A Peptide Targeting Inflammatory CNS Lesions in the EAE Rat Model of Multiple Sclerosis

Multiple sclerosis is characterized by inflammatory lesions dispersed throughout the central nervous system (CNS) leading to severe neurological handicap. Demyelination, axonal damage, and blood brain barrier alterations are hallmarks of this pathology, whose precise processes are not fully understood. In the experimental autoimmune encephalomyelitis (EAE) rat model that mimics many features of human multiple sclerosis, the phage display strategy was applied to select peptide ligands targeting inflammatory sites in CNS. Due to the large diversity of sequences after phage display selection, a bioinformatics procedure called "PepTeam" designed to identify peptides mimicking naturally occurring proteins was used, with the goal to predict peptides that were not background noise. We identified a circular peptide CLSTASNSC called "Ph48" as an efficient binder of inflammatory regions of EAE CNS sections including small inflammatory lesions of both white and gray matter. Tested on human brain endothelial cells hCMEC/D3, Ph48 was able to bind efficiently when these cells were activated with IL1β to mimic inflammatory conditions. The peptide is therefore a candidate for further analyses of the molecular alterations in inflammatory lesions.

Role of host cell traversal by the malaria sporozoite during liver infection

Malaria sporozoites cross the liver sinusoidal barrier, target Kupffer cells and endothelial cells with cell traversal inhibiting sporozoite clearance.

Malaria infection starts when the sporozoite stage of the Plasmodium parasite is injected into the skin by a mosquito. Sporozoites are known to traverse host cells before finally invading a hepatocyte and multiplying into erythrocyte-infecting forms, but how sporozoites reach hepatocytes in the liver and the role of host cell traversal (CT) remain unclear. We report the first quantitative imaging study of sporozoite liver infection in rodents. We show that sporozoites can cross the liver sinusoidal barrier by multiple mechanisms, targeting Kupffer cells (KC) or endothelial cells and associated or not with the parasite CT activity. We also show that the primary role of CT is to inhibit sporozoite clearance by KC during locomotion inside the sinusoid lumen, before crossing the barrier. By being involved in multiple steps of the sporozoite journey from the skin to the final hepatocyte, the parasite proteins mediating host CT emerge as ideal antibody targets for vaccination against the parasite.

Origins and unconventional behavior of neutrophils in developing zebrafish

The first leukocytes that arise in the development of vertebrate embryos are the primitive macrophages, which differentiate in the yolk sac and then quickly invade embryonic tissues. These macrophages have been considered to constitute a separate lineage, giving rise to no other cell type. Using an in vivo photoactivatable cell tracer in the transparent zebrafish (Danio rerio) embryo, we demonstrated that this lineage also gave rise to an equal or higher number of neutrophilic granulocytes. We were surprised to find that the differentiation of these primitive neutrophils occurs only after primitive myeloid progenitors have dispersed in the tissues. By 2 days after fertilization, these neutrophils have become the major leukocyte type found wandering in the epidermis and mesenchyme. Like the primitive macrophages, all primitive and larval neutrophils express PU.1 and L-plastin and they are highly attracted to local infections, yet only a small fraction of them phagocytose microbes, and to a much lesser extent per cell than the macrophages. They are also attracted to variously stressed or malformed tissues, suggesting a wider role than antimicrobial defense.

Chemokine transport across human vascular endothelial cells

Leukocyte migration across vascular endothelium is mediated by chemokines that are either synthesized by the endothelium or transferred across the endothelium from the tissue. The mechanism of transfer of two chemokines, CXCL10 (interferon gamma-inducible protein [IP]-10) and CCL2 (macrophage chemotactic protein [MCP]-1), was compared across dermal and lung microvessel endothelium and saphenous vein endothelium. The rate of transfer depended on both the type of endothelium and the chemokine. The permeability coefficient (Pe) for CCL2 movement across saphenous vein was twice the value for dermal endothelium and four times that for lung endothelium. In contrast, the Pe value for CXCL10 was lower for saphenous vein endothelium than the other endothelia. The differences in transfer rate between endothelia was not related to variation in paracellular permeability using a paracellular tracer, inulin, and immunoelectron microscopy showed that CXCL10 was transferred from the basal membrane in a vesicular compartment, before distribution to the apical membrane. Although all three endothelia expressed high levels of the receptor for CXCL10 (CXCR3), the transfer was not readily saturable and did not appear to be receptor dependent. After 30 min, the chemokine started to be reinternalized from the apical membrane in clathrin-coated vesicles. The data suggest a model for chemokine transcytosis, with a separate pathway for clearance of the apical surface.

