Targeted Stem Cell Therapy Coupling Angiogenesis and Osteogenesis for Bone Defect

描述（由申请人提供）：骨髓间充质干细胞（MSC）在再生医学中的潜力越来越受到关注。在可以利用间充质干细胞再生的不同组织中，骨具有更大的潜力，原因包括：间充质干细胞是成骨成骨细胞的祖细胞，而骨是间充质干细胞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陷中的潜力。骨缺损的主要问题之一是骨折的延迟愈合或不愈合。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将在未来几年增加。在美国，每年估计有600万例骨折，其中约10%变为骨不连。因此，成功解决这一问题的新治疗方法将极大地有利于医疗保健和经济。很明显，大多数无菌性不愈合骨折需要不同程度的生物强化。因此，利用MSC作为基因工程干细胞来源，将血管生成与成骨结合起来的新治疗方法将极大地促进患者管理，降低发病率和经济负担。尽管间充质干细胞具有再生潜力，但间充质干细胞治疗的局限性之一是移植细胞在体内的靶向性归巢。我们最近开发了一种通过瞬时异位表达1421整合素来增强骨髓间充质干细胞骨特异性归巢的方法。这一策略不仅显著增加了骨内间充质干细胞的数量，而且大大减少了肺内间充质干细胞的夹闭。利用这种靶向方法，我们最近证明了MSC，通过基因工程产生BMP2，在骨质疏松症小鼠模型的头几个月显著改善了骨密度。我们实验室使用表达VEGF的基因工程MSC对节段性骨缺损进行的进一步初步研究表明，血管重构显著。这些研究结果为骨折不愈合的新治疗方法的发展提供了独特的方向。在复杂骨折和不愈合中，限制有效骨诱导的另一个原因是缺乏足够数量的间充质干细胞。因此，通过外周动员和增殖内源性丰富间充质干细胞的策略将大大增加骨化。这种方法将是治疗骨质疏松症患者常见的不愈合骨折和多发骨折的理想方法。内源性间充质干细胞在这些病理中使用的另一个优势是相关的血管损伤，因为间充质干细胞也被证明在血管再生中有效。结合这两个方面，本研究的目的是在临床前小鼠模型中测试靶向干细胞治疗，结合成骨和血管生成诱导剂对不愈合骨折的作用，并确定使用生长因子和诱导动员的化合物对内源性MSC的外周动员和增殖的治疗潜力。这些研究的积极结果可能导致新的和有效的骨修复治疗策略的发展。

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. PUBLIC HEALTH RELEVANCE: A major problem in skeletal defects is non-union of bone fractures. The potential of bone marrow- derived mesenchymal stem cells (MSC) in regenerative medicine is increasingly gaining attention especially for diseases affecting the skeleton since 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 non-union bone defects, which are difficult to treat.