Pathogenesis Of Mycobacterium Tuberculosis Research Articles

Structural insights into the regulation mechanism of Mycobacterium tuberculosis MftR.

Mycobacterium tuberculosis, the pathogen of the deadly disease tuberculosis, depends on the redox cofactor mycofactocin (MFT) to adapt toand survive under hypoxic conditions. MftR is a TetR family transcription regulator that binds upstream of the MFT gene cluster and controls MFT synthesis. To elucidate the structural basis underlying MftR regulation, we determined the crystal structure of Mycobacterium tuberculosis MftR (TB-MftR). The structure revealed an interconnected hydrogen bond network in the α1-α2-α3 helices of helix-turn-helix (HTH) DNA-binding domain that is essential for nucleic acid interactions. The ligand-binding domain contains a hydrophobic cavity enclosing long-chain fatty acyl-CoAs like the key regulatory ligand oleoyl-CoA. Despite variations in ligand-binding modes, comparative analyses suggest regulatory mechanisms are largely conserved across TetR family acyl-CoA sensors. By elucidating the intricate structural mechanisms governing DNA and ligand binding by TB-MftR, our study enhances understanding of the regulatory roles of this transcription factor under hypoxic conditions, providing insights that could inform future research into Mycobacterium tuberculosis pathogenesis.

FIP200 promotes Mycobacterium tuberculosis pathogenesis independent of its role in autophagy

Abstract Tuberculosis, caused by Mycobacterium tuberculosis (Mtb), remains a critical health issue. Xenophagy, the targeting of Mtb to autophagosomes within infected cells is ineffective at controlling Mtb replication in vivo. We discovered that autophagy-associated proteins function outside of xenophagy to impact Mtb pathogenesis. We reveal a distinct autophagy-independent function of FIP200 in CD11c+ alveolar macrophages (AMs) to control Mtb burden in mice lungs at 7 days post-infection. Intra-tracheal airway labelling shows that despite the abundance of inflammatory cells, including AMs, in airway and interstitium, airway resident AMs precisely exhibit better infection control in Fip200fl/fl-LysM-Cre mice lungs.FIP200, beyond its role in autophagy, is shown to regulate signaling pathways to suppress TNF-induced apoptosis and promote cell survival. Compared to flox control, loss of Fip200 resulted in significantly higher apoptosis in AMs, in the lungs of naïve mice, which is sustained during infection. We also observed higher reactive oxygen species production by the AMs in lungs. This observation extends to Streptococcus pneumoniae infection, where loss of FIP200 in CD11c+ AMs caused similar increase in apoptosis and ROS,with reduced bacterial burden in mouse lungs. Thus, we propose a model where the FIP200 inhibits the apoptosis and ROS production in AMs, which impairs the antimicrobial defense in these cells, thus promoting Mtb infection in the airways following infection.

Roles of Lipolytic enzymes in Mycobacterium tuberculosis pathogenesis.

Mycobacterium tuberculosis (Mtb) is a bacterial pathogen that can endure for long periods in an infected patient, without causing disease. There are a number of virulence factors that increase its ability to invade the host. One of these factors is lipolytic enzymes, which play an important role in the pathogenic mechanism of Mtb. Bacterial lipolytic enzymes hydrolyze lipids in host cells, thereby releasing free fatty acids that are used as energy sources and building blocks for the synthesis of cell envelopes, in addition to regulating host immune responses. This review summarizes the relevant recent studies that used in vitro and in vivo models of infection, with particular emphasis on the virulence profile of lipolytic enzymes in Mtb. A better understanding of these enzymes will aid the development of new treatment strategies for TB. The recent work done that explored mycobacterial lipolytic enzymes and their involvement in virulence and pathogenicity was highlighted in this study. Lipolytic enzymes are expected to control Mtb and other intracellular pathogenic bacteria by targeting lipid metabolism. They are also potential candidates for the development of novel therapeutic agents.

Mycobacterium tuberculosis antigen 85B modifies BCG-induced antituberculosis immunity and favors pathogen survival.

