Transcriptomic analyses of joint tissues during osteoarthritis development in a rat model reveal dysregulated mechanotransduction and extracellular matrix pathways

Transcriptomic changes in joint tissues during the development of osteoarthritis (OA) are of interest for the discovery of biomarkers and mechanisms of disease. The objective of this study was to use the rat medial meniscus transection (MMT) model to discover stage and tissue-specific transcriptomic changes. Sham or MMT surgeries were performed in mature rats. Cartilage, menisci and synovium were scored for histopathological changes at 2, 4 and 6 weeks post-surgery and processed for RNA-sequencing. Differentially expressed genes (DEG) were used to identify pathways and mechanisms. Published transcriptomic datasets from animal models and human OA were used to confirm and extend present findings. The total number of DEGs was already high at 2 weeks (723 in meniscus), followed by cartilage (259) and synovium (42) and declined to varying degrees in meniscus and synovium but increased in cartilage at 6 weeks. The most upregulated genes included tenascins. The 'response to mechanical stimulus' and extracellular matrix-related pathways were enriched in both cartilage and meniscus. Pathways that were enriched in synovium at 4 weeks indicate processes related to synovial hyperplasia and fibrosis. Synovium also showed upregulation of IL-11 and several MMPs. The mechanical stimulus pathway included upregulation of the mechanoreceptors PIEZO1, PIEZO2 and TRPV4 and nerve growth factor. Analysis of data from prior RNA-sequencing studies of animal models and human OA support these findings. These results indicate several shared pathways that are affected during OA in cartilage and meniscus and support the role of mechanotransduction and other pathways in OA pathogenesis.骨关节炎（Osteoarthritis, OA）发生进程中，关节组织的转录组变化对于疾病生物标志物的发掘及致病机制研究具有重要意义。本研究旨在利用大鼠内侧半月板横断术（medial meniscus transection, MMT）模型，探究具有阶段特异性与组织特异性的转录组变化。研究对成熟大鼠实施假手术或MMT手术，并于术后2、4、6周分别对软骨、半月板及滑膜进行组织病理学评分，随后采集样本进行RNA测序（RNA-sequencing）。通过差异表达基因（differentially expressed genes, DEG）分析，筛选相关通路并阐释致病机制。本研究整合已发表的动物模型及人类OA相关转录组数据集，对本研究结果进行验证与拓展。术后2周时，差异表达基因总数已处于较高水平（半月板中达723个），其次为软骨（259个）与滑膜（42个）；至术后6周时，半月板与滑膜中的DEG数量呈不同程度下降，而软骨中的DEG数量则有所上升。表达上调最为显著的基因包括腱糖蛋白家族成员。在软骨与半月板中均富集到“机械刺激应答”及细胞外基质相关通路。术后4周滑膜组织中富集的通路，则与滑膜增生及纤维化相关。滑膜组织中还可见IL-11及多种基质金属蛋白酶（matrix metalloproteinases, MMPs）的表达上调。机械刺激应答通路中，机械感受器PIEZO1、PIEZO2、TRPV4及神经生长因子的表达均呈上调趋势。对既往动物模型及人类OA的RNA测序研究数据进行分析后，结果进一步支持本研究的发现。本研究结果揭示了OA发生过程中软骨与半月板共有的多条受影响通路，并证实了机械转导及其他通路在OA致病过程中的作用。