Several Routes to the Same Destination: Inhibition of Phagosome-Lysosome Fusion by Mycobacterium tuberculosis

Combating Tuberculosis via Restoring the Host Immune Capacity by Targeting M. tb Kinases and Phosphatases

Mycobacterium tuberculosis (M. tb) is a remarkably versatile pathogen that possesses a unique ability to counteract the host's defence mechanisms to control the infection. Several mycobacterial protein kinases and phosphatases were found to play a key role in impeding phagosome maturation in macrophages and accordingly blocking the phagosome-lysosome fusion, therefore allowing the bacteria to survive. During phagocytosis, both M. tb and the host's phagocytic cells develop mechanisms to fight each other, resulting in pathogen elimination or survival. In this respect, M. tb uses a phosphorylation-based signal transduction mechanism, whereby it senses extracellular signals from the host and initiates the appropriate adaptation responses. Indeed, the ability of M. tb to exist in different states in the host (persistent quiescent state or actively replicating mode) is mainly mediated through protein phosphorylation/dephosphorylation signalling. The M. tb regulatory and defensive responses coordinate different aspects of the bacilli's physiology, for instance, cell wall components, metabolic activity, virulence, and growth. Herein, we will discuss the implication of M. tb kinases and phosphatases in hijacking the host immune system, perpetuating the infection. In addition, the role of PknG, MPtpA, MPtpB, and SapM inhibitors in resetting the host immune system will be highlighted.

Identification of immune-associated genes involved in latent Mycobacterium marinum infection

Tuberculosis (TB) is a high mortality infectious disease caused by Mycobacterium tuberculosis (Mtb), and often develops into latent infection. About 5～10% of latent infections turn into active tuberculosis when the host immune system becomes deficient. Therefore, exploring the latent infection mechanism of Mtb is pivotal for the prevention and treatment of tuberculosis. We first established the zebrafish latent infection model and the chronic infection model utilizing Mycobacterium marinum, which has the highly similar gene background to Mtb. Using the latent infection model, we characterized the gene expression profiles and found 462 genes expressed differentially in the latent period and chronic tuberculosis infection. These differentially expressed genes are involved in various biological processes including transcription, transcriptional regulation, organism development, and immune responses. Among them, nineteen immune-related genes were found to express differentially in the latent period. By analyzing immune related protein network, the genes in the center of the network, including Nos2b, TNFα, IL1, TNFβ, TLR1, TLR2, and TLR4b, displayed significant deferential expression in latent infection and chronic infection period of zebrafish, suggesting that these genes might play an important role in controlling latent infection of Mtb. Identifying immune biomarker related to the status of tuberculosis latent infection might lead to novel strategy for diagnosis and treatment.

Interaction of Glycemic Control and Statin Use on Diabetes-Tuberculosis Treatment Outcome: A Nested Case-Control Study

This study aims to explore the interaction of glycemic control and statin use on the treatment outcomes of pulmonary tuberculosis-diabetes comorbidity (PTB-DM) patients. A nested case-control study was conducted in a tuberculosis patients' cohort. We defined cases as patients who experienced unfavorable outcomes. Glycemic control was estimated at the baseline. Statin use was obtained from medical records. The multivariate logistic regression models were developed, and the interaction table invented by Andersson was adopted to analyze the interaction of glycemic control and statin use on treatment outcomes. A total of 2,047 patients were included in this study. There was a significant interaction between glycemic control and statin use on the treatment outcomes. Patients with good glycemic control and no statin use (OR = 0.464, 95% CI: 0.360-0.623) had a lower risk of unfavorable outcomes than those with poor glycemic control and statin use (OR = 0.604, 95% CI: 0.401-0.734). Patients with good glycemic control and statin use had the lowest risk of unfavorable outcomes (OR = 0.394, 95% CI: 0.264-0.521). Glycemic control in diabetes-tuberculosis treatment should be paid considerable attention. Patients can benefit from statin use even if they have poor glycemic control. Patients with good glycemic control and statin use can have the best outcomes.

Group A Streptococcus induces lysosomal dysfunction in THP-1 macrophages

The human-specific bacterial pathogen group A Streptococcus (GAS) is a significant cause of morbidity and mortality. Macrophages are important to control GAS infection, but previous data indicate that GAS can persist in macrophages. In this study, we detail the molecular mechanisms by which GAS survives in THP-1 macrophages. Our fluorescence microscopy studies demonstrate that GAS is readily phagocytosed by macrophages, but persists within phagolysosomes. These phagolysosomes are not acidified, which is in agreement with our findings that GAS cannot survive in low pH environments. We find that the secreted pore-forming toxin Streptolysin O (SLO) perforates the phagolysosomal membrane, allowing leakage of not only protons but also large proteins including the lysosomal protease cathepsin B. Additionally, GAS recruits CD63/LAMP-3, which may contribute to lysosomal permeabilization, especially in the absence of SLO. Thus, although GAS does not inhibit fusion of the lysosome with the phagosome, it has multiple mechanisms to prevent proper phagolysosome function, allowing for persistence of the bacteria within the macrophage. This has important implications for not only the initial response but also the overall functionality of the macrophages, which may lead to the resulting pathologies in GAS infection. Our data suggest that therapies aimed at improving macrophage function may positively impact patient outcomes in GAS infection.

