Graded Calorie Restriction Causes Graded Slowing of Epigenetic Ageing in Mice

DNA methylation variation is associated with chronological ageing. Calorie restriction (CR) prolongs lifespan and healthspan in many species. Our hypothesis is that CR has an impact on DNA methylation patterns with increased CR leading to slower epigenetic ageing. We studied the effects of graded CR in male C57BL/6J mice on liver DNA methylation. Mice were fed ad libitum (AL) in the dark-phase or restricted by 10%, 20%, 30% or 40% from 5-months old for 19-months. Livers were collected in surviving mice at 24-months old and DNA methylation measured. Comparisons were made to 8-month-old AL fed mice. DNA methylation was significantly related to graded CR in a subset of cytosine-guanine dinucleotide (CpG) sites. In a substantially similar subset of CpG sites, DNA methylation in 24-month-old mice fed 40CR moved towards the values in 8-month-old AL fed mice, resulting in an average effective epigenetic age of about 12-months, indicative of slower epigenetic ageing. DNA methylation at several CpG sites was sensitive to glucose intolerance and circulating insulin levels, consistent with the impact of this nutrient sensing pathway on ageing. We focussed on genes where multiple CpG sites were significant for DNA methylation change with CR and found many have been implicated in age-associated liver diseases. In summary, the benefits of CR include modification of epigenetic signatures in the direction of slower ageing, consistent with the life extending effects of CR. Whether this effect is causal for the life extension under CR, and the mechanism by which it occurs remain unanswered questions.