Caramés Beatriz, Taniguchi Noboru, Otsuki Shuhei, Blanco Francisco J, Lotz Martin
The Scripps Research Institute, 10550 North Torrey, Pines Road, La Jolla, CA 92037, USA.
Arthritis Rheum. 2010 Mar;62(3):791-801. doi: 10.1002/art.27305.
Autophagy is a process for turnover of intracellular organelles and molecules that protects cells during stress responses. We undertook this study to evaluate the potential roles of Unc-51-like kinase 1 (ULK1), an inducer of autophagy, Beclin1, a regulator of autophagy, and microtubule-associated protein 1 light chain 3 (LC3), which executes autophagy, in the development of osteoarthritis (OA) and in cartilage cell death.
Expression of ULK1, Beclin1, and LC3 was analyzed in normal and OA human articular cartilage and in knee joints of mice with aging-related and surgically induced OA, using immunohistochemistry and Western blotting. Poly(ADP-ribose) polymerase (PARP) p85 expression was used to determine the correlation between cell death and autophagy.
ULK1, Beclin1, and LC3 were constitutively expressed in normal human articular cartilage. ULK1, Beclin1, and LC3 protein expression was reduced in OA chondrocytes and cartilage, but these 3 proteins were strongly expressed in the OA cell clusters. In mouse knee joints, loss of glycosaminoglycans (GAGs) was observed at ages 9 months and 12 months and in the surgical OA model, 8 weeks after knee destabilization. Expression of ULK1, Beclin1, and LC3 decreased together with GAG loss, while PARP p85 expression was increased.
Autophagy may be a protective or homeostatic mechanism in normal cartilage. In contrast, human OA and aging-related and surgically induced OA in mice are associated with a reduction and loss of ULK1, Beclin1, and LC3 expression and a related increase in apoptosis. These results suggest that compromised autophagy represents a novel mechanism in the development of OA.
自噬是细胞内细胞器和分子更新的过程，在应激反应中保护细胞。我们开展本研究以评估自噬诱导剂Unc-51样激酶1（ULK1）、自噬调节因子Beclin1以及执行自噬的微管相关蛋白1轻链3（LC3）在骨关节炎（OA）发展及软骨细胞死亡中的潜在作用。
采用免疫组织化学和蛋白质印迹法，分析正常和OA患者关节软骨以及衰老相关和手术诱导性OA小鼠膝关节中ULK1、Beclin1和LC3的表达。使用聚（ADP-核糖）聚合酶（PARP）p85表达来确定细胞死亡与自噬之间的相关性。
ULK1、Beclin1和LC3在正常人体关节软骨中组成性表达。OA软骨细胞和软骨中ULK1、Beclin1和LC3蛋白表达降低，但这三种蛋白在OA细胞簇中强烈表达。在小鼠膝关节中，9个月和12个月龄时以及手术性OA模型中膝关节失稳8周后观察到糖胺聚糖（GAG）丢失。ULK1、Beclin1和LC3的表达随GAG丢失而降低，而PARP p85表达增加。
自噬可能是正常软骨中的一种保护或稳态机制。相比之下，人类OA以及小鼠衰老相关和手术诱导性OA与ULK1、Beclin1和LC3表达的减少和丧失以及细胞凋亡相关增加有关。这些结果表明自噬受损是OA发展中的一种新机制。
