Heparin-binding hemagglutinin HBHA from Mycobacterium tuberculosis affects actin polymerisation

Comparative transcriptomics reveals common and strain-specific responses of human macrophages to infection with Mycobacterium tuberculosis and Mycobacterium bovis BCG

Mycobacterium tuberculosis (MTB) and Mycobacterium bovis (M. bovis) are closely related pathogenic mycobacteria known to cause chronic pulmonary infections in both humans and animals. Despite sharing nearly identical genomes and virulence factors, these two bacteria display variations in host tropism, epidemiology, and clinical presentations. M. bovis Bacillus Calmette-Guérin (BCG) is an attenuated strain of M. bovis commonly utilized as a vaccine for tuberculosis (TB). Nevertheless, the molecular underpinnings of these distinctions and the intricacies of host-pathogen interactions remain areas of ongoing research. In this study, a comparative transcriptomic analysis was conducted on human leukemia macrophages (THP-1) infected with either MTB H37Rv or M. bovis BCG (Tokyo strain) to elucidate common and strain-specific responses at the transcriptional level. RNA sequencing was utilized to characterize the transcriptomes of human primary macrophages infected with MTB or BCG at 6 and 24 h post-infection. The findings indicate that both MTB and BCG induce substantial and dynamic alterations in the transcriptomes of THP-1, with a notable overlap in the quantity and extent of differentially expressed genes (DEGs). Moreover, gene ontology (GO) enrichment analysis unveiled shared pathways related to immune response, cytokine signaling, and apoptosis. The immune response of macrophages to bacterial infections at 6 h exhibited significantly greater intensity compared to that at 24 h. Furthermore, distinct gene sets displaying notable variances between MTB and BCG infections were identified. The profound impact of MTB infection on macrophage gene expression, particularly within the initial 6 h, was evident. Additionally, downregulation of pathways such as Focal adhesion, Rap1 signaling pathway, and Regulation of actin cytoskeleton was observed. The pathways associated with inflammation reactions and cell apoptosis exhibited significant differences, with BCG triggering macrophage apoptosis and MTB enhancing the survival of intracellular bacteria. Our findings reveal that MTB and BCG provoke similar yet distinct transcriptional responses in human macrophages, indicating variations in their pathogenesis and ability to adapt to host environments. These results offer novel insights into the molecular mechanisms governing host-pathogen interactions and may contribute to a deeper understanding of TB pathogenesis.

Central Nervous System Tuberculosis in a Murine Model: Neurotropic Strains or a New Pathway of Infection?

Tuberculosis (TB) of the central nervous system (CNS) is a lethal and incapacitating disease. Several studies have been performed to understand the mechanism of bacterial arrival to CNS, however, it remains unclear. Although the interaction of the host, the pathogen, and the environment trigger the course of the disease, in TB the characteristics of these factors seem to be more relevant in the genesis of the clinical features of each patient. We previously tested three mycobacterial clinical isolates with distinctive genotypes obtained from the cerebrospinal fluid of patients with meningeal TB and showed that these strains disseminated extensively to the brain after intratracheal inoculation and pulmonary infection in BALB/c mice. In this present study, BALB/c mice were infected through the intranasal route. One of these strains reaches the olfactory bulb at the early stage of the infection and infects the brain before the lungs, but the histological study of the nasal mucosa did not show any alteration. This observation suggests that some mycobacteria strains can arrive directly at the brain, apparently toward the olfactory nerve after infecting the nasal mucosa, and guides us to study in more detail during mycobacteria infection the nasal mucosa, the associated connective tissue, and nervous structures of the cribriform plate, which connect the nasal cavity with the olfactory bulb.

