Severe glucose-6-phosphate dehydrogenase deficiency leads to susceptibility to infection and absent NETosis.

BACKGROUND: Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common enzymatic disorder of red blood cells in human subjects, causing hemolytic anemia linked to impaired nicotinamide adenine dinucleotide phosphate (NADPH) production and imbalanced redox homeostasis in erythrocytes. Because G6PD is expressed by a variety of hematologic and nonhematologic cells, a broader clinical phenotype could be postulated in G6PD-deficient patients. We describe 3 brothers with severe G6PD deficiency and susceptibility to bacterial infection. OBJECTIVE: We sought to study the molecular pathophysiology leading to susceptibility to infection in 3 siblings with severe G6PD deficiency. METHODS: Blood samples of 3 patients with severe G6PD deficiency were analyzed for G6PD enzyme activity, cellular oxidized nicotinamide adenine dinucleotide phosphate/NADPH levels, phagocytic reactive oxygen species production, neutrophil extracellular trap (NET) formation, and neutrophil elastase translocation. RESULTS: In these 3 brothers strongly reduced NADPH oxidase function was found in granulocytes, leading to impaired NET formation. Defective NET formation has thus far been only observed in patients with the NADPH oxidase deficiency chronic granulomatous disease, who require antibiotic and antimycotic prophylaxis to prevent life-threatening bacterial and fungal infections. CONCLUSION: Because severe G6PD deficiency can be a phenocopy of chronic granulomatous disease with regard to the cellular and clinical phenotype, careful evaluation of neutrophil function seems mandatory in these patients to decide on appropriate anti-infective preventive measures. Determining the level of G6PD enzyme activity should be followed by analysis of reactive oxygen species production and NET formation to decide on required antibiotic and antimycotic prophylaxis.

Analysis of LC3-Associated Phagocytosis and Antigen Presentation.

The noncanonical macroautophagy pathway, LC3-associated phagocytosis (LAP) has recently emerged as an important catabolic process involved during exogenous antigen processing. It has been described that in human macrophages and dendritic cells the direct recruitment of LC3 to the phagosomal membrane is associated with its maturation impairment, allowing the stabilization of the cargo to prolong antigen presentation on major histocompatibility complex (MHC) class II molecules.In this chapter, we describe methods to monitor, manipulate, and understand the role of LAP during MHC class II presentation. We show how to enhance LAP formation resulting in antigen presentation by using zymosan or beads coated with Candida albicans extract. Then, we describe how to determine the localization of Rab7 or Lamp2 on LC3-phagosomes by confocal microscopy, a useful technique to follow phagosome maturation. Finally, we propose an assay to understand how MHC class II antigen presentation can be modulated by the LAP pathway.

Therapeutic value of oral supplementation with melon superoxide dismutase and wheat gliadin combination.

Dietary antioxidant supplementation has been popular in Western countries. Various supplements have been developed in recent years, and research has been gathered from both animal and clinical research trials. In this review, the therapeutic value of oral administration of a combination of melon superoxide dismutase (SOD) and a vegetable polymer (gliadin) is evaluated. Critical examination of the effects of SOD-gliadin supplementation is carried out, with an emphasis on its impact on oxidative stress levels and on endogenous antioxidant pathways. Overall analysis of peer-reviewed published data suggests that intake of SOD-gliadin might have advantageous health effects. These conclusions are dependent on the condition or pathology under consideration. In general, the authors, who analyzed SOD-gliadin supplementation, support the use of SOD-gliadin supplementation as a complementary treatment rather than a therapeutic treatment. To further clarify the importance of dietary SOD-gliadin administration, additional large-scale clinical trials are recommended.

LC3-associated phagocytosis.

A recent report from our group has described that upon engulfment of pathogens, a subset of phagosomes is formed to preserve antigens for prolonged presentation on MHC class II molecules. The distinctive feature of these particular vesicles is their coating with LC3/Atg8, a key component of the autophagy machinery. Here we discuss the possible outcomes of LC3-associated phagocytosis and its implications in the context of immunity.

Macroautophagy Proteins Assist Epstein Barr Virus Production and Get Incorporated Into the Virus Particles.

