HIF-2alpha, a Novel Regulator of Osteoblastogenesis

摘要 提高我们对控制骨量和成骨细胞分化的机制的理解是至关重要的。 揭示骨骼疾病的发病机制，并找出治疗方法。 成骨细胞在低氧(低氧)环境中工作。低氧诱导的转录因子 因子-1a(HIF1)和HIF2是细胞对低氧反应的关键介质。两种转录因子 在成骨细胞系的细胞中表达。据报道，HIF1是骨形成的积极调节因子。 和成骨细胞分化。相反，HIF2在骨量控制和成骨细胞生物学中的作用是 人们对此仍知之甚少。我们最近培育出了携带功能丧失和功能获得的突变小鼠 应用PRX1-CRE技术检测肢芽间充质祖细胞中HIF2的突变对这些问题的初步分析 突变小鼠提示，HIF2是成骨细胞形成和骨形成的负调控因子，通过 直接作用于成骨细胞谱系上的细胞。从机制上讲，我们收集到的初步证据表明， 它正在成为成骨细胞分化的负调控因子，可能介导HIF2依赖的 成骨细胞生成障碍。我们的发现构成了一种范式转变，即HIF信号的激活 途径与成骨细胞活性增加有关，而不是减少。此外，它们还暗示 与其他类型的细胞一样，HIF1和HIF2在成骨细胞中具有相反的功能。另外，我们的初选 数据显示，肢芽间充质祖细胞中HIF2的缺失增加了两边的骨量 骨小梁和皮质骨。HIF2可以被小分子选择性地抑制，其中一些目前 在携带与高水平HIF2活性相关的病理的患者的临床试验中，如透明细胞 肾癌。因此，确定HIF2是否以及如何控制成骨细胞生成和骨量 不仅将扩大和加深我们对缺氧信号通路在骨骼中的作用的理解 但也可以为治疗慢性疾病如骨质疏松症中出现的低骨量提供一个新的靶点 随着年龄的增长。因此，在这个建议中，我们试图证明成骨细胞HIF2在 骨骼发育和成年期(目标1)。此外，我们将确定成骨细胞HIF2是否控制 通过直接作用于间充质祖细胞并以Sox9依赖的方式形成成骨细胞(目的 2)。 好了！

ABSTRACT Advancing our understanding of the mechanisms that control bone mass and osteoblast differentiation is crucial to unveil the pathogenesis of skeletal diseases and identify therapeutical approaches for their treatment. Osteoblastic cells operate in a low oxygen (hypoxic) environment. The transcription factors Hypoxia Inducible Factor-1a (HIF1) and HIF2 are critical mediators of the cellular response to hypoxia. Both transcription factors are expressed in cells of the osteoblast lineage. HIF1 was reported to be a positive regulator of bone formation and osteoblast differentiation. Conversely, the role of HIF2 in the control of bone mass and osteoblast biology is still poorly understood. We recently generated mutant mice carrying loss-of-function and gain-of-function mutations of HIF2 in mesenchymal progenitors of the limb bud by using PRX1-Cre. Preliminary analysis of these mutant mice suggested that HIF2 is a negative regulator of osteoblastogenesis and bone formation through a direct action on cells on the osteoblast lineage. Mechanistically, we gathered preliminary evidence that Sox9, which is emerging as a negative regulator of osteoblast differentiation, is likely to mediate the HIF2-dependent impairment of osteoblastogenesis. Our findings constitute a paradigm shift as activation of the HIF signaling pathway has been associated with increased, rather than decreased, osteoblast activity. Moreover, they imply that, as in other cell types, HIF1 and HIF2 have opposing functions in osteoblastic cells. Also, our preliminary data showed that loss of HIF2 in mesenchymal progenitors of the limb bud increases bone mass in both trabecular and cortical bone. HIF2 can be selectively inhibited by small molecules, some of which are currently in clinical trials in patients carrying pathologies associated with high levels of HIF2 activity such as clear cell renal carcinoma. Therefore, determining whether and how HIF2 controls osteoblastogenesis and bone mass not only will expand and deepen our understanding of the role of the hypoxia signaling pathway in the skeleton but could also provide a novel target for the treatment of low bone mass seen in chronic diseases, osteoporosis and with aging. In this proposal, we thus seek to demonstrate that osteoblastic HIF2 regulates bone mass during skeletal development and in adulthood (Aim 1). Moreover, we will establish whether osteoblastic HIF2 controls osteoblastogenesis through a direct action on mesenchymal progenitors and in a Sox9-dependent manner (Aim 2). !