Tracing Hematopoietic Precursor Migration to Successive Hematopoietic Organs during Zebrafish Development

Although the ontogeny of hematopoietic stem cells (HSCs) in vertebrates has been studied intensely, a lineage relationship between the HSCs found in the developmentally successive hematopoietic organs remains to be shown. By using an in situ photoactivatable cell tracer in the transparent zebrafish embryo, we demonstrated that definitive blood precursors appeared between the dorsal aorta and axial vein, validating the homology of this tissue with the AGM (aorta-gonad-mesonephros) of amniotes. These cells first migrated through the blood to a previously undescribed caudal hematopoietic tissue (CHT), where they differentiated, expanded, and further migrated to seed the definitive hematopoietic organs, the thymus and kidney. Immigrants on the way to the thymus expressed c-myb and ikaros but not rag1; they were probably no longer HSCs, however, because they lacked scl and runx1 expression, unlike immigrants to the kidney. The CHT thus has a hematopoietic function similar to that of the mammalian fetal liver.

Histopathological and cognitive defects induced by Nef in the brain

Complex mechanisms of human immunodeficiency virus type-1 (HIV-1) brain pathogenesis suggest the contribution of individual HIV-1 gene products. Among them, the Nef protein has been reported to harbor a major determinant of pathogenicity in AIDS-like disease. The goal of the present study was to determine whether Nef protein expressed in vivo by primary macrophages could induce a brain toxicity also affecting the behavior of the rat. To achieve this goal we grafted Nef-transduced macrophages into the rat hippocampus. Two months post-transplantation, we observed that Nef induces monocyte/macrophage recruitment, expression of TNF-alpha, and astrogliosis. No apoptotic event was detected. We further demonstrated that Nef neurotoxicity is associated with cognitive deficits.

Capsule structure changes associated with Cryptococcus neoformans crossing of the blood-brain barrier

Cryptococcus neoformans is a yeast responsible for disseminated meningoencephalitis in patients with cellular immune defects. The major virulence factor is the polysaccharide capsule. We took advantage of a relevant murine model of disseminated meningoencephalitis to study the early events associated with blood-brain barrier (BBB) crossing. Mice were sacrificed at 1, 6, 24, and 48 hours post-intravenous inoculation, and classical histology, electron microscopy, and double immunofluorescence were used to study tissues and yeasts. Crossing of the BBB occurred early after inoculation, did not involve the choroid plexus but instead occurred at the level of the cortical capillaries, and caused early and severe damage to the structure of the microvessels. Seeding of the leptomeninges was not the primary event but occurred secondary to leakage of cortical pseudocysts. Organ invasion was associated with changes in cryptococcal capsule structure and cell size, which differed in terms of magnitude and kinetics, depending on both the organs involved, and potentially, on the bed structure of the local capillary. The rapid changes in capsule structure could contribute to inability of the host immune response to control cryptococcal infection in extrapulmonary spaces.

Chemokines, chemokine receptors and adhesion molecules on different human endothelia: discriminating the tissue-specific functions that affect leucocyte migration

The selective accumulation of different leucocyte populations during inflammation is regulated by adhesion molecules and chemokines expressed by vascular endothelium. This study examined how chemokine production and the expression of adhesion molecules and chemokine receptors vary between endothelia from different vascular beds. Human saphenous vein endothelium was compared with lung and dermal microvascular endothelia and with umbilical vein endothelium and a bone-marrow endothelial cell line. All endothelia produced CCL2 and CXCL8 constitutively, whereas CXCL10 and CCL5 were only secreted after tumour necrosis factor (TNF)-alpha or interferon (IFN)-gamma stimulation. In combination with TNF-alpha, IFN-gamma suppressed CXCL8 but enhanced CCL5 and CXCL10, whereas transforming growth factor (TGF)-beta reduced secretion of all chemokines. Basal chemokine secretion was higher from umbilical vein than other endothelial cells. Chemokine receptors, CXCR1, CXCR3 and CCR3, were present on all endothelia but highest on saphenous vein. CCR4, CCR5, CCR6, CXCR2, CXCR4 and CXCR5 were also detected at variable levels on different endothelia. The variation between endothelia in chemokine secretion was much greater than the variations in adhesion molecules, both on resting cells and following cytokine stimulation. These results indicate that it is the tissue-specific variations in endothelial chemokine secretion rather than variations in adhesion molecules that can explain the different patterns of inflammation and leucocyte traffic seen in non-lymphoid tissues.