Epstein Barr virus (EBV) persists as a latent herpes virus infection in the majority of the adult human population. The virus can reactivate from this latent infection into lytic replication for virus particle production. Here, we report that autophagic membranes, which engulf cytoplasmic constituents during macroautophagy and transport them to lysosomal degradation, are stabilized by lytic EBV replication in infected epithelial and B cells. Inhibition of autophagic membrane formation compromises infectious particle production and leads to the accumulation of viral DNA in the cytosol. Vice versa, pharmacological stimulation of autophagic membrane formation enhances infectious virus production. Atg8/LC3, an essential macroautophagy protein and substrate anchor on autophagic membranes, was found in virus preparations, suggesting that EBV recruits Atg8/LC3 coupled membranes to its envelope in the cytosol. Our data indicate that EBV subverts macroautophagy and uses autophagic membranes for efficient envelope acquisition during lytic infection.

Autophagy proteins stabilize pathogen-containing phagosomes for prolonged MHC II antigen processing.

Antigen preservation for presentation is a hallmark of potent antigen-presenting cells. In this paper, we report that in human macrophages and dendritic cells, a subset of phagosomes gets coated with Atg8/LC3, a component of the molecular machinery of macroautophagy, and maintains phagocytosed antigens for prolonged presentation on major histocompatibility complex class II molecules. These Atg8/LC3-positive phagosomes are formed around the antigen with TLR2 agonists and require reactive oxygen species production by NOX2 for their generation. A deficiency in the NOX2-dependent formation of these antigen storage phagosomes could contribute to compromise antifungal immune control in chronic granulomatous disease patients.

Checking the garbage bin for problems in the house, or how autophagy assists in antigen presentation to the immune system.

Macroautophagy was originally discovered as a nutrient salvage pathway during starvation. By now it has not only become clear that degradation of cytoplasmic constituents via transport by autophagosomes to lysosomes can be used for innate and adaptive immunity, but that the core machinery assists antigen presentation to the immune system by a variety of vesicular transport pathways. All of these rely on the presentation of small protein waste fragments, which are generated by a variety of catabolic pathways, including macroautophagy, on major histocompatibility complex (MHC) molecules. In this review, we will point out how classical macroautophagy, as well as phagocytosis and exocytosis, which both benefit from the core autophagic machinery, assist in antigen presentation on MHC class I and II molecules to CD8+ and CD4+ T cells, respectively. Finally to high-light that macroautophagy is always intimately interconnected with cell death in addition to the various supported vesicular transport function, its role in lymphocyte, especially T cell, development and function will be discussed. From this body of work a picture is emerging that the core machinery of macroautophagy can be used for a variety of vesicular transport pathways and to modulate cell survival, besides its classical role in delivering intracellular material for lysosomal degradation.

Leishmania mitochondrial peroxiredoxin plays a crucial peroxidase-unrelated role during infection: insight into its novel chaperone activity.

Two-cysteine peroxiredoxins are ubiquitous peroxidases that play various functions in cells. In Leishmania and related trypanosomatids, which lack catalase and selenium-glutathione peroxidases, the discovery of this family of enzymes provided the molecular basis for peroxide removal in these organisms. In this report the functional relevance of one of such enzymes, the mitochondrial 2-Cys peroxiredoxin (mTXNPx), was investigated along the Leishmania infantum life cycle. mTXNPx null mutants (mtxnpx(-)) produced by a gene replacement strategy, while indistinguishable from wild type promastigotes, were found unable to thrive in a murine model of infection. Unexpectedly, however, the avirulent phenotype of mtxnpx(-) was not due to lack of the peroxidase activity of mTXNPx as these behaved like controls when exposed to oxidants added exogenously or generated by macrophages during phagocytosis ex vivo. In line with this, mtxnpx(-) were also avirulent when inoculated into murine hosts unable to mount an effective oxidative phagocyte response (B6.p47(phox-/-) and B6.RAG2(-/-) IFN-γ(-/-) mice). Definitive conclusion that the peroxidase activity of mTXNPx is not required for parasite survival in mice was obtained by showing that a peroxidase-inactive version of this protein was competent in rescuing the non-infective phenotype of mtxnpx(-). A novel function is thus proposed for mTXNPx, that of a molecular chaperone, which may explain the impaired infectivity of the null mutants. This premise is based on the observation that the enzyme is able to suppress the thermal aggregation of citrate synthase in vitro. Also, mtxnpx(-) were more sensitive than controls to a temperature shift from 25°C to 37°C, a phenotype reminiscent of organisms lacking specific chaperone genes. Collectively, the findings reported here change the paradigm which regards all trypanosomatid 2-Cys peroxiredoxins as peroxide-eliminating devices. Moreover, they demonstrate, for the first time, that these 2-Cys peroxiredoxins can be determinant for pathogenicity independently of their peroxidase activity.

