Cytosolic phospholipase A2 participates with TNF-alpha in the induction of apoptosis of human macrophages infected with Mycobacterium tuberculosis H37Ra

Caveolin-1 affects early mycobacterial infection and apoptosis in macrophages and mice

Tuberculosis, caused by Mycobacterium tuberculosis, remains one of the deadliest infections in humans. Because Mycobacterium bovis Bacillus Calmette-Guérin (BCG) share genetic similarities with Mycobacterium tuberculosis, it is often used as a model to elucidate the molecular mechanisms of more severe tuberculosis infection. Caveolin-1 has been implied in many physiological processes and diseases, but it's role in mycobacterial infections has barely been studied. We isolated macrophages from Wildtype or Caveolin-1 deficient mice and analyzed hallmarks of infection, such as internalization, induction of autophagy and apoptosis. For in vivo assays we intravenously injected mice with BCG and investigated tissues for bacterial load with colony-forming unit assays, bioactive lipids with mass spectrometry and changes of protein expressions by Western blotting. Our results revealed that Caveolin-1 was important for early killing of BCG infection in vivo and in vitro, controlled acid sphingomyelinase (Asm)-dependent ceramide formation, apoptosis and inflammatory cytokines upon infection with BCG. In accordance, Caveolin-1 deficient mice and macrophages showed higher bacterial burdens in the livers. The findings indicate that Caveolin-1 plays a role in infection of mice and murine macrophages with BCG, by controlling cellular apoptosis and inflammatory host response. These clues might be useful in the fight against tuberculosis.

Identification of urine biomarkers predictive of prolonged QTc interval in multidrug-resistant tuberculosis patients treated with bedaquiline

The most frequent adverse event associated with bedaquiline (BDQ) is the QTc interval prolongation; however, there was no biomarkers that could be used to predict the occurrence of QTc prolongation in BDQ-treated patients. In this study, we employed the ultra-high performance liquid chromatography-MS/MS (UHPLC-MS/MS) to generate metabolic profiling for the discovery of potential predictive urine biomarkers of QTc prolongation in these patients. Untargeted metabolomic technique was used to concentrate the differential metabolic pathway, and targeted metabolomic technique was subsequently performed to identify predictive biomarkers for QTc prolongation. A total of 45 rifampicin-resistant TB (RR-TB) and multidrug-resistant TB (MDR-TB) patients were enrolled in our study, including 15 RR/MDR-TB patients with QTc interval prolongation (QIP) and 30 RR/MDR-TB patients with QTc interval un-prolongations (QIU). Untargeted technique revealed that the lipid metabolism was the most differential metabolic pathway between two groups. Further targeted technique identified four differential metabolites, including betaine, LPE (18:2), LPE (20:3), and LPE (20:4). The combined analysis of metabolisms revealed that the combined use of LPE (20:3) and LPE (20:4) had the best performance for predicting the occurrence of QTc prolongation in TB patients, yielding a sensitivity of 87.4% and a specificity of 78.5%. In addition, with the progression of BDQ treatment, the LPEs exhibited persistent difference in the BDQ-treated TB patients experiencing QTc interval prolongation. In conclusion, our data demonstrate that the combined use of LPE (20:3) and LPE (20:4) yields promising performance for predicting the occurrence of QTc interval prolongation in BDQ-treated patients.

Alterations of lipid-related genes during anti-tuberculosis treatment: insights into host immune responses and potential transcriptional biomarkers

Background

The optimal diagnosis and treatment of tuberculosis (TB) are challenging due to underdiagnosis and inadequate treatment monitoring. Lipid-related genes are crucial components of the host immune response in TB. However, their dynamic expression and potential usefulness for monitoring response to anti-TB treatment are unclear.

Methodology

In the present study, we used a targeted, knowledge-based approach to investigate the expression of lipid-related genes during anti-TB treatment and their potential use as biomarkers of treatment response.

Results and discussion

The expression levels of 10 genes (ARPC5, ACSL4, PLD4, LIPA, CHMP2B, RAB5A, GABARAPL2, PLA2G4A, MBOAT2, and MBOAT1) were significantly altered during standard anti-TB treatment. We evaluated the potential usefulness of this 10-lipid-gene signature for TB diagnosis and treatment monitoring in various clinical scenarios across multiple populations. We also compared this signature with other transcriptomic signatures. The 10-lipid-gene signature could distinguish patients with TB from those with latent tuberculosis infection and non-TB controls (area under the receiver operating characteristic curve > 0.7 for most cases); it could also be useful for monitoring response to anti-TB treatment. Although the performance of the new signature was not better than that of previous signatures (i.e., RISK6, Sambarey10, Long10), our results suggest the usefulness of metabolism-centric biomarkers.

Conclusions

Lipid-related genes play significant roles in TB pathophysiology and host immune responses. Furthermore, transcriptomic signatures related to the immune response and lipid-related gene may be useful for TB diagnosis and treatment monitoring.

Herp regulates intracellular survival of Mycobacterium tuberculosis H37Ra in macrophages by regulating reactive oxygen species-mediated autophagy

IMPORTANCE

Several studies have suggested that endoplasmic reticulum (ER) stress is important in the pathogenesis of infectious diseases; however, the precise function of ER stress regulation and the role of Herp as a regulator in Mtb H37Ra-induced ER stress remain elusive. Therefore, our study investigated ER stress and autophagy associated with Herp expression in Mycobacterium tuberculosis-infected macrophages to determine the role of Herp in the pathogenesis of tuberculosis.

Tuberculosis is associated with sputum metabolome variations, irrespective of patient sex or HIV status: an untargeted GCxGC-TOFMS study

INTRODUCTION

Various studies have identified TB-induced metabolome variations. However, in most of these studies, a large degree of variation exists between individual patients.

OBJECTIVES

To identify differential metabolites for TB, independent of patients' sex or HIV status.

METHODS

Untargeted GCxGC/TOF-MS analyses were applied to the sputum of 31 TB + and 197 TB- individuals. Univariate statistics were used to identify metabolites which are significantly different between TB + and TB- individuals (a) irrespective of HIV status, and (b) with a HIV + status. Comparisons a and b were repeated for (i) all participants, (ii) males only and (iii) females only.

RESULTS

Twenty-one compounds were significantly different between the TB + and TB- individuals within the female subgroup (11% lipids; 10% carbohydrates; 1% amino acids, 5% other and 73% unannotated), and 6 within the male subgroup (20% lipids; 40% carbohydrates; 6% amino acids, 7% other and 27% unannotated). For the HIV + patients (TB + vs. TB-), a total of 125 compounds were significant within the female subgroup (16% lipids; 8% carbohydrates; 12% amino acids, 6% organic acids, 8% other and 50% unannotated), and 44 within the male subgroup (17% lipids; 2% carbohydrates; 14% amino acids related, 8% organic acids, 9% other and 50% unannotated). Only one annotated compound, 1-oleoyl lysophosphaditic acid, was consistently identified as a differential metabolite for TB, irrespective of sex or HIV status. The potential clinical application of this compound should be evaluated further.

CONCLUSIONS

Our findings highlight the importance of considering confounders in metabolomics studies in order to identify unambiguous disease biomarkers.

