NG2/CSPG4 regulates cartilage degeneration during TMJ osteoarthritis. NG2/CSPG4 regulates cartilage degeneration during TMJ osteoarthritis

Changes in the mechanical homeostasis of the temporomandibular joint (TMJ) can lead to the initiation and progression of degenerative arthropathies such as osteoarthritis (OA). Cells sense and engage with their mechanical microenvironment through interactions with the extracellular matrix. In the mandibular condylar cartilage, the pericellular microenvironment is composed of type VI collagen. NG2/CSPG4 is a transmembrane proteoglycan that binds with type VI collagen, and has been implicated in the cell stress response through mechanical loading-sensitive signaling networks including ERK 1/2. The objective of this study is to define the role of NG2/CSPG4 in the initiation and progression of TMJ OA and to determine if NG2/CSPG4 engages ERK 1/2 in a mechanical loading dependent manner. In vivo, we induced TMJ OA in control and NG2/CSPG4 knockout mice using a surgical destabilization approach. In control mice, NG2/CSPG4 is depleted during the early stages of TMJ OA and NG2/CSPG4 knockout mice have more severe cartilage degeneration, elevated expression of key OA proteases, and suppression of OA matrix synthesis genes. In vitro, we characterized the transcriptome and protein from control and NG2/CSPG4 knockout cells and found significant dysregulation of the ERK 1/2 signaling axis. To characterize the mechanobiological response of NG2/CSPG4, we applied mechanical loads on cell-agarose-collagen scaffolds using a compression bioreactor and illustrate that NG2/CSPG4 knockout cells fail to mechanically activate ERK 1/2 and are associated with changes in the expression of the same key OA biomarkers measured in vivo. Together, these findings implicate NG2/CSPG4 in the mechanical homeostasis of TMJ cartilage and in the progression of degenerative arthropathies including OA. Overall design: Comparative gene expression profiling analysis of RNA-seq data comparing c57/BL6J and NG2/CSPG4 knockout primary mandibular fibrochondrocytes collected from 10-14 day old pups Data analysis published in Reed et al, "NG2/CSPG4 regulates cartilage degeneration during TMJ osteoarthritis". Frontiers in Dental Medicine Sequencing and bioinformatic analysis done by LC Sciences

颞下颌关节（temporomandibular joint, TMJ）的机械稳态改变，可引发骨关节炎（osteoarthritis, OA）这类退行性关节病的发生与进展。细胞通过与细胞外基质的相互作用，感知并响应其机械微环境。在下颌髁突软骨中，细胞周微环境由VI型胶原蛋白构成。NG2/CSPG4是一种可结合VI型胶原蛋白的跨膜蛋白聚糖，其通过包括ERK 1/2在内的机械负荷敏感信号网络参与细胞应激反应。本研究旨在明确NG2/CSPG4在颞下颌关节骨关节炎发生与进展中的作用，并探究NG2/CSPG4是否以机械负荷依赖的方式调控ERK 1/2信号通路。体内实验中，我们通过外科失稳方法在对照组与NG2/CSPG4基因敲除小鼠中诱导颞下颌关节骨关节炎。结果显示，对照组小鼠的NG2/CSPG4在颞下颌关节骨关节炎早期即被耗竭，而NG2/CSPG4基因敲除小鼠的软骨退变程度更严重，关键骨关节炎蛋白水解酶的表达水平升高，且骨关节炎基质合成相关基因的表达受到抑制。体外实验中，我们对对照组与NG2/CSPG4基因敲除细胞的转录组与蛋白质组进行了表征，发现ERK 1/2信号轴存在显著失调。为表征NG2/CSPG4的机械生物学响应，我们利用压缩生物反应器对细胞-琼脂糖-胶原蛋白支架施加机械负荷，结果表明NG2/CSPG4基因敲除细胞无法机械激活ERK 1/2，且其与体内检测到的关键骨关节炎生物标志物表达变化相关。综上，本研究结果表明NG2/CSPG4参与颞下颌关节软骨的机械稳态维持，并在包括骨关节炎在内的退行性关节病进展中发挥作用。整体实验设计：对采集自10~14日龄幼崽的C57/BL6J与NG2/CSPG4基因敲除原代下颌纤维软骨细胞的RNA测序数据进行比较基因表达谱分析。本研究数据分析成果发表于Reed等人题为"NG2/CSPG4 regulates cartilage degeneration during TMJ osteoarthritis"的论文，刊载于《Frontiers in Dental Medicine》。测序与生物信息学分析由LC Sciences完成。