Gene expression patterns in bone following mechanical loading

The advent of high-throughput measurements of gene expression and bioinformatics analysis methods offers new ways to study gene expression patterns. The primary goal of this study was to determine the time sequence for gene expression in a bone subjected to mechanical loading, during key periods of the bone formation process, including expression of matrix-related genes, the appearance of active osteoblasts, and bone desensitization. A standard model for bone loading was employed in which the right forelimb was loaded axially for three minutes per day, while the left forearm served as a non-loaded, contralateral control. We evaluated loading-induced gene expression over a time course of 4 hours to 32 days after the first loading session. Six distinct, time-dependent patterns of gene expression were identified over the time course and categorized into three primary clusters: genes upregulated early in the time course, genes upregulated during matrix formation, and genes downregulated during matrix formation. Genes were then grouped based on function and/or signaling pathways. Many gene groups known to be important in loading-induced bone formation were identified within the clusters, including AP-1-related genes in the early response cluster, matrix-related genes in the upregulated gene clusters, and Wnt/ß-catenin signaling pathway inhibitors in the downregulated gene clusters. Several novel gene groups were identified as well, including chemokine-related genes which were upregulated early but downregulated later in the time course, solute carrier genes which were both up- and downregulated, and muscle-related genes which were primarily downregulated.高通量基因表达检测技术与生物信息学分析方法的问世，为基因表达模式的研究提供了全新路径。本研究的核心目标为解析机械载荷作用下的骨骼在骨形成关键阶段的基因表达时序，涵盖基质相关基因表达、活性成骨细胞（osteoblasts）的出现以及骨脱敏过程。本研究采用标准骨加载模型：对右侧前肢实施轴向加载，每日加载时长3分钟，左侧前肢作为未加载的对侧对照样本。我们对首次加载后4小时至32天的时间范围内，加载诱导的基因表达情况进行了系统性检测与评估。研究期间共鉴定出6种不同的时间依赖性基因表达模式，并将其划分为三大核心聚类簇：早期上调基因簇、基质形成阶段上调基因簇以及基质形成阶段下调基因簇。随后，研究人员根据基因功能及（或）信号通路对基因进行了分组归类。聚类簇中鉴定出诸多已知与加载诱导骨形成密切相关的基因家族，包括早期应答簇中的激活蛋白1（AP-1）相关基因、上调基因簇中的基质相关基因，以及下调基因簇中的Wnt/β-连环蛋白（Wnt/ß-catenin）信号通路抑制剂。此外还鉴定出多个全新的基因家族：包括早期上调但后期下调的趋化因子相关基因、兼具上调与下调表达模式的溶质载体（solute carrier）基因，以及以表达下调为主的肌肉相关基因。