Therapeutic potential of the sphingosine kinase 1 inhibitor, PF-543

PF-543 is a sphingosine kinase 1（SPHK1）inhibitor developed by Pfizer and is currently considered the most potent selective SPHK1 inhibitor. SPHK1 catalyses the production of sphingosine 1-phosphate (S1P) from sphingosine. It is the rate-limiting enzyme of S1P production, and there is substantial evidence to support a very important role for sphingosine kinase in health and disease. This review is the first to summarize the role and mechanisms of PF-543 as an SPHK1 inhibitor in anticancer, antifibrotic, and anti-inflammatory processes, providing new therapeutic leads and ideas for future research and clinical trials.

Biological functions of bacterial lysophospholipids

Lysophospholipids (LPLs) are lipid-derived metabolic intermediates in the cell membrane. The biological functions of LPLs are distinct from their corresponding phospholipids. In eukaryotic cells LPLs are important bioactive signaling molecules that regulate many important biological processes, but in bacteria the function of LPLs is still not fully defined. Bacterial LPLs are usually present in cells in very small amounts, but can strongly increase under certain environmental conditions. In addition to their basic function as precursors in membrane lipid metabolism, the formation of distinct LPLs contributes to the proliferation of bacteria under harsh circumstances or may act as signaling molecules in bacterial pathogenesis. This review provides an overview of the current knowledge of the biological functions of bacterial LPLs including lysoPE, lysoPA, lysoPC, lysoPG, lysoPS and lysoPI in bacterial adaptation, survival, and host-microbe interactions.

Transcriptome analysis of the impact of diabetes as a comorbidity on tuberculosis

BACKGROUND

Diabetes mellitus patients with pulmonary tuberculosis (DMTB) comorbidity has been recognized as a major obstacle towards achieving the World Health Organization goal of reducing the tuberculosis incidence rate by 90% in 2035. Host immune responses affected by diabetes can lead to increased susceptibility, severity and poor treatment outcomes in DMTB patients, and the underlying mechanisms have not yet been fully elucidated. This study aimed to identify key immunological and cellular components that contribute to increased morbidity and mortality in DMTB cases.

METHODS

We performed RNA-Seq of total RNA isolated from peripheral blood mononuclear cells from 3 TB, 3 diabetes mellitus, and 3 DMTB patients and healthy controls, and analyzed differential expression, pathway enrichment and clustering of differentially-expressed genes (DEGs) to identify biological pathways altered specifically in DMTB patients.

RESULTS

Bioinformatic analysis of DEGs suggested that enhanced inflammatory responses, small GTPases, the protein kinase C signaling pathway, hemostasis and the cell cycle pathway are likely implicated in the pathogenesis of the DMTB comorbidity.

CONCLUSION

The DMTB comorbidity is associated with an altered transcriptome and changes in various biological pathways. Our study provides new insights on the pathological mechanism that may aid the development of host-directed therapies for this increasingly prevalent disease in high TB burden countries.

Mycobacterium tuberculosis encodes a YhhN family membrane protein with lysoplasmalogenase activity that protects against toxic host lysolipids

The pathogen Mycobacterium tuberculosis (M.tb) resides in human macrophages, wherein it exploits host lipids for survival. However, little is known about the interaction between M.tb and macrophage plasmalogens, a subclass of glycerophospholipids with a vinyl ether bond at the sn-1 position of the glycerol backbone. Lysoplasmalogens, produced from plasmalogens by hydrolysis at the sn-2 carbon by phospholipase A2, are potentially toxic but can be broken down by host lysoplasmalogenase, an integral membrane protein of the YhhN family that hydrolyzes the vinyl ether bond to release a fatty aldehyde and glycerophospho-ethanolamine or glycerophospho-choline. Curiously, M.tb encodes its own YhhN protein (MtbYhhN), despite having no endogenous plasmalogens. To understand the purpose of this protein, the gene for MtbYhhN (Rv1401) was cloned and expressed in Mycobacterium smegmatis (M.smeg). We found the partially purified protein exhibited abundant lysoplasmalogenase activity specific for lysoplasmenylethanolamine or lysoplasmenylcholine (pLPC) (Vmax∼15.5 μmol/min/mg; Km∼83 μM). Based on cell density, we determined that lysoplasmenylethanolamine, pLPC, lysophosphatidylcholine, and lysophosphatidylethanolamine were not toxic to M.smeg cells, but pLPC and LPC were highly toxic to M.smeg spheroplasts, which are cell wall-deficient mycobacterial forms. Importantly, spheroplasts prepared from M.smeg cells overexpressing MtbYhhN were protected from membrane disruption/lysis by pLPC, which was rapidly depleted from the media. Finally, we found that overexpression of full-length MtbYhhN in M.smeg increased its survival within human macrophages by 2.6-fold compared to vector controls. These data support the hypothesis that MtbYhhN protein confers a growth advantage for mycobacteria in macrophages by cleaving toxic host pLPC into potentially energy-producing products.

The Impact of the Ca2+-Independent Phospholipase A2β (iPLA2β) on Immune Cells

The Ca²⁺-independent phospholipase A₂β (iPLA₂β) is a member of the PLA₂ family that has been proposed to have roles in multiple biological processes including membrane remodeling, cell proliferation, bone formation, male fertility, cell death, and signaling. Such involvement has led to the identification of iPLA₂β activation in several diseases such as cancer, cardiovascular abnormalities, glaucoma, periodontitis, neurological disorders, diabetes, and other metabolic disorders. More recently, there has been heightened interest in the role that iPLA₂β plays in promoting inflammation. Recognizing the potential contribution of iPLA₂β in the development of autoimmune diseases, we review this issue in the context of an iPLA₂β link with macrophages and T-cells.

The Innate Immune Response to Mycobacterium tuberculosis Infection

Infection with Mycobacterium tuberculosis causes >1.5 million deaths worldwide annually. Innate immune cells are the first to encounter M. tuberculosis, and their response dictates the course of infection. Dendritic cells (DCs) activate the adaptive response and determine its characteristics. Macrophages are responsible both for exerting cell-intrinsic antimicrobial control and for initiating and maintaining inflammation. The inflammatory response to M. tuberculosis infection is a double-edged sword. While cytokines such as TNF-α and IL-1 are important for protection, either excessive or insufficient cytokine production results in progressive disease. Furthermore, neutrophils-cells normally associated with control of bacterial infection-are emerging as key drivers of a hyperinflammatory response that results in host mortality. The roles of other innate cells, including natural killer cells and innate-like T cells, remain enigmatic. Understanding the nuances of both cell-intrinsic control of infection and regulation of inflammation will be crucial for the successful development of host-targeted therapeutics and vaccines.

Urocortin participates in LPS-induced apoptosis of THP-1 macrophages via S1P-cPLA2 signaling pathway

There is little literature showing the effect of urocortin (UCN) on macrophage apoptosis. The underlying mechanism is also unclear. This work was to investigate the involvement of UCN in the regulation of LPS-induced macrophage apoptosis and hence in the prevention from the atherosclerotic lesion development through targeting PLA2. Flow cytometry analysis showed that cell apoptosis was increased by more than 50% after LPS treatment in human THP-1 macrophage. Lp-PLA2 and cPLA2 were found to mediate LPS-induced macrophage apoptosis and NF-κB differentially influenced the expression of Lp-PLA2 and cPLA2. However, the reverse regulation of the expression of Lp-PLA2 and cPLA2 by NF-κB suggested that NF-κB may not be a key target for regulating macrophage apoptosis. Interestingly, we found that the approximate three folds upregulation of cPLA2 was in line with the induction of S1P formation and cell apoptosis by LPS. Inversely, LPS obviously decreased UCN expression by about 50% and secretion by about 25%. Both the enzyme inhibitor and knockdown expression of cPLA2 could completely abolish LPS-induced cell apoptosis. In addition, suppression of S1P synthesis by Sphk1 inhibitor PF-543 reduced the expression of cPLA2 and cell apoptosis but at the same time restored the normal level of UCN in cell culture supernatant. Furthermore, addition of exogenous UCN also reversed LPS-induced expression of cPLA2 and apoptosis. Taken together, UCN may be the reverse regulator of LPS-S1P-cPLA2-apoptosis pathway, thereby contributing to the prevention from the formation of unstable plaques.

