title: Endoplasmic reticulum stress mediates nitric oxide-induced chondrocyte apoptosis.
abstract: Nitric oxide (NO) is one of the most important mediators of chondrocyte apoptosis, which is a notable feature of cartilage degeneration. While apoptosis of chondrocytes is induced by p53, NO can also induce endoplasmic reticulum (ER) stress, which may be involved in the process of NO-induced chondrocyte apoptosis. The aims of this study were to determine whether NO-induced ER stress (ERS) leads to apoptosis of chondrocytes and to investigate the temporal relationship between the expression of C/EBP-homologous protein (CHOP), an ERS-associated apoptotic molecule, and the expression of p53 during apoptosis in NO-stimulated chondrocytes. Rat chondrocytes were stimulated by sodium nitroprusside (SNP), a NO donor. Real-time polymerase chain reaction (PCR) was performed to analyze the mRNA expression of CHOP, glucose-regulated protein (GRP78) and p53. Apoptosis of chondrocytes was quantified using an enzyme-linked immunosorbent assay (ELISA). SNP-treated chondrocytes showed an increase in CHOP and GRP78 mRNA expression and underwent apoptosis. Sodium 4-phenylbutyrate (PBA), an ERS inhibitor, reduced CHOP and GRP78, as well as SNP-stimulated apoptosis of chondrocytes, without affecting the SNP-dependent generation of NO. In addition, the blockade of CHOP following siRNA transfection reduced SNP-induced apoptosis of chondrocytes. The CHOP expression increased after apoptosis was detected in the SNP-treated chondrocytes, whereas the p53 expression increased prior to apoptosis. These data demonstrated that NO-induced ERS leads chondrocytes to apoptosis, although this effect appears to be limited to persistent impairment of NO stimulation. These findings may provide insight into the pathology of cartilage degeneration.
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Life Sciences, Kumamoto University, Chuo-ku, Kumamoto 860-8556, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Takada
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Life Sciences, Kumamoto University, Chuo-ku, Kumamoto 860-8556, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Hirose
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Life Sciences, Kumamoto University, Chuo-ku, Kumamoto 860-8556, Japan.
authors.forename: Soichiro
authors.initials: S
authors.lastname: Yamabe
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Life Sciences, Kumamoto University, Chuo-ku, Kumamoto 860-8556, Japan.
authors.forename: Yushuke
authors.initials: Y
authors.lastname: Uehara
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Life Sciences, Kumamoto University, Chuo-ku, Kumamoto 860-8556, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Mizuta
keywords: apoptosis; chondrocyte; endoplasmic reticulum stress; nitric oxide; p53