Role of Cathepsins in Mycobacterium tuberculosis Survival in Human Macrophages

Cathepsin Z is a conserved susceptibility factor underlying tuberculosis severity

Tuberculosis (TB) outcomes vary widely, from asymptomatic infection to mortality, yet most animal models do not recapitulate human phenotypic and genotypic variation. The genetically diverse Collaborative Cross mouse panel models distinct facets of TB disease that occur in humans and allows identification of genomic loci underlying clinical outcomes. We previously mapped a TB susceptibility locus on mouse chromosome 2. Here, we identify cathepsin Z ( Ctsz ) as a lead candidate underlying this TB susceptibility and show that Ctsz ablation leads to increased bacterial burden, CXCL1 overproduction, and decreased survival in mice. Ctsz disturbance within murine macrophages enhances production of CXCL1, a known biomarker of TB severity. From a Ugandan household contact study, we identify significant associations between CTSZ variants and TB disease severity. Finally, we examine patient-derived TB granulomas and report CTSZ localization within granuloma-associated macrophages, placing human CTSZ at the host-pathogen interface. These findings implicate a conserved CTSZ-CXCL1 axis in humans and genetically diverse mice that mediates TB disease severity.

ACOD1-mediated lysosomal membrane permeabilization contributes to Mycobacterium tuberculosis-induced macrophage death

Mycobacterium tuberculosis (Mtb) primarily infects macrophages. In vitro without antibiotics, wild-type Mtb hastens death of the macrophages, but the processes leading to rapid cell death are not well understood. Our earlier work indicated that the death of Mtb-infected mouse macrophages in vitro is markedly exacerbated by induction of interferon-β (IFN-β) [L. Zhang et al., J. Exp. Med. 18, e20200887 (2021)]. Here, we identified a key downstream response to IFN-β in the context of Mtb infection as the massive induction of cis-aconitate decarboxylase (ACOD1), not only in its canonical subcellular localization in mitochondria but also in the cytosol, where it bound to the lysosome-stabilizing protein HSP70. ACOD1's product, itaconate, protected Mtb-infected macrophages. However, the contrasting and predominant effect of high-level ACOD1 expression was to act in a noncatalytic manner to promote HSP70's degradation, leading to lysosomal membrane permeabilization (LMP). Mtb-induced macrophage death was markedly diminished by inhibitors of cysteine proteases, consistent with lysosome-mediated cell death. Neither ACOD1 inhibitors nor cysteine protease inhibitors are suitable for potential host-directed therapy (HDT) of tuberculosis. Instead, this work directs attention to how ACOD1 acts nonenzymatically to promote the degradation of HSP70.

Granuloma Annulare Exhibits Mixed Immune and Macrophage Polarization Profiles with Spatial Transcriptomics

Granuloma annulare (GA) is an idiopathic condition characterized by granulomatous inflammation in the skin. Prior studies have suggested that GA develops from various triggers, leading to a complex interplay involving innate and adaptive immunity, tissue remodeling, and fibrosis. Macrophages are the major immune cells comprising GA granulomas; however, the molecular drivers and inflammatory signaling cascade behind macrophage activation are poorly understood. Histologically, GA exhibits both palisaded and interstitial patterns on histology; however, the molecular composition of GA at the spatial level remains unexplored. GA is a condition without Food and Drug Administration-approved therapies despite the significant impact of GA on QOL. Spatial transcriptomics is a valuable tool for profiling localized, genome-wide gene expression changes across tissues, with emerging applications in clinical medicine. To improve our understanding of the spatially localized gene expression patterns underlying GA, we profiled the spatial gene expression landscape from 6 patients with GA. Our findings revealed mixed T helper 1 and T helper 2 signals comprising the GA microenvironment and spatially distinct M1 and M2 macrophage polarization characteristics. IFN-γ and TNF signals emerged as important regulators of GA granulomatous inflammation, and IL-32 emerged as a key driver of granulomatous inflammation. Overall, our spatial transcriptomics data indicate that GA exhibits mixed immune and macrophage polarization.

The multifaceted roles of cathepsins in immune and inflammatory responses: implications for cancer therapy, autoimmune diseases, and infectious diseases

The cathepsin family comprises lysosomal proteases that play essential roles in various physiological processes, including protein degradation, antigen presentation, apoptosis, and tissue remodeling. Dysregulation of cathepsin activity has been linked to a variety of pathological conditions, such as cancer, autoimmune diseases, and neurodegenerative disorders. Understanding the functions of cathepsins is crucial for gaining insights into their roles in both health and disease, as well as for developing targeted therapeutic approaches. Emerging research underscores the significant involvement of cathepsins in immune cells, particularly T cells, macrophages, dendritic cells, and neutrophils, as well as their contribution to immune-related diseases. In this review, we systematically examine the impact of cathepsins on the immune system and their mechanistic roles in cancer, infectious diseases, autoimmune and neurodegenerative disorders, with the goal of identifying novel therapeutic strategies for these conditions.

Application of antimicrobial peptides as next-generation therapeutics in the biomedical world

Antimicrobial peptide (AMP), also called host defense peptide, is a part of the innate immune system in eukaryotic organisms. AMPs are also produced by prokaryotes in response to stressful conditions and environmental changes. They have a broad spectrum of activity against both Gram positive and Gram negative bacteria. They are also effective against viruses, fungi, parasites, and cancer cells. AMPs are cationic or amphipathic in nature, but in recent years cationic AMPs have attracted a lot of attention because cationic AMPs can easily interact with negatively charged bacterial and cancer cell membranes through electrostatic interaction. AMPs can also eradicate bacterial biofilms and have broad-spectrum activity against multidrug resistant (MDR) bacteria. Although the main target site for AMPs is the cell membrane, they can also disrupt bacterial cell walls, interfere with protein folding and inhibit enzymatic activity. In recent centuries antibiotics are gradually losing their potential because of the continuous rise of antibiotic resistant bacteria. Therefore, there is an urgent need to develop novel therapeutic approaches to treat MDR bacteria, and AMP is such an alternative treatment option over conventional antibiotics. Several communicable diseases like tuberculosis and non-communicable diseases such as cancer can be treated by using AMPs. One of the major advantages of using AMP is that it works with high specificity and does not cause any harm to normal tissue. AMPs can be modified to improve their efficacy. In this narrative review, we are focusing on the potential application of AMPs in medical science.

Mycobacterium avium inhibits protein kinase C and MARCKS phosphorylation in human cystic fibrosis and non-cystic fibrosis cells

In cystic fibrosis (CF), there is abnormal translocation and function of the cystic fibrosis transmembrane conductance regulator (CFTR) and an upregulation of the epithelial sodium channel (ENaC). This leads to hyperabsorption of sodium and fluid from the airway, dehydrated mucus, and an increased risk of respiratory infections. In this study, we performed a proteomic assessment of differentially regulated proteins from CF and non-CF small airway epithelial cells (SAEC) that are sensitive to Mycobacterium avium. CF SAEC and normal non-CF SAEC were infected with M. avium before the cells were harvested for protein. Protein kinase C (PKC) activity was greater in the CF cells compared to the non-CF cells, but the activity was significantly attenuated in both cell types after infection with M. avium compared to vehicle. Western blot and densitometric analysis showed a significant increase in cathepsin B protein expression in M. avium infected CF cells. Myristoylated alanine rich C-kinase substrate (MARCKS) protein was one of several differentially expressed proteins between the groups that was identified by mass spectrometry-based proteomics. Total MARCKS protein expression was greater in CF cells compared to non-CF cells. Phosphorylation of MARCKS at serine 163 was also greater in CF cells compared to non-CF cells after treating both groups of cells with M. avium. Taken together, MARCKS protein is upregulated in CF cells and there is decreased phosphorylation of the protein due to a decrease in PKC activity and presumably increased cathepsin B mediated proteolysis of the protein after M. avium infection.

