Microsatellite instability and compromised mismatch repair gene expression during in vitro passaging of monoclonal human T lymphocytes.

An age-related accumulation of DNA damage caused by increased insult and/or decreased repair, could contribute to impaired cellular function. DNA mismatch repair (MMR), the main postreplicative correction pathway, can be monitored by assessing microsatellite instability and has been reported to decrease with age. Here, we analyzed the involvement of the MMR system in the accumulation of genetic damage in a cultured monoclonal human T lymphocyte model. We correlated microsatellite instability (MSI) and MMR gene expression, and replicative senescence of CD4+ clones derived from young, old and centenarian individuals or from CD34+ precursors. Cells were analyzed for MSI at five loci (CD4, VWA, Fes, D2S123, and BAT26), for the methylation status of MLH1 and MSH2 gene promoters, and for the expression of the MMR genes MSH2, MSH6, MSH3, MLH1, PMS2, and PMS1. MSI increased with increasing culture passages, particularly in the CD34+ progenitor-derived clones, but also in those from adult T cells. MSI and MMR gene expression were found to correlate, mostly due to a reduced expression of the components of MutL heterodimers, pointing to a role of MMR in the acquisition of DNA damage with in vitro aging.