Mycobacterial small noncoding RNAs MTS0997 and MTS1338 are novel virulence factors of M. tuberculosis

Abstract

Introduction: Small RNAs of intracellular pathogenic bacteria not only adapt the bacterial transcript to changing environmental conditions, but also interact with the transcriptome of the infected organism, thereby interfering with the antibacterial defense.

Aims and objectives: We investigated the role of small RNAs of M. tuberculosis, MTS1338 and MTS0997, as regulators that trigger a cascade of reactions for damping macrophage (mph) damaging factors.

Methods: Mycobacteria growth inhibition in vitro assay was used to assess Mph activity. Mph (human alveolar (AM) or peritoneal mouse) were co-cultured in vitro with M. tuberculosis H37Rv wt, ΔMTS1338, and ΔMTS0997. After 72 hours of incubation, the viability of Mtb was assessed by the selective inclusion of [³H]-Uracil. The expression level of cytokines/chemokines genes were analyzed by TaqMan PCR Assay.

Results: Differences in the survival of wild-type, ∆MTS0997 and ∆MTS1338 M. tuberculosis were detected in AM. Growth of ΔMTS1338 is better restricted by AM than that of ∆ MTS0997. Activation of mouse peritoneal Mph infected with wild-type, ∆MTS0997 and ∆MTS1338 Mtb was evaluated by the level of cytokine expression. Differences were registered between all groups compared. Mph infection of wt and ΔMTS0997 leads to an increase in the expression of proinflammatory cytokines TNF, IL-11, IL-1β and NF-IL6. Infection with ∆MTS1338 mutant leads to a significantly greater increase in the expression of NF-IL6, Aif1, and MARCO.

Conclusions: The deletion of MTS0997 and MTS1338 decreases bacterial “virulence”. Mutants are more efficient in Mphs activation and are more readily cleared by Mphs as compared with wt strain.