Division of Diabetes, and Endocrinology, Department of Internal Medicine, Kobe University Graduate School of Medicine, Japan.
Bone. 2012 Jul;51(1):158-67. doi: 10.1016/j.bone.2012.04.017. Epub 2012 May 2.
Bone morphogenetic proteins (BMPs) are critical for bone regeneration and induce ectopic bone formation in vivo. The constitutively activating mutation (R206H) of the BMP type 1 receptor, activin A type 1 receptor/activin-like kinase 2 (ACVR1/ALK2), underlies the molecular pathogenesis of fibrodysplasia ossificans progressiva (FOP) in which heterotopic ossification occurs in muscle tissue. In the present study, we performed a comparative DNA microarray analysis between stable empty vector- and ALK2(R206H)-transfected mouse myoblastic C2C12 cells. Forty genes were identified whose expression was increased >3.5 times in the experimental group versus the control. The bone formation-related factor, Tmem119, was included in this group. Osteoblast differentiation markers and mineralization were enhanced in C2C12 cells stably expressing Tmem119. Differentiation of myoblastic cells into myotubes was suppressed but differentiation into chondrocytes was little affected. Transcriptional activity of the BMP-2 signaling molecules, Smad1/5, was increased even in the absence of exogenous BMP-2. Endogenous BMP-2 levels positively correlated with Tmem119 levels. A BMP-2/4 neutralizing antibody and dorsomorphin, an ALK2 inhibitor, antagonized Tmem119-enhanced alkaline phosphatase (ALP) levels. Tmem119 siRNA antagonized the BMP-2-induced ALP and osteocalcin, but not Runx2 and Osterix, mRNAs, in C2C12 cells. In conclusion, Tmem119 levels were increased by the FOP-associated constitutively activating ALK2 mutation in myoblasts. The data show that Tmem119 promotes the differentiation of myoblasts into osteoblasts and the interaction with the BMP signaling pathway likely occurs downstream of Runx2 and Osterix in myoblasts. Tmem119 may play a critical role in the commitment of myoprogenitor cells to the osteoblast lineage.
骨形态发生蛋白（BMPs）对于骨再生至关重要，并在体内诱导异位骨形成。BMP 型 1 受体（激活素 A 型 1 受体/激活素样激酶 2，ACVR1/ALK2）的组成性激活突变（R206H）是纤维发育不良性骨化性进展（FOP）的分子发病机制的基础，其中异位骨化发生在肌肉组织中。在本研究中，我们对稳定的空载体和 ALK2（R206H）转染的鼠成肌细胞 C2C12 细胞进行了比较 DNA 微阵列分析。在实验组与对照组相比，有 40 个基因的表达增加了 3.5 倍以上。该组包括骨形成相关因子 Tmem119。在稳定表达 Tmem119 的 C2C12 细胞中，成骨细胞分化标记物和矿化增强。成肌细胞向肌管的分化受到抑制，但向软骨细胞的分化影响较小。即使没有外源性 BMP-2，BMP-2 信号分子 Smad1/5 的转录活性也增加。内源性 BMP-2 水平与 Tmem119 水平呈正相关。BMP-2/4 中和抗体和 ALK2 抑制剂 Dorsomorphin 拮抗 Tmem119 增强的碱性磷酸酶（ALP）水平。Tmem119 siRNA 拮抗 BMP-2 诱导的 C2C12 细胞中 ALP 和骨钙素，但不拮抗 Runx2 和 Osterix mRNA。总之，FOP 相关的组成性激活 ALK2 突变在成肌细胞中增加了 Tmem119 的水平。数据表明，Tmem119 促进成肌细胞向成骨细胞分化，并且与 BMP 信号通路的相互作用可能发生在成肌细胞中 Runx2 和 Osterix 下游。Tmem119 可能在肌前体细胞向成骨细胞谱系的定向中起关键作用。
