SGTB Promotes the Caspase-Dependent Apoptosis in Chondrocytes of Osteoarthritis.

The purpose of this study is to investigate the expression of small glutamine-rich tetratricopeptide repeat (TPR)-containing β (SGTB) in articular cartilage of osteoarthritis (OA) and analyze the relationship between SGTB and chondrocyte apoptosis. We established an OA rat model by the meniscal/ligamentous injury (MLI) modeling method and observed the expression of SGTB in articular cartilage by immunohistochemistry and RT-PCR. Human SW1353 chondrosarcoma cells were treated with interleukin-1β (IL-1β) to mimic the OA-like chondrocyte injury in vitro, and Western blot was employed to examine the IL-1β-induced expression of SGTB and active caspase-3. The co-localization of SGTB and active caspase-3 was confirmed by immunofluorescence. We knocked down SGTB expression by RNA interference (RNAi) and overexpressed SGTB by plasmid transfection. Western blot was carried out to detect the knockdown/overexpressing efficiency of SGTB and evaluate its effects on IL-1β-stimulated expression of active caspase-3 in SW1353 cells. Annexin V/propidium iodide staining was used to detect chondrocyte apoptosis. Then, Western blot was carried out to examine the IL-1β-induced expression of Hsp70 and evaluate SGTB effects on IL-1β-stimulated expression of Hsp70 in SW1353 cells. SGTB expression was significantly up-regulated in articular cartilage of OA rat model. IL-1β stimulation increased the expression of SGTB and active caspase-3 in SW1353 cells. SGTB co-localized with active caspase-3 in IL-1β-treated SW1353 cells. SGTB inhibition significantly reduced IL-1β-stimulated expression of active caspase-3 in SW1353 cells. In line with this, overexpressing SGTB via Myc-SGTB transfection increased the active caspase-3 level in IL-1β-stimulated SW1353 cells. Moreover, flow cytometry assay demonstrated that SGTB knockdown alleviated IL-1β-induced apoptosis, but it was increased in SW1353 cells that overexpressed SGTB. Overexpressing SGTB via Myc-SGTB transfection decreased the Hsp70 level in IL-1β-stimulated SW1353 cells. Our results suggested that SGTB positively regulate the activation of caspase-3 by negatively regulating the activity of Hsp70 and might promote chondrocyte apoptosis in OA. This study may provide a novel insight into the pathophysiology of OA and a potential therapeutic target for its treatment.