Host-directed therapy with amiodarone in preclinical models restricts mycobacterial infection and enhances autophagy

Mycobacterium tuberculosis (Mtb) as well as nontuberculous mycobacteria are intracellular pathogens whose treatment is extensive and increasingly impaired due to the rise of mycobacterial drug resistance. The loss of antibiotic efficacy has raised interest in the identification of host-directed therapeutics (HDT) to develop novel treatment strategies for mycobacterial infections. In this study, we identified amiodarone as a potential HDT candidate that inhibited both intracellular Mtb and Mycobacterium avium in primary human macrophages without directly impairing bacterial growth, thereby confirming that amiodarone acts in a host-mediated manner. Moreover, amiodarone induced the formation of (auto)phagosomes and enhanced autophagic targeting of mycobacteria in macrophages. The induction of autophagy by amiodarone is likely due to enhanced transcriptional regulation, as the nuclear intensity of the transcription factor EB, the master regulator of autophagy and lysosomal biogenesis, was strongly increased. Furthermore, blocking lysosomal degradation with bafilomycin impaired the host-beneficial effect of amiodarone. Finally, amiodarone induced autophagy and reduced bacterial burden in a zebrafish embryo model of tuberculosis, thereby confirming the HDT activity of amiodarone in vivo. In conclusion, we have identified amiodarone as an autophagy-inducing antimycobacterial HDT that improves host control of mycobacterial infections.

IMPORTANCE

Due to the global rise in antibiotic resistance, there is a strong need for alternative treatment strategies against intracellular bacterial infections, including Mycobacterium tuberculosis (Mtb) and non-tuberculous mycobacteria. Stimulating host defense mechanisms by host-directed therapy (HDT) is a promising approach for treating mycobacterial infections. This study identified amiodarone, an antiarrhythmic agent, as a potential HDT candidate that inhibits the survival of Mtb and Mycobacterium avium in primary human macrophages. The antimycobacterial effect of amiodarone was confirmed in an in vivo tuberculosis model based on Mycobacterium marinum infection of zebrafish embryos. Furthermore, amiodarone induced autophagy and inhibition of the autophagic flux effectively impaired the host-protective effect of amiodarone, supporting that activation of the host (auto)phagolysosomal pathway is essential for the mechanism of action of amiodarone. In conclusion, we have identified amiodarone as an autophagy-inducing HDT that improves host control of a wide range of mycobacteria.

Cystatin F Depletion in Mycobacterium tuberculosis-Infected Macrophages Improves Cathepsin C/Granzyme B-Driven Cytotoxic Effects on HIV-Infected Cells during Coinfection

Cystatin F (CstF) is a protease inhibitor of cysteine cathepsins, including those involved in activating the perforin/granzyme cytotoxic pathways. It is targeted at the endolysosomal pathway but can also be secreted to the extracellular milieu or endocytosed by bystander cells. CstF was shown to be significantly increased in tuberculous pleurisy, and during HIV coinfection, pleural fluids display high viral loads. In human macrophages, our previous results revealed a strong upregulation of CstF in phagocytes activated by interferon γ or after infection with Mycobacterium tuberculosis (Mtb). CstF manipulation using RNA silencing led to increased proteolytic activity of lysosomal cathepsins, improving Mtb intracellular killing. In the present work, we investigate the impact of CstF depletion in macrophages during the coinfection of Mtb-infected phagocytes with lymphocytes infected with HIV. The results indicate that decreasing the CstF released by phagocytes increases the major pro-granzyme convertase cathepsin C of cytotoxic immune cells from peripheral blood-derived lymphocytes. Consequently, an observed augmentation of the granzyme B cytolytic activity leads to a significant reduction in viral replication in HIV-infected CD4+ T-lymphocytes. Ultimately, this knowledge can be crucial for developing new therapeutic approaches to control both pathogens based on manipulating CstF.

Proteomic analysis of granulomas from cattle and pigs naturally infected with Mycobacterium tuberculosis complex by MALDI imaging

Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) has recently gained prominence for its ability to provide molecular and spatial information in tissue sections. This technology has the potential to uncover novel insights into proteins and other molecules in biological and immunological pathways activated along diseases with a complex host-pathogen interaction, such as animal tuberculosis. Thus, the present study conducted a data analysis of protein signature in granulomas of cattle and pigs naturally infected with the Mycobacterium tuberculosis complex (MTC), identifying biological and immunological signaling pathways activated throughout the disease. Lymph nodes from four pigs and four cattle, positive for the MTC by bacteriological culture and/or real-time PCR, were processed for histopathological examination and MALDI-MSI. Protein identities were assigned using the MaTisse database, and protein-protein interaction networks were visualized using the STRING database. Gene Ontology (GO) analysis was carried out to determine biological and immunological signaling pathways in which these proteins could participate together with Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. Distinct proteomic profiles between cattle and pig granulomas were displayed. Noteworthy, the GO analysis revealed also common pathways among both species, such as "Complement activation, alternative pathway" and "Tricarboxylic acid cycle", which highlight pathways that are conserved among different species infected by the MTC. In addition, species-specific terms were identified in the current study, such as "Natural killer cell degranulation" in cattle or those related to platelet and neutrophil recruitment and activation in pigs. Overall, this study provides insights into the immunopathogenesis of tuberculosis in cattle and pigs, opening new areas of research and highlighting the importance, among others, of the complement activation pathway and the regulation of natural killer cell- and neutrophil-mediated immunity in this disease.

Unveiling the Roles of Cysteine Proteinases F and W: From Structure to Pathological Implications and Therapeutic Targets

Cysteine cathepsins F and W are members of the papain-like cysteine protease family, which have distinct structural features and functional roles in various physiological and pathological processes. This review provides a comprehensive overview of the current understanding of the structure, biological functions, and pathological implications of cathepsins F and W. Beginning with an introduction to these proteases, we delve into their structural characteristics and elucidate their unique features that dictate their enzymatic activities and substrate specificity. We also explore the intricate involvement of cathepsins F and W in malignancies, highlighting their role as potential biomarkers and therapeutic targets in cancer progression. Furthermore, we discuss the emerging roles of these enzymes in immune response modulation and neurological disorders, shedding light on their implications in autoimmune and neurodegenerative diseases. Finally, we review the landscape of inhibitors targeting these proteases, highlighting their therapeutic potential and challenges in clinical translation. This review brings together the diverse facets of cysteine cathepsins F and W, providing insights into their roles in health and disease and guiding future investigations for therapeutic advances.

Mycobacterium tuberculosis resides in lysosome-poor monocyte-derived lung cells during chronic infection

Mycobacterium tuberculosis (Mtb) infects lung myeloid cells, but the specific Mtb-permissive cells and host mechanisms supporting Mtb persistence during chronic infection are incompletely characterized. We report that after the development of T cell responses, CD11clo monocyte-derived cells harbor more live Mtb than alveolar macrophages (AM), neutrophils, and CD11chi monocyte-derived cells. Transcriptomic and functional studies revealed that the lysosome pathway is underexpressed in this highly permissive subset, characterized by less lysosome content, acidification, and proteolytic activity than AM, along with less nuclear TFEB, a regulator of lysosome biogenesis. Mtb infection does not drive lysosome deficiency in CD11clo monocyte-derived cells but promotes recruitment of monocytes that develop into permissive lung cells, mediated by the Mtb ESX-1 secretion system. The c-Abl tyrosine kinase inhibitor nilotinib activates TFEB and enhances lysosome functions of macrophages in vitro and in vivo, improving control of Mtb infection. Our results suggest that Mtb exploits lysosome-poor lung cells for persistence and targeting lysosome biogenesis is a potential host-directed therapy for tuberculosis.

VapC12 ribonuclease toxin modulates host immune response during Mycobacterium tuberculosis infection

Mechanistic understanding of antibiotic persistence is a prerequisite in controlling the emergence of MDR cases in Tuberculosis (TB). We have reported that the cholesterol-induced activation of VapC12 ribonuclease is critical for disease persistence in TB. In this study, we observed that relative to the wild type, mice infected with ΔvapC12 induced a pro-inflammatory response, had a higher pathogen load, and responded better to the anti-TB treatment. In a high-dose infection model, all the mice infected with ΔvapC12 succumbed early to the disease. Finally, we reported that the above phenotype of ΔvapC12 was dependent on the presence of the TLR4 receptor. Overall, the data suggests that failure of a timely resolution of the early inflammation by the ΔvapC12 infected mice led to hyperinflammation, altered T-cell response and high bacterial load. In conclusion, our findings suggest the role of the VapC12 toxin in modulating the innate immune response of the host in ways that favor the long-term survival of the pathogen inside the host.

