Harrington Laboratory for Molecular Orthopedics, Department of Orthopedic Surgery, University of Kansas Medical Center, Kansas City, KS 66160, USA.
J Bone Miner Res. 2011 Aug;26(8):1974-86. doi: 10.1002/jbmr.397.
The development of disease-modifying pharmacologic therapy for osteoarthritis (OA) currently faces major obstacles largely because the regulatory mechanisms for the function of adult articular chondrocytes remain unclear. We previously demonstrated that lack of Nfat1, one of the nuclear factor of activated T cells (NFAT) transcription factors, causes OA-like changes in adult mice. This study aimed to identify whether Nfat1 specifically regulates adult articular chondrocyte function and its age-dependent regulatory mechanism using both Nfat1-deficient and wild-type mice. Deletion of Nfat1 did not induce OA-like articular chondrocyte dysfunction (e.g., overexpression of proinflammatory cytokines and matrix-degrading proteinases) until the adult stage. RNAi-mediated Nfat1 knockdown caused dysfunction of wild-type adult articular chondrocytes. Nfat1 expression in wild-type articular chondrocytes was low in the embryonic but high in the adult stage. Chromatin immunoprecipitation assays demonstrated that an increase in Nfat1 expression in articular chondrocytes was associated with increased H3K4me2 (a histone modification linked to transcriptional activation), whereas a decrease in Nfat1 expression in articular chondrocytes was correlated with increased H3K9me2 (a histone modification linked to transcriptional repression). Knockdown of lysine-specific demethylase-1 (Lsd1) in embryonic articular chondrocytes upregulated Nfat1 expression concomitant with increased H3K4me2 at the Nfat1 promoter. Knockdown of Jmjc-containing histone demethylase-2a (Jhdm2a) in 6-month articular chondrocytes downregulated Nfat1 expression concomitant with increased H3K9me2 at the Nfat1 promoter. These results suggest that Nfat1 is an essential transcriptional regulator of chondrocyte homeostasis in adult articular cartilage. Age-dependent Nfat1 expression in articular chondrocytes is regulated by dynamic histone methylation, one of the epigenetic mechanisms that regulate gene transcription.
骨关节炎（OA）的疾病修饰性药物治疗的发展目前面临着重大障碍，主要是因为成人关节软骨细胞功能的调节机制仍不清楚。我们之前的研究表明，核因子活化 T 细胞（NFAT）转录因子之一 Nfat1 的缺失会导致成年小鼠出现 OA 样变化。本研究旨在使用 Nfat1 缺陷型和野生型小鼠来确定 Nfat1 是否特异性调节成年关节软骨细胞的功能及其年龄依赖性调节机制。直到成年阶段，Nfat1 的缺失并没有诱导出类似 OA 的关节软骨细胞功能障碍（例如，促炎细胞因子和基质降解蛋白酶的过度表达）。RNAi 介导的 Nfat1 敲低导致野生型成年关节软骨细胞功能障碍。野生型关节软骨细胞中 Nfat1 的表达在胚胎期较低，但在成年期较高。染色质免疫沉淀分析表明，关节软骨细胞中 Nfat1 表达的增加与 H3K4me2 的增加（与转录激活相关的组蛋白修饰）相关，而关节软骨细胞中 Nfat1 表达的减少与 H3K9me2 的增加（与转录抑制相关的组蛋白修饰）相关。胚胎期关节软骨细胞中赖氨酸特异性去甲基酶-1（Lsd1）的敲低会同时上调 Nfat1 表达和 Nfat1 启动子处的 H3K4me2。6 月龄关节软骨细胞中 Jmjc 包含的组蛋白去甲基酶-2a（Jhdm2a）的敲低会同时下调 Nfat1 表达和 Nfat1 启动子处的 H3K9me2。这些结果表明，Nfat1 是成年关节软骨中软骨细胞稳态的一个重要转录调节因子。关节软骨细胞中 Nfat1 的年龄依赖性表达受动态组蛋白甲基化调节，组蛋白甲基化是调节基因转录的表观遗传机制之一。
