miR-1224 Expression Is Increased in Human Macrophages after Infection with Bacillus Calmette-Guérin (BCG)

Tuberculosis (TB) remains a major threat to human health. Understanding the strategies mycobacteria take to overcome immune defense is important in order to control the infection. Micro (mi)RNAs are master regulators of most pathways in the human body.  Infection with mycobacterium impacts upon the host metabolic pathways as they are subverted to obtain the nutrition for intracellular TB survival. In this study, we aimed to investigate the effect of Bacillus Calmette-Guérin (BCG) infection on the expression of three miRNAs (miR-1224, -484 and -425), which are important in infection and in the regulation of metabolic pathways. Peripheral blood monocyte-derived macrophage (MDM) cultures were prepared and infected with BCG at a multiplicity of infection (MOI)=10 or left uninfected as a control. 72h post-infection, RNA was extracted from the cultured cells and cDNA synthesis and real-time PCR performed. Expression levels miRNAs were normalized to the levels of U6 snRNA (Rnu6) using the 2-ΔΔCt method. Infection with BCG resulted in a highly significant increase in miR-1224 expression (24.4±3.8-fold induction) in human MDMs. The induction of miR-484 (1.8±0.3-fold increase) and of miR-425 (1.2±0.2-fold increase) was less increased compared to miR-1224. Mycobacterium tolerates a hostile microenvironment by escaping from lysosomal degradation and providing a lipid-rich niche by trigger with and re-pattering host metabolism. This study highlighted the potential roles of miRNAs in host responses upon mycobacterium infection.