Tuberculosis is one of the deadliest infectious diseases worldwide. Mycobacterium tuberculosis has developed strategies not only to evade host immunity but also to manipulate it for its survival. We investigated whether Mycobacterium tuberculosis exploited the immunogenicity of Ag85B, one of its major secretory proteins, to redirect host antituberculosis immunity to its advantage. We found that administration of Ag85B protein to mice vaccinated with Bacillus Calmette-Guérin impaired the protection elicited by vaccination, causing a more severe infection when mice were challenged with Mycobacterium tuberculosis. Ag85B administration reduced Bacillus Calmette-Guérin-induced CD4 T-cell activation and IFN-γ, CCL-4, and IL-22 production in response to Mycobacterium tuberculosis-infected cells. On the other hand, it promoted robust Ag85B-responsive IFN-γ-producing CD4 T cells, expansion of a subset of IFN-γ/IL-10-producing CD4+FOXP3+Treg cells, differential activation of IL-17/IL-22 responses, and activation of regulatory and exhaustion pathways, including programmed death ligand 1 expression on macrophages. All this resulted in impaired intracellular Mycobacterium tuberculosis growth control by systemic immunity, both before and after the Mycobacterium tuberculosis challenge. Interestingly, Mycobacterium tuberculosis infection itself generated Ag85B-reactive inflammatory immune cells incapable of clearing Mycobacterium tuberculosis in both unvaccinated and Bacillus Calmette-Guérin-vaccinated mice. Our data suggest that Mycobacterium tuberculosis can exploit the strong immunogenicity of Ag85B to promote its own survival and spread. Since Ag85B is normally secreted by replicating bacteria and is commonly found in the lungs of the Mycobacterium tuberculosis-infected host, our findings may advance the understanding on the mechanisms of Mycobacterium tuberculosis pathogenesis and immune evasion.

BACH1 promotes tissue necrosis and Mycobacterium tuberculosis susceptibility

Oxidative stress triggers ferroptosis, a form of cellular necrosis characterized by iron-dependent lipid peroxidation, and has been implicated in Mycobacterium tuberculosis (Mtb) pathogenesis. We investigated whether Bach1, a transcription factor that represses multiple antioxidant genes, regulates host resistance to Mtb. We found that BACH1 expression is associated clinically with active pulmonary tuberculosis. Bach1 deletion in Mtb-infected mice increased glutathione levels and Gpx4 expression that inhibit lipid peroxidation. Bach1−/− macrophages exhibited increased resistance to Mtb-induced cell death, while Mtb-infected Bach1-deficient mice displayed reduced bacterial loads, pulmonary necrosis and lipid peroxidation concurrent with increased survival. Single-cell RNA-seq analysis of lungs from Mtb-infected Bach1−/− mice revealed an enrichment of genes associated with ferroptosis suppression. Bach1 depletion in Mtb-infected B6.Sst1S mice that display human-like necrotic lung pathology also markedly reduced necrosis and increased host resistance. These findings identify Bach1 as a key regulator of cellular and tissue necrosis and host resistance in Mtb infection.

Mycobacterial phosphodiesterase Rv0805 is a virulence determinant and its cyclic nucleotide hydrolytic activity is required for propionate detoxification.

Cyclic AMP (cAMP) signaling is essential to Mycobacterium tuberculosis (Mtb) pathogenesis. However, the roles of phosphodiesterases (PDEs) Rv0805, and the recently identified Rv1339, in cAMP homeostasis and Mtb biology are unclear. We found that Rv0805 modulates Mtb growth within mice, macrophages and on host-associated carbon sources. Mycobacterium bovis BCG grown on a combination of propionate and glycerol as carbon sources showed high levels of cAMP and had a strict requirement for Rv0805 cNMP hydrolytic activity. Supplementation with vitamin B12 or spontaneous genetic mutations in the pta-ackA operon restored the growth of BCGΔRv0805 and eliminated propionate-associated cAMP increases. Surprisingly, reduction of total cAMP levels by ectopic expression of Rv1339 restored only 20% of growth, while Rv0805 complementation fully restored growth despite a smaller effect on total cAMP levels. Deletion of an Rv0805 localization domain also reduced BCG growth in the presence of propionate and glycerol. We propose that localized Rv0805 cAMP hydrolysis modulates activity of a specialized pathway associated with propionate metabolism, while Rv1339 has a broader role in cAMP homeostasis. Future studies will address the biological roles of Rv0805 and Rv1339, including their impacts on metabolism, cAMP signaling and Mtb pathogenesis.

