Elie Metchnikoff, who was 50 years old, became more concerned about the effects of aging in 1895. The Russian Nobel Prize-winning scientist and founder of immunology Elie Metchnikoff turned his attention to gerontology, a term he invented.He was fascinated at the role of intestinal bacteria in health and disease. He suggested that people from eastern Europe would live longer if they ate more fermented foods that contained lactic acid bacteria.Although it was popular at the time this theory linked gut microbes to healthy ageing was mostly ignored by scientists up until recently. The importance of the trillions upon trillions bacteria in the regulation of health and disease is now well-known.Since almost a decade, evidence has been mounting that the composition of the microbiome changes with age. My research at University College Cork in 2012 showed that microbiome diversity was associated with health outcomes later in life, including frailty.However, we don't know enough about the effects of the microbiome upon brain aging.2017 was a year that we revisited Metchnikoff’s ideas and placed them in the context brain aging. We found that aging caused changes in the microbiota, immune system, which were associated with anxiety and cognitive decline.This study, as many others in the field, showed a correlation between aging and these variables. However, it did not prove one thing was worse than the other.We found that mice with middle-aged brains could be affected by a microbiota-targeted diet rich in prebiotic inulin. This prebiotic feeds beneficial bacteria in their gut and can reduce the effects of aging. It was not clear if the microbiota caused brain aging to slow down.Our latest study shows that many of the negative effects of aging on memory, learning, and immunity can be reversed by transplanting the microbiome of young mice into older mice. We demonstrated that the old mice found a hidden platform quicker by transferring fecal microbiota from young mice to them using a maze.(Gallica Digital Library/Wikimedia)Above: Elie Metchnikoff acknowledged the importance of the microbiome in the health and longevity of our bodies.The immune connectionInflammation levels rise with age across all organ systems, including the brain. It is evident that brain aging is influenced by immune processes. However, more attention is being paid to the role of microglia, a particular immune cell.Ironically, these cells are the same type Metchnikoff observed in the microscope in different tissues in the late 1800s. Now we know that activation of these cells are under constant regulation by our gut microbiome.The next step was to determine if the negative effects that aging has on immunity can be reversed by transplanting microbiota from old mice to young. In fact, inflammation was reduced in large part.We also found that brain chemicals involved in memory and learning (the hippocampus), were more similar to that of young mice after the microbiota transplant. These results prove that the microbiome is essential for maintaining a healthy brain in old ages.Metchnikoff's departure from immunology was it premature to understand the secrets of ageing. Further research is needed to determine the relative role of immune changes in mice that received young microbiota.But two big questions remain. But there are two big questions. Can we apply these amazing findings to the human condition?Mice are not humansIt is quite different to look at humans when you work with mice that have very specific genetics, diets and microbiomes. These findings should not be taken as gospel. For people who wish to revitalize their brains, we are not advocating fecal transfusions.These studies suggest that future focus will be on microbiota-targeted diets or bacteria-based treatments to promote optimal gut health and immunity, in order for the brain to stay young and healthy. These strategies will prove to be more appealing.Metchnikoff's general tenets seem to be right: Protecting your gut microbes could be the key to the fountain of youth. The longevity rate has increased markedly with advances in healthcare.We cannot stop time. However, we can create treatments to protect our brains.It is important to continue to study how gut microbes can rewind certain hallmarks of an older brain.John Cryan is Vice President Research & Innovation at University College Cork.This article was republished by The Conversation under Creative Commons. You can read the original article.
