Low-grade chronic inflammation is known to be associated with ageing and is often referred to as ‘inflammaging.’
When gut bacteria from elderly mice were transplanted into younger animals, the young germ-free mice displayed the characteristic inflammaging typically seen in their seniors, found the research team led by the University Medical Centre Groningen, Netherlands.
Research has that elderly humans have an altered gut bacteria composition compared with younger adults. However, the direction of cause and effect between microbiome make-up and the inflammaging process had previously not been established. This is the first study to provide evidence of the causal direction.
“Our data seem to support the hypothesis that the altered gut microbiota composition in aged individuals contributes at least partially to the chronic low grade inflammatory state observed during ageing,” wrote lead author Dr Floris Fransen.
"Since inflammaging is thought to contribute to many diseases associated with ageing, and we now find that the gut microbiota plays a role in this process, strategies that alter the gut microbiota composition in the elderly could reduce inflammaging and promote healthy ageing," explained Fransen. "Strategies that are known to alter gut microbiota composition include changes in diet, probiotics, and prebiotics".
Genus-specific effect?
The researchers also investigated which bacterial types might be responsible for the inflammaging.
“We show by transferring aged microbiota to young germ-free mice that certain bacterial species within the aged microbiota promote inflammaging,” wrote the scientists.
“This effect was associated with lower levels of Akkermansia and higher levels of TM7 bacteria and Proteobacteria in the aged microbiota after transfer,” they added.
In previous research, TM7 and Proteobacteria (in particular genus Desulfovibrio) have been associated with increased intestinal permeability and inflammatory bowel disease, findings which are consistent with this study.
“The aged microbiota promoted inflammation in the small intestine in the germ-free mice and enhanced leakage of inflammatory bacterial components into the circulation was observed,” noted the authors.
Inflammaging may contribute to the aetiology of age-related diseases such as stroke, dementia and cardiovascular disease, suggest the researchers. However, the presence of inflammatory bacteria in the bloodstream resulting from gut permeability may also be involved in other conditions including obesity, metabolic syndrome and liver inflammation, previous research has identified.
Immune Response
Immune response in the elderly is recognised to be less effective than in younger adults. In this study, analysis of spleen, lymph nodes and small intestinal tissues showed an immune response in germ-free mice who had received bacterial transplants from conventional old mice, but not from young ones. This result suggests that the altered microbiota plays some part in the immune response in the elderly, propose the scientists.
The explanation for the different microbiota composition in the elderly is not established and may be multifactorial.
"It is likely a combination of factors such as reduced physical activity, changes in diet, but also as part of a natural process," hypothesises Fransen.
Although this study provides evidence of the microbiome’s influence on inflammaging in mice, its applicability in humans has yet to be demonstrated.
"Both in humans and mice there is a correlation between altered gut microbiota composition and inflammaging, but the link between the two remains to be proven in humans" concludes Fransen.
Source: Frontiers in Immunology
Published online, doi: 10.3389/fimmu.2017.01385
“Aged gut microbiota contributes to systemical inflammaging after transfer to germ-free mice”
Authors: Floris Fransen et al