Are Passaged Chondrocytes Phenotypically Similar to Meniscal Fibrochondrocytes?

The knee menisci are heterogeneous fibrocartilages with regional variations in phenotype and extracellular matrix composition reflecting varying functional demands. The inner (compressive) region is generally described as closer to cartilage, with higher aggrecan and collagen II contents and rounded cells resembling articular chondrocytes^1,2, while the outer (tensile) third of the meniscus is fibrous and vascularized with cells described as fibroblast-like. Some studies have suggested that passaged chondrocytes can be used as a source for engineering fibrocartilage due to their tendency to become more “fibrous”^3,4. However, the characteristics of isolated and passaged cells have not been quantitatively compared to the behaviors of meniscal cells. In fact, despite a qualitative understanding of phenotypic variations within the meniscus and between meniscal cells and chondrocytes, no metrics have been identified to quantitatively distinguish fibrochondrocytes from chondrocytes. In this study, we evaluated the gene expression profiles of serially passaged chondrocytes in the context of the expression profiles of articular chondrocytes and meniscal fibrochondrocytes in native tissue isolated from different anatomical regions, with a focus on genes important to the production and regulation of the extracellular matrix.