Mycobacterium tuberculosis response to stress from reactive oxygen and nitrogen species

E3 ubiquitin ligase CBLB regulates innate immune responses and bacterial dissemination during nontuberculous mycobacteria infection

Nontuberculous mycobacteria (NTM) are emerging opportunistic pathogens causing pulmonary infection to fatal disseminated disease. NTM infections are steadily increasing in children and adults, and immune-compromised individuals are at a greater risk of fatal infections. The NTM disease's adverse pathology and resistance to antibiotics have further worsened the therapeutic measures. Innate immune regulators are potential targets for therapeutics to NTM, especially in a T cell-suppressed population, and many ubiquitin ligases modulate pathogenesis and innate immunity during infections, including mycobacterial infections. Here, we investigated the role of an E3 ubiquitin ligase, Casitas B-lineage lymphoma proto-oncogene B (CBLB), in immunocompromised mouse models of NTM infection. We found that CBLB is essential to prevent bacterial growth and dissemination. Cblb deficiency debilitated natural killer cells, inflammatory monocytes, and macrophages in vivo. However, Cblb deficiency in macrophages did not wane its ability to inhibit bacterial growth or production of reactive oxygen species or interferon γ production by natural killer cells in vitro. CBLB restricted NTM growth and dissemination by promoting early granuloma formation in vivo. Our study shows that CBLB bolsters innate immune responses and helps prevent the dissemination of NTM during compromised T cell immunity.

Impact of N-Acetyl Cysteine (NAC) on Tuberculosis (TB) Patients-A Systematic Review

Sustained TB infection overproduces reactive oxygen species (ROS) as a host defense mechanism. Research shows ROS is destructive to lung tissue. Glutathione (GSH) neutralizes ROS, although it is consumed. NAC is a precursor of GSH synthesis, and administering an appropriate dose of NAC to patients with respiratory conditions may enhance lung recovery and replenish GSH. The present review searched for articles reporting on the effects of NAC in TB treatment from 1960 to 31 May 2022. The PICO search strategy was used in Google Scholar, PubMed, SciFinder, and Wiley online library databases. The COVIDENCE tool was used to delete inappropriate content. We eventually discovered five clinical trials, one case report, seven reviews, in vitro research, and four experimental animal studies from the twenty-four accepted articles. The use of NAC resulted in increased GSH levels, decreased treatment time, and was safe with minimal adverse events. However, the evidence is currently insufficient to estimate the overall effects of NAC, thus the study warrants more NAC clinical trials to demonstrate its effects in TB treatment.

Proteome Profiling of Mycobacterium tuberculosis Cells Exposed to Nitrosative Stress

Reactive nitrogen species (RNS) are secreted by human cells in response to infection by Mycobacterium tuberculosis (Mtb). Although RNS can kill Mtb under some circumstances, Mtb can adapt and survive in the presence of RNS by a process that involves modulation of gene expression. Previous studies focused primarily on stress-related changes in the Mtb transcriptome. This study unveils changes in the Mtb proteome in response to a sub-lethal dose of nitric oxide (NO) over several hours of exposure. Proteins were identified using liquid chromatography coupled with electrospray ionization mass spectrometry (LC-MS/MS). A total of 2911 Mtb proteins were identified, of which 581 were differentially abundant (DA) after exposure to NO in at least one of the four time points (30 min, 2 h, 6 h, and 20 h). The proteomic response to NO was marked by two phases, with few DA proteins in the early phase and a multitude of DA proteins in the later phase. The efflux pump Rv1687 stood out as being the only protein more abundant at all the time points and might play a role in the early protection of Mtb against nitrosative stress. These changes appeared to be compensatory in nature, contributing to iron homeostasis, energy metabolism, and other stress responses. This study thereby provides new insights into the response of Mtb to NO at the level of proteomics.

The Macrophage Response to Mycobacterium tuberculosis and Opportunities for Autophagy Inducing Nanomedicines for Tuberculosis Therapy

The major causative agent of tuberculosis (TB), i.e., Mycobacterium tuberculosis (Mtb), has developed mechanisms to evade host defense responses and persist within host cells for prolonged periods of time. Mtb is also increasingly resistant to existing anti-TB drugs. There is therefore an urgent need to develop new therapeutics for TB and host directed therapies (HDTs) hold potential as effective therapeutics for TB. There is growing interest in the induction of autophagy in Mtb host cells using autophagy inducing compounds (AICs). Nanoparticles (NPs) can enhance the effect of AICs, thus improving stability, enabling cell targeting and providing opportunities for multimodal therapy. In this review, we focus on the macrophage responses to Mtb infection, in particular, the mechanistic aspects of autophagy and the evasion of autophagy by intracellular Mtb. Due to the overlap between the onset of autophagy and apoptosis; we also focus on the relationship between apoptosis and autophagy. We will also review known AICs in the context of Mtb infection. Finally, we discuss the applications of NPs in inducing autophagy with the intention of sharing insights to encourage further research and development of nanomedicine HDTs for TB therapy.