A VLP-Based Vaccine Displaying HBHA and MTP Antigens of Mycobacterium tuberculosis Induces Protective Immune Responses in M. tuberculosis H37Ra Infected Mice

Heparin-binding hemagglutinin (HBHA) and M. tuberculosis pili (MTP) are important antigens on the surface of Mycobacterium tuberculosis. To display these antigens effectively, the fusion protein HBHA-MTP with a molecular weight of 20 kD (L20) was inserted into the receptor-binding hemagglutinin (HA) fragment of influenza virus and was expressed along with matrix protein M1 in Sf9 insect cells to generate influenza virus-like particles (LV20 in short). The results showed that the insertion of L20 into the envelope of the influenza virus did not affect the self-assembly and morphology of LV20 VLPs. The expression of L20 was successfully verified by transmission electron microscopy. Importantly, it did not interfere with the immunogenicity reactivity of LV20 VLPs. We demonstrated that LV20 combined with the adjuvant composed of DDA and Poly I: C (DP) elicited significantly higher antigen-specific antibodies and CD4+/CD8+ T cell responses than PBS and BCG vaccination in mice. It suggests that the insect cell expression system is an excellent protein production system, and LV20 VLPs could be a novel tuberculosis vaccine candidate for further evaluation.

A universal stress protein upregulated by hypoxia has a role in Burkholderia cenocepacia intramacrophage survival: Implications for chronic infection in cystic fibrosis

Universal stress proteins (USPs) are ubiquitously expressed in bacteria, archaea, and eukaryotes and play a lead role in adaptation to environmental conditions. They enable adaptation of bacterial pathogens to the conditions encountered in the human niche, including hypoxia, oxidative stress, osmotic stress, nutrient deficiency, or acid stress, thereby facilitating colonization. We previously reported that all six USP proteins encoded within a low-oxygen activated (lxa) locus in Burkholderia cenocepacia showed increased abundance during chronic colonization of the cystic fibrosis (CF) lung. However, the role of USPs in chronic cystic fibrosis infection is not well understood. Structural modeling identified surface arginines on one lxa-encoded USP, USP76, which suggested it mediated interactions with heparan sulfate. Using mutants derived from the B. cenocepacia strain, K56-2, we show that USP76 is involved in host cell attachment. Pretreatment of lung epithelial cells with heparanase reduced the binding of the wild-type and complement strains but not the Δusp76 mutant strain, indicating that USP76 is directly or indirectly involved in receptor recognition on the surface of epithelial cells. We also show that USP76 is required for growth and survival in many conditions associated with the CF lung, including acidic conditions and oxidative stress. Moreover, USP76 also has a role in survival in macrophages isolated from people with CF. Overall, while further elucidation of the exact mechanism(s) is required, we can conclude that USP76, which is upregulated during chronic infection, is involved in bacterial survival within CF macrophages, a hallmark of Burkholderia infection.

Mycobacterium bovis Bacillus Calmette-Guérin-Infected Dendritic Cells Induce TNF-α-Dependent Cell Cluster Formation That Promotes Bacterial Dissemination through an In Vitro Model of the Blood-Brain Barrier

CNS tuberculosis (CNSTB) is the most severe manifestation of extrapulmonary tuberculosis infection, but the mechanism of how mycobacteria cross the blood-brain barrier (BBB) is not well understood. In this study, we report a novel murine in vitro BBB model combining primary brain endothelial cells, Mycobacterium bovis bacillus Calmette-Guérin-infected dendritic cells (DCs), PBMCs, and bacterial Ag-specific CD4⁺ T cells. We show that mycobacterial infection limits DC mobility and also induces cellular cluster formation that has a similar composition to pulmonary mycobacterial granulomas. Within the clusters, infection from DCs disseminates to the recruited monocytes, promoting bacterial expansion. Mycobacterium-induced in vitro granulomas have been described previously, but this report shows that they can form on brain endothelial cell monolayers. Cellular cluster formation leads to cluster-associated damage of the endothelial cell monolayer defined by mitochondrial stress, disorganization of the tight junction proteins ZO-1 and claudin-5, upregulation of the adhesion molecules VCAM-1 and ICAM-1, and increased transmigration of bacteria-infected cells across the BBB. TNF-α inhibition reduces cluster formation on brain endothelial cells and mitigates cluster-associated damage. These data describe a model of bacterial dissemination across the BBB shedding light on a mechanism that might contribute to CNS tuberculosis infection and facilitate treatments.

