Eomes-dependent mitochondrial regulation promotes survival of pathogenic CD4+ T cells during inflammation

The mechanisms whereby Eomes controls tissue accumulation of T cells and strengthens inflammation remain ill-defined. Here, we show that Eomes deletion in antigen-specific CD4+ T cells is sufficient to protect against central nervous system (CNS) inflammation. While Eomes is dispensable for the initial priming of CD4+ T cells, it is required for long-term maintenance of CNS-infiltrating CD4+ T cells. We reveal that the impact of Eomes on effector CD4+ T cell longevity is associated with sustained expression of multiple genes involved in mitochondrial organization and functions. Accordingly, epigenetic studies demonstrate that Eomes supports mitochondrial function by direct binding to either metabolism-associated genes or mitochondrial transcriptional modulators. Besides, the significance of these findings was confirmed in CD4+ T cells from healthy donors and multiple sclerosis patients. Together, our data reveal a new mechanism by which Eomes promotes severity and chronicity of inflammation via the enhancement of CD4+ T cell mitochondrial functions and resistance to stress-induced cell death.

The interferon-inducible GTPase MxB promotes capsid disassembly and genome release of herpesviruses

Host proteins sense viral products and induce defence mechanisms, particularly in immune cells. Using cell-free assays and quantitative mass spectrometry, we determined the interactome of capsid-host protein complexes of herpes simplex virus and identified the large dynamin-like GTPase myxovirus resistance protein B (MxB) as an interferon-inducible protein interacting with capsids. Electron microscopy analyses showed that cytosols containing MxB had the remarkable capability to disassemble the icosahedral capsids of herpes simplex viruses and varicella zoster virus into flat sheets of connected triangular faces. In contrast, capsids remained intact in cytosols with MxB mutants unable to hydrolyse GTP or to dimerize. Our data suggest that MxB senses herpesviral capsids, mediates their disassembly, and thereby restricts the efficiency of nuclear targeting of incoming capsids and/or the assembly of progeny capsids. The resulting premature release of viral genomes from capsids may enhance the activation of DNA sensors, and thereby amplify the innate immune responses.

Human cytomegalovirus-induced host protein citrullination is crucial for viral replication

Citrullination is the conversion of arginine-to-citrulline by protein arginine deiminases (PADs), whose dysregulation is implicated in the pathogenesis of various types of cancers and autoimmune diseases. Consistent with the ability of human cytomegalovirus (HCMV) to induce post-translational modifications of cellular proteins to gain a survival advantage, we show that HCMV infection of primary human fibroblasts triggers PAD-mediated citrullination of several host proteins, and that this activity promotes viral fitness. Citrullinome analysis reveals significant changes in deimination levels of both cellular and viral proteins, with interferon (IFN)-inducible protein IFIT1 being among the most heavily deiminated one. As genetic depletion of IFIT1 strongly enhances HCMV growth, and in vitro IFIT1 citrullination impairs its ability to bind to 5’-ppp-RNA, we propose that viral-induced IFIT1 citrullination is a mechanism of HCMV evasion from host antiviral resistance. Overall, our findings point to a crucial role of citrullination in subverting cellular responses to viral infection.

Citrullination is a posttranslational modification of arginines. Here, the authors show that HCMV infection increases citrullination of host and virus proteins to promote infection and that citrullinated interferon-inducible protein IFIT1 is impaired in RNA binding, as a potential mechanism of evasion.

Interactomic affinity profiling by holdup assay: Acetylation and distal residues impact the PDZome-binding specificity of PTEN phosphatase

Protein domains often recognize short linear protein motifs composed of a core conserved consensus sequence surrounded by less critical, modulatory positions. PTEN, a lipid phosphatase involved in phosphatidylinositol 3-kinase (PI3K) pathway, contains such a short motif located at the extreme C-terminus capable to recognize PDZ domains. It has been shown that the acetylation of this motif could modulate the interaction with several PDZ domains. Here we used an accurate experimental approach combining high-throughput holdup chromatographic assay and competitive fluorescence polarization technique to measure quantitative binding affinity profiles of the PDZ domain-binding motif (PBM) of PTEN. We substantially extended the previous knowledge towards the 266 known human PDZ domains, generating the full PDZome-binding profile of the PTEN PBM. We confirmed that inclusion of N-terminal flanking residues, acetylation or mutation of a lysine at a modulatory position significantly altered the PDZome-binding profile. A numerical specificity index is also introduced as an attempt to quantify the specificity of a given PBM over the complete PDZome. Our results highlight the impact of modulatory residues and post-translational modifications on PBM interactomes and their specificity.

