Regulating Osteoblast Proliferation and Differentiation

调节成骨细胞增殖和分化

• 批准号: 6929127
• 负责人: HYUN-DUCK NAH-CEDERQUIST
• 金额: $ 32.87万
• 依托单位: CHILDREN'S HOSP OF PHILADELPHIA
• 依托单位国家: 美国
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-08-01 至 2009-07-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6929127
• 关键词: RNA interference; bone development; bone morphogenetic proteins; cell differentiation; cell growth regulation; cell proliferation; fibroblast growth factor; flow cytometry; gel mobility shift assay; genetically modified animals; in situ hybridization; laboratory mouse; light microscopy; northern blottings; osteoblasts; osteogenesis; phosphorylation; polymerase chain reaction; receptor expression

DESCRIPTION (provided by applicant): Acquisition and maintenance of normal bone mass requires an adequate number of proliferative osteogenic precursor cells as well as the differentiated functions of osteoblasts. A reduction in the osteoblast precursor cell population or under-performing osteoblasts has been associated with abnormal development of the skeleton, as well as impaired bone remodeling and fracture healing in aging patients. Increasingly, it is being recognized that local factors, including fibroblast growth factors (FGFs), are crucial regulators of the cellular events associated with the osteogenic process. The bone-inducing effects of FGFs are mediated through four high affinity receptors (FgfR1-4), with FgfR1 and 2 being the major receptors expressed in bone. However the mechanisms of FGF's bone inducing effect as well as specific functions of each FgfR in osteogenesis remain elusive. In this study, we will test the hypothesis that temporally expressed FgfR1 and FgfR2 coordinates osteogenic cell proliferation and differentiation to promote bone growth. In developing bones, expression of FgfR2 is mainly restricted to highly proliferative osteoblast precursor cells and decreases with maturation. Concomitant with FgfR2 down-regulation, cell proliferation decreases and FgfR1 expression increases in differentiating osteoblasts. Collective data from our preliminary transgenic mouse and in vitro cell culture studies suggest that FgfR1 and FgfR2 both positively contribute to bone formation but may have differential roles in the regulation of bone cell proliferation and differentiation. The loss of FgfR2 and FgfR1 function results in drastically reduced intramembranous and trabecular bone mass in mice, while gain of FgfR2 function appears to stimulate bone formation. Our in vitro preliminary data suggest that FgfR2 stimulates cell proliferation but inhibits late differentiation and that Rtmx2, BMP-2 and Stat1 may be downstream mediators of FgfR2 functions. Therefore, we propose that FgfR2 plays a significant role in expanding the differentiation-competent early osteogenic cell population, by stimulating both cell proliferation and early osteogenic differentiation via increases in Runx2 and/or BMP-2 and phosphorylation of Stat1. We propose further that late osteogenic differentiation requires down-regulation of FgfR2 and perhaps also up-regulation ofFgfR1. Our hypothesis will be tested in a complementary set of in vitro and in vivo studies, utilizing transgenic and gene knock out approaches to selectively modulate either FgfR1 or FgfR2 activity.

描述（申请人提供）：正常骨量的获得和维持需要足够数量的增殖性成骨前体细胞以及成骨细胞的分化功能。成骨细胞前体细胞群的减少或性能不佳的成骨细胞与骨骼发育异常以及老年患者骨重塑和骨折愈合受损有关。人们越来越认识到，包括成纤维细胞生长因子（FGF）在内的局部因素是与成骨过程相关的细胞事件的关键调节因子。 FGF 的骨诱导作用是通过四种高亲和力受体 (FgfR1-4) 介导的，其中 FgfR1 和 2 是骨中表达的主要受体。然而，FGF 骨诱导作用的机制以及每个 FgfR 在成骨中的具体功能仍不清楚。在本研究中，我们将检验暂时表达的 FgfR1 和 FgfR2 协调成骨细胞增殖和分化以促进骨生长的假设。在发育中的骨骼中，FgfR2 的表达主要限于高度增殖的成骨细胞前体细胞，并随着成熟而降低。伴随 FgfR2 下调，分化的成骨细胞中细胞增殖减少，FgfR1 表达增加。我们初步转基因小鼠和体外细胞培养研究的集体数据表明，FgfR1 和 FgfR2 都对骨形成有积极作用，但在骨细胞增殖和分化的调节中可能具有不同的作用。 FgfR2 和 FgfR1 功能的丧失导致小鼠膜内骨量和小梁骨量急剧减少，而 FgfR2 功能的获得似乎会刺激骨形成。我们的体外初步数据表明，FgfR2 刺激细胞增殖，但抑制晚期分化，并且 Rtmx2、BMP-2 和 Stat1 可能是 FgfR2 功能的下游介质。因此，我们认为 FgfR2 通过增加 Runx2 和/或 BMP-2 以及 Stat1 的磷酸化来刺激细胞增殖和早期成骨分化，从而在扩大具有分化能力的早期成骨细胞群中发挥重要作用。我们进一步提出，晚期成骨分化需要 FgfR2 的下调，或许还需要 FgfR1 的上调。我们的假设将在一组互补的体外和体内研究中得到检验，利用转基因和基因敲除方法选择性调节 FgfR1 或 FgfR2 活性。