Structural and dynamic studies provide insights into specificity and allosteric regulation of ribonuclease as, a key enzyme in mycobacterial virulence

Ribonuclease AS (RNase AS) is a crucial enzyme for virulence of Mycobacterium tuberculosis. We previously observed that RNase AS structurally resembles RNase T from Escherichia coli, an important enzyme for tRNA maturation and turnover. Here, we combine X-ray crystallography and molecular dynamics (MD) to investigate the specificity and dynamic properties of substrate binding. Both X-ray and MD data provide structural determinants that corroborate the strict substrate specificity of RNase AS to cleave only adenosine residues, due to the structural features of adenine base. Beside suggesting tRNA as most likely substrate of RNase AS, MD and modeling studies identify key enzyme-ligand interactions, both involving the catalytic site and the double helix region of tRNA, which is locked by interactions with a set of arginine residues. The MD data also evidence a ligand-induced conformational change of the enzyme which is transferred from one chain to the adjacent one. These data will explain the dimeric nature of both RNase AS and RNase T, with two catalytic grooves composed of both chains. Also, they account for the dichotomy of tRNA, which contains both the substrate poly(A) chain and an inhibiting double strand RNA. Indeed, they provide a possible mechanism of allosteric regulation, which unlocks one catalytic groove when the second groove is inhibited by the double strand region of tRNA. Finally, a full comprehension of the molecular details of tRNA maturation processes is essential to develop novel strategies to modulate RNA processing, for therapeutic purposes. AbbreviationsMDmolecular dynamicsPDBProtein Data BankRMSDroot mean square deviationRMSFroot mean square fluctuationRNAribonucleotidic acidRNase ASRibonuclease ASCommunicated by Ramasamy H. Sarma.

The Mycobacterial HBHA Protein: A Promising Biomarker for Tuberculosis

A major goal in tuberculosis (TB) research is the identification, among the subjects infected with Mycobacterium tuberculosis (Mtb), of those with active TB, or at higher risk of developing active disease, from the latently infected subjects. The classical heterogeneity of Mtb infection and TB disease is a major obstacle toward the identification of reliable biomarkers that can stratify Mtb infected subjects based on disease risk. The heparin-binding haemagglutinin (HBHA) is a mycobacterial surface antigen that is implicated in tuberculosis (TB) pathogenesis. The host immune response against HBHA varies depending on the TB status and several studies are supporting the role of HBHA as a useful biomarker of TB.

Inactivated Lactobacillus plantarum Carrying a Surface-Displayed Ag85B-ESAT-6 Fusion Antigen as a Booster Vaccine Against Mycobacterium tuberculosis Infection

Vaccination is considered the most effective strategy for controlling tuberculosis (TB). The existing vaccine, the Bacille Calmette-Guérin (BCG), although partially protective, has a number of limitations. Therefore, there is a need for developing new TB vaccines and several strategies are currently exploited including the use of viral and bacterial delivery vectors. We have previously shown that Lactobacillus plantarum (Lp) producing Ag85B and ESAT-6 antigens fused to a dendritic cell-targeting peptide (referred to as Lp_DC) induced specific immune responses in mice. Here, we analyzed the ability of two Lp-based vaccines, Lp_DC and Lp_HBD (in which the DC-binding peptide was replaced by an HBD-domain directing the antigen to non-phagocytic cells) to activate antigen-presenting cells, induce specific immunity and protect mice from Mycobacterium tuberculosis infection. We tested two strategies: (i) Lp as BCG boosting vaccine (a heterologous regimen comprising parenteral BCG immunization followed by intranasal Lp boost), and (ii) Lp as primary vaccine (a homologous regimen including subcutaneous priming followed by intranasal boost). The results showed that both Lp constructs applied as a BCG boost induced specific cellular immunity, manifested in T cell proliferation, antigen-specific IFN-γ responses and multifunctional T cells phenotypes. More importantly, intranasal boost with Lp_DC or Lp_HBD enhanced protection offered by BCG, as shown by reduced M. tuberculosis counts in lungs. These findings suggest that Lp constructs could be developed as a potential mucosal vaccine platform against mycobacterial infections.