Deciphering the Unexpected Binding Capacity of the Third PDZ Domain of Whirlin to Various Cochlear Hair Cell Partners

Hearing is a mechanical and neurochemical process, which occurs in the hair cells of inner ear that converts the sound vibrations into electrical signals transmitted to the brain. The multi-PDZ scaffolding protein whirlin plays a critical role in the formation and function of stereocilia exposed at the surface of hair cells. In this article, we reported seven stereociliary proteins that encode PDZ binding motifs (PBM) and interact with whirlin PDZ3, where four of them are first reported. We solved the atomic resolution structures of complexes between whirlin PDZ3 and the PBMs of myosin 15a, CASK, harmonin a1 and taperin. Interestingly, the PBM of CASK and taperin are rare non-canonical PBM, which are not localized at the extreme C terminus. This large capacity to accommodate various partners could be related to the distinct functions of whirlin at different stages of the hair cell development.

The Cytomegalovirus Tegument Protein UL35 Antagonizes Pattern Recognition Receptor-Mediated Type I IFN Transcription

The rapid activation of pattern recognition receptor (PRR)-mediated type I interferon (IFN) signaling is crucial for the host response to infection. In turn, human cytomegalovirus (HCMV) must evade this potent response to establish life-long infection. Here, we reveal that the HCMV tegument protein UL35 antagonizes the activation of type I IFN transcription downstream of the DNA and RNA sensors cGAS and RIG-I, respectively. We show that ectopic expression of UL35 diminishes the type I IFN response, while infection with a recombinant HCMV lacking UL35 induces an elevated type I IFN response compared to wildtype HCMV. With a series of luciferase reporter assays and the analysis of signaling kinetics upon HCMV infection, we observed that UL35 downmodulates PRR signaling at the level of the key signaling factor TANK-binding kinase 1 (TBK1). Finally, we demonstrate that UL35 and TBK1 co-immunoprecipitate when co-expressed in HEK293T cells. In addition, we show that a previously reported cellular binding partner of UL35, O-GlcNAc transferase (OGT), post-translationally GlcNAcylates UL35, but that this modification is not required for the antagonizing effect of UL35 on PRR signaling. In summary, we have identified UL35 as the first HCMV protein to antagonize the type I IFN response at the level of TBK1, thereby enriching our understanding of how this important herpesvirus escapes host immune responses.

High-Throughput Production of a New Library of Human Single and Tandem PDZ Domains Allows Quantitative PDZ-Peptide Interaction Screening Through High-Throughput Holdup Assay

PDZ domains recognize PDZ Binding Motifs (PBMs) at the extreme C-terminus of their partner proteins. The human proteome contains 266 identified PDZ domains, the PDZome, spread over 152 proteins. We previously developed the "holdup" chromatographic assay for high-throughput determination of PDZ-PBM affinities. In that work, we had used an expression library of 241 PDZ constructs (the "PDZome V.1"). Here, we cloned, produced, and characterized a new bacterial expression library ("PDZome V.2"), which comprises all the 266 known human PDZ domains as well as 37 PDZ tandem constructs. To ensure the best expression level, folding, and solubility, all construct boundaries were redesigned using available structural data and all DNA sequences were optimized for Escherichia coli expression. Consequently, all the PDZ constructs are produced in a soluble form. Precise quantification and quality control were carried out. The binding profiles previously published using "PDZome V.1" were reproduced and completed using the novel "PDZome V.2" library. We provide here the detailed description of the high-throughput protocols followed through the PDZ gene synthesis and cloning, PDZ production, holdup assay and data treatment.

