Fibrinogen regulates the cytotoxicity of mycobacterial trehalose dimycolate but is not required for cell recruitment, cytokine response, or control of mycobacterial infection

Underestimated Manipulative Roles of Mycobacterium tuberculosis Cell Envelope Glycolipids During Infection

The Mycobacterium tuberculosis cell envelope has been evolving over time to make the bacterium transmissible and adaptable to the human host. In this context, the M. tuberculosis cell envelope contains a peripheral barrier full of lipids, some of them unique, which confer M. tuberculosis with a unique shield against the different host environments that the bacterium will encounter at the different stages of infection. This lipid barrier is mainly composed of glycolipids that can be characterized by three different subsets: trehalose-containing, mannose-containing, and 6-deoxy-pyranose-containing glycolipids. In this review, we explore the roles of these cell envelope glycolipids in M. tuberculosis virulence and pathogenesis, drug resistance, and further, how these glycolipids may dictate the M. tuberculosis cell envelope evolution from ancient to modern strains. Finally, we address how these M. tuberculosis cell envelope glycolipids are impacted by the host lung alveolar environment, their role in vaccination and masking host immunity, and subsequently the impact of these glycolipids in shaping how M. tuberculosis interacts with host cells, manipulating their immune response to favor the establishment of an infection.

Mycobacterial trehalose 6,6'-dimycolate induced vascular occlusion is accompanied by subendothelial inflammation

Mycobacterium tuberculosis (MTB) is a pathogen that infects and kills millions yearly. The mycobacterium's cell wall glycolipid trehalose 6,6'-dimycolate (TDM) has been used historically to model MTB induced inflammation and granuloma formation. Alterations to the model can significantly influence the induced pathology. One such method incorporates intraperitoneal pre-exposure, after which the intravenous injection of TDM generates pathological damage effectively mimicking the hypercoagulation, thrombus formation, and tissue remodeling apparent in lungs of infected individuals. The purpose of these experiments is to examine the histological inflammation involved in the TDM mouse model that induces development of the hemorrhagic response. TDM induced lungs of C57BL/6 mice to undergo granulomatous inflammation. Further histological examination of the peak response demonstrated tissue remodeling consistent with hypercoagulation. The observed vascular occlusion indicates that obstruction likely occurs due to subendothelial localized activity leading to restriction of blood vessel lumens. Trichrome staining revealed that associated damage in the hypercoagulation model is consistent with intra endothelial cell accumulation of innate cells, bordered by collagen deposition in the underlying parenchyma. Overall, the hypercoagulation model represents a comparative pathological instrument for understanding mechanisms underlying development of hemorrhage and vascular occlusion seen during MTB infection.

S-Trap, an Ultrafast Sample-Preparation Approach for Shotgun Proteomics

The success of shotgun proteomic analysis depends largely on how samples are prepared. Current approaches (such as those that are gel-, solution-, or filter-based), although being extensively employed in the field, are time-consuming and less effective with respect to the repetitive sample processing, recovery, and overall yield. As an alternative, the suspension trapping (S-Trap) filter has been commercially available very recently in the format of a single or 96-well filter plate. In contrast to the conventional filter-aided sample preparation (FASP) approach, which utilizes a molecular weight cut-off (MWCO) membrane as the filter and requires hours of processing before digestion-ready proteins can be obtained, the S-Trap employs a three-dimensional porous material as filter media and traps particulate protein suspensions with the subsequent depletion of interfering substances and in-filter digestion. Due to the large (submicron) pore size, each centrifugation cycle of the S-Trap filter only takes 1 min, which significantly reduces the total processing time from approximately 3 h by FASP to less than 15 min, suggesting an ultrafast sample-preparation approach for shotgun proteomics. Here, we comprehensively evaluate the performance of the individual S-Trap filter and 96-well filter plate in the context of global protein identification and quantitation using whole-cell lysate and clinically relevant sputum samples.

