Daniel Gonzalez-Dunia

Anaplastic Lymphoma Kinase Is a Dependence Receptor Whose Proapoptotic Functions Are Activated by Caspase Cleavage

ABSTRACT Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase, initially discovered as part of the NPM-ALK fusion protein, resulting from the t(2;5) translocation that is frequently associated with anaplastic large-cell lymphomas. The native ALK protein is normally expressed in the developing and, at a weaker level, adult nervous system. We recently demonstrated that the oncogenic, constitutively kinase-activated NPM-ALK protein was antiapoptotic when expressed in Jurkat lymphoblastic cells treated with cytotoxic drugs. In contrast, we now show that Jurkat cells overexpressing the wild-type ALK receptor are more sensitive to doxorubicin-induced apoptosis than parental cells. Moreover, the ALK protein is cleaved during apoptosis in a caspase-dependent manner. Mutation of aspartic residues to asparagine allowed us to map the caspase cleavage site in the juxtamembrane region of ALK. In order to assess the role of ALK in neural cell-derived tissue, we transiently expressed ALK in the 13.S.1.24 rat neuroblast immortalized cell line. ALK expression led to apoptotic cell death of the neuroblasts. ALK ligation by specific activating antibodies decreased ALK-facilitated apoptosis in both lymphoid and neuronal cell lines. Moreover, ALK transfection reduced the survival of primary cultures of cortical neurons. Thus, ALK has a proapoptotic activity in the absence of ligand, whereas it is antiapoptotic in the presence of its ligand and when the kinase is intrinsically activated. These properties place ALK in the growing family of dependence receptors.

Pertussis Toxin Reduces the Number of Splenic Foxp3+ Regulatory T Cells

Pertussis toxin (PTx) is a bacterial toxin used to enhance the severity of experimental autoimmune diseases such as experimental autoimmune encephalomyelitis. It is known to promote permeabilization of the blood-brain barrier, maturation of APC, activation of autoreactive lymphocytes and alteration of lymphocyte migration. In this study, we show that i.v. injection of PTx in mice induces a decrease in the number of splenic CD4+CD25+ regulatory T cells (Treg cells). Furthermore, PTx not only induces a depletion of the dominant CD4+CD25+Foxp3+ subpopulation of splenic Treg cells, but also reduces to a similar extent the CD4+CD25−Foxp3+ subpopulation. On a per cell basis, the suppressive properties of the remaining Treg cells are not modified by PTx treatment. The reduction in splenic Treg cells is associated with preferential migration of these cells to the liver. Additionally, Treg cells exhibit a high sensitivity to PTx-mediated apoptosis in vitro. Finally, in vivo depletion of Treg cells by injection of an anti-CD25 Ab, and PTx treatment, present synergistic experimental autoimmune encephalomyelitis exacerbating effects. Therefore, we identify a new effect of PTx and provide an additional illustration of the influence of microbial components on the immune system affecting the balance between tolerance, inflammation and autoimmunity.

Neurons as targets for T cells in the nervous system

Accumulating evidence shows that T cells penetrate the central nervous system (CNS) parenchyma in several autoimmune, infectious, and degenerative neurological diseases. The structural and functional consequences for CNS neurons of their encounter with activated T cells have been investigated in several experimental systems, including ex vivo co-cultures, electrophysiology, and in vivo imaging. Here, we review the modalities of neuron/T cell interactions. We substantiate the contention that T cells are directly responsible for neuronal damage in a large number of neurological diseases and discuss mechanisms of neuronal damage mediated by distinct T cell subsets, the impact of which differs depending on the disease. Finally, we describe how a better understanding of the mechanisms at play offers new possibilities for therapeutic intervention.

Borna disease virus blocks potentiation of presynaptic activity through inhibition of protein kinase C signaling.

