Differential gene expression profiles of long bones of telomerase deficient mice (G3-mTERC-/-)

Telomere shortening due to telomerase deficiency leads to accelerated senescence of human skeletal (mesenchymal) stem cells (MSC) in vitro. In order to study the role of telomere shortening in vivo, we studied the phenotype of telomerase deficient mice caused by absence of telomerase RNA component (TERC-/-). TERC-/- exhibited accelerated age-related bone loss starting at 3 months of age and during 12 months follow up. Bone histomorphometry revealed decreased mineralized surface and bone formation rate as well as increased osteoclast number and size in TERC-/-. Also, serum total deoxy-pyridinoline (tDPD) was increased in TERC-/-. MSC isolated from TERC-/- exhibited intrinsic defects with reduced total number, lower proliferation rate, decreased expression of osteoblastic (OB) differentiation markers and formed less in vivo ectopic bone compared to WT cells. The TERC-/--MSC cultures accumulated a larger proportion of senescent beta-galactosidase+ cells and cells exhibiting DNA damage positive for gamma-H2AX. Micro-array analysis of bones of TERC-/- and WT revealed significant over-expression of a large number of pro-inflammatory genes and signaling pathways in TERC-/- known to control osteoclast (OC) differentiation. In accordance with that, serum from TERC-/- enhanced OC formation in control bone marrow cultures. Our data demonstrate two mechanisms for age-related bone loss caused by telomerase deficiency: intrinsic osteoblastic defects and creation of pro-inflammatory osteoclast-activating microenvironment. Approaches for re-telomerization of MSC may provide a novel approach for abolishing age-related bone loss. control (WT) and the test (G3 - mTERC-/-) samples端粒酶缺陷所致的端粒缩短，可在体外加速人类骨骼间充质干细胞（mesenchymal stem cells, MSC）的衰老。为探究端粒缩短在体内的作用，本研究针对端粒酶RNA组分缺失引发的端粒酶缺陷小鼠（TERC-/-）的表型展开分析。TERC-/-小鼠自3月龄起便出现加速的年龄相关性骨丢失，该表型在12个月的随访周期中持续存在。骨组织形态计量学分析显示，TERC-/-小鼠的矿化表面面积与骨形成速率均降低，而破骨细胞（osteoclast, OC）的数量与体积则有所增加。此外，TERC-/-小鼠的血清总脱氧吡啶啉（total deoxy-pyridinoline, tDPD）水平升高。与野生型（wild type, WT）细胞相比，从TERC-/-小鼠体内分离得到的MSC存在固有缺陷：细胞总数减少、增殖速率降低、成骨细胞（osteoblastic, OB）分化标志物的表达水平下调，且体内异位骨形成能力减弱。TERC-/-来源的MSC培养物中，衰老型β-半乳糖苷酶阳性（β-galactosidase+）细胞与γ-H2AX阳性的DNA损伤细胞的占比均有所升高。对TERC-/-与WT小鼠的骨骼进行基因芯片（micro-array）分析后发现，TERC-/-小鼠体内大量促炎基因与信号通路的表达显著上调，而这些基因与通路均已知可调控破骨细胞（OC）的分化。与此一致的是，TERC-/-小鼠的血清可在对照骨髓培养物中促进OC的形成。本研究数据证实，端粒酶缺陷所致的年龄相关性骨丢失存在两种机制：一是成骨细胞固有缺陷，二是形成了促炎型破骨细胞激活微环境。针对MSC的端粒重新激活策略，或许可为逆转年龄相关性骨丢失提供全新的治疗思路。本研究使用的样本分为对照（野生型，WT）与实验组（G3-mTERC-/-）。