Matrix metalloproteinase inhibitors enhance the efficacy of frontline drugs against Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) remains a grave threat to world health with emerging drug resistant strains. One prominent feature of Mtb infection is the extensive reprogramming of host tissue at the site of infection. Here we report that inhibition of matrix metalloproteinase (MMP) activity by a panel of small molecule inhibitors enhances the in vivo potency of the frontline TB drugs isoniazid (INH) and rifampicin (RIF). Inhibition of MMP activity leads to an increase in pericyte-covered blood vessel numbers and appears to stabilize the integrity of the infected lung tissue. In treated mice, we observe an increased delivery and/or retention of frontline TB drugs in the infected lungs, resulting in enhanced drug efficacy. These findings indicate that targeting Mtb-induced host tissue remodeling can increase therapeutic efficacy and could enhance the effectiveness of current drug regimens.

Mycobacterium tuberculosis (Mtb) continues to be the leading cause of death from a single infectious agent worldwide, leading to 1.8 million deaths in 2015. The long treatment required (6–9 months), with all of its incumbent problems, can promote the emergence of multidrug-resistant (MDR) TB strains, so strategies to shorten the treatment duration are in dire need. Mtb’s success as a pathogen hinges on its ability to remodel the host tissue, characterized by extracellular matrix (ECM) deposition and leaky vascularization. Here we report that inhibition of matrix metalloproteinases (MMPs) significantly enhances the potency of frontline TB antibiotics. These MMP inhibitors increase the relative proportion of healthy blood vessels versus leaky dysfunctional vessels at the infection site, and enhance drug delivery and/or retention. Our study highlights the potential of targeting Mtb-induced host tissue remodeling to enhance the efficacy of current frontline antibiotics. It also suggests an alternative therapeutic strategy to repair the leaky blood vessels in TB granulomas to enhance drug delivery. Repurposing of MMP inhibitors may hold the key to shortening TB treatments and combating the emergence of MDR strains.

Serum amyloid A, protein Z, and C4b-binding protein β chain as new potential biomarkers for pulmonary tuberculosis

The aim of this study was to discover novel biomarkers for pulmonary tuberculosis (TB). Differentially expressed proteins in the serum of patients with TB were screened and identified by iTRAQ-two dimensional liquid chromatography tandem mass spectrometry analysis. A total of 79 abnormal proteins were discovered in patients with TB compared with healthy controls. Of these, significant differences were observed in 47 abnormally expressed proteins between patients with TB or pneumonia and chronic obstructive pulmonary disease (COPD). Patients with TB (n = 136) exhibited significantly higher levels of serum amyloid A (SAA), vitamin K-dependent protein Z (PROZ), and C4b-binding protein β chain (C4BPB) than those in healthy controls (n = 66) (P<0.0001 for each) albeit significantly lower levels compared with those in patients with pneumonia (n = 72) (P<0.0001 for each) or COPD (n = 72) (P<0.0001, P<0.0001, P = 0.0016, respectively). After 6 months of treatment, the levels of SAA and PROZ were significantly increased (P = 0.022, P<0.0001, respectively), whereas the level of C4BPB was significantly decreased (P = 0.0038) in treated TB cases (n = 72). Clinical analysis showed that there were significant differences in blood clotting and lipid indices in patients with TB compared with healthy controls, patients with pneumonia or COPD, and treated TB cases (P<0.05). Correlation analysis revealed significant correlations between PROZ and INR (rs = 0.414, P = 0.044), and between C4BPB and FIB (rs = 0.617, P = 0.0002) in patients with TB. Receiver operating characteristic curve analysis revealed that the area under the curve value of the diagnostic model combining SAA, PROZ, and C4BPB to discriminate the TB group from the healthy control, pneumonia, COPD, and cured TB groups was 0.972, 0.928, 0.957, and 0.969, respectively. Together, these results suggested that SAA, PROZ, and C4BPB may serve as new potential biomarkers for TB. Our study may thus provide experimental data for the differential diagnosis of TB.

