Fate and Regulation of Fracture-induced Prx1 Cells

项目总结 骨折愈合是一个精心安排的再生过程，但在很大程度上仍不清楚。揭示了细胞 控制骨折修复的分子机制将有助于确定新的治疗靶点来治疗患者 这是一个与临床相关的问题，每年影响美国60万人。 自体骨移植是治疗骨不连的黄金标准，但它有许多缺点：它们具有侵入性，成本高昂， 风险很大，有时甚至没有效果。因此，存在着对替代和新疗法的迫切和未得到满足的需求 来治疗非工会。这项建议的最终目标是获得关于关键驱动机制的新知识 修复骨折，并设计它们以促进愈合。骨折后骨骼的高度再生能力 意味着成体祖细胞的存在有助于修复过程。然而，大自然和 这些祖细胞的表达模式仍然难以捉摸。我们发现了一个离散的血管周围种群 表达PRX1(PRX1+)的细胞，驻留在公认的再生壁龛中。通过调查功能，我们 已发现骨折诱导Prx1表达和PRX1+表达的细胞有助于骨折修复 过程中，但细胞在分化过程中失去PRX1的表达。我们还发现，在骨折修复过程中，PRX1+ 细胞共表达BMP2和CXCL12。在进一步探索这个相声的路上，我们发现 在PRX1骨软骨前体细胞中缺乏BMP2的小鼠发现骨折愈合受损， 以PRX1和细胞因子CXCL12异常持续增加为特征。这些异常现象 用恢复愈合的CXCL12受体拮抗剂AMD3100纠正。最后，通过使用体内和 在体外方法中，我们已经表明BMP2通过CXCL12信号调节PRX1的表达。当前 知识和这些令人兴奋的新奇观察为核心假设设定了科学前提 这一建议，即PRX1表达细胞是骨折修复及其承诺的十字路口 它们的PRX1表达模式受BMP2之间适时的相互作用调节 和CXCL12。为了检验这一新的假设，本文提出了两个具体目标。AIM 1旨在确定 PRX1和PRX1表达细胞的需求及其在骨折修复中的命运和性质。AIM 2是专门设计的 为了确定PRX1的表达和PRX1+细胞命运的调节机制 BMP2和CXCL12在骨折修复过程中的相互作用将采用综合方法来处理 通过结合一代特别的基因工程小鼠，细胞追踪； 动物模型的教育使用；药理学和细胞移植研究；以及体外研究。一支由 已经召集了专家研究调查员，以确保项目的成功完成。它是 预计这项研究产生的新发现将具有重大的生物医学意义和 暗示：a)理解控制骨折愈合的细胞和分子机制；和b) 为开发治疗骨不连的药理学和细胞临床试验奠定基础。

PROJECT SUMMARY Fracture healing is a well-orchestrated regenerative process that remains largely unknown. Revealing the cellular and molecular mechanisms governing fracture repair will help identify novel therapeutic targets to treat patients that suffer of non-unions, a clinically relevant problem that affects annually 600,000 people in the United States. Bone autografts, the gold-standard treatment for non-unions, have multiple drawbacks: they are invasive, costly, risky, and sometime ineffective. Therefore, there is an urgent and unmet need for alternative and novel therapies to treat non-unions. The ultimate goal of this proposal is to gain new knowledge on pivotal mechanisms driving fracture repair and to devise them to promote healing. The highly regenerative ability of bones after fracture implies the existence of adult progenitors that contribute to the reparative process. However, the nature and the expression pattern of these progenitors is still elusive. We have discovered a discrete population of perivascular cells expressing Prx1 (Prx1+) that reside in recognized regenerative niches. By investigating functionality, we have found that facture elicits Prx1expression and Prx1+ expressing cells that contribute to the fracture repair process, but cells lose Prx1 expression with differentiation. We have also found that during fracture repair, Prx1+ cells co-express BMP2 and CXCL12. On the way to further explore this crosstalk, we discovered that the impaired fracture healing found in mice lacking a full complement of BMP2 in Prx1 osteochondroprogenitors, was characterized by an abnormally persistent increase of Prx1 and the cytokine CXCL12. These abnormalities were corrected by AMD3100, a CXCL12 receptor antagonist that restored healing. Lastly, by using in vivo and in vitro approaches, we have indicated that BMP2 through CXCL12 signaling regulates Prx1 expression. Current knowledge and these exciting novel observations set the scientific premise to the central hypothesis of this proposal, namely that Prx1 expressing cells are a crossroad in fracture repair and their commitment to regeneration and their Prx1 expression pattern is regulated by a well-timed interplay between BMP2 and CXCL12. Two specific aims are proposed to test this novel hypothesis. Aim 1 is designed to determine the requirement of Prx1 and Prx1 expressing cells and their fate and nature during fracture repair. Aim 2 is designed to determine the mechanisms by which the expression of Prx1 and the fate of Prx1+ cells is regulated by the interplay between BMP2 and CXCL12 during fracture repair. A comprehensive approach will be applied to accomplish the proposed aims, by combining generation of ad hoc genetically engineered mice; cell-tracing; educated use of animal models; pharmacological and cell transplant studies; and in vitro studies. A team of expert research investigators has been assembled to ensure successful achievement of the project. It is expected that the novel findings generated from this research will have major biomedical relevance and implications for: a) understanding the cellular and molecular mechanisms governing fracture healing; and b) laying the groundwork for the development of pharmacological and cell-based clinical trials to treat non-unions.