Targeted Stem Cell Therapy Coupling Angiogenesis and Osteogenesis for Bone Defect

描述(申请人提供)：骨髓间充质干细胞(MSC)在再生医学中的潜力日益受到关注。在MSC可以再生的不同组织中，骨具有更大的潜力，原因包括：MSC是成骨细胞的前体细胞，而骨是MSC在体内的天然生态位。因此，开发最佳使用MSC的策略应该认识到它们在通常难以治疗的骨缺损中的潜力。骨缺损的主要问题之一是骨折延迟愈合或骨不连。人口统计数据显示，由于人口年龄的稳步上升，肌肉骨骼系统的并发症在未来几年将会增加。在美国，每年估计有600万例骨折，其中约10%成为骨不连。因此，成功解决这一问题的新治疗方法将极大地惠及医疗保健和经济。很明显，大多数无菌骨不连骨折需要不同程度的生物强化。因此，利用骨髓间充质干细胞作为基因工程干细胞来源将血管生成和成骨结合起来的新的治疗方法将极大地促进患者的管理，降低发病率和经济负担。尽管MSC具有再生潜力，但MSC治疗的局限性之一是体内移植细胞的靶向性归巢。我们最近开发了一种方法，通过瞬时、异位表达1421整合素来增强MSC的骨特异性归巢。这一策略不仅显著增加了MSC归巢到骨骼中的数量，还极大地减少了MSC在肺中的滞留。使用这种靶向方法，我们最近证明了，通过基因工程产生BMP2的MSC在最初的几个月里显著改善了骨质疏松小鼠的骨密度。在我们实验室的节段性骨缺损中，使用表达血管内皮生长因子的基因工程MSC进行的其他初步研究显示，显著的血管重塑。这些研究结果为开发一种治疗骨不连的新方法提供了独特的方向。在复杂的骨折和骨不连中，限制有效骨诱导的另一个原因是缺乏足够数量的MSC。因此，通过外周动员和增殖来丰富内源性MSC的策略将极大地增强骨化。这样的方法将是治疗骨不连和多发性骨折的理想方法，这也是骨质疏松症患者常见的。在这些病理中使用内源性MSC的另一个优点是相关的血管损伤，因为MSC也被证明在血管再生中有效。结合这两个方面，建议的研究的目的是在临床前的小鼠模型中测试定向干细胞治疗、成骨和血管生成诱导剂联合治疗骨不连的效果，并确定使用生长因子和动员诱导化合物进行外周动员和内源性MSC增殖的治疗潜力。这些研究的积极结果可能导致开发新的有效的骨修复治疗策略。

DESCRIPTION (provided by applicant): The potential of bone marrow-derived mesenchymal stem cells (MSC) in regenerative medicine is increasingly gaining attention. Among different tissues that can be regenerated using MSC, bone has greater potential for reasons including: MSC are the progenitor cells for bone-forming osteoblasts, and bone is the natural niche for MSC in the body. Thus, development of strategies to optimally use MSC should realize their potential in bone defects that are normally difficult to treat. One of the major problems in skeletal defects is the delayed healing or non-union of bone fractures. Demographic data reveal that due to the steadily rising age of the population, complications with the musculoskeletal system will increase during the coming years. Each year in the United States, there is an estimated six million fractures of which about 10% become non-union. Thus, new therapeutic approaches to successfully address this problem will hugely benefit health care and the economy. It is evident that the majority of aseptic non-union fractures require a variable degree of biological enhancement. Thus, new therapeutic approaches coupling angiogenesis to osteogenesis using MSC as genetically-engineered stem cell source will greatly advance patient management and reduce morbidity and economic burden. Despite the regenerative potential of MSC, one of the limitations in MSC therapy is target- specific homing of transplanted cells in vivo. We recently developed a method to enhance bone-specific homing of MSC by transient, ectopic expression of 1421 integrin. This strategy not only resulted in a significant increase in MSC homed to bone, but also greatly reduced the entrapment of MSC in the lungs. Using this targeting approach, we recently demonstrated that MSC, genetically-engineered to produce BMP2, significantly improved bone density during first few months in a mouse model of osteoporosis. Additional preliminary studies in a segmental bone defect from our lab using genetically-engineered MSC expressing VEGF demonstrated significant vascular remodeling. Results from these studies provide unique direction for the development of a new therapeutic approach for non-union fractures. In complicated fractures and non- unions, another reason that limits effective osteoinduction is the lack of MSC in sufficient numbers. Thus, strategies to enrich the MSC endogenously through peripheral mobilization and proliferation would greatly augment ossification. Such an approach will be ideal to treat non-union fractures and multiple fractures, which are also commonly encountered in patients with osteoporosis. An added advantage to the use of endogenous MSC in these pathologies is associated vascular damage, since MSC have also been shown to be effective in vascular regeneration. Combining these two aspects, the aims of the proposed studies is to test the effects of targeted stem cell therapy, coupling osteogenic and angiogenic inducers for non-union fractures in a preclinical mouse model, and to determine the therapeutic potential of peripheral mobilization and proliferation of endogenous MSC using growth factors and mobilization-inducing compounds. A positive outcome of these studies could lead to the development of new and effective treatment strategies for bone repair.