Uehara Y, Hirose J, Yamabe S, Okamoto N, Okada T, Oyadomari S, Mizuta H
Department of Orthopaedic Surgery, Faculty of Life Sciences, Kumamoto University, 1-1-1 Honjo, Chuo-ku, Kumamoto 860-8556, Japan.
Department of Orthopaedic Surgery, Kumamoto University Hospital, 1-1-1 Honjo, Chuo-ku, Kumamoto 860-8556, Japan.
Osteoarthritis Cartilage. 2014 Jul;22(7):1007-17. doi: 10.1016/j.joca.2014.04.025. Epub 2014 May 2.
When endoplasmic reticulum (ER) stress, i.e., the excessive accumulation of unfolded proteins in ER, endangers homeostasis, apoptosis is induced by C/EBP homologous protein (Chop). In osteoarthritis (OA) cartilage, Chop expression and apoptosis increase as degeneration progresses. We investigated the role of Chop in murine chondrocyte apoptosis and in the progression of cartilage degeneration.
We induced experimental OA in Chop-knockout (Chop(-/-)) mice by medial collateral ligament transection and meniscectomy and compared cartilage degeneration, apoptosis, and ER stress in Chop(-/-)- and wild-type (Chop(+/+)) mice. In our in vitro experiments we treated murine Chop(-/-) chondrocytes with the ER stress inducer tunicamycin (TM) and evaluated apoptosis, ER stress, and chondrocyte function.
In vivo, the degree of ER stress was similar in Chop(-/-)- and Chop(+/+) mice. However, in Chop(-/-) mice apoptosis and cartilage degeneration were lower by 26.4% and 42.4% at 4 weeks, by 26.8% and 44.9% at 8 weeks, and by 26.9% and 32.3% at 12 weeks after surgery than Chop(+/+) mice, respectively. In vitro, the degree of ER stress induction by TM was similar in Chop(-/-)- and Chop(+/+) chondrocytes. On the other hand, apoptosis was 55.3% lower and the suppression of collagen type II and aggrecan mRNA was 21.0% and 23.3% less, and the increase of matrix metalloproteinase-13 mRNA was 20.0% less in Chop(-/-)- than Chop(+/+) chondrocytes.
Our results indicate that Chop plays a direct role in chondrocyte apoptosis and that Chop-mediated apoptosis contributes to the progression of cartilage degeneration in mice.
当内质网（ER）应激，即未折叠蛋白在ER中过度积累危及内环境稳定时，C/EBP同源蛋白（Chop）会诱导细胞凋亡。在骨关节炎（OA）软骨中，随着退变进展，Chop表达和细胞凋亡增加。我们研究了Chop在小鼠软骨细胞凋亡及软骨退变进展中的作用。
我们通过切断内侧副韧带和切除半月板在Chop基因敲除（Chop(-/-)）小鼠中诱导实验性OA，并比较Chop(-/-)小鼠和野生型（Chop(+/+)）小鼠的软骨退变、细胞凋亡及ER应激情况。在体外实验中，我们用ER应激诱导剂衣霉素（TM）处理小鼠Chop(-/-)软骨细胞，并评估细胞凋亡、ER应激及软骨细胞功能。
在体内，Chop(-/-)小鼠和Chop(+/+)小鼠的ER应激程度相似。然而，在Chop(-/-)小鼠中，术后4周细胞凋亡和软骨退变分别比Chop(+/+)小鼠低26.4%和42.4%，8周时分别低26.8%和44.9%，12周时分别低26.9%和32.3%。在体外，TM诱导的ER应激程度在Chop(-/-)软骨细胞和Chop(+/+)软骨细胞中相似。另一方面，Chop(-/-)软骨细胞的细胞凋亡比Chop(+/+)软骨细胞低55.3%，II型胶原和聚集蛋白聚糖mRNA的抑制分别少21.0%和23.3%，基质金属蛋白酶-13 mRNA的增加少20.0%。
我们的结果表明，Chop在软骨细胞凋亡中起直接作用，且Chop介导的细胞凋亡促进了小鼠软骨退变的进展。