Infection by Borna disease virus (BDV) enables the study of the molecular mechanisms whereby a virus can persist in the central nervous system and lead to altered brain function in the absence of overt cytolysis and inflammation. This neurotropic virus infects a wide variety of vertebrates and causes behavioral diseases. The basis of BDV-induced behavioral impairment remains largely unknown. Here, we investigated whether BDV infection of neurons affected synaptic activity, by studying the rate of synaptic vesicle (SV) recycling, a good indicator of synaptic activity. Vesicular cycling was visualized in cultured hippocampal neurons synapses, using an assay based on the uptake of an antibody directed against the luminal domain of synaptotagmin I. BDV infection did not affect elementary presynaptic functioning, such as spontaneous or depolarization-induced vesicular cycling. In contrast, infection of neurons with BDV specifically blocked the enhancement of SV recycling that is observed in response to stimuli-induced synaptic potentiation, suggesting defects in long-term potentiation. Studies of signaling pathways involved in synaptic potentiation revealed that this blockade was due to a reduction of the phosphorylation by protein kinase C (PKC) of proteins that regulate SV recycling, such as myristoylated alanine-rich C kinase substrate (MARCKS) and Munc18–1/nSec1. Moreover, BDV interference with PKC-dependent phosphorylation was identified downstream of PKC activation. We also provide evidence suggesting that the BDV phosphoprotein interferes with PKC-dependent phosphorylation. Altogether, our results reveal a new mechanism by which a virus can cause synaptic dysfunction and contribute to neurobehavioral disorders.

Functional and Genetic Analysis of Two CD8 T Cell Subsets Defined by the Level of CD45RC Expression in the Rat

Differential cytokine production by T cells plays an important role in the outcome of the immune response. We show that the level of CD45RC expression differentiates rat CD8 T cells in two subpopulations, CD45RChigh and CD45RClow, that have different cytokine profiles and functions. Upon in vitro stimulation, in an Ag-presenting cell-independent system, CD45RChigh CD8 T cells produce IL-2 and IFN-γ while CD45RClow CD8 T cells produce IL-4, IL-10, and IL-13. In vitro, these subsets also exhibit different cytotoxic and suppressive functions. The CD45RChigh/CD45RClow CD8 T cell ratio was determined in Lewis (LEW) and Brown-Norway (BN) rats. These two rat strains differ with respect to the Th1/Th2 polarization of their immune responses and to their susceptibility to develop distinct immune diseases. The CD45RChigh/CD45RClow CD8 T cell ratio is higher in LEW than in BN rats, and this difference is dependent on hemopoietic cells. Linkage analysis in a F2(LEW × BN) intercross identified two quantitative trait loci on chromosomes 9 and 20 controlling the CD45RChigh/CD45RClow CD8 T cell ratio. This genetic control was confirmed in congenic rats. The region on chromosome 9 was narrowed down to a 1.2-cM interval that was found to also control the IgE response in a model of Th2-mediated disorder. Identification of genes that control the CD45RChigh/CD45RClow CD8 T cell subsets in these regions could be of great interest for the understanding of the pathophysiology of immune-mediated diseases.

A viral peptide that targets mitochondria protects against neuronal degeneration in models of Parkinson’s disease

Mitochondrial dysfunction is a common feature of many neurodegenerative disorders, notably Parkinsons disease. Consequently, agents that protect mitochondria have strong therapeutic potential. Here, we sought to divert the natural strategy used by Borna disease virus (BDV) to replicate in neurons without causing cell death. We show that the BDV X protein has strong axoprotective properties, thereby protecting neurons from degeneration both in tissue culture and in an animal model of Parkinsons disease, even when expressed alone outside of the viral context. We also show that intranasal administration of a cell-permeable peptide derived from the X protein is neuroprotective. We establish that both the X protein and the X-derived peptide act by buffering mitochondrial damage and inducing enhanced mitochondrial filamentation. Our results open the way to novel therapies for neurodegenerative diseases by targeting mitochondrial dynamics and thus preventing the earliest steps of neurodegenerative processes in axons.

High reproducibility of two-dimensional liquid chromatography using pH-driven fractionation with a pressure-resistant electrode

Automated two-dimensional liquid chromatography using the PF2D system from Beckman Coulter provides a fractionation platform well suited for differential proteomic studies. To date, the reliability and reproducibility of PF2D has not been accurately tested. Here, we used an optimized software and a pressure-resistant pH electrode, allowing a precise and reproducible control of the pH limits for each fraction during PF2D. We tested the reliability of this improved system by performing several rounds of fractionation using the same protein extract. Three UV maps were generated, leading to 54 chromatograms and more than 3000 protein peaks. Using semi-automated software for peak-to-peak comparison between 2D-LC chromatograms, we demonstrate that the peak concordance is very high. The rates of concordance were higher in the second dimension repeatability tests, indicating that the limiting factors for 2D-LC reproducibility rely on the pI fractionation and sample preparation steps. The reproducibility between maps was closely related to pH curves similarities, further stressing the need of careful pH adjustment and precise electrode calibration.

