Cerebral small vessel disease (SVD) is one of the most common degenerative vessel disorders of the aging brain. White matter hyperintensities (WMH) on magnetic resonance imaging (MRI) are viewed as typical markers of SVD and are associated with an increased risk of stroke, dementia, and death. Advancing age is the strongest predictor of WMH prevalence and severity. Recent studies have developed a novel biomarker of aging, termed “epigenetic clock”, based on DNA methylation levels at specific sites across the genome, which are strongly correlated with chronological age. The deviation of the DNA methylation (DNAm)-predicted age from the chronological age, defined as “age acceleration”, is used as an index of an individual’s rate of aging. Here, we estimated blood DNAm age in African-Americans from the Atherosclerosis Risk in Communities (ARIC) study using two methodologies, and examined the cross-sectional association between WMH on MRI and measures of accelerated epigenetic aging.
We hypothesized that DNAm age acceleration, defined as the residual value from the regression of the predicted DNAm age onto chronological age, is associated with greater WMH burden independently of chronological age and other known risk factors, including sex, body mass index, systolic blood pressure, hypertension, diabetes, and current smoking.
DNA methylation was measured using the Illumina HM450 array on genomic DNA extracted from blood samples of African-American participants of the ARIC study. We estimated DNAm age using two published algorithms in 713 individuals aged 51-73 with both DNAm and brain MRI data. Linear regression models were used to estimate the association of the natural log-transformed WMH burden with each measure of age acceleration adjusting for covariates.
Age acceleration was significantly associated with WMH burden and results were similar for both estimates of DNAm age. Each unit increase in WMH burden (on the log scale) was associated with a 1.2 and 1.3 year increase in DNAm age after accounting for chronological age and other known risk factors (P=0.01 and 0.004). Further adjustment for blood cell composition did not meaningfully change these results.
In this population-based study of middle-aged to older African-American adults, we report evidence of an association between accelerated epigenetic aging of blood and increased WMH burden, independent of known risk factors, including chronologic age. Additional studies are ongoing to clarify whether DNAm age is simply a marker of the rate of aging or reflects biological mechanisms implicated in the aging of the cerebral white matter.