Interaction of the CD43 Sialomucin with the Mycobacterium tuberculosis Cpn60.2 Chaperonin Leads to Tumor Necrosis Factor Alpha Production

PPE38-Secretion-Dependent Proteins of M. tuberculosis Alter NF-kB Signalling and Inflammatory Responses in Macrophages

It was previously shown that secretion of PE-PGRS and PPE-MPTR proteins is abolished in clinical M. tuberculosis isolates with a deletion in the ppe38-71 operon, which is associated with increased virulence. Here we investigate the proteins dependent on PPE38 for their secretion and their role in the innate immune response using temporal proteomics and protein turnover analysis in a macrophage infection model. A decreased pro-inflammatory response was observed in macrophages infected with PPE38-deficient M. tuberculosis CDC1551 as compared to wild type bacteria. We could show that dampening of the pro-inflammatory response is associated with activation of a RelB/p50 pathway, while the canonical inflammatory pathway is active during infection with wild type M. tuberculosis CDC1551. These results indicate a molecular mechanism by which M. tuberculosis PE/PPE proteins controlled by PPE38 have an effect on modulating macrophage responses through NF-kB signalling.

Caloric Restriction Promotes Immunometabolic Reprogramming Leading to Protection from Tuberculosis

There is a strong relationship between metabolic state and susceptibility to Mycobacterium tuberculosis (MTB) infection, with energy metabolism setting the basis for an exaggerated immuno-inflammatory response, which concurs with MTB pathogenesis. Herein, we show that controlled caloric restriction (CR), not leading to malnutrition, protects susceptible DBA/2 mice against pulmonary MTB infection by reducing bacterial load, lung immunopathology, and generation of foam cells, an MTB reservoir in lung granulomas. Mechanistically, CR induced a metabolic shift toward glycolysis, and decreased both fatty acid oxidation and mTOR activity associated with induction of autophagy in immune cells. An integrated multi-omics approach revealed a specific CR-induced metabolomic, transcriptomic, and proteomic signature leading to reduced lung damage and protective remodeling of lung interstitial tightness able to limit MTB spreading. Our data propose CR as a feasible immunometabolic manipulation to control MTB infection, and this approach offers an unexpected strategy to boost immunity against MTB.

Mycobacterium bovis BCG promotes IL-10 expression by establishing a SYK/PKCα/β positive autoregulatory loop that sustains STAT3 activation

Mycobacterium ensures its survival inside macrophages and long-term infection by subverting the innate and adaptive immune response through the modulation of cytokine gene expression profiles. Different Mycobacterium species promote the expression of TGFβ and IL-10, which, at the early stages of infection, block the formation of the phagolysosome, thereby securing mycobacterial survival upon phagocytosis, and at later stages, antagonize IFNγ production and functions. Despite the key role of IL-10 in mycobacterium infection, the signal transduction pathways leading to IL-10 expression in infected macrophages are poorly understood. Here, we report that Mycobacterium bovis BCG promotes IL-10 expression and cytokine production by establishing a SYK/PKCα/β positive feedback loop that leads to STAT3 activation.

Rv2346c enhances mycobacterial survival within macrophages by inhibiting TNF-α and IL-6 production via the p38/miRNA/NF-κB pathway

The intracellular survival of Mycobacterium tuberculosis (Mtb) has a central role in the pathogenesis of tuberculosis. Mtb Rv2346c is a member of 6-kDa early secreted antigenic target family of proteins, which are known to inhibit the host immune responses to promote bacillary persistence in macrophages. However, the mechanism through which Rv2346c participates in Mtb pathogenesis is unclear. In the present study, recombinant Rv2346c protein was synthesized and used to treat Bacillus Calmette–Guérin (BCG)-infected macrophages. The results showed that Rv2346c inhibited the proliferation of BCG-infected macrophages and enhanced the survival of BCG in macrophages. Tumor necrosis factor-α (TNF-α) and interleukin (IL)-6 were upregulated during BCG infection but downregulated by Rv2346c. Additional experiments showed that nuclear transcription factor-κB (NF-κB) in BCG-infected macrophages induced the production of TNF-α and IL-6. In addition, miR-155 and miR-99b had a suppressive effect on NF-κB, and the expression of these miRNAs was promoted by p38. Furthermore, Rv2346c was shown to decrease the activation of NF-κB, whereas it enhanced the phosphorylation of p38 and the expression of miR-155 and miR-99b. The function of Rv2346c was also verified in Mtb-infected mice. The results showed that Rv2346c increased the observed bacterial load and lung injury and downregulated TNF-α and IL-6 in vivo. Overall, our results reveal that Rv2346c enhances mycobacterial survival in macrophages via inhibiting the production of TNF-α and IL-6 in a p38/miRNA/NF-κB pathway-dependent manner, suggesting that Rv2346c acts as a crucial virulence factor in Mtb infection and has potential use as a target for anti-tuberculosis therapy.