4-(Benzyloxy)phenol-induced p53 exhibits antimycobacterial response triggering phagosome-lysosome fusion through ROS-dependent intracellular Ca2+ pathway in THP-1 cells

Drug-resistant tuberculosis (TB) outbreak has emerged as a global public health crisis. Therefore, new and innovative therapeutic options like host-directed therapies (HDTs) through novel modulators are urgently required to overcome the challenges associated with TB. In the present study, we have investigated the anti-mycobacterial effect of 4-(Benzyloxy)phenol. Cell-viability assay asserted that 50 μM of 4-(Benzyloxy)phenol was not cytotoxic to phorbol 12-myristate 13-acetate (PMA) differentiated THP-1 (dTHP-1) cells. It was observed that 4-(Benzyloxy)phenol activates p53 expression by hindering its association with KDM1A. Increased ROS, intracellular Ca2+ and phagosome-lysosome fusion, were also observed upon 4-(Benzyloxy)phenol treatment. 4-(Benzyloxy)phenol mediated killing of intracellular mycobacteria was abrogated in the presence of specific inhibitors of ROS, Ca2+ and phagosome-lysosome fusion like NAC, BAPTA-AM, and W7, respectively. We further demonstrate that 4-(Benzyloxy)phenol mediated enhanced ROS production is mediated by acetylation of p53. Blocking of p53 acetylation by Pifithrin-α (PFT- α) enhanced intracellular mycobacterial growth by blocking the mycobactericidal effect of 4-(Benzyloxy)phenol. Altogether, the results showed that 4-(Benzyloxy)phenol executed its anti-mycobacterial effect by modulating p53-mediated ROS production to regulate phagosome-lysosome fusion through Ca2+ production.

Mycobacterium tuberculosis inhibits METTL14-mediated m6A methylation of Nox2 mRNA and suppresses anti-TB immunity

Internal N6-methyladenosine (m6A) modifications are among the most abundant modifications of messenger RNA, playing a critical role in diverse biological and pathological processes. However, the functional role and regulatory mechanism of m6A modifications in the immune response to Mycobacterium tuberculosis infection remains unknown. Here, we report that methyltransferase-like 14 (METTL14)-dependent m6A methylation of NAPDH oxidase 2 (Nox2) mRNA was crucial for the host immune defense against M. tuberculosis infection and that M. tuberculosis-secreted antigen EsxB (Rv3874) inhibited METTL14-dependent m6A methylation of Nox2 mRNA. Mechanistically, EsxB interacted with p38 MAP kinase and disrupted the association of TAB1 with p38, thus inhibiting the TAB1-mediated autophosphorylation of p38. Interaction of EsxB with p38 also impeded the binding of p38 with METTL14, thereby inhibiting the p38-mediated phosphorylation of METTL14 at Thr72. Inhibition of p38 by EsxB restrained liquid-liquid phase separation (LLPS) of METTL14 and its subsequent interaction with METTL3, preventing the m6A modification of Nox2 mRNA and its association with the m6A-binding protein IGF2BP1 to destabilize Nox2 mRNA, reduce ROS levels, and increase intracellular survival of M. tuberculosis. Moreover, deletion or mutation of the phosphorylation site on METTL14 impaired the inhibition of ROS level by EsxB and increased bacterial burden or histological damage in the lungs during infection in mice. These findings identify a previously unknown mechanism that M. tuberculosis employs to suppress host immunity, providing insights that may empower the development of effective immunomodulators that target M. tuberculosis.

Differential Regulation of TFEB-Induced Autophagy during Mtb Infection and Starvation

Through the promotion of phagolysosome formation, autophagy has emerged as a crucial mechanism to eradicate intracellular Mycobacterium tuberculosis (Mtb). A cell-autonomous host defense mechanism called lysosome biogenesis and autophagy transports cytoplasmic cargos and bacterial phagosomes to lysosomes for destruction during infection. Similar occurrences occurred in stressful or starvation circumstances and led to autophagy, which is harmful to the cell. It is interesting to note that under both hunger and infection states, the transcription factor EB (TFEB) acts as a master regulator of lysosomal activities and autophagy. This review highlighted recent research on the multitier regulation of TFEB-induced autophagy by a variety of host effectors and Mtb sulfolipid during Mtb infection and starvation. In general, the research presented here sheds light on how lysosome biogenesis and autophagy are differentially regulated by the TFEB during Mtb infection and starvation.