Prenatal alcohol exposure impairs autophagy in neonatal brain cortical microvessels

Brain developmental lesions are a devastating consequence of prenatal alcohol exposure (PAE). We recently showed that PAE affects cortical vascular development with major effects on angiogenesis and endothelial cell survival. The underlying molecular mechanisms of these effects remain poorly understood. This study aimed at characterizing the ethanol exposure impact on the autophagic process in brain microvessels in human fetuses with fetal alcohol syndrome (FAS) and in a PAE mouse model. Our results indicate that PAE induces an increase of autophagic vacuole number in human fetal and neonatal mouse brain cortical microvessels. Subsequently, ex vivo studies using green fluorescent protein (GFP)-LC3 mouse microvessel preparations revealed that ethanol treatment alters autophagy in endothelial cells. Primary cultures of mouse brain microvascular endothelial cells were used to characterize the underlying molecular mechanisms. LC3 and p62 protein levels were significantly increased in endothelial cells treated with 50 mM ethanol. The increase of autophagic vacuole number may be due to excessive autophagosome formation associated with the partial inhibition of the mammalian target of rapamycin pathway upon ethanol exposure. In addition, the progression from autophagosomes to autolysosomes, which was monitored using autophagic flux inhibitors and mRFP-EGFP vector, showed a decrease in the autolysosome number. Besides, a decrease in the Rab7 protein level was observed that may underlie the impairment of autophagosome-lysosome fusion. In addition, our results showed that ethanol-induced cell death is likely to be mediated by decreased mitochondrial integrity and release of apoptosis-inducing factor. Interestingly, incubation of cultured cells with rapamycin prevented ethanol effects on autophagic flux, ethanol-induced cell death and vascular plasticity. Taken together, these results are consistent with autophagy dysregulation in cortical microvessels upon ethanol exposure, which could contribute to the defects in angiogenesis observed in patients with FAS. Moreover, our results suggest that rapamycin represents a potential therapeutic strategy to reduce PAE-related brain developmental disorders.

NMDA receptor blockade in the developing cortex induces autophagy-mediated death of immature cortical GABAergic interneurons: An ex vivo and in vivo study in Gad67-GFP mice

In neonates, excitotoxicity is a major process involved in hypoxic-ischemic brain lesions, and several research groups have suggested the use of NMDA antagonists for neuroprotection. However, despite their clinical interest, there is more and more evidence suggesting that, in the immature brain, these molecules exert deleterious actions on migrating GABAergic interneurons by suppressing glutamatergic trophic inputs. Consequently, preventing the side effects of NMDA antagonists would be therapeutically useful. Because macroautophagy is involved in the adaptive response to trophic deprivation, the aim of the present study was to investigate the impact of autophagy modulators on the MK801-induced death of immature GABAergic interneurons and to characterize the crosstalk between autophagic and apoptotic mechanisms in this cell type. Ex vivo, using cortical slices from NMRI and Gad67-GFP mice, we show that blockade of the NMDA receptor results in an accumulation of autophagosomes due to the disruption of the autophagic flux. This effect precedes the activation of the mitochondrial apoptotic pathway, and the degeneration of immature GABAergic neurons present in developing cortical layers II-IV and is prevented by 3-MA, an autophagy inhibitor. In contrast, modulators of autophagy (3-MA, rapamycin) do not interfere with the anti-excitotoxic and neuroprotective effect of MK801 observed in deep layers V and VI. In vivo, 3-MA blocks the rapid increase in caspase-3 cleavage induced by the blockade of NMDA receptors and prevents the resulting long-term decrease in Gad67-GFP neurons in layers II-IV. Together, these data suggest that, in the developing cortex, the suppression of glutamatergic inputs through NMDA receptor inhibition results in the impairment of the autophagic flux and the subsequent switch to apoptotic death of immature GABAergic interneurons. The concomitant inhibition of autophagy prevents this pro-apoptotic action of the NMDA blocker and favors the long-term rescue of GABAergic interneurons without interfering with its neuroprotective actions. The use of autophagy modulators in the developing brain would create new opportunities to prevent the side effects of NMDA antagonists used for neuroprotection or anesthesia.

