Factors Regulating Development of Appendicular Skeletal Progenitors

 描述(申请人提供)：骨骼疾病，如骨关节炎和骨/软骨创伤，目前很难或不可能治疗。产生特定骨骼祖细胞的能力可能为使用再生医学方法的新治疗方法提供基础。为了实现这一点，了解骨骼祖细胞是如何在发育过程中产生的是至关重要的。尤其是，当侧板中胚层经历上皮到间充质的转变时，附件骨祖细胞就会产生，产生间充质骨祖细胞，然后从体轴向外迁移，形成肢芽。破译刺激肢体骨祖细胞生成的机制对于了解和治疗附件骨缺陷具有重要意义。最近的研究表明，维甲酸(RA)是维生素A的一种活性代谢物，是产生前肢骨骼祖细胞所必需的：对RA缺陷突变小鼠胚胎的研究表明，RA可以阻止前肢骨骼祖细胞的生长，但不能阻止后肢的萌发。RA信号是由RA合成酶控制的，包括将视黄醇(维生素A)代谢成视黄醛的视黄醇脱氢酶10(RDH10)，以及将视黄醛代谢成视黄醛的视黄醛脱氢酶2(RALDH2；ALDH1A2)。有趣的是，最近的一项全基因组关联研究表明，RA的前肢特异作用表明，严重的手部骨关节炎(最常见的关节炎形式)，而不是髋关节或膝关节骨关节炎， 与人类ALDH1A2基因变异体有关，该基因变异体在关节软骨中表达较低。RA通过作为核内RA受体的配基直接调节基因转录，将RA反应元件结合在靶基因附近。在发育过程中，Raldh2-/-胚胎(缺乏RA活性)不能诱导Tbx5的表达，Tbx5是已知的最早的前肢发育标志，而Rdh10-/-胚胎(RA活性大大降低)表现出Tbx5表达延迟，限制在较小的区域。初步研究表明，RA的作用模式之一可能是抑制树干成纤维细胞生长因子信号，从而允许Tbx5表达的开始。然而，可能存在RA作用的替代机制，包括RA对Tbx5的直接调节或RA对Hox4/5基因的调节，这可能是诱导Tbx5在前肢领域所必需的。我们将使用遗传功能丧失的方法来揭示RA通过与Tbx5、Hox基因和成纤维细胞生长因子信号相互作用来刺激侧板中胚层分化为前肢骨骼祖细胞命运的机制。这个项目将产生有关产生附件骨祖细胞所需的信号机制的重要基本信息，这可能有助于骨骼疾病的治疗。

 DESCRIPTION (provided by applicant): Skeletal disorders such as osteoarthritis and bone/cartilage wounds are currently difficult or impossible to treat. The ability to generate specific skeletal progenitor cells may provide the basis for new treatment therapies using a regenerative medicine approach. In order for this to occur it is essential to understand how skeletal progenitors arise during development. Appendicular skeletal progenitors, in particular, are generated when lateral plate mesoderm undergoes an epithelial-to- mesenchymal transition to generate mesenchymal skeletal progenitors that migrate away from the body axis to form the limb buds. Deciphering the mechanism that stimulates the generation of limb skeletal progenitors is important for understanding and treating appendicular skeletal defects. Recent studies have shown that retinoic acid (RA), an active metabolite of vitamin A, is required specifically for generation of forelimb skeletal progenitors: studies on RA-deficient mutant mouse embryos demonstrated a blockage of forelimb but not hindlimb budding. RA signaling is controlled by RA-synthesizing enzymes, including retinol dehydrogenase 10 (RDH10) that metabolizes retinol (vitamin A) to retinaldehyde, followed by retinaldehyde dehydrogenase 2 (RALDH2; ALDH1A2) that metabolizes retinaldehyde to RA. Interestingly, a forelimb-specific role for RA was shown by a recent genome-wide association study showing that severe osteoarthritis of the hand (the most common form of arthritis), but not hip or knee osteoarthritis, is associated with human ALDH1A2 gene variants that exhibit lower expression in articular cartilage. RA directly regulates gene transcription by functioning as a ligand for nuclear RA receptors that bind RA response elements near target genes. During development, Raldh2-/- embryos (that lack RA activity) fail to induce expression of Tbx5, the earliest known marker of forelimb development, whereas Rdh10-/- embryos (with greatly reduced RA activity) exhibit delayed Tbx5 expression limited to a smaller domain. Preliminary studies suggest that one mode of RA action may be repression of trunk FGF signaling to permit onset of Tbx5 expression. However, alternative mechanisms of RA action may exist including direct RA regulation of Tbx5 or RA regulation of Hox4/5 genes that may be required for induction of Tbx5 in the forelimb field. We will use a genetic loss-of-function approach to uncover the mechanism through which RA interacts with Tbx5, Hox genes, and FGF signaling to stimulate differentiation of lateral plate mesoderm to a forelimb skeletal progenitor fate. This project will generate important basic information on the signaling mechanisms needed for generation of appendicular skeletal progenitors that may aid in the treatment of skeletal disorders.