Analysis of the machinery and intermediates of the 5hmC-mediated DNA demethylation pathway in aging on samples from the MARK-AGE Study

Abstract

Gradual changes in the DNA methylation landscape occur throughout aging virtually in all human tissues. A widespread reduction of 5-methylcytosine (5mC), associated with highly reproducible site-specific hypermethylation, characterizes the genome in aging. Therefore, an equilibrium seems to exist between general and directional deregulating events concerning DNA methylation controllers, which may underpin the age-related epigenetic changes. In this context, 5mC-hydroxylases (TET enzymes) are new potential players. In fact, TETs catalyze the stepwise oxidation of 5mC to 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC) and 5-carboxylcytosine (5caC), driving the DNA demethylation process based on thymine DNA glycosylase (TDG)-mediated DNA repair pathway. The present paper reports the expression of DNA hydroxymethylation components, the levels of 5hmC and of its derivatives in peripheral blood mononuclear cells of age-stratified donors recruited in several European countries in the context of the EU Project ‘MARK-AGE’. The results provide evidence for an age-related decline of TET1, TET3 and TDG gene expression along with a decrease of 5hmC and an accumulation of 5caC. These associations were independent of confounding variables, including recruitment center, gender and leukocyte composition. The observed impairment of 5hmC-mediated DNA demethylation pathway in blood cells may lead to aberrant transcriptional programs in the elderly.

High Dietary Fat Intake Affects DNA Methylation/Hydroxymethylation in Mouse Heart: Epigenetic Hints for Obesity‐Related Cardiac Dysfunction

“…Analysis of cytosine modifications was assessed by dot‐blot assay as previously described . Briefly, DNA was extracted from hearts by using phenol‐chloroform‐isoamyl alcohol method.…”

Measuring biological aging in humans: A quest

“…Although the role of 5hmC has not definitively been established, contrary to 5mC that is thought to inhibit gene expression, 5hmC is enriched in coding regions of actively transcribed genes and some studies have shown positive correlations with expression levels (Branco, Ficz, & Reik, ; Colquitt, Allen, Barnea, & Lomvardas, ; Yu et al, ). There is evidence that hydroxymethylation increases with aging in several brain regions, including the hippocampus, while declining in peripheral mononuclear cells (Szulwach et al, , Valentini et al, ). Brain hydroxymethylation has also been associated with age‐related neurodegenerative diseases such as Alzheimer's disease (Zhao et al, ).…”

The influence of aging on the methylation status of brain‐derived neurotrophic factor gene in blood

“…Overall, the results of the present study suggest that aging may cause secondary DNAm changes, although the precise mechanism of age‐associated changes in DNAm is unknown. Valentini and associates demonstrated an age‐related decline of TET1 in human peripheral blood mononuclear cells. TET1 reportedly plays an important role in the conversion of 5‐methylcytosine to 5‐hydorxymethycytosine, as the first step in the DNA demethylation pathway.…”