Leishmania infection upregulates and engages host macrophage Argonaute 1, and system-wide proteomics reveals Argonaute 1-dependent host response

Leishmania donovani, an intracellular protozoan parasite, is the causative agent of visceral leishmaniasis, the most severe form of leishmaniasis in humans. It is becoming increasingly clear that several intracellular pathogens target host cell RNA interference (RNAi) pathways to promote their survival. Complexes of Argonaute proteins with small RNAs are core components of the RNAi. In this study, we investigated the potential role of host macrophage Argonautes in Leishmania pathogenesis. Using Western blot analysis of Leishmania donovani-infected macrophages, we show here that Leishmania infection selectively increased the abundance of host Argonaute 1 (Ago1). This increased abundance of Ago1 in infected cells also resulted in higher levels of Ago1 in active Ago-complexes, suggesting the preferred use of Ago1 in RNAi in Leishmania-infected cells. This analysis used a short trinucleotide repeat containing 6 (TNRC6)/glycine-tryptophan repeat protein (GW182) protein-derived peptide fused to Glutathione S-transferase as an affinity matrix to capture mature Ago-small RNAs complexes from the cytosol of non-infected and Leishmania-infected cells. Furthermore, Ago1 silencing significantly reduced intracellular survival of Leishmania, demonstrating that Ago1 is essential for Leishmania pathogenesis. To investigate the role of host Ago1 in Leishmania pathogenesis, a quantitative whole proteome approach was employed, which showed that expression of several previously reported Leishmania pathogenesis-related proteins was dependent on the level of macrophage Ago1. Together, these findings identify Ago1 as the preferred Argonaute of RNAi machinery in infected cells and a novel and essential virulence factor by proxy that promotes Leishmania survival.

Modulation of Cystatin F in Human Macrophages Impacts Cathepsin-Driven Killing of Multidrug-Resistant Mycobacterium tuberculosis

Tuberculosis (TB) treatment relies primarily on 70-year-old drugs, and prophylaxis suffers from the lack of an effective vaccine. Among the 10 million people exhibiting disease symptoms yearly, 450,000 have multidrug or extensively drug-resistant (MDR or XDR) TB. A greater understanding of host and pathogen interactions will lead to new therapeutic interventions for TB eradication. One of the strategies will be to target the host for better immune bactericidal responses against the TB causative agent Mycobacterium tuberculosis (Mtb). Cathepsins are promising targets due to their manipulation of Mtb with consequences such as decreased proteolytic activity and improved pathogen survival in macrophages. We recently demonstrated that we could overcome this enzymatic blockade by manipulating protease inhibitors such as cystatins. Here, we investigate the role of cystatin F, an inhibitor that we showed previously to be strongly upregulated during Mtb infection. Our results indicate that the silencing of cystatin F using siRNA increase the proteolytic activity of cathepsins S, L, and B, significantly impacting pathogen intracellular killing in macrophages. Taken together, these indicate the targeting of cystatin F as a potential adjuvant therapy for TB, including MDR and XDR-TB.

Mycobacterium tuberculosis resides in lysosome-poor monocyte-derived lung cells during chronic infection

Mycobacterium tuberculosis (Mtb) persists in lung myeloid cells during chronic infection. However, the mechanisms allowing Mtb to evade elimination are not fully understood. Here, we determined that in chronic phase, CD11clo monocyte-derived lung cells termed MNC1 (mononuclear cell subset 1), harbor more live Mtb than alveolar macrophages (AM), neutrophils, and less permissive CD11chi MNC2. Transcriptomic and functional studies of sorted cells revealed that the lysosome biogenesis pathway is underexpressed in MNC1, which have less lysosome content, acidification, and proteolytic activity than AM, and less nuclear TFEB, a master regulator of lysosome biogenesis. Mtb infection does not drive lysosome deficiency in MNC1. Instead, Mtb recruits MNC1 and MNC2 to the lungs for its spread from AM to these cells via its ESX-1 secretion system. The c-Abl tyrosine kinase inhibitor nilotinib activates TFEB and enhances lysosome function of primary macrophages and MNC1 and MNC2 in vivo, improving control of Mtb infection. Our results indicate that Mtb exploits lysosome-poor monocyte-derived cells for in vivo persistence, suggesting a potential target for host-directed tuberculosis therapy.

GRaNIE and GRaNPA: inference and evaluation of enhancer-mediated gene regulatory networks

Enhancers play a vital role in gene regulation and are critical in mediating the impact of noncoding genetic variants associated with complex traits. Enhancer activity is a cell-type-specific process regulated by transcription factors (TFs), epigenetic mechanisms and genetic variants. Despite the strong mechanistic link between TFs and enhancers, we currently lack a framework for jointly analysing them in cell-type-specific gene regulatory networks (GRN). Equally important, we lack an unbiased way of assessing the biological significance of inferred GRNs since no complete ground truth exists. To address these gaps, we present GRaNIE (Gene Regulatory Network Inference including Enhancers) and GRaNPA (Gene Regulatory Network Performance Analysis). GRaNIE (https://git.embl.de/grp-zaugg/GRaNIE) builds enhancer-mediated GRNs based on covariation of chromatin accessibility and RNA-seq across samples (e.g. individuals), while GRaNPA (https://git.embl.de/grp-zaugg/GRaNPA) assesses the performance of GRNs for predicting cell-type-specific differential expression. We demonstrate their power by investigating gene regulatory mechanisms underlying the response of macrophages to infection, cancer and common genetic traits including autoimmune diseases. Finally, our methods identify the TF PURA as a putative regulator of pro-inflammatory macrophage polarisation.

ESAT-6 a Major Virulence Factor of Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb), the causative agent of human tuberculosis (TB), is one of the most successfully adapted human pathogens. Human-to-human transmission occurs at high rates through aerosols containing bacteria, but the pathogen evolved prior to the establishment of crowded populations. Mtb has developed a particular strategy to ensure persistence in the host until an opportunity for transmission arises. It has refined its lifestyle to obviate the need for virulence factors such as capsules, flagella, pili, or toxins to circumvent mucosal barriers. Instead, the pathogen uses host macrophages, where it establishes intracellular niches for its migration into the lung parenchyma and other tissues and for the induction of long-lived latency in granulomas. Finally, at the end of the infection cycle, Mtb induces necrotic cell death in macrophages to escape to the extracellular milieu and instructs a strong inflammatory response that is required for the progression from latency to disease and transmission. Common to all these events is ESAT-6, one of the major virulence factors secreted by the pathogen. This narrative review highlights the recent advances in understanding the role of ESAT-6 in hijacking macrophage function to establish successful infection and transmission and its use as a target for the development of diagnostic tools and vaccines.

Mycobacterium tuberculosis resides in lysosome-poor monocyte-derived lung cells during chronic infection

Mycobacterium tuberculosis (Mtb) infects cells in multiple lung myeloid cell subsets and causes chronic infection despite innate and adaptive immune responses. However, the mechanisms allowing Mtb to evade elimination are not fully understood. Here, using new methods, we determined that after T cell responses have developed, CD11clo monocyte-derived lung cells termed MNC1 (mononuclear cell subset 1), harbor more live Mtb compared to alveolar macrophages (AM), neutrophils, and less permissive CD11chi MNC2. Bulk RNA sequencing of sorted cells revealed that the lysosome biogenesis pathway is underexpressed in MNC1. Functional assays confirmed that Mtb-permissive MNC1 have less lysosome content, acidification, and proteolytic activity than AM, and less nuclear TFEB, a master regulator of lysosome biogenesis. Mtb infection does not drive lysosome deficiency in MNC1 in vivo. Instead, Mtb recruits MNC1 and MNC2 to the lungs for its spread from AM to these cell subsets as a virulence mechanism that requires the Mtb ESX-1 secretion system. The c-Abl tyrosine kinase inhibitor nilotinib activates TFEB and enhances lysosome function of primary macrophages in vitro and MNC1 and MNC2 in vivo, improving control of Mtb infection. Our results indicate that Mtb exploits lysosome-poor monocyte-derived cells for in vivo persistence, suggesting a potential target for host-directed tuberculosis therapy.

