Responses of each cartilaginous layer of mandibular condyle to external stimuli and the association with progressive condylar resorption

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The modulation process of superficial zone protein (SZP), a lubricant in temporomandibular joint, was clarified. The expression of SZP was higher in the superficial layer of condylar cartilage than that in other layers. In addition, the expression of SZP was down-regulated by a proinflammatory cytokine, IL-1β, leading to a deterioration of lubrication and degenerative changes in TMJ under inflammatory conditions. Hyaluronan (HA) is a major lubricant in synovila fluid, and low moleculer weight HA was accumulated in TMJ under excessive loading. The synthesis of low moleculer weight HA in synovial membrane cells was up-regulated by IL-1β. At the same time, the degradation of HA by hyaluronidase expressed by synovial membrane cells was enhanced by IL-1β. These results suggested a possible mechanism of fragmentation of HA in TMJ under inflammatory conditions. In addition, it was suggested that low molecular weight HA affects the expression of SZP through cells surface receptor in synovial membrane cells.