Evaluation of the Immunogenicity of Recombinant Espb, Espc Proteins from Mycobacterium Tuberculosis and the Fusion Espc/Espb Protein in BALB/C Mice.

Two newly identified proteins, EspB and EspC are involved in the pathogenesis of Mycobacterium tuberculosis. The objective of the present study was to evaluate the immunogenicity of recombinant EspC, EspB, and EspC/EspB fusion proteins in mice. BALB/c mice were immunized subcutaneously with recombinant EspC, EspB, and fusion EspC/EspB proteins, three times with along with Quil-A as an adjuvant. The cellular and humoral immune responses were evaluated by quantifying IFN-γ, IL-4, IgG, IgG1, and IgG2a antibodies against the antigens. The results showed that the mice immunized with recombinant EspC, EspB, and EspC/EspB proteins did not produce IL-4, whereas IFN-γ was secreted in response to all three proteins. EspC/EspB group produced significant amounts of IFN-γ in response to stimulation with all the three recombinant proteins (P<0.001). In mice immunized with EspC, high levels of IFN-γ were detected in response to EspC/EspB, and EspC (P<0.0001); while mice immunized with EspB produced lower levels of IFN-γ in response to EspC/EspB, and EspB (P<0.05).Mice immunized with recombinant EspC, EspB, and EspC/EspB proteins exhibited significantly high levels of IgG and IgG2a/IgG1 ratio (P< 0.001). Moreover, high levels of IgG and IgG2a were detected in the sera of mice immunized with EspC/EspB fusion protein. All the three recombinant proteins induced Th1-type immune responses in mice against EspB and EspC; however, EspC/EspB protein is more desirable due to the presence of epitopes from both EspC and EspB proteins and the production of immune responses against both.

Mycobacterium tuberculosis Rv0494 Protein Contributes to Mycobacterial Persistence.

Fatty acid metabolism plays an important role in the survival and pathogenesis of Mycobacterium tuberculosis. During dormancy, lipids are considered to be the main source of energy. A previous study found that Rv0494 is a starvation-inducible, lipid-responsive transcriptional regulator. However, the role of Rv0494 in bacterial persister survival has not been studied. We constructed a Rv0494 deletion mutant strain of Mycobacterium tuberculosis H37Rv and evaluated the susceptibility of the mutant strain to antibiotics using a persistence test. We found that mutations in Rv0494 lead to survival defects of persisters, which reflected in increased sensitivity to isoniazid. We conclude that Rv0494 is important for persister survival and may serve as a good target for developing new antibiotics that kill persister bacteria for improved treatment of persistent bacterial infections.

Doxycycline as a Potential MMP-1 Inhibitor for the Treatment of Spondylitis Tuberculosis: A Study in Rabbit Model.