Development of Chitosan Particles Loaded with siRNA for Cystatin C to Control Intracellular Drug-Resistant Mycobacterium tuberculosis

The golden age of antibiotics for tuberculosis (TB) is marked by its success in the 1950s of the last century. However, TB is not under control, and the rise in antibiotic resistance worldwide is a major threat to global health care. Understanding the complex interactions between TB bacilli and their host can inform the rational design of better TB therapeutics, including vaccines, new antibiotics, and host-directed therapies. We recently demonstrated that the modulation of cystatin C in human macrophages via RNA silencing improved the anti-mycobacterial immune responses to Mycobacterium tuberculosis infection. Available in vitro transfection methods are not suitable for the clinical translation of host-cell RNA silencing. To overcome this limitation, we developed different RNA delivery systems (DSs) that target human macrophages. Human peripheral blood-derived macrophages and THP1 cells are difficult to transfect using available methods. In this work, a new potential nanomedicine based on chitosan (CS-DS) was efficiently developed to carry a siRNA-targeting cystatin C to the infected macrophage models. Consequently, an effective impact on the intracellular survival/replication of TB bacilli, including drug-resistant clinical strains, was observed. Altogether, these results suggest the potential use of CS-DS in adjunctive therapy for TB in combination or not with antibiotics.

HIV/Mtb Co-Infection: From the Amplification of Disease Pathogenesis to an “Emerging Syndemic”

Human immunodeficiency virus (HIV) and Mycobacterium tuberculosis (Mtb) are pathogens responsible for millions of new infections each year; together, they cause high morbidity and mortality worldwide. In addition, late-stage HIV infection increases the risk of developing tuberculosis (TB) by a factor of 20 in latently infected people, and even patients with controlled HIV infection on antiretroviral therapy (ART) have a fourfold increased risk of developing TB. Conversely, Mtb infection exacerbates HIV pathogenesis and increases the rate of AIDS progression. In this review, we discuss this reciprocal amplification of HIV/Mtb coinfection and how they influence each other’s pathogenesis. Elucidating the infectious cofactors that impact on pathogenesis may open doors for the design of new potential therapeutic strategies to control disease progression, especially in contexts where vaccines or the sterile clearance of pathogens are not effectively available.

Role of MHC class I pathways in Mycobacterium tuberculosis antigen presentation

MHC class I antigen processing is an underappreciated area of nonviral host–pathogen interactions, bridging both immunology and cell biology, where the pathogen’s natural life cycle involves little presence in the cytoplasm. The effective response to MHC-I foreign antigen presentation is not only cell death but also phenotypic changes in other cells and stimulation of the memory cells ready for the next antigen reoccurrence. This review looks at the MHC-I antigen processing pathway and potential alternative sources of the antigens, focusing on Mycobacterium tuberculosis (Mtb) as an intracellular pathogen that co-evolved with humans and developed an array of decoy strategies to survive in a hostile environment by manipulating host immunity to its own advantage. As that happens via the selective antigen presentation process, reinforcement of the effective antigen recognition on MHC-I molecules may stimulate subsets of effector cells that act earlier and more locally. Vaccines against tuberculosis (TB) could potentially eliminate this disease, yet their development has been slow, and success is limited in the context of this global disease’s spread. This review’s conclusions set out potential directions for MHC-I-focused approaches for the next generation of vaccines.

Specific preadaptations of Rhodococcus equi cooperate with its Virulence-associated protein A during macrophage infection

Gram-positive Rhodococcus equi (Prescotella equi) is a lung pathogen of foals and immunocompromised humans. Intra-macrophage multiplication requires production of the bacterial Virulence-associated protein A (VapA) which is released into the phagosome lumen. VapA pH-neutralizes intracellular compartments allowing R. equi to multiply in an atypical macrophage phagolysosome. Here, we show that VapA does not support intra-macrophage growth of several other bacterial species demonstrating that only few bacteria have the specific preadaptations needed to profit from VapA. We show that the closest relative of R. equi, environmental Rhodococcus defluvii (Prescotella defluvii), does not multiply in macrophages at 37°C even when VapA is present because of its thermosensitivity but it does so once the infection temperature is lowered providing rare experimental evidence for 'thermal restriction'. Using growth experiments with isolated macrophage lysosomes and modified infection schemes we provide evidence that R. equi resists the attack by phagolysosome contents at low pH for several hours. During this time, R. equi produces and secretes VapA which enables it to grow at the expense of lysosome constituents. We present arguments that, under natural infection conditions, R. equi is VapA-less during the initial encounter with the host. This has important implications for vaccine development.

Mycobacterium tuberculosis Evasion of Guanylate Binding Protein-Mediated Host Defense in Mice Requires the ESX1 Secretion System

Cell-intrinsic immune mechanisms control intracellular pathogens that infect eukaryotes. The intracellular pathogen Mycobacterium tuberculosis (Mtb) evolved to withstand cell-autonomous immunity to cause persistent infections and disease. A potent inducer of cell-autonomous immunity is the lymphocyte-derived cytokine IFNγ. While the production of IFNγ by T cells is essential to protect against Mtb, it is not capable of fully eradicating Mtb infection. This suggests that Mtb evades a subset of IFNγ-mediated antimicrobial responses, yet what mechanisms Mtb resists remains unclear. The IFNγ-inducible Guanylate binding proteins (GBPs) are key host defense proteins able to control infections with intracellular pathogens. GBPs were previously shown to directly restrict Mycobacterium bovis BCG yet their role during Mtb infection has remained unknown. Here, we examine the importance of a cluster of five GBPs on mouse chromosome 3 in controlling Mycobacterial infection. While M. bovis BCG is directly restricted by GBPs, we find that the GBPs on chromosome 3 do not contribute to the control of Mtb replication or the associated host response to infection. The differential effects of GBPs during Mtb versus M. bovis BCG infection is at least partially explained by the absence of the ESX1 secretion system from M. bovis BCG, since Mtb mutants lacking the ESX1 secretion system become similarly susceptible to GBP-mediated immune defense. Therefore, this specific genetic interaction between the murine host and Mycobacteria reveals a novel function for the ESX1 virulence system in the evasion of GBP-mediated immunity.

Liposomal Delivery of Saquinavir to Macrophages Overcomes Cathepsin Blockade by Mycobacterium tuberculosis and Helps Control the Phagosomal Replicative Niches

Mycobacterium tuberculosis is able to establish a chronic colonization of lung macrophages in a controlled replication manner, giving rise to a so-called latent infection. Conversely, when intracellular bacteria undergo actively uncontrolled replication rates, they provide the switch for the active infection called tuberculosis to occur. Our group found that the pathogen is able to manipulate the activity of endolysosomal enzymes, cathepsins, directly at the level of gene expression or indirectly by regulating their natural inhibitors, cystatins. To provide evidence for the crucial role of cathepsin manipulation for the success of tuberculosis bacilli in their intracellular survival, we used liposomal delivery of saquinavir. This protease inhibitor was previously found to be able to increase cathepsin proteolytic activity, overcoming the pathogen induced blockade. In this study, we demonstrate that incorporation in liposomes was able to increase the efficiency of saquinavir internalization in macrophages, reducing cytotoxicity at higher concentrations. Consequently, our results show a significant impact on the intracellular killing not only to reference and clinical strains susceptible to current antibiotic therapy but also to multidrug- and extensively drug-resistant (XDR) Mtb strains. Altogether, this indicates the manipulation of cathepsins as a fine-tuning strategy used by the pathogen to survive and replicate in host cells.

