Not too fat to fight: The emerging role of macrophage fatty acid metabolism in immunity to Mycobacterium tuberculosis

Predictive metabolite signatures for risk of progression to active TB from QuantiFERON supernatants of household contacts of TB patients

The identification of individuals with the greatest risk of progression to active tuberculosis (TB) disease from the huge reservoir of Mycobacterium tuberculosis (Mtb) infected individuals continues to remain an arduous ascent in the global effort to control TB. In a two-year prospective study, we analysed metabolic profiles in the unstimulated and TB antigen stimulated QuantiFERON supernatants of 14 healthy household contacts (HHCs) who progressed to TB disease (Progressors) and 14 HHCs who remained healthy (Non-Progressors). We identified 21 significantly dysregulated metabolites in the TB antigen-stimulated QuantiFERON supernatants of Progressors, of which the combination of Malic acid and N-Arachidonoylglycine had maximum AUC of 0.99. Eighteen significantly dysregulated metabolites were identified in the unstimulated QuantiFERON supernatants of Progressors, among which the combination of Orotic acid and the phosphatidylcholines PC (O-34:1), PC (O-18:1(9Z)/16:0), PC (O-18:1(11Z)/16:0) had the maximum AUC of 0.98. Most of the dysregulated metabolites belonged to the pathways of fatty acid metabolism, lipid metabolism and nitric oxide metabolism. Validation of these metabolic signatures in large, diverse cohorts would pave way for the development of a robust test that can identify individuals at high risk of TB for targetted intervention of TB disease.

Host and bacterial lipid metabolism during tuberculosis infections: possibilities to synergise host- and bacteria-directed therapies

Mycobacterium tuberculosis (Mtb) is the causative pathogen of tuberculosis, the most lethal infectious disease resulting in 1.3 million deaths annually. Treatments against Mtb are increasingly impaired by the growing prevalence of antimicrobial drug resistance, which necessitates the development of new antibiotics or alternative therapeutic approaches. Upon infecting host cells, predominantly macrophages, Mtb becomes critically dependent on lipids as a source of nutrients. Additionally, Mtb produces numerous lipid-based virulence factors that contribute to the pathogen's ability to interfere with the host's immune responses and to create a lipid rich environment for itself. As lipids, lipid metabolism and manipulating host lipid metabolism play an important role for the virulence of Mtb, this review provides a state-of-the-art overview of mycobacterial lipid metabolism and concomitant role of host metabolism and host-pathogen interaction therein. While doing so, we will emphasize unexploited bacteria-directed and host-directed drug targets, and highlight potential synergistic drug combinations that hold promise for the development of new therapeutic interventions.

Host-Pathogen Interaction Interface: Promising Candidate Targets for Vaccine-Induced Protective and Memory Immune Responses

Vaccine formulations are a successful strategy against pathogen transmission because vaccine candidates induce effective and long-lasting memory immune responses (B and CD4+ T cells) at systemic and mucosal sites. Extracellular vesicles of lipoproteins, bioactive compounds from plants and invertebrates (sponges) encapsulated in liposomes, and glycoproteins can target these sites. The vaccine candidates developed can mimic microbial pathogens in a way that successfully links the innate and adaptive immune responses. In addition, vaccines plus adjuvants promote and maintain an inflammatory response. In this review, we aimed to identify the host-pathogen interface as a rich source of candidate targets for vaccine-induced protective and long-lasting memory immune responses.

Cannabinoid receptor type 2 agonist GP1a attenuates macrophage activation induced by M. bovis-BCG by inhibiting NF-κB signaling

Tuberculosis (TB) is one of the leading causes of death worldwide and a major public health problem. Immune evasion mechanisms and antibiotic resistance highlight the need to better understand this disease and explore alternative treatment approaches. Mycobacterial infection modulates the macrophage response and metabolism to persist and proliferate inside the cell. Cannabinoid receptor type 2 (CB2) is expressed mainly in leukocytes and modulates the course of inflammatory diseases. Therefore, our study aimed to evaluate the effects of the CB2-selective agonist GP1a on irradiated Mycobacterium bovis-BCG (iBCG)-induced J774A.1 macrophage activation. We observed increased expression of CB2 in macrophages after iBCG stimulation. The pretreatment with CB2-agonists, GP1a, JWH-133, and GW-833972A (10 µM), reduced iBCG-induced TNF-α and IL-6 release by these cells. Moreover, the CB2-antagonist AM630 (200 nM) treatment confirmed the activity of GP1a on CB2 by scale down its effect on cytokine production. GP1a pretreatment (10 µM) also inhibited the iBCG-induced production of inflammatory mediators as prostaglandin (PG)E2 and nitric oxide by macrophages. Additionally, GP1a pretreatment also reduced the transcription of proinflammatory genes (inos, il1b, and cox2) and genes related to lipid metabolism (dgat1, acat1, plin2, atgl, and cd36). Indeed, lipid droplet accumulation was reduced by GP1a treatment, which was partially blockade by AM630 pretreatment. Finally, GP1a pretreatment reduced the activation of the NF-κB signaling pathway. In conclusion, the activation of CB2 by GP1a modulated the macrophage response to iBCG by reducing inflammatory mediator levels and metabolic reprogramming.

Differential expression of genes associated with lipid import, β-oxidation and lactate oxidation induced by Mycobacterium tuberculosis curli pili in broth culture compared to intracellular bacilli within THP-1 macrophages

Introduction. The adhesin, Mycobacterium tuberculosis curli pili (MTP), assists the pathogen in attachment, invasion and disease progression. Previously, this adhesin was demonstrated to contribute to the pathogen's cell wall functions and fatty acid metabolism and affects total metabolite abundance in central carbon metabolism and fatty acid metabolism of the host. The accumulation/depletion of metabolites is reliant on the gene expression of proteins involved in the import, transport and breakdown of substrates.Gap statement. MTP has not been investigated in relation to genes involved in import/transport/breakdown of substrates.Aim. This study aimed to investigate the possible regulatory role of MTP in modulating metabolic changes of the pathogen in different microenvironments.Methods. Ribonucleic acid was harvested from bacterial broth cultures of adhesin-proficient and adhesin-deficient M. tuberculosis. These strains were also used to infect differentiated THP-1 macrophages for 4 h prior to isolation of intracellular bacteria, RNA extraction and reverse transcription real-time quantitative PCR. The expression levels of selected genes involved in fatty acid transport (lucA, mce1D, mceG, Rv2799, Rv0966c and omamB), β-oxidation (fadA5 and fadB), lactate oxidation (lldD1 and lldD2) and gluconeogenic carbon flow (pckA) were analysed by absolute quantification.Results. The gene expression levels of lucA, mce1D and pckA were significantly lower, and those of Rv2799, Rv0966c, mceG, fadA5 and lldD2 were significantly higher in the adhesin-proficient cultured bacterial strains relative to the Δmtp strain. The intracellular adhesin-proficient bacteria displayed significantly higher gene expression levels of Rv2799 and significantly lower gene expression levels of Rv0966c, fadA5, lldD1 and pckA relative to the Δmtp strain. Interestingly, during early infection, the intracellular Δmtp displayed significantly increased expression of omamB, mceG, fadB, lldD1 and lldD2 relative to the broth culture. This trend was inverted in the WT models.Conclusion. MTP are significantly associated with the regulation of genes involved in lipid transport, β-oxidation and lactate oxidation.

Immunometabolic reprogramming in macrophages infected with active and dormant Cryptococcus neoformans: differential modulation of respiration, glycolysis, and fatty acid utilization

Dormancy is an adaptation in which cells reduce their metabolism, transcription, and translation to stay alive under stressful conditions, preserving the capacity to reactivate once the environment reverts to favorable conditions. Dormancy and reactivation of Cryptococcus neoformans (Cn) are closely linked to intracellular residency within macrophages. Our previous work showed that in vitro murine macrophages rely on the viable but not cultivable (VBNC-a dormancy phenotype) fungus from active Cn, with striking differences in immunometabolic gene expression. Here, we analyzed the influence of VBNC and active Cn on the immunometabolism of infected macrophages, combining metabolic gene expression, mitochondrial membrane potential (ΔΨm), oxygen consumption analysis, and uptake of glucose and fatty acids. The active fungus induced mitochondrial depolarization, and increased glycolysis and mitochondrial oxygen consumption. VBNC infection in bone marrow-derived macrophage (BMDM) caused an attenuated modification in mitochondrial metabolism. However, we found differences in BMDM infected with VBNC vs those infected with active fungus, where VBNC induced an increment in fatty acid uptake in M0 and M1 BMDM, measured by incorporation of BODIPY-palmitate, accompanied by an increase in expression of fatty acid transporters Fabp1 and Fabp4. Overall, distinct fatty acid-related responses induced by VBNC and active Cn suggest different immunomodulatory reactions, depending on the microbial growth stage. We posit that, for VBNC, some of these macrophage metabolic responses reflect the establishment of prolonged microbial intracellular residency and possibly initial stages of granuloma formation.

