Vacuolar Protein Sorting 4B (VPS4B) Regulates Apoptosis of Chondrocytes via p38 Mitogen-Activated Protein Kinases (MAPK) in Osteoarthritis

To aim of this study is to investigate the expression of VPS4B (vacuolar protein sorting 4B) in articular cartilage with osteoarthritis (OA) and to analyze the relationship between VPS4B and chondrocyte apoptosis. We established an OA rat model by the MLI (meniscal/ligamentous injury) modeling method, and we observed the expression of VPS4B in articular cartilage through immunohistochemistry and reverse transcription polymerase chain reaction (RT-PCR). Human SW1353 chondrosarcoma cells were treated with IL-1 beta to mimic the OA-like chondrocyte injury in vitro, and Western blot was employed to examine the IL-1 beta-induced expression of VPS4B, phosphorylated p38, and apoptotic markers, namely active caspase-3 and cleaved poly (ADP-ribose) polymerase (PARP). The co-localization of VPS4B and active caspase 3 was confirmed through immunofluorescence. We knocked down VPS4B expression through RNA interference. Western blot was carried out to detect the knockdown efficiency of VPS4B and evaluate its effects on IL-1 beta-stimulated expression of apoptotic markers and phosphorylated p38 in SW1353 cells. Annexin V/propidium iodide (PI) staining was used to detect chondrocyte apoptosis. VPS4B expression was significantly upregulated in articular cartilage of OA rat model. IL-1 beta stimulation increased the expression of VPS4B, apoptotic markers, and phosphorylated p38 in SW1353 cells. VPS4B co-localized with active caspase 3 in IL-1 beta-treated SW1353 cells. VPS4B inhibition significantly reduced IL-1 beta-stimulated expression of apoptotic markers and phosphorylated p38 in SW1353 cells. Moreover, flow cytometry assay demonstrated that VPS4B knockdown alleviated IL-1 beta-induced apoptosis. Our results suggested that VPS4B might facilitate chondrocyte apoptosis in OA via p38 MAPK signaling pathway. This study may provide a novel insight into the pathophysiology of OA and a potential therapeutic target for its treatment.