Long-term in vitro expansion of osteoarthritic human articular chondrocytes do not alter genetic stability: A microsatellite instability analysis

In this study, we investigated genetic damage acquisition during in vitro culture of human osteoarthritic (OA) chondrocytes to evaluate their safety for use in regenerative medicine clinical applications. In particular, we have addressed the impact of long-term in vitro culture on simple sequence repeat stability, to evaluate the involvement of the mismatch repair system (MMR) in the accumulation of genetic damage. MMR, the main post-replicative correction pathway, has a fundamental role in maintaining genomic stability and can be monitored by assessing microsatellite instability (MSI). MMR activity has been reported to decrease with age not only in vivo, but also in vitro in relationship to culture passages. OA chondrocytes from seven donors were cultured corresponding to 13-29 population doublings. Aliquots of the cells were collected and analyzed for MSI at five DNA loci (CD4, VWA, FES, TPOX, and P53) and for MMR gene expression at each subculture. Genetic stability was confirmed throughout the culture period. MMR genes demonstrated a strong coordination at the transcriptional level among the different components; expression levels were very low, in accordance with the observed genetic stability. The reduced expression of MMR genes might underline no need for increasing DNA repair control in the culture conditions tested, in which no genetic damage was evidenced. These data argue for the safety of chondrocytes for cellular therapies and are encouraging for the potential use of in vitro expanded OA chondrocytes, supporting the extension of autologous cell therapy procedures to degenerative articular diseases.