Tuberculosis (TB) of the spine is a highly disruptive disease, especially in underdeveloped and developing countries. This condition requires standard TB treatment for 9-18 months, which increases patient risk of drug-resistant TB. Consequently, this raises the concern of adopting additional therapies to shorten the treatment duration, improve the efficacy of anti-TB drugs, and further decrease damage in the affected tissues and organs. Matrix metalloproteinase- (MMP-) 1 is a key regulator of the destruction of the extracellular matrix and associated proteins and is a new potential target for TB treatment research. In the present study, we investigated the effects of doxycycline as an MMP-1 inhibitor in patients with spondylitis TB. Seventy-two New Zealand white rabbits with spondylitis TB were divided into 12 different groups based on incubation period (2, 4, 6, and 8 weeks) and doxycycline administration (without, 1 mg/kg body weight (BW), and 5 mg/kg BW). We observed the course of infection through the blood concentration changes and immunohistochemical examination of MMP-1, in addition to BTA staining, culture, polymerase chain reaction (PCR), and histopathological examination. Treatment with once daily 5 mg/kg BW doxycycline significantly improved the blood MMP-1 level (p < 0.05) compared with the placebo and 1 mg/kg BW doxycycline. A significantly reduced ongoing infection and a higher healing rate were demonstrated in rabbits with a higher doxycycline dose through BTA staining, culture, PCR, and histopathology. Various degrees of vertebral endplates, vertebral body, and intervertebral disc destruction were observed in 32 rabbits with positive histopathological findings, in addition to positive inflammatory cell infiltration, characterized by numerous lymphocytes, macrophages, and epithelial cells, as well as abundant granulation tissue and necrotic substances proximal to the inoculated vertebral area. Bone and intervertebral disc destructions were more apparent in the untreated rabbits. Our study demonstrated the potential of doxycycline as an adjunctive treatment in spondylitis TB. However, limitations remain regarding the differences in the pathogenesis and virulence of Mycobacterium tuberculosis between rabbit and human systems, sample size, and the dose-dependent effect of doxycycline. Further studies are needed to address these issues.

Mouse Models for Mycobacterium tuberculosis Pathogenesis: Show and Do Not Tell.

Science has been taking profit from animal models since the first translational experiments back in ancient Greece. From there, and across all history, several remarkable findings have been obtained using animal models. One of the most popular models, especially for research in infectious diseases, is the mouse. Regarding research in tuberculosis, the mouse has provided useful information about host and bacterial traits related to susceptibility to the infection. The effect of aging, sexual dimorphisms, the route of infection, genetic differences between mice lineages and unbalanced immunity scenarios upon Mycobacterium tuberculosis infection and tuberculosis development has helped, helps and will help biomedical researchers in the design of new tools for diagnosis, treatment and prevention of tuberculosis, despite various discrepancies and the lack of deep study in some areas of these traits.

S-Adenosylmethionine-responsive cystathionine β-synthase modulates sulfur metabolism and redox balance in Mycobacterium tuberculosis.

Methionine and cysteine metabolisms are important for the survival and pathogenesis of Mycobacterium tuberculosis (Mtb). The transsulfuration pathway converts methionine to cysteine and represents an important link between antioxidant and methylation metabolism in diverse organisms. Using a combination of biochemistry and cryo–electron microscopy, we characterized the first enzyme of the transsulfuration pathway, cystathionine β-synthase (MtbCbs) in Mtb. We demonstrated that MtbCbs is a heme-less, pyridoxal-5′-phosphate–containing enzyme, allosterically activated by S-adenosylmethionine (SAM). The atomic model of MtbCbs in its native and SAM-bound conformations revealed a unique mode of SAM-dependent allosteric activation. Further, SAM stabilized MtbCbs by sterically occluding proteasomal degradation, which was crucial for supporting methionine and redox metabolism in Mtb. Genetic deficiency of MtbCbs reduced Mtb survival upon homocysteine overload in vitro, inside macrophages, and in mice coinfected with HIV. Thus, the MtbCbs-SAM axis constitutes an important mechanism of coordinating sulfur metabolism in Mtb.

Mycobacterium tuberculosis PknK Substrate Profiling Reveals Essential Transcription Terminator Protein Rho and Two-Component Response Regulators PrrA and MtrA as Novel Targets for Phosphorylation.