Alterations of lipid-related genes during anti-tuberculosis treatment: insights into host immune responses and potential transcriptional biomarkers

Background

The optimal diagnosis and treatment of tuberculosis (TB) are challenging due to underdiagnosis and inadequate treatment monitoring. Lipid-related genes are crucial components of the host immune response in TB. However, their dynamic expression and potential usefulness for monitoring response to anti-TB treatment are unclear.

Methodology

In the present study, we used a targeted, knowledge-based approach to investigate the expression of lipid-related genes during anti-TB treatment and their potential use as biomarkers of treatment response.

Results and discussion

The expression levels of 10 genes (ARPC5, ACSL4, PLD4, LIPA, CHMP2B, RAB5A, GABARAPL2, PLA2G4A, MBOAT2, and MBOAT1) were significantly altered during standard anti-TB treatment. We evaluated the potential usefulness of this 10-lipid-gene signature for TB diagnosis and treatment monitoring in various clinical scenarios across multiple populations. We also compared this signature with other transcriptomic signatures. The 10-lipid-gene signature could distinguish patients with TB from those with latent tuberculosis infection and non-TB controls (area under the receiver operating characteristic curve > 0.7 for most cases); it could also be useful for monitoring response to anti-TB treatment. Although the performance of the new signature was not better than that of previous signatures (i.e., RISK6, Sambarey10, Long10), our results suggest the usefulness of metabolism-centric biomarkers.

Conclusions

Lipid-related genes play significant roles in TB pathophysiology and host immune responses. Furthermore, transcriptomic signatures related to the immune response and lipid-related gene may be useful for TB diagnosis and treatment monitoring.

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.

Initial immune response after exposure to Mycobacterium tuberculosis or to SARS-COV-2: similarities and differences

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb) and Coronavirus disease-2019 (COVID-19), whose etiologic agent is severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), are currently the two deadliest infectious diseases in humans, which together have caused about more than 11 million deaths worldwide in the past 3 years. TB and COVID-19 share several aspects including the droplet- and aerosol-borne transmissibility, the lungs as primary target, some symptoms, and diagnostic tools. However, these two infectious diseases differ in other aspects as their incubation period, immune cells involved, persistence and the immunopathological response. In this review, we highlight the similarities and differences between TB and COVID-19 focusing on the innate and adaptive immune response induced after the exposure to Mtb and SARS-CoV-2 and the pathological pathways linking the two infections. Moreover, we provide a brief overview of the immune response in case of TB-COVID-19 co-infection highlighting the similarities and differences of each individual infection. A comprehensive understanding of the immune response involved in TB and COVID-19 is of utmost importance for the design of effective therapeutic strategies and vaccines for both diseases.

Abdominal Lymphadenopathies: Lymphoma, Brucellosis or Tuberculosis? Multidisciplinary Approach-Case Report and Review of the Literature

Abdominal pain represents a frequent symptom for referral to emergency departments and/or internal medicine outpatient setting. Similarly, fever, fatigue and weight loss are non-specific manifestations of disease. The present case describes the diagnostic process in a patient with abdominal pain and a palpable abdominal mass. Abdominal ultrasonography confirmed the presence of a mass in the mesogastrium. Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) scans oriented toward calcific lymphadenopathies with increased metabolism in the positron emission tomography-computed tomography (PET-CT) scan. Laboratory examinations were inconclusive, although serology for Brucella and the Quantiferon test were positive. After multidisciplinary discussion, the patient underwent surgical excision of the abdominal mass. Histological examination excluded malignancies and oriented toward brucellosis in a patient with latent tuberculosis. The patient was treated with rifampin 600 mg qd and doxycycline 100 mg bid for 6 weeks with resolution of the symptoms. In addition, rifampin was continued for a total of 6 months in order to treat latent tuberculosis. This case underlines the need for a multidisciplinary approach in the diagnostic approach to abdominal lymphadenopathies.

EphH, a unique epoxide hydrolase encoded by Rv3338 is involved in the survival of Mycobacterium tuberculosis under in vitro stress and vacuolar pH-induced changes

Introduction

Mycobacterium tuberculosis (Mtb), one of the deadliest human pathogen, has evolved with different strategies of survival inside the host, leading to a chronic state of infection. Phagosomally residing Mtb encounters a variety of stresses, including increasing acidic pH. To better understand the host-pathogen interaction, it is imperative to identify the role of various genes involved in the survivability of Mtb during acidic pH environment.