The Cell Wall Hydrolytic NlpC/P60 Endopeptidases in Mycobacterial Cytokinesis: A Structural Perspective

In preparation for division, bacteria replicate their DNA and segregate the newly formed chromosomes. A division septum then assembles between the chromosomes, and the mother cell splits into two identical daughters due to septum degradation. A major constituent of bacterial septa and of the whole cell wall is peptidoglycan (PGN), an essential cell wall polymer, formed by glycan chains of β−(1-4)-linked-N-acetylglucosamine (GlcNAc) and N-acetylmuramic acid (MurNAc), cross-linked by short peptide stems. Depending on the amino acid located at the third position of the peptide stem, PGN is classified as either Lys-type or meso-diaminopimelic acid (DAP)-type. Hydrolytic enzymes play a crucial role in the degradation of bacterial septa to split the cell wall material shared by adjacent daughter cells to promote their separation. In mycobacteria, a key PGN hydrolase, belonging to the NlpC/P60 endopeptidase family and denoted as RipA, is responsible for the degradation of septa, as the deletion of the gene encoding for this enzyme generates abnormal bacteria with multiple septa. This review provides an update of structural and functional data highlighting the central role of RipA in mycobacterial cytokinesis and the fine regulation of its catalytic activity, which involves multiple molecular partners.

Lectins of Mycobacterium tuberculosis - rarely studied proteins

The importance of bacterial lectins for adhesion, pathogenicity, and biofilm formation is well established for many Gram-positive and Gram-negative bacteria. However, there is very little information available about lectins of the tuberculosis-causing bacterium, Mycobacterium tuberculosis (Mtb). In this paper we review previous studies on the carbohydrate-binding characteristics of mycobacteria and related Mtb proteins, discussing their potential relevance to Mtb infection and pathogenesis.

The role of epigenetics, bacterial and host factors in progression of Mycobacterium tuberculosis infection

Tuberculosis (TB) infection caused by Mycobacterium tuberculosis (Mtb) is still a persistent global health problem, particularly in developing countries. The World Health Organization (WHO) reported a mortality rate of about 1.8 million worldwide due to TB complications in 2015. The Bacillus Calmette-Guérin (BCG) vaccine was introduced in 1921 and is still widely used to prevent TB development. This vaccine offers up to 80% protection against various forms of TB; however its efficacy against lung infection varies among different geographical settings. Devastatingly, the development of various forms of drug-resistant TB strains has significantly impaired the discovery of effective and safe anti-bacterial agents. Consequently, this necessitated discovery of new drug targets and novel anti-TB therapeutics to counter infection caused by various Mtb strains. Importantly, various factors that contribute to TB development have been identified and include bacterial resuscitation factors, host factors, environmental factors and genetics. Furthermore, Mtb-induced epigenetic changes also play a crucial role in evading the host immune response and leads to bacterial persistence and dissemination. Recently, the application of GeneXpert MTB/RIF^® to rapidly diagnose and identify drug-resistant strains and discovery of different molecular markers that distinguish between latent and active TB infection has motivated and energised TB research. Therefore, this review article will briefly discuss the current TB state, highlight various mechanisms employed by Mtb to evade the host immune response as well as to discuss some modern molecular techniques that may potentially target and inhibit Mtb replication.