Autophagy of pathogens alarms the immune system and participates in its effector functions.

Macroautophagy is a main catabolic pathway of eukaryotic cells, delivering cytoplasmic constituents for lysosomal degradation. Originally described as a starvation response, it has now been realised that macroautophagy supports many aspects of innate and adaptive immunity by facilitating innate pathogen detection and antigen presentation, as well as pathogen clearance and lymphocyte expansion. In the first half of this review, we summarise new insights into substrate selection and macroautophagic support of vesicular transport pathways, which underlie macroautophagic regulation of afferent and efferent immunity to pathogens, as outlined in the second half of the review. Applying this increased mechanistic understanding to infectious disease settings should allow us to identify further pathways for pathogen restriction, which can be explored for therapeutic manipulations of macro-autophagy.

Mitochondrial redox metabolism in trypanosomatids is independent of tryparedoxin activity.

Tryparedoxins (TXNs) are oxidoreductases unique to trypanosomatids (including Leishmania and Trypanosoma parasites) that transfer reducing equivalents from trypanothione, the major thiol in these organisms, to sulfur-dependent peroxidases and other dithiol proteins. The existence of a TXN within the mitochondrion of trypanosomatids, capable of driving crucial redox pathways, is considered a requisite for normal parasite metabolism. Here this concept is shown not to apply to Leishmania. First, removal of the Leishmania infantum mitochondrial TXN (LiTXN2) by gene-targeting, had no significant effect on parasite survival, even in the context of an animal infection. Second, evidence is presented that no other TXN is capable of replacing LiTXN2. In fact, although a candidate substitute for LiTXN2 (LiTXN3) was found in the genome of L. infantum, this was shown in biochemical assays to be poorly reduced by trypanothione and to be unable to reduce sulfur-containing peroxidases. Definitive conclusion that LiTXN3 cannot directly reduce proteins located within inner mitochondrial compartments was provided by analysis of its subcellular localization and membrane topology, which revealed that LiTXN3 is a tail-anchored (TA) mitochondrial outer membrane protein presenting, as characteristic of TA proteins, its N-terminal end (containing the redox-active domain) exposed to the cytosol. This manuscript further proposes the separation of trypanosomatid TXN sequences into two classes and this is supported by phylogenetic analysis: i) class I, encoding active TXNs, and ii) class II, coding for TA proteins unlikely to function as TXNs. Trypanosoma possess only two TXNs, one belonging to class I (which is cytosolic) and the other to class II. Thus, as demonstrated for Leishmania, the mitochondrial redox metabolism in Trypanosoma may also be independent of TXN activity. The major implication of these findings is that mitochondrial functions previously thought to depend on the provision of electrons by a TXN enzyme must proceed differently.

The cytosolic tryparedoxin of Leishmania infantum is essential for parasite survival.

Leishmania infantum cytosolic tryparedoxin (LiTXN1) can be regarded as a potential candidate for drug targeting. This redox active molecule, which belongs to the thioredoxin superfamily, is one constituent of the hydroperoxide elimination cascade in L. infantum and may also be involved in other cellular processes such as DNA synthesis or host-parasite interaction. In order to validate LiTXN1 as a drug target we have employed a gene replacement strategy. We observed that substitution of both chromosomal LiTXN1 alleles was only possible upon parasite complementation with an episomal copy of the gene. Furthermore, contrary to control parasites carrying the empty vector, both the insect and the mammalian stages of L. infantum retained the episomal copy of LiTXN1 in the absence of drug pressure. These results confirm the essentiality of LiTXN1 throughout the life cycle of the parasite, namely in the disease-causing amastigote stage. In addition, the data obtained showed that disruption of one allele of this gene leads only to a 25% reduction in the expression of LiTXN1. Even though this does not affect promastigote growth and susceptibility to hydrogen peroxide, ex vivo infection assays suggest that wild-type levels of LiTXN1 are required for optimal L. infantum virulence.

