ESAT-6 Protein of Mycobacterium tuberculosis Increases Holotransferrin-Mediated Iron Uptake in Macrophages by Downregulating Surface Hemochromatosis Protein HFE

The efflux pumps Rv1877 and Rv0191 play differential roles in the protection of Mycobacterium tuberculosis against chemical stress

Background

It was previously shown that GlnA3sc enabled Streptomyces coelicolor to survive in excess polyamines. However, subsequent studies revealed that Rv1878, the corresponding Mycobacterium tuberculosis (M.tb) ortholog, was not essential for the detoxification of spermine (Spm), in M.tb. On the other hand, the multi-drug efflux pump Rv1877 was previously shown to enable export of a wide range of compounds, while Rv0191 was shown to be more specific to chloramphenicol.

Rationale

Therefore, we first wanted to determine if detoxification of Spm by efflux can be achieved by any efflux pump, or if that was dependent upon the function of the pump. Next, since Rv1878 was found not to be essential for the detoxification of Spm, we sought to follow-up on the investigation of the physiological role of Rv1878 along with Rv1877 and Rv0191.

Approach

To evaluate the specificity of efflux pumps in the mycobacterial tolerance to Spm, we generated unmarked ∆rv1877 and ∆rv0191 M.tb mutants and evaluated their susceptibility to Spm. To follow up on the investigation of any other physiological roles they may have, we characterized them along with the ∆rv1878 M.tb mutant.

Results

The ∆rv1877 mutant was sensitive to Spm stress, while the ∆rv0191 mutant was not. On the other hand, the ∆rv1878 mutant grew better than the wild-type during iron starvation yet was sensitive to cell wall stress. The proteins Rv1877 and Rv1878 seemed to play physiological roles during hypoxia and acidic stress. Lastly, the ∆rv0191 mutant was the only mutant that was sensitive to oxidative stress.

Conclusion

The multidrug MFS-type efflux pump Rv1877 is required for Spm detoxification, as opposed to Rv0191 which seems to play a more specific role. Moreover, Rv1878 seems to play a role in the regulation of iron homeostasis and the reconstitution of the cell wall of M.tb. On the other hand, the sensitivity of the ∆rv0191 mutant to oxidative stress, suggests that Rv0191 may be responsible for the transport of low molecular weight thiols.

Mycobacterium tuberculosis virulence protein ESAT-6 influences M1/M2 polarization and macrophage apoptosis to regulate tuberculosis progression

BACKGROUND

Tuberculosis (TB) is an infectious disease caused by infection with Mycobacterium tuberculosis (Mtb), and it remains one of the major threats to human health worldwide. To our knowledge, the polarization of M1/M2 macrophages were critical innate immune cells which play important roles in regulating the immune response during TB progression.

OBJECTIVE

We aimed to explore the potential mechanisms of M1/M2 macrophage polarization in TB development.

METHODS

THP-1 macrophages were treated with early secreted antigenic target of 6 kDa (ESAT-6) protein for an increasing time. The polarization profiles, apoptosis levels of M1 and M2 macrophages were detected by RT-qPCR, immunofluorescence, Western blot and flow cytometry.

RESULTS

ESAT-6 initially promoted the generation of pro-inflammatory M1-polarized macrophages in THP-1 cells within 24 h, which were suppressed by further ESAT-6 treatment at 30-42 h. Interestingly, ESAT-6 continuously promoted M2 polarization of THP-1 cells, thereby maintaining the anti-inflammatory response in a time-dependent manner. In addition, ESAT-6 promoted apoptotic cell death in M1-polarized macrophages, which had little effects on apoptosis of M2-phenotype of macrophages. Then, the potential underlying mechanisms were uncovered, and we verified that ESAT-6 increased the protein levels of TLR4, MyD88 and NF-κB to activate the TLR4/MyD88/NF-κB pathway within 24 h, and this signal pathway was significantly inactivated at 36 h post-treatment. Interestingly, the following experiments confirmed that ESAT-6 TLR4/MyD88/NF-κB pathway-dependently regulated M1/M2 polarization and apoptosis of macrophage in THP-1 cells.

CONCLUSION

Our study investigated the detailed effects and mechanisms of M1/M2 macrophages in regulating innate responses during TB development, which provided a new perspective on the development of treatment strategies for this disease.

Mycobacterium tuberculosis and its clever approaches to escape the deadly macrophage

Mycobacterium tuberculosis (Mt.b), a deadly disease causer, is a facultative parasite. This microorganism has developed several methods to defend itself, once internalized within specialised vacuoles in the macrophages. A wide array of receptors like the complement receptor mannose receptors, scavenger receptor assists the entry of the microbe within the phagocytic macrophages. However, Mt.b is clever enough to protect itself from the hostile environment of the macrophage thereby prevailing within it. The microbe can efficiently inhibit processes like phagosome-lysosome fusion, acidification of phagosomes, release of proinflammatory cytokines and stop crucial events like apoptosis. Additionally, it also adopts resistance to killing by reactive oxygen intermediates and reactive nitrogen intermediates. There are multiple genes both in host and the pathogen which are involved in this successful survival of Mt.b. The regulation of phagolysosome fusion is mediated by proteins such as Coronin, TlyA, SapM, PnkG, EsxH. The microbe has certain mechanisms to even acquire iron from the host cell, to withstand iron deprivation as a mode of host's defence mechanism. This review focuses on the various defensive adaptations acquired by Mt.b for fighting against the deprived conditions existing within the macrophages and their capability of proliferating successfully within it, thereby resulting in a diseased condition.

