PDK1 promotes apoptosis of chondrocytes via modulating MAPK pathway in osteoarthritis.

3-Phosphoinositide dependent protein kinase-1 (PDK1), a serine threonine kinase, belongs to the AGC kinase family and is associated with apoptosis. The aim of this study was to investigate the expression of PDK1 (3-Phosphoinositide dependent protein kinase-1) in articular cartilage with osteoarthritis (OA) and to analyze the relationship between PDK1 and chondrocyte apoptosis. Immunohistochemistry and RT-PCR analysis showed that the expression of PDK1 in articular cartilage of OA patients and healthy controls. IL-1ß-stimulated SW1353 cells were used to imitate the OA-like chondrocyte injury in vitro, and IL-1ß-induced the expression of PDK1, apoptotic markers(PARP, caspase-3), and phosphorylated p38 were detected by Western blot. The co-localization of PDK1 and Cleaved-caspase3 was confirmed through immunofluorescence. Knocking down PDK1 expression through PDK1 siRNA. Western blot was performed to detect the knockdown efficiency of PDK1 and the impact of PDK1 knockout on IL-1ß-induced expression of apoptotic markers and phosphorylated p38 in SW1353 cells. Flow Cytometry-Based Annexin V/PI Staining was used to exam chondrocyte apoptosis. Our experimental results suggested that PDK1 may promote chondrocyte apoptosis in OA via p38 MAPK signaling pathway.

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-1ß to mimic the OA-like chondrocyte injury in vitro, and Western blot was employed to examine the IL-1ß-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-1ß-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-1ß stimulation increased the expression of VPS4B, apoptotic markers, and phosphorylated p38 in SW1353 cells. VPS4B co-localized with active caspase 3 in IL-1ß-treated SW1353 cells. VPS4B inhibition significantly reduced IL-1ß-stimulated expression of apoptotic markers and phosphorylated p38 in SW1353 cells. Moreover, flow cytometry assay demonstrated that VPS4B knockdown alleviated IL-1ß-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.