Leishmania infantum: provision of reducing equivalents to the mitochondrial tryparedoxin/tryparedoxin peroxidase system.

Within the mitochondrion of Leishmania infantum, hydroperoxide metabolism relies on the activity of tryparedoxin-dependent peroxidases (TXNPxs). Tryparedoxins (TXNs) are thioredoxin-related oxidoreductases, which in vitro are reduced by the trypanothione reductase/trypanothione [TR/T(SH)(2)] redox couple. Still, there is no evidence that this actually occurs in the mitochondrion. This communication addresses the question of how the mitochondrial TXN/TXNPx system is reduced. First, using a digitonin fractionation assay, we show that TR activity is absent from the L. infantum mitochondrion. The possibility that this organelle possesses alternative electron sources for TXN/TXNPx is then investigated. Biochemical assays performed with purified recombinant enzymes, revealed that TR and T(SH)(2) can be replaced, albeit less efficiently, by the dihydrolipoamide dehydrogenase/lipoamide redox system as TXN/TXNPx electron donor. This result challenges the classical view that T(SH)(2) is the only reductant for TXNs and add new prospects regarding the involvement of 2-oxo acid dehydrogenase complexes in L. infantum mitochondrial hydroperoxide metabolism.

Catalysis and structural properties of Leishmania infantum glyoxalase II: trypanothione specificity and phylogeny.

The glyoxalase pathway catalyzes the formation of d-lactate from methylglyoxal, a toxic byproduct of glycolysis. In trypanosomatids, trypanothione replaces glutathione in this pathway, making it a potential drug target, since its selective inhibition might increase methylglyoxal concentration in the parasites. Two glyoxalase II structures were solved. One with a bound spermidine molecule (1.8 A) and the other with d-lactate at the active site (1.9 A). The second structure was obtained by crystal soaking with the enzyme substrate (S)-d-lactoyltrypanothione. The overall structure of Leishmania infantum glyoxalase II is very similar to its human counterpart, with important differences at the substrate binding site. The crystal structure of L. infantum glyoxalase II is the first structure of this enzyme from trypanosomatids. The differential specificity of glyoxalase II toward glutathione and trypanothione moieties was revealed by differential substrate binding. Evolutionary analysis shows that trypanosomatid glyoxalases II diverged early from eukaryotic enzymes, being unrelated to prokaryotic proteins.

LuxS impacts on LytA-dependent autolysis and on competence in Streptococcus pneumoniae.

The ubiquitous protein LuxS with S-ribosylhomocysteinase activity is involved in S-adenosyl methionine detoxification, C-1 unit recycling and the production of autoinducers that allow the cell to sense and respond to cell density. Independent reports describe the impact of LuxS deficiency on Streptococcus pneumoniae virulence in the mouse. In vitro, LuxS deficiency confers discrete phenotypes. A combined approach using genetic dissection and mixed-culture experiments allowed the involvement of LuxS in the developmental physiology of S. pneumoniae to be investigated. Functional LuxS was found to be related on the one hand to down-regulation of competence, and on the other hand to attenuation of autolysis in cultures entering stationary phase. The competence phenotype of luxS mutant bacteria was complemented by media conditioned by competence-defective ComAB0 bacteria, but not by BSA. The autolytic phenotype was complemented by BSA, but not by conditioned supernatants. It is suggested that the impact of LuxS on competence, but not on autolysis, involves cell-cell communication. The phenotype of luxS mutant strains reveals a hierarchy in the competence regulatory networks of S. pneumoniae.

Protein serine/threonine kinase StkP positively controls virulence and competence in Streptococcus pneumoniae.

In the Streptococcus pneumoniae genome, stkP, encoding a membrane-associated serine/threonine kinase, is not redundant (L. Novakova, S. Romao, J. Echenique, P. Branny, and M.-C. Trombe, unpublished results). The data presented here demonstrate that StkP belongs to the signaling network involved in competence triggering in vitro and lung infection and bloodstream invasion in vivo. In competence, functional StkP is required for activation of comCDE upstream of the autoregulated ring orchestrated by the competence-stimulating peptide. This is the first description of positive regulation of comCDE transcription in balance with its repression by CiaRH.