Synthesis of plant-based, self-adjuvanted, dual antigen specific to Mycobacterium tuberculosis as a novel tuberculosis subunit vaccine that elicits immunogenicity in rabbit

OBJECTIVES

The only approved vaccine, Bacillus Calmette Guérin (BCG) used in global tuberculosis (TB) immunization programmes has been very effective in childhood TB but not in adult pulmonary and latent TB. Moreover, the emergence of multi-drug resistance-TB cases demands either to increase efficiency of BCG or replace it with the one with improved efficacy.

RESULTS

A novel combination of two most effective secreted protein antigens specific for Mycobacterium tuberculosis (Mtb), ESAT-6 and MPT-64 (but not present in BCG strains) fused with a cholera toxin B subunit (CTB) and tagged with 6xHis was expressed for the first time in Escherichia coli as well as in transgenic cucumber plants developed using Agrobacterium tumefaciens-mediated transformation. The recombinant fusion protein (His6x.CTB-ESAT6-MPT64) expressed in E. coli was purified by a single-step affinity chromatography and used to produce polyclonal antibodies in rabbit. The transgenic cucumber lines were confirmed by polymerase chain reaction (PCR), Southern blot hybridization, reverse transcriptase PCR (RT-PCR), real-time PCR (qRT-PCR) and expression of recombinant fusion protein by western blot analysis and its quantification by enzyme-linked immunosorbent assay (ELISA). A maximum value of the fusion protein, 478 ng.g^-1 (0.030% of the total soluble protein) was obtained in a transgenic cucumber line. Rabbit immunized orally showed a significant increase in serum IgG levels against the fusion protein as compared to the non-immunized rabbit.

CONCLUSIONS

Stable expression of Mtb antigens with CTB in edible cucumber plants (whose fruits are eaten raw) in sufficient amount possibly would facilitate development of a safe, affordable and orally delivered self-adjuvanted, novel dual antigen based subunit vaccine against TB.

Negative pressure promotes macrophage M1 polarization after Mycobacterium tuberculosis infection via the lncRNA XIST/microRNA-125b-5p/A20/NF-κB axis

Experiments have demonstrated the regulation of long noncoding RNA (lncRNA) in tuberculosis (TB), and negative pressure treatment has been associated with the alleviation of TB. Here, we investigated the interaction of negative pressure and the lncRNA X-inactive specific transcript (XIST) in modulating Mycobacterium tuberculosis (MTB) infection. Initially, we established an in vitro cell model of MTB infection and an in vivo mouse model of MTB infection, followed by treatment with negative pressure. Then, we examined the expression of XIST, followed by analysis of the downstream miRNA of XIST. XIST was overexpressed or underexpressed through cell transfection to examine its effects on macrophage polarization via the miR-125b-5p/A2 axis. The MTB models were characterized by upregulated XIST and downregulated miR-125b-5p. XIST bound to miR-125b-5p, leading to its downregulation, and thus causing higher MTB survival in an ESAT-6-dependent manner. Additionally, negative pressure treatment decreased MTB-driven XIST expression through downregulation of A20 (an NF-κB repressor) via miR-125b-5 expression, promoting the M1 polarization program in macrophages through activation of the NF-κB pathway. In summary, negative pressure treatment after MTB infection can promote the polarization of macrophages to the proinflammatory M1 phenotype by regulating the XIST/miR-125b-5p/A20/NF-κB axis.

Moonlighting by PPE2 Protein: Focus on Mycobacterial Virulence

In Mycobacterium tuberculosis, ∼10% of its genome encodes the proline-glutamic acid and proline-proline-glutamic acid (PPE) family of proteins, some of which were recently established to be key players in mycobacterial virulence. PPE2 (Rv0256c) is one among these proteins that we found to have pleiotropic effects during mycobacterial infection. PPE2 weakens the innate immune system by disturbing NO and reactive oxygen species production and myeloid hematopoiesis. We showed that PPE2 is unique for having nuclear localization signal, DNA binding domain, and SRC homology 3 (PXXP) binding domain, which enable it to interfere with the host immune system. Interestingly, PPE2 is a secretary protein, expressed during active tuberculosis (TB) infection, and is involved in facilitating survival of M. tuberculosis Thus, PPE2 could be a valuable drug target for developing effective therapeutics against TB. In this article, we describe possible roles of PPE2 in TB pathogenesis and the importance of PPE2 as a novel therapeutic target against TB.