Manipulation of the N-terminal sequence of the Borna disease virus X protein improves its mitochondrial targeting and neuroprotective potential

To favor their replication, viruses express proteins that target diverse mammalian cellular pathways. Due to the limited size of many viral genomes, such proteins are endowed with multiple functions, which require targeting to different subcellular compartments. One salient example is the X protein of Borna disease virus, which is expressed both at the mitochondria and in the nucleus. Moreover, we recently demonstrated that mitochondrial X protein is neuroprotective. In this study, we sought to examine the mechanisms whereby the X protein transits between subcellular compartments and to define its localization signals, to enhance its mitochondrial accumulation and thus, potentially, its neuroprotective activity. We transfected plasmids expressing fusion proteins bearing different domains of X fused to enhanced green fluorescent protein (eGFP) and compared their subcellular localization to that of eGFP. We observed that the 5–16 domain of X was responsible for both nuclear export and mitochondrial targeting and identified critical residues for mitochondrial localization. We next took advantage of these findings and constructed mutant X proteins that were targeted only to the mitochondria. Such mutants exhibited enhanced neuroprotective properties in compartmented cultures of neurons grown in microfluidic chambers, thereby confirming the parallel between mitochondrial accumulation of the X protein and its neuroprotective potential.—Ferré C. A., Davezac, N., Thouard, A., Peyrin, J. M., Belenguer, P., Miquel, M.‐C., Gonzalez‐Dunia, D., Szelechowski, M. Manipulation of the N‐terminal sequence of the Borna disease virus X protein improves its mitochondrial targeting and neuroprotective potential. FASEB J. 30, 1523–1533 (2016). www.fasebj.org

Production and purification of non replicative canine adenovirus type 2 derived vectors.

Adenovirus (Ad) derived vectors have been widely used for short or long-term gene transfer, both for gene therapy and vaccine applications. Because of the frequent pre-existing immunity against the classically used human adenovirus type 5, canine adenovirus type 2 (CAV2) has been proposed as an alternative vector for human gene transfer. The well-characterized biology of CAV2, together with its ease of genetic manipulation, offer major advantages, notably for gene transfer into the central nervous system, or for inducing a wide range of protective immune responses, from humoral to cellular immunity. Nowadays, CAV2 represents one of the most appealing nonhuman adenovirus for use as a vaccine vector. This protocol describes a simple method to construct, produce and titer recombinant CAV2 vectors. After cloning the expression cassette of the gene of interest into a shuttle plasmid, the recombinant genomic plasmid is obtained by homologous recombination in the E. coli BJ5183 bacterial strain. The resulting genomic plasmid is then transfected into canine kidney cells expressing the complementing CAV2-E1 genes (DK-E1). A viral amplification enables the production of a large viral stock, which is purified by ultracentrifugation through cesium chloride gradients and desalted by dialysis. The resulting viral suspension routinely has a titer of over 10(10) infectious particles per ml and can be directly administrated in vivo.

Borna disease virus phosphoprotein impairs the developmental program controlling neurogenesis and reduces human GABAergic neurogenesis.

It is well established that persistent viral infection may impair cellular function of specialized cells without overt damage. This concept, when applied to neurotropic viruses, may help to understand certain neurologic and neuropsychiatric diseases. Borna disease virus (BDV) is an excellent example of a persistent virus that targets the brain, impairs neural functions without cell lysis, and ultimately results in neurobehavioral disturbances. Recently, we have shown that BDV infects human neural progenitor cells (hNPCs) and impairs neurogenesis, revealing a new mechanism by which BDV may interfere with brain function. Here, we sought to identify the viral proteins and molecular pathways that are involved. Using lentiviral vectors for expression of the bdv-p and bdv-x viral genes, we demonstrate that the phosphoprotein P, but not the X protein, diminishes human neurogenesis and, more particularly, GABAergic neurogenesis. We further reveal a decrease in pro-neuronal factors known to be involved in neuronal differentiation (ApoE, Noggin, TH and Scg10/Stathmin2), demonstrating that cellular dysfunction is associated with impairment of specific components of the molecular program that controls neurogenesis. Our findings thus provide the first evidence that a viral protein impairs GABAergic human neurogenesis, a process that is dysregulated in several neuropsychiatric disorders. They improve our understanding of the mechanisms by which a persistent virus may interfere with brain development and function in the adult.