Collagen degradation in tuberculosis pathogenesis: the biochemical consequences of hosting an undesired guest

The scenario of chemical reactions prompted by the infection by Mycobacterium tuberculosis is huge. The infection generates a localized inflammatory response, with the recruitment of neutrophils, monocytes, and T-lymphocytes. Consequences of this immune reaction can be the eradication or containment of the infection, but these events can be deleterious to the host inasmuch as lung tissue can be destroyed. Indeed, a hallmark of tuberculosis (TB) is the formation of lung cavities, which increase disease development and transmission, as they are sites of high mycobacterial burden. Pulmonary cavitation is associated with antibiotic failure and the emergence of antibiotic resistance. For cavities to form, M. tuberculosis induces the overexpression of host proteases, like matrix metalloproteinases and cathepsin, which are secreted from monocyte-derived cells, neutrophils, and stromal cells. These proteases destroy the lung parenchyma, in particular the collagen constituent of the extracellular matrix (ECM). Namely, in an attempt to destroy infected cells, the immune reactions prompted by mycobacterial infections induce the destruction of vital regions of the lung, in a process that can become fatal. Here, we review structure and function of the main molecular actors of ECM degradation due to M. tuberculosis infection and the proposed mechanisms of tissue destruction, mainly attacking fibrillar collagen. Importantly, enzymes responsible for collagen destruction are emerging as key targets for adjunctive therapies to limit immunopathology in TB.

Association of Mycobacterium Proteins with Lipid Droplets

Mycobacterium tuberculosis is a global pathogen of significant medical importance. A key aspect of its life cycle is the ability to enter into an altered physiological state of nonreplicating persistence during latency and resist elimination by the host immune system. One mechanism by which M. tuberculosis facilitates its survival during latency is by producing and metabolizing intracytoplasmic lipid droplets (LDs). LDs are quasi-organelles consisting of a neutral lipid core such as triacylglycerol surrounded by a phospholipid monolayer and proteins. We previously reported that PspA (phage shock protein A) associates with LDs produced in Mycobacterium In particular, the loss or overproduction of PspA alters LD homeostasis in Mycobacterium smegmatis and attenuates the survival of M. tuberculosis during nonreplicating persistence. Here, M. tuberculosis PspA (PspA_Mtb) and a ΔpspA M. smegmatis mutant were used as model systems to investigate the mechanism by which PspA associates with LDs and determine if other Mycobacterium proteins associate with LDs using a mechanism similar to that for PspA. Through this work, we established that the amphipathic helix present in the first α-helical domain (H1) of PspA is both necessary and sufficient for the targeting of this protein to LDs. Furthermore, we identified other Mycobacterium proteins that also possess amphipathic helices similar to PspA H1, including a subset that localize to LDs. Altogether, our results indicate that amphipathic helices may be an important mechanism by which proteins target LDs in prokaryotes.IMPORTANCEMycobacterium spp. are one of the few prokaryotes known to produce lipid droplets (LDs), and their production has been linked to aspects of persistent infection by M. tuberculosis Unfortunately, little is known about LD production in these organisms, including how LDs are formed, their function, or the identity of proteins that associate with them. In this study, an established M. tuberculosis LD protein and a surrogate Mycobacterium host were used as model systems to study the interactions between proteins and LDs in bacteria. Through these studies, we identified a commonly occurring protein motif that is able to facilitate the association of proteins to LDs in prokaryotes.

A structural overview of mycobacterial adhesins: Key biomarkers for diagnostics and therapeutics

Adherence, colonization, and survival of mycobacteria in host cells require surface adhesins, which are attractive pharmacotherapeutic targets. A large arsenal of pilus and non-pilus adhesins have been identified in mycobacteria. These adhesins are capable of interacting with host cells, including macrophages and epithelial cells and are essential to microbial pathogenesis. In the last decade, several structures of mycobacterial adhesins responsible for adhesion to either macrophages or extra cellular matrix proteins have been elucidated. In addition, key structural and functional information have emerged for the process of mycobacterial adhesion to epithelial cells, mediated by the Heparin-binding hemagglutinin (HBHA). In this review, we provide an overview of the structural and functional features of mycobacterial adhesins and discuss their role as important biomarkers for diagnostics and therapeutics. Based on the reported data, it appears clear that adhesins are endowed with a variety of different structures and functions. Most adhesins play important roles in the cell life of mycobacteria and are key virulence factors. However, they have adapted to an extracellular life to exert a role in host-pathogen interaction. The type of interactions they form with the host and the adhesin regions involved in binding is partly known and is described in this review.

