Bone Morphogenetic Protein Signals Are Required for Cartilage Formation and Differently Regulate Joint Development During Skeletogenesis
作者:Noriyuki Tsumaki、Takanobu Nakase、Takahiro Miyaji、Masaaki Kakiuchi、Tomoatsu Kimura、Takahiro Ochi、Hideki Yoshikawa
DOI:10.1359/jbmr.2002.17.5.898
日期:——
The bone morphogenetic protein (BMP) family consists of a large number of members and has diverse biological activities during development. Various tissues express pleural BMP family members, which seem to cooperatively regulate developmental events. Here, multiple BMP signals were inactivated in chondrocytes to clarify the function of BMPs during skeletogenesis. To obtain tissue‐specific inactivation, Noggin gene (Nog) was overexpressed in cartilage under the control of α2(XI) collagen gene (Col11a2) promoter/enhancer sequences. The resultant transgenic mice lacked most of their cartilaginous components, suggesting that cartilage does not develop without BMP signals. These effects seem to be mediated through down‐regulation of Sox9 expression. Conversely, specific BMP signals were activated in the skeleton by targeted expression of Bmp4 in cartilage and the resultant phenotype was compared with that of transgenic mice expressing growth and differentiation factor‐5 (GDF‐5), another BMP family member. Overactivity of Bmp4 in the skeleton caused an increase of cartilage production and enhanced chondrocyte differentiation, as GDF5 expression did, but it did not disturb joint formation as GDF5 did. During skeletogenesis, unique roles of each BMP may reside in the regulation of joint development. Together with the common effect on the cartilage overproduction by Bmp4 and GDF5 overactivation, loss of cartilage by inactivation of multiple BMPs in Noggin transgenic mice indicates that signals for cartilage production are reinforced by multiple BMPs exclusively. These conclusions may account for the reason why multiple BMPs are coexpressed in cartilage.
骨形态发生蛋白(BMP)家族由大量成员组成,在发育过程中具有多种生物活动。不同组织表达多种BMP家族成员,它们似乎协同调控发育事件。在这里,研究人员在软骨细胞中失活了多条BMP信号通路,以阐明BMP在骨骼发生过程中的功能。为了实现组织特异性失活,研究者在软骨内过表达了Noggin基因(Nog),该基因在α2(XI)胶原基因(Col11a2)启动子/增强子序列的控制下进行表达。结果转基因小鼠缺乏大部分软骨成分,表明没有BMP信号软骨无法发育。这些效应似乎是通过下调Sox9的表达来介导的。相反,特定BMP信号在骨骼中通过靶向在软骨中表达Bmp4而被激活,结果表型与表达生长与分化因子5(GDF-5)的转基因小鼠进行了比较,后者是另一个BMP家族成员。Bmp4在骨骼中的过度活性导致软骨生成增加,并增强了软骨细胞分化,类似于GDF5的作用,但并未如GDF5那样干扰关节形成。在骨骼发育过程中,各个BMP在关节发育调控中的独特作用可能存在。Bmp4和GDF5的过度激活共同对软骨过度生成产生影响,而在Noggin转基因小鼠中失活多条BMP信号则表明,软骨生成的信号是由多条BMP独立增强的。这些结论可能解释了为什么多种BMP在软骨中共同表达的原因。