AIM OF THE STUDY To investigate the roles of endoplasmic reticulum (ER) transmembrane sensor inositol-requiring enzyme-1 (IRE1)α signaling in ER stress-induced chondrocyte apoptosis, and to determine the molecular mechanisms underlying chondroprotective activity of 5,7,3',4'-tetramethoxyflavone (TMF) from Murraya exotica. MATERIALS AND METHODS IRE1α was knocked down by siRNA transfection in chondrocytes, which were harvested from rats' knee cartilages. Chondrocytes with IRE1α deficiency were administrated with tunicamycin (TM) and TMF. Chondrocyte apoptosis was quantified by flow cytometry and DAPI/TUNEL staining. Expression of mRNA and proteins was quantified by quantitative reverse transcription polymerase chain reaction (qRT-PCR) and western-blot, respectively. RESULTS IRE1α deficiency significantly increased the rate of TM-induced chondrocyte apoptosis, down-regulated the expression of pro-survival factors XBP1S and Bcl-2, and up-regulated pro-apoptotic factors CHOP, p-JNK, and caspase-3. TMF suppressed TM-induced chondrocyte apoptosis by activating the expression of IRE1α, which reversed the expression patterns of downstream pro-survival and pro-apoptotic factors due to IRE1α deficiency. CONCLUSION The mechanism of TMF in protecting chondrocytes against ER stress-induced apoptosis might be associated with regulating the activity of ER sensor IRE1α and its downstream pathway.

中文翻译：

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5,7,3'，4'-四甲氧基黄酮可通过调节IRE1α途径保护软骨细胞免受内质网应激诱导的细胞凋亡。

研究目的探讨内质网（ER）跨膜传感器肌醇需要酶-1（IRE1）α信号在内质网应激诱导的软骨细胞凋亡中的作用，并确定5,7,3软骨保护活性的分子机制产自Murrayaotica的'，4'-四甲氧基黄酮（TMF）。材料与方法IRE1α被siRNA转染到软骨细胞中，而该软骨细胞是从大鼠的膝盖软骨中获得的。将具有IRE1α缺乏症的软骨细胞与衣霉素（TM）和TMF一起使用。通过流式细胞仪和DAPI / TUNEL染色定量软骨细胞凋亡。mRNA和蛋白质的表达分别通过定量逆转录聚合酶链反应（qRT-PCR）和western-blot进行定量。结果IRE1α缺乏显着增加TM诱导的软骨细胞凋亡率，下调促生存因子XBP1S和Bcl-2的表达，并上调促凋亡因子CHOP，p-JNK和caspase-3。TMF通过激活IRE1α的表达来抑制TM诱导的软骨细胞凋亡，从而逆转由于IRE1α缺乏而引起的下游促存活和促凋亡因子的表达模式。结论TMF保护软骨细胞抵抗内质网应激诱导的凋亡的机制可能与调控内质网传感器IRE1α的活性及其下游通路有关。TMF通过激活IRE1α的表达来抑制TM诱导的软骨细胞凋亡，从而逆转由于IRE1α缺乏而引起的下游促存活和促凋亡因子的表达模式。结论TMF保护软骨细胞抵抗内质网应激诱导的凋亡的机制可能与调控内质网传感器IRE1α的活性及其下游通路有关。TMF通过激活IRE1α的表达来抑制TM诱导的软骨细胞凋亡，从而逆转由于IRE1α缺乏而引起的下游促存活和促凋亡因子的表达模式。结论TMF保护软骨细胞抵抗内质网应激诱导的凋亡的机制可能与调控内质网传感器IRE1α的活性及其下游通路有关。