Hydrostatic Pressure Influences HIF-2 Alpha Expression in Chondrocytes

Hypoxia-inducible factor (HIF)-2 alpha is considered to play a major role in the progression of osteoarthritis. Recently, it was reported that pressure amplitude influences HIF-2 alpha expression in murine endothelial cells. We examined whether hydrostatic pressure is involved in expression of HIF-2 alpha in articular chondrocytes. Chondrocytes were cultured and stimulated by inflammation or hydrostatic pressure of 0, 5, 10, or 50 MPa. After stimulation, heat shock protein (HSP) 70, HIF-2 alpha, nuclear factor kappa B (NF-kappa B), matrix metalloproteinase (MMP)-13, MMP-3, and vascular endothelial growth factor (VEGF) gene expression were evaluated. The levels of all gene expression were increased by inflammatory stress. When chondrocytes were exposed to a hydrostatic pressure of 5 MPa, HIF-2 alpha, MMP-13, and MMP-3 gene expression increased significantly although those of HSP70 and NF-kappa B were not significantly different from the control group. In contrast, HIF-2 alpha gene expression did not increase under a hydrostatic pressure of 50 MPa although HSP70 and NF-kappa B expression increased significantly compared to control. We considered that hydrostatic pressure of 5 MPa could regulate HIF-2 alpha independent of NF-kappa B, because the level of HIF-2 alpha gene expression increased significantly without upregulation of NF-kappa B expression at 5 MPa. Hydrostatic pressure may influence cartilage degeneration, inducing MMP-13 and MMP-3 expression through HIF-2 alpha.