Human T-cell lymphotropic virus oncoprotein Tax represses TGF-beta 1 signaling in human T cells via c-Jun activation: a potential mechanism of HTLV-I leukemogenesis

Human T-cell leukemia virus I is the etiologic agent of adult T-cell leukemia (ATL), an aggressive T-cell malignancy. The viral oncoprotein Tax, through the activation of nuclear factorkappaB (NF-kappaB), CCAAT-enhancer binding protein (CREB), and activated protein-1 (AP-1) pathways, is a transcriptional regulator of critical genes for T-cell homeostasis. In ATL cells, activated AP-1 complexes induce the production of transforming growth factor beta1 (TGF-beta1). TGF-beta1 is an inhibitor of T-cell proliferation and cytotoxicity. Here we show that, in contrast to normal peripheral T cells, ATL cells are resistant to TGF-beta1-induced growth inhibition. The retroviral transduction of the Tax protein in peripheral T cells resulted in the loss of TGF-beta1 sensitivity. Transient transfection of Tax in HepG2 cells specifically inhibited Smad/TGF-beta1 signaling in a dose-dependent manner. In the presence of Tax transfection, increasing amounts of Smad3 restored TGF-beta1 signaling. Tax mutants unable to activate NF-kappaB or CREB pathways were also able to repress Smad3 transcriptional activity. Next we have demonstrated that Tax inhibits TGF-beta1 signaling by reducing the Smad3 DNA binding activity. However, Tax did not decrease the expression and the nuclear translocation of Smad3 nor did it interact physically with Smad3. Rather, Tax induced c-Jun N-terminal kinase (JNK) activity and c-Jun phosphorylation, leading to the formation of Smad3/c-Jun complexes. Whereas c-Jun alone abrogates Smad3 DNA binding, cotransfection of Tax and of a dominant-negative form of JNK or a c-Jun antisense-restored Smad3 DNA binding activity and TGF-beta1 responsiveness. In ATL and in normal T cells transduced by Tax, c-Jun was constitutively phosphorylated. Thus, we describe a new function of Tax, as a repressor of TGF-beta1 signaling through JNK/c-Jun constitutive activation, which may play a critical role in ATL leukemogenesis.

Zinc-induced inhibition of protein synthesis and reduction of connexin-43 expression and intercellular communication in mouse cortical astrocytes

Zinc released from a subpopulation of glutamatergic synapses, mainly localized in the cerebral cortex and the hippocampus, facilitates or reduces glutamatergic transmission by acting on neuronal AMPA and NMDA receptors, respectively. However, neurons are not the only targets of zinc. In the present study, we provide evidence that zinc inhibits protein synthesis in cultured astrocytes from the cerebral cortex of embryonic mice. This inhibition, which reached 85% in the presence of 100 micro m zinc, was partially and slowly reversible and resulted from the successive inhibition of the elongation and the initiation steps of the protein translation process. This was assessed by measuring the phosphorylation level of the elongation factor eEF-2 and of the alpha subunit of the initiation factor eIF-2. Due to the rapid turnover of connexin-43 that forms junction channels in cultured astrocytes, the zinc-induced decrease of protein synthesis led to a partial disappearance of connexin-43, which was associated with an inhibition of the cellular coupling in the astrocytic syncitium. In conclusion, zinc not only inhibits protein synthesis in neurons, as previously demonstrated, but also in astrocytes. The resulting decrease in the intercellular communication between astrocytes should alter the function of surrounding neurons as well as their survival.