Itaconate promotes a wound resolving phenotype in pro-inflammatory macrophages

Pathological conditions associated with dysfunctional wound healing are characterized by impaired remodelling of extracellular matrix (ECM), increased macrophage infiltration, and chronic inflammation. Macrophages also play an important role in wound healing as they drive wound closure by secretion of molecules like transforming growth factor beta-1 (TGF-β). As the functions of macrophages are regulated by their metabolism, local administration of small molecules that alter this might be a novel approach for treatment of wound-healing disorders. Itaconate is a tricarboxylic acid (TCA) cycle-derived metabolite that has been associated with resolution of macrophage-mediated inflammation. However, its effects on macrophage wound healing functions are unknown. In this study, we investigated the effects of the membrane-permeable 4-octyl itaconate (4-OI) derivative on ECM scavenging by cultured human blood monocyte-derived macrophages (hMDM). We found that 4-OI reduced signalling of p38 mitogen-activated protein kinase (MAPK) induced by the canonical immune stimulus lipopolysaccharide (LPS). Likely as a consequence of this, the production of the inflammatory mediators like tumor necrosis factor (TNF)-α and cyclooxygenase (COX)-2 were also reduced. On the transcriptional level, 4-OI increased expression of the gene coding for TGF-β (TGFB1), whereas expression of the collagenase matrix metalloprotease-8 (MMP8) was reduced. Furthermore, surface levels of the anti-inflammatory marker CD36, but not CD206 and CD11c, were increased in these cells. To directly investigate the effect of 4-OI on scavenging of ECM by macrophages, we developed an assay to measure uptake of fibrous collagen. We observed that LPS promoted collagen uptake and that this was reversed by 4-OI-induced signaling of nuclear factor erythroid 2-related factor 2 (NRF2), a regulator of cellular resistance to oxidative stress and the reduced glycolytic capacity of the macrophage. These results indicate that 4-OI lowers macrophage inflammation, likely promoting a more wound-resolving phenotype.

Cysteine cathepsins: A long and winding road towards clinics

Biomedical research often focuses on properties that differentiate between diseased and healthy tissue; one of the current focuses is elevated expression and altered localisation of proteases. Among these proteases, dysregulation of cysteine cathepsins can frequently be observed in inflammation-associated diseases, which tips the functional balance from normal physiological to pathological manifestations. Their overexpression and secretion regularly exhibit a strong correlation with the development and progression of such diseases, making them attractive pharmacological targets. But beyond their mostly detrimental role in inflammation-associated diseases, cysteine cathepsins are physiologically highly important enzymes involved in various biological processes crucial for maintaining homeostasis and responding to different stimuli. Consequently, several challenges have emerged during the efforts made to translate basic research data into clinical applications. In this review, we present both physiological and pathological roles of cysteine cathepsins and discuss the clinical potential of cysteine cathepsin-targeting strategies for disease management and diagnosis.

The Upregulation of Cathepsin G Is Associated with Resistance to Bovine Paratuberculosis

An in silico genomic-transcriptomic combined approach allowed the identification of a polymorphism (cis-eQTL-rs41976219) in the Bos taurus genome associated with the CTSG mRNA expression in bovine blood samples, which suggests that individual genetic variation might modulate the CTSG transcriptional response. In the current study, a sandwich ELISA is used to measure the CTSG protein levels in supernatants of monocyte-derived macrophages (MDMs) isolated from cows with the AA (n = 5) and AC (n = 11) genotypes for the rs41976219 and infected ex vivo with MAP. Cows with the AC genotype have significantly higher CTSG protein levels (1.85 ng/mL) in the supernatants of enriched CD14+-MDMs after 2 h of infection when compared with infected CD14+-MDMs from cows with the AA genotype (1.68 ng/mL). Statistically significant differences in the intracellular MAP load at 7 d p.i. are observed between animals with the AA (2.16 log CFUs) and AC (1.44 log CFUs) genotypes. Finally, the association between the rs41976219 allelic variants and resistance to PTB is tested in a larger cattle population (n = 943) classified according to the presence (n = 442) or absence (n = 501) of PTB-associated lesions. The presence of the two minor alleles in the rs41976219 (CC) is more frequent among healthy cows than in cows with PTB-associated lesions in gut tissues (2.2% vs. 1.4%, OR = 0.61). In agreement with this, the CTSG levels in plasma samples of cows without lesions in gut tissues and with the CC (n = 8) genotype are significantly higher than in the plasmas of cows with the AA + AC (n = 36) genotypes.

Amyloid deposition in granuloma of tuberculosis patients: A single-center pilot study

The formation of granuloma is one of the characteristic features of tuberculosis. Besides, elevated serum amyloid A (SAA) protein level is the indicator for chronic inflammation associated with tuberculosis. The linkage between tuberculosis and SAA-driven secondary amyloidosis is well documented. However, SAA-derived amyloid onset and deposition start sites are not well understood in tuberculosis. We hypothesized that granuloma could be a potential site for amyloid deposition because of the presence of SAA protein and proteases, cleaving SAA into aggregation-prone fragments. 150 tuberculosis patients were identified and biopsies were collected from the affected organs. Patients showing eosinophilic hyaline-rich deposits within granuloma and its periphery were further screened for the presence of amyloid deposits. Upon Congo red staining, these hyaline deposits exhibited characteristic apple-green birefringence under polarized light, confirming their amyloid nature in 20 patients. Further upon Immuno-histochemical staining with anti-SAA antibody, the amyloid enriched areas showed positive immunoreactivity. In this pilot study, we have shown granuloma as a potential site for serum amyloid A derived amyloid deposition in tuberculosis patients. This study would expand the clinical and fundamental research for understanding the mechanism of amyloid formation in granuloma underlying tuberculosis and other chronic inflammatory conditions.

Bordetella pertussis outer membrane vesicles as virulence factor vehicles that influence bacterial interaction with macrophages

Gram-negative pathogenic bacteria constitutively shed outer membrane vesicles (OMVs) which play a significant role in the host-pathogen interaction, eventually determining the outcome of the infection. We previously found that Bordetella pertussis, the etiological agent of whooping cough, survives the innate interaction with human macrophages remaining alive inside these immune cells. Adenylate cyclase (CyaA), one of the main toxins of this pathogen, was found involved in the modulation of the macrophage defense response, eventually promoting bacterial survival within the cells. We here investigated whether B. pertussis OMVs, loaded with most of the bacterial toxins and CyaA among them, modulate the macrophage response to the bacterial infection. We observed that the pre-incubation of macrophages with OMVs led to a decreased macrophage defense response to the encounter with the bacteria, in a CyaA dependent way. Our results suggest that CyaA delivered by B. pertussis OMVs dampens macrophages protective function by decreasing phagocytosis and the bactericidal capability of these host cells. By increasing the chances of bacterial survival to the innate encounter with the macrophages, B. pertussis OMVs might play a relevant role in the course of infection, promoting bacterial persistence within the host and eventually, shaping the whole infection process.

Spatial localization of cathepsins: Implications in immune activation and resolution during infections

Cathepsins were first described, as endolysosomal proteolytic enzymes in reference to the organelles where they degrade the bulk of endogenous and exogenous substrates in a slightly acidic environment. These substrates include pathogens internalized via endocytosis and/or marked for destruction by autophagy. However, the role of cathepsins during infection far exceeds that of direct digestion of the pathogen. Cathepsins have been extensively investigated in the context of tumour associated immune cells and chronic inflammation. Several cathepsin-dependent immune responses develop in the endocytic pathway while others take place in the cytosol, the nucleus, or in the extracellular space. In this review we highlight the spatial localization of cathepsins and their implications in immune activation and resolution pathways during infection.

Human M1 macrophages express unique innate immune response genes after mycobacterial infection to defend against tuberculosis

Mycobacterium tuberculosis (Mtb) is responsible for approximately 1.5 million deaths each year. Though 10% of patients develop tuberculosis (TB) after infection, 90% of these infections are latent. Further, mice are nearly uniformly susceptible to Mtb but their M1-polarized macrophages (M1-MΦs) can inhibit Mtb in vitro, suggesting that M1-MΦs may be able to regulate anti-TB immunity. We sought to determine whether human MΦ heterogeneity contributes to TB immunity. Here we show that IFN-γ-programmed M1-MΦs degrade Mtb through increased expression of innate immunity regulatory genes (Inregs). In contrast, IL-4-programmed M2-polarized MΦs (M2-MΦs) are permissive for Mtb proliferation and exhibit reduced Inregs expression. M1-MΦs and M2-MΦs express pro- and anti-inflammatory cytokine-chemokines, respectively, and M1-MΦs show nitric oxide and autophagy-dependent degradation of Mtb, leading to increased antigen presentation to T cells through an ATG-RAB7-cathepsin pathway. Despite Mtb infection, M1-MΦs show increased histone acetylation at the ATG5 promoter and pro-autophagy phenotypes, while increased histone deacetylases lead to decreased autophagy in M2-MΦs. Finally, Mtb-infected neonatal macaques express human Inregs in their lymph nodes and macrophages, suggesting that M1 and M2 phenotypes can mediate immunity to TB in both humans and macaques. We conclude that human MФ subsets show unique patterns of gene expression that enable differential control of TB after infection. These genes could serve as targets for diagnosis and immunotherapy of TB.