Immunometabolism during Mycobacterium tuberculosis Infection

Over a quarter of the world's population is infected with Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB). Approximately 3.4% of new and 18% of recurrent cases of TB are multidrug-resistant (MDR) or rifampicin-resistant. Recent evidence has shown that certain drug-resistant strains of Mtb modulate host metabolic reprogramming, and therefore immune responses, during infection. However, it remains unclear how widespread these mechanisms are among circulating MDR Mtb strains and what impact drug-resistance-conferring mutations have on immunometabolism during TB. While few studies have directly addressed metabolic reprogramming in the context of drug-resistant Mtb infection, previous literature examining how drug-resistance mutations alter Mtb physiology and differences in the immune response to drug-resistant Mtb provides significant insights into how drug-resistant strains of Mtb differentially impact immunometabolism.

Macrophage polarization is linked to Ca2+-independent phospholipase A2β-derived lipids and cross-cell signaling in mice

Phospholipases A₂ (PLA₂s) catalyze hydrolysis of the sn-2 substituent from glycerophospholipids to yield a free fatty acid (i.e., arachidonic acid), which can be metabolized to pro- or anti-inflammatory eicosanoids. Macrophages modulate inflammatory responses and are affected by Ca²⁺-independent phospholipase A₂ (PLA₂)β (iPLA₂β). Here, we assessed the link between iPLA₂β-derived lipids (iDLs) and macrophage polarization. Macrophages from WT and KO (iPLA₂β-/-) mice were classically M1 pro-inflammatory phenotype activated or alternatively M2 anti-inflammatory phenotype activated, and eicosanoid production was determined by ultra-performance LC ESI-MS/MS. As a genotypic control, we performed similar analyses on macrophages from RIP.iPLA₂β.Tg mice with selective iPLA₂β overexpression in β-cells. Compared with WT, generation of select pro-inflammatory prostaglandins (PGs) was lower in iPLA₂β^-/- , and that of a specialized pro-resolving lipid mediator (SPM), resolvin D2, was higher; both changes are consistent with the M2 phenotype. Conversely, macrophages from RIP.iPLA₂β.Tg mice exhibited an opposite landscape, one associated with the M1 phenotype: namely, increased production of pro-inflammatory eicosanoids (6-keto PGF₁α, PGE₂, leukotriene B₄) and decreased ability to generate resolvin D2. These changes were not linked with secretory PLA₂ or cytosolic PLA₂α or with leakage of the transgene. Thus, we report previously unidentified links between select iPLA₂β-derived eicosanoids, an SPM, and macrophage polarization. Importantly, our findings reveal for the first time that β-cell iPLA₂β-derived signaling can predispose macrophage responses. These findings suggest that iDLs play critical roles in macrophage polarization, and we posit that they could be targeted therapeutically to counter inflammation-based disorders.

Characterisation of genes differentially expressed in macrophages by virulent and attenuated Mycobacterium tuberculosis through RNA-Seq analysis

Tuberculosis (TB) remains a global healthcare issue. Understanding the host-pathogen interactions in TB is vital to develop strategies and therapeutic tools for the control of Mycobacterium tuberculosis (Mtb). In this study, transcriptome analyses of macrophages infected with either the virulent Mtb strain H37Rv (Rv) or the avirulent Mtb strain H37Ra (Ra) were carried out and 750 differentially expressed genes (DEGs) were identified. As expected, the DEGs were mainly involved in the induction of innate immune responses against mycobacterial infections. Among the DEGs, solute carrier family 7 member 2 (Slc7a2) was more strongly expressed in Ra-infected macrophages. Induction of SLC7A2 was important for macrophages to control the intracellular survival of Mtb. Our results imply that SLC7A2 plays an important role in macrophages during Mtb infection. Our findings could prove useful for the development of new therapeutic strategies to control TB infection.

TNFR2 unlocks a RIPK1 kinase activity-dependent mode of proinflammatory TNFR1 signaling

TNF is not only a major effector molecule of PAMP/DAMP-activated macrophages, but also regulates macrophage function and viability. We recently demonstrated that TNFR2 triggers necroptosis in macrophages with compromised caspase activity by two cooperating mechanisms: induction of endogenous TNF with subsequent stimulation of TNFR1 and depletion of cytosolic TRAF2-cIAP complexes. Here we show that TNFR2 activation in caspase-inhibited macrophages results in the production of endogenous TNF and TNFR1 stimulation followed by upregulation of A20, TRAF1, IL-6, and IL-1β. Surprisingly, TNFR1-mediated induction of IL-6 and IL-1β was clearly evident in response to TNFR2 stimulation but occurred not or only weakly in macrophages selectively and directly stimulated via TNFR1. Moreover, TNFR2-induced TNFR1-mediated gene induction was largely inhibited by necrostatin-1, whereas upregulation of A20 and TRAF1 by direct and exclusive stimulation of TNFR1 remained unaffected by this compound. Thus, treatment with TNFR2/ZVAD enables TNFR1 in macrophages to stimulate gene induction via a pathway requiring RIPK1 kinase activity. TNFR2/ZVAD-induced production of IL-6 and IL-1β was largely blocked in necroptosis-resistant MLKL- and RIPK3-deficient macrophages, whereas induction of A20 and TRAF1 remained unaffected. In sum, our results show that in caspase-inhibited macrophages TNFR2 not only triggers TNF/TNFR1-mediated necroptosis but also TNF/TNFR1-mediated RIPK3/MLKL-dependent and -independent gene induction.

Mito-xenophagic killing of bacteria is coordinated by a metabolic switch in dendritic cells

Chlamydiae are bacterial pathogens that grow in vacuolar inclusions. Dendritic cells (DCs) disintegrate these compartments, thereby eliminating the microbes, through auto/xenophagy, which also promotes chlamydial antigen presentation via MHC I. Here, we show that TNF-α controls this pathway by driving cytosolic phospholipase (cPLA)2-mediated arachidonic acid (AA) production. AA then impairs mitochondrial function, which disturbs the development and integrity of these energy-dependent parasitic inclusions, while a simultaneous metabolic switch towards aerobic glycolysis promotes DC survival. Tubulin deacetylase/autophagy regulator HDAC6 associates with disintegrated inclusions, thereby further disrupting their subcellular localisation and stability. Bacterial remnants are decorated with defective mitochondria, mito-aggresomal structures, and components of the ubiquitin/autophagy machinery before they are degraded via mito-xenophagy. The mechanism depends on cytoprotective HSP25/27, the E3 ubiquitin ligase Parkin and HDAC6 and promotes chlamydial antigen generation for presentation on MHC I. We propose that this novel mito-xenophagic pathway linking innate and adaptive immunity is critical for effective DC-mediated anti-bacterial resistance.

