Proteoglycan expression is influenced by mechanical load in TMJ discs

The expression and assembly of the extracellular matrix are profoundly associated with adaptive and pathological responses of the temporomandibular joint (TMJ). To better understand the adaptive responses of the TMJ disc to mechanical loading, we examined the expression of 2 modular proteoglycans and 10 small leucine-rich proteoglycans (SLRPs) at the mRNA and protein levels and determined the contents of proteoglycan-related glycosaminoglycans (GAGs) in rat TMJ discs in response to altered mechanical loading caused by an incisal bite plane. One hundred thirty 7-week-old male Wistar rats were assigned to control and bite plane groups. TMJ disc thickness and the intensity of toluidine blue staining of metachromasia increased in the posterior band after 2 weeks of wearing the bite plane. GAG content increased significantly in the bite plane group after 2 weeks. Quantitative real-time RT-PCR (reverse transcription polymerase chain reaction) analysis indicated that biglycan and chondroadherin mRNA levels increased after 2 weeks and that the level of decorin mRNA increased at 4 weeks. Versican mRNA levels increased after 3 weeks, particularly for the V0 and V1 versican isoforms, which carry more GAG attachment sites than do the V2 and V3 isoforms. Western analysis demonstrated a corresponding increase in the levels of versican, biglycan, and decorin core proteins at 4 weeks in the bite plane group. These results indicate that mechanical loading differentially influences proteoglycan mRNA expression and protein accumulation in the TMJ disc. The change in proteoglycan mRNA and protein levels may lead to the modulation of matrix-matrix and cell-matrix interactions and has important biological significance for adaptation to complicated biomechanical requirements and for tissue maintenance in the TMJ disc.