Dynamic human liver proteome atlas reveals functional insights into disease pathways

Deeper understanding of liver pathophysiology would benefit from a comprehensive quantitative proteome resource at cell type resolution to predict outcome and design therapy. Here, we quantify more than 150,000 sequence-unique peptides aggregated into 10,000 proteins across total liver, the major liver cell types, time course of primary cell cultures, and liver disease states. Bioinformatic analysis reveals that half of hepatocyte protein mass is comprised of enzymes and 23% of mitochondrial proteins, twice the proportion of other liver cell types. Using primary cell cultures, we capture dynamic proteome remodeling from tissue states to cell line states, providing useful information for biological or pharmaceutical research. Our extensive data serve as spectral library to characterize a human cohort of non-alcoholic steatohepatitis and cirrhosis. Dramatic proteome changes in liver tissue include signatures of hepatic stellate cell activation resembling liver cirrhosis and providing functional insights. We built a web-based dashboard application for the interactive exploration of our resource (www.liverproteome.org).

Spotted Fever Group Rickettsia Trigger Species-Specific Alterations in Macrophage Proteome Signatures with Different Impacts in Host Innate Inflammatory Responses

The molecular details underlying differences in pathogenicity between Rickettsia species remain to be fully understood. Evidence points to macrophage permissiveness as a key mechanism in rickettsial virulence. Different studies have shown that several rickettsial species responsible for mild forms of rickettsioses can also escape macrophage-mediated killing mechanisms and establish a replicative niche within these cells. However, their manipulative capacity with respect to host cellular processes is far from being understood. A deeper understanding of the interplay between mildly pathogenic rickettsiae and macrophages and the commonalities and specificities of host responses to infection would illuminate differences in immune evasion mechanisms and pathogenicity. We used quantitative proteomics by sequential windowed data independent acquisition of the total high-resolution mass spectra with tandem mass spectrometry (SWATH-MS/MS) to profile alterations resulting from infection of THP-1 macrophages with three mildly pathogenic rickettsiae: Rickettsia parkeri, Rickettsia africae, and Rickettsia massiliae, all successfully proliferating in these cells. We show that all three species trigger different proteome signatures. Our results reveal a significant impact of infection on proteins categorized as type I interferon responses, which here included several components of the retinoic acid-inducible gene I (RIG-1)-like signaling pathway, mRNA splicing, and protein translation. Moreover, significant differences in protein content between infection conditions provide evidence for species-specific induced alterations. Indeed, we confirm distinct impacts on host inflammatory responses between species during infection, demonstrating that these species trigger different levels of beta interferon (IFN-β), differences in the bioavailability of the proinflammatory cytokine interleukin 1β (IL-1β), and differences in triggering of pyroptotic events. This work reveals novel aspects and exciting nuances of macrophage-Rickettsia interactions, adding additional layers of complexity between Rickettsia and host cells' constant arms race for survival. IMPORTANCE The incidence of diseases caused by Rickettsia has been increasing over the years. It has long been known that rickettsioses comprise diseases with a continuous spectrum of severity. There are highly pathogenic species causing diseases that are life threatening if untreated, others causing mild forms of the disease, and a third group for which no pathogenicity to humans has been described. These marked differences likely reflect distinct capacities for manipulation of host cell processes, with macrophage permissiveness emerging as a key virulence trait. However, what defines pathogenicity attributes among rickettsial species is far from being resolved. We demonstrate that the mildly pathogenic Rickettsia parkeri, Rickettsia africae, and Rickettsia massiliae, all successfully proliferating in macrophages, trigger different proteome signatures in these cells and differentially impact critical components of innate immune responses by inducing different levels of beta interferon (IFN-β) and interleukin 1β (IL-1β) and different timing of pyroptotic events during infection. Our work reveals novel nuances in rickettsia-macrophage interactions, offering new clues to understand Rickettsia pathogenicity.

Real-Time Simultaneous Imaging of Acidification and Proteolysis in Single Phagosomes Using Bifunctional Janus-Particle Probes

The digestion of pathogens inside phagosomes by immune cells occurs through a sequence of reactions including acidification and proteolysis, but how the reactions are orchestrated in the right order is unclear due to a lack of methods to simultaneously measure more than one reaction in phagosomes. Here we report a bifunctional Janus-particle probe to simultaneously monitor acidification and proteolysis in single phagosomes in live cells. Each probe consists of a pH reporter and a proteolysis reporter that are spatially separated but function concurrently. Using the Janus probes, we found the acidic pH needed to initiate and maintain proteolysis, revealing the mechanism for the sequential occurrence of both reactions during pathogen digestion. We showed how bacterium-derived lipopolysaccharides alter the acidification and proteolysis in phagosomes. This study showcases Janus-particle probes as a generally applicable tool for monitoring multiple reactions in intracellular vesicles.

Modulation of Cystatin C in Human Macrophages Improves Anti-Mycobacterial Immune Responses to Mycobacterium tuberculosis Infection and Coinfection With HIV

Tuberculosis owes its resurgence as a major global health threat mostly to the emergence of drug resistance and coinfection with HIV. The synergy between HIV and Mycobacterium tuberculosis (Mtb) modifies the host immune environment to enhance both viral and bacterial replication and spread. In the lung immune context, both pathogens infect macrophages, establishing favorable intracellular niches. Both manipulate the endocytic pathway in order to avoid destruction. Relevant players of the endocytic pathway to control pathogens include endolysosomal proteases, cathepsins, and their natural inhibitors, cystatins. Here, a mapping of the human macrophage transcriptome for type I and II cystatins during Mtb, HIV, or Mtb-HIV infection displayed different profiles of gene expression, revealing cystatin C as a potential target to control mycobacterial infection as well as HIV coinfection. We found that cystatin C silencing in macrophages significantly improves the intracellular killing of Mtb, which was concomitant with an increased general proteolytic activity of cathepsins. In addition, downmodulation of cystatin C led to an improved expression of the human leukocyte antigen (HLA) class II in macrophages and an increased CD4⁺ T-lymphocyte proliferation along with enhanced IFN-γ secretion. Overall, our results suggest that the targeting of cystatin C in human macrophages represents a promising approach to improve the control of mycobacterial infections including multidrug-resistant (MDR) TB.

Cathepsins and Their Endogenous Inhibitors in Host Defense During Mycobacterium tuberculosis and HIV Infection

The moment a very old bacterial pathogen met a young virus from the 80's defined the beginning of a tragic syndemic for humanity. Such is the case for the causative agent of tuberculosis and the human immunodeficiency virus (HIV). Syndemic is by definition a convergence of more than one disease resulting in magnification of their burden. Both pathogens work synergistically contributing to speed up the replication of each other. Mycobacterium tuberculosis (Mtb) and HIV infections are in the 21st century among the leaders of morbidity and mortality of humankind. There is an urgent need for development of new approaches for prevention, better diagnosis, and new therapies for both infections. Moreover, these approaches should consider Mtb and HIV as a co-infection, rather than just as separate problems, to prevent further aggravation of the HIV-TB syndemic. Both pathogens manipulate the host immune responses to establish chronic infections in intracellular niches of their host cells. This includes manipulation of host relevant antimicrobial proteases such as cathepsins or their endogenous inhibitors. Here we discuss recent understanding on how Mtb and HIV interact with cathepsins and their inhibitors in their multifactorial functions during the pathogenesis of both infections. Particularly we will address the role on pathogen transmission, during establishment of intracellular chronic niches and in granuloma clinical outcome and tuberculosis diagnosis. This area of research will open new avenues for the design of innovative therapies and diagnostic interventions so urgently needed to fight this threat to humanity.

