The Secret Behind Dogs' Different Lifespans: Why Do Large Breeds Age Faster at the Molecular Level?

Large dogs have shorter lifespans. By examining changes in DNA, researchers have now found key clues to the difference in aging speed between large and small dogs.

Zomit: Big dogs have shorter lives; Now, by examining DNA changes, researchers have found key clues to the difference in the aging speed of large and small dogs.

The lifespan of large dogs is usually shorter than that of small dogs; Great Danes and Mastiffs rarely live more than a decade, while Chihuahuas may live twice as long. The exact cause of this difference remains unclear, but new research findings suggest that older dogs age faster at the molecular level, and that chemical changes in DNA may explain part of the difference.

According to Live Science, in a new study, researchers investigated the chemical changes in dogs' DNA. These changes, called DNA methylation, occur when small chemical groups called methyl groups are added to DNA. These changes can affect the access of proteins to DNA and the activity of genes and help regulate gene expression.

The pattern of DNA methylation predictably changes with age. By examining these changes, scientists have built epigenetic clocks; Tools used to estimate the biological age of organisms. Unlike chronological age, biological age is a reflection of body condition and changes related to the aging process.

"In studies of various species, including humans, scientists have used epigenetic data to build clocks that track the aging process," says Arizona State University biologist and co-author Blaise Marriner.

Large dogs age faster than small dogs per year of life

Dogs are a good option for studying aging because of the information their owners record about their diet, lifestyle, and health status. Using blood samples from 894 dogs participating in the Long-Term Canine Aging Study Project at the University of Washington, Marriner and colleagues developed epigenetic clocks. The samples then allowed the researchers to examine age-related changes in the dogs' blood immune cells. These cells are active throughout the body, and for this reason, researchers consider them to be a suitable indicator for evaluating aging in the whole body.

The results showed that DNA methylation changes are closely related to biological aging. Dogs with a higher-than-expected epigenetic age had a higher risk of dying from any cause. Comparing dogs with different sizes also showed that their aging speed is not the same. "Based on our biomarker, the epigenetic clock, large dogs aged slightly faster than small dogs per year of life," says Noah Snydermeckler, a genomicist at Arizona State University and one of the study's authors.

Reduction of methyl groups in parts of DNA called transposable elements is among the epigenetic changes associated with larger size. These elements, also known as "jump genes", have the possibility of moving in the genome. Although methyl groups help to inhibit this transfer, loss of methylation can overactivate these genes and cause inflammation in addition to damage to other genes; A process that intensifies with increasing age.

Based on this, the researchers suggest that the uncontrolled activity of the mutant genes contributes to the faster aging of large dogs. However, the findings of the study alone do not prove this possible relationship as a definitive cause.

Researchers also observed other changes in the DNA of old dogs. For example, methylation increased with age in some regions of the genome that had fewer methyl groups. While the regions with high methylation gradually lost part of their methyl groups. Also, the dogs' immune cells became more similar to each other in terms of epigenetic patterns with increasing age.

Mariner considers this phenomenon called "loss of cellular identity" to be one of the important hypotheses about body changes in the aging process. Immune cells become specialized for specific tasks, such as fighting cancer or killing viruses. Research shows that the greater similarity of these cells to each other may reduce their ability to perform specific tasks.

Humans have been breeding larger dogs for generations. Snydermeckler suggests that this choice to increase body size may come at a cost to the dogs' health. He explains that the body must strike a balance between rapid growth, tissue maintenance, and investment in the immune system and body integrity. But this explanation is only a hypothesis for now; Because the current research did not directly investigate the cause of the difference in epigenetic aging of large and small dogs.

The research group plans to build more accurate epigenetic clocks by recruiting more dogs and following them over longer periods. Current models explain only part of the epigenetic age differences in dogs, Snydermeckler says. The researchers also want to build predictive models to help dog owners identify age-related health problems early.

Dogs get some human diseases and share a living environment with humans. According to Snydermeckler, molecular investigation of the effect of environmental factors and life experiences on the health and aging of dogs can help to better understand the effect of these factors on humans who live in similar environments. As a result, the findings of such research may also help to better understand human aging.