Gut Exosomes May Drive Ageing Throughout the Body

Most research into gut health has concentrated on the bacteria themselves – establishing which microbes inhabit the gut and how dietary choices alter them.

This approach assumes that bacteria perform all the significant functions, with the rest of the gut serving merely as the setting in which they exist.

Yet the cells that line the gut continuously release something unrelated to bacteria: minute particles carrying proteins and fragments of genetic code that move through intestinal fluid.

A recent study examined these particles and uncovered a factor overlooked by bacteria-centred theories of gut ageing.

The gut’s secret messengers

Scientists at Marshall University’s Joan C. Edwards School of Medicine investigated an idea that is attracting increasing attention in ageing research.

Older animals commonly develop leakier gut linings, persistent inflammation and metabolic difficulties. The researchers asked whether the gut is simply harmed by ageing, or whether it actively sends ageing signals throughout the body.

Dr Abdelnaby Khalyfa, a professor of biomedical sciences, focused on exosomes released into the intestinal tract.

Exosomes are tiny vesicles emitted by cells across the body. They carry proteins, RNA fragments and other molecules between tissues.

They represent one of the principal mechanisms through which cells communicate over long distances.

Inside tiny gut particles

Previous research demonstrated that exosomes can carry small regulators known as microRNAs from cell to cell, adjusting gene activity in their destination cells.

Their contents depend on the donor. The team proposed that ageing alters this cargo, which then affects the recipient.

To investigate, the scientists gathered gut exosomes from young and old mice before transferring them between age groups.

Young mice were given exosomes from the older group, whereas older mice received those from younger animals.

Gut particles accelerate ageing

Young mice receiving cargo from old mice experienced more than a minor chemical shift. Their intestinal linings became leakier and their inflammation markers increased.

Their metabolic patterns began to mirror those seen in substantially older animals. Insulin signalling – the body’s key mechanism for moving sugar from the bloodstream into cells – deteriorated.

Normally, healthy young mice would not develop insulin resistance following a short transfer of gut particles, yet this is what occurred.

Young particles reverse damage

The other half of the experiment produced an even more notable result. In older mice given exosomes from young donors, several metabolism-related problems associated with ageing improved, including a stronger intestinal barrier and reduced inflammation.

This result in both directions distinguishes the study from earlier transplantation research.

Scientists had long believed that young donors might carry something capable of partly restoring an aged system, although the responsible component remained unidentified.

The team has now isolated the likely factor: not bacteria or food, but the secreted particles themselves.

Ageing weakens gut defences

The gut barrier is a lining just one cell thick, separating bacteria, food and waste within the intestine from the bloodstream.

When this barrier is intact, those contents stay in their proper place. If it becomes permeable, bacterial fragments and substances that trigger inflammation can enter circulation.

Long-term contact with these escaped fragments has been associated with numerous age-related conditions.

A recent study reported that older adults with leakier gut barriers had poorer cardiovascular risk profiles, including increased blood glucose and changed fat metabolism.

The Marshall team’s results indicate that exosomes may contribute to this deterioration from the outset.

Reading the molecular code

Alongside the transfer experiments, the researchers recorded the contents of the exosomes through multi-omic profiling, combining protein analysis with RNA sequencing.

Exosomes from old mice contained high levels of molecules with profiles associated with pathways connected to cancer, brain and behavioural changes, and metabolic difficulties.

Particles from younger mice had a markedly different composition.

The patterns also varied between male and female mice, suggesting that ageing could send somewhat different chemical signals according to sex.

Inflammation’s hidden trigger

Low-level inflammation throughout the body – often termed inflammaging – is increasingly recognised as a shared feature of age-related disease.

One review bringing together decades of findings linked it with heart disease, diabetes, neurodegeneration and frailty.

“This study helps clarify how the physiological stressors associated with biological aging may accelerate biological processes linked to aging and disease,” said Khalyfa.

The paper does not suggest that exosomes alone account for inflammaging. However, it firmly adds them to the list of possible drivers.

Future anti-ageing therapies

Applying these findings to people will require direct measurements of gut exosomes in older individuals, as well as clinical trials.

The researchers have already identified particular molecules within these particles that may become diagnostic markers and, eventually, treatment targets.

Before this research, this process was unknown. Ageing changes the cargo carried by the gut’s tiniest messengers, and those altered contents can move a young body towards an older biological state – or partly restore an old one.

Should exosomes be filtered or altered, clinicians may eventually be able to address age-related decline without changing either gut bacteria or diet.