Biological and Epidemiological Consequences of MTBC Diversity

Tuberculosis is caused by different groups of bacteria belonging to the Mycobacterium tuberculosis complex (MTBC). The combined action of human factors, environmental conditions and bacterial virulence determine the extent and form of human disease. MTBC virulence is a composite of different clinical phenotypes such as transmission rate and disease severity among others. Clinical phenotypes are also influenced by cellular and immunological phenotypes. MTBC phenotypes are determined by the genotype, therefore finding genotypes responsible for clinical phenotypes would allow discovering MTBC virulence factors. Different MTBC strains display different cellular and clinical phenotypes. Strains from Lineage 5 and Lineage 6 are metabolically different, grow slower, and are less virulent. Also, at least certain groups of Lineage 2 and Lineage 4 strains are more virulent in terms of disease severity and human-to-human transmission. Because phenotypic differences are ultimately caused by genotypic differences, different genomic loci have been related to various cellular and clinical phenotypes. However, defining the impact of specific bacterial genomic loci on virulence when other bacterial determinants, human and environmental factors are also impacting the phenotype would contribute to a better knowledge of tuberculosis virulence and ultimately benefit tuberculosis control.

Mitochondria-localized phospholipase A2, AoPlaA, in Aspergillus oryzae displays phosphatidylethanolamine-specific activity and is involved in the maintenance of mitochondrial phospholipid composition

In mammals, cytosolic phospholipases A₂ (cPLA₂s) play important physiological roles by releasing arachidonic acid, a precursor for bioactive lipid mediators, from the biological membranes. In contrast, fungal cPLA₂-like proteins are much less characterized and their roles have remained elusive. AoPlaA is a cPLA₂-like protein in the filamentous fungus Aspergillus oryzae which, unlike mammalian cPLA₂, localizes to mitochondria. In this study, we investigated the biochemical and physiological functions of AoPlaA. Recombinant AoPlaA produced in E. coli displayed Ca²⁺-independent lipolytic activity. Mass spectrometry analysis demonstrated that AoPlaA displayed PLA₂ activity to phosphatidylethanolamine (PE), but not to other phospholipids, and generated 1-acylated lysoPE. Catalytic site mutants of AoPlaA displayed almost no or largely reduced activity to PE. Consistent with PE-specific activity of AoPlaA, AoplaA-overexpressing strain showed decreased PE content in the mitochondrial fraction. In contrast, AoplaA-disruption strain displayed increased content of cardiolipin. AoplaA-overexpressing strain, but not its counterparts overexpressing the catalytic site mutants, exhibited retarded growth at low temperature, possibly because of the impairment of the mitochondrial function caused by excess degradation of PE. These results suggest that AoPlaA is a novel PE-specific PLA₂ that plays a regulatory role in the maintenance of mitochondrial phospholipid composition.

Activation of TNFR2 sensitizes macrophages for TNFR1-mediated necroptosis

Macrophages express TNFR1 as well as TNFR2 and are also major producers of tumor necrosis factor (TNF), especially upon contact with pathogen-associated molecular patterns. Consequently, TNF not only acts as a macrophage-derived effector molecule but also regulates the activity and viability of macrophages. Here, we investigated the individual contribution of TNFR1 and TNFR2 to TNF-induced cell death in macrophages. Exclusive stimulation of TNFR1 showed no cytotoxic effect whereas selective stimulation of TNFR2 displayed mild cytotoxicity. Intriguingly, the latter was strongly enhanced by the caspase inhibitor zVAD-fmk. The strong cytotoxic activity of TNFR2 in the presence of zVAD-fmk was reversed by necrostatin-1, indicating necroptotic cell death. TNFR1- and TNF-deficient macrophages turned out to be resistant against TNFR2-induced cell death. In addition, the cIAP-depleting SMAC mimetic BV6 also enforced TNF/TNFR1-mediated necroptotic cell death in the presence of zVAD-fmk. In sum, our data suggest a model in which TNFR2 sensitizes macrophages for endogenous TNF-induced TNFR1-mediated necroptosis by the known ability of TNFR2 to interfere with the survival activity of TRAF2-cIAP1/2 complexes.

Polarization of Macrophages toward M2 Phenotype Is Favored by Reduction in iPLA2β (Group VIA Phospholipase A2)

Macrophages are important in innate and adaptive immunity. Macrophage participation in inflammation or tissue repair is directed by various extracellular signals and mediated by multiple intracellular pathways. Activation of group VIA phospholipase A₂ (iPLA₂β) causes accumulation of arachidonic acid, lysophospholipids, and eicosanoids that can promote inflammation and pathologic states. We examined the role of iPLA₂β in peritoneal macrophage immune function by comparing wild type (WT) and iPLA₂β^-/- mouse macrophages. Compared with WT, iPLA₂β^-/- macrophages exhibited reduced proinflammatory M1 markers when classically activated. In contrast, anti-inflammatory M2 markers were elevated under naïve conditions and induced to higher levels by alternative activation in iPLA₂β^-/- macrophages compared with WT. Induction of eicosanoid (12-lipoxygenase (12-LO) and cyclooxygenase 2 (COX2))- and reactive oxygen species (NADPH oxidase 4 (NOX4))-generating enzymes by classical activation pathways was also blunted in iPLA₂β^-/- macrophages compared with WT. The effects of inhibitors of iPLA₂β, COX2, or 12-LO to reduce M1 polarization were greater than those to enhance M2 polarization. Certain lipids (lysophosphatidylcholine, lysophosphatidic acid, and prostaglandin E₂) recapitulated M1 phenotype in iPLA₂β^-/- macrophages, but none tested promoted M2 phenotype. These findings suggest that (a) lipids generated by iPLA₂β and subsequently oxidized by cyclooxygenase and 12-LO favor macrophage inflammatory M1 polarization, and (b) the absence of iPLA₂β promotes macrophage M2 polarization. Reducing macrophage iPLA₂β activity and thereby attenuating macrophage M1 polarization might cause a shift from an inflammatory to a recovery/repair milieu.

Analysis of serum metabolic profile by ultra-performance liquid chromatography-mass spectrometry for biomarkers discovery: application in a pilot study to discriminate patients with tuberculosis

BACKGROUND

Tuberculosis (TB) is a chronic wasting inflammatory disease characterized by multisystem involvement, which can cause metabolic derangements in afflicted patients. Metabolic signatures have been exploited in the study of several diseases. However, the serum that is successfully used in TB diagnosis on the basis of metabolic profiling is not by much.

METHODS

Orthogonal partial least-squares discriminant analysis was capable of distinguishing TB patients from both healthy subjects and patients with conditions other than TB. Therefore, TB-specific metabolic profiling was established. Clusters of potential biomarkers for differentiating TB active from non-TB diseases were identified using Mann-Whitney U-test. Multiple logistic regression analysis of metabolites was calculated to determine the suitable biomarker group that allows the efficient differentiation of patients with TB active from the control subjects.

RESULTS

From among 271 participants, 12 metabolites were found to contribute to the distinction between the TB active group and the control groups. These metabolites were mainly involved in the metabolic pathways of the following three biomolecules: Fatty acids, amino acids, and lipids. The receiver operating characteristic curves of 3D, 7D, and 11D-phytanic acid, behenic acid, and threoninyl-γ-glutamate exhibited excellent efficiency with area under the curve (AUC) values of 0.904 (95% confidence interval [CI]: 0863-0.944), 0.93 (95% CI: 0.893-0.966), and 0.964 (95% CI: 00.941-0.988), respectively. The largest and smallest resulting AUCs were 0.964 and 0.720, indicating that these biomarkers may be involved in the disease mechanisms. The combination of lysophosphatidylcholine (18:0), behenic acid, threoninyl-γ-glutamate, and presqualene diphosphate was used to represent the most suitable biomarker group for the differentiation of patients with TB active from the control subjects, with an AUC value of 0.991.

