胞的主要基因。NGFI-B蛋白通过靶基因启动子中的NGFI-B反应元件（NBREs）调节转录和细胞分化。Nurr 1蛋白通过野生型（WT）而非突变型（mut）NBRE反式激活大鼠骨钙素启动子。PTH诱导PPARgamma辅活化剂PGC-1 α。反过来，PGC-1 α强烈增强了Nurr 1诱导的WT，但没有mut，OCN启动子的反式激活，表明Nurr 1与NBRE的结合在NGFI-B靶启动子的转录体组装中至关重要。我们观察到，共识PPARgamma响应元件（PPRE）包含NBRE。事实上，重组和PTH诱导的Nurr 1蛋白结合到一个共识PPRE。有趣的是，除了与PGC 1 α协同作用外，Nurr 1和Nur 77还与PPARgamma的强制性伴侣RXR异源二聚化。这些数据表明，NGFI-B和PPARgamma信号传导可能集中在含PPRE的启动子上。我们认为NGFI-B蛋白下调PPARgamma反应基因，从而促进成骨而非脂肪生成。为此，PTH抑制原代成骨细胞中的靶基因CD 36 PPARg。我们假设NGFI-B基因是成骨细胞分化和功能的关键介质，通过靶向启动子调控和选择性辅因子募集。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节，2）检测PTH诱导和NGFI-B与PGC-1 α的相互作用，3）研究靶向NGFI-B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.