microRNA-721 is a host regulator of TNF-IRF1 axis in Leishmania infected macrophage

MicroRNAs (miRNAs) are small noncoding RNAs that play critical roles in regulating immune responses and have emerged as potential biomarkers and therapeutic targets in complex diseases. Leishmaniasis is a neglected disease that compromises host immunity and is associated with challenging treatments regimens. Leishmania amazonensis (L. amazonensis), an intracellular protozoan parasite, causes cutaneous leishmaniasis by replicating inside mammalian macrophages to establish infection. In this context, miRNAs have emerged as vital post-transcriptional factors that regulate the inflammatory landscape during infection. In this study, we aimed to analyze the function of miR-721 in macrophages during L. amazonensis infection by integrating in silico miR-721 target prediction with RNAseq data from macrophages of two distinct mouse genotypes, resistant C57BL/6 and susceptible BALB/c. We found that miR-721 is induced in macrophages infected with L. amazonensis, but is not in LPS-stimulated macrophages, suggesting a TLR4-independent activation. Integrating miR-721 target prediction with comparative transcriptomic analyses in resistant C57BL/6 and susceptible BALB/c models revealed the TNF-IRF1 axis as a primary miR-721-associated regulatory network. Specifically, miR-721 is predicted to target the 3UTRs of Tnf and Irf1 to suppress the inflammatory response. Functional inhibition of miR-721 successfully restored Tnf and Irf1 expression and reduced the amastigote burden over 24 hours. Furthermore, we showed that the miR-721/TNF-IRF1 axis regulates downstream genes associated with macrophage response, such as Serpine1, Csf1, Cd69 and Maf. Our work demonstrated that Leishmania induces miR-721, which negatively modulates the TNF-IRF1 axis, thereby suppressing the immune response and favoring parasite persistence. While C57BL/6 macrophages exhibit a robust activation of the TNF-IRF1 network, promoting inflammatory response, BALB/c macrophage showed a breakdown of this network. This was associated with post-transcriptional suppression of inflammatory responses, thereby favoring parasite persistence. These findings link miR-721 to the establishment of macrophage polarization, providing relevant insights into the mechanisms of parasite subversion of the host immune response.