Osteoporosis and osteoblast differentiation in mouse models of accelerated aging

描述（由申请人提供）：与年龄相关的骨质流失的一个基本方面是老年人骨骼中成骨细胞增殖能力下降和分化受损。在包括骨在内的大多数人类组织中，端粒随着年龄的增长而缩短，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（MSCs））细胞复制性衰老的原因，因此MSCs中的端粒状态很可能是骨形成的关键组成部分。骨质疏松症常见于Werner （Wrn）和先天性角化不良（DC）早衰综合征。Wrn解旋酶的靶点之一是端粒DNA，但小鼠的长端粒和丰富的端粒酶减少了端粒对Wrn的需求，因此Wrn敲除小鼠是健康的。在一个将Wrn突变与端粒酶（Terc）敲除小鼠的端粒缩短结合起来的加速衰老模型中，已经观察到包括骨在内的增殖组织中的合成缺陷。据推测，基因组维持分子如TERC和WRN的缺乏通过损害MSCs向成骨细胞分化的能力而导致骨量表型低和骨微结构异常。进一步假设，有效的成骨细胞分化取决于功能性MSCs和造血干细胞（hsc）的存在。利用微ct分析和骨组织形态学，本研究将建立WRN和TERC分子与骨结构保真度（包括微结构和骨密度）之间的关系。我们将确定Wrn-/-、Terc-/-和Wrn-/- Terc-/-小鼠中年龄相关的骨异常是否与成骨细胞分化缺陷和/或破骨细胞生成潜力增加有关，并将检查突变小鼠中由MSC损伤引起的合成代谢缺陷是否与复制性衰老和/或端粒缩短/脱帽有关。我们还将评估MSCs和hsc对成骨细胞分化的贡献，通过这些细胞祖细胞的选择性和非选择性骨髓移植，并分析它们减少与年龄相关的骨质疏松变化的能力。骨质疏松症和相关的高骨折风险是老年人的一个后果和主要的临床挑战。Wrn-/- terc -/-突变小鼠再现了以骨形成能力下降为特征的老年性骨质疏松症，并提供了一个系统来测试干细胞替代以改善与年龄相关的骨质疏松症。

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.