Overexpressing miR-222-3p in cultured Mycobacterium Tuberculosis-infected macrophages does not affect their bacteriostatic activity

Tuberculosis, a disease caused by the bacterium Mycobacterium tuberculosis, is a major public health concern. Innate and adaptive immunity provide robust defense against pathogens. However, M. tuberculosis, which co-evolved with humans, has acquired many mechanisms to evade the immune response and ensure its intracellular existence and long-term survival within the host. Moreover, emerging evidence suggests that this secretive bacterium can alter expression of regulatory noncoding RNAs (including microRNAs), leading to dysregulation of biological processes underlying tuberculosis pathogenesis. For example, miR-222-3p has been shown to regulate the functional reprogramming of macrophages and is involved in the regulation of host innate immunity. Previously, we demonstrated the important role of miR-222-3p as a biological marker of tuberculosis activity. To confirm their biological targets and understand their role in the pathogenesis of tuberculosis, many research groups are working to establish functional relationships between miRNA expression under different conditions and their actual biological action using molecular biology and bioinformatics methods. In the present study, we demonstrated the effect of miR-222-3p overexpression on several functions of human macrophages of monocytic origin activated with M. tuberculosis antigens in in vitro culture. Specifically, we found that miR-222-3p overexpression significantly decreased IL-6 and IFNγ expression and increased IL-1β and cxcl10 expression in cultures of uninfected macrophages. Infected macrophages overexpressing miR-222-3p were characterized by increased NF-κB and IL-6 expression, as were infected macrophages without transfection. Another important finding was that miR-222-3p overexpression caused a small but significant increase in reactive nitrogen species production by infected macrophages, but did not affect their bacteriostatic activity against M. tuberculosis. Elucidating the functions of different microRNAs in regulating different pathogenic pathways in TB may lead to discovering new therapeutic targets. The detailed study of microRNAs that regulate immune-associated pathways will be useful for the design of miRNA mimetic molecules, either as inhibitors or as activators. Immune effects induced by miRNA drugs are currently a major challenge for miRNA therapeutics.