Methods

Bio-informatic and enzymatic analysis were used to identify Mtb gene, Rv3338, as epoxide hydrolase. Subsequently, CRISPRi knockdown strategy was used to decipher its role for Mtb survival during acidic stress, nutrient starvation and inside macrophages. Confocal microscopy was used to analyse its role in subverting phagosomal acidification within macrophage.

Results

The present work describes the characterization of Rv3338 which was previously known to be associated with the aprABC locus induced while encountering acidic stress within the macrophage. Bio-informatic analysis demonstrated its similarity to epoxide hydrolase, which was confirmed by enzymatic assays, thus, renamed EphH. Subsequently, we have deciphered its indispensable role for Mtb in protection from acidic stress by using the CRISPRi knockdown strategy. Our data demonstrated the pH dependent role of EphH for the survival of Mtb during nutrient starvation and in conferring resistance against elevated endogenous ROS levels during stress environment.

Conclusion

To the best of our knowledge, this is the first report of an EH of Mtb as a crucial protein for bacterial fitness inside the host, a phenomenon central to its pathogenesis.

An ultra-sensitive rifampicin electrochemical sensor based on Fe3O4 nanoparticles anchored Multiwalled Carbon nanotube modified glassy carbon electrode

This study aimed to guide future sensor studies against other pharmaceutical drugs by synthesizing Fe₃O₄NPs@MWCNT metallic nanoparticles (NPs). Side damage caused by excessive accumulation of tuberculosis drugs in the body can cause clots in the organs, and cause serious damage such as heart attack and respiratory failure, and threaten human life. Therefore, the development of sensors sensitive to various antibiotics in this study is important for human health. In this study, the sensitivity of Fe₃O₄ NPs to tuberculosis drug (rifampicin) was evaluated by catalytic reaction using bare/GCE, MWCNT/GCE, and Fe₃O₄NPs@MWCNT/GCE electrodes. First of all, Fe₃O₄ NPs were successfully synthesized for the study and MWCNT/GCE and Fe₃O₄ NPs@MWCNT/GCE electrodes were formed with the modification of the MWCNT support material. It was observed that the Fe₃O₄ NPs@MWCNT/GCE electrode gave the highest signal against the other electrodes. The morphological structure of Fe₃O₄ NPs was determined by various characterization techniques such as Transmission Electron Microscopy (TEM), Fourier Transmission Infrared Spectroscopy (FTIR), ultraviolet-visible (UV-Vis), and X-ray differential (XRD) and the obtained NPs were used for sensor studies, and it was observed that the current intensity increased as the scanning speed of each electrode increased in CV and DPV measurements. The average size of Fe₃O₄ NPs was found to be 7.32 ± 3.2 nm. Anodic current peaks occurred in the linear range of 2-25 μM. According to the results obtained from the measurements, the limit of detection (LOD) value was calculated as 0.64 μM limit of quantification (LOQ) 1.92 μM.

Manipulation and exploitation of host immune system by pathogenic Mycobacterium tuberculosis for its advantage

Mycobacterium tuberculosis (Mtb) can become a long-term infection by evading the host immune response. Coevolution of Mtb with humans has resulted in its ability to hijack the host's immune systems in a variety of ways. So far, every Mtb defense strategy is essentially dependent on a subtle balance that, if shifted, can promote Mtb proliferation in the host, resulting in disease progression. In this review, the authors summarize many important and previously unknown mechanisms by which Mtb evades the host immune response. Besides recently found strategies by which Mtb manipulates the host molecular regulatory machinery of innate and adaptive immunity, including the intranuclear regulatory machinery, costimulatory molecules, the ubiquitin system and cellular intrinsic immune components will be discussed. A holistic understanding of these immune-evasion mechanisms is of foremost importance for the prevention, diagnosis and treatment of tuberculosis and will lead to new insights into tuberculosis pathogenesis and the development of more effective vaccines and treatment regimens.