CONCLUSION

The metabolic analysis results identified new serum biomarkers that can distinguish TB from non-TB diseases. The metabolomics-based analysis provides specific insights into the biology of TB and may offer new avenues for TB diagnosis.

Host-directed therapeutics for tuberculosis: can we harness the host?

Treatment of tuberculosis (TB) remains challenging, with lengthy treatment durations and complex drug regimens that are toxic and difficult to administer. Similar to the vast majority of antibiotics, drugs for Mycobacterium tuberculosis are directed against microbial targets. Although more effective drugs that target the bacterium may lead to faster cure of patients, it is possible that a biological limit will be reached that can be overcome only by adopting a fundamentally new treatment approach. TB regimens might be improved by including agents that target host pathways. Recent work on host-pathogen interactions, host immunity, and host-directed interventions suggests that supplementing anti-TB therapy with host modulators may lead to shorter treatment times, a reduction in lung damage caused by the disease, and a lower risk of relapse or reinfection. We undertook this review to identify molecular pathways of the host that may be amenable to modulation by small molecules for the treatment of TB. Although several approaches to augmenting standard TB treatment have been proposed, only a few have been explored in detail or advanced to preclinical and clinical studies. Our review focuses on molecular targets and inhibitory small molecules that function within the macrophage or other myeloid cells, on host inflammatory pathways, or at the level of TB-induced lung pathology.

Cytosolic phospholipase A2 and eicosanoids modulate life, death and function of human osteoclasts in vitro

INTRODUCTION

Eicosanoids are important in bone physiology but the specific function of phopholipase enzymes has not been determined in osteoclasts. The objective of this is study was to determine the presence of cPLA2 in human in vitro-differentiated osteoclasts as well as osteoclasts in situ from bone biopsies.

MATERIALS AND METHODS

Osteoclastogenesis, apoptosis, bone resorption and the modulation of actin cytoskeleton assays were performed on osteoclasts differentiated in vitro. Immunohistochemistry was done in differentiated osteoclasts as well as on bone biopsies.

RESULTS

Human osteoclasts from normal, fetal, osteoarthritic, osteoporotic and Pagetic bone biopsies express cPLA2 and stimulation with RANKL increases cPLA2 phosphorylation in vitro. Inhibition of cPLA2 increased osteoclastogenesis and decreased apoptosis but decreased the capacity of osteoclasts to generate actin rings and to resorb bone.

DISCUSSION AND CONCLUSIONS

These results suggest that cPLA2 modulates osteoclast functions and could be a useful target in bone diseases with hyperactivated osteoclasts.

Identification of predictive biomarkers of disease state in transition dairy cows

In dairy cows, periparturient disease states, such as metritis, mastitis, and laminitis, are leading to increasingly significant economic losses for the dairy industry. Treatments for these pathologies are often expensive, ineffective, or not cost-efficient, leading to production losses, high veterinary bills, or early culling of the cows. Early diagnosis or detection of these conditions before they manifest themselves could lower their incidence, level of morbidity, and the associated economic losses. In an effort to identify predictive biomarkers for postpartum or periparturient disease states in dairy cows, we undertook a cross-sectional and longitudinal metabolomics study to look at plasma metabolite levels of dairy cows during the transition period, before and after becoming ill with postpartum diseases. Specifically we employed a targeted quantitative metabolomics approach that uses direct flow injection mass spectrometry to track the metabolite changes in 120 different plasma metabolites. Blood plasma samples were collected from 12 dairy cows at 4 time points during the transition period (-4 and -1 wk before and 1 and 4 wk after parturition). Out of the 12 cows studied, 6 developed multiple periparturient disorders in the postcalving period, whereas the other 6 remained healthy during the entire experimental period. Multivariate data analysis (principal component analysis and partial least squares discriminant analysis) revealed a clear separation between healthy controls and diseased cows at all 4 time points. This analysis allowed us to identify several metabolites most responsible for separating the 2 groups, especially before parturition and the start of any postpartum disease. Three metabolites, carnitine, propionyl carnitine, and lysophosphatidylcholine acyl C14:0, were significantly elevated in diseased cows as compared with healthy controls as early as 4 wk before parturition, whereas 2 metabolites, phosphatidylcholine acyl-alkyl C42:4 and phosphatidylcholine diacyl C42:6, could be used to discriminate healthy controls from diseased cows 1 wk before parturition. A 3-metabolite plasma biomarker profile was developed that could predict which cows would develop periparturient diseases, up to 4 wk before clinical symptoms appearing, with a sensitivity of 87% and a specificity of 85%. This is the first report showing that periparturient diseases can be predicted in dairy cattle before their development using a multimetabolite biomarker model. Further research is warranted to validate these potential predictive biomarkers.

Cell death paradigms in the pathogenesis of Mycobacterium tuberculosis infection

Cell death or senescence is a fundamental event that helps maintain cellular homeostasis, shapes the growth of organism, and provides protective immunity against invading pathogens. Decreased or increased cell death is detrimental both in infectious and non-infectious diseases. Cell death is executed both by regulated enzymic reactions and non-enzymic sudden collapse. In this brief review we have tried to summarize various cell death modalities and their impact on the pathogenesis of Mycobacterium tuberculosis.

Bisgma stimulates prostaglandin E2 production in macrophages via cyclooxygenase-2, cytosolic phospholipase A2, and mitogen-activated protein kinases family

BACKGROUND

Bisphenol A-glycidyl-methacrylate (BisGMA) employs as a monomer in dental resins. The leakage of BisGMA from composite resins into the peripheral environment can result in inflammation via macrophage activation. Prostaglandin E2 (PGE2) is a key regulator of immunopathology in inflammatory reactions. Little is known about the mechanisms of BisGMA-induced PGE2 expression in macrophage. The aim of this study was to evaluate the signal transduction pathways of BisGMA-induced PGE2 production in murine RAW264.7 macrophages.

METHODOLOGY/PRINCIPAL FINDINGS

Herein, we demonstrate that BisGMA can exhibit cytotoxicity to RAW264.7 macrophages in a dose- and time-dependent manner (p<0.05). In addition, PGE2 production, COX-2 expression, and cPLA2 phosphorylation were induced by BisGMA on RAW264.7 macrophages in a dose- and time-dependent manner (p<0.05). Moreover, BisGMA could induce the phosphorylation of ERK1/2 pathway (MEK1/2, ERK1/2, and Elk), p38 pathway (MEK3/6, p38, and MAPKAPK2), and JNK pathway (MEK4, JNK, and c-Jun) in a dose- and time-dependent manner (p<0.05). Pretreatment with AACOCF3, U0126, SB203580, and SP600125 significantly diminished the phosphorylation of cPLA2, ERK1/2, p38, and JNK stimulated by BisGMA, respectively (p<0.05). BisGMA-induced cytotoxicity, cPLA2 phosphorylation, PGE2 generation, and caspases activation were reduced by AACOCF3, U0126, SB203580, and SP600125, respectively (p<0.05).

CONCLUSIONS

These results suggest that BisGMA induced-PGE2 production may be via COX-2 expression, cPLA2 phosphorylation, and the phosphorylation of MAPK family. Cytotoxicity mediated by BisGMA may be due to caspases activation through the phosphorylation of cPLA2 and MAPKs family.

