Virginia Commonwealth University, Richmond, VA 23284, USA.
Mayo Clinic College of Medicine, Rochester, MN 55905, USA.
Bone. 2024 Feb;179:116973. doi: 10.1016/j.bone.2023.116973. Epub 2023 Nov 21.
Age- and disuse-related bone loss both result in decreases in bone mineral density, cortical thickness, and trabecular thickness and connectivity. Disuse induces changes in the balance of bone formation and bone resorption like those seen with aging. There is a need to experimentally compare these two mechanisms at a structural and transcriptomic level to better understand how they may be similar or different. Bone microarchitecture and biomechanical properties were compared between 6- and 22-month-old C57BL/6 J male control mice and 6-month-old mice that were hindlimb unloaded (HLU) for 3 weeks. Epiphyseal trabecular bone was the compartment most affected by HLU and demonstrated an intermediate bone phenotype between age-matched controls and aged controls. RNA extracted from whole-bone marrow-flushed tibiae was sequenced and analyzed. Differential gene expression analysis additionally included 4-month-old male mice unloaded for 3 weeks compared to age-matched controls. Gene ontology analysis demonstrated that there were age-dependent differences in differentially expressed genes in young adult mice. Genes related to downregulation of cellular processes were most affected in 4-month-old mice after disuse whereas those related to mitochondrial function were most affected in 6-month-old mice. Cell-cycle transition was downregulated with aging. A publicly available dataset (GSE169292) from 3-month female C57BL/6 N mice unloaded for 7 days was included in ingenuity pathway analysis (IPA) with the other datasets. IPA was used to identify the leading canonical pathways and upstream regulators in each HLU age group. IPA identified "Senescence Pathway" as the second leading canonical pathway enriched in mice exposed to HLU. HLU induced activation of the senescence pathway in 3-month and 4-month-old mice but inhibited it in 6-month-old mice. In conclusion, we demonstrate that hindlimb unloading and aging initiate similar changes in bone microarchitecture and gene expression. However, aging is responsible for more significant transcriptome and tissue-level changes compared to hindlimb unloading.
年龄相关性和废用性骨丢失都会导致骨矿物质密度、皮质厚度和小梁厚度及连通性降低。废用会引起骨形成和骨吸收的平衡变化，类似于衰老时的变化。有必要在结构和转录组水平上对这两种机制进行实验比较，以更好地了解它们可能相似还是不同。比较了 6 月龄和 22 月龄 C57BL/6J 雄性对照小鼠与 6 月龄后腿去负荷（HLU）3 周的小鼠的骺板小梁骨的微观结构和生物力学特性。骺板小梁骨是受 HLU 影响最大的部位，表现出介于同龄对照和老龄对照之间的中间骨表型。从全骨髓冲洗的胫骨中提取 RNA 进行测序和分析。差异基因表达分析还包括与同龄对照相比，3 周龄去负荷的 4 月龄雄性小鼠。基因本体分析表明，年轻成年小鼠的差异表达基因存在年龄依赖性差异。在去负荷后，与细胞过程下调相关的基因在 4 月龄小鼠中受影响最大，而与线粒体功能相关的基因在 6 月龄小鼠中受影响最大。细胞周期的转变随年龄的增长而下降。将来自 3 月龄 C57BL/6N 雌性小鼠的公共数据集（GSE169292）与其他数据集一起纳入 Ingenuity 通路分析（IPA）。IPA 用于识别每个 HLU 年龄组中的主要经典途径和上游调节剂。IPA 确定“衰老途径”是在暴露于 HLU 的小鼠中富集的第二大主要经典途径。HLU 诱导 3 月龄和 4 月龄小鼠衰老途径的激活，但抑制 6 月龄小鼠的激活。总之，我们证明了后肢去负荷和衰老会导致骨微观结构和基因表达发生相似的变化。然而，与后肢去负荷相比，衰老会导致更显著的转录组和组织水平的变化。