M, Saurabh A, Zarin S, Mitra DK, Hasnain SE, Ehtesham NZ. Mycobacterium tuberculosis Methyltransferase Rv1515c Can Suppress Host Defense Mechanisms by Modulating Immune Functions Utilizing a Multipronged Mechanism

Mycobacterium tuberculosis (M. tb) gene Rv1515c encodes a conserved hypothetical protein exclusively present within organisms of MTB complex and absent in non-pathogenic mycobacteria. In silico analysis revealed that Rv1515c contain S-adenosylmethionine binding site and methyltransferase domain. The DNA binding and DNA methyltransferase activity of Rv1515c was confirmed in vitro. Knock-in of Rv1515c in a model mycobacteria M. smegmatis (M. s_Rv1515c) resulted in remarkable physiological and morphological changes and conferred the recombinant strain with an ability to adapt to various stress conditions, including resistance to TB drugs. M. s_Rv1515c was phagocytosed at a greater rate and displayed extended intra-macrophage survival in vitro. Recombinant M. s_Rv1515c contributed to enhanced virulence by suppressing the host defense mechanisms including RNS and ROS production, and apoptotic clearance. M. s_Rv1515c, while suppressing the phagolysosomal maturation, modulated pro-inflammatory cytokine production and also inhibited antigen presentation by downregulating the expression of MHC-I/MHC-II and co-stimulatory signals CD80 and CD86. Mice infected with M. s_Rv1515c produced more Treg cells than vector control (M. s_Vc) and exhibited reduced effector T cell responses, along-with reduced expression of macrophage activation markers in the chronic phase of infection. M. s_Rv1515c was able to survive in the major organs of mice up to 7 weeks post-infection. These results indicate a crucial role of Rv1515c in M. tb pathogenesis.

Overexpression of VPS11 antagonizes the promoting effect of miR-542-3p on Mycobacterium tuberculosis survival in macrophages by regulating autophagy

Impaired autophagy is an important cause of Mycobacterium tuberculosis survival in macrophages. VPS11 is an important regulator of autophagy; decreased VPS11 expression has been observed in macrophages after tuberculosis (TB) infection. Gene ontology data revealed that various miRNAs (for example, miR-542-3p) were upregulated in macrophages upon TB infection; thus, these miRNAs were likely to reduce VPS11 expression. In this study, both TB patients and healthy subjects were enrolled, and the levels of VPS11 and some miRNAs in their blood macrophages were measured. Moreover, various macrophages were cultured and infected with M. tuberculosis. Luciferase reporter, RNA pulldown, and RNA immunoprecipitation assays were performed to determine the regulatory effect of miR-542-3p on VPS11 expression. Results showed that VPS11 expression was downregulated, whereas miR-542-3p expression was upregulated in blood macrophages after TB infection. TB infection reduced VPS11 levels in two human macrophages in vitro, but not in mouse macrophages. This might be because the seed sequence exists in the VPS11 3' untranslated region in humans, but is absent in mice and rats. miR-542-3p promoted M. tuberculosis survival in human macrophages, but VPS11 overexpression antagonized the promoting effect of miR-542-3p. Further, VPS11 was confirmed as a target of miR-542-3p. Overexpression of VPS11 or depletion of miR-542-3p promoted autophagy, which was suppressed upon TB infection. In summary, VPS11 overexpression antagonized the promoting effect of miR-542-3p on M. tuberculosis survival in macrophages by regulating autophagy.

Diverse Cell Death Mechanisms Are Simultaneously Activated in Macrophages Infected by Virulent Mycobacterium tuberculosis

Macrophages are necessary to eliminate pathogens. However, some pathogens have developed mechanisms to avoid the immune response. One of them is modulating the cell death mechanism to favor pathogen survival. In this study, we evaluated if virulent Mycobacterium tuberculosis (M. tb) can simultaneously activate more than one cell death mechanism. We infected human monocyte-derived macrophages (MDM) in vitro with avirulent (H37Ra) and virulent (H37Rv) strains, and then we measured molecules involved in apoptosis, necroptosis, and pyroptosis. Our data showed that H37Rv infection increased the BCL-2 transcript and protein, decreased the BAX transcript, and increased phosphorylated BCL-2 at the protein level. Moreover, H37Rv infection increased the expression of the molecules involved in the necroptotic pathway, such as ASK1, p-38, RIPK1, RIPK3, and caspase-8, while H37Ra increased caspase-8 and decreased RIPK3 at the transcriptional level. In addition, NLRP3 and CASP1 expression was increased at low MOI in both strains, while IL-1β was independent of virulence but dependent on infection MOI, suggesting the activation of pyroptosis. These findings suggest that virulent M. tb inhibits the apoptosis mediated by BCL-2 family molecules but, at the same time, increases the expression of molecules involved in apoptosis, necroptosis, and pyroptosis at the transcriptional and protein levels, probably as a mechanism to avoid the immune response and guarantee its survival.

