On this episode of X10, we talk about the how the gut microbiome is connected with aging and the role of gut bacteria in the immune response.
You’ve probably heard about the gut microbiome, the community of countless microbes living in your intestines, as it’s been a hot topic for several years. There’s regular news about how it affects yet another aspect of our biology, but have you ever considered whether it plays a part in aging?
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Microbiome research has grown tremendously over the past two decades. We now know that the microbiome is involved in lots of important things, from modulating your immune response to influencing your hormone balance. As more data has become available and improved sequencing techniques have made it easier to study the microbiome, researchers have started to look at whether the microbiome might be linked with aging.
We know that the microbiome changes during a person’s life. It’s usually established in the womb and reaches an adult-like state after the first few years of life. From then on, diet becomes a major factor shaping the composition of the gut microbiome, though other factors can affect it, too. Studies have found differences between the microbial communities in the guts of older and younger people. Older people seem to have less diverse gut microbiomes, but it’s not clear whether that’s a cause or consequence of aging.
A 2019 study found that healthy elderly people had a more diverse microbiome, but that still doesn’t answer the question. Some studies in model organisms have shown that adding certain kinds of microbes increases lifespan, so the composition of the microbiome probably affects lifespan in humans, but we can’t say for sure. In fact, there’s a good chance that changes in the microbiome play a role in aging and are affected by aging. That’s not just because biology tends to be messy that way; it also makes sense if you think about the mechanisms involved.
Take immune response, for example. We know that aspects of our immune system change as we age. Changes in our immune response affect which bacteria are tolerated within the gut, which changes the make-up of the microbiome. At the same time, we know that the microbiome affects the systemic immune response and even the expression of immune-related genes, so changes in the microbiome could contribute to how the immune system changes with age.
Likewise, changes in the permeability of the gut membrane with age affect the composition of the microbiome, but they also seem to happen in response to metabolites produced by the microbiome. Microbial metabolites are also good candidates for how the microbiome could influence aging. A paper published in 2017 showed a pretty clear link between the two.
The researchers grew nematodes with mutated E. coli bacteria in their microbiomes. The E. coli produced more of a molecule known as colanic acid, and nematodes carrying these bacteria lived longer than those with normal E. coli. It seems like the colanic acid somehow affected the nematods’ mitochondria, though the exact mechanism isn’t yet clear.
The team even showed that the same extension in lifespan could be accomplished by feeding colanic acid to nematodes with normal E. coli, avoiding the need to mess about with the microbiome. That’s nice, because it means at least some of the benefits of a healthy microbiome might be available through drugs or supplements. In the long run, of course, the goal is to have as healthy a microbiome as possible. To do that, we’ll need to understand what constitutes a healthy microbiome and figure out how that affects and is affected by aging.
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