ArfGAP1 restricts Mycobacterium tuberculosis entry by controlling the actin cytoskeleton

The interaction of Mycobacterium tuberculosis (Mtb) with pulmonary epithelial cells is critical for early stages of bacillus colonization and during the progression of tuberculosis. Entry of Mtb into epithelial cells has been shown to depend on F-actin polymerization, though the molecular mechanisms are still unclear. Here, we demonstrate that mycobacterial uptake into epithelial cells requires rearrangements of the actin cytoskeleton, which are regulated by ADP-ribosylation factor 1 (Arf1) and phospholipase D1 (PLD1), and is dependent on the M3 muscarinic receptor (M₃R). We show that this pathway is controlled by Arf GTPase-activating protein 1 (ArfGAP1), as its silencing has an impact on actin cytoskeleton reorganization leading to uncontrolled uptake and replication of Mtb. Furthermore, we provide evidence that this pathway is critical for mycobacterial entry, while the cellular infection with other pathogens, such as Shigella flexneri and Yersinia pseudotuberculosis, is not affected. Altogether, these results reveal how cortical actin plays the role of a barrier to prevent mycobacterial entry into epithelial cells and indicate a novel role for ArfGAP1 as a restriction factor of host-pathogen interactions.

Heparin-binding Hemagglutinin of Mycobacterium tuberculosis Is an Inhibitor of Autophagy

Airway epithelial cell is often the initial site of attack by pathogens, and cell death is commonly caused by internalization of Mycobacterium tuberculosis (Mtb). However, the mechanism of interaction between epithelial cells and Mtb is not well understood. In this study, we investigated the role of the heparin-binding hemagglutinin (HBHA) protein of Mtb in the function of epithelial cells. In particular, the autophagy of A549 cells was determined based on microtubule-associated protein 1 light chain 3 alpha (LC3) activity. Autophagosome formation was detected by Monodansylcadaverine (MDC) staining and immune fluorescence staining of LC3. Autophagy could be significantly suppressed by HBHA protein. In addition, the LDH assay results showed that HBHA treatment could induce death on A549 cells. To explore the form of cell death, we detected the activity of caspase-3 and LDH release of A549 cells in the presence or absence of caspase inhibitor Z-VAD-FMK. Results demonstrated that HBHA treatment could induce apoptosis of A549 cells. To further confirm these results, we constructed the recombinant Mycobacterium smegmatis (MS) expressing HBHA (rMS-HBHA) and explored the influence of rMS-HBHA on the function of A549 cells. rMS-HBHA infection significantly inhibited LC3 expression and the maturation of autophagosomes in A549 cells. Subsequently, we infected A549 cells with MS and detected the viability of intracellular MS by CFU counts. rMS-HBHA showed higher survival and replication capacity in A549 cells than those of the wild-type MS. Finally, infection of A549 cells with rMS-HBHA caused further apoptosis. These findings suggested that rMS-HBHA could inhibit autophagy, promote its survival and replication within A549 cells, and subsequently induce apoptosis on infected cells to facilitate infection.