ABSTRACTThe Mycobacterium tuberculosis protein kinase K regulates growth adaptation by facilitating mycobacterial survival in response to a variety of in vitro and in vivo stress conditions. Here, we further add that pknK transcription is responsive to carbon and nitrogen starvation signals. The increased survival of an M. tuberculosis ΔpknK mutant strain under carbon- and nitrogen-limiting growth conditions compared to the wild-type (WT) H37Rv suggests an integral role of PknK in regulating growth during metabolic stress. To identify the downstream targets of PknK-mediated signaling, we compared phosphoproteomic and transcription profiles of mycobacterial strains overexpressing WT and phosphorylation-defective PknK. Results implicate PknK as a signaling protein that can regulate several enzymes involved in central metabolism, transcription regulation, and signal transduction. A key finding of this study was the identification of two essential two-component response regulator (RR) proteins, PrrA and MtrA, and Rho transcription terminator, as unique targets for PknK. We confirm that PknK interacts with and phosphorylates PrrA, MtrA, and Rho in vivo. PknK-mediated phosphorylation of MtrA appears to increase binding of the RR to the cognate probe DNA. However, dual phosphorylation of MtrA and PrrA response regulators by PknK and their respective cognate sensor kinases in vitro showed nominal additive effect on the mobility of the protein-DNA complex, suggesting the presence of a potential fine-tuning of the signal transduction pathway which might respond to multiple cues.IMPORTANCE Networks of gene regulation and signaling cascades are fundamental to the pathogenesis of Mycobacterium tuberculosis in adapting to the continuously changing intracellular environment in the host. M. tuberculosis protein kinase K is a transcription regulator that responds to diverse environmental signals and facilitates stress-induced growth adaptation in culture and during infection. This study identifies multiple signaling interactions of PknK and provides evidence that PknK can change the transcriptional landscape during growth transitions by connecting distinctly different signal transduction and regulatory pathways essential for mycobacterial survival.

CD84 is a Suppressor of T and B Cell Activation during Mycobacterium tuberculosis Pathogenesis.

ABSTRACTInterest in host-directed therapies as alternatives/adjuncts to antibiotic treatment has resurged with the increasing prevalence of antibiotic-resistant tuberculosis (TB). Immunotherapies that reinvigorate immune responses by targeting immune checkpoints like PD-1/PD-L1 have proved successful in cancer therapy. Immune cell inhibitory receptors that trigger Mycobacterium tuberculosis-specific immunosuppression, however, are unknown. Here, we show that the levels of CD84, a SLAM family receptor, increase in T and B cells in lung tissues from M. tuberculosis-infected C57BL/6 mice and in peripheral blood mononuclear cells (PBMCs) from pulmonary TB patients. M. tuberculosis challenge experiments using CD84-deficient C57BL/6 mice suggest that CD84 expression likely leads to T and B cell immunosuppression during M. tuberculosis pathogenesis and also plays an inhibitory role in B cell activation. Importantly, CD84-deficient mice showed improved M. tuberculosis clearance and longer survival than M. tuberculosis-infected wild-type (WT) mice. That CD84 is a putative M. tuberculosis infection-specific inhibitory receptor suggests it may be a suitable target for the development of TB-specific checkpoint immunotherapies.IMPORTANCE Immune checkpoint therapies, such as targeting checkpoints like PD-1/PD-L1, have proved successful in cancer therapy and can reinvigorate immune responses. The potential of this approach for treating chronic infectious diseases like TB has been recognized, but a lack of suitable immunotherapeutic targets, i.e., immune cell inhibitory receptors that trigger immunosuppression specifically during Mycobacterium tuberculosis pathogenesis, has limited the application of this strategy in the development of new TB therapies. Our focus in this study was to address this gap and search for an M. tuberculosis-specific checkpoint target. Our results suggest that CD84 is a putative inhibitory receptor that may be a suitable target for the development of TB-specific checkpoint immunotherapies.

Pharmacological and genetic activation of cAMP synthesis disrupts cholesterol utilization in Mycobacterium tuberculosis.

There is a growing appreciation for the idea that bacterial utilization of host-derived lipids, including cholesterol, supports Mycobacterium tuberculosis (Mtb) pathogenesis. This has generated interest in identifying novel antibiotics that can disrupt cholesterol utilization by Mtb in vivo. Here we identify a novel small molecule agonist (V-59) of the Mtb adenylyl cyclase Rv1625c, which stimulates 3’, 5’-cyclic adenosine monophosphate (cAMP) synthesis and inhibits cholesterol utilization by Mtb. Similarly, using a complementary genetic approach that induces bacterial cAMP synthesis independent of Rv1625c, we demonstrate that inducing cAMP synthesis is sufficient to inhibit cholesterol utilization in Mtb. Although the physiological roles of individual adenylyl cyclase enzymes in Mtb are largely unknown, here we demonstrate that the transmembrane region of Rv1625c is required during cholesterol metabolism. Finally, the pharmacokinetic properties of Rv1625c agonists have been optimized, producing an orally-available Rv1625c agonist that impairs Mtb pathogenesis in infected mice. Collectively, this work demonstrates a role for Rv1625c and cAMP signaling in controlling cholesterol metabolism in Mtb and establishes that cAMP signaling can be pharmacologically manipulated for the development of new antibiotic strategies.