Advances in Host-Pathogen Interactions in Tuberculosis: Emerging Strategies for Therapeutic Intervention

Tuberculosis (TB) remains one of the most challenging infectious diseases, with Mycobacterium tuberculosis (Mtb) employing sophisticated mechanisms to evade host immunity and establish persistent infections. This review explores recent advances in understanding Mtb's immune evasion strategies; granuloma dynamics; and emerging immunotherapeutic approaches. Key findings highlight the manipulation of host autophagy; metabolic reprogramming; and cytokine pathways by Mtb to sustain its survival within host cells. Insights into granuloma formation reveal the critical role of bacterial lipids; immune modulation; and hypoxia-driven dormancy in maintaining chronic infection. Innovative therapeutic strategies, including host-directed therapies; epigenetic interventions; and immunomodulators, hold promise for improving TB management and combating drug-resistant strains. Despite these advancements, significant challenges remain, including the development of effective vaccines; addressing latent TB; and ensuring equitable access to novel treatments. The integration of advanced technologies such as artificial intelligence and multi-omics approaches, alongside global collaboration, is essential to overcome these hurdles. This review underscores the importance of a multidisciplinary approach to tackling TB, with the ultimate goal of eradicating this global health threat.

Sesamol hinders the proliferation of intracellular bacteria by promoting fatty acid metabolism and decreasing excessive inflammation

The extraintestinal pathogenic Escherichia coli (ExPEC) is a significant zoonotic bacterial pathogen that can cause severe infections and potentially cross-transmit between different hosts. The treatment of clinical bacterial infections is challenging because of the increasingly severe problem of drug resistance. The development of new strategies for managing bacterial infections is essential. Host-acting antibacterial compound (HAC)-based host-directed therapy (HDT) has emerged as a promising approach to combat bacterial infections by targeting host-pathogen interactions and bacterial intracellular survival strategies. In this study, we conducted a cell-based screening to identify compounds that can inhibit the survival and proliferation of ExPEC within host cells. Our screening revealed that sesamol effectively inhibited ExPEC proliferation but had no effect on the natural growth of bacteria. Analysis of the transcriptome data revealed that sesamol has the ability to increase the metabolism of host fatty acids while also suppressing excessive inflammation. Mechanistic studies have shown that sesamol-induced PPAR-β activation is crucial for increased fatty acid metabolism and clearance of intracellular bacteria. Furthermore, sesamol treatment demonstrated protective effects against ExPEC infection in both Galleria mellonella and mouse models, suggesting its potential use for treating diseases caused by intracellular bacterial pathogens and as a lead compound for further development of anti-infection drugs on the basis of the HDT strategy.

Intratumoral microbiota, fatty acid metabolism, and tumor microenvironment constitute an unresolved trinity in colon adenocarcinoma

The intratumoral microbiota, fatty acid metabolism (FAM), and tumor microenvironment (TME) all provide insights into the management of colon adenocarcinoma (COAD). But the biological link among the three remains unclear. Here, we analyzed intratumoral microbiome samples and matched host transcriptome samples from 420 patients with COAD in The Cancer Genome Atlas (TCGA). All patients were divided into two subtypes (FAM_high and FAM_low) based on the Gene set variation analysis (GSVA) score of FAM pathway. Furthermore, we found significant difference in the intratumoral microbiota signatures between the two subtypes. In-depth analysis suggested that specific microbes in tumors may indirectly modify the TME, particularly stromal cell populations, by modulating the FAM process. More importantly, the crosstalk between the three can have a significant impact on prognosis, response to immunotherapy, and drug sensitivity of patients. Pathological image profiling showed that changes in the TME originating from intratumoral microbiota disturbance could be reflected in pathological image features. In summary, our study provides novel insights into the biological links among the intratumoral microbiota, FAM, and the TME in COAD, and offer guidance for the therapeutic opportunities that target intratumoral microbes.

Identification of an Isoxazole Derivative as an Antitubercular Compound for Targeting the FadD Enzymes of Mycobacterium tuberculosis

FadD32, a fatty acyl-AMP ligase, plays an indispensable role in mycobacterial mycolic acid synthesis and is a validated target for tuberculosis (TB) drug development. The crystal structure of Mycobacterium tuberculosis (Mtb)FadD32 has laid the foundation of structure-based drug discovery against this crucial enzyme. Here, we screened the "isoxazole" scaffold containing molecules against MtbFadD32 and identified a compound 2,4-dibromo-6-[3-(trifluoromethyl)-1,2-oxazol-5-yl]phenol (M1) with specific inhibitory activity against Mtb. Kinetics experiments showed that M1 inhibits MtbFadD32 and MtbFadD28 activity. The transcriptomics response of Mtb disclosed M1-mediated regulation of mycobacterial decisive genes involved in cell wall synthesis, consequently creating unfavorable conditions for Mtb survival. Further, M1 curtails the Mtb survival in infected macrophages and reduces Mtb burden and tubercular granulomas in a chronic infection model of BALB/c mice. Our findings provide an effective chemical scaffold to inhibit MtbFadD32 with the potential to inhibit multiple MtbFadD family of enzymes for further development as a promising candidate for treating TB.

Integrated virtual screening and MD simulation study to discover potential inhibitors of mycobacterial electron transfer flavoprotein oxidoreductase

Tuberculosis (TB) continues to be a major global health burden, with high incidence and mortality rates, compounded by the emergence and spread of drug-resistant strains. The limitations of current TB medications and the urgent need for new drugs targeting drug-resistant strains, particularly multidrug-resistant (MDR) and extensively drug-resistant (XDR) TB, underscore the pressing demand for innovative anti-TB drugs that can shorten treatment duration. This has led to a focus on targeting energy metabolism of Mycobacterium tuberculosis (Mtb) as a promising approach for drug discovery. This study focused on repurposing drugs against the crucial mycobacterial protein, electron transfer flavoprotein oxidoreductase (EtfD), integral to utilizing fatty acids and cholesterol as a carbon source during infection. The research adopted an integrative approach, starting with virtual screening of approved drugs from the ZINC20 database against EtfD, followed by molecular docking, and concluding with molecular dynamics (MD) simulations. Diacerein, levonadifloxacin, and gatifloxacin were identified as promising candidates for repurposing against TB based on their strong binding affinity, stability, and interactions with EtfD. ADMET analysis and anti-TB sensitivity predictions assessed their pharmacokinetic and therapeutic potential. Diacerein and levonadifloxacin, previously unexplored in anti-tuberculous therapy, along with gatifloxacin, known for its efficacy in drug-resistant TB, have broad-spectrum antimicrobial properties and favorable pharmacokinetic profiles, suggesting potential as alternatives to current TB treatments, especially against resistant strains. This study underscores the efficacy of computational drug repurposing, highlighting bacterial energy metabolism and lipid catabolism as fruitful targets. Further research is necessary to validate the clinical suitability and efficacy of diacerein, levonadifloxacin, and gatifloxacin, potentially enhancing the arsenal against global TB.

Olink proteomics and lipidomics analysis of serum from patients infected with non-tuberculous mycobacteria and Mycobacterium tuberculosis

BACKGROUND

Non-tuberculous mycobacterial (NTM) and Mycobacterium tuberculosis (MTB) infections are difficult to diagnose and treat, significantly burdening global health. The host immune status is generally believed to be associated with the onset and progression of NTM and MTB infections, but its specific impact remains unclear.

METHODS

In the present study, proteomics and lipidomics analysis of serum from normal controls (n = 26) and patients with MTB (n = 26), rapidly growing NTM (RGM, n = 15), and slowly growing NTM (SGM, n = 21) were conducted using the Olink technique based on a highly sensitive and specific neighborhood extension assay and the lipidomics technique.

RESULTS

IFN-γ, CXCL9, CXCL10, CXCL11, and CXCL13, etc. were simultaneously upregulated in MTB, RGM, and SGM, while lipids FAHFA 22:3, FAHFA 26:4, FAHFA 24:4, FAHFA 20:5, FAHFA 18:2 simultaneously downregulated. IL8, CCL3, CXCL5, and MCP-2, etc. were simultaneously upregulated in RGM and SGM compared to MTB, as well as PCs, LPCs, PEs, and LPEs. Compared with RGM, IL7, CD27, CCL17, CXCL12, and LPC 28:7-SN2 were downregulated in SGM. Pathway analyses revealed that tuberculosis, sphingolipid signaling pathway, and adipocytokine signaling pathway were regulated at the protein level and metabolite level. Diagnostic panels comprising immune-associated proteins and lipids greatly enhance diagnostic specificity and sensitivity.