Mycobacterium tuberculosis adhesins: potential biomarkers as anti-tuberculosis therapeutic and diagnostic targets

Adhesion to host cells is a precursor to host colonization and evasion of the host immune response. Conversely, it triggers the induction of the immune response, a process vital to the host’s defence against infection. Adhesins are microbial cell surface molecules or structures that mediate the attachment of the microbe to host cells and thus the host–pathogen interaction. They also play a crucial role in bacterial aggregation and biofilm formation. In this review, we discuss the role of adhesins in the pathogenesis of the aetiological agent of tuberculosis, Mycobacterium tuberculosis. We also provide insight into the structure and characteristics of some of the characterized and putative M. tuberculosis adhesins. Finally, we examine the potential of adhesins as targets for the development of tuberculosis control strategies.

Stringent homology-based prediction of H. sapiens-M. tuberculosis H37Rv protein-protein interactions

BACKGROUND

H. sapiens-M. tuberculosis H37Rv protein-protein interaction (PPI) data are essential for understanding the infection mechanism of the formidable pathogen M. tuberculosis H37Rv. Computational prediction is an important strategy to fill the gap in experimental H. sapiens-M. tuberculosis H37Rv PPI data. Homology-based prediction is frequently used in predicting both intra-species and inter-species PPIs. However, some limitations are not properly resolved in several published works that predict eukaryote-prokaryote inter-species PPIs using intra-species template PPIs.

RESULTS

We develop a stringent homology-based prediction approach by taking into account (i) differences between eukaryotic and prokaryotic proteins and (ii) differences between inter-species and intra-species PPI interfaces. We compare our stringent homology-based approach to a conventional homology-based approach for predicting host-pathogen PPIs, based on cellular compartment distribution analysis, disease gene list enrichment analysis, pathway enrichment analysis and functional category enrichment analysis. These analyses support the validity of our prediction result, and clearly show that our approach has better performance in predicting H. sapiens-M. tuberculosis H37Rv PPIs. Using our stringent homology-based approach, we have predicted a set of highly plausible H. sapiens-M. tuberculosis H37Rv PPIs which might be useful for many of related studies. Based on our analysis of the H. sapiens-M. tuberculosis H37Rv PPI network predicted by our stringent homology-based approach, we have discovered several interesting properties which are reported here for the first time. We find that both host proteins and pathogen proteins involved in the host-pathogen PPIs tend to be hubs in their own intra-species PPI network. Also, both host and pathogen proteins involved in host-pathogen PPIs tend to have longer primary sequence, tend to have more domains, tend to be more hydrophilic, etc. And the protein domains from both host and pathogen proteins involved in host-pathogen PPIs tend to have lower charge, and tend to be more hydrophilic.

CONCLUSIONS

Our stringent homology-based prediction approach provides a better strategy in predicting PPIs between eukaryotic hosts and prokaryotic pathogens than a conventional homology-based approach. The properties we have observed from the predicted H. sapiens-M. tuberculosis H37Rv PPI network are useful for understanding inter-species host-pathogen PPI networks and provide novel insights for host-pathogen interaction studies.

Neurons are host cells for Mycobacterium tuberculosis

Mycobacterium tuberculosis infection of the central nervous system is thought to be initiated once the bacilli have breached the blood brain barrier and are phagocytosed, primarily by microglial cells. In this study, the interactions of M. tuberculosis with neurons in vitro and in vivo were investigated. The data obtained demonstrate that neurons can act as host cells for M. tuberculosis. M. tuberculosis bacilli were internalized by murine neuronal cultured cells in a time-dependent manner after exposure, with superior uptake by HT22 cells compared to Neuro-2a cells (17.7% versus 9.8%). Internalization of M. tuberculosis bacilli by human SK-N-SH cultured neurons suggested the clinical relevance of the findings. Moreover, primary murine hippocampus-derived neuronal cultures could similarly internalize M. tuberculosis. Internalized M. tuberculosis bacilli represented a productive infection with retention of bacterial viability and replicative potential, increasing 2- to 4-fold within 48 h. M. tuberculosis bacillus infection of neurons was confirmed in vivo in the brains of C57BL/6 mice after intracerebral challenge. This study, therefore, demonstrates neurons as potential new target cells for M. tuberculosis within the central nervous system.

