New Delhi: A new study has found that large dogs die younger because their cells and genomes deteriorate faster. Published in the journal Science on 8 October, the study looked at over 900 dogs from 120 different breeds — large and small — to understand the reason why large dogs, on average, have shorter lifespans than smaller ones.
Rather than acute diseases or faster physical ageing, researchers from the Arizona State University found the answer at the cellular level. They conducted epigenetic analysis of the different dog breeds and their ageing, and saw that the DNA methylation loss in larger dogs is higher than in smaller dogs, causing them to age faster biologically.
“To directly estimate biological ageing rather than relying on lifespan endpoints, we used DNA methylation (DNAm), an established molecular biomarker of age,” said the study.
DNA methylation is essentially a process through which your body regulates how genes are expressed; the study explained it as an on/off switch for genes. This methylation process, however, does not stay stable over time, and as people age, it becomes more irregular and randomised.
This irregularity in methylation, known as demethylation, causes changes in transposable elements in the dogs’ bodies. Transposable elements are often referred to as ‘jumping genes’ and are segments of DNA that can move around the genome. Normally, the cell keeps them heavily methylated and locked down to prevent DNA damage. But with age, these elements lose methylation, which can destabilise the genome.
It’s not just about size
The study found that larger dogs exhibit 31 per cent greater loss of methylation, as compared to smaller dogs. This means that their bodies age biologically faster and lose crucial genomic functions faster than smaller dogs.
Even if a Pomeranian and a German Shepherd are both four years old, the study explained that the German Shepherd is biologically older, and thus its cells deteriorate faster. Chronological age is not the same as biological age, and thus it seems like larger dogs have shorter lifespans.
Also, the study found that this faster ageing is not restricted to size differences in dogs. Sex also plays a major role here, with male dogs displaying faster methylation loss as compared to female dogs, a phenomenon also found in humans and other mammals.
The study looked at a total of 1,640 methylomes, or maps of methylation tags, from 894 pet dogs. This was to ensure that the study was done in real-world settings, with family pets that ate, slept, and drank in regular environments, rather than in experimental animals in cages.
(Edited by Aamaan Alam Khan)