Effect of passage and topography on gene expression of temporomandibular joint disc cells

The temporomandibular joint (TMJ) disc is maintained by a population of fibrochondrocytes. Although articular chondrocytes exhibit zonal differences and de-differentiate in monolayer culture, such variations are unknown for fibrochondrocytic populations. This study's objective was to define topographical cellular variations in the porcine TMJ disc and investigate changes in the disc's gene expression levels over multiple passages using quantitative reverse transcriptase polymerase chain reaction. For topographical characterization, samples were acquired from posterior, anterior, lateral, medial, and intermediate zone sections and subdivided into inferior and superior halves. For passage characterization, cells were plated and passaged for 35 days, with samples acquired at every passage. The medial region had the lowest expression of genes indicative of fibroblastic activity, but in general, topographical variations were limited. Passage effects were evident; gene expression levels of aggrecan, collagen type I, and collagen type II dropped 20%, 23%, and 73% per passage, respectively. In contrast, decorin and glyseraldehyde-3-phosphate dehydrogenase gene expression increased 33% and 27% per passage, respectively. These data indicate that TMJ disc cells undergo significant changes due to monolayer expansion, experiencing losses in major chondrocytic markers (aggrecan and collagen type II) and fibroblastic markers (collagen type I) and posing a serious impediment to studies in which cell passaging is required.