Mechanobiology of fracture healing during skeletal disuse

项目摘要/摘要 肌肉骨骼卸载(废弃)导致的肌肉和骨量及强度降低 骨质疏松症(骨质疏松症)长期以来一直与骨折风险增加、骨愈合障碍和更糟糕的情况有关 病人的结果。目前的疾病治疗药物主要集中在骨靶向治疗(抗- 吸收率和甲状旁腺激素)，在治疗对骨骼健康至关重要的肌肉损失方面仍然无效 维修和降低跌倒风险。虽然骨损伤后的早期康复和物理康复是 众所周知，它有助于骨折愈合和肌肉恢复，但我们对它的了解仍然存在空白 骨性骨折后合适的机械加载方案--由于对如何进行的了解有限 停用会影响骨折愈合的机制生物学。在初步工作中，我们开发了一种小鼠模型 在后肢卸载、有或无活动的情况下，废弃状态下的骨折愈合。这个模型概括了 废用期间骨修复的许多临床特征(骨骼肌量减少，减少 放射学骨痂形成)有新的发现，如骨痂血管改变和破骨细胞生成 它们会因移位而减弱。这项提案中概述的目标寻求大大扩展我们的 直接以肌肉和/或骨骼为靶点的非侵入性加载方式的初步研究 废弃过程中愈伤组织机械生物学的关键细胞和分子介质。在被指导的K99 这笔赠款的一部分，我们将利用非侵入性光遗传学和直接胫骨负载来确定最佳 在废弃期间增加骨痂愈合、生物力学完整性和肌肉质量的机械输入(目标1)。 接下来，我们将使用高通量技术(RNAseq和流式细胞术)来研究 废弃期间非侵入性加载影响骨痂机械生物学的潜在机制(目标2)。 在R00阶段，Buettmann博士将利用最近的机械学发现来确定条件 机械敏感分子在废弃状态下协调负荷诱导的骨折愈合中的作用 (目标3)。这些见解将有助于弥合我们对废用如何改变愈伤组织的理解上的一个重大差距 机械生物学以及如何利用机械调节的分子来改善骨折愈合和 骨软骨症“高危”患者的康复。这些发现，由于临床前模型的 可译性，也可能对其他与受损骨折相关的病理产生深远的影响 治愈和改变机械感觉，如衰老、肥胖/糖尿病和荷尔蒙剥夺。Dr。 Buettmann组建了一个指导团队和具有骨骼专业知识的合作者 再生/骨免疫学(Olivares-Navarrete博士)、光遗传学和肌肉-骨骼机械调节 (Megan Killian博士)，肌肉骨骼生物信息学(Charles Farber博士)，生物力学(Hannah Dailey博士) 和机械生物学(亨利·多纳休博士)。这个项目将为Buettmann博士准备一个独立的 通过为R01获取必要的培训和研究数据，在肌肉骨骼研究方面的研究生涯 同等奖。

PROJECT SUMMARY/ABSTRACT Decreased muscle and bone mass and strength resulting from musculoskeletal unloading (disuse osteosarcopenia) has long been associated with increased fracture risk, impaired bone healing and worse patient outcomes. Current disease modifying drugs are centered primarily on bone targeted therapies (anti- resorptives and PTH), and remain ineffective at targeting muscle loss that appears crucial for healthy bone repair and reducing fall risk. Although early reambulation and physical rehabilitation following bone injury is known to be beneficial for fracture healing and muscle recovery, there remains a gap in our knowledge of the appropriate mechanical loading regimens following osteosarcopenic fracture due to limited knowledge of how disuse affects fracture healing mechanobiology. In preliminary work, we have a developed a murine model of fracture healing during disuse by hindlimb unloading, with and without remobilization. This model recapitulates many clinical features of bone repair during disuse (decreased skeletal muscle mass, decreased radiographical callus formation) with new findings such as altered callus vascularity and osteoclastogenesis that are attenuated with reambulation. The aims outlined in this proposal seek to greatly expand upon our preliminary studies by using non-invasive loading modalities targeting muscle and or bone directly to determine the critical cellular and molecular mediators of callus mechanobiology during disuse. In the mentored K99 portion of this grant, we will utilize non-invasive optogenetics and direct tibial loading to determine optimal mechanical inputs to increase callus healing, biomechanical integrity, and muscle mass during disuse (Aim 1). Next using high-throughput techniques (RNAseq and flow cytometry), we will investigate the potential underlying mechanisms by which non-invasive loading affects callus mechanobiology during disuse (Aim 2). During the R00 phase, Dr. Buettmann will leverage recent mechanistic findings to determine the conditional role of mechanosensitive molecules in coordinating load-induced alterations in fracture healing during disuse (Aim 3). These insights will help bridge a significant gap in our understanding of how disuse alters callus mechanobiology and how mechanically-regulated molecules can be leveraged to improve fracture healing and rehabilitation in osteosarcopenic “high risk” patients. These findings, owing to the preclinical model’s translatability, could also have far-reaching implications for other pathologies associated with impaired fracture healing and altered mechanosensation such as aging, obesity/diabetes, and hormonal deprivation. Dr. Buettmann has assembled a mentoring team and collaborators with expertise in bone regeneration/osteoimmunology (Drs. Olivares-Navarrete), optogenetics and muscle-bone mechanoregulation (Dr. Megan Killian), musculoskeletal bioinformatics (Dr. Charles Farber), biomechanics (Dr. Hannah Dailey) and mechanobiology (Dr. Henry Donahue). This project will prepare Dr. Buettmann for an independent research career in musculoskeletal research by acquiring the necessary training and research data for an R01 equivalent award.