A recombinant bovine adenoviral mucosal vaccine expressing mycobacterial antigen-85B generates robust protection against tuberculosis in mice

Although the BCG vaccine offers partial protection, tuberculosis remains a leading cause of infectious disease death, killing ∼1.5 million people annually. We developed mucosal vaccines expressing the autophagy-inducing peptide C5 and mycobacterial Ag85B-p25 epitope using replication-defective human adenovirus (HAdv85C5) and bovine adenovirus (BAdv85C5) vectors. BAdv85C5-infected dendritic cells (DCs) expressed a robust transcriptome of genes regulating antigen processing compared to HAdv85C5-infected DCs. BAdv85C5-infected DCs showed enhanced galectin-3/8 and autophagy-dependent in vitro Ag85B-p25 epitope presentation to CD4 T cells. BCG-vaccinated mice were intranasally boosted using HAdv85C5 or BAdv85C5 followed by infection using aerosolized Mycobacterium tuberculosis (Mtb). BAdv85C5 protected mice against tuberculosis both as a booster after BCG vaccine (>1.4-log10 reduction in Mtb lung burden) and as a single intranasal dose (>0.5-log10 reduction). Protection was associated with robust CD4 and CD8 effector (TEM), central memory (TCM), and CD103+/CD69+ lung-resident memory (TRM) T cell expansion, revealing BAdv85C5 as a promising mucosal vaccine for tuberculosis.

Repurposing Saquinavir for Host-Directed Therapy to Control Mycobacterium Tuberculosis Infection

Despite the available antibiotics, tuberculosis (TB) has made its return since the 90’s of the last century as a global threat mostly due to co-infection with HIV, to the emergence of drug resistant strains and the lack of an effective vaccine. Host-directed strategies could be exploited to improve treatment efficacy, contain drug-resistant strains, improve immune responses and reduce disease severity. Macrophages in the lungs are often found infected with Mycobacterium tuberculosis (Mtb) and/or with HIV. The long-term survival of lung macrophages infected with Mtb or with HIV, together with their ability to produce viral particles, especially during TB, makes these niches major contributors to the pathogenicity of the infection. Among the available drugs to control HIV infection, protease inhibitors (PIs), acting at post-integrational stages of virus replication cycle, are the only drugs able to interfere with virus production and release from macrophages during chronic infection. For Mtb we recently found that the pathogen induces a general down-regulation of lysosomal proteases, helping bacteria to establish an intracellular niche in macrophages. Here we found that the PI saquinavir, contrary to ritonavir, is able to induce an increase of endolysosomal proteases activity especially of cathepsin S in Mtb infected macrophages and during co-infection with HIV. Our results indicate that saquinavir treatment of infected macrophages led not only to a significant intracellular killing of Mtb but also: (i) to an improved expression of the HLA class II antigen presentation machinery at the cell surface; (ii) to increased T-lymphocyte priming and proliferation; and (iii) to increased secretion of IFN-γ. All together the results indicate saquinavir as a potential host directed therapy for tuberculosis.

Tolerance of Listeria monocytogenes to biocides used in food processing environments

Listeria monocytogenes is a foodborne pathogen that causes a life-threatening disease in humans known as listeriosis. Contamination of food during processing is the main route of transmission of Listeria monocytogenes. Therefore, biocides play a crucial role in food processing environments as they act as the first line of defense in the prevention and control of L. monocytogenes. Residues of biocides may be present at sublethal concentrations after disinfection. This, unfortunately, subjects L. monocytogenes to selection pressure, giving rise to tolerant strains, which pose a threat to food safety and public health. This review will give a brief description of L. monocytogenes, the clinical manifestation, treatment of listeriosis as well as recently recorded outbreaks. The article will then discuss the current literature on the ability of L. monocytogenes strains to tolerate biocides especially quaternary ammonium compounds as well as the mechanisms of tolerance towards biocides including the activation of efflux pump systems.

Lysophosphatidylcholine Enhances Bactericidal Activity by Promoting Phagosome Maturation via the Activation of the NF-κB Pathway during Salmonella Infection in Mouse Macrophages

Salmonella enterica serovar Typhimurium (S. Typhimurium) is a facultative intracellular pathogen that causes salmonellosis and mortality worldwide. S. Typhimurium infects macrophages and survives within phagosomes by avoiding the phagosome-lysosome fusion system. Phagosomes sequentially acquire different Rab GTPases during maturation and eventually fuse with acidic lysosomes. Lysophosphatidylcholine (LPC) is a bioactive lipid that is associated with the generation of chemoattractants and reactive oxygen species (ROS). In our previous study, LPC controlled the intracellular growth of Mycobacterium tuberculosis by promoting phagosome maturation. In this study, to verify whether LPC enhances phagosome maturation and regulates the intracellular growth of S. Typhimurium, macrophages were infected with S. Typhimurium. LPC decreased the intracellular bacterial burden, but it did not induce cytotoxicity in S. Typhimuriuminfected cells. In addition, combined administration of LPC and antibiotic significantly reduced the bacterial burden in the spleen and the liver. The ratios of the colocalization of intracellular S. Typhimurium with phagosome maturation markers, such as early endosome antigen 1 (EEA1) and lysosome-associated membrane protein 1 (LAMP-1), were significantly increased in LPC-treated cells. The expression level of cleaved cathepsin D was rapidly increased in LPCtreated cells during S. Typhimurium infection. Treatment with LPC enhanced ROS production, but it did not affect nitric oxide production in S. Typhimurium-infected cells. LPC also rapidly triggered the phosphorylation of IκBα during S. Typhimurium infection. These results suggest that LPC can improve phagosome maturation via ROS-induced activation of NF-κB pathway and thus may be developed as a therapeutic agent to control S. Typhimurium growth.

Cathepsins in Bacteria-Macrophage Interaction: Defenders or Victims of Circumstance?

Macrophages are the first encounters of invading bacteria and are responsible for engulfing and digesting pathogens through phagocytosis leading to initiation of the innate inflammatory response. Intracellular digestion occurs through a close relationship between phagocytic/endocytic and lysosomal pathways, in which proteolytic enzymes, such as cathepsins, are involved. The presence of cathepsins in the endo-lysosomal compartment permits direct interaction with and killing of bacteria, and may contribute to processing of bacterial antigens for presentation, an event necessary for the induction of antibacterial adaptive immune response. Therefore, it is not surprising that bacteria can control the expression and proteolytic activity of cathepsins, including their inhibitors – cystatins, to favor their own intracellular survival in macrophages. In this review, we summarize recent developments in defining the role of cathepsins in bacteria-macrophage interaction and describe important strategies engaged by bacteria to manipulate cathepsin expression and activity in macrophages. Particularly, we focus on specific bacterial species due to their clinical relevance to humans and animal health, i.e., Mycobacterium, Mycoplasma, Staphylococcus, Streptococcus, Salmonella, Shigella, Francisella, Chlamydia, Listeria, Brucella, Helicobacter, Neisseria, and other genera.

Variations in Antimicrobial Activities of Human Monocyte-Derived Macrophage and Their Associations With Tuberculosis Clinical Manifestations

Macrophages play a significant role in preventing infection through antimicrobial activities, particularly acidification, and proteolysis. Mycobacterium tuberculosis (Mtb) infection can lead to diverse outcomes, from latent asymptomatic infection to active disease involving multiple organs. Monocyte-derived macrophage is one of the main cell types accumulating in lungs following Mtb infection. The variation of intracellular activities of monocyte-derived macrophages in humans and the influence of these activities on the tuberculosis (TB) spectrum are not well understood. By exploiting ligand-specific bead-based assays, we investigated macrophage antimicrobial activities real-time in healthy volunteers (n = 53) with 35 cases of latent TB (LTB), and those with active TB (ATB), and either pulmonary TB (PTB, n = 70) or TB meningitis (TBM, n = 77). We found wide person-to-person variations in acidification and proteolytic activities in response to both non-immunogenic IgG and pathogenic ligands comprising trehalose 6,6'−dimycolate (TDM) from Mtb or β-glucan from Saccharamyces cerevisiase. The variation in the macrophage activities remained similar regardless of stimuli; however, IgG induced stronger acidification activity than immunogenic ligands TDM (P = 10⁻⁵, 3 × 10⁻⁵ and 0.01 at 30, 60, and 90 min) and β-glucan (P = 10⁻⁴, 3 × 10⁻⁴ and 0.04 at 30, 60, and 90 min). Variation in proteolysis activity was slightly higher in LTB than in ATB (CV = 40% in LTB vs. 29% in ATB, P = 0.03). There was no difference in measured antimicrobial activities in response to TDM and bacterial killing in macrophages from LTB and ATB, or from PTB and TBM. Our results indicate that antimicrobial activities of monocyte-derived macrophages vary among individuals and show immunological dependence, but suggest these activities cannot be solely responsible for the control of bacterial replication or dissemination in TB.

