When it comes to susceptibility to infection, the results were unequivocal: 24 hours after infection, germ-free mice harbored 10,000 times more L. monocytogenes bacteria in their small intestines and about 1,000 times more Listeria in their mesenteric lymph nodes than did the conventional mice.
At the level of miRNA, however, the differences were not immediately evident: the most highly expressed miRNAs were produced at the same levels in both types of mice and they didn't change much after infection. Nevertheless, the production of five miRNAs decreased after infection only in the conventional mice, indicating that the presence of the microbiota influences the level of miRNA expression.
"We found that even though the intestinal miRNA signature is globally stable, Listeria infection can affect the host miRNA response in a microbiota-dependent manner," says Cossart. When paralleled with the lower susceptibility of the conventional mice to infection, these down-regulated regulatory molecules present an intriguing result, write the authors.
Cossart says that this study and others indicate that miRNA may be involved in protecting the host from infection, but their precise role isn't yet clear. She notes that although this study was conducted in mice, miRNA and the protein coding gene targets they regulate may be very similar in mice and in humans. Cossart and her colleagues are planning to follow up on the work to try and figure out what impacts the changes in miRNA expression mean for the networks of protein-coding genes they regulate.
|Contact: Jim Sliwa|
American Society for Microbiology