Prokaryotic expression and functional analysis of the Mb1514 gene in Mycobacterium bovis

The ability of mycobacteria to grow and invade target tissues is the key component in the process of Mycobacterium bovis infection. Therefore, analysis of the proteins responsible for cell invasion will assist clinicians in combating bovine tuberculosis. The Mb1514 gene of M. bovis encodes a hypothetical invasion protein (designated here as MbINV protein), whose function has not yet been directly identified. In this study, the Mb1514 gene from M. bovis was cloned, and expressed in E. coli. The recombinant MbINV protein (a single band of approximately 28 kDa) was purified for biological analysis. Our data demonstrated that recombinant MbINV protein significantly inhibited the viability of RAW264.7 macrophages in a dose-dependent manner (P < 0.05), and induced cell necrosis, indicating that the protein is toxic. MbINV protein infection significantly enhanced the mRNA expression levels of TNF-α, IL-1β, and NOS2 (P < 0.01), suggesting that MbINV protein may be one of the virulence factors which directly interact with macrophages and modulate the host immune response to M. bovis. An invasion inhibition assay showed that MbINV-inhibited M. bovis invasion of RAW264.7 cells in a concentration-dependant manner, demonstrating it is an invasion protein.

Drug resistant clinical isolates of Mycobacterium tuberculosis from different genotypes exhibit differential host responses in THP-1 cells

Mycobacterium tuberculosis (MTB) persistently infects and survives within the host macrophages. Substantial genotypic variation exists among MTB strains which correlate with their interactions with the host. The present study was designed to establish a correlation, if any, between infection and induction of innate immune response by genetically diverse drug resistant MTB isolates from India. For this purpose, three clinical isolates from ancient and modern lineages, along with H37Ra and H37Rv were evaluated for intracellular growth, phagocytic index, induction of proinflammatory cytokines and apoptosis following infection in THP-1 cell line. A wide variation in the induction of cytokines was revealed subsequent to infection with different strains. EAI-5 strain from ancient lineage 1, induced higher proinflammatory responses, higher apoptosis and moderate intracellular growth compared to other strains, in contrast, for Beijing strain of modern lineage 2, all three parameters were lowest among the clinical isolates. Further, the responses induced by LAM-6 from modern lineage 4 were at a moderate level, similar to the laboratory strain H37Rv which also belongs to lineage 4. Thus, these profiles were specific to their respective lineages and/or genotypes and independent of their drug resistance status. Further, a positive correlation, among TNF-α, IL-1β, IL-6 and IL-12 induced in infected THP-1 cells was demonstrated. In addition, induction of all pro-inflammatory cytokines correlated well with the host cell apoptosis. A positive correlation was observed between phagocytic index in the category of ‘>10 bacilli/cell’ and induction of apoptosis, only for virulent strains, indicating that initial accumulation of MTB strains inside the host cell may be an important determining factor for different innate responses.

Heme catabolism by heme oxygenase-1 confers host resistance to Mycobacterium infection

Heme oxygenases (HO) catalyze the rate-limiting step of heme degradation. The cytoprotective action of the inducible HO-1 isoform, encoded by the Hmox1 gene, is required for host protection against systemic infections. Here we report that upregulation of HO-1 expression in macrophages (M) is strictly required for protection against mycobacterial infection in mice. HO-1-deficient (Hmox1(-/-)) mice are more susceptible to intravenous Mycobacterium avium infection, failing to mount a protective granulomatous response and developing higher pathogen loads, than infected wild-type (Hmox1(+/+)) controls. Furthermore, Hmox1(-/-) mice also develop higher pathogen loads and ultimately succumb when challenged with a low-dose aerosol infection with Mycobacterium tuberculosis. The protective effect of HO-1 acts independently of adaptive immunity, as revealed in M. avium-infected Hmox1(-/-) versus Hmox1(+/+) SCID mice lacking mature B and T cells. In the absence of HO-1, heme accumulation acts as a cytotoxic pro-oxidant in infected M, an effect mimicked by exogenous heme administration to M. avium-infected wild-type M in vitro or to mice in vivo. In conclusion, HO-1 prevents the cytotoxic effect of heme in M, contributing critically to host resistance to Mycobacterium infection.

A distal enhancer controls cytokine-dependent human cPLA2α gene expression

Specific control of group IVA cytosolic phospholipase A2 (cPLA2α or PLA2G4A) expression modulates arachidonic acid production, thus tightly regulating the downstream effects of pro- and anti-inflammatory eicosanoids. The significance of this pathway in human disease is apparent in a range of pathologies from inflammation to tumorigenesis. While much of the regulation of cPLA2α has focused on posttranslational phosphorylation of the protein, studies on transcriptional regulation of this gene have focused only on proximal promoter regions. We have identified a DNase I hypersensitive site encompassing a 5' distal enhancer element containing a highly conserved consensus AP-1 site involved in transcriptional activation of cPLA2α by interleukin (IL)-1β. Chromatin immunoprecipitation (ChIP), knockdown, knockout, and overexpression analyses have shown that c-Jun acts both in a negative and positive regulatory role. Transcriptional activation of cPLA2α occurs through the phosphorylation of c-Jun in conjunction with increased association of C/EBPβ with the distal novel enhancer. The association of C/EBPβ with the transcriptional activation complex does not require an obvious DNA binding site. These data provide new and important contributions to the understanding of cPLA2α regulation at the transcriptional level, with implications for eicosanoid metabolism, cellular signaling, and disease pathogenesis.

Dying to live: how the death modality of the infected macrophage affects immunity to tuberculosis

Virulent Mycobacterium tuberculosis (Mtb) inhibits apoptosis and triggers necrosis of host macrophages to evade innate delay in the initiation of adaptive immunity. Necrosis is a mechanism used by bacteria to exit macrophage, evade the host defenses, and disseminate while apoptosis is associated with diminished pathogen viability. We have recently demonstrated that eicosanoids regulate cell death program of either human or murine macrophages infected with Mtb. We have defined prostaglandin E2 (PGE2) as a pro-apoptotic host lipid mediator which protects against necrosis. In contrast, lipoxin A4 (LXA4) is a pro-necrotic lipid mediator which suppresses PGE2 synthesis, resulting in mitochondrial damage and inhibition of plasma membrane repair mechanisms; this ultimately leads to the induction of necrosis. Thus, the balance between PGE2 and LXA4 determines whether Mtb-infected macrophages undergo apoptosis or necrosis and this balance determines the outcome of infection.

Analysis of pyroptosis in bacterial infection

Eukaryotic cells undergo death by several different mechanisms: apoptosis, a cell death that prevents inflammatory response; necrosis, when the cell membrane lyses and all the intracellular content is spilled outside; and pyroptosis, a cell death that is accompanied by the release of inflammatory cytokines by the dying cells. Pyroptosis is designed to attract a nonspecific innate response to the site of infection or tumor. In this chapter, we describe the methods used to study pyroptosis in a mammalian cell. The model organism used is Mycobacterium tuberculosis, which suppresses pyroptosis by macrophages, and possibly in dendritic cells.