Comparative Analysis on Proteomics Profiles of Intracellular and Extracellular M.tb and BCG From Infected Human Macrophages

Tuberculosis is the second cause in infectious diseases leading to human death. Understanding the virulence mechanism is inevitable if the disease needs to be fully cured. Therefore, this study aimed to reveal this mechanism by comparing proteomic profiles of intracellular and extracellular virulent strain M.tb and bacille Calmette–Guérin (BCG) from infected THP-1cells. First, M.tb and BCG infected THP-1 at MOI 10:1. Twelve hours postinfection, intracellular bacteria of M.tb and BCG were collected, whereas the two bacilli cultured in 7H9 broth media were used as the control. Then four groups of bacilli were subjected to proteomic analysis, and differential proteomic profiles between M.tb and BCG were comparatively analyzed with bioinformatics tools. As a result, we identified a total of 1,557 proteins. Further, they were divided into four groups for comparison of M.tb versus BCG under 7H9 culture (shorten as out), M.tb in (intracellular) versus M.tb out, BCG in versus BCG out and M.tb in versus BCG in. Between M.tb in versus BCG in, a total of 211 differentially expressed proteins were found. Eight proteins like ESAT-6 distributed in six RDs and some known proteins related to virulence. Besides, five uncharacterized proteins were differentially expressed. Further analysis revealed enriched pathways were associated with glyoxylate and dicarboxylate metabolism pathways. In M.tb out versus BCG out, a total of 144 differential proteins were identified and mainly involved in metabolism pathways. Then, 121 differential proteins in the group of M.tb in versus M.tb out were enriched in ribosome and oxidative phosphorylation related to adaptation to the host environment. The group of BCG in versus BCG out shared the same trend of different pathways to the M.tb in versus M.tb out. Finally, 42 proteins were identified to be up-regulated only in intracellular M.tb including eight RD proteins, whereas 22 up-regulated uniquely in intracellular BCG. Besides, only two proteins (Pks13 and Rv1405c) were commonly up-regulated in intracellular M.tb and BCG. Further, some unknown proteins were uniquely up-regulated in the intracellular M.tb and BCG. These findings provide valuable data for further exploration of molecular mechanism for M.tb virulence and BCG immune response.

Two-component sensor histidine kinases of Mycobacterium tuberculosis: beacons for niche navigation

Intracellular bacterial pathogens such as Mycobacterium tuberculosis are remarkably adept at surviving within a host, employing a variety of mechanisms to counteract host defenses and establish a protected niche. Constant surveying of the environment is key for pathogenic mycobacteria to discern their immediate location and coordinate the expression of genes necessary for adaptation. Two‐component systems efficiently perform this role, typically comprised of a transmembrane sensor kinase and a cytoplasmic response regulator. In this review, we describe the role of two‐component systems in bacterial pathogenesis, focusing predominantly on the role of sensor kinases of M. tuberculosis. We highlight important features of sensor kinases in mycobacterial infection, discuss ways in which these signaling proteins sense and respond to environments, and how this is attuned to their intracellular lifestyle. Finally, we discuss recent studies which have identified and characterized inhibitors of two‐component sensor kinases toward establishing a new strategy in anti‐mycobacterial therapy.

Repurposing diphenylbutylpiperidine-class antipsychotic drugs for host-directed therapy of Mycobacterium tuberculosis and Salmonella enterica infections

The persistent increase of multidrug-resistant (MDR) Mycobacterium tuberculosis (Mtb) infections negatively impacts Tuberculosis treatment outcomes. Host-directed therapies (HDT) pose an complementing strategy, particularly since Mtb is highly successful in evading host-defense by manipulating host-signaling pathways. Here, we screened a library containing autophagy-modulating compounds for their ability to inhibit intracellular Mtb-bacteria. Several active compounds were identified, including two drugs of the diphenylbutylpiperidine-class, Fluspirilene and Pimozide, commonly used as antipsychotics. Both molecules inhibited intracellular Mtb in pro- as well as anti-inflammatory primary human macrophages in a host-directed manner and synergized with conventional anti-bacterials. Importantly, these inhibitory effects extended to MDR-Mtb strains and the unrelated intracellular pathogen, Salmonella enterica serovar Typhimurium (Stm). Mechanistically Fluspirilene and Pimozide were shown to regulate autophagy and alter the lysosomal response, partly correlating with increased bacterial localization to autophago(lyso)somes. Pimozide's and Fluspirilene's efficacy was inhibited by antioxidants, suggesting involvement of the oxidative-stress response in Mtb growth control. Furthermore, Fluspirilene and especially Pimozide counteracted Mtb-induced STAT5 phosphorylation, thereby reducing Mtb phagosome-localized CISH that promotes phagosomal acidification. In conclusion, two approved antipsychotic drugs, Pimozide and Fluspirilene, constitute highly promising and rapidly translatable candidates for HDT against Mtb and Stm and act by modulating the autophagic/lysosomal response by multiple mechanisms.

