A group of researchers from the Center for Neuroscience and Cell Biology (CNC) of the University of Coimbra (UC) has found new relevant molecular mechanisms for the infection of human cells by bacteria responsible for the development of serious food poisonings, according to a study published in the conceited journal “Nature Microbiology”.
Shigella and Salmonella are two groups of bacteria responsible for food poisonings, among other diseases. These 2 types of bacteria are strongly related with the development of disorders such as dysentery and gastroenteritis, pretty common and worldwide deadly, especially in underdeveloped countries.
“These 2 bacteria, Salmonella and Shigella, are extremely relevant in the public health point of view. Both are associated with the onset of food poisonings, as Salmonella is more prevalent in developed countries, and Shigella in underdeveloped countries, where it is associated with a high mortality rate in children under the age of 5 years”, refers Ana Eulálio, group leader at CNC and co senior researcher of this study. “We wanted to understand more about the host-pathogen interaction in these two species, and compared them, to evaluate common points and differences in the infections of these bacteria”, concludes the researchers.
The study, published in the Nature group journal had as main aim to understand how microRNAs, little RNA sequences non-coding of our genetic code with a regulatory role, control the different steps of the life cycle of both Shigella and Salmonella, particularly the invasion and replication stages in our cells. The starting point for this study consisted in the identification, by a high-throughput screening, the role of each on the 2500 microRNA in the human genetic code in the different infection stages of these bacteria.
“The role of microRNA during infection by many viruses is already pretty established. However, little is known about the role of these sequences in bacterial infections. The first analysis allowed us to identify more than 100 microRNA sequences with an important role in the different infection stages of these bacteria. More importantly, we did not just evaluate the microRNA by itself, but also its respective cellular functions which are targeted of their action”, adds Miguel Mano, also a CNC group leader and co senior researcher of this study. “This analysis allowed us also to determine that the action of some microRNA corresponded to a defense mechanism of our cells, as other were modulated by the bacteria to subvert our cellular mechanisms”, refers the researchers.
Afterwards, the team of researchers proceeded to the evaluation of the role of some of these microRNA in epithelial human cells infected with both types of bacteria. They observed that, in the case of Shigella, the microRNA 3668, 4732-5p and 6073 prevented the bacterial movement within the cell and its dissemination to neighboring cells. In the case of Salmonella, they saw there was a reduction of the microRNA let-7i-3p by the action of the bacteria, with the main aim of modifying the environment in the interior of specific vesicles within the cell – the endolysosomes – and so, to favor the bacterial replication and consequential dissemination. To prove this last observation, the researchers also observed that, in a swine animal model infected with Salmonella, there was also a decrease of this microRNA associated with the infection.
“The identification of these microRNA are not the end of the story, but its beginning. The most part of the developed work was the analysis of the function, new targets, and pathways within the regulated cells by the various microRNA sequences, as well as their impact during infection. We observed 2 types of different impacts: in Shigella we saw how microRNA stopped the movement of the bacterium within the cell, and between cells, inhibiting their dissemination. In Salmonella we saw that let-7i-3p regulates processes that prevent the replication of the bacterium within the cell”, adds Ana Eulálio. “The validation of the swine model for Salmonella infection is very relevant, as its infection is very similar to the one in humans, and these animals are normally infected by this bacterium”, refers the researcher.
In the future, the researcher group plans to better characterize the role of microRNA in the infection of other bacteria, and further explore these sequences in the host-pathogen context. The evaluation of the regulated actions by the different microRNA in the caused infections by bacteria could be a milestone in the development of therapeutic strategies directly targeted to cell processes, which may be targeted by these microRNA.
“The study allowed to obtain an extensive microRNA list involved in the different stages of the infection of these two bacteria. This list is accessible to all the scientific community. In the future, it will be important to apply this methodology which we optimized to other bacteria to better understand the cellular and molecular mechanisms that regulate the host-pathogen interaction in different harmful bacteria to public health”, adds Miguel Mano. “Therapeutically, to evaluate which actions are regulated by each microRNA in different stages of the bacterial infection, we can develop specific approaches against the new targets we identified, not to prevent the infection, but to reduce the infection and bacterial dissemination in our cells”, finalizes.
More than Ana Eulálio and Miguel Mano, the study had the participation of Ana Rita Cruz, former CNC researchers, as first author, as well as by Inês Lopes and Ricardo Silva, CNC researchers. The study “Functional screenings reveal different requirements for host microRNAs in Salmonella and Shigella infection” also had the collaboration of researchers from institutions from Germany, Spain, France and Italy, and may be read in https://doi.org/10.1038/s41564-019-0614-3.
Créditos: Ana Eulálio, João Cardoso e Miguel Mano