Inflammatory cytokines via up-regulation of aquaporins deteriorated the pathogenesis of early osteoarthritis

BACKGROUND: Inflammatory cytokines enhanced the progress of the pathogenesis of osteoarthritis, however the mechanisms remain unclear. The objective is to determine aquaporins (AQPs) in the pathogenesis of osteoarthritis. METHODS AND FINDINGS: Primary rat articular chondrocytes were treated with IL-1β to mimic the early stage of osteoarthritis in vitro. Early osteoarthritis animal model was established by intra-articular injection of 4% papain. Micro- or ultra-structure histopathologic changes, cell viability, apoptosis cells and cell membrane permeability, locations and expressions of AQP1 and AQP3 and matrix were detected in the cartilage or in the chondrocytes of knee. IL-1β could reduce the chondrocytes viability, increase the apoptosis cells, and also impair the cell membrane and organelles. IL-1β significantly induced the up-regulation of AQP1 and AQP3 in the chondrocytes. In the chondrocytes, AQPs were mainly clustered in both membrane and perinuclear region of cytoplasm, while higher AQPs were detected in the superficial and middle layers of the cartilage. With the up-regulation of AQPs, the cartilage matrix was considerably decreased in both the chondrocytes and in the osteoarthritis cartilage. In the early osteoarthritis rat model, serum and synovial fluid confirmed that higher IL-1β could increase the expressions of AQPs, and decrease the cartilage matrix in both the chondrocytes and the cartilage. CONCLUSIONS: Inflammatory cytokine IL-1β via up-regulation of AQPs caused the abnormal metabolism of water transport and loss of the cartilage matrix in the chondrocytes, and ultimately exacerbated the pathogenesis of early osteoarthritis. Therefore, AQPs may be a candidate therapeutic target for prevention and treatment of osteoarthritis.