Stringent DDI-based prediction of H. sapiens-M. tuberculosis H37Rv protein-protein interactions

BACKGROUND

H. sapiens-M. tuberculosis H37Rv protein-protein interaction (PPI) data are very important information to illuminate the infection mechanism of M. tuberculosis H37Rv. But current H. sapiens-M. tuberculosis H37Rv PPI data are very scarce. This seriously limits the study of the interaction between this important pathogen and its host H. sapiens. Computational prediction of H. sapiens-M. tuberculosis H37Rv PPIs is an important strategy to fill in the gap. Domain-domain interaction (DDI) based prediction is one of the frequently used computational approaches in predicting both intra-species and inter-species PPIs. However, the performance of DDI-based host-pathogen PPI prediction has been rather limited.

RESULTS

We develop a stringent DDI-based prediction approach with emphasis on (i) differences between the specific domain sequences on annotated regions of proteins under the same domain ID and (ii) calculation of the interaction strength of predicted PPIs based on the interacting residues in their interaction interfaces. We compare our stringent DDI-based approach to a conventional DDI-based approach for predicting PPIs based on gold standard intra-species PPIs and coherent informative Gene Ontology terms assessment. The assessment results show that our stringent DDI-based approach achieves much better performance in predicting PPIs than the conventional approach. Using our stringent DDI-based approach, we have predicted a small set of reliable H. sapiens-M. tuberculosis H37Rv PPIs which could be very useful for a variety of related studies. We also analyze the H. sapiens-M. tuberculosis H37Rv PPIs predicted by our stringent DDI-based approach using cellular compartment distribution analysis, functional category enrichment analysis and pathway enrichment analysis. The analyses support the validity of our prediction result. Also, based on an analysis of the H. sapiens-M. tuberculosis H37Rv PPI network predicted by our stringent DDI-based approach, we have discovered some important properties of domains involved in host-pathogen PPIs. We find that both host and pathogen proteins involved in host-pathogen PPIs tend to have more domains than proteins involved in intra-species PPIs, and these domains have more interaction partners than domains on proteins involved in intra-species PPI.

CONCLUSIONS

The stringent DDI-based prediction approach reported in this work provides a stringent strategy for predicting host-pathogen PPIs. It also performs better than a conventional DDI-based approach in predicting PPIs. We have predicted a small set of accurate H. sapiens-M. tuberculosis H37Rv PPIs which could be very useful for a variety of related studies.

Protective and therapeutic efficacy of Mycobacterium smegmatis expressing HBHA-hIL12 fusion protein against Mycobacterium tuberculosis in mice

Tuberculosis (TB) remains a major worldwide health problem. The only vaccine against TB, Mycobacterium bovis Bacille Calmette-Guerin (BCG), has demonstrated relatively low efficacy and does not provide satisfactory protection against the disease. More efficient vaccines and improved therapies are urgently needed to decrease the worldwide spread and burden of TB, and use of a viable, metabolizing mycobacteria vaccine may be a promising strategy against the disease. Here, we constructed a recombinant Mycobacterium smegmatis (rMS) strain expressing a fusion protein of heparin-binding hemagglutinin (HBHA) and human interleukin 12 (hIL-12). Immune responses induced by the rMS in mice and protection against Mycobacterium tuberculosis (MTB) were investigated. Administration of this novel rMS enhanced Th1-type cellular responses (IFN-γ and IL-2) in mice and reduced bacterial burden in lungs as well as that achieved by BCG vaccination. Meanwhile, the bacteria load in M. tuberculosis infected mice treated with the rMS vaccine also was significantly reduced. In conclusion, the rMS strain expressing the HBHA and human IL-12 fusion protein enhanced immunogencity by improving the Th1-type response against TB, and the protective effect was equivalent to that of the conventional BCG vaccine in mice. Furthermore, it could decrease bacterial load and alleviate histopathological damage in lungs of M. tuberculosis infected mice.