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，最常见的侏儒症的遗传原因是软骨发育不全，这一发现证明了FGFR3的突变。这意味着FGFR3下游的通路是控制骨骼生长的中心。我们的目标是了解FGFR3在骨骼生长发育过程中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。我们推测FGFR3通过加速细胞衰老途径抑制细胞增殖，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，这些数据表明，FGFR3减少了处于S期的软骨细胞的数量，并减缓了软骨细胞和骨祖细胞的分化速度。有趣的是，FGFR3抑制了骨形态发生蛋白4(BMP4)在软骨细胞和软骨膜骨祖细胞中的表达，提示FGFR3可能通过调节BMP4的表达而使软骨膜中的骨生长与骨痂生长板的生长同步。尽管有这些知识，但关于FGFR3如何抑制骨骼生长仍有许多需要了解的地方。具体地说，FGFR3抑制细胞增殖的途径是什么？FGFR3下游抑制软骨膜和软骨细胞分化的介体是什么？如果不了解这些基本问题，就不太可能设计出针对软骨发育不全等侏儒症的介入治疗方法。我们将针对这些问题并通过追求以下特定目标来验证我们的假说：1)通过验证FGFR3加速细胞周期衰老的假说来研究FGFR3如何抑制软骨细胞的增殖；2a)通过靶向BMP4在转基因小鼠的软骨中表达BMP4来确定BMP4作为FGFR3信号的介导者的作用；以及2b)使用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。这些研究将利用独特的试剂，包括我们在初步研究期间创造的FGFR3转基因小鼠。使用这些试剂，我们可以直接测试FGFR3对BMP4表达变化的影响。这些研究将从根本上促进我们对生长板和软骨膜的联系的理解，并揭开FGFR3和BMP4新的生长调控通路。我们预计这些研究将提出控制骨骼生长和促进软骨修复和再生的新方法。

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.