Meniscus Gene Expression Profiling: Inner and Outer Zone Tissue Comparison to Cartilage and Passaged Monolayer Meniscus Cells
Meniscus injuries are common and while surgical strategies have improved, there is a need for alternative therapeutics to improve long-term outcomes and prevent post-traumatic osteoarthritis. Current research efforts in regenerative therapies and tissue engineering are hindered by a lack of understanding of meniscus cell biology and a poorly defined meniscus cell phenotype. This study utilized bulk RNA-sequencing to identify unique and overlapping transcriptomic profiles in cartilage, inner and outer zone meniscus tissue, and passaged inner and outer zone meniscus cells. The greatest transcriptomic differences were identified when comparing meniscus tissue to monolayer cultured cells (> 4,600 differentially expressed genes (DEGs)) and meniscus tissue to cartilage (> 3,100 DEGs). While zonal differences exist within the meniscus tissue (205 DEGs between inner and outer zone meniscus tissue), meniscus resident cells are more similar to each other than to either cartilage or monolayer meniscus cells. Additionally, we identified and validated LUM and PRRX1 as potential markers for meniscus tissue and ACTA2, FSTL1, SFRP2, and TAGLN as novel markers for meniscus cell dedifferentiation. Our data contribute significantly to the current characterization of meniscus cells and provide an important foundation for future work in meniscus cell biology, regenerative medicine, and tissue engineering. Overall design: RNA was isolated from porcine inner and outer zone meniscus tissue, cartilage (n=3/tissue type), and passage 3 inner (n=3) and outer zone (n=2) meniscus cells.  RNA-Sequencing was performed and differential expression due to tissue type, zone, and cell passaging/dedifferentiation was assessed.