THE ROLE OF THE EXTRACELLULAR MATRIX IN SCARLESS TENDON HEALING

 描述（由申请人提供）：肌腱撕裂是一种常见的肌肉骨骼损伤，愈合后功能结构无法恢复。肌腱不能恢复功能性结构导致损伤进展和手术修复后再撕裂的高发生率。无瘢痕肌腱愈合，恢复天然组织特性，可以改善手术结果或完全消除手术修复的需要，但通常不会在出生后的哺乳动物中观察到。成年Murphy Roths Large（MRL/MpJ）小鼠表现出再生能力的发现使这种小鼠品系成为研究成年再生愈合机制的令人兴奋的模型。对MRL/MpJ小鼠再生机制的研究产生了涉及全身和局部组织水平的假设，但没有结论性数据。拟议的研究询问MRL/MpJ小鼠的全身环境及其肌腱的局部环境对无瘢痕肌腱愈合的贡献。我们的假设是，MRL/MpJ肌腱的无瘢痕愈合是由一种独特的临时细胞外基质（ECM）介导的，该基质促进了基质产生细胞的排列和增殖，但由于基质金属蛋白酶9（MMP 9）的分解代谢活性增加，最终不会导致过度的基质沉积。除了我们发表的数据显示MRL/MpJ小鼠在中间物质冲压损伤中表现出改善的愈合外，支持这一新假设的其他证据包括：（1）数据表明再生MRL/MpJ小鼠中的临时ECM在结构和组成上不同于B6肌腱愈合中的临时ECM;（2）数据表明在愈合的早期阶段，MRL/MpJ肌腱在这种明显不同和更好对齐的临时ECM序列的背景下表现出增加的细胞增殖和改善的对齐，以及（3）相关数据显示MMP 9和临时ECM的表达增加，临时ECM被更好对齐的长期ECM取代。我们建议询问全身和局部因素，有助于合成MRL/MpJ的独特的临时ECM（目的2），并阐明这种临时ECM在调节细胞反应（目的1）的作用。我们还将探索来自MRL/MpJ愈合肌腱的临时ECM的治疗潜力，以促进瘢痕介导的B6小鼠中的无瘢痕肌腱愈合（目的3）。新的显微外科技术和近交系小鼠品系被用来解偶联全身环境和肌腱的无瘢痕肌腱愈合的贡献。肌腱器官培养也用于确定来自再生MRL/MpJ小鼠的临时ECM在调节导致无瘢痕肌腱愈合的细胞活性中的作用。这些研究通过分离先天肌腱和全身环境对无瘢痕肌腱愈合的贡献，为治疗干预的发展奠定了基础。MRL/MpJ的临时ECM作为治疗干预的潜在效用，利用导致无瘢痕肌腱愈合的生物和结构队列，可能对肌腱组织工程领域具有高度影响力。

 DESCRIPTION (provided by applicant): Tendon tears are common musculoskeletal injuries that heal without restoration of the functional structure. Failure of healing tendons to restore th functional structure leads to progression of injury and high incidence of retear after surgical repair. Scarless tendon healing, with restored native tissue properties, could improve surgical outcome or eliminate the need for surgical repair altogether, but is not typically observed in postnatal mammals. The discovery that adult Murphy Roths Large (MRL/MpJ) mice exhibit a regenerative capacity has distinguished this mouse strain as an exciting model to investigate mechanisms that underlie adult regenerative healing. Investigation into the regenerative mechanisms of MRL/MpJ mice has generated hypotheses that implicate both, the systemic and local tissue level, but no conclusive data exists. The proposed studies interrogate the contribution of the systemic environment of the MRL/MpJ mouse and the local environment of its tendon to scarless tendon healing. Our hypothesis is that scarless healing in MRL/MpJ tendons is mediated by a unique provisional extracellular matrix (ECM) that promotes improved alignment and proliferation of matrix producing cells but does not ultimately lead to excessive matrix deposition due to increased catabolic activity of Matrix Metalloproteinase 9 (MMP9). In addition to our published data that show that MRL/MpJ mice exhibit improved healing in midsubstance punch injuries, additional evidence that supports this novel hypothesis includes: (1) data that show that the provisional ECM in regenerative MRL/MpJ mice differs in structure and composition than the provisional ECM in healing B6 tendons; (2) data that show that during the early phases of healing, MRL/MpJ tendons exhibit increased cell proliferation and improved alignment in the context of this distinctly different and better aligned provisional ECM; and (3) correlated data that show increased expression of MMP9 and a provisional ECM that is replaced by a better aligned long term ECM. We propose to interrogate the systemic and local factors that contribute to synthesis of MRL/MpJ's unique provisional ECM (Aim 2) and elucidate the role of this provisional ECM in modulating the cellular response (Aim 1). We will also explore the therapeutic potential of the provisional ECM derived from MRL/MpJ healing tendons to promote scarless tendon healing in scarmediated B6 mice (Aim 3). Novel microsurgical techniques and inbred mouse strains are utilized to uncouple the contribution of the systemic environment and the tendon to scarless tendon healing. Tendon organ culture is also employed to determine the role of the provisional ECM from regenerative MRL/MpJ mice in modulating the cellular activity that leads to scarless tendon healing. These studies set the foundation for development of therapeutic interventions by isolating the contributions of the innate tendon and the systemic environment to scarless tendon healing. The potential utility of MRL/MpJ's provisional ECM as a therapeutic intervention that harnesses the biological and structural queues that lead to scarless tendon healing could be highly impactful for the field of tendon tissue engineering.