Gut bacteria and gut movement: how microbes kick-start digestion in newborns
We already know that gut bacteria matter in newborns. But exactly how the microbial residents of the gut contribute, right from the start of life, to motility itself -- the rhythmic contracting and relaxing of the gut wall that pushes food forward -- has remained an open question. New research in zebrafish offers a surprising answer.
Researchers publishing in Science found that the signalling molecule IL-22, a cytokine normally associated with immune response and gut wall protection, plays a crucial role early in the lives of zebrafish larvae. IL-22 is secreted by enteroendocrine cells: specialised cells in the gut wall capable of releasing both hormones and immune signals. That IL-22 stimulates gut motility -- but only when the right bacteria are present.
Zebrafish larvae are a classic model for studying early gut development because their transparent bodies allow direct microscopic observation in a living animal. The researchers compared larvae with a normal gut microbiome to germ-free larvae, animals raised without any bacteria at all. In the germ-free group, normal gut motility failed to develop, even when IL-22 was available. The microbiota turned out to be essential for IL-22 to have any effect on the gut muscle.
Why this matters beyond zebrafish
The enteroendocrine cell has become an increasingly hot topic in research. For a long time, these cells were seen purely as producers of gut hormones that regulate digestion -- think of substances that influence feelings of fullness or signal the pancreas. In recent years, however, it has become clear that they also communicate directly with the nervous system, and now it turns out they use immune signals to control gut motility as well.
This research suggests that the relationship between gut bacteria and gut function is established very early in life, through a hormone-immune-microbiome axis that has not previously been described in such direct terms. That has implications for our understanding of gut problems in premature infants, in children whose microbiome has been disrupted by antibiotic use, and possibly in adults with functional gut disorders such as irritable bowel syndrome.
The link to ageing
There is a direct connection to longevity: the gut microbiome changes as you age, and impaired gut motility is one of the most common complaints among older people. If IL-22 and the microbiota work together to regulate gut movement, then the decline of certain bacterial strains later in life -- a well-documented phenomenon -- could contribute to the reduced gut motility that affects so many older adults. Whether and how this connection plays out in humans has yet to be investigated.