Acid Sphingomyelinase Contributes to the Control of Mycobacterial Infection via a Signaling Cascade Leading from Reactive Oxygen Species to Cathepsin D

Tuberculosis, caused by Mycobacterium tuberculosis, is one of the most severe diseases worldwide. The initial pulmonary localization of the pathogen often develops into systemic infection with high lethality. The present work investigated the role of sphingolipids, specifically the function of acid sphingomyelinase (Asm) and ceramide, in infection of murine macrophages in vitro and mice in vivo with Mycobacterium bovis Bacillus Calmette-Guérin (BCG). In vitro, we investigated macrophages from wild-type (wt) and Asm deficient (Asm^−/−) mice to define signaling events induced by BCG infection and mediated by Asm. We demonstrate that infection of wt macrophages results in activation of Asm, which increases reactive oxygen species (ROS) via stimulation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. ROS promote BCG degradation by cathepsin D. Asm deficiency in macrophages abrogates these effects. In vivo studies reveal that wt mice rapidly control BCG infection, while Asm^−/− mice fail to control the infection and kill the bacteria. Transplantation of wt macrophages into Asm^−/− mice reversed their susceptibility to BCG, demonstrating the importance of Asm in macrophages for defense against BCG. These findings indicate that Asm is important for the control of BCG infection.

Secreted cystatins decrease proliferation and enhance apoptosis of human leukemic cells

Cysteine proteases are implicated in proteolysis events favoring cancer cell growth, spread, and death by apoptosis. Herein, we have studied whether the net growth and survival of the leukemic cell lines Jurkat, U937, and HL‐60 are affected by external addition of five proteins acting as natural cysteine protease inhibitors. None of the cystatins examined (A, C, D, and E/M) or chagasin showed consistent effects on Fas‐induced apoptosis when evaluated at 1 µm. In contrast, when the intrinsic apoptosis pathway was activated by hydrogen peroxide, addition of cystatin D augmented caspase‐3‐like activity within all three cell lines. Flow cytometric analysis of U937 cells also showed increased numbers of annexin V‐positive cells when hydrogen peroxide was used to initiate apoptosis and cells were cultured in the presence of cystatin D or C. Moreover, stimulation of hydrogen peroxide‐induced apoptotic U937 cells with either cystatin C or D resulted in a dose‐dependent decrease in the number of cells. Cell viability was also decreased when U937 cells were cultured in the presence of cystatin C or D (1–9 µm) only, demonstrating that these cystatins can reduce cell proliferation by themselves in addition to enhancing apoptosis induced by oxidative stress. These effects on U937 cells were paralleled by internalization of cystatins C and D, indicating these effects are caused by downregulation of intracellular proteolysis. External addition of cystatins C and D to HL‐60 and Jurkat cells demonstrated similar degrees of cystatin D uptake and decreased viability as for U937 cells, indicating that these effects are general for leukemic cells.

The flavonoids of Sophora flavescens exerts anti-inflammatory activity via promoting autophagy of Bacillus Calmette-Guérin-stimulated macrophages

Tuberculosis (TB), a highly infectious air-borne disease, has remained a global health problem. Conventional treatment and preventions such as antibiotics and Bacilli Calmette-Guerin (BCG) vaccine can be unreliable. In view of the increasing prevalence of anti-TB drug resistance, adjunctive therapy may be necessary to shorten the recovery time. We have previously shown that flavonoids in the medicinal herb Sophora flavescens exhibit anti-inflammatory and bactericidal activities. The aim of this study was to investigate the molecular and cellular characteristics of flavonoids of S. flavescens (FSF) in BCG-stimulated macrophages for assessing their roles in anti-inflammation and autophagy. Mouse alveolar macrophage (MH-S) cell line and primary mouse peritoneal macrophages were stimulated in vitro with heat-inactivated BCG and treated with FSF, with or without autophagy inhibitor Bafilomycin A1 (BafA1). Gene expression was analyzed using quantitative PCR, and cytokine/chemokine release was analyzed by Milliplex assay and ELISA. Autophagy-related proteins were quantified by Western blot and flow cytometry, and autophagolysosomes were detected using fluorescence microscopy. In both MH-S cell line and mouse peritoneal macrophages stimulated by heat-inactivated BCG, FSF was found to up-regulate autophagy-related proteins microtubule-associated protein 1A/1B-light chain 3 (LC3) and protein 62 (p62), and suppress the induced proinflammatory cytokine TNF-α, CCL5, and IL-6. FSF actively modulates immune processes through suppressing BCG-mediated inflammation by promoting autophagy in MH-S cells and mouse peritoneal macrophages. We suggest that FSF may be useful as an adjunctive therapeutic agent for TB infection by modulating cell survival through autophagy and reducing inflammation.

A simple purification procedure of buffalo lung cathepsin H, its properties and influence of buffer constituents on the enzyme activity

BACKGROUND

Cathepsin H (E.C.3.4.22.16) belongs to a family of lysosomal cysteine protease which regulates diverse normal biological processes mainly in intracellular proteolysis.

METHODS

Purification of cathepsin H from an unstudied system i.e. buffalo lung has been achieved by a simple process developed after incorporating appropriate alteration in the available methods for isolation of the enzyme from other sources. The use of DEAE-Cellulose and SP-Sephadex C-50 helped in better and simultaneous separation of cathepsin B and H up to homogeneity.

RESULTS

The SDS-PAGE result showed buffalo cathepsin H to be a single-chain molecule having MW, NH2- and COOH- terminal residues of 25.4 kDa, Lys and Val respectively. The enzyme was a glycoprotein with pI of 6.2; it hydrolyzed Leu-NA (Vmax/Km = 301.6) as the most efficient substrate followed by Arg-NA, Arg-Arg-NA and BANA. Buffalo enzyme showed maximum activity at 36 °C, pH 6.75 and at a buffer concentration of 2 × 10-3 M.

CONCLUSION

Catheptic activity was found to be quite stable at least for 20-30 min between pH 4.5-7.0, buffer concentration of 1 × 10-2 to 4 × 10-2 M and the temperature resistance up to 36 °C. The effects of various substances present in the buffers routinely used for the assay of catheptic activity revealed that the activity of buffalo lung cathepsin H depends not only qualitatively but also quantitatively on the constituents of assay buffer.

GENERAL SIGNIFICANCE

This study seems to provide valuable information regarding the biochemistry of cathepsin H in general as well as influence of buffer constituents on enzyme activity and physiological role in particular.

Towards new TB vaccines

Mycobacterium tuberculosis remains the leading cause of death attributed to a single infectious organism. Bacillus Calmette-Guerin (BCG), the standard vaccine against M. tuberculosis, is thought to prevent only 5% of all vaccine-preventable deaths due to tuberculosis, thus an alternative vaccine is required. One of the principal barriers to vaccine development against M. tuberculosis is the complexity of the immune response to infection, with uncertainty as to what constitutes an immunological correlate of protection. In this paper, we seek to give an overview of the immunology of M. tuberculosis infection, and by doing so, investigate possible targets of vaccine development. This encompasses the innate, adaptive, mucosal and humoral immune systems. Though MVA85A did not improve protection compared with BCG alone in a large-scale clinical trial, the correlates of protection this has revealed, in addition to promising results from candidate such as VPM1002, M72/ASO1E and H56:IC31 point to a brighter future in the field of TB vaccine development.