Mutation on lysX from Mycobacterium avium hominissuis impacts the host-pathogen interaction and virulence phenotype

The lysX gene from Mycobacterium avium hominissuis (MAH) is not only involved in cationic antimicrobial resistance but also regulates metabolic activity. An MAH lysX deficient mutant was shown to exhibit a metabolic shift at the extracellular state preadapting the bacteria to the conditions inside host-cells. It further showed stronger growth in human monocytes. In the present study, the LysX activity on host-pathogen interactions were analyzed. The lysX mutant from MAH proved to be more sensitive toward host-mediated stresses such as reactive oxygen species. Further, the lysX mutant exhibited increased inflammatory response in PBMC and multinucleated giant cell (MGC) formation in human macrophages during infection studies. Coincidentally, the lysX mutant strain revealed to be more reproductive in the Galleria mellonella infection model. Together, these data demonstrate that LysX plays a role in regulating the bacillary load in host organisms and the lack of lysX gene facilitates MAH adaptation to intracellular host-habitat, thereby suggesting an essential role of LysX in the modulation of host-pathogen interaction.

The Echo of Pulmonary Tuberculosis: Mechanisms of Clinical Symptoms and Other Disease-Induced Systemic Complications

Clinical symptoms of active tuberculosis (TB) can range from a simple cough to more severe reactions, such as irreversible lung damage and, eventually, death, depending on disease progression. In addition to its clinical presentation, TB has been associated with several other disease-induced systemic complications, such as hyponatremia and glucose intolerance. Here, we provide an overview of the known, although ill-described, underlying biochemical mechanisms responsible for the clinical and systemic presentations associated with this disease and discuss novel hypotheses recently generated by various omics technologies. This summative update can assist clinicians to improve the tentative diagnosis of TB based on a patient's clinical presentation and aid in the development of improved treatment protocols specifically aimed at restoring the disease-induced imbalance for overall homeostasis while simultaneously eradicating the pathogen. Furthermore, future applications of this knowledge could be applied to personalized diagnostic and therapeutic options, bettering the treatment outcome and quality of life of TB patients.

The Immune Escape Mechanisms of Mycobacterium Tuberculosis

Epidemiological data from the Center of Disease Control (CDC) and the World Health Organization (WHO) statistics in 2017 show that 10.0 million people around the world became sick with tuberculosis. Mycobacterium tuberculosis (MTB) is an intracellular parasite that mainly attacks macrophages and inhibits their apoptosis. It can become a long-term infection in humans, causing a series of pathological changes and clinical manifestations. In this review, we summarize innate immunity including the inhibition of antioxidants, the maturation and acidification of phagolysosomes and especially the apoptosis and autophagy of macrophages. Besides, we also elaborate on the adaptive immune response and the formation of granulomas. A thorough understanding of these escape mechanisms is of major importance for the prevention, diagnosis and treatment of tuberculosis.

The Deconstructed Granuloma: A Complex High-Throughput Drug Screening Platform for the Discovery of Host-Directed Therapeutics Against Tuberculosis

Mycobacterium tuberculosis (Mtb) continues to be a threat to Global Public Health, and its control will require an array of therapeutic strategies. It has been appreciated that high-throughput screens using cell-based assays to identify compounds targeting Mtb within macrophages represent a valuable tool for drug discovery. However, the host immune environment, in the form of lymphocytes and cytokines, is completely absent in a chemical screening platform based on infected macrophages alone. The absence of these players unnecessarily limits the breadth of novel host target pathways to be interrogated. In this study, we detail a new drug screening platform based on dissociated murine TB granulomas, named the Deconstructed Granuloma (DGr), that utilizes fluorescent Mtb reporter strains screened in the host immune environment of the infection site. The platform has been used to screen a collection of known drug candidates. Data from a representative 384-well plate containing known anti-bacterial compounds are shown, illustrating the robustness of the screening platform. The novel deconstructed granuloma platform represents an accessible, sensitive and robust high-throughput screen suitable for the inclusive interrogation of immune targets for Host-Directed Therapeutics.

