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)对骨代谢有显著的合成代谢作用。然而，甲状旁腺素合成代谢作用的分子介体尚不清楚。我们的研究集中在甲状旁腺激素诱导的初级基因，作为转录因子来靶向晚期基因的表达，并传播成骨功能的变化。我们已经确定NGFI-B核孤儿受体(Nurr1、Nur77、NOR-1)是甲状旁腺素诱导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(NBRE)调节转录和细胞分化。Nurr1蛋白通过野生型(WT)而不是突变型(MUT)NBRE反式激活大鼠骨钙素启动子。PTH诱导PPAR-γ共激活因子PGC-1α的表达。PGC-1α反过来强烈地增强了Nurr1诱导的WT的反式激活，但没有mut，OCN启动子，这表明Nurr1与NBRE的结合在NGFI-B靶向启动子上的转录体组装中起着关键作用。我们观察到共识PPARGamma反应元件(PPRE)包含NBRE。事实上，重组和甲状旁腺激素诱导的Nurr1蛋白结合到一个共识的PPRE。有趣的是，除了与PGC1pha协同作用外，Nurr1和Nur77还与PPARGamma的必需合作伙伴RXR进行异源二聚。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。我们认为，NGFI-B蛋白下调PPAR-伽马反应基因，从而促进成骨而不是脂肪生成。为此，甲状旁腺素抑制了原代成骨细胞中的PPARg，靶基因CD36。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。我们的具体目的是：1)研究NGFI-B核孤儿受体对成骨细胞转录的调控；2)检测PTH对PGC-1α的诱导作用及NGFI-B与PGC-1α的相互作用；3)研究靶向NGFI-B过表达对体内骨骼的影响。

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.