Trehalose 6,6-Dimycolate from Mycobacterium tuberculosis Induces Hypercoagulation

Tuberculosis (TB) remains a global health concern. Trehalose 6'6-dimycolate (TDM) activates innate inflammation and likely also stimulates chronic inflammation observed during disease progression. Noninfectious models using purified TDM oil/water emulsions elicit pathologic findings observed in patients with TB. We introduce a new TDM model that promotes inflammatory lung pathologic findings and vascular occlusion and hemorrhage. C57BL/6 and BALB/c mice were injected with 10 μg of i.p. TDM in light mineral oil (TDM-IP). At day 7, another injection of 10 μg of i.v. TDM in oil/water emulsion was given (TDM-IV). The i.p./i.v. TDM (TDM-IVIP) group was compared with mice injected once with i.v. or i.p. TDM. The responses to TDM-IP, TDM-IV, or TDM-IPIV were consistent between mouse strains. Mice that received TDM-IV and TDM-IPIV had inflammatory pathologic findings with increases in inflammatory and T-cell cytokines, and the TDM-IPIV group had further enhancement of IL-10 and granulocyte-macrophage colony-stimulating factor. The TDM-IPIV group had increased CD4(+) T cells in lung tissue, significantly increased coagulation, decreased clot formation time, and increased maximum clot firmness. Masson's trichrome staining revealed increased deposition of collagen in the occluded vasculature. TDM-IPIV promotes a hypercoagulopathy state, independent of inflammation. This new model argues that TDM is sufficient to generate the hypercoagulopathy observed in patients with TB.

Tissue factor expression by myeloid cells contributes to protective immune response against Mycobacterium tuberculosis infection

Tissue factor (TF) is a transmembrane glycoprotein that plays an essential role in hemostasis by activating coagulation. TF is also expressed by monocytes/macrophages as part of the innate immune response to infections. In the current study, we determined the role of TF expressed by myeloid cells during Mycobacterium tuberculosis (M. tb) infection by using mice lacking the TF gene in myeloid cells (TF(Δ) ) and human monocyte derived macrophages (MDMs). We found that during M. tb infection, a deficiency of TF in myeloid cells was associated with reduced inducible nitric oxide synthase (iNOS) expression, enhanced arginase 1 (Arg1) expression, enhanced IL-10 production and reduced apoptosis in infected macrophages, which augmented M. tb growth. Our results demonstrate that a deficiency of TF in myeloid cells promotes M2-like phenotype in M .tb infected macrophages. A deficiency in TF expression by myeloid cells was also associated with reduced fibrin deposition and increased matrix metalloproteases (MMP)-2 and MMP-9 mediated inflammation in M. tb infected lungs. Our studies demonstrate that TF expressed by myeloid cells has newly recognized abilities to polarize macrophages and to regulate M. tb growth.

Role of tissue factor in Mycobacterium tuberculosis-induced inflammation and disease pathogenesis

Tuberculosis (TB) is a chronic lung infectious disease characterized by severe inflammation and lung granulomatous lesion formation. Clinical manifestations of TB include hypercoagulable states and thrombotic complications. We previously showed that Mycobacterium tuberculosis (M.tb) infection induces tissue factor (TF) expression in macrophages in vitro. TF plays a key role in coagulation and inflammation. In the present study, we investigated the role of TF in M.tb-induced inflammatory responses, mycobacterial growth in the lung and dissemination to other organs. Wild-type C57BL/6 and transgenic mice expressing human TF, either very low levels (low TF) or near to the level of wild-type (HTF), in place of murine TF were infected with M.tb via aerosol exposure. Levels of TF expression, proinflammatory cytokines and thrombin-antithrombin complexes were measured post M.tb infection and mycobacterial burden in the tissue homogenates were evaluated. Our results showed that M.tb infection did not increase the overall TF expression in lungs. However, macrophages in the granulomatous lung lesions in all M.tb-infected mice, including low TF mice, showed increased levels of TF expression. Conspicuous fibrin deposition in the granuloma was detected in wild-type and HTF mice but not in low TF mice. M.tb infection significantly increased expression levels of cytokines IFN-γ, TNF-α, IL-6 and IL-1ß in lung tissues. However, no significant differences were found in proinflammatory cytokines among the three experimental groups. Mycobacterial burden in lungs and dissemination into spleen and liver were essentially similar in all three genotypes. Our data indicate, in contrast to that observed in acute bacterial infections, that TF-mediated coagulation and/or signaling does not appear to contribute to the host-defense in experimental tuberculosis.

