MicroRNA regulation of osteoblast physiology and glucocorticoid signaling

内源性糖皮质激素对于正常的骨生理学是至关重要的。然而，糖皮质激素过量，由于 全身给药或综合征如库欣氏病，引起骨质减少和代谢紊乱， disorder.总的来说，糖皮质激素受体信号必须严格控制，以获得最佳的骨骼健康。我们 将microRNA-433（miR-433）鉴定为成骨细胞谱系中糖皮质激素信号传导的负调节因子。 在体外，miR-433活性的抑制使间充质细胞对糖皮质激素的反应更敏感， 增加糖皮质激素受体在细胞核中的驻留，表明miR-433可能靶向机制 旨在限制细胞对糖皮质激素信号的反应。 除了对糖皮质激素信号传导的影响，miR-433是成骨细胞的负调节因子。 分化miR-433随着成骨细胞分化的进展而减少，并且miR-433活性的抑制 增加成骨细胞标记基因表达。为了更好地了解miR-433在骨中的功能，我们 产生在成骨细胞中表达miR-433竞争性抑制剂（坚韧诱饵）的转基因小鼠。 来自miR-433诱骗小鼠的颅骨具有增加的骨钙素和直接miR-433的mRNA。 目标Runx 2此外，miR-433诱饵小鼠显示出增加的骨小梁和皮质骨厚度，这是由于 骨形成增加，尽管分子机制仍有待确定。 我们建议验证miR-433靶向成骨细胞生成关键基因和途径的假设 以及限制糖皮质激素受体信号传导。 在目标1中，我们将全面表征男性和女性miR-433的骨骼表型， 引诱老鼠成熟和衰老。我们还将使用非偏倚方法鉴定miR-433靶点，以更好地 了解miR-433如何调节成骨细胞生物学。在目标2中，我们将确定 miR-433在分子水平上限制糖皮质激素的反应性，以及确定miR-433的影响。 433对骨对外源性糖皮质激素过量的反应。 总体影响：miR-433是糖皮质激素反应性和成骨细胞的一种新的阴性 分化糖皮质激素过量是骨质减少最常见的继发性原因， 对糖皮质激素的敏感性受多种机制调节。理解相互作用 成骨细胞生成和糖皮质激素信号传导对于设计新的策略以限制不良反应是至关重要的。 糖皮质激素过量对骨骼的影响。

Endogenous glucocorticoids are critical for normal bone physiology. However, glucocorticoid excess, due to systemic administration or syndromes such as Cushing’s disease, causes osteopenia and metabolic disorder. Overall, glucocorticoid receptor signaling must be tightly controlled for optimal bone health. We identified microRNA-433 (miR-433) as negative regulator of glucocorticoid signaling in the osteoblast lineage. In vitro, inhibition of miR-433 activity made mesenchymal cells more responsive to glucocorticoids and increased glucocorticoid receptor residence in the nucleus, suggesting that miR-433 may target mechanisms designed to limit the responsiveness of cells to glucocorticoid signaling. In addition to effects on glucocorticoid signaling, miR-433 is a negative regulator of osteoblastic differentiation. miR-433 decreases as osteoblast differentiation progresses, and inhibition of miR-433 activity increases osteoblastic maker gene expression. To better understand the function of miR-433 in bone, we generated transgenic mice expressing a miR-433 competitive inhibitor (tough decoy) in osteoblastic cells. Calvarial bone from the miR-433 decoy mice has increased mRNA for osteocalcin and the direct miR-433 target Runx2. Further, miR-433 decoy mice display increased trabecular and cortical bone thickness due to increased bone formation, although molecular mechanisms remain to be identified. We propose to test the hypothesis that miR-433 targets genes and pathways critical for osteoblastogenesis and for limiting glucocorticoid receptor signaling. In Aim 1, we will comprehensively characterize the skeletal phenotype of both male and female miR-433 decoy mice in maturity and aging. We will also identify miR-433 targets using a non-biased approach, to better understand how miR-433 regulates osteoblast biology. In Aim 2, we will determine the mechanisms by which miR-433 limits glucocorticoid responsiveness at a molecular level, as well as determining the impact of miR- 433 on the response of bone to exogenous glucocorticoids excess. Overall Impact: miR-433 is a novel negative of both glucocorticoid responsiveness and osteoblast differentiation. Glucocorticoid excess is the most common secondary cause of osteopenia, and tissue sensitivity to glucocorticoids is regulated by multiple mechanisms. Understanding the interaction between osteoblastogenesis and glucocorticoid signaling is critical for the design of novel strategies to limit the adverse effects of glucocorticoid excess on the skeleton.