Neurogenesis-independent antidepressant-like effects on behavior and stress axis response of a dual orexin receptor antagonist in a rodent model of depression

Growing evidence indicates that an increase of orexin (or hypocretin) signaling is involved in the pathophysiology of major depression, but little is known regarding the causal link between the orexinergic system and depressive-like states. Here we blocked orexin receptors in mice subjected to unpredictable chronic mild stress (UCMS) to investigate putative antidepressant-like effects of this treatment, as well as the underlying mechanisms. BALB/c mice were exposed to 9 weeks of UCMS and from the third week onward treated daily with fluoxetine (20 mg/kg per day, per os) or with the dual orexin receptor antagonist almorexant (100 mg/kg per day, per os). The effects of UCMS regimen and pharmacological treatments were assessed by physical measures and behavioral testing. The dexamethasone suppression test was performed to examine the integrity of the negative feedback of the hypothalamic-pituitary-adrenal (HPA) axis, and immunohistochemical markers were used to assess cell proliferation (Ki-67), immature newborn neurons (doublecortin), and mature newborn neurons (5-bromo-2'-deoxyuridine/NeuN) in the dorsal and ventral parts of the hippocampus. Our results show that 7 weeks of fluoxetine or almorexant treatments counteract the UCMS-induced physical and behavioral alterations. Both treatments prevented the HPA axis dysregulation caused by UCMS, but only fluoxetine reversed the UCMS-induced decrease of hippocampal cell proliferation and neurogenesis, while chronic almorexant treatment decreased cell proliferation and neurogenesis specifically in the ventral hippocampus. Taken together, this is the first evidence that pharmacological blockade of the orexinergic system induces a robust antidepressant-like effect and the restoration of stress-related HPA axis defect independently from a neurogenic action.

Diagnosis of congenital toxoplasmosis at birth: what is the value of testing for IgM and IgA?

Recommendations vary on the best combination of tests to use for the diagnosis of subclinical congenital toxoplasmosis at birth. The diagnostic accuracy of IgM and IgA tests was assessed in the context of routine clinical practice on 233 newborns with congenital toxoplasmosis and 661 healthy controls. IgM/IgA sensibility and specificity were compared in cord and postnatal samples. Both tests were considerably more specific in neonatal blood (IgM: 98%; IgA: 100%) than in cordblood (IgM: 85%; IgA: 88%). Sensitivity for IgM and IgA was not significantly different in neonatal blood (61% and 60%, respectively) and cord blood (67% and 54%, respectively). Combining IgM and IgA increased the overall sensitivity to 73% without any significant loss in specificity (98%). The influence of the date of maternal infection on the sensitivity and negative predictive value was also clearly demonstrated.

CONCLUSION

Because of their relatively low cost compared to more sophisticated methods, IgM and IgA tests should remain the main method for the routine diagnosis of congenital toxoplasmosis although follow up is essential to identify the Ca. 25% of infected children who are missed at birth on the basis of these tests.

A second European collaborative study on polymerase chain reaction for Toxoplasma gondii, involving 15 teams

In order to investigate the accuracy and practicability of the polymerase chain reaction (PCR) in the antenatal diagnosis of congenital toxoplasmosis, a collaborative study involving 15 European laboratories was performed under the auspices of the Biomed 2 Programme of the European Community. Each team received 12 aliquots (four negative, eight positive) of 'artificial samples' made of amniotic fluid spiked with tachyzoites of the RH strain of Toxoplasma gondii. Each team performed its own PCR protocol (all were different). Nine of the 15 laboratories were able to detect a single parasite, but two of the 15 found all samples negative. Four of the 15 laboratories found one or more control samples to be falsely positive. This study highlights the lack of homogeneity between PCR protocols and performance and underlines the need for an external quality assurance scheme which could provide 'reference' samples that could be used by any laboratory wanting to establish and maintain an accurate diagnostic test based on PCR.

Value of cerebrospinal fluid cytochemical examination for the diagnosis of congenital toxoplasmosis at birth in France

BACKGROUND

Because of routine screening and treatment of pregnant women for Toxoplasma infection in France, most neonates born to mothers who seroconverted during pregnancy are either not infected or asymptomatic. Early diagnosis relies mainly on radiologic, ophthalmologic and biologic tests. Cerebrospinal fluid (CSF) cytochemical evaluation is one of several tests performed in parallel to increase the overall sensitivity of the diagnostic evaluation. Our goal was to assess the value of cytochemical examination and to confirm whether using a portion of available CSF for this analysis is legitimate.

