Regulation of HSCs and HSC-Derived Osteoblasts in Osteogenesis Imperfecta

描述（由申请人提供）：成骨不全症（Osteogenesis imperfecta， OI）是一种常染色体显性遗传病，由编码I型胶原蛋白（COL1AI或COL1A2）的两个基因之一的突变引起，是最常见的遗传性骨病。成骨不全的特点是骨基质数量轻度到重度减少，导致反复骨折和骨畸形。在美国，成骨不全的发病率估计为每20,000个活产儿中有1个。现在还没有治愈成骨不全症的方法。治疗的目的是增加整体骨骼强度以防止骨折。长期服用这些药物也有副作用；因此，在成骨不全症中，有几种策略正在进行实验，以增强骨重塑，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。我们还证明造血干细胞在正常骨转换和非稳定骨折修复过程中产生成骨细胞和骨细胞。我们对oim小鼠的初步数据显示，移植的小鼠的小梁和皮质参数得到了显著改善，这些小鼠移植了单一增强绿色荧光蛋白（EGFP+） HSC克隆群体。我们还表明，HSC移植导致体内沉积胶原并形成骨的功能性成骨细胞的形成。这些研究和我们的数据表明，成骨细胞可以来自一种新的来源，即造血干细胞。因此，本研究旨在验证造血干细胞可以在成骨不全症中产生成骨细胞的假设，了解促进其动员和成骨的分子因素可能对成骨不全症具有治疗价值。目的1是建立造血干细胞可以产生成骨细胞的移植研究，利用骨导向胶原I型启动子控制下具有视觉标记的小鼠造血干细胞，这允许在成骨细胞谱系的不同阶段特异性鉴定细胞。利用在造血细胞中表达GFP的小鼠和在非造血组织中表达红色荧光蛋白（RFP）的小鼠，我们将从造血干细胞进行谱系追踪。目的2是表征成骨不全患者造血干细胞骨重建的影响因素，并明确调节造血干细胞向成骨细胞分化的分子机制。我们将在体内和体外研究影响造血干细胞动员和向成骨细胞分化的因素。这项研究的发现将具有重要意义，因为它们可以应用于长期研究，以增强和加速成骨不全的骨愈合。这将通过使用和调节造血干细胞为许多骨疾病和损伤开辟许多新的治疗途径。

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.