CONCLUSION

This integrated multi-omics analysis provides a more comprehensive understanding of the molecular landscape of NTM and MTB, which may provide molecular targets for specialized therapies.

Mycobacterium LacI-type Transcription Regulator Rv3575c Affects Host Innate Immunity by Regulating Bacterial mce4 Operon-Mediated Cholesterol Transport

Mycobacterium tuberculosis has evolved a highly specialized system to snatch essential nutrients from its host, among which host-derived cholesterol has been established as one main carbon source for M. tuberculosis to survive within granulomas. The uptake, catabolism, and utilization of cholesterol are important for M. tuberculosis to sustain within the host largely via remodeling of the bacterial cell walls. However, the regulatory mechanism of cholesterol uptake and its impact on bacterium fate within infected hosts remain elusive. Here, we found that M. tuberculosis LacI-type transcription regulator Rv3575c negatively regulates its mce4 family gene transcription. Overexpression of Rv3575c impaired the utilization of cholesterol as the sole carbon source by Mycobacterium smegmatis, activating the host's innate immune response and triggering cell pyroptosis. The M. smegmatis homologue of Rv3575c MSMEG6044 knockout showed enhanced hydrophobicity and permeability of the cell wall and resistance to ethambutol, suppressed the host innate immune response to M. smegmatis, and promoted the survival of M. smegmatis in macrophages and infected mouse lungs, leading to reduced transcriptional levels of TNFα and IL-6. In summary, these data indicate a role of Rv3575c in the pathogenesis of mycobacteria and reveal the key function of Rv3575c in cholesterol transport in mycobacteria.

Arginine methylation and respiratory disease

Arginine methylation, a vital post-translational modification, plays a pivotal role in numerous cellular functions such as signal transduction, DNA damage response and repair, regulation of gene transcription, mRNA splicing, and protein interactions. Central to this modification is the role of protein arginine methyltransferases (PRMTs), which have been increasingly recognized for their involvement in the pathogenesis of various respiratory diseases. This review begins with an exploration of the biochemical underpinnings of arginine methylation, shedding light on the intricate molecular regulatory mechanisms governed by PRMTs. It then delves into the impact of arginine methylation and the dysregulation of arginine methyltransferases in diverse pulmonary disorders. Concluding with a focus on the therapeutic potential and recent advancements in PRMT inhibitors, this article aims to offer novel perspectives and therapeutic avenues for the management and treatment of respiratory diseases.

Crosstalk between macrophages and immunometabolism and their potential roles in tissue repair and regeneration

Immune metabolism is a result of many specific metabolic reactions, such as glycolysis, the tricarboxylic acid (TCA) pathway, the pentose phosphate pathway (PPP), mitochondrial oxidative phosphorylation (OXPHOS), fatty acid oxidation (FAO), fatty acid biosynthesis (FAs) and amino acid pathways, which promote cell proliferation and maintenance with structural and pathological energy to regulate cellular signaling. The metabolism of macrophages produces many metabolic intermediates that play important regulatory roles in tissue repair and regeneration. The metabolic activity of proinflammatory macrophages (M1) mainly depends on glycolysis and the TCA cycle system, but anti-inflammatory macrophages (M2) have intact functions of the TCA cycle, which enhances FAO and is dependent on OXPHOS. However, the metabolic mechanisms of macrophages in tissue repair and regeneration have not been well investigated. Thus, we review how three main metabolic mechanisms of macrophages, glucose metabolism, lipid metabolism, and amino acid metabolism, regulate tissue repair and regeneration.

Epigenetic programming of host lipid metabolism associated with resistance to TST/IGRA conversion after exposure to Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) exposure leads to a range of outcomes including clearance, latent TB infection (LTBI), and pulmonary tuberculosis (TB). Some heavily exposed individuals resist tuberculin skin test (TST) and interferon-gamma (IFNγ) release assay (IGRA) conversion (RSTR), which suggests that they employ IFNγ-independent mechanisms of Mtb control. Here, we compare monocyte epigenetic profiles of RSTR and LTBI from a Ugandan household contact cohort. Chromatin accessibility did not differ between uninfected RSTR and LTBI monocytes. By contrast, methylation significantly differed at 174 CpG sites and across 63 genomic regions. Consistent with previous transcriptional findings in this cohort, differential methylation was enriched in lipid- and cholesterol-associated pathways including the genes APOC3, KCNQ1, and PLA2G3. In addition, methylation was enriched in Hippo signaling, which is associated with cholesterol homeostasis and includes CIT and SHANK2. Lipid export and Hippo signaling pathways were also associated with gene expression in response to Mtb in RSTR as well as IFN stimulation in monocyte-derived macrophages (MDMs) from an independent healthy donor cohort. Moreover, serum-derived high-density lipoprotein from RSTR had elevated ABCA1-mediated cholesterol efflux capacity (CEC) compared to LTBI. Our findings suggest that resistance to TST/IGRA conversion is linked to regulation of lipid accumulation in monocytes, which could facilitate early Mtb clearance among RSTR subjects through IFNγ-independent mechanisms.IMPORTANCETuberculosis (TB) remains an enduring global health challenge with millions of deaths and new cases each year. Despite recent advances in TB treatment, we lack an effective vaccine or a durable cure. While heavy exposure to Mycobacterium tuberculosis often results in latent TB latent infection (LTBI), subpopulations exist that are either resistant to infection or contain Mtb with interferon-gamma (IFNγ)-independent mechanisms not indicative of LTBI. These resisters provide an opportunity to investigate the mechanisms of TB disease and discover novel therapeutic targets. Here, we compare monocyte epigenetic profiles of RSTR and LTBI from a Ugandan household contact cohort. We identify methylation signatures in host lipid and cholesterol pathways with potential relevance to early TB clearance before the sustained IFN responses indicative of LTBI. This adds to a growing body of literature linking TB disease outcomes to host lipids.

Host-pathogen interactions from a metabolic perspective: methods of investigation

Metabolism shapes immune homeostasis in health and disease. This review presents the range of methods that are currently available to investigate the dialog between metabolism and immunity at the systemic, tissue and cellular levels, particularly during infection.

pH-Sensitive Fluorescent Probe in Nanogel Particles as Theragnostic Agent for Imaging and Elimination of Latent Bacterial Cells Residing Inside Macrophages

Rhodamine 6G (R6G) and 4-nitro-2,1,3-benzoxadiazole (NBD) linked through a spacer molecule spermidine (spd), R6G-spd-NBD, produces a fluorescent probe with pH-sensitive FRET (Förster (fluorescence) resonance energy transfer) effect that can be useful in a variety of diagnostic applications. Specifically, cancer cells can be spotted due to a local decrease in pH (Warburg effect). In this research, we applied this approach to intracellular infectious diseases-namely, leishmaniasis, brucellosis, and tuberculosis, difficult to treat because of their localization inside macrophages. R6G-spd-NBD offers an opportunity to detect such bacteria and potentially deliver therapeutic targets to treat them. The nanogel formulation of the R6G-spd-NBD probe (nanoparticles based on chitosan or heparin grafted with lipoic acid residues, Chit-LA and Hep-LA) was obtained to improve the pH sensitivity in the desired pH range (5.5-7.5), providing selective visualization and targeting of bacterial cells, thereby enhancing the capabilities of CLSM (confocal laser scanning microscopy) imaging. According to AFM (atomic force microscopy) data, nanogel particles containing R6G-spd-NBD of compact structure and spherical shape are formed, with a diameter of 70-100 nm. The nanogel formulation of the R6G-spd-NBD further improves absorption and penetration into bacteria, including those located inside macrophages. Due to the negative charge of the bacteria surface, the absorption of positively charged R6G-spd-NBD, and even more so in the chitosan derivatives' nanogel particles, is pronounced. Additionally, with a pH-sensitive R6G-spd-NBD fluorescent probe, the macrophages' lysosomes can be easily distinguished due to their acidic pH environment. CLSM was used to visualize samples of macrophage cells containing absorbed bacteria. The created nanoparticles showed a significant selectivity to model E. coli vs. Lactobacillus bacterial cells, and the R6G-spd-NBD agent, being a mild bactericide, cleared over 50% E.coli in conditions where Lactobacillus remained almost unaffected. Taken together, our data indicate that R6G-spd-NBD, as well as similar compounds, can have value not only for diagnostic, but also for theranostic applications.