Effect of Protein O-Mannosyltransferase (MSMEG_5447) on M. smegmatis and Its Survival in Macrophages

Protein O-mannosyltransferase (PMT) catalyzes an initial step of protein O-mannosylation of Mycobacterium tuberculosis (Mtb) and plays a crucial role for Mtb survival in the host. To better understand the role of PMT in the host innate immune response during mycobacterial infection, in this study, we utilized Mycobacterium smegmatis pmt (MSMEG_5447) gene knockout strain, ΔM5447, to infect THP-1 cells. Our results revealed that the lack of MSMEG_5447 not only impaired the growth of M. smegmatis in 7H9 medium but also reduced the resistance of M. smegmatis against lysozyme and acidic stress in vitro. Macrophage infection assay showed that ΔM5447 displayed attenuated growth in macrophages at 24 h post-infection. The production of TNF-α and IL-6 and the activation of transcription factor NF-κB were decreased in ΔM5447-infected macrophages, which were further confirmed by transcriptomic analysis. Moreover, ΔM5447 failed to inhibit phagosome–lysosome fusion in macrophages. These findings revealed that PMT played a role in modulating the innate immune responses of the host, which broaden our understanding for functions of protein O-mannosylation in mycobacterium–host interaction.

Autophagy as a Target for Drug Development Of Skin Infection Caused by Mycobacteria

Pathogenic mycobacteria species may subvert the innate immune mechanisms and can modulate the activation of cells that cause disease in the skin. Cutaneous mycobacterial infection may present different clinical presentations and it is associated with stigma, deformity, and disability. The understanding of the immunopathogenic mechanisms related to mycobacterial infection in human skin is of pivotal importance to identify targets for new therapeutic strategies. The occurrence of reactional episodes and relapse in leprosy patients, the emergence of resistant mycobacteria strains, and the absence of effective drugs to treat mycobacterial cutaneous infection increased the interest in the development of therapies based on repurposed drugs against mycobacteria. The mechanism of action of many of these therapies evaluated is linked to the activation of autophagy. Autophagy is an evolutionary conserved lysosomal degradation pathway that has been associated with the control of the mycobacterial bacillary load. Here, we review the role of autophagy in the pathogenesis of cutaneous mycobacterial infection and discuss the perspectives of autophagy as a target for drug development and repurposing against cutaneous mycobacterial infection.

Lipoarabinomannan as a Point-of-Care Assay for Diagnosis of Tuberculosis: How Far Are We to Use It?

Tuberculosis (TB) is still a severe public health problem; the current diagnostic tests have limitations that delay treatment onset. Lipoarabinomannan (LAM) is a glycolipid that is a component of the cell wall of the bacillus Mycobacterium tuberculosis, the etiologic agent of TB. This glycolipid is excreted as a soluble form in urine. The World Health Organization has established that the design of new TB diagnostic methods is one of the priorities within the EndTB Strategy. LAM has been suggested as a biomarker to develop diagnostic tests based on its identification in urine, and it is one of the most prominent candidates to develop point-of-care diagnostic test because urine samples can be easily collected. Moreover, LAM can regulate the immune response in the host and can be found in the serum of TB patients, where it probably affects a wide variety of host cell populations, consequently influencing the quality of both innate and adaptive immune responses during TB infection. Here, we revised the evidence that supports that LAM could be used as a tool for the development of new point-of-care tests for TB diagnosis, and we discussed the mechanisms that could contribute to the low sensitivity of diagnostic testing.

The cell biology of inflammation: From common traits to remarkable immunological adaptations

Tissue damage triggers a rapid and robust inflammatory response in order to clear and repair a wound. Remarkably, many of the cell biology features that underlie the ability of leukocytes to home in to sites of injury and to fight infection—most of which are topics of intensive current research—were originally observed in various weird and wonderful translucent organisms over a century ago by Elie Metchnikoff, the “father of innate immunity,” who is credited with discovering phagocytes in 1882. In this review, we use Metchnikoff’s seminal lectures as a starting point to discuss the tremendous variety of cell biology features that underpin the function of these multitasking immune cells. Some of these are shared by other cell types (including aspects of motility, membrane trafficking, cell division, and death), but others are more unique features of innate immune cells, enabling them to fulfill their specialized functions, such as encapsulation of invading pathogens, cell–cell fusion in response to foreign bodies, and their self-sacrifice as occurs during NETosis.

