Effects of mechanical load on the expression and activity of hyaluronidase in cultured synovial membrane cells.

Hyaluronan (HA) has lubricating and buffering functions in joints. Mechanical load is a regulatory factor of HA metabolism in joints, and HA synthesis by synovial membrane cells is modulated by mechanical load. However, the effects of mechanical load on HA catabolism by hyaluronidase (HYAL) in synovial membrane cells remain unclear. The purpose of this study was to evaluate the effects of cyclic tensile load on the expression and activity of HYAL in synovial membrane cells. A cyclic tensile load of 22.8% cell elongation was applied to cultured rabbit synovial membrane cells for 3 to 48 h with or without cycloheximide. HYAL1 and HYAL2 mRNA levels were evaluated by means of real-time polymerase chain reaction (PCR) analysis. HYAL activity in the cell culture was analyzed by means of HA zymography with or without HYAL2-small interfering (si) RNA. Levels of both HYAL1 and HYAL2 mRNA were up-regulated significantly (p < 0.01) by the cyclic tensile load with or without cycloheximide. HYAL activity was detected in the loaded cell cultures and was suppressed substantially by HYAL2-siRNA. HYAL activity was undetectable in unloaded cell cultures. These results show that a cyclic tensile load induces the expression and activity of HYAL in synovial membrane cells, suggesting that increased HYAL by mechanical load affects HA catabolism in synovial fluid.