Myriocin enhances the clearance of M. tuberculosis by macrophages through the activation of PLIN2

Myriocin is an inhibitor of de novo synthesis of sphingolipids and ceramides. In this research, we showed myriocin could significantly reduce Mtb burden and histopathological inflammation in mice. However, the underlying mechanism remains unclear. RNA-seq analysis revealed a significant increase in gene expression of PLIN2/CD36/CERT1 after myriocin treatment. The reduced bactericidal burden was only reversed after silencing the lipid droplets (LDs) surface protein PLIN2. This suggests that myriocin enhances the ability of macrophages to clear Mtb depending on the PLIN2 gene, which is part of the PPARγ pathway. Indeed, we observed a significant increase in the number of LDs following myriocin treatment.IMPORTANCEMycobacterium tuberculosis has the ability to reprogram host cell lipid metabolism and alter the antimicrobial functions of infected macrophages. The sphingolipids, such as ceramides, are the primary host lipids utilized by the bacteria, making the sphingomyelinase/ceramide system critical in Mtb infections. Surprisingly, the antimicrobial effect of myriocin was found to be independent of its role in reducing ceramides, but instead, it depends on the lipid droplets surface protein PLIN2. Our findings provide a novel mechanism for how myriocin enhances Mtb clearance in macrophages.

Macrophage polarization and its impact on idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a lung disease that worsens over time, causing fibrosis in the lungs and ultimately resulting in respiratory failure and a high risk of death. Macrophages play a crucial role in the immune system, showing flexibility by transforming into either pro-inflammatory (M1) or anti-inflammatory (M2) macrophages when exposed to different stimuli, ultimately impacting the development of IPF. Recent research has indicated that the polarization of macrophages is crucial in the onset and progression of IPF. M1 macrophages secrete inflammatory cytokines and agents causing early lung damage and fibrosis, while M2 macrophages support tissue healing and fibrosis by releasing anti-inflammatory cytokines. Developing novel treatments for IPF relies on a thorough comprehension of the processes involved in macrophage polarization in IPF. The review outlines the regulation of macrophage polarization and its impact on the development of IPF, with the goal of investigating the possible therapeutic benefits of macrophage polarization in the advancement of IPF.

Protein-energy restriction-induced lipid metabolism disruption causes stable-to-progressive disease shift in Mycobacterium avium-infected female mice

BACKGROUND

Disease susceptibility and progression of Mycobacterium avium complex pulmonary disease (MAC-PD) is associated with multiple factors, including low body mass index (BMI). However, the specific impact of low BMI on MAC-PD progression remains poorly understood. This study aims to examine the progression of MAC-PD in the context of low BMI, utilising a disease-resistant mouse model.

METHODS

We employed a MAC infection-resistant female A/J mouse model to compare the progression of MAC-PD under two dietary conditions: one group was fed a standard protein diet, representing protein-energy unrestricted conditions, and the other was fed a low protein diet (LPD), representing protein-energy restriction.

FINDINGS

Our results reveal that protein-energy restriction significantly exacerbates MAC-PD progression by disrupting lipid metabolism. Mice fed an LPD showed elevated fatty acid levels and related gene expressions in lung tissues, similar to findings of increased fatty acids in the serum of patients who exhibited the MAC-PD progression. These mice also exhibited increased CD36 expression and lipid accumulation in macrophages upon MAC infection. In vitro experiments emphasised the crucial role of CD36-mediated palmitic acid uptake in bacterial proliferation. Importantly, in vivo studies demonstrated that administering anti-CD36 antibody to LPD-fed A/J mice reduced macrophage lipid accumulation and impeded bacterial growth, resulting in remarkable slowing disease progression.

INTERPRETATION

Our findings indicate that the metabolic status of host immune cells critically influences MAC-PD progression. This study highlights the potential of adequate nutrient intake in preventing MAC-PD progression, suggesting that targeting CD36-mediated pathways might be a host-directed therapeutic strategy to managing MAC infection.

FUNDING

This research was funded by the National Research Foundation of Korea, the Korea Research Institute of Bioscience and Biotechnology, and the Korea National Institute of Health.

The impact of Mycobacterium tuberculosis on the macrophage cholesterol metabolism pathway

Mycobacterium tuberculosis (Mtb) is an intracellular pathogen capable of adapting and surviving within macrophages, utilizing host nutrients for its growth and replication. Cholesterol is the main carbon source during the infection process of Mtb. Cholesterol metabolism in macrophages is tightly associated with cell functions such as phagocytosis of pathogens, antigen presentation, inflammatory responses, and tissue repair. Research has shown that Mtb infection increases the uptake of low-density lipoprotein (LDL) and cholesterol by macrophages, and enhances de novo cholesterol synthesis in macrophages. Excessive cholesterol is converted into cholesterol esters, while the degradation of cholesterol esters in macrophages is inhibited by Mtb. Furthermore, Mtb infection suppresses the expression of ATP-binding cassette (ABC) transporters in macrophages, impeding cholesterol efflux. These alterations result in the massive accumulation of cholesterol in macrophages, promoting the formation of lipid droplets and foam cells, which ultimately facilitates the persistent survival of Mtb and the progression of tuberculosis (TB), including granuloma formation, tissue cavitation, and systemic dissemination. Mtb infection may also promote the conversion of cholesterol into oxidized cholesterol within macrophages, with the oxidized cholesterol exhibiting anti-Mtb activity. Recent drug development has discovered that reducing cholesterol levels in macrophages can inhibit the invasion of Mtb into macrophages and increase the permeability of anti-tuberculosis drugs. The development of drugs targeting cholesterol metabolic pathways in macrophages, as well as the modification of existing drugs, holds promise for the development of more efficient anti-tuberculosis medications.

MicroRNA-144-3p Inhibits Host Lipid Catabolism and Autophagy by Targeting PPARα and ABCA1 During Mycobacterium Tuberculosis Infection

MicroRNA-mediated metabolic reprogramming recently has been identified as an important strategy for Mycobacterium tuberculosis (Mtb) to evade host immune responses. However, it is unknown what role microRNA-144-3p (miR-144-3p) plays in cellular metabolism during Mtb infection. Here, we report the meaning of miR-144-3p-mediated lipid accumulation for Mtb-macrophage interplay. Mtb infection was shown to upregulate the expression of miR-144-3p in macrophages. By targeting peroxisome proliferator-activated receptor α (PPARα) and ATP-binding cassette transporter A1 (ABCA1), miR-144-3p overexpression promoted lipid accumulation and bacterial survival in Mtb-infected macrophages, while miR-144-3p inhibition had the opposite effect. Furthermore, reprogramming of host lipid metabolism by miR-144-3p suppressed autophagy in response to Mtb infection. Our findings uncover that miR-144-3p regulates host metabolism and immune responses to Mtb by targeting PPARα and ABCA1, suggesting a potential host-directed tuberculosis therapy by targeting the interface of miRNA and lipid metabolism.

Multi-omics analysis reveals that linoleic acid metabolism is associated with variations of trained immunity induced by distinct BCG strains

Trained immunity is one of the mechanisms by which BCG vaccination confers persistent nonspecific protection against diverse diseases. Genomic differences between the different BCG vaccine strains that are in global use could result in variable protection against tuberculosis and therapeutic effects on bladder cancer. In this study, we found that four representative BCG strains (BCG-Russia, BCG-Sweden, BCG-China, and BCG-Pasteur) covering all four genetic clusters differed in their ability to induce trained immunity and nonspecific protection. The trained immunity induced by BCG was associated with the Akt-mTOR-HIF1α axis, glycolysis, and NOD-like receptor signaling pathway. Multi-omics analysis (epigenomics, transcriptomics, and metabolomics) showed that linoleic acid metabolism was correlated with the trained immunity-inducing capacity of different BCG strains. Linoleic acid participated in the induction of trained immunity and could act as adjuvants to enhance BCG-induced trained immunity, revealing a trained immunity-inducing signaling pathway that could be used in the adjuvant development.

Triggering Receptor Expressed on Myeloid Cells 2 Mediates the Involvement of M2-Type Macrophages in Pulmonary Tuberculosis Infection

Background

Macrophage play a significant work in the development of tuberculosis. This study aims to investigate the relationship between TREM2 and macrophage polarization, as well as the related cytokines.

Methods

This study involved 43 pulmonary tuberculosis patients and 37 healthy controls. Enzyme-linked immunosorbent assay (ELISA) was used to detect the expression levels of M1/M2 macrophage-related cytokines IL-10 and IL-12 in the peripheral blood of pulmonary tuberculosis patients. The relative mRNA expression levels of TREM2, IL-10 and IL-12 were detected using quantitative real-time PCR (qRT-PCR). Additionally, Spearman rank correlation analysis was used to preliminarily assess the correlation between TREM2 and M1 / M2 macrophages. Hematoxylin-eosin (HE) staining was performed to observe the pathological manifestations of pulmonary tuberculosis lesions. Immunohistochemical (IHC) staining was used to observe the localization of the macrophage-specific molecule CD68, the M1 specific molecule iNOS, the M2 specific molecule CD163, and TREM2.

