Mechanical response of chondrocyte under intermittent hydrostatic pressure loading.-Regeneration of Articular Cartilage

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Chondrocytes were isolated from the articular cartilage of rabbit joints. The cells were exposed to 0.5 Hz of intermittent hydrostatic pressure(IHP) ranging from 1-5 MPa for 1 hr. After 30 minutes of pressure loading, total RNA was extracted and analyzed by competitive RT-PCR for mRNA expression relating to cartilage metabolism. The expression of proteoglycan did not changed following the exposure to 5 MPa of IHP, but the expression of collagen type II markedly increased. The expression of collagen type I and X were not detected in all cells. These results showed that the exposure to 5 MPa of IHP could inhibit terminal differentiation of chondrocytes and enhance cartilage metabolism. Five MPa of IHP had positive effect on cartilage metabolism.Human periodontal ligament(hPDL) cells were also loaded to 0.5 Hz of IHP ranging from 1-6 MPa for 1 hr. The exposure to 6 MPa of IHP enhanced the expression of IL-6, IL-8, RANKL and OPG. IL-6 and IL-8 are inflammatory cytokines, and RANKL and OPG are cytokines relating to osteoclasts differentiation. Six MPa of hydrostatic pressure is reported as a human physiological occlusal pressure level. These results demonstrated that physiological IHP had effect on inflammatory cytokines expression and bone metabolism.These findings provide a clue to elucidation of a part of the pathogenesis of osteoarthritis.