PDGF-regulated stem cells and bone disease

骨骼的生长和愈合能力是可能的，因为出生后的骨骼干细胞（SSCs）持续存在， 最终生成成骨细胞。血小板衍生生长因子受体β（PDGFRβ）表达于 SSCs和成骨细胞，但其功能作用尚未在体内表征。最近，人类与 已报道PDGFRB中的功能获得性突变表现出骨骼疾病， 儿童或青少年时期的骨质流失或骨骼过度生长。然而，靶细胞类型和分子 PDGFRβ驱动的骨骼疾病的潜在机制尚不清楚。申请人的长期目标是 发展对PDGF通路如何调节间充质细胞可塑性的机制理解。骨 因为成骨细胞产生富含胶原蛋白的有机基质，称为类骨质， 矿化成骨细胞可塑性和胶原蛋白产生的缺陷可能是由 PDGF通路。因此，本提案的具体目标是确定PDGF调节机制， 控制SSC的细菌及其对骨骼疾病的贡献。这个项目的基本假设是， PDGFRβ通过调节下游效应子的平衡调节SSC增殖和分化。 信号转导子和转录激活子（STAT）家族。Aim 1将使用SSC靶向Cre/lox ap- 诱导PDGFRβ激活突变和组合STAT缺失，并确定是否 STAT在体内介导骨疾病。来源于突变小鼠骨骼的原代SSC将用于研究 门控PDGFRβ调节的STAT信号转导是否在体外或之后调节SSC自我更新和分化 移植作为替代方法，PDGFRβ激活突变将靶向软骨细胞。 目的2将描述新的小鼠模型，这些小鼠模型具有PDGFRβ激活突变，最常见于 Penttinen综合征和Kosaki过度生长综合征，分别为V665 A和P584 R。Aim 2还将 探索激酶抑制剂对具有功能获得性PDGFRβ信号传导的小鼠的益处。AIM 3将研究小鼠 PDGFRβ功能获得和丧失突变，以确定PDGFRβ调节的过程。 SSCs及其后代在出生后骨骼生长过程中的作用。突变细胞将被命运映射，以确定如何 不同水平的PDGFRβ活性调节体内增殖、分化和细胞命运。这项工作是前- 预计将确定PDGFRβ信号通路如何介导骨生成， 信号传导产生骨骼疾病，这将指向新的治疗策略和更好的应用。 骨修复的方法这些项目的结果将大大促进对南南合作规则的理解， 保守的机制。关于介导疾病相关PDG的信号通路和细胞类型的信息- FRβ信号传导将为骨骼疾病的新治疗方法的开发提供信息。和识别 PDGFRβ在骨生长中的特殊作用将开始确立其作为治疗的分子靶点。这一切 信息将改善患病或受损骨骼的结构和功能的恢复。

The growth and healing ability of the skeleton is possible because postnatal skeletal stem cells (SSCs) contin- ually generate bone-forming osteoblasts. Platelet-derived growth factor receptor β (PDGFRβ) is expressed on SSCs and osteoblasts, but its functional roles have not been characterized in vivo. Recently, humans with gain-of-function mutations in PDGFRB have been reported to exhibit skeletal disease involving progressive bone loss or skeletal overgrowth during childhood or adolescence. However, the target cell type and molecular mechanisms underlying PDGFRβ-driven skeletal disease are unknown. The applicant’s long-term goal is to develop a mechanistic understanding of how the PDGF pathway regulates mesenchymal cell plasticity. Bone forms because osteoblasts produce collagen-rich organic matrix called osteoid, which subsequently becomes mineralized into bone. Defects in cell plasticity and collagen production may underlie bone diseases driven by the PDGF pathway. Therefore, the specific objective in this proposal is to identify PDGF-regulated mecha- nisms controlling SSCs and their contribution to skeletal disease. The hypothesis underlying this project is that PDGFRβ regulates SSC proliferation and differentiation through the balance of downstream effectors of the signal transducer and activator of transcription (STAT) family. Aim 1 will use an SSC-targeted Cre/lox ap- proach to induce PDGFRβ activating mutations and combinatorial STAT deletions, and determine whether STATs mediate bone disease in vivo. Primary SSCs derived from mutant mouse bones will be used to investi- gate whether PDGFRβ-regulated STAT signaling regulates SSC self-renewal and differentiation in vitro or after transplantation. As an alternative approach, PDGFRβ activating mutations will be targeted to chondrocytes. Aim 2 will characterize new mouse models with the PDGFRβ activating mutations most commonly found in Penttinen syndrome and Kosaki overgrowth syndrome, V665A and P584R, respectively. Aim 2 will also ex- plore the benefits of kinase inhibitors for mice with gain-of-function PDGFRβ signaling. Aim 3 will study mice with gain- and loss-of-function mutations in PDGFRβ to identify the processes by which PDGFRβ regulates SSCs and their progeny during postnatal skeleton growth. Mutant cells will be fate mapped to determine how different levels of PDGFRβ activity regulate proliferation, differentiation, and cell fate in vivo. This work is ex- pected to define how the PDGFRβ signaling pathway mediates osteogenesis and how too much or too little signaling generates diseases of the skeleton, which will point to novel therapeutic strategies and better ap- proaches for bone repair. The results of these projects will significantly advance understanding of SSC regula- tory mechanisms. Information about signaling pathways and cell types that mediate disease-associated PDG- FRβ signaling will inform the development of new therapeutic approaches for skeletal diseases. And identifying the specific role of PDGFRβ in bone growth will begin to establish it as a molecular target for therapy. All of this information will improve the restoration of structure and function to diseased or damaged bones.