Regulation of HSCs and HSC-Derived Osteoblasts in Osteogenesis Imperfecta

描述（由申请人提供）：成骨不全（OI）是一种常染色体显性遗传疾病，由编码I型胶原蛋白的两个基因（COL 1A 1或COL 1A 2）之一突变引起，是最常见的遗传性骨病。OI的特征是骨基质量轻度至重度减少，导致反复骨折和骨畸形。在美国，OI的发病率估计为每20，000例活产1例。目前还没有治愈OI的方法。治疗的目的是增加整体骨强度，以防止骨折。长期使用药物治疗有其自身的副作用;因此，在OI中正在实验性地测试几种策略以增强骨重建，其中之一是使用干细胞。我们已经证明造血干细胞（HSC）移植可以改善oim小鼠的骨缺损。我们还证实了在正常骨转换以及非稳定性骨折修复过程中，HSC产生成骨细胞和骨细胞。我们的初步数据从oim小鼠移植的克隆人口来源于一个单一的增强型绿色荧光蛋白（EGFP+）HSC表明移植小鼠的小梁和皮质参数的显着改善。我们还表明，HSC移植导致功能性成骨细胞的形成，沉积胶原蛋白并在体内形成骨。这些研究和我们的数据表明，成骨细胞可以来自一个新的来源，即HSC。因此，本研究的目的是验证HSC在成骨细胞分化中的作用，并了解促进HSC动员和成骨的分子因子对成骨细胞的分化具有治疗价值。目的1是建立HSC可以产生成骨细胞，采用来自小鼠的HSC的移植研究，所述小鼠具有在骨定向胶原I型启动子控制下的视觉标记，这允许特异性鉴定成骨细胞谱系的各个阶段的细胞。利用在造血细胞中表达GFP和在非造血组织中表达红色荧光蛋白（RFP）的小鼠，我们将从HSC进行谱系追踪。目的2的目标是表征在OI中通过HSC修饰骨重建的因素，并确定调节HSC分化为成骨细胞的分子机制。本研究将在体外和体内研究各种因素对HSC动员及其向成骨细胞分化的影响。这项研究的结果将是重要的，因为它们可以应用于长期研究，以加强和加速骨愈合的OI。这将通过使用和调节HSC为许多骨疾病和损伤的治疗开辟许多新的途径。

DESCRIPTION (provided by applicant): Osteogenesis imperfecta (OI), an autosomal dominant disorder caused by a mutation in one of the two genes that encode type I collagen (COL1AI or COL1A2), is the most common hereditary bone disease. OI is characterized by mild to severe reduction in the quantity of bone matrix that leads to repeated fractures and bone deformity. In the United States, the incidence of OI is estimated to be 1 per 20,000 live births. A present there is no cure for OI. Treatment is aimed at increasing overall bone strength to prevent fracture. Long-term treatment with the drugs has its own side effects; therefore several strategies are being tested experimentally in OI to enhance bone remodeling, one of them being the use of stem cells. We have shown that hematopoietic stem cell (HSC) transplantation can ameliorate the bone defects seen in oim mice. We also demonstrated that HSCs gives rise to osteoblasts and osteocytes during normal bone turnover as well as non- stabilized fracture repair. Our preliminary data from oim mice transplanted with a clonal population derived from a single enhanced green fluorescent protein (EGFP+) HSC demonstrates a significant improvement in the trabecular and the cortical parameters in engrafted mice. We also show that HSC transplantation leads to the formation of functional osteoblasts that deposited collagen and formed bone in vivo. These studies and our data suggest that osteoblasts can be derived from a novel source, i.e. HSCs. Thus, this proposal is to test the hypothesis that HSCs can give rise to osteoblasts in OI and understanding the molecular factors that promote its mobilization as well as osteogenesis could have therapeutic value in OI. Aim 1 is to establish that HSCs can give rise to osteoblasts employing transplantation studies with HSCs derived from mice having visual markers under the control of a bone directed collagen type I promoter, which allows for specific identification of cells at various stages of osteoblast lineage. Utilizing the mice expressing GFP in the hematopoietic cells and Red Fluorescent Protein (RFP) in the non-hematopoietic tissues we will do lineage tracing from the HSCs. The goals of Aim 2 are to characterize the factors modifying bone reconstitution by HSCs in OI and define the molecular mechanisms regulating HSC differentiation to osteoblasts. Effect of factors on mobilization of HSCs and their differentiation to osteoblasts will be studied both in vitro and in vivo. Findings from this study ill be significant in that they can be applied to long-term studies to enhance and accelerate bone healing in OI. This will open many new avenues of therapy for a number of bone diseases and injuries through the use and modulation of HSCs.