Department of Orthopaedic and Neuro-Musculoskeletal Surgery, Faculty of Life Sciences, Kumamoto University, Kumamoto, Japan.
Int J Exp Pathol. 2011 Aug;92(4):232-42. doi: 10.1111/j.1365-2613.2010.00758.x. Epub 2011 Feb 5.
Endoplasmic reticulum (ER) stress has been shown to participate in many disease pathologies. Although recent reports have demonstrated that ER stress in chondrocytes is present in human osteoarthritis (OA), its role in the pathology of cartilage degeneration, such as chondrocyte apoptosis, remains unclear. In the present study, we investigated the expression of phosphorylated PERK (pPERK), ubiquitin (Ub), GRP78, CHOP, phosphorylated JNK (pJNK) and cleaved caspase-3 (C-CASP3) and the mRNA splicing of XBP1 (XBP1 splicing) in human OA cartilage by immunohistochemistry and RT-PCR. Additionally, human chondrocytes were treated with several concentrations of tunicamycin, an ER stress inducer, to assess the impact of ER stress on the mRNA expression of CHOP, XBP1 splicing and apoptosis, as determined by real-time PCR, RT-PCR and ELISA analyses respectively. In human OA cartilage, the number of chondrocytes expressing pPERK, Ub, CHOP and pJNK positively correlated with cartilage degeneration and the number of C-CASP3-positive chondrocytes. XBP1 splicing and GRP78 expression in severe OA containing the greatest number of C-CASP3-positive chondrocytes were similar to the levels in mild OA, however, XBP1 splicing was higher in moderate OA than in mild and severe OA. Tunicamycin dose dependently increased CHOP expression and apoptosis of cultured chondrocytes. Although tunicamycin upregulated XBP1 splicing in cultured chondrocytes, its impact on XBP1 splicing was weakened at higher concentrations. In conclusion, the present results indicate that ER stress may contribute to chondrocyte apoptosis along with OA progression, which was closely associated with an enhanced apoptotic response and a reduced protective response by the cells.
内质网（ER）应激已被证明参与许多疾病的病理过程。虽然最近的报道表明软骨细胞中的 ER 应激存在于人类骨关节炎（OA）中，但它在软骨退变（如软骨细胞凋亡）的病理学中的作用尚不清楚。在本研究中，我们通过免疫组织化学和 RT-PCR 研究了人 OA 软骨中磷酸化 PERK（pPERK）、泛素（Ub）、GRP78、CHOP、磷酸化 JNK（pJNK）和 cleaved caspase-3（C-CASP3）的表达以及 XBP1 的 mRNA 剪接（XBP1 剪接）。此外，用人 ER 应激诱导剂衣霉素处理人软骨细胞，分别通过实时 PCR、RT-PCR 和 ELISA 分析评估 ER 应激对 CHOP、XBP1 剪接和凋亡的 mRNA 表达的影响。在人 OA 软骨中，表达 pPERK、Ub、CHOP 和 pJNK 的软骨细胞数量与软骨退变以及 C-CASP3 阳性软骨细胞数量呈正相关。在包含最多 C-CASP3 阳性软骨细胞的严重 OA 中，XBP1 剪接和 GRP78 表达与轻度 OA 相似，但中度 OA 中的 XBP1 剪接高于轻度和重度 OA。衣霉素剂量依赖性地增加培养软骨细胞中的 CHOP 表达和凋亡。尽管衣霉素上调了培养软骨细胞中的 XBP1 剪接，但在较高浓度下，其对 XBP1 剪接的影响减弱。总之，本研究结果表明 ER 应激可能与 OA 进展一起导致软骨细胞凋亡，这与细胞增强的凋亡反应和减弱的保护反应密切相关。