Results

The lesions of pulmonary tuberculosis patients showed Langhans multinucleated macrophages and tuberculous granulomas. The ELISA results indicated that the expression levels of IL-10 and IL-12 were significantly increased in peripheral blood of pulmonary tuberculosis patients. Additionally, the relative mRNA expression levels of TREM2, IL-10 and IL-12 were also significantly higher in the pulmonary tuberculosis group. Furthermore, a positive correlation was observed between TREM2 and IL-10, which are secreted by M2 macrophages. IHC revealed significant positivity of TREM2 and macrophage-related markers in tuberculous granuloma. Specifically, TREM2 and M2 macrophage marker CD163 were significantly expressed in the cytoplasm and membrane of Langhans multinucleated macrophages.

Conclusion

The role of macrophage polarization in pulmonary tuberculosis is significant, and further investigation is needed to understand relationship between TREM2 and M2 macrophages.

Epigenetic programming of host lipid metabolism associates with resistance to TST/IGRA conversion after exposure to Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) exposure leads to a range of outcomes including clearance, latent TB infection (LTBI), and pulmonary tuberculosis (TB). Some heavily exposed individuals resist tuberculin skin test (TST) and interferon gamma release assay (IGRA) conversion (RSTR), which suggests that they employ IFNγ-independent mechanisms of Mtb control. Here, we compare monocyte epigenetic profiles of RSTR and LTBI from a Ugandan household contact cohort. Chromatin accessibility did not differ between uninfected RSTR and LTBI monocytes. In contrast, methylation significantly differed at 174 CpG sites and across 63 genomic regions. Consistent with previous transcriptional findings in this cohort, differential methylation was enriched in lipid and cholesterol associated pathways including in the genes APOC3, KCNQ1, and PLA2G3. In addition, methylation was enriched in Hippo signaling, which is associated with cholesterol homeostasis and includes CIT and SHANK2. Lipid export and Hippo signaling pathways were also associated with gene expression in response to Mtb in RSTR as well as IFN stimulation in monocyte-derived macrophages (MDMs) from an independent healthy donor cohort. Moreover, serum-derived HDL from RSTR had elevated ABCA1-mediated cholesterol efflux capacity (CEC) compared to LTBI. Our findings suggest that resistance to TST/IGRA conversion is linked to regulation of lipid accumulation in monocytes, which could facilitate early Mtb clearance among RSTR subjects through IFNγ-independent mechanisms.

Lipid droplets in pathogen infection and host immunity

As the hub of cellular lipid metabolism, lipid droplets (LDs) have been linked to a variety of biological processes. During pathogen infection, the biogenesis, composition, and functions of LDs are tightly regulated. The accumulation of LDs has been described as a hallmark of pathogen infection and is thought to be driven by pathogens for their own benefit. Recent studies have revealed that LDs and their subsequent lipid mediators contribute to effective immunological responses to pathogen infection by promoting host stress tolerance and reducing toxicity. In this comprehensive review, we delve into the intricate roles of LDs in governing the replication and assembly of a wide spectrum of pathogens within host cells. We also discuss the regulatory function of LDs in host immunity and highlight the potential for targeting LDs for the diagnosis and treatment of infectious diseases.

Tuberculosis and lung cancer: metabolic pathways play a key role

Despite the fact that some cases of tuberculosis (TB) are undiagnosed and untreated, it remains a serious global public health issue. In the diagnosis, treatment, and control of latent and active TB, there may be a lack of effectiveness. An understanding of metabolic pathways can be fundamental to treat latent TB infection and active TB disease. Rather than targeting Mycobacterium tuberculosis, the control strategies aim to strengthen host responses to infection and reduce chronic inflammation by effectively enhancing host resistance to infection. The pathogenesis and progression of TB are linked to several metabolites and metabolic pathways, and they are potential targets for host-directed therapies. Additionally, metabolic pathways can contribute to the progression of lung cancer in patients with latent or active TB. A comprehensive metabolic pathway analysis is conducted to highlight lung cancer development in latent and active TB. The current study aimed to emphasize the association between metabolic pathways of tumor development in patients with latent and active TB. Health control programs around the world are compromised by TB and lung cancer due to their special epidemiological and clinical characteristics. Therefore, presenting the importance of lung cancer progression through metabolic pathways occurring upon TB infection can open new doors to improving control of TB infection and active TB disease while stressing that further evaluations are required to uncover this correlation.

Cholesterol-Mediated Coenzyme A Depletion in Catabolic Mutants of Mycobacteria Leads to Toxicity

Cholesterol is a critical growth substrate for Mycobacterium tuberculosis (Mtb) during infection, and the cholesterol catabolic pathway has been targeted for the development of new antimycobacterial agents. A key metabolite in cholesterol catabolism is 3aα-H-4α(3'-propanoate)-7aβ-methylhexahydro-1,5-indanedione (HIP). Many of the HIP metabolites are acyl-coenzyme A (CoA) thioesters, whose accumulation in deletion mutants can cause cholesterol-mediated toxicity. We used LC-MS/MS analysis to demonstrate that deletion of genes involved in HIP catabolism leads to acyl-CoA accumulation with concomitant depletion of free CoASH, leading to dysregulation of central metabolic pathways. CoASH and acyl-CoAs inhibited PanK, the enzyme that catalyzes the first step in the transformation of pantothenate to CoASH. Inhibition was competitive with respect to ATP with Kic values ranging from 9 μM for CoASH to 57 μM for small acyl-CoAs and 180 ± 30 μM for cholesterol-derived acyl-CoA. These findings link two critical metabolic pathways and suggest that therapeutics targeting cholesterol catabolic enzymes could both prevent the utilization of an important growth substrate and simultaneously sequester CoA from essential cellular processes, leading to bacterial toxicity.

Association between fatty acid metabolism gene mutations and Mycobacterium tuberculosis transmission revealed by whole genome sequencing

BACKGROUND

Fatty acid metabolism greatly promotes the virulence and pathogenicity of Mycobacterium tuberculosis (M.tb). However, the regulatory mechanism of fatty acid metabolism in M.tb remains to be elucidated, and limited evidence about the effects of gene mutations in fatty acid metabolism on the transmission of M.tb was reported.

RESULTS

Overall, a total of 3193 M.tb isolates were included in the study, of which 1596 (50%) were genomic clustered isolates. Most of the tuberculosis isolates belonged to lineage2(n = 2744,85.93%), followed by lineage4(n = 439,13.75%) and lineage3(n = 10,0.31%).Regression results showed that the mutations of gca (136,605, 317G > C, Arg106Pro; OR, 22.144; 95% CI, 2.591-189.272), ogt(1,477,346, 286G > C ,Gly96Arg; OR, 3.893; 95%CI, 1.432-10.583), and rpsA (1,834,776, 1235 C > T, Ala412Val; OR, 3.674; 95% CI, 1.217-11.091) were significantly associated with clustering; mutations in gca and rpsA were also significantly associated with clustering of lineage2. Mutation in arsA(3,001,498, 885 C > G, Thr295Thr; OR, 6.278; 95% CI, 2.508-15.711) was significantly associated with cross-regional clusters. We also found that 20 mutation sites were positively correlated with cluster size, while 11 fatty acid mutation sites were negatively correlated with cluster size.

CONCLUSION

Our research results suggested that mutations in genes related to fatty acid metabolism were related to the transmission of M.tb. This research could help in the future control of the transmission of M.tb.

The oxidation of steroid derivatives by the CYP125A6 and CYP125A7 enzymes from Mycobacterium marinum

The members of the bacterial cytochrome P450 (CYP) monooxygenase family CYP125, catalyze the oxidation of steroid derivatives including cholesterol and phytosterols, as the initial activating step in their catabolism. However, several bacterial species contain multiple genes encoding CYP125 enzymes and other CYP enzymes which catalyze cholesterol/cholest-4-en-3-one hydroxylation. An important question is why these bacterium have more than one enzyme with overlapping substrate ranges capable of catalyzing the terminal oxidation of the alkyl chain of these sterols. To further understand the role of these enzymes we investigated CYP125A6 and CYP125A7 from Mycobacterium marinum with various cholesterol analogues. These have modifications on the A and B rings of the steroid and we assessed the substrate binding and catalytic activity of these with each enzyme. CYP125A7 gave similar results to those reported for the CYP125A1 enzyme from M. tuberculosis. Differences in the substrate binding and catalytic activity with the cholesterol analogues were observed with CYP125A6. For example, while cholesteryl sulfate could bind to both enzymes it was only oxidized by CYP125A6 and not by CYP125A7. CYP125A6 generated higher levels of metabolites with the majority of C-3 and C-7 substituted cholesterol analogues such 7-ketocholesterol. However, 5α-cholestan-3β-ol was only oxidized by CYP125A7 enzyme. The cholest-4-en-3-one and 7-ketocholesterol-bound forms of the CYP125A6 and CYP125A7 enzymes were modelled using AlphaFold. The structural models highlighted differences in the binding modes of the steroid derivatives within the same enzyme. Significant changes in the binding mode of the steroids between these CYP125 enzymes and other bacterial cholesterol oxidizing enzymes, CYP142A3 and CYP124A1, were also seen. Despite this, all these models predicted the selectivity for terminal methyl hydroxylation, in agreement with the experimental data.

