Clinical isolates of the modern Mycobacterium tuberculosis lineage 4 evade host defense in human macrophages through eluding IL-1β-induced autophagy

Abstract

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), has infected over 1.7 billion people worldwide and causes 1.4 million deaths annually. Recently, genome sequence analysis has allowed the reconstruction of Mycobacterium tuberculosis complex (MTBC) evolution, with the identification of seven phylogeographic lineages: four referred to as evolutionarily “ancient”, and three “modern”. The MTBC strains belonging to “modern” lineages appear to show enhanced virulence that may have warranted improved transmission in humans over ancient lineages through molecular mechanisms that remain to be fully characterized. To evaluate the impact of MTBC genetic diversity on the innate immune response, we analyzed intracellular bacterial replication, inflammatory cytokine levels, and autophagy response in human primary macrophages infected with MTBC clinical isolates belonging to the ancient lineages 1 and 5, and the modern lineage 4. We show that, when compared to ancient lineage 1 and 5, MTBC strains belonging to modern lineage 4 show a higher rate of replication, associated to a significant production of proinflammatory cytokines (IL-1β, IL-6, and TNF-α) and induction of a functional autophagy process. Interestingly, we found that the increased autophagic flux observed in macrophages infected with modern MTBC is due to an autocrine activity of the proinflammatory cytokine IL-1β, since autophagosome maturation is blocked by an interleukin-1 receptor antagonist. Unexpectedly, IL-1β-induced autophagy is not disadvantageous for the survival of modern Mtb strains, which reside within Rab5-positive phagosomal vesicles and avoid autophagosome engulfment. Altogether, these results suggest that autophagy triggered by inflammatory cytokines is compatible with a high rate of intracellular bacilli replication and may therefore contribute to the increased pathogenicity of the modern MTBC lineages.

Inhibition of Transglutaminase 2 as a Potential Host-Directed Therapy Against Mycobacterium tuberculosis

“…These results underscore the usefulness of the quantitative analysis of AIPD to monitor authophagy in macrophages infected with Mtb. Of note, we also observed autophagic flux induction in non-infected macrophages (in BCG-and Mtb-infected cells), probably resulting from the cytokines released by infected cells (24,25) that can act in paracrine mode.…”

“…However, the role of basal autophagy in infected macrophages appears to be more complex. We have recently demonstrated that Mtb strains from ancient and modern lineages have a different impact on the basal autophagy flux (25). While the ancient lineages impair the autophagic flux, infection with the modern strains leads to a stimulation of this process, which is dependent on the increased production of IL1-β triggered by these mycobacteria (25).…”

“…We have recently demonstrated that Mtb strains from ancient and modern lineages have a different impact on the basal autophagy flux (25). While the ancient lineages impair the autophagic flux, infection with the modern strains leads to a stimulation of this process, which is dependent on the increased production of IL1-β triggered by these mycobacteria (25). This induction of autophagy is however ineffective in restricting Mtb growth but rather correlates with more exuberant Mtb replication, perhaps by sustaining its metabolic requirements in the infected cells (25,44).…”

“…Mtb strains belonging to different phylogeographic lineages show different pathogenetic properties, with implications in terms of virulence, extent of disease, transmission, and epidemic potentials (25,(27)(28)(29). Mtb strains belonging to modern lineages showed enhanced virulence compared with strains of the ancient lineages, and recent data from our group indicate a different ability to induce and evade autophagy by modern vs. ancient strains (25). To investigate whether treatment with TG2 inhibitors could restrict the intracellular replication of Mtb belonging to different lineages, THP-1 cells were infected with Mtb clinical isolates of the modern Euro-American (H3 clade) and East Asian (Beijing) lineages and of the ancient lineage EAI (EAI_MAN).…”

“…Infection of human peripheral blood monocyte cells (PBMCs) with Mtb results in the formation of granuloma-like structures (GLS) that are emerging as a valuable ex vivo model of TB (31,32). To investigate the activity of these HDTs against TB, PBMCs were infected with Mtb H37Rv and with the clinical strain Mtb H3, which in hMDM showed enhanced virulence compared with other Mtb reference and clinical strains (25). Following infection with Mtb, cysteamine, or cystamine was added in infected GLS at day 6 p.i.…”