title: Enhanced apoptotic and reduced protective response in chondrocytes following endoplasmic reticulum stress in osteoarthritic cartilage.
abstract: 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.
authors.affiliation: Department of Orthopaedic and Neuro-Musculoskeletal Surgery, Faculty of Life Sciences, Kumamoto University, Kumamoto, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Takada
authors.forename: Jun
authors.initials: J
authors.lastname: Hirose
authors.forename: Kei
authors.initials: K
authors.lastname: Senba
authors.forename: Soichiro
authors.initials: S
authors.lastname: Yamabe
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Oike
authors.forename: Tomomi
authors.initials: T
authors.lastname: Gotoh
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Mizuta
mesh_terms: D000368:Aged; D017209:Apoptosis / Q000502:physiology*; D002356:Cartilage / Q000378:metabolism / Q000473:pathology* / Q000503:physiopathology; D002478:Cells, Cultured; D019902:Chondrocytes / Q000378:metabolism / Q000473:pathology*; D004721:Endoplasmic Reticulum / Q000502:physiology*; D000091342:Endoplasmic Reticulum Chaperone BiP; D016326:Extracellular Matrix Proteins / Q000378:metabolism; D005260:Female; D006360:Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D048670:MAP Kinase Kinase 4 / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000378:metabolism / Q000473:pathology* / Q000503:physiopathology; D012189:Retrospective Studies; D013312:Stress, Physiological / Q000502:physiology*; D051742:Transcription Factor CHOP / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism; D019892:eIF-2 Kinase / Q000378:metabolism
chemical_list: D000091342:Endoplasmic Reticulum Chaperone BiP; D016326:Extracellular Matrix Proteins; D006360:Heat-Shock Proteins; D048670:MAP Kinase Kinase 4; D051742:Transcription Factor CHOP; D025801:Ubiquitin; D019892:eIF-2 Kinase; C497249:DDIT3 protein, human; C000717247:HSPA5 protein, human