Host-pathogen redox dynamics modulate Mycobacterium tuberculosis pathogenesis

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis, encounters variable and hostile environments within the host. A major component of these hostile conditions is reductive and oxidative stresses induced by factors modified by the host immune response, such as oxygen tension, NO or CO gases, reactive oxygen and nitrogen intermediates, the availability of different carbon sources and changes in pH. It is therefore essential for Mtb to continuously monitor and appropriately respond to the microenvironment. To this end, Mtb has developed various redox-sensitive systems capable of monitoring its intracellular redox environment and coordinating a response essential for virulence. Various aspects of Mtb physiology are regulated by these systems, including drug susceptibility, secretion systems, energy metabolism and dormancy. While great progress has been made in understanding the mechanisms and pathways that govern the response of Mtb to the host's redox environment, many questions in this area remain unanswered. The answers to these questions are promising avenues for addressing the tuberculosis crisis.

Mycobacterium tuberculosis EsxL inhibits MHC-II expression by promoting hypermethylation in class-II transactivator loci in macrophages

Mycobacterium tuberculosis is known to modulate the host immune responses to facilitate its persistence inside the host cells. One of the key mechanisms includes repression of class-II transactivator (CIITA) and MHC-II expression in infected macrophages. However, the precise mechanism of CIITA and MHC-II down-regulation is not well studied. M. tuberculosis 6-kDa early secretory antigenic target (ESAT-6) is a known potent virulence and antigenic determinant. The M. tuberculosis genome encodes 23 such ESAT-6 family proteins. We herein report that M. tuberculosis and M. bovis bacillus Calmette-Guérin infection down-regulated the expression of CIITA/MHC-II by inducing hypermethylation in histone H3 lysine 9 (H3K9me2/3). Further, we showed that M. tuberculosis ESAT-6 family protein EsxL, encoded by Rv1198, is responsible for the down-regulation of CIITA/MHC-II by inducing H3K9me2/3. We further report that M. tuberculosis esxL induced the expression of nitric-oxide synthase, NO production, and p38 MAPK pathway, which in turn was responsible for the increased H3K9me2/3 in CIITA via up-regulation of euchromatic histone-lysine N-methyltransferase 2 (G9a). In contrast, inhibition of nitric-oxide synthase, p38 MAPK, and G9a abrogated H3K9me2/3, resulting in increased CIITA expression. A chromatin immunoprecipitation assay confirmed that hypermethylation at the promoter IV region of CIITA is mainly responsible for CIITA down-regulation and subsequent antigen presentation. We found that co-culture of macrophages infected with esxL-expressing M. smegmatis and mouse splenocytes led to down-regulation of IL-2, a key cytokine involved in T-cell proliferation. In summary, we demonstrate that M. tuberculosis EsxL inhibits antigen presentation by enhancing H3K9me2/3 at the CIITA promoter, thereby repressing its expression through NO and p38 MAPK activation.

The Mycobacterium tuberculosis transcriptional landscape under genotoxic stress

Background

As an intracellular human pathogen, Mycobacterium tuberculosis (Mtb) is facing multiple stressful stimuli inside the macrophage and the granuloma. Understanding Mtb responses to stress is essential to identify new virulence factors and pathways that play a role in the survival of the tubercle bacillus. The main goal of this study was to map the regulatory networks of differentially expressed (DE) transcripts in Mtb upon various forms of genotoxic stress. We exposed Mtb cells to oxidative (H₂O₂ or paraquat), nitrosative (DETA/NO), or alkylation (MNNG) stress or mitomycin C, inducing double-strand breaks in the DNA. Total RNA was isolated from treated and untreated cells and subjected to high-throughput deep sequencing. The data generated was analysed to identify DE genes encoding mRNAs, non-coding RNAs (ncRNAs), and the genes potentially targeted by ncRNAs.

Results

The most significant transcriptomic alteration with more than 700 DE genes was seen under nitrosative stress. In addition to genes that belong to the replication, recombination and repair (3R) group, mainly found under mitomycin C stress, we identified DE genes important for bacterial virulence and survival, such as genes of the type VII secretion system (T7SS) and the proline-glutamic acid/proline-proline-glutamic acid (PE/PPE) family. By predicting the structures of hypothetical proteins (HPs) encoded by DE genes, we found that some of these HPs might be involved in mycobacterial genome maintenance. We also applied a state-of-the-art method to predict potential target genes of the identified ncRNAs and found that some of these could regulate several genes that might be directly involved in the response to genotoxic stress.

Conclusions

Our study reflects the complexity of the response of Mtb in handling genotoxic stress. In addition to genes involved in genome maintenance, other potential key players, such as the members of the T7SS and PE/PPE gene family, were identified. This plethora of responses is detected not only at the level of DE genes encoding mRNAs but also at the level of ncRNAs and their potential targets.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3132-1) contains supplementary material, which is available to authorized users.