Trehalose 6,6'-dimycolate--a coat to regulate tuberculosis immunopathogenesis

Tuberculosis (TB) remains a significant public health burden worldwide. Treatment of this disease requires a minimum of six months and there is no vaccine available for the most common form of the disease. Increasing evidence suggests that the mycobacterial glycolipid trehalose 6,6' dimycolate (TDM; cord factor) plays a key role in the pathogenesis of TB disease. TDM protects the TB bacilli from macrophage-mediated killing, inhibits effective antigen presentation, and reduces the formation of protective T-cell responses. TDM promotes initiation of granuloma formation and likely plays a role in caseation. Furthermore, TDM may contribute to the development of post primary disease. Receptors for TDM were recently described and are expected to contribute to our knowledge of the molecular pathogenesis of TB disease. In this manner, understanding TDM may prove promising towards development of targeted TB therapeutics to limit clinical pathologies.

A proteomics approach to the identification of plasma biomarkers for latent tuberculosis infection

A proteomic analysis was performed to screen the potential latent tuberculosis infection (LTBI) biomarkers. A training set of spectra was used to generate diagnostic models, and a blind testing set was used to determine the accuracy of the models. Candidate peptides were identified using nano-liquid chromatography-electrospray ionization–tandem mass spectrometry. Based on the training set results, 3 diagnostic models recognized LTBI subjects with good cross-validation accuracy. In the blind testing set, LTBI subjects could be identified with sensitivities and specificities of 85.20% to 88.90% and 85.7% to 100%, respectively. Additionally, 14 potential LTBI biomarkers were identified, and all proteins were identified for the first time through proteomics in the plasma of healthy, latently infected individuals. In all, proteomic pattern analyses can increase the accuracy of LTBI diagnosis, and the data presented here provide novel insights into potential mechanisms involved in LTBI.

The discovery and identification of a candidate proteomic biomarker of active tuberculosis

BACKGROUND

Noninvasive and convenient biomarkers for early diagnosis of tuberculosis (TB) remain an urgent need. The aim of this study was to discover and identify potential biomarkers specific for TB.

METHODS

The surface-enhanced laser desorption ionization time of flight mass spectrometry (SELDI-TOF MS) combined with weak cation exchange (WCX) magnetic beads was used to screen serum samples from 180 cases of TB and 211 control subjects. A classification model was established by Biomarker Pattern Software (BPS). Candidate protein biomarkers were purified by reverse phase-high performance liquid chromatography (RP-HPLC), identified by MALDI-TOF MS, LC-MS/MS and validated using enzyme-linked immunosorbent assay (ELISA).

RESULTS

A total of 35 discriminating m/z peaks were detected that were related to TB (P < 0.01). The model of biomarkers based on the four biomarkers (2554.6, 4824.4, 5325.7, and 8606.8 Da) was established which could distinguish TB from controls with the sensitivity of 83.3% and the specificity of 84.2%. The candidate biomarker with m/z of 2554.6 Da was found to be up-regulated in TB patients, and was identified as a fragment of fibrinogen, alpha polypeptide isoform alpha-E preproprotein. Analysis in 22 patients with TB showed increased fibrinogen degradation product (FDP) (5,005 ± 1,297 vs. 4,010 ± 1,181 ng/mL, P < 0.05) and in 142 patients showed elevated plasma fibrinogen levels.

CONCLUSIONS

A diagnostic model for TB with high sensitivity and specificity was developed using mass spectrometry combined with magnetic beads. Fibrinogen was identified as a potential biomarker for TB and showed diagnostic values in clinical application.

