Osteoporosis and osteoblast differentiation in mouse models of accelerated aging

描述(由申请人提供)：与年龄相关的骨丢失的一个基本方面是老年人骨骼中成骨细胞的增殖能力降低和分化障碍。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，由于端粒缩短是包括成骨细胞和间充质干细胞(MSCs)在内的培养细胞中细胞复制衰老的原因，因此MSCs中的端粒状态可能是骨形成的关键组成部分。骨质疏松症在Werner(WRN)和先天性角化不良(DC)早衰综合征中很常见。WRN解旋酶的靶标之一是端粒DNA，但小鼠的长端粒和丰富的端粒酶使端粒对WRN的需求减少，因此WRN基因敲除小鼠是健康的。在结合WRN突变和端粒酶(Terc)基因敲除小鼠端粒缩短的加速衰老模型中，观察到包括骨骼在内的增殖性组织中的合成缺陷。基因组维持分子如TERC和WRN的缺失可能通过影响MSCs向成骨细胞分化的能力而导致骨量减少、表型异常和微结构异常。进一步推测，有效的成骨细胞分化依赖于功能性MSCs和造血干细胞的存在。利用显微CT分析和骨组织形态计量学，这项建议将建立WRN和TERC分子与结构骨保真度之间的关系，包括微结构和骨密度。我们将确定WRN-/-、Terc-/-和WRN-/-Terc-/-小鼠的年龄相关骨异常是否与成骨细胞分化不足和/或破骨细胞生成潜能增加有关，并将检查突变小鼠因MSC损伤而导致的合成代谢缺陷是否与复制性衰老和/或端粒缩短/去封顶有关。我们还将通过选择性和非选择性的骨髓移植来评估MSCs和HSCs在成骨细胞分化中的作用，并分析它们减少年龄相关性骨质疏松变化的能力。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高骨折风险。WRN-/-Terc-/-突变小鼠概括了以骨形成能力降低为特征的老年性骨质疏松症，并提供了一种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.