Early innate cell interactions with Mycobacterium tuberculosis in protection and pathology of tuberculosis

Tuberculosis (TB) remains a significant global health challenge, claiming the lives of up to 1.5 million individuals annually. TB is caused by the human pathogen Mycobacterium tuberculosis (Mtb), which primarily infects innate immune cells in the lungs. These immune cells play a critical role in the host defense against Mtb infection, influencing the inflammatory environment in the lungs, and facilitating the development of adaptive immunity. However, Mtb exploits and manipulates innate immune cells, using them as favorable niche for replication. Unfortunately, our understanding of the early interactions between Mtb and innate effector cells remains limited. This review underscores the interactions between Mtb and various innate immune cells, such as macrophages, dendritic cells, granulocytes, NK cells, innate lymphocytes-iNKT and ILCs. In addition, the contribution of alveolar epithelial cell and endothelial cells that constitutes the mucosal barrier in TB immunity will be discussed. Gaining insights into the early cellular basis of immune reactions to Mtb infection is crucial for our understanding of Mtb resistance and disease tolerance mechanisms. We argue that a better understanding of the early host-pathogen interactions could inform on future vaccination approaches and devise intervention strategies.

Biomimetic System Based on Reconstituted Macrophage Membranes for Analyzing and Selection of Higher-Affinity Ligands Specific to Mannose Receptor to Develop the Macrophage-Focused Medicines

Progress in macrophage research is crucial for numerous applications in medicine, including cancer and infectious diseases. However, the existing methods to manipulate living macrophages are labor-intense and inconvenient. Here, we show that macrophage membranes can be reconstituted after storage for months at 4 °C, with their CD206 receptor selectivity and specificity being similar to those in the living cells. Then, we have developed a mannose ligand, specific to CD206, linked with PEG as an IR spectroscopy marker to detect binding with the macrophage receptor. PEG was selected due to its unique adsorption band of the C-O-C group at IR spectra, which does not overlap with other biomolecules' spectroscopic feature. Next, competitive binding assay versus the PEG-bound ligand has enabled the selection of other higher-affinity ligands specific to CD206. Furthermore, those higher-affinity ligands were used to differentiate activated macrophages in a patient's bronchoalveolar (BAL) or nasopharyngeal (NPL) lavage. CD206- control cells (HEK293T) showed only non-specific binding. Therefore, biochips based on reconstituted macrophage membranes as well as PEG-trimannoside as an IR spectroscopic marker can be used to develop new methods facilitating macrophage research and macrophage-focused drug discovery.

Cell lipid biology in infections: an overview

Lipids are a big family of molecules with a vast number of functions in the cell membranes, within the cytoplasm, and extracellularly. Lipid droplets (LDs) are the most common storage organelles and are present in almost every tissue type in the body. They also have structural functions serving as building blocks of cellular membranes and may be precursors of other molecules such as hormones, and lipoproteins, and as messengers in signal transduction. Fatty acids (FAs), such as sterol esters and triacylglycerols, are stored in LDs and are used in β-oxidation as fuel for tricarboxylic acid cycle (TCA) and adenosine triphosphate (ATP) generation. FA uptake and entrance in the cytoplasm are mediated by membrane receptors. After a cytoplasmic round of α- and β-oxidation, FAs are guided into the mitochondrial matrix by the L-carnitine shuttle system, where they are fully metabolized, and enter the TCA cycle. Pathogen infections may lead to impaired lipid metabolism, usage of membrane phospholipids, and LD accumulation in the cytoplasm of infected cells. Otherwise, bacterial pathogens may use lipid metabolism as a carbon source, thus altering the reactions and leading to cellular and organelles malfunctioning. This review aims to describe cellular lipid metabolism and alterations that occur upon infections.

Defensive-lipid droplets: Cellular organelles designed for antimicrobial immunity

Microbes have developed many strategies to subvert host organisms, which, in turn, evolved several innate immune responses. As major lipid storage organelles of eukaryotes, lipid droplets (LDs) are an attractive source of nutrients for invaders. Intracellular viruses, bacteria, and protozoan parasites induce and physically interact with LDs, and the current view is that they "hijack" LDs to draw on substrates for host colonization. This dogma has been challenged by the recent demonstration that LDs are endowed with a protein-mediated antibiotic activity, which is upregulated in response to danger signals and sepsis. Dependence on host nutrients could be a generic "Achilles' heel" of intracellular pathogens and LDs a suitable chokepoint harnessed by innate immunity to organize a front-line defense. Here, we will provide a brief overview of the state of the conflict and discuss potential mechanisms driving the formation of the 'defensive-LDs' functioning as hubs of innate immunity.

Deciphering the biosynthesis of a novel lipid in Mycobacterium tuberculosis expands the known roles of the nitroreductase superfamily

Mycobacterium tuberculosis's (Mtb) success as a pathogen is due in part to its sophisticated lipid metabolic programs, both catabolic and biosynthetic. Several of Mtb lipids have specific roles in pathogenesis, but the identity and roles of many are unknown. Here, we demonstrated that the tyz gene cluster in Mtb, previously implicated in resistance to oxidative stress and survival in macrophages, encodes the biosynthesis of acyl-oxazolones. Heterologous expression of tyzA (Rv2336), tyzB (Rv2338c) and tyzC (Rv2337c) resulted in the biosynthesis of C12:0-tyrazolone as the predominant compound, and the C12:0-tyrazolone was identified in Mtb lipid extracts. TyzA catalyzed the N-acylation of l-amino acids, with highest specificity for l-Tyr and l-Phe and lauroyl-CoA (kcat/KM = 5.9 ± 0.8 × 103 M-1s-1). In cell extracts, TyzC, a flavin-dependent oxidase (FDO) of the nitroreductase (NTR) superfamily, catalyzed the O2-dependent desaturation of the N-acyl-L-Tyr produced by TyzA, while TyzB, a ThiF homolog, catalyzed its ATP-dependent cyclization. The substrate preference of TyzB and TyzC appear to determine the identity of the acyl-oxazolone. Phylogenetic analyses revealed that the NTR superfamily includes a large number of broadly distributed FDOs, including five in Mtb that likely catalyze the desaturation of lipid species. Finally, TCA1, a molecule with activity against drug-resistant and persistent tuberculosis, failed to inhibit the cyclization activity of TyzB, the proposed secondary target of TCA1. Overall, this study identifies a novel class of Mtb lipids, clarifies the role of a potential drug target, and expands our understanding of the NTR superfamily.

Characteristics of Mycobacterium tuberculosis PtpA interaction and activity on the alpha subunit of human mitochondrial trifunctional protein, a key enzyme of lipid metabolism

During Mycobacterium tuberculosis (Mtb) infection, the virulence factor PtpA belonging to the protein tyrosine phosphatase family is delivered into the cytosol of the macrophage. PtpA interacts with numerous eukaryotic proteins modulating phagosome maturation, innate immune response, apoptosis, and potentially host-lipid metabolism, as previously reported by our group. In vitro, the human trifunctional protein enzyme (hTFP) is a bona fide PtpA substrate, a key enzyme of mitochondrial β-oxidation of long-chain fatty acids, containing two alpha and two beta subunits arranged in a tetramer structure. Interestingly, it has been described that the alpha subunit of hTFP (ECHA, hTFPα) is no longer detected in mitochondria during macrophage infection with the virulent Mtb H37Rv. To better understand if PtpA could be the bacterial factor responsible for this effect, in the present work, we studied in-depth the PtpA activity and interaction with hTFP_α. With this aim, we performed docking and in vitro dephosphorylation assays defining the P-Tyr-271 as the potential target of mycobacterial PtpA, a residue located in the helix-10 of hTFP_α, previously described as relevant for its mitochondrial membrane localization and activity. Phylogenetic analysis showed that Tyr-271 is absent in TFP_α of bacteria and is present in more complex eukaryotic organisms. These results suggest that this residue is a specific PtpA target, and its phosphorylation state is a way of regulating its subcellular localization. We also showed that phosphorylation of Tyr-271 can be catalyzed by Jak kinase. In addition, we found by molecular dynamics that PtpA and hTFP_α form a stable protein complex through the PtpA active site, and we determined the dissociation equilibrium constant. Finally, a detailed study of PtpA interaction with ubiquitin, a reported PtpA activator, showed that additional factors are required to explain a ubiquitin-mediated activation of PtpA. Altogether, our results provide further evidence supporting that PtpA could be the bacterial factor that dephosphorylates hTFP_α during infection, potentially affecting its mitochondrial localization or β-oxidation activity.

