IL-7 promoted the development of thymic DN3 cells in aged mice via DNA demethylation of Bcl2 and c-Myc genes.

ABSTRACT

IL-7 promotes the development of thymic double negative (DN) T cells during ß-selection, which might contribute to the remission of aging-associated thymic involution. Methylation levels of CpG sites is correlated with aging and modulates the development. To determine the involvement of DNA methylation/demethylation instructed by IL-7 signaling during the expansion of double negative (DN) T cells, the aged mice were treated with recombinant Adeno-Associated Virus 2-mediated IL-7 (rAAV2-IL-7) and the DNA methylation/demethylation modifications in this process were analyzed. The results showed that rAAV2-IL-7 increased the number of thymocytes, especially the DN3 thymocytes during ß-selection in aged mice. With aging, the methylation levels of Bcl2 and c-Myc promoter regions were increased in DN3 cells. Following rAAV2-IL-7 treatment, DNA methyltransferase Dnmt3a and Dnmt3b decreased, DNA demethylation factors TET2 and TET3 increased, and the methylation levels of Bcl2 and c-Myc in DN3 cells were reduced during DN3 stage in aged mice, consequently, resulting in the upregulation of Bcl2 and c-Myc and the larger increase of DN3 cells in thymus. In conclusion, these findings showed that Bcl2 and c-Myc genes of DN3 cells had an increased DNA methylation levels in aged mice compared to the young, and the hypermethylation in aged mice could be restored following rAAV2-IL-7 treatment.