Μελέτη της ακετυλίωσης και της μεθυλίωσης στην αναδιοργάνωση της χρωματίνης κατά τη γήρανση

Abstract

The term epigenetic changes of chromatin is used to describe changes in the regulation of gene activity and expression, that are not dependent on gene sequence. The most studied epigenetic changes are histone post-translational modifications and DNA methylation. These studies have shown that epigenetic changes play an important role in a broad range of biological functions and also that their deregulation is involved in many disease states. Moreover, a large body of data has correlated epigenetic changes with the aging process. However, the mode by which these changes exert their effects on gene expression and their mechanisms of action still need further clarification. The first part of the present study was focused on the epigenetic changes of chromatin that occur in age-related genes. The first candidate was H1.0, a gene that encodes for a DNA linker histone variant that has been shown to be related to both in vivo and in vitro aging. In the present study, H1.0 mRNA levels were found to be elevated in both Go phase and PHA-activated lymphocytes of old donors as compared to young. These observations are in agreement with results for the levels of histone acetylation that were found to be higher in the old donor samples as compared to those of the young samples, for the entire H1.0 gene region and especially around the promoter region of the gene. Additionally, the same histone acetylation changes were also found in fibroblasts from young and old donors. Histone H3K4 trimethylation didn’t seem to have important age-related changes in lymphocytes, mainly because the differences observed didn’t correlate with the H1.0 mRNA levels. Lastly, neither H1.0 mRNA levels nor changes in histone modification levels (acetylation and H3K4me3) were found to occur as a function of age in the third aging cell system used in this study, i.e., monocytes and in vitro differentiated dendritic cells. The second gene that was analyzed was DFNA5, a gene whose expression levels were found to change during development from previous studies in mice. In the present thesis work, microarray and real time PCR analyses of monocytes and in vitro differentiated dendritic cells from donors of different age groups showed that this gene’s mRNA levels change, both as a function of differentiation of monocytes to dendritic cells, and as a function of age. More particularly, DFNA5 expression levels were found to be higher in dendritic cells as compared to monocytes. With respect to age, DFNA5 expression levels were higher in dendritic cells of newborns as compared 213 to the dendritic cells of adult donors. The study of histone post-translational modifications revealed that there are age-related epigenetic changes around the DFNA5 gene region, but different to those observed in the H1.0 gene. H3K4 trimethylation (Η3Κ4me3), a histone modification associated with active genes, was found to be higher in the dendritic cells derived from newborns as compared to those from adult donors. On the contrary, H3K27 trimethylation, an epigenetic mark of silenced…