DNA methylation patterns of LINE-1 and Alu for pre-symptomatic dementia in type 2 diabetes.

The identification of early markers of dementia is important for higher-risk populations such as those with type 2 diabetes (T2D). Retrotransposons, including long interspersed nuclear element 1 (LINE-1) and Alu, comprise ~40% of the human genome. Although dysregulation of these retrotransposons can induce aberrant gene regulation and genomic instability, their role in the development of pre-symptomatic dementia (PSD) among T2D patients is unknown. Here, we examined locus-specific changes in LINE-1 and Alu methylation in PSD and the potential to offset these changes via supplementation with folate and vitamin B12. We interrogated DNA methylation patterns corresponding to 22,352 probes for LINE-1 and Alu elements using publicly-available Illumina Infinium 450K methylation datasets from i) an 18-month prospective study in 28 T2D patients (GSE62003) and ii) an intervention study in which 44 individuals were supplemented with folic acid (400 µg/day) and vitamin B12 (500 µg/day) over two years (GSE74548). We identified 714 differentially methylated positions (DMP) mapping to retrotransposons in T2D patients who developed PSD in comparison to those who did not (PFDR < 0.05), comprised of 2.4% (228 probes) of all LINE-1 probes and 3.8% (486 probes) of all Alu probes. These loci were enriched in genes with functions related to Alzheimer's disease and cognitive decline, including GNB5, GNG7 and PKN3 (p < 0.05). In older individuals supplemented with folate/vitamin B12, 85 (11.9%) PSD retrotransposon loci showed significant changes in methylation (p < 0.05): participants with the MTHFR CC genotype predominantly showed hypermethylation at these loci, while hypomethylation was observed more frequently in those with the TT genotype. In T2D patients, LINE-1 and Alu elements are differentially methylated in PSD in a locus-specific manner and may offer clinical utility in monitoring risk of dementia. Further work is required to examine the potential for dietary supplementation in lowering the risk of PSD.

Dietary Intervention Modifies DNA Methylation Age Assessed by the Epigenetic Clock.

SCOPE: Alterations in DNA methylation patterns are correlated with aging, environmental exposures, and disease pathophysiology; the possibility of reverting or preventing these processes through dietary intervention is gaining momentum. In particular, methyl donors that provide S-adenosyl-methionine for one-carbon metabolism and polyphenols such as flavanols that inhibit the activity of DNA methyltransferases (DNMTs) can be key modifiers of epigenetic patterns. METHODS AND RESULTS: DNA methylation patterns are assessed in publicly available Illumina Infinium 450K methylation datasets from intervention studies with either folic acid + vitamin B12 (GSE74548) or monomeric and oligomeric flavanols (MOF) (GSE54690) in 44 and 13 participants, respectively. Global DNA methylation levels are increased in unmethylated regions such as CpG islands and shores following folic acid + vitamin B12 supplementation and decreased in highly methylated regions, including shelves and open-seas, following intervention with MOF. After supplementation with folic acid + vitamin B12, epigenetic age, estimated by the Horvath "epigenetic clock" model, is reduced in women with the MTHFR 677CC genotype. CONCLUSIONS: The effects of supplementation with folic acid + vitamin B12 and MOF on DNA methylation age are dependent upon gender and MTHFR genotype. Additionally, the findings demonstrate the potential for these dietary factors to modulate global DNA methylation profiles.