Fibrin facilitates both innate and T cell-mediated defense against Yersinia pestis

The Gram-negative bacterium Yersinia pestis causes plague, a rapidly progressing and often fatal disease. The formation of fibrin at sites of Y. pestis infection supports innate host defense against plague, perhaps by providing a nondiffusible spatial cue that promotes the accumulation of inflammatory cells expressing fibrin-binding integrins. This report demonstrates that fibrin is an essential component of T cell-mediated defense against plague but can be dispensable for Ab-mediated defense. Genetic or pharmacologic depletion of fibrin abrogated innate and T cell-mediated defense in mice challenged intranasally with Y. pestis. The fibrin-deficient mice displayed reduced survival, increased bacterial burden, and exacerbated hemorrhagic pathology. They also showed fewer neutrophils within infected lung tissue and reduced neutrophil viability at sites of liver infection. Depletion of neutrophils from wild-type mice weakened T cell-mediated defense against plague. The data suggest that T cells combat plague in conjunction with neutrophils, which require help from fibrin to withstand Y. pestis encounters and effectively clear bacteria.

Mycobacterium tuberculosis exploits human interferon γ to stimulate macrophage extracellular trap formation and necrosis

Human neutrophils form extracellular traps during M. tuberculosis infection, but a similar phenomenon has not been reported in human macrophages. Here we demonstrate that M. tuberculosis induces release of extracellular traps from human macrophages. This process is regulated by elastase activity, previously shown to regulate formation of extracellular traps by neutrophils. Interestingly, formation of extracellular traps by macrophages during M. tuberculosis infection is inducible by interferon γ (IFN-γ). These traps are mainly produced by heavily infected macrophages. Accordingly, IFN-γ is found to stimulate M. tuberculosis aggregation in macrophages. Both IFN-γ–inducible events, extracellular trap formation and mycobacterial aggregation, require the ESX-1 secretion system. In addition, IFN-γ is found to enhance ESX-1–mediated macrophage necrosis. In the absence of ESX-1, IFN-γ does not restore any extracellular trap formation, mycobacterial aggregation, or macrophage necrosis. Thus, initial characterization of macrophage extracellular trap formation due to M. tuberculosis infection led to the uncovering of a novel role for IFN-γ in amplifying multiple effects of the mycobacterial ESX-1.

Mycobacterium tuberculosis infection and tissue factor expression in macrophages

A number of earlier studies reported the occurrence of thrombotic complications, particularly disseminated intravascular coagulation and deep vein thrombosis, in tuberculosis (TB) patients. The aberrant expression of tissue factor (TF), the primary activator of coagulation cascade, is known to be responsible for thrombotic disorders in many diseases including bacterial infections. Further, expression of TF by cells of the monocyte/macrophage lineage is also shown to contribute to the development and progression of local and systemic inflammatory reactions. In the present study, we have investigated whether Mycobacterium tuberculosis (Mtb) infection induces TF expression in macrophages, and various host and pathogenic factors responsible for TF expression. We have tested the effect of live virulent Mtb H37Rv, gamma-irradiated Mtb H37Rv (γ-Mtb) and various components derived from Mtb H37Rv on TF expression in macrophages. The data presented in the manuscript show that both live virulent Mtb and γ-Mtb treatments markedly increased TF activity in macrophages, predominantly in the CD14⁺ macrophages. Detailed studies using γ-Mtb showed that the increased TF activity in macrophages following Mtb treatment is the result of TF transcriptional activation. The signaling pathways of TF induction by Mtb appears to be distinct from that of LPS-induced TF expression. Mtb-mediated TF expression is dependent on cooperation of CD14/TLR2/TLR4 and probably yet another unknown receptor/cofactor. Mtb cell wall core components, mycolyl arabinogalactan peptidoglycan (mAGP), phosphatidylinositol mannoside-6 (PIM6) and lipomannan (LM) were identified as factors responsible for induction of TF in the order of mAGP>PIM6>LM. A direct contact between bacteria and macrophage and not Mtb-released soluble factors is critical for TF induction by Mtb. In summary, our data show that Mtb induces TF expression in macrophages and Mtb signaling pathways that elicit TF induction require cooperation of multiple receptors, co-receptors/co-factors including Toll-like receptors. The importance of TF in granuloma formation and containment of Mtb is discussed.