Innate Immunity Holding the Flanks until Reinforced by Adaptive Immunity against Mycobacterium tuberculosis Infection

T cells play a cardinal role in imparting protection against Mycobacterium tuberculosis (Mtb). However, ample time is required before T-cells are able to evoke efficient effector responses in the lung, where the mycobacterium inflicts disease. This delay in T cells priming, which is termed as lag phase, provides sufficient time for Mtb to replicate and establish itself within the host. In contrast, innate immunity efficiently curb the growth of Mtb during initial phase of infection through several mechanisms. Pathogen recognition by innate cells rapidly triggers a cascade of events, such as apoptosis, autophagy, inflammasome formation and nitric oxide production to kill intracellular pathogens. Furthermore, bactericidal mechanisms such as autophagy and apoptosis, augment the antigen processing and presentation, thereby contributing substantially to the induction of adaptive immunity. This manuscript highlights the role of innate immune mechanisms in restricting the survival of Mtb during lag phase. Finally, this article provides new insight for designing immuno-therapies by targeting innate immune mechanisms to achieve optimum immune response to cure TB.

Metabolic crosstalk between host and pathogen: sensing, adapting and competing

Our understanding of bacterial pathogenesis is dominated by the cell biology of the host-pathogen interaction. However, the majority of metabolites that are used in prokaryotic and eukaryotic physiology and signalling are chemically similar or identical. Therefore, the metabolic crosstalk between pathogens and host cells may be as important as the interactions between bacterial effector proteins and their host targets. In this Review we focus on host-pathogen interactions at the metabolic level: chemical signalling events that enable pathogens to sense anatomical location and the local physiology of the host; microbial metabolic pathways that are dedicated to circumvent host immune mechanisms; and a few metabolites as central points of competition between the host and bacterial pathogens.

Statin adjunctive therapy shortens the duration of TB treatment in mice

BACKGROUND

The repurposing of existing agents may accelerate TB drug development. Recently, we reported that the lipid-lowering drug simvastatin, when added to the first-line antitubercular regimen, reduces the lung bacillary burden in chronically infected mice.

OBJECTIVES

We investigated whether the addition of simvastatin to the first-line regimen (isoniazid/rifampicin/pyrazinamide) shortens the duration of curative TB treatment in mice.

METHODS

Mycobacterium tuberculosis-infected THP-1 cells were exposed to simvastatin to determine the effect of statins on the activity of first-line anti-TB drug activity and intracellular rifampicin concentration. Single-dose and steady-state pharmacokinetic studies guided optimized simvastatin dosing in vivo. BALB/c mice were aerosol-infected with M. tuberculosis H37Rv and drug treatment was initiated 6 weeks post-infection. Separate groups of mice received standard TB treatment with or without simvastatin. Relapse rates were assessed 3 months after discontinuation of each treatment regimen. MALDI-MS imaging was used to image the cholesterol content of mouse lung lesions.

RESULTS

Simvastatin significantly enhanced the bactericidal activity of first-line drugs against intracellular M. tuberculosis without altering intracellular rifampicin concentrations. Adjunctive treatment with 60 mg/kg simvastatin shortened the time required to achieve culture-negative lungs from 4.5 to 3.5 months. Following 2.5, 3.5 and 4.5 months of treatment, relapse rates were 100%, 50% and 0%, respectively, in the control group and 50% (P = 0.03), 20% and 0%, respectively, in the statin group. Simvastatin did not alter plasma or lung lesion cholesterol levels.

CONCLUSIONS

Statins are attractive candidates for host-directed, adjunctive TB therapy. Further preclinical studies are needed to define the optimal statin and dosing.

Identification of potential Mycobacterium tuberculosis topoisomerase I inhibitors: a study against active, dormant and resistant tuberculosis

Mycobacterium tuberculosis (Mtb) topoisomerase I (Topo I), involved in the relaxation of negatively supercoiled DNA, plays an important role in the viability of pathogen Mtb. Being one of the most significant enzymes; it also takes part in crucial biological pathways such as transcription and replication of the pathogen. The present study aims at the development of Mtb Topo I 3D protein structure which in turn was employed for the virtual screening of compound libraries in a process of identification of a hit molecule. The identified hit, hydroxycamptothecin, was active at 6.25 μM which was further derivatized synthetically into fifteen novel analogues. Among these, four compounds (3b, 3g, 3h and 3l) emerged to be active displaying IC50 values ranging from 2.9 to 9.3 μM against Mtb Topo I and were non-cytotoxic at 25 μM. These four compounds also proved their efficacy when tested against active, dormant and resistant forms of Mtb. The most potent inhibitor 3b was screened for in vivo anti-mycobacterial activity using zebrafish model and was found to be more effective when compared to first line anti-tubercular drugs, isoniazid and rifampicin. The binding affinity of this compound towards Mtb Topo I was analyzed by differential scanning fluorimetry which resulted in a positive shift in melting temperature when compared to the native protein thereby proving its stabilization effect over protein.