The markers and risk stratification model of intracranial aneurysm instability in a large Chinese cohort

Intracranial aneurysm is the leading cause of nontraumatic subarachnoid hemorrhage. Evaluating the unstable (rupture and growth) risk of aneurysms is helpful to guild decision-making for unruptured intracranial aneurysms (UIA). This study aimed to develop a model for risk stratification of UIA instability. The UIA patients from two prospective, longitudinal multicenter Chinese cohorts recruited from January 2017 to January 2022 were set as the derivation cohort and validation cohort. The primary endpoint was UIA instability, comprising aneurysm rupture, growth, or morphology change, during a 2-year follow-up. Intracranial aneurysm samples and corresponding serums from 20 patients were also collected. Metabolomics and cytokine profiling analysis were performed on the derivation cohort (758 single-UIA patients harboring 676 stable UIAs and 82 unstable UIAs). Oleic acid (OA), arachidonic acid (AA), interleukin 1β (IL-1β), and tumor necrosis factor-α (TNF-α) were significantly dysregulated between stable and unstable UIAs. OA and AA exhibited the same dysregulated trends in serums and aneurysm tissues. The feature selection process demonstrated size ratio, irregular shape, OA, AA, IL-1β, and TNF-α as features of UIA instability. A machine-learning stratification model (instability classifier) was constructed based on radiological features and biomarkers, with high accuracy to evaluate UIA instability risk (area under curve (AUC), 0.94). Within the validation cohort (492 single-UIA patients harboring 414 stable UIAs and 78 unstable UIAs), the instability classifier performed well to evaluate the risk of UIA instability (AUC, 0.89). Supplementation of OA and pharmacological inhibition of IL-1β and TNF-α could prevent intracranial aneurysms from rupturing in rat models. This study revealed the markers of UIA instability and provided a risk stratification model, which may guide treatment decision-making for UIAs.

The oxidation of cholesterol derivatives by the CYP124 and CYP142 enzymes from Mycobacterium marinum

The CYP124 and CYP142 families of bacterial cytochrome P450 monooxygenases (CYPs), catalyze the oxidation of methyl branched lipids, including cholesterol, as one of the initial activating steps in their catabolism. Both enzymes are reported to supplement the CYP125 family of P450 enzymes. These CYP125 enzymes are found in the same bacteria, and are the primary cholesterol/cholest-4-en-3-one metabolizing enzymes. To further understand the role of the CYP124 and CYP142 cytochrome P450s we investigated the Mycobacterium marinum enzymes, MmarCYP124A1 and CYP142A3, with various cholesterol analogues with modifications on the A and B rings of the steroid. We assessed the substrate binding and catalytic activity of each enzyme. Neither enzyme could bind or oxidize cholesteryl acetate or 3,5-cholestadiene, which have modifications at the C3 hydroxyl moiety of cholesterol. The CYP142 enzyme was better able to accommodate and oxidize cholesterol analogues which have changes on the A/B rings including cholesterol-5α,6α-epoxide and diastereomers of 5-cholestan-3-ol. The CYP124 enzyme was more tolerant of changes at C7 of the cholesterol B ring, e.g., 7-ketocholesterol than in the A ring. The selectivity for oxidation at the ω-carbon of a branched chain was observed in all steroids that were oxidized. The 7-ketocholesterol-bound MmarCYP124A1 enzyme from M. marinum, was structurally characterized by X-ray crystallography to 1.81Å resolution. The 7-ketocholesterol-bound X-ray crystal structure of the MmarCYP124A1 enzyme revealed that the substrate binding mode of this cholesterol derivative was altered compared to those observed with other non-steroidal ligands. The structure provided an explanation for the selectivity of the enzyme for terminal methyl hydroxylation.

Comparative serum lipid and immunohematological values among adult pulmonary tuberculosis and tuberculosis lymphadenitis cases and their association with sputum bacilli load and time to culture positivity in Northwestern Ethiopia

BACKGROUND

The serum lipid and immunohematological values of tuberculosis lymphadenitis (TBLN) patients is poorly documented relative to pulmonary tuberculosis (PTB) cases. Therefore, the aim of this study was to investigate the serum lipid and immunohematological values of patients with TBLN in comparison with PTB (PTB) patients.

METHODS

An institution-based comparative cross-sectional study was conducted in Northwest Ethiopia from March to December 2021. The study participants were bacteriologically confirmed PTB (n = 82) and TBLN (n = 94) cases with no known comorbidity and whose ages was greater than 18 years and with no current pregnancy. Independent sample t-test, one-way ANOVA, box plot, and correlation matrix were used to analyze the data.

RESULTS

The body mass index (BMI), CD4 + T cell count, and high-density lipoprotein-Cholesterol (HDL-C) values were significantly higher among TBLN cases compared with PTB cases. Additionally, the total white blood cell (WBC) count, hemoglobin (Hb), total Cholesterol (CHO) and creatinine (Cr) values were relatively higher among TBLN than PTB (P > 0.05). On the reverse, the platelet count and triacylglycerol (TAG) values were relatively higher among PTB than in TBLN cases. While the mean days of culture positivity were 11.6 days for TBLN, the mean days of culture positivity were 14.0 days for PTB. Anemia and serum lipid values showed no correlation with sputum bacilli load and time to culture positivity.

CONCLUSION

Tuberculous lymphadenitis patients were well-endowed with serum lipid, immunological and nutritional status compared with PTB cases. Hence, the high incidence rate of TBLN in Ethiopia could not be explained by low peripheral immunohematological values, malnutrition, Anemia, and dyslipidemia. Further study for identifying the predictors for TBLN in Ethiopia is highly desirable.

The role of immunometabolism in macrophage polarization and its impact on acute lung injury/acute respiratory distress syndrome

Lung macrophages constitute the first line of defense against airborne particles and microbes and are key to maintaining pulmonary immune homeostasis. There is increasing evidence suggesting that macrophages also participate in the pathogenesis of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), including the modulation of inflammatory responses and the repair of damaged lung tissues. The diversity of their functions may be attributed to their polarized states. Classically activated or inflammatory (M1) macrophages and alternatively activated or anti-inflammatory (M2) macrophages are the two main polarized macrophage phenotypes. The precise regulatory mechanism of macrophage polarization is a complex process that is not completely understood. A growing body of literature on immunometabolism has demonstrated the essential role of immunometabolism and its metabolic intermediates in macrophage polarization. In this review, we summarize macrophage polarization phenotypes, the role of immunometabolism, and its metabolic intermediates in macrophage polarization and ALI/ARDS, which may represent a new target and therapeutic direction.

Click-chemistry-based protocol to quantitatively assess fatty acid uptake by Mycobacterium tuberculosis in axenic culture and inside mouse macrophages

Mycobacterium tuberculosis (Mtb) hijacks host-derived fatty acids (FAs) to sustain its intracellular growth inside host cells. Here, we present a click-chemistry-based protocol to assess FA import by Mtb in axenic culture or inside mouse macrophages. We describe the use of alkyne analogs of natural FAs as an alternative to structurally altered fluorescent derivatives or hazardous radiolabeled FAs. We also detail quantitative analyses of FA uptake at single bacterial or host cell level by flow cytometry and confocal fluorescence microscopy. For complete details on the use and execution of this protocol, please refer to Laval et al. (2021).1.

Exploration of Lipid Metabolism Alterations in Children with Active Tuberculosis Using UHPLC-MS/MS

Metabolic profiling using nonsputum samples has demonstrated excellent performance in diagnosing infectious diseases. But little is known about the lipid metabolism alternation in children with tuberculosis (TB). Therefore, the study was performed to explore lipid metabolic changes caused by Mycobacterium tuberculosis infection and identify specific lipids as diagnostic biomarkers in children with TB using UHPLC-MS/MS. Plasma samples obtained from 70 active TB children, 21 non-TB infectious disease children, and 21 healthy controls were analyzed by a partial least-squares discriminant analysis model in the training set, and 12 metabolites were identified that can separate children with TB from non-TB controls. In the independent testing cohort with 49 subjects, three of the markers, PC (15:0/17:1), PC (17:1/18:2), and PE (18:1/20:3), presented with high diagnostic values. The areas under the curve of the three metabolites were 0.904, 0.833, and 0.895, respectively. The levels of the altered lipid metabolites were found to be associated with the severity of the TB disease. Taken together, plasma lipid metabolites are potentially useful for diagnosis of active TB in children and would provide insights into the pathogenesis of the disease.

