Transport of miR-766-3p to A549 cells by plasma-derived exosomes and its effect on intracellular survival of Mycobacterium tuberculosis by regulating NRAMP1 expression in A549 cells

Exosomal microRNAs (miRNAs) in circulation were recognized as potential biomarkers for the diagnosis of multiple diseases. However, its potential as a diagnostic hallmark for tuberculosis (TB) has yet to be explored. Here, we comprehensively analyze miRNA profiles in exosomes derived from the plasma of active TB patients and healthy persons to evaluate its efficacy in TB diagnosis. Small-RNA transcriptomic profiling analysis identified a total of 14 differentially expressed miRNAs (DEmiRNAs), among which the diagnostic potential of exosomal miR-766-3p, miR-376c-3p, miR-1283, and miR-125a-5p was evident from their respective areas under the ROC curve, which were 0.8963, 0.8313, 0.8097, and 0.8050, respectively. The bioinformatics analysis and Luciferase reporter assays confirmed that the 3'-untranslated region of natural resistance-associated macrophage protein 1 (NRAMP1) mRNA was targeted by miR-766-3p. The exosomes could be internalized by the A549 cells in co-culturing experiments. Furthermore, both increased miR-766-3p and decreased NRAMP1 expression were observed in Mtb-infected A549 cells. MiR-766-3p overexpression reduced the NRAMP1 levels, but increased intracellular Mtb, suggesting that miR-766-3p may facilitate Mtb survival by targeting NRAMP1. Moreover, miR-766-3p-transfected cells exhibited increased apoptosis and reduced proliferation following Mtb infection. Taken together, circulating exosomal miR-766-3p, miR-1283, miR-125a-5p, and miR-376c-3p may serve as candidate hallmarks for TB diagnosis where the presence of miR-766-3p seems associated with the vulnerability to Mtb infection in humans and could be a new molecular target for therapeutic intervention of TB.