Efficient transfer of HTLV-1 tax gene in various primary and immortalized cells using a flap lentiviral vector

Human T cell leukemia virus type 1 (HTLV-1) causes two major diseases: adult T-cell leukemia-lymphoma and tropical spastic paraparesis/HTLV-1 associated myelopathy (TSP/HAM). In order to understand the involvement of Tax protein in HTLV-1 pathogenesis, we constructed a HIV-1 based lentiviral vector containing the central DNA flap sequence and either the green fluorescent protein (GFP) or the HTLV-1 tax genes. Using these vectors, GFP and tax genes were introduced in several primary and immortalized cells of endothelial, lymphoid, astrocytic or macrophagic origin. As assessed by GFP expression, up to 100% efficiency of transduction was obtained for all cell types tested. Tax expression was detected by Western blot and immuno-fluorescence in the transduced cells. After transduction, the Tax transcriptional activity was confirmed by the transactivation of HTLV-1 LTR-lacZ or HTLV-1 LTR-GFP reporter genes. Increased CD25 and HLA DR expression was observed in human peripheral blood lymphocytes transduced with the Tax vector. These results indicate that both pathways of Tax transactivation, CREB (viral LTR) and NF-kappa B (CD25 and HLA DR), are functional after transduction by TRIP Tax vector. Therefore, this vector provides a useful tool for investigating the role of the Tax viral protein in the pathogenesis of diseases linked to HTLV-1 infection.

In vivo neuronal tracing with GFP-TTC gene delivery

The retrograde transport and transynaptic transfer properties of the nontoxic tetanus toxin C-fragment (TTC) can be used to visualize specific neural pathways or to deliver biomolecules in the central nervous system (CNS). Here we tested different delivery techniques to explore the potential use of a new GFP-TTC fusion construct for use as a genetic tracer in vivo. Plasmids encoding GFP-TTC were targeted to brain regions using intracerebral grafted transfected cells or adenoviral transduction. Transport was monitored using GFP fluorescence. We show that following GFP-TTC synthesis in grafted transfected cells, the TTC fragment alone, with no signal peptide, is necessary and sufficient to provide secretion and uptake of the fusion protein into neighboring neurons around the injection site. Using an adenoviral vector to express the fusion protein into brain neurons, we show that transduced neurons can deliver the fusion protein specifically into connected neurons, demonstrating that synaptic transfer in the CNS can be visualized with GFP-TTC.

Brain engraftment of autologous macrophages transduced with a lentiviral flap vector: an approach to complement brain dysfunctions

Transplantation of ex vivo gene-corrected autologous cells represents an attractive therapeutic approach for brain diseases. Among the cells of the central nervous system, brain macrophages are promising candidates due to their role in tissue homeostasis and their implication in several neurological diseases. Up to now, gene transfer into macrophages has proven difficult by most currently available gene delivery methods. We describe herein, an efficient transduction of rat bone marrow-derived and brain macrophages with an HIV-1-derived vector containing a central DNA flap and encoding the GFP reporter gene (TRIP-DeltaU3-GFP). In primary cultures of macrophages our results show that more than 90% of the cells were transduced by the TRIP vector and that GFP expression remained stable for 1 month without cytopathic effect. In vivo, transplants of transduced macrophages into the striatum of adult rats exhibited long-term expression of GFP up to 3 months. Transduced macrophages were observed around the brain injection site and exhibited the brain macrophage/microglia phenotype. There was no significant sign of astrogliosis around the graft. These results confirm the potential of lentiviral vectors for efficient and stable ex vivo transduction of macrophages. Moreover, transduced autologous macrophages appear as a valuable vehicle for long-term and localized gene expression into the brain.

Expression and detection of macrophage-tropic HIV-1 gp120 in the brain using conformation-dependent antibodies

HIV-1 envelope proteins gp120 and gp41 are likely to play a role in the pathogenesis of HIV-associated neurocognitive disorders. While detection of gp120 in HIV-infected cell cultures is easy, it has not yet been possible to identify gp120 in human or animal brains in situ. The difficulty in detecting gp120 could be due to low expression levels of the protein, to the shedding of gp120 from infected macrophages/microglia, or to the use of inappropriate gp-specific antibodies. We addressed these questions by analyzing the subcellular localization, oligomeric structure, and shedding behavior of gp120 from a macrophage-tropic, CCR5-dependent primary isolate, BX08, expressed by a Semliki Forest virus replicon (SFVenvBX08) in vitro. We used the same SFV system injected in vivo into the rat brain in an attempt to detect gp120 in situ. Our results show that gp120/41 is expressed as monomers, dimers, and trimers in cell culture. Immunocytochemical analysis revealed that intracytoplasmic gp120 can be recognized by an anti-V3 antibody, whereas gp120 at the plasma membrane is detected exclusively by a conformation-dependent antibody. In the rat brain, the SFV vector allows gene expression in neurons from day 3 to day 9 after injection without any apparent brain damage nor reactive astrogliosis. In SFVenvBX08-infected neurons only conformation-dependent antibodies allowed gp120 labeling. These results suggest that previous difficulties in detecting gp120 in brain tissues may be due to the use of antibodies which were unable to recognize gp120 at the plasma membrane.

