Osteoporosis and osteoblast differentiation in mouse models of accelerated aging

描述（由申请人提供）：年龄相关性骨丢失的一个基本方面是老年人骨中成骨细胞增殖能力降低和分化受损。端粒在大多数人类组织中随着年龄的增长而缩短，包括骨，并且由于端粒缩短是培养细胞（包括成骨细胞和间充质干细胞（MSC））中细胞复制衰老的原因，因此MSC中的端粒状态可能是骨形成的关键组成部分。骨质疏松症常见于Werner（Wernern）和先天性角化不良（DC）早衰综合征。端粒的DNA是WRN解旋酶的靶点之一，但小鼠中较长的端粒和丰富的端粒酶使端粒对WRN的需求最小化，因此WRN敲除小鼠是健康的。在一个加速衰老的模型中，结合了端粒酶（Terc）基因敲除小鼠的端粒缩短和突变，已经观察到包括骨在内的增殖组织中的合成缺陷。假设基因组维持分子如TERC和WRN的缺陷通过损害MSC分化成成骨细胞的能力而导致低骨量表型和骨的微结构异常。进一步假设有效的成骨细胞分化取决于功能性MSC和造血干细胞（HSC）的存在。利用显微CT分析和骨组织形态计量学，该建议将建立WRN和TERC分子与结构骨保真度（包括微结构和骨密度）之间的关系。我们将确定是否年龄相关的骨异常在BRN-/-，Terc-/-和BRN-/- Terc-/-小鼠与成骨细胞分化和/或破骨细胞生成潜力增加的缺陷，并将检查是否合成代谢缺陷由于MSC损伤突变小鼠与复制衰老和/或端粒缩短/脱帽。我们还将评估MSC和HSC对成骨细胞分化的贡献，通过选择性和非选择性骨髓移植这些细胞祖细胞，并分析其减少年龄相关性增生性变化的能力。老年人的一个后果和主要的临床挑战是骨质疏松症和相关的骨折高风险。该突变小鼠重现了以骨形成能力降低为特征的老年性骨质疏松症，并提供了测试干细胞替代以改善年龄相关性骨质疏松症的系统。

DESCRIPTION (provided by applicant): A fundamental aspect of age-related bone loss is the decreased proliferative capacity and impaired differentiation of osteoblasts in the bone of older individuals. Telomeres shorten with age in most human tissues, including bone, and since telomere shortening is a cause of cellular replicative senescence in cultured cells, including osteoblasts and mesenchymal stem cells (MSCs), it is likely that telomere status in MSCs is a critical component of bone formation. Osteoporosis is common in the Werner (Wrn) and Dyskeratosis congenita (DC) premature aging syndromes. One of the targets of the Wrn helicase is telomeric DNA, but the long telomeres and abundant telomerase in mice minimize the need for WRN at telomeres, and thus Wrn knockout mice are healthy. In a model of accelerated aging that combines the Wrn mutation with the shortened telomeres of telomerase (Terc) knockout mice, synthetic defects in proliferative tissues, including bone, have been observed. It is hypothesized that deficiencies in genome maintenance molecules such as TERC and WRN cause a low bone mass phenotype and microarchitectural abnormalities of bone by impairing the ability of MSCs to differentiate into osteoblasts. It is further hypothesized that effective osteoblast differentiation depends on the presence of functional MSCs and hematopoietic stem cells (HSCs). Using micro-CT analysis and bone histomorphometry, this proposal will establish the relationship between the WRN and TERC molecules and structural bone fidelity, including microarchitecture and bone density. We will determine if age-related bone abnormalities in Wrn-/-, Terc-/- and Wrn -/- Terc-/- mice are related to deficiencies in osteoblast differentiation and/or increased osteoclastogenic potential, and will examine whether anabolic defects due to MSC impairment in mutant mice are associated with replicative senescence and/or telomere shortening/uncapping. We will also assess the contributions of MSCs and HSCs to osteoblast differentiation by selective and nonselective bone marrow transplantation of these cellular progenitors and analysis of their ability to reduce age-related osteoporotic changes. A consequence and major clinical challenge in the elderly is osteoporosis and associated high risk of fracture. The Wrn-/-Terc -/- mutant mouse recapitulates senile osteoporosis characterized by decreased bone-forming capacity and provides a system to test stem cell replacement for amelioration of age-related osteoporosis.