Epigenetic Aging is Accelerated in Large Dogs versus Small Dogs
Smaller dog breeds live for longer than larger dog breeds, which perhaps allows some insight into mechanisms of aging. Researchers here find that age-related change in the epigenetic regulation of nuclear DNA structure and gene expression proceeds more rapidly in larger dogs, particularly in regions containing transposable elements. Transposable elements are the remnants of ancient viral infections, capable of copying themselves across the genome when active, a form of damage that can break gene sequences. The virus-like particles created by expression of transposable elements provoke inflammatory responses, and thus loss of transposable element suppression contributes the disruptive chronic inflammation of aging. This study adds to the existing body of evidence suggesting that transposable element activation resulting from epigenetic change provides a meaningful contribution to mammalian aging.
Comparative studies across species have identified mechanisms associated with exceptional longevity, but they are less well suited to identifying the molecular drivers of aging variation among individuals within a species. Domestic dogs provide a model for addressing this challenge because body size strongly predicts lifespan, with larger breeds living substantially shorter lives than smaller breeds despite sharing many physiological and environmental conditions.
We generated 1640 methylomes from 894 companion dogs enrolled in the Dog Aging Project and paired these data with detailed demographic and genetic information. Using these data, we developed highly accurate DNA methylation (DNAm) age predictors with a median average error of 0.82 years. We found that dogs with epigenetic ages older than expected exhibited elevated mortality risk, demonstrating that DNAm captures biologically meaningful variation in aging. Larger dogs, males, and younger individuals showed molecular profiles consistent with accelerated epigenetic aging.
Age-associated differential methylation was highly structured by genomic context. Promoters generally gained methylation with age, whereas introns and transposable elements (TEs) predominantly lost methylation with age. Sex differences in age effects were most pronounced on the X chromosome, whereas size-associated differences were greatest in TEs: larger dogs had 31% stronger age-associated TE demethylation than smaller dogs. This amplification was widespread across TE classes and evolutionary lineages, including long interspersed nuclear elements (LINEs), short interspersed nuclear elements, LINE2s, and DNA transposons, but was most pronounced in evolutionarily young LINE1s.