Multifactorial drug-resistance phenomenon in acute leukemias: impact of P170-MDR1, LRP56 protein, glutathione-transferases and metallothionein systems on clinical outcome

The multidrug resistance phenomenon can be observed in cases which do not express the P170 protein and these cases are suspected as having activated different resistance phenomena. Four phenomena were studied at the time of diagnosis in a series of 35 lymphoblastic and 25 myeloblastic acute (de novo) leukemias, by an immunocytochemical method. Two energetic drug transport processes were investigated: the classical MDR/P170 and the P110/LRP56 proteins, and two physiological detoxifying activities such as the glutathione transferases (GST alpha, mu, pi) and the metallothioneins (Mts). The results demonstrate that these phenomena are independent but their synergic activity can increase their impact on the outcome. P110/LRP56 positive cases demonstrated 48.8% complete remission (CR) rate compared to 71.4% for negative tests. When P170 and P110 were both positive or negative, the CR rates were 27.3% and 81.8% respectively (p = 0.0120), and survival curves were also different (p = 0.030). The CR rate in AML or ALL is weakly affected by GST pi, alpha or mu but relapses are more frequently observed for Positive-GST pi ALL (p = 0.0658). Patients with both P170 and GST pi positive reactions had a 53.3% CR rate compared to 78.9% for both negative reactions. Survival curves for these two groups were different. The CR rate in AMl was 100% for Mts positive and 43.7% for negative cases (p = 0.050), however the median survival was totally different for these two groups (p = 0.046). CR rates were 26.6% for patients who were P170 positive and Mts negative compared to 100% for P170 negative and Mts positive (p = 0.038) patients. Survival curves were also different (p = 0.0510). We conclude that these four mechanisms induce an independent drug resistance but their synergic action increase their impact on the outcome. The metallothioneins seem to have a major impact on the drug resistance phenomenon and its effect should be investigated with high priority, in the light of these results.

P-glycoprotein (P-170) and CD34 expression in adult acute myeloid leukemia (AML)

We investigated the prognosis value of CD34 and P-170 expression in blast cells of adult patients affected by de novo acute myeloid leukemia (AML). CD34 antigen was analyzed by indirect immunofluorescence (IFI) and alkaline phosphatase-labeled streptavidin biotine (AP-LSAB) in 62 patients (median age: 51 years). P-170 expression was determined by AP-LSAB in 51 cases using JSB1 and C219 monoclonal antibodies. All patients were treated with conventional chemotherapy induction regimen. Follow-up was from 6 to 79 months. Complete remission (CR) rate was not statistically different between CD34+ and CD34- patients (67 vs. 84%, p = 0.2). The duration of CR and survival were not influenced by CD34 expression. Karyotype abnormalities were more frequent among MDR+ patients (65 vs. 21%, p < 0.01). CR rate was statistically lower in MDR+ patients as compared to MDR- patients (63 vs. 96%, p = 0.01). Median disease-free survival (DFS) was shorter for MDR+ patients but the difference was not significant (5 vs. 10 months, p = 0.09). Patients who were positive for both parameters CD34 and P-170, had a poor prognosis with a 50 vs. 100% CR rate for CD34/P-170 negative patients, (p = 0.002), a lower median DFS (3 vs. 12 months, p = 0.01) and overall survival (OS) (3 vs. 14.5 months, p = 0.01). Results of cytogenetic analysis did not influence CR rate but the relapse rate was higher, although not significant, for the patients with unfavorable karyotype (63 vs. 33%). The seven CD34+/MDR+ patients with poor prognosis karyotype had a statistically lower CR rate, median DFS and OS than the 7 CD34-/MDR- patients with normal or favorable karyotype (CR: 29% vs. 100%, p = 0.02), (DFS: 3 vs. > 12 months, p = 0.01), (OS: 4 vs. > 12 months, p = 0.02). Our data indicate that P-170 but not CD34 expression is predictive for a lower CR rate. The identification of a bad prognosis subgroup of CD34+/MDR+ AML patients (and especially those with poor prognosis karyotype) has to be confirmed on larger series using uniform methodology.