OSTEOGENESIS IMPERFECTA, AND NITRIC OXIDE THERAPY

描述(由申请人提供)：I型胶原突变发生在大多数成骨不全(OI)病例中，根据突变部位和突变的性质(例如，OI)导致广泛的表型。什么残基替代甘氨酸或是否发生外显子跳跃)、突变的杂合性或纯合性，以及其他遗传和生理变量。四个主要的OI类别(I-IV型)和最近的三个新的OI类别(V-VI型)显示了不同的骨骼、结缔组织和神经肌肉表现。常见的OI骨骼特征在程度、持续时间和发病时间上各不相同，包括骨骼生长减少、骨密度降低、骨畸形和骨折发生率增加。由于OI突变引起的胶原基质的改变导致细胞外基质特性异常，并与骨、血管和其他组织中的其他基质分子或细胞相互作用。在骨骼中，这可能导致骨转换增强，破骨细胞、成骨细胞和/或骨细胞数量的改变，以及骨的净损失。破骨细胞和成骨细胞的募集和活性与骨血管系统密切相关，因此，骨血管系统在正常的骨发育、形成、重塑和修复过程中起着至关重要的作用，而骨血管系统的病理改变在各种骨骼疾病中影响这些过程。与OI相关的血管紊乱(如血管完整性丧失、血管侵袭受损、血管表型、结构或功能改变)的研究较少，但也可能出现在早发性青春期前OI(III型和IV型)，潜在表明OI病理中骨吸收/重塑和血管相关变化之间的功能相互关系。通常，OI用抗吸收双磷酸盐治疗，这种药物已被证明在减少OI相关的骨丢失和骨折频率方面取得了部分成功。然而，在不断增长的儿科骨骼中使用这种持久的抗吸收双膦酸类药物越来越受到关注。因此，需要改进的策略和治疗药物来管理和减轻OI相关的骨丢失、畸形和骨折频率。这里提出的一种可能的新方法是给药一氧化氮(NO)，这是一种已知在正常生理和病理中发挥主要血管保护和骨保护作用的关键信号分子。在血管系统中，NO对血压、血管生成、血小板聚集、循环细胞与内皮的相互作用等关键过程起着重要的调节作用。在骨组织中，近十年来与NO相关的研究已经发现了令人信服的证据，表明生理水平的NO可以引起多种骨保护反应，包括将机械刺激转化为成骨细胞的合成代谢反应，修改骨血管生成，抑制破骨细胞诱导的RANKL表达和信号转导，以及抑制成熟破骨细胞在体外和体内的骨吸收。没有一种治疗方法是通过硝酸甘油等无毒的NO供体物质提供的，它正在成为一种潜在的安全有效的抗绝经后骨质疏松症治疗方法，与双膦酸类药物一样。我们推测，没有一种疗法可能是治疗OI的双膦酸盐的有效替代品。因此，这项建议的一个主要目标是在一个具有良好特征的人类IV型OI的小鼠敲入模型(BrtlIV)中测试NO治疗的有效性，以了解它是否改善骨骼骨量减少和伴随的骨折频率。第二个目标将是研究NO可能发挥OI治疗作用的分子机制，包括NO抑制破骨细胞/成骨细胞骨重建过程的可能性，这可能导致与OI成骨相关的骨量减少。这项建议的一个主要目标是测试一氧化氮(硝酸甘油)治疗在具有良好特征的人类IV型OI小鼠模型中的有效性，以了解一氧化氮治疗是否改善了成骨不全的骨骼骨量减少和伴随的骨折频率。

DESCRIPTION (provided by applicant): Type I collagen mutations occurring in the majority of cases of osteogenesis imperfecta (OI) cause a broad range of phenotypes depending upon the mutational site and nature of the mutations (eg. what residue substitutes for Gly or if exon skipping occurs), hetero- or homozygosity of the mutation, and other genetic and physiological variables. The four predominant OI (Type I-IV) classes and the three more recent (Type V-VII) novel OI categories demonstrate various skeletal, connective tissue, and neuromuscular manifestations. Common OI skeletal characteristics that vary in degree, duration, and onset include diminished skeletal growth, decreased bone density, bone deformity, and an increased incidence of fractures. Alterations in collagen matrices due to OI mutations result in abnormal extracellular matrix properties and interactions with other matrix molecules or cells in bone, vascular, and other tissues. In bone, this may lead to enhanced bone turnover, alterations in osteoclast, osteoblast and/or osteocyte numbers, and a net loss of bone. The recruitment and activity of osteoclasts and osteoblasts are intimately linked with the bone vasculature, and the latter therefore plays critical roles throughout normal bone development, formation, remodeling, and repair, while pathological alterations in bone vasculature impact these processes in various skeletal diseases. OI-related vascular disturbances (eg. loss of vessel integrity, impaired vascular invasion, changes in vascular phenotype, architecture or function) are less well studied but may also appear in the early onset pre-pubertal forms of OI (Types III and IV), potentially indicating functional interrelationships between bone resorption/remodeling and vascular-associated changes in OI pathology. Typically, OI is treated with anti-resorptive bisphosphonates, agents that have proven partially successful for reducing the severity of OI-related bone loss and fracture frequency. However, administration of such long-lasting anti-resorptive bisphosphonates in the growing pediatric skeleton is of some increasing concern. Consequently, improved strategies and therapeutic agents to manage and alleviate OI-associated bone loss, deformity, and fracture frequency are needed. One possible novel approach proposed here focuses on the administration of nitric oxide (NO), a key signal molecule known to exert major vasculoprotective, as well as osteoprotective, roles in normal physiology and pathology. In the vasculature, NO importantly regulates blood pressure, angiogenesis, platelet aggregation, circulating cell interactions with the endothelium, and other critical processes. In bone, NO-related research in the last decade has uncovered compelling evidence that physiological levels of NO evoke multiple osteoprotective responses, ranging from transduction of mechanical stimuli into osteoblast anabolic responses, modification of bone angiogenesis, suppression of osteoclast- inductive RANKL expression and signaling, and inhibition of bone resorption by mature osteoclasts in vitro and in vivo. NO therapy, supplied via a non-toxic NO donor substance like nitroglycerin, is emerging as a potential safe and effective anti-resorptive treatment for postmenopausal osteoporosis, on par with bisphosphonates. We hypothesize that NO therapy might be an effective alternative to bisphosphonates for treating OI. Therefore, a primary goal of this proposal is to test the efficacy of NO therapy in a well-characterized murine knock-in model (BrtlIV) of human Type IV OI to learn if it improves skeletal osteopenia and accompanying fracture frequency. A second goal will be to investigate molecular mechanisms through which NO may exert OI therapeutic effects, including the potential for NO to inhibit osteoclast/osteoblast bone remodeling processes that may contribute to the osteopenia associated with OI Osteogenesis Imperfecta is a heritable connective tissue disorder characterized by increased bone fragility ("brittle bone") that affects both males and females equally and occurs across all racial and ethnic groups. A primary goal of this proposal is to test the efficacy of nitric oxide (nitroglycerin) therapy in a well-characterized mouse model of human Type IV OI to learn if Nitric oxide therapy improves skeletal osteopenia and accompanying fracture frequency in osteogenesis imperfecta.