Proteomic analysis of plasma from Holstein cows testing positive for Mycobacterium avium subsp. paratuberculosis (MAP)

Johne's disease (JD) is a widespread and economically important chronic inflammatory disease of the small intestine of ruminants caused by Mycobacterium avium subsp. paratuberculosis (MAP). Although there are several techniques available for diagnosis of JD, their sensitivity is questionable. New proteome profiling methods, such as serum/plasma protein fingerprinting by 2-Dimensional Fluorescence Difference Gel Electrophoresis (2D-DIGE), may therefore be useful for identifying novel protein biomarkers of MAP infection. In this study, plasma samples were collected from 380 Holstein cows and screened for the presence of MAP infection using the M.pt. Johne's antibody Kit (IDEXX). Five negative (MAP-), and 5 strongly positive (MAP+) cows were selected for proteomic analysis. Highly abundant proteins were depleted from the plasma samples using the ProteoMiner technology (Bio-Rad) to enhance the resolution of low abundance proteins. Plasma samples from MAP-, MAP+, and a pooled internal control were labelled with different fluorescent dyes and separated based on their isoelectrical point (IP) and then their molecular weight. Gel images of the fluorescent plasma protein maps were acquired using a Typhoon scanner and analyzed using the DeCyder software. Proteins that were differentially expressed were excised from the gels, trypsin digested, and subjected to MS/MS analysis for identification. Six proteins were identified as being up-regulated at least 2-fold in MAP+ cows including: transferrin, gelsolin isoforms α & β (actin binding protein - ABP), complement subcomponent C1r, complement component C3, amine oxidase - copper containing 3 (AOC3), and coagulation factor II (thrombin) (p<0.05). Two proteins that were down-regulated approximately 2-fold in the MAP+ cows included coagulation factor XIII -B polypeptide (COAFXIII), and fibrinogen γ chain (FGG) and its precursor.

Neutrophils Promote Mycobacterial Trehalose Dimycolate-Induced Lung Inflammation via the Mincle Pathway

Trehalose 6,6'-dimycolate (TDM), a cord factor of Mycobacterium tuberculosis (Mtb), is an important regulator of immune responses during Mtb infections. Macrophages recognize TDM through the Mincle receptor and initiate TDM-induced inflammatory responses, leading to lung granuloma formation. Although various immune cells are recruited to lung granulomas, the roles of other immune cells, especially during the initial process of TDM-induced inflammation, are not clear. In this study, Mincle signaling on neutrophils played an important role in TDM-induced lung inflammation by promoting adhesion and innate immune responses. Neutrophils were recruited during the early stage of lung inflammation following TDM-induced granuloma formation. Mincle expression on neutrophils was required for infiltration of TDM-challenged sites in a granuloma model induced by TDM-coated-beads. TDM-induced Mincle signaling on neutrophils increased cell adherence by enhancing F-actin polymerization and CD11b/CD18 surface expression. The TDM-induced effects were dependent on Src, Syk, and MAPK/ERK kinases (MEK). Moreover, coactivation of the Mincle and TLR2 pathways by TDM and Pam3CSK4 treatment synergistically induced CD11b/CD18 surface expression, reactive oxygen species, and TNFα production by neutrophils. These synergistically-enhanced immune responses correlated with the degree of Mincle expression on neutrophil surfaces. The physiological relevance of the Mincle-mediated anti-TDM immune response was confirmed by defective immune responses in Mincle⁻/⁻ mice upon aerosol infections with Mtb. Mincle-mutant mice had higher inflammation levels and mycobacterial loads than WT mice. Neutrophil depletion with anti-Ly6G antibody caused a reduction in IL-6 and monocyte chemotactic protein-1 expression upon TDM treatment, and reduced levels of immune cell recruitment during the initial stage of infection. These findings suggest a new role of Mincle signaling on neutrophils during anti-mycobacterial responses.