Biomarkers of inflammation, immunosuppression and stress with active disease are revealed by metabolomic profiling of tuberculosis patients

Although tuberculosis (TB) causes more deaths than any other pathogen, most infected individuals harbor the pathogen without signs of disease. We explored the metabolome of >400 small molecules in serum of uninfected individuals, latently infected healthy individuals and patients with active TB. We identified changes in amino acid, lipid and nucleotide metabolism pathways, providing evidence for anti-inflammatory metabolomic changes in TB. Metabolic profiles indicate increased activity of indoleamine 2,3 dioxygenase 1 (IDO1), decreased phospholipase activity, increased abundance of adenosine metabolism products, as well as indicators of fibrotic lesions in active disease as compared to latent infection. Consistent with our predictions, we experimentally demonstrate TB-induced IDO1 activity. Furthermore, we demonstrate a link between metabolic profiles and cytokine signaling. Finally, we show that 20 metabolites are sufficient for robust discrimination of TB patients from healthy individuals. Our results provide specific insights into the biology of TB and pave the way for the rational development of metabolic biomarkers for TB.

Mycobacterium tuberculosis modulates macrophage lipid-sensing nuclear receptors PPARγ and TR4 for survival

Mycobacterium tuberculosis-macrophage interactions are key to pathogenesis and clearance of these bacteria. Although interactions between M. tuberculosis-associated lipids and TLRs, non-TLRs, and opsonic receptors have been investigated, interactions of these lipids and infected macrophage lipid repertoire with lipid-sensing nuclear receptors expressed in macrophages have not been addressed. In this study, we report that M. tuberculosis-macrophage lipids can interact with host peroxisome proliferator-activated receptor γ and testicular receptor 4 to ensure survival of the pathogen by modulating macrophage function. These two lipid-sensing nuclear receptors create a foamy niche within macrophage by modulating oxidized low-density lipoprotein receptor CD36, phagolysosomal maturation block by induction of IL-10, and a blunted innate response by alternative polarization of the macrophages, which leads to survival of M. tuberculosis. These results also suggest possible heterologous ligands for peroxisome proliferator-activated receptor γ and testicular receptor 4 and are suggestive of adaptive or coevolution of the host and pathogen. Relative mRNA expression levels of these receptors in PBMCs derived from clinical samples convincingly implicate them in tuberculosis susceptibility. These observations expose a novel paradigm in the pathogenesis of M. tuberculosis amenable for pharmacological modulation.

Induction of group IVC phospholipase A2 in allergic asthma: transcriptional regulation by TNFα in bronchoepithelial cells

Airway inflammation in allergen-induced asthma is associated with eicosanoid release. These bioactive lipids exhibit anti- and pro-inflammatory activities with relevance to pulmonary pathophysiology. We hypothesized that sensitization/challenge using an extract from the ubiquitous fungus Aspergillus fumigatus in a mouse model of allergic asthma would result in altered phospholipase gene expression, thus modulating the downstream eicosanoid pathway. We observed the most significant induction in the group IVC PLA2 (phospholipase A2) [also known as cPLA2γ (cytosolic PLA2γ) or PLA2G4C]. Our results infer that A. fumigatus extract can induce cPLA2γ levels directly in eosinophils, whereas induction in lung epithelial cells is most likely to be a consequence of TNFα (tumour necrosis factor α) secretion by A. fumigatus-activated macrophages. The mechanism of TNFα-dependent induction of cPLA2γ gene expression was elucidated through a combination of promoter deletions, ChIP (chromatin immunoprecipitation) and overexpression studies in human bronchoepithelial cells, leading to the identification of functionally relevant CRE (cAMP-response element), NF-κB (nuclear factor κB) and E-box promoter elements. ChIP analysis demonstrated that RNA polymerase II, ATF-2 (activating transcription factor 2)-c-Jun, p65-p65 and USF (upstream stimulating factor) 1-USF2 complexes are recruited to the cPLA2γ enhancer/promoter in response to TNFα, with overexpression and dominant-negative studies implying a strong level of co-operation and interplay between these factors. Overall, our results link cytokine-mediated alterations in cPLA2γ gene expression with allergic asthma and outline a complex regulatory mechanism.

cPLA2α-mediated actin rearrangements downstream of the Akt signaling is required for Cronobacter sakazakii invasion into brain endothelial cells

Cronobacter sakazakii (C. sakazakii) is an opportunistic pathogen that causes sepsis and meningitis in neonate. The molecular mechanism involved in the pathogenesis of C. sakazakii meningitis remains unclear. In this study, we found that C. sakazakii invasion was significantly decreased in human brain microvascular endothelial cells (HBMEC) treated with cytosolic phospholipases A(2)α (cPLA(2)α) inhibitor. Increased phosphorylation of cPLA(2)α was observed in HBMEC infected with C. sakazakii, which was prevented by treatment with cPLA(2)α inhibitor. cPLA(2)α knockdown in HBMEC significantly attenuated C. sakazakii invasion into HBMEC. Immunofluorescence demonstrated that the rearrangements of actin filaments in HBMEC induced by C. sakazakii were effectively blocked by either treatment with cPLA(2)α inhibitor or transfection with cPLA(2)α siRNA. Interestingly, we found that C. sakazakii infection promoted the aggregation of phosphorylated cPLA(2)α, which was associated with depolymerized actin filaments in HBMEC. Furthermore, our data revealed that cPLA(2)α acts downstream of Akt signaling pathway in HBMEC stimulated with C. sakazakii. Taken together, our results illustrated that cPLA(2)α-mediated actin filament rearrangements downstream of Akt activation is required for C. sakazakii invasion into brain endothelial cells.

Phospholipase A(2) of peroxiredoxin 6 has a critical role in tumor necrosis factor-induced apoptosis

Peroxiredoxin 6 (Prdx6) is a bifunctional enzyme with peroxidase and phospholipase A(2) (PLA(2)) activities. Although the cellular function of the peroxidase of Prdx6 has been well elucidated, the function of the PLA(2) of Prdx6 is largely unknown. Here, we report a novel function for the PLA(2) in regulating TNF-induced apoptosis through arachidonic acid (AA) release and interleukin-1β (IL-1β) production. Prdx6 knockdown (Prdx6(KD)) in human bronchial epithelial cells (BEAS2B) shows severe decreases of peroxidase and PLA(2) activities. Surprisingly, Prdx6(KD) cells are markedly resistant to apoptosis induced by TNF-α in the presence of cycloheximide, but are highly sensitive to hydrogen peroxide-induced apoptosis. Furthermore, the release of AA and the production of IL-1β induced by proinflammatory stimuli, such as TNF-α, LPS, and poly I/C, are severely decreased in Prdx6(KD) cells. More interestingly, the restoration of Prdx6 expression with wild-type Prdx6, but not PLA(2)-mutant Prdx6 (S32A), in Prdx6(KD) cells dramatically induces the recovery of TNF-induced apoptosis, AA release, and IL-1β production, indicating specific roles for the PLA(2) activity of Prdx6. Our results provide new insights into the distinct roles of bifunctional Prdx6 with peroxidase and PLA(2) activities in oxidative stress-induced and TNF-induced apoptosis, respectively.

Tuberculosis: new aspects of an old disease

Tuberculosis is an ancient infectious disease that remains a threat for public health around the world. Although the etiological agent as well as tuberculosis pathogenesis is well known, the molecular mechanisms underlying the host defense to the bacilli remain elusive. In this paper we focus on the innate immunity of this disease reviewing well-established and consensual mechanisms like Mycobacterium tuberculosis interference with phagosome maturation, less consensual mechanism like nitric oxide production, and new mechanisms, such as mycobacteria translocation to the cytosol, autophagy, and apoptosis/necrosis proposed mainly during the last decade.