METHODS

The individual performance of each of the two cytochemical tests and their combined value when used in parallel were assessed. These findings were then compared with the anti-Toxoplasma IgM and IgA serum titers and the clinical, ophthalmologic and radiologic findings at birth.

RESULTS

CSF cytochemical analysis was possible in only 52% of the 233 children in the study. Our results in 112 children indicated poor sensitivity estimates. There was no significant change in the posttest probability of infection compared with the pretest estimation of risk in cases of a negative finding. After a mean follow-up of 80 months there was no evidence that CSF cytochemistry helped predict the risk of sequelae.

CONCLUSION

In our setting cytochemical examination did not significantly contribute to the diagnosis of congenital infection at birth. Because of the limited quantity of CSF available, we suggest the use of other methods with higher yield.

[Importance of antiproteases in the treatment of microsporidia and/or cryptosporidia infections in HIV-seropositive patients]

Diarrhea due to infection with Microsporidium (M) or Cryptosporidium (C) raises significant therapeutic challenges in HIV-infected patients. The usefulness of protease inhibitor therapy was evaluated in 20 HIV-positive patients with positive tests for M and/or C. There were 17 men and three women with a mean age of 42.5 years (range, 26-64 years). Two patients had category B disease and 18 category C disease according to the 1993 CDC classification scheme (CD4 count before therapy, 72/mm3; mean viral burden, 4.6 log). Seventeen patients had chronic diarrhea (due to M in 12 cases and to C in five), and the remaining three patients were asymptomatic M carriers. Clinical symptoms resolved after addition to the antiretroviral regimen of indinavir (n = 17) or saquinavir (n = 3). Mean weight gain was 10.5 kg. Karnofsky's index improved. Twelve patients, including one of the three who were asymptomatic at baseline, had negative follow-up stool cultures. The mean CD4 count increase was 125/mm3, and the mean viral burden decrease was 1.285 log. These data suggest that protease inhibitors may be capable of eradicating M and/or C infection refractory to other treatments. The reason for this effect may involve partial restoration of immune function due to inhibition of HIV replication.

Identification of Encephalitozoon intestinalis in travelers with chronic diarrhea by specific PCR amplification

With the use of Weber's modified trichrome and Uvitex 2B techniques, spores of microsporidia were detected in the stools of four travelers presenting clinically with chronic diarrhea. The general health of these patients was not impaired, and human immunodeficiency virus screening was negative. Immune evaluation, including the study of lymphocytic subpopulations, assay of serum immunoglobulins, and an intradermal multitest, showed normal results. Molecular identification of microsporidian species was based on the PCR amplification of a small-subunit rRNA sequence followed by HinfI endonuclease restriction. Encephalitozoon intestinalis microsporidiosis was thus shown in two of the four patients examined. In two patients, therapy based on albendazole made stools devoid of microsporidian spores without influence on the intestinal disorders. The pathogenic role of E. intestinalis in immunocompetent individuals remains to be demonstrated.

[HBV-DNA assay by hybridization in solution. Value of low levels measured with the Abbott-Genostics device]

Quantitation of HBV-DNA is the most precise test for measuring viral replication. A commercial liquid phase hybridation test (Abbott) is now commonly used for diagnosis and monitoring of chronic hepatitis B. Interpretation of weak positive results obtained with this test are often difficult. Fifty-four sera with a concentration lower than 12 pg/ml with the Abbott HBV-DNA assay were tested with another commercial hybridation assay (Digene-Murex) and with an in-house PCR test. PCR is positive in 24 sera among the 35 HBs antigen positive sera, but is always negative in HBs Antigene negative sera. All the HBe Antigen positive sera were positive with the PCR test. A positive result was obtained with the Digene test in only 14 sera, 13 of them were confirmed by PCR. Ten sera among the remaining 11 PCR positive sera had a low HBV-DNA concentration but under the Digene cut-off level (10 pg/ml). The sensitivity could be greatly enforced with a lower cut-off level without any lack of specificity. The PCR test remains very helpful for sera with low concentration of HBV-DNA.