IL-17 and the microbiome in the human female reproductive tract - IL-17 e il microbioma nel tratto riproduttivo femminile umano

The maternal immune response is crucial to all stages of pregnancy, particularly in the early stages of implantation and placentation. Evidence of dysregulation of maternal immunity impacting fertility is accumulating. This study, focuses on a cohort of 30 women undergoing assisted reproductive technologies (ART), 12 of whom had a successful pregnancy and 18 of whom failed to sustain a successful pregnancy. We had found activation of the IL-17A pathway in endometrial biopsies from the unsuccessful pregnancy group compared with the women who became pregnant, as well as elevated levels of IL-17A protein in h serum and endometrium. We therefore aimed to better characterize the roles that IL-17A and the other cytokines belonging to the IL-17 family might play in regulating female fertility. In the first instance, evolutionary analysis was performed of the IL-17 family of proteins and their correlation with female fertility in the Eutherian, Metatherian and Prototherian mammalian clades, which are known to have different reproductive strategies and pregnancy-related processes. Protein sequences of each of the IL-17s were collected from protein databases within NCBI or ENSEMBL repositories for representative species within each clade. Phylogenetic trees were constructed using different algorithms based on the multiple sequence alignments (MSA) of the IL-17s using MEGA software. These analyses showed that IL-17A and IL-17F from different species cluster always together, regardless of the algorithm selected. The same happens for IL-17B and IL-17D and for IL-17C and IL-25. The fact that each IL-17 cluster by family member for all the species indicates vertical inheritance of the IL-17 family during evolution and confirming their status as orthologs. The microbiome of the female reproductive tract (FRT) is only now being studied in any detail. We proposed that alterations in the FRT microbiome may induce immunological changes which could affect fertility. For the second approach, given that IL-17A regulates the response against bacterial infections, the endometrial microbiome from the successful and non-successful cohort samples was analyzed to identify whether the increased levels of this protein were due to a dysbiosis. Bacterial DNA was extracted from the endometrial biopsies and sequenced with 16S sequencing, and then analyzed using Rstudio. We identified increased bacterial diversity in samples of women who failed to get pregnant. Furthermore, Lactobacillus spp. abundance in the pregnant group correlated weakly with serum IL-17A levels measured by ELISA with a p-value of 0.046. We also aimed to identify the modulation of IL-17s induced by bacterial infections by using an Ishikawa endometrial tumor cell line infected with bacteria-derived lipopolysaccharide (LPS). We found increased expression of IL-17s mRNA particularly IL-25 and IL-17C. In conclusion, IL-17s are conserved in mammalian evolution, thus they might have similar functions among mammalian taxa. We identified a different microbiome composition in the women who failed to get pregnant. However, the small number of samples does not allow us to define a healthy versus a non-healthy microbiome for ART success. The levels of IL-17A in those women, significantly correlate with numbers of Lactobacillus spp., thus there may be a role played by IL-17A in the FRT in modulating the microbiome. Further studies focusing on other member of IL-17 family, such as IL-25 and IL-17C, might shed light in defining their impact on the microbiome and in female fertility.