Tissue engineering application of endochondral ossification for bone regeneration

描述(申请人提供)：目前可用于治疗大型节段性缺损的骨移植技术通常会产生血运不佳和宿主整合不良的替代组织，导致与骨坏死或移位相关的临床失败。因此，在创伤、骨折不愈合、脊柱融合、骨坏死和节段性截骨(如肿瘤切除)的治疗过程中，仍有一个显著的未得到满足的需要来改善临床结果。组织工程学是一种很有前途的促进骨再生的策略。然而，骨组织工程中通过成骨直接刺激骨形成的一般方法在很大程度上是不成功的。在这项建议中，我们通过软骨中间体来实现骨再生。这个过程被称为软骨内骨化，是长骨形成的正常发育机制，也是大多数骨折愈合的途径。我推测，通过软骨性中间体的骨再生将产生一种在形式和功能上都与天然骨相似的新组织。为了验证这一假设，我将在一个临界大小的小鼠骨缺损中比较软骨移植的骨再生和黄金标准的骨移植技术。为了支持这一方法，我有初步的数据表明，含有肥大的软骨细胞的软骨移植可以促进血管良好和完整的骨再生。除了评估软骨移植与骨移植再生骨的质量外，我还将确定修复发生的机制。根据我的假设，骨再生将通过软骨内成骨过程发生，导致肥大的软骨细胞凋亡，并产生宿主来源的骨再生。然而，初步数据表明，供体软骨通过一种尚未解决的机制促进骨再生。我将使用遗传和细胞标记技术在整个修复过程中追踪细胞表型，以评估软骨如何修复大型骨缺损。这项研究建议的第二个目的是将通过软骨内成骨促进骨再生的概念转化为临床可行的技术。为了实现这一点，我将设计生物修饰的合成支架，促进间充质干细胞(MSCs)形成肥大的软骨。支架的设计将根据软骨内成骨的过程调整不同的降解率，以优化体内的骨再生。在早期的研究中，我已经在组织工程支架中表征了间充质干细胞的肥大成熟，并开发了一种针对软骨形成而调整的基质金属蛋白酶-7生物反应系统。这些目标共同解决了一个重要的临床问题，即通过一种能够改进当前骨再生技术的可翻译技术。此外，这个项目是专门为满足我与肌肉骨骼再生相关的长期职业目标而设计的，通过利用多能祖细胞和生物响应支架来概括临床相关活体模型的正常发育和/或修复机制。

DESCRIPTION (provided by applicant): Bone graft technologies currently available to treat large segmental defects typically generate replacement tissue with poor vascularity and poor host integration that leads to clinical failures associated with osteonecrosis or dislodgement. As a result, there is a significant unmet need to improve the clinical outcome in procedures treating trauma, fracture non-unions, spinal fusion, osteonecrosis, and segmental bone osteotomies such as those created upon tumor removal. Tissue engineering is a promising strategy to promote bone regeneration. However, the general approach in bone tissue engineering to directly stimulate bone formation through osteogenesis has been largely unsuccessful. In this proposal we approach bone regeneration through a cartilage intermediate. This process, called endochondral ossification, is the normal developmental mechanism for formation of long bones, and is the pathway through which the majority of fractures heal. I hypothesize that bone regeneration through a chondrogenic intermediate will produce a neotissue that resembles the native bone in both form and function. To test this hypothesis I will compare bone regeneration from a cartilage graft to the gold-standard bone graft technique in a critically sized murine bone defect. In support of this approach, I have preliminary data demonstrating that a cartilage graft containing hypertrophic chondrocytes promotes a well-vascularized and integrated bone regenerate. In addition to evaluating the quality of bone regenerated by a cartilage graft versus bone graft, I will determine the mechanism through which repair occurs. According to my hypothesis, bone regeneration will occur through the process of endochondral ossification, resulting in apoptosis of hypertrophic chondrocytes and producing a bone regenerate that is host derived. However, preliminary data indicate that donor cartilage is contributing to the bone regenerate through an unresolved mechanism. I will use genetic and cell labeling techniques to trace the cell phenotype throughout this repair process to evaluate how the cartilage heals large bone defects. The second aim of this research proposal is to translate the concept of promoting bone regeneration through endochondral ossification into a clinically viable technology. To accomplish this I will design biologically modified synthetic scaffolds that promote formation of hypertrophic cartilage from mesenchymal stem cells (MSCs). Scaffold will be designed with variable degradation rates tuned to the process of endochondral ossification to optimize bone regeneration in vivo. In earlier studies I have characterized hypertrophic maturation of MSCs in tissue-engineered scaffolds and developed a MMP-7 bioresponsive system tuned to chondrogenesis. Together these aims address an important clinical problem with a translatable technology capable of improving current bone regeneration techniques. Furthermore this project was specifically designed to meet my long-term career objective related to musculoskeletal regeneration by utilizing multipotent progenitor cells and bioresponsive scaffolds to recapitulate normal development and/or repair mechanisms in clinically relevant in vivo models.