Age-associated bimodal transcriptional drift reduces intergenic disparities in transcription.

This study addressed the question of how well the quantitative transcriptome structure established in early life is maintained and how consistently it appears with increasing age, and if there is age-associated alteration of gene expression (A3GE), how much influence the Huntington's disease (HD) genotype exerts on it. We examined 285 exonic sequences of 175 genes using targeted PCR sequencing in skeletal muscle, brain, and splenic CD4+ T cells of wild-type and HD mice. In contrast to the muscle and brain, T cells exhibited large A3GE, suggesting a strong contribution to functional decline of the organism. This A3GE was markedly intensified in age-matched HD T cells, which exhibited accelerated aging as determined by reduced telomere length. Regression analysis suggested that gene expression levels change at a rate of approximately 3% per month with age. We found a bimodal relationship in A3GE in T cells in that weakly expressed genes in young mice were increasingly transcribed in older animals whereas highly expressed genes in the young were decreasingly expressed with age. This bimodal transcriptional drift in the T cell transcriptome data causes the differences in transcription rate between genes to progressively reduce with age.