Protein acylation links metabolism and the control of signal transduction, transcription regulation, growth, and pathogenicity in Actinobacteria

Actinobacteria have a complex life cycle, including morphological and physiological differentiation which are often associated with the biosynthesis of secondary metabolites. Recently, increased interest in post-translational modifications (PTMs) in these Gram-positive bacteria has highlighted the importance of PTMs as signals that provide functional diversity and regulation by modifying proteins to respond to diverse stimuli. Here, we review the developments in research on acylation, a typical PTM that uses acyl-CoA or related metabolites as donors, as well as the understanding of the direct link provided by acylation between cell metabolism and signal transduction, transcriptional regulation, cell growth, and pathogenicity in Actinobacteria.

Mycobacterium tuberculosis induces delayed lipid droplet accumulation in dendritic cells depending on bacterial viability and virulence

Tuberculosis remains a global health threat with high morbidity. Dendritic cells (DCs) participate in the acute and chronic inflammatory responses to Mycobacterium tuberculosis (Mtb) by directing the adaptive immune response and are present in lung granulomas. In macrophages, the interaction of lipid droplets (LDs) with mycobacteria-containing phagosomes is central to host-pathogen interactions. However, the data available for DCs are still a matter of debate. Here, we reported that bone marrow-derived DCs (BMDCs) were susceptible to Mtb infection and replication at similar rate to macrophages. Unlike macrophages, the analysis of gene expression showed that Mtb infection induced a delayed increase in lipid droplet-related genes and proinflammatory response. Hence, LD accumulation has been observed by high-content imaging in late periods. Infection of BMDCs with killed H37Rv demonstrated that LD accumulation depends on Mtb viability. Moreover, infection with the attenuated strains H37Ra and Mycobacterium bovis-BCG induced only an early transient increase in LDs, whereas virulent Mtb also induced delayed LD accumulation. In addition, infection with the BCG strain with the reintroduced virulence RD1 locus induced higher LD accumulation and bacterial replication when compared to parental BCG. Collectively, our data suggest that delayed LD accumulation in DCs is dependent on mycobacterial viability and virulence.

Lipid droplets as multifunctional organelles related to the mechanism of evasion during mycobacterial infection

Tuberculosis (TB) is an infectious disease caused by the bacteria of the Mycobaterium tuberculosis (Mtb) complex. The modulation of the lipid metabolism has been implicated in the immune response regulation, including the formation of lipid droplets (LD)s, LD-phagosome association and eicosanoid synthesis. Mtb, M. bovis BCG and other pathogenic mycobacteria, as well as wall components, such as LAM, can induce LDs formation in a mechanism involving surface receptors, for instance TLRs, CD36, CD14, CD11b/CD18 and others. In addition, the activation of the lipid-activated nuclear receptor PPARγ is involved in the mechanisms of LD biogenesis, as well as in the modulation of the synthesis of lipid mediators. In infected cells, LDs are sites of compartmentalized prostaglandin E₂ synthesis involved in macrophage deactivation, bacterial replication and regulation of the host cytokine profile. LDs also have a function in vesicle traffic during infection. Rab7 and RILP, but not Rab5, are located on LDs of infected macrophages, suggesting that LDs and phagosomes could exchange essential proteins for phagosomal maturation, interfering in mycobacterial survival. The pharmacological inhibition of LDs biogenesis affects the bacterial replication and the synthesis of lipid mediators and cytokines, suggesting that LDs may be new targets for antimicrobial therapies. However, it is still controversial if the accumulation of LDs favors the mycobacterial survival acting as an escape mechanism, or promotes the host resistance to infection. Thus, in this mini-review we discuss recent advances in understanding the important role of LDs in the course of infections and the implications for the pathophysiology of mycobacteriosis.

A Persistent Tuberculosis Outbreak in the UK Is Characterized by Hydrophobic fadB4-Deficient Mycobacterium tuberculosis That Replicates Rapidly in Macrophages

The genetic diversity of Mycobacterium tuberculosis can influence disease severity and transmissibility. To better understand how this diversity influences individuals and communities, we phenotyped M. tuberculosis that was causing a persistent outbreak in the East Midlands, United Kingdom. Compared to nonoutbreak isolates, bacilli had higher lipid contents and more hydrophobic cell surfaces. In macrophage infection models, the bacteria increased more rapidly, provoked the enhanced accumulation of macrophage lipid droplets and enhanced the secretion of IL-1β. Natural deletions in fadB4, nrdB, and plcC distinguished the outbreak isolates from other lineage 3 isolates in the region. fadB4 is annotated with a putative role in cell envelope biosynthesis, so the loss of this gene has the potential to alter the interactions of bacteria with immune cells. Reintroduction of fadB4 to the outbreak strain led to a phenotype that more closely resembled those of nonoutbreak strains. The improved understanding of the microbiological characteristics and the corresponding genetic polymorphisms that associate with outbreaks have the potential to inform tuberculosis control. IMPORTANCE Tuberculosis (TB) killed 1.5 million people in 2020 and affects every country. The extent to which the natural genetic diversity of Mycobacterium tuberculosis influences disease manifestation at both the individual and epidemiological levels remains poorly understood. Insights into how pathogen polymorphisms affect patterns of TB have the potential to translate into clinical and public health practice. Two distinct lineage 3 strains isolated from local TB outbreaks, one of which (CH) was rapidly terminated and the other of which (Lro) persistently transmitted for over a decade, provided us with an opportunity to study these issues. We compared genome sequences, microbiological characteristics, and early immune responses that were evoked upon infection. Our results indicate that the natural lack of fadB4 in the Lro strain contributes to its unique features.

Immune cell interactions in tuberculosis

Despite having been identified as the organism that causes tuberculosis in 1882, Mycobacterium tuberculosis has managed to still evade our understanding of the protective immune response against it, defying the development of an effective vaccine. Technology and novel experimental models have revealed much new knowledge, particularly with respect to the heterogeneity of the bacillus and the host response. This review focuses on certain immunological elements that have recently yielded exciting data and highlights the importance of taking a holistic approach to understanding the interaction of M. tuberculosis with the many host cells that contribute to the development of protective immunity.

Modulating macrophage function to reinforce host innate resistance against Mycobacterium avium complex infection

Mycobacterium avium complex (MAC) is the main causative agent of infectious diseases in humans among nontuberculous mycobacteria (NTM) that are ubiquitous organisms found in environmental media such as soil as well as in domestic and natural waters. MAC is a primary causative agent of NTM-lung disease that threaten immunocompromised or structural lung disease patients. The incidence and the prevalence of M. tuberculosis infection have been reduced, while MAC infections and mortality rates have increased, making it a cause of global health concern. The emergence of drug resistance and the side effects of long-term drug use have led to a poor outcome of treatment regimens against MAC infections. Therefore, the development of host-directed therapy (HDT) has recently gained interest, aiming to accelerate mycobacterial clearance and reversing lung damage by employing the immune system using a novel adjuvant strategy to improve the clinical outcome of MAC infection. Therefore, in this review, we discuss the innate immune responses that contribute to MAC infection focusing on macrophages, chief innate immune cells, and host susceptibility factors in patients. We also discuss potential HDTs that can act on the signaling pathway of macrophages, thereby contributing to antimycobacterial activity as a part of the innate immune response during MAC infection. Furthermore, this review provides new insights into MAC infection control that modulates and enhances macrophage function, promoting host antimicrobial activity in response to potential HDTs and thus presenting a deeper understanding of the interactions between macrophages and MACs during infection.

In the Thick of It: Formation of the Tuberculous Granuloma and Its Effects on Host and Therapeutic Responses

The defining pathology of tuberculosis is the granuloma, an organized structure derived from host immune cells that surrounds infecting Mycobacterium tuberculosis. As the location of much of the bacteria in the infected host, the granuloma is a central point of interaction between the host and the infecting bacterium. This review describes the signals and cellular reprogramming that drive granuloma formation. Further, as a central point of host-bacterial interactions, the granuloma shapes disease outcome by altering host immune responses and bacterial susceptibility to antibiotic treatment, as discussed herein. This new understanding of granuloma biology and the signaling behind it highlights the potential for host-directed therapies targeting the granuloma to enhance antibiotic access and tuberculosis-specific immune responses.