Mystery of why big dogs age faster than small ones finally solved

Scientists say they’ve finally solved a longstanding mystery – why big dogs age faster than little dogs.

It has long been understood that smaller dogs tend to have longer lifespans than larger ones, bucking a wider trend in the animal kingdom that often sees bigger creatures living longer. But until now, scientists haven’t known why dogs are different.

However, new research suggests it all comes down to canine DNA and a “jumping” gene called LINE1.

LINE1 genes are self-replicating and can copy and insert themselves throughout a dog’s genetic systems.

These genes are usually kept in check by a gene activity-regulating process called “DNA methylation.” But when methylation is lost, their activity can increase, damaging DNA in the process and speeding aging.

And crucially, larger dogs lose 35 percent more LINE1 gene methylation than smaller dogs, a new analysis of 864 dogs enrolled in the multi-year, nationwide Dog Aging Project shows.

“This is one of the clearest molecular signatures we’ve seen that aligns with the well-known size-lifespan tradeoff in dogs,” Blaise Mariner, an author of the findings and researcher at Arizona State University, explained in a statement.

“It suggests that faster aging in larger dogs may be driven, at least in part, by reduced control over these ‘jumping genes.’”

Surprisingly, the study also uncovered differences between male and female big dogs revealing that females may experience more LINE1 gene-jumping.

“This was an unexpected result,” Brianah McCoy, who co-led the work, said. “It challenges some of our assumptions about how the X chromosome is regulated and highlights the complexity of epigenetic aging.”

Previously, experts had cited faster aging rates and shorter lifespans for the difference in the lifespans of man’s larger best friends, but had not understood why this happened.

Recent research from the University of Arizona revealed that large dog brains don’t age faster than smaller dog brains, too, indicating the animals died before seeing cognitive decline.

Although more research is needed to determine whether LINE1 activity is a cause or consequence of aging, the researchers hope these findings will help scientists develop methods to extend the lifespan of large dogs – for their benefit and ours.

“Dogs provide an extraordinary model for understanding aging because they show dramatic variation in lifespan within a single species,” senior study author Noah Snyder-Mackler, a professor at Arizona State University, said

“Our work suggests that transposable elements may be a fundamental part of the aging process across mammals,” he added.

“If that’s the case, targeting these elements or the mechanisms that regulate them could be a promising avenue for future therapies to extend the health span in humans.”