Defective autophagy in chondrocytes with Kashin-Beck disease but higher than osteoarthritis

This study was undertaken to monitor autophagy in chondrocytes with Kashin-Beck disease (KBD) and osteoarthritis (OA).

The identification and quantification of autophagy were morphologically visualized by transmission electron microscopy (TEM), together with immunohistochemical localization of Beclin1 and LC3 in cartilage, and immunoblotting of cellular Beclin1, LC3 and p62/SQSTM1 in the normal, KBD and OA groups. Sequentially, regulated-autophagy genes (ATG) were analyzed by IPA software and validated by quantitative real-time polymerase chain reaction (qRT-PCR). Cytotoxicity of cell death was measured by fluorescence detection and flow cytometry (FCM). The co-localization and measurement of autophagy and mitochondria/reactive oxygen species (ROS) were carried out.

KBD chondrocytes exhibited a variety of abnormal cellular contents including nuclei, mitochondrial, glycogen deposits and microfilaments, and OA chondrocytes mainly presented swelled endocytoplasmic reticulum (ER). Beclin1 and LC3 were reduced both in KBD and OA compared with normal controls; however, the two proteins and p62 in KBD were in a higher level than OA. Simultaneously, KBD chondrocytes showed 45 genes that were different from normal controls and 92 genes different from OA, whose functions were mainly involved in cell morphology, cellular functions, cell death and survival. Autophagy was negatively correlated with apoptosis in the three kinds of chondrocytes, and the rates decreased when autophagy was induced by rapamycin. Similarly, KBD and OA chondrocytes showed lower autophagy and higher ROS production compared with the normal chondrocytes.

Autophagy was defective in KBD chondrocytes, but it was higher than in OA. The insufficient autophagy may be associated with apoptosis and mitochondrial change in the pathogenesis of KBD and OA.