Getting old is an inescapable fact of life, like wet British summers. But age may not be entirely due to processes in our body cells. Instead, our bodies may age in part because of the actions of microorganisms like bacteria, which interfere with our biology.
“Are we older than we could be due to interactions with other species?” asks at the National Museum of Natural History in Paris, France. He and his colleagues have reviewed information from published studies relating to ageing and argue that this is likely, because organisms that live on or in the bodies of animals – including humans – have incentives to interfere with the ageing process. He calls these organisms “age distorters”.
Treatments that target these processes might help older people fight off infections, including covid-19.
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Ageing runs far deeper than wrinkled skin and greying hair. As we get older, our bodies gradually work less well. For instance, our brains struggle to learn new things as we age, and at the cellular level, our DNA becomes less stable.
Ageing doesn’t seem to be simply a matter of inevitable wear and tear: to some extent, it is preprogrammed into our biology. There are several ideas about why this happens. For example, mutations that are only harmful later in life, after an organism has reproduced, might not be strongly selected against by evolution. Alternatively, some organisms may prioritise reproducing over living longer.
All of this may be true, says Bapteste, but we should also consider the role of other organisms. “No organism lives alone and all organisms are in interaction with others,” he says.
Viruses in our bodies are particularly likely to interfere with ageing, argues Bapteste. They must invade our cells to reproduce, which requires them to counteract the cells’ defensive mechanisms – and doing so can affect our ageing process because the genes that code for those mechanisms are often involved in ageing. “There is a mechanical overlap between defence mechanisms and ageing genes,” says Bapteste. “That makes it pretty obvious that viruses will interfere with those genes.”
For instance, Bapteste and his colleagues found published evidence that the human immunodeficiency virus (HIV), which causes AIDS, –which might help explain why people with HIV can experience accelerated ageing.
Furthermore, a microorganism need not be as harmful as HIV to interfere with our ageing processes, says Bapteste. For instance, Drosophila fruit flies raised in the presence of Acetobacteraceae species of bacteria tended to have shorter than usual lifespans, while those raised in the presence of certain Lactobacillus bacteria .
“What matters is if there are conflicting evolutionary interests between two partners that come to share a common body,” he says. “If there are conflicting interests, which is almost always the case, then the way they [the two organisms] use resources is going to be different.”
“Overall it makes sense” and the evidence from HIV patients is “compelling”, says at the Karolinska Institute in Stockholm, Sweden. She cautions that many of the studies Bapteste uses to bolster his case were done in non-human organisms, and the effects may be smaller in humans – a pattern seen in studies of other age-related processes.
The most promising avenue to fight the process may be to target age-distorting mechanisms – like those of HIV – that weaken people’s immune systems, says Hägg. In line with this, a showed that when old mice were given “senolytic” drugs that selectively killed aged cells, they were better able to fight off a mouse coronavirus. The “de-aged” mice survived longer and produced more antibodies against the virus. Hägg says older people treated in a similar way might have a better chance of surviving covid-19.
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