Angiogenic activity of sera from pulmonary tuberculosis patients in relation to IL-12p40 and TNFα serum levels

The role of angiogenesis in the pathogenesis of tuberculosis (TB) is not clear. The aim of this study was to examine the effect of sera from TB patients on angiogenesis induced by different subsets of normal human mononuclear cells (MNC) in relation to IL-12p40 and TNFα serum levels. Serum samples from 36 pulmonary TB patients and from 22 healthy volunteers were evaluated. To assess angiogenic reaction the leukocytes-induced angiogenesis test according to Sidky and Auerbach was performed. IL-12p40 and TNFα serum levels were evaluated by ELISA. Sera from TB patients significantly stimulated angiogenic activity of MNC compared to sera from healthy donors and PBS (p < 0.001). The number of microvessels formed after injection of lymphocytes preincubated with sera from TB patients was significantly lower compared to the number of microvessels created after injection of MNC preincubated with the same sera (p < 0.016). However, the number of microvessels created after the injection of lymphocytes preincubated with sera from healthy donors or with PBS alone was significantly higher (p < 0.017). The mean levels of IL-12p40 and TNFα were significantly elevated in sera from TB patients compared to healthy donors. We observed a correlation between angiogenic activity of sera from TB patients and IL-12p40 and TNFα serum levels (p < 0.01). Sera from TB patients constitute a source of mediators that participate in angiogenesis and prime monocytes for production of proangiogenic factors. The main proangiogenic effect of TB patients’ sera is mediated by macrophages/monocytes. TNFα and IL-12p40 may indirectly stimulate angiogenesis in TB.

Apoptosis is an innate defense function of macrophages against Mycobacterium tuberculosis

Two different forms of death are commonly observed when Mycobacterium tuberculosis (Mtb)-infected macrophages die: (i) necrosis, a death modality defined by cell lysis and (ii) apoptosis, a form of death that maintains an intact plasma membrane. Necrosis is a mechanism used by bacteria to exit the macrophage, evade host defenses, and spread. In contrast, apoptosis of infected macrophages is associated with diminished pathogen viability. Apoptosis occurs when tumor necrosis factor activates the extrinsic death domain pathway, leading to caspase-8 activation. In addition, mitochondrial outer membrane permeabilization leading to activation of the intrinsic apoptotic pathway is required. Both pathways lead to caspase-3 activation, which results in apoptosis. We have recently demonstrated that during mycobacterial infection, cell death is regulated by the eicosanoids, prostaglandin E(2) (proapoptotic) and lipoxin (LX)A(4) (pronecrotic). Although PGE(2) protects against necrosis, virulent Mtb induces LXA(4) and inhibits PGE(2) production. Under such conditions, mitochondrial inner membrane damage leads to macrophage necrosis. Thus, virulent Mtb subverts eicosanoid regulation of cell death to foil innate defense mechanisms of the macrophage.

Lipid bodies in inflammatory cells: structure, function, and current imaging techniques

Lipid bodies (LBs), also known as lipid droplets, have increasingly been recognized as functionally active organelles linked to diverse biological functions and human diseases. These organelles are actively formed in vivo within cells from the immune system, such as macrophages, neutrophils, and eosinophils, in response to different inflammatory conditions and are sites for synthesis and storage of inflammatory mediators. In this review, the authors discuss structural and functional aspects of LBs and current imaging techniques to visualize these organelles in cells engaged in inflammatory processes, including infectious diseases. The dynamic morphological aspects of LBs in leukocytes as inducible, newly formable organelles, elicitable in response to stimuli that lead to cellular activation, contribute to the evolving understanding of LBs as organelles that are critical regulators of different inflammatory diseases, key markers of leukocyte activation, and attractive targets for novel anti-inflammatory therapies.

Development of new antituberculous drugs based on bacterial virulence factors interfering with host cytokine networks

The worldwide increase in the prevalence of tuberculosis (TB), especially multidrug-resistant TB and extensively drug-resistant TB, is an important global health concern, and new effective drugs are urgently needed. Information on the genome of Mycobacterium tuberculosis (MTB) and various mycobacterial virulence genes is leading to the identification of genes that code for new drug targets. Mycobacterium tuberculosis (MTB) is resistant to the antimicrobial mechanisms of host macrophages and can survive and replicate in macrophages for long periods, resulting in a persistent infection. Mycobacterial virulence factors suppress macrophage bactericidal functions partly via their downregulatory effects on the host antimicrobial cytokine networks, consisting of proinflammatory, immunopotentiating, and Th1-inducing cytokines. Thus, for the development of unique drugs that exhibit antimycobacterial action through novel mechanisms, it is reasonable to search for targets among bacterial genes encoding virulence factors which interfere with the host cytokine responses protective to mycobacterial pathogens. In this review, we discuss the profiles of cytokine networks related to host resistance to mycobacteria, including the mechanisms of downregulation of host antimycobacterial immunity due to immunosuppressive cytokines, which are occasionally induced in the advanced stages of TB. We also highlight the development of antituberculous drugs based on bacterial virulence factors interfering with the host antimycobacterial cytokine network.

Activation of group IVC phospholipase A(2) by polycyclic aromatic hydrocarbons induces apoptosis of human coronary artery endothelial cells

Exposure to environmental pollutants, such as polycyclic aromatic hydrocarbons (PAHs) found in coal tar mixtures and tobacco sources, is considered a significant risk factor for the development of heart disease in humans. The goal of this study was to determine the influence of PAHs present at a Superfund site on human coronary artery endothelial cell (HCAEC) phospholipase A(2) (PLA(2)) activity and apoptosis. Extremely high levels of 12 out of 15 EPA high-priority PAHs were present in both the streambed and floodplain sediments at a site where an urban creek and its adjacent floodplain were extensively contaminated by PAHs and other coal tar compounds. Nine of the 12 compounds and a coal tar mixture (SRM 1597A) activated group IVC PLA(2) in HCAECs, and activation of this enzyme was associated with histone fragmentation and poly (ADP) ribose polymerase (PARP) cleavage. Genetic silencing of group IVC PLA(2) inhibited both (3)H-fatty acid release and histone fragmentation by PAHs and SRM 1597A, indicating that individual PAHs and a coal tar mixture induce apoptosis of HCAECs via a mechanism that involves group IVC PLA(2). Western blot analysis of aortas isolated from feral mice (Peromyscus leucopus) inhabiting the Superfund site showed increased PARP and caspase-3 cleavage when compared to reference mice. These data suggest that PAHs induce apoptosis of HCAECs via activation of group IVC PLA(2).

Evasion of innate immunity by Mycobacterium tuberculosis: is death an exit strategy?

Virulent Mycobacterium tuberculosis inhibits apoptosis and triggers necrosis of host macrophages to evade innate immunity and delay the initiation of adaptive immunity. By contrast, attenuated M. tuberculosis induces macrophage apoptosis, an innate defence mechanism that reduces bacterial viability. In this Opinion article, we describe how virulent M. tuberculosis blocks production of the eicosanoid lipid mediator prostaglandin E(2) (PGE(2)). PGE(2) production by infected macrophages prevents mitochondrial damage and initiates plasma membrane repair, two processes that are crucial for preventing necrosis and inducing apoptosis. Thus, M. tuberculosis-mediated modulation of eicosanoid production determines the death modality of the infected macrophage, which in turn has a substantial impact on the outcome of infection.