FGF3 RECEPTOR/BMP4: PATHWAYS REGULATING SKELETAL GROWTH

成纤维细胞生长因子受体3 （FGFR3）是软骨内骨生长的主要调节因子，这一发现证明了侏儒症最常见的遗传原因，软骨发育不全，是由FGFR3突变引起的。这意味着FGFR3的下游通路是控制骨骼生长的核心。我们的目标是了解FGFR3在骨骼生长和发育过程中用于控制细胞增殖和分化的信号通路。了解这些途径将导致控制骨骼生长的新干预措施，并提出促进软骨修复和再生的方法。我们假设FGFR3通过加速细胞衰老途径抑制细胞增殖，并通过抑制BMP4表达抑制细胞分化。这些假设是我们的初步数据的直接结果，这些数据显示FGFR3减少了s期软骨细胞的数量，减缓了软骨细胞和骨祖细胞分化的速度。有趣的是，FGFR3抑制软骨细胞和软骨膜成骨细胞中骨形态发生蛋白4 （bone morphogenetic protein 4, BMP4）的表达，表明FGFR3可能通过调节BMP4的表达，使软骨膜中的骨生长与骨骺生长板的生长同步。尽管有这些知识，关于FGFR3如何抑制骨骼生长仍有许多有待了解的地方。具体来说，FGFR3用来抑制细胞增殖的途径是什么？ FGFR3的下游抑制软骨膜细胞和软骨细胞分化的介质是什么？不了解这些基本问题，就很难设计出针对软骨发育不全等侏儒症的介入性治疗方法。我们将通过追求以下具体目标来解决这些问题并测试我们的假设：1)通过测试FGFR3加速细胞周期衰老的假设来研究FGFR3如何抑制软骨细胞增殖；2a)通过靶向转基因小鼠软骨表达BMP4，确定BMP4作为FGFR3信号传导介质的作用；2b)利用cre-lox系统在转基因小鼠中表达BMP4，研究BMP4在软骨和软骨膜中的单独和联合作用。这些研究将使用独特的试剂，包括FGFR3转基因小鼠，在我们的初步研究中创建。使用这些试剂，我们可以直接测试FGFR3的影响是BMP4表达改变的后果。这些研究将从根本上推进我们对生长板和软骨膜之间的交流的理解，并揭示FGFR3和BMP4新的生长调控途径。我们预计这些研究将提出新的方法来控制骨骼生长和促进软骨修复和再生。

Fibroblast growth factor receptor 3 (FGFR3) is a chief regulator of endochondral bone growth, as evidenced by the discovery that the most common genetic cause of dwarfism, achondroplasia, results from mutations in FGFR3. This implies that pathways downstream of FGFR3 are central to the control of skeletal growth. Our goals are to understand the signaling pathways used by FGFR3 to control cell proliferation and differentiation during skeletal growth and development. Understanding these pathways will lead to novel interventions for the control of skeletal growth and suggest approaches for promoting cartilage repair and regeneration. We hypothesize that FGFR3 inhibits cell proliferation by accelerating pathways of cell senescence and inhibits cell differentiation by repressing BMP4 expression. These hypotheses are a direct consequence of our preliminary data showing that FGFR3 reduces the number of chondrocytes in S-phase and slows the rate of chondrocyte and osteoprogenitor cell differentiation. Intriguingly, FGFR3 represses the expression of bone morphogenetic protein 4 (BMP4) both in chondrocytes and perichondrial osteoprogenitor cells, suggesting that FGFR3 may synchronize bone growth in the perichondrium with the growth of the epiphyseal growth plate by modulating BMP4 expression. Despite this knowledge, much remains to be learned about how FGFR3 inhibits skeletal growth. Specifically, what are the pathways used by FGFR3 to inhibit cell proliferation and what are the mediators downstream of FGFR3 that inhibit perichondrial and chondrocyte differentiation? Without understanding these fundamental questions there is little hope of designing interventional treatments for dwarfing conditions such as achondroplasia. We will address these questions and test our hypotheses by pursuing the following specific aims: 1) Investigate how FGFR3 inhibits chondrocyte proliferation by testing the hypothesis that FGFR3 accelerates cell cycle senescence; 2a) Determine how BMP4 acts as a mediator of FGFR3 signaling by targeting the expression of BMP4 to cartilage of transgenic mice and 2b) Using a cre-lox system to express BMP4 in transgenic mice, investigate the separate and combined roles of BMP4 in cartilage and the perichondrium. These studies will utilize unique reagents, including FGFR3 transgenic mice, created during our preliminary studies. Using these reagents we can directly test what effects of FGFR3 are consequences of altered BMP4 expression. These studies will fundamentally advance our understanding of the communication of the growth plate and the perichondrium and unravel novel growth regulatory pathways of FGFR3 and BMP4. We anticipate these studies will suggest new ways to control skeletal growth and to promote cartilage repair and regeneration.