The Interplay Between Systemic Inflammation, Oxidative Stress, and Tissue Remodeling in Tuberculosis

Significance: Excessive and prolonged proinflammatory responses are associated with oxidative stress, which is commonly observed during chronic tuberculosis (TB). Such condition favors tissue destruction and consequently bacterial spread. A tissue remodeling program is also triggered in chronically inflamed sites, facilitating a wide spectrum of clinical manifestations. Recent Advances: Since persistent and exacerbated oxidative stress responses have been associated with severe pathology, a number of studies have suggested that the inhibition of this augmented stress response by improving host antioxidant status may represent a reasonable strategy to ameliorate tissue damage in TB. Critical Issues: This review summarizes the interplay between oxidative stress, systemic inflammation and tissue remodeling, and its consequences in promoting TB disease. We emphasize the most important mechanisms associated with stress responses that contribute to the progression of TB. We also point out important host immune components that may influence the exacerbation of cellular stress and the subsequent tissue injury. Future Directions: Further research should reveal valuable targets for host-directed therapy of TB, preventing development of severe immunopathology and disease progression. Antioxid. Redox Signal. 34, 471-485.

Metabolic Regulation of Immune Responses to Mycobacterium tuberculosis: A Spotlight on L-Arginine and L-Tryptophan Metabolism

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), is a leading cause of death worldwide. Despite decades of research, there is still much to be uncovered regarding the immune response to Mtb infection. Here, we summarize the current knowledge on anti-Mtb immunity, with a spotlight on immune cell amino acid metabolism. Specifically, we discuss L-arginine and L-tryptophan, focusing on their requirements, regulatory roles, and potential use as adjunctive therapy in TB patients. By continuing to uncover the immune cell contribution during Mtb infection and how amino acid utilization regulates their functions, it is anticipated that novel host-directed therapies may be developed and/or refined, helping to eradicate TB.

Distinct functional properties of secretory l-asparaginase Rv1538c involved in phagosomal survival of Mycobacterium tuberculosis

The emergence of drug-resistant Mycobacterium tuberculosis (Mtb) stains has escalated the need for developing more efficient drugs and therapeutic strategies against tuberculosis. Here we functionally annotate a secretory mycobacterial asparaginase Rv1538c (MtA) and describe its biochemical properties. MtA primarily existed as dimer along with a minor population of multimers. Circular dichroism and fluorescence spectroscopy demonstrated a compact structure in Tris HCl buffer at pH 8.0. Under these conditions it also displayed optimum activity. It retained ∼40% activity at pH 5.5, supporting its physiological relevance in acidic phagosomal environment. MtA contravened classical Michaelis-Menten kinetics and exhibited product inhibition profile, yielding a K_cat of 869.4 s^-1 and an apparent K_m of 8.36 mM. We report the presence of several antigenic epitopes and a C-terminal YXXXD/E motif in MtA, hinting towards its potential to interact or influence host immune system. This was supported by our observation of morphological changes in MtA-treated human B lymphoblasts. We propose that MtA is a dual purpose enzyme used by Mtb to survive inside its host by; 1) ammonia-mediated neutralization of the phagosomal acidic pH and 2) inducing stress to primary immune cells and compromising the host immune response. Overall, this study contributes to our understanding of the biological role of mycobacterial asparaginase opening avenues for developing effective TB therapeutics.

New insights into the evasion of host innate immunity by Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) is an extremely successful intracellular pathogen that causes tuberculosis (TB), which remains the leading infectious cause of human death. The early interactions between Mtb and the host innate immune system largely determine the establishment of TB infection and disease development. Upon infection, host cells detect Mtb through a set of innate immune receptors and launch a range of cellular innate immune events. However, these innate defense mechanisms are extensively modulated by Mtb to avoid host immune clearance. In this review, we describe the emerging role of cytosolic nucleic acid-sensing pathways at the host-Mtb interface and summarize recently revealed mechanisms by which Mtb circumvents host cellular innate immune strategies such as membrane trafficking and integrity, cell death and autophagy. In addition, we discuss the newly elucidated strategies by which Mtb manipulates the host molecular regulatory machinery of innate immunity, including the intranuclear regulatory machinery, the ubiquitin system, and cellular intrinsic immune components. A better understanding of innate immune evasion mechanisms adopted by Mtb will provide new insights into TB pathogenesis and contribute to the development of more effective TB vaccines and therapies.

Metformin in tuberculosis: beyond control of hyperglycemia

Two global epidemics, diabetes mellitus (DM) and tuberculosis (TB), have converged making their control even more challenging. We herein have reviewed metformin's (MTF) effect on patients with active and latent TB, as well as discussed its newly discovered biological mechanisms in mycobacteria. Mounting evidence suggests that MTF provides better outcomes in TB patients, especially those with DM. The mechanisms by which MTF produces its benefits are multiple. Though metformin's potential has been proven in patients with DM, larger and more thorough clinical trials, in DM and non-DM-TB patients, need to be conducted. MTF could be added to the arsenal of anti-TB drugs, aiding in the goal of TB eradication worldwide.