Knockdown of the Type-II Fatty acid synthase gene hadC in mycobacterium fortuitum does not affect its growth, biofilm formation, and survival under stress.

Mycobacterial fatty acid synthase Type-II (FAS-II) components are major virulence factors exploited as potential targets for developing novel antimycobacterial drugs. The FAS-II enzyme 3-hydroxyacyl-ACP dehydratase (HadC) is important for biofilm development and pathogenesis of Mycobacterium tuberculosis and other mycobacterial species. Literature review and homology search led to the identification of Mycobacterium fortuitum MFhadC gene. Functional interaction study of MFHadC protein was done using STRING. M. fortuitum MFhadC over-expressing (HS) and knockdown (HA) strains were constructed and validated by expression analysis using quantitative polymerase chain reaction. The strains were analyzed for growth behavior and surface spreading ability. Biofilm formation was assayed through crystal violet assay, viability count, and basic fuchsin staining. In addition, survival of the strains was studied under in vitro nutrient starvation and detergent stress. STRING analysis showed the interaction of HadC with proteins involved in biofilm formation. The strains HS and HA showed spreading ability on the agarose surface, exhibiting translocation patterns similar to the vector control strain. All three strains showed a similar amount of biofilm formation when analyzed using crystal violet assay, viability count, and basic fuchsin staining. The strains showed no deviation in survival when incubated under nutrient starvation and detergent stress. Our results suggest that MFhadC may not be important for the formation and maintenance of biofilm, a factor critically important in M. fortuitum pathogenicity. However, not essential for survival and growth, MFhadC maintains the viability of M. fortuitum under a nutrient-starved environment. Collectively, MFhadC may not be used as a biofilm-specific marker for M. fortuitum.

Changes of lymphocyte subsets in smear-negative pulmonary tuberculosis.

The host immune system plays an important role in the pathogenesis and defense mechanism of Mycobacterium tuberculosis (Mtb). This study aimed to explore the different changes in the immune system between smear-negative pulmonary tuberculosis (PTB) and smear-positive PTB patients. A total of 85 active PTB patients and 50 healthy adults were enrolled. The participants were divided into smear-negative PTB, smear-positive PTB, and control groups. Chest computed tomography (CT) and lymphocyte subgroup counts in peripheral blood were measured in all participants. There were higher numbers of CD4 + T-cells, NK cells, and pulmonary cavities in the smear-positive PTB group, whereas the numbers of B-ells were significantly increased in the smear-negative PTB group. Smear-negative PTB showed fewer pulmonary cavities, mild inflammatory response, lower numbers of immune cells, and higher numbers of B- cells.

HigB1 Toxin in Mycobacterium tuberculosis Is Upregulated During Stress and Required to Establish Infection in Guinea Pigs.

The extraordinary expansion of Toxin Antitoxin (TA) modules in the genome of Mycobacterium tuberculosis has received significant attention over the last few decades. The cumulative evidence suggests that TA systems are activated in response to stress conditions and are essential for M. tuberculosis pathogenesis. In M. tuberculosis, Rv1955-Rv1956-Rv1957 constitutes the only tripartite TAC (Toxin Antitoxin Chaperone) module. In this locus, Rv1955 (HigB1) encodes for the toxin and Rv1956 (HigA1) encodes for antitoxin. Rv1957 encodes for a SecB-like chaperone that regulates HigBA1 toxin antitoxin system by preventing HigA1 degradation. Here, we have investigated the physiological role of HigB1 toxin in stress adaptation and pathogenesis of Mycobacterium tuberculosis. qPCR studies revealed that higBA1 is upregulated in nutrient limiting conditions and upon exposure to levofloxacin. We also show that the promoter activity of higBA1 locus in M. tuberculosis is (p)ppGpp dependent. We observed that HigB1 locus is non-essential for M. tuberculosis growth under different stress conditions in vitro. However, guinea pigs infected with higB1 deletion strain exhibited significantly reduced bacterial loads and pathological damage in comparison to the animals infected with the parental strain. Transcriptome analysis suggested that deletion of higB1 reduced the expression of genes involved in virulence, detoxification and adaptation. The present study describes the role of higB1 toxin in M. tuberculosis physiology and highlights the importance of higBA1 locus during infection in host tissues.

The Role of NRF2 in Mycobacterial Infection.

The incidence of pulmonary nontuberculous mycobacterial (NTM) infection is increasing worldwide, and its clinical outcomes with current chemotherapies are unsatisfactory. The incidence of tuberculosis (TB) is still high in Africa, and the existence of drug-resistant tuberculosis is also an important issue for treatment. To discover and develop new efficacious anti-mycobacterial treatments, it is important to understand the host-defense mechanisms against mycobacterial infection. Nuclear erythroid 2 p45-related factor-2 (NRF2) is known to be a major regulator of various antioxidant response element (ARE)-driven cytoprotective gene expressions, and its protective role has been demonstrated in infections. However, there are not many papers or reviews regarding the role of NRF2 in mycobacterial infectious disease. Therefore, this review focuses on the role of NRF2 in the pathogenesis of Mycobacterium tuberculosis and Mycobacterium avium infection.

Pre-existing mycobacterial infection modulates Candida albicans-driven pyroptosis.

Active tuberculosis patients are at high risk of coinfection with opportunistic fungal pathogen Candida albicans. However, the molecular mechanisms that orchestrate pathogenesis of Mycobacterium tuberculosis (Mtb)-C. albicans coinfection remain elusive. In the current study, we utilize a mouse model to demonstrate that Mtb promotes a macrophage environment that is conducive for C. albicans survival. Mtb-dependent protein kinase Cζ-WNT signalling axis induces expression of an E3 ubiquitin ligase, constitutive photomorphogenesis protein 1 (COP1). A secondary infection of C. albicans in such Mtb-infected macrophages causes COP1 to mediate the proteasomal degradation of interferon regulatory factor 9 (IRF9), a cardinal factor that we identified to arbitrate an inflammatory programmed cell death, pyroptosis. In vivo experiments mimicking a pre-existing Mtb infection demonstrate that inhibition of pyroptosis in mice results in increased C. albicans burden and aberrant lung tissue architecture, leading to increased host mortality. Together, our study reveals the crucial role of pyroptosis regulation for manifesting a successful C. albicans-Mtb coinfection.

Cholesterol-dependent transcriptome remodeling reveals new insight into the contribution of cholesterol to Mycobacterium tuberculosis pathogenesis

Mycobacterium tuberculosis (Mtb) is an obligate human pathogen that can adapt to the various nutrients available during its life cycle. However, in the nutritionally stringent environment of the macrophage phagolysosome, Mtb relies mainly on cholesterol. In previous studies, we demonstrated that Mtb can accumulate and utilize cholesterol as the sole carbon source. However, a growing body of evidence suggests that a lipid-rich environment may have a much broader impact on the pathogenesis of Mtb infection than previously thought. Therefore, we applied high-resolution transcriptome profiling and the construction of various mutants to explore in detail the global effect of cholesterol on the tubercle bacillus metabolism. The results allow re-establishing the complete list of genes potentially involved in cholesterol breakdown. Moreover, we identified the modulatory effect of vitamin B12 on Mtb transcriptome and the novel function of cobalamin in cholesterol metabolite dissipation which explains the probable role of B12 in Mtb virulence. Finally, we demonstrate that a key role of cholesterol in mycobacterial metabolism is not only providing carbon and energy but involves also a transcriptome remodeling program that helps in developing tolerance to the unfavorable host cell environment far before specific stress-inducing phagosomal signals occur.