Tam Thanh Quach

Novel Human Transitional B Cell Populations Revealed by B Cell Depletion Therapy

Transitional cells represent a crucial step in the differentiation and selection of the mature B cell compartment. Human transitional B cells have previously been variably identified based on the high level of expression of CD10, CD24, and CD38 relative to mature B cell populations and are expanded in the peripheral blood following rituximab-induced B cell-depletion at reconstitution. In this study, we take advantage of the gradual acquisition of the ABCB1 transporter during B cell maturation to delineate refined subsets of transitional B cells, including a late transitional B cell subset with a phenotype intermediate between T2 and mature naive. This late transitional subset appears temporally following the T1 and T2 populations in the peripheral compartment after rituximab-induced B cell reconstitution (and is thus termed T3) and is more abundant in normal peripheral blood than T1 and T2 cells. The identity of this subset as a developmental intermediate between early transitional and mature naive B cells was further supported by its ability to differentiate to naive during in vitro culture. Later transitional B cells, including T2 and T3, are found at comparatively increased frequencies in cord blood and spleen but were relatively rare in bone marrow. Additional studies demonstrate that transitional B cells mature across a developmental continuum with gradual up-regulation of mature markers, concomitant loss of immature markers, and increased responsiveness to BCR cross-linking in terms of proliferation, calcium flux, and survival. The characterization of multiple transitional B cell subpopulations provides important insights into human B cell development.

Actions of betahistine at histamine receptors in the brain

The actions of betahistine (N alpha-methyl-2-pyridylethylamine) on brain histamine receptors were investigated in a series of biological models. [3H]Mepyramine binding to H1-receptors in membranes from guinea-pig cerebellum was inhibited by betahistine with a Ki value of 31 microM. The binding of [3H]mepyramine in brain of the living mouse was inhibited by betahistine in high dosages (150-300 mg/kg). In slices from mouse cerebral cortex, betahistine induced [3H]glycogen hydrolysis in a concentration-dependent manner with an EC50 value of 9.0 microM with a maximal effect 57% that of histamine. Mepyramine and triprolidine, two H1-receptor antagonists, inhibited the betahistine-induced glycogenolysis with Ki values of 28 nM and 7 nM respectively. In slices from guinea-pig hippocampus, betahistine stimulated the accumulation of cyclic AMP in the presence of 5 microM impromidine, a H2-receptor agonist. The maximal effect represented 22% of that elicited by histamine at the H1-receptor and the EC50 value was 32.4 microM. Mepyramine at 0.1 microM partially blocked the response to betahistine. Together these various observations indicate that betahistine is a partial agonist at cerebral H1-receptors. Finally, betahistine was not an agonist at histamine H3-autoreceptors but was a rather potent antagonist of the inhibitory effect of exogenous histamine on [3H]histamine release elicited by K+ depolarisation in slices from rat cerebral cortex (Ki = 6.9 microM).

Ulip/CRMP proteins are recognized by autoantibodies in paraneoplastic neurological syndromes

Anti‐CV2 autoantibodies have recently been discovered in patients with paraneoplastic neurological diseases (PND). These disorders are associated with neuronal degeneration, mediated by autoimmune processes, in patients with systemic cancer. Anti‐CV2 autoantibodies recognize a brain protein of 66 kDa developmentally regulated and specifically expressed by a subpopulation of oligodendrocytes in the adult brain. Here, we demonstrate that anti‐CV2 sera recognize several post‐translationally modified forms of Ulip4/CRMP3, a member of a protein family related to the axonal guidance and homologous to the Unc‐33 gene product in Caenorhabditis elegans. The sequence of the human Ulip4/CRMP3 was determined and the gene localized to chromosome 10q25.2–q26, a region mutated in glioblastomas and containing tumour suppressor genes. The identification of the Ulip/CRMP proteins as recognized by anti‐CV2 sera should provide new insights into the role of Ulip/CRMPs in oligodendrocytes and into pathophysiology of PND.

Involvement of collapsin response mediator proteins in the neurite extension induced by neurotrophins in dorsal root ganglion neurons.

The pattern of sensory neuron extensions and connections is established during embryonic development through complex and varied guidance cues that control motility of growth cones and neurite morphogenesis. Semaphorins and neurotrophins are molecules that act as such cues. Collapsin response mediator proteins (CRMPs) are thought to be part of the semaphorin signal transduction pathway implicated in semaphorin-induced growth cone collapse. In this report, we present evidence that CRMPs are also involved in the neurite extension controlled by neurotrophins. We found that specific antibodies and the dominant-negative mutant protein for CRMP2 both potentiated the neurite extension induced by NGF, while specific antibodies and the corresponding mutant protein for CRMP1 both abolished the neurite extension induced by NT3. Our data suggest that CRMP2 has a negative effect on neurite extension induced by NGF and CRMP1 participates in the neurite formation/extension induced by NT3. These results point to a function for CRMPs in the regulation of neurite outgrowth induced by neurotrophins in sensory neurons.

A Role for the Neuronal Protein Collapsin Response Mediator Protein 2 in T Lymphocyte Polarization and Migration

The semaphorin-signaling transducer collapsin response mediator protein 2 (CRMP2) has been identified in the nervous system where it mediates Sema3A-induced growth cone navigation. In the present study, we provide first evidence that CRMP2 is present in the immune system and plays a critical role in T lymphocyte function. CRMP2 redistribution at the uropod in polarized T cells, a structural support of lymphocyte motility, suggests that it may regulate T cell migration. This was evidenced in primary T cells by small-interfering RNA-mediated CRMP2 gene silencing and blocking Ab, as well as CRMP2 overexpression in Jurkat T cells tested in a chemokine- and semaphorin-mediated transmigration assay. Expression analysis in PBMC from healthy donors showed that CRMP2 is enhanced in cell subsets bearing the activation markers CD69+ and HLA-DR+. Heightened expression in T lymphocytes of patients suffering from neuroinflammatory disease with enhanced T cell-transmigrating activity points to a role for CRMP2 in pathogenesis. The elucidation of the signals and mechanisms that control this pathway will lead to a better understanding of T cell trafficking in physiological and pathological situations.

POP66, a Paraneoplastic encephalomyelitis-related antigen, is a marker of adult oligodendrocytes

Paraneoplastic neurological diseases are disorders of the central nervous system, associated with neuronal degeneration in patients with systemic cancer, but are not a direct result of the tumor mass or metastasis. The biological diagnosis of these syndromes is based mainly on the detection, in the patients serum and cerebrospinal fluid, of autoantibodies (anti-Hu, anti-Yo, for example), suggesting an autoimmune orgin for these disorders. Recently, we described novel autoantibodies (anti-CV2 autontibodies) associated with paraneoplastic neurological disease, which recognize a 66 kDa brain protein. We named this antigen POP66, for Paraneoplastic Oligodendrocyte Protein of 66 kDa molecular weight, as in the adult human, rat, and mouse brain, it is specifically expressed by a subpopulation of oligodendrocytes. This cell type sepcificity was surprising given the fact that the cell loss in the brains of patients with anti-CV2 autoantibodies is neuronal. POP66-positive oligodendrocytes follows an increasing dorsal-to-ventral gradinet, which may be related to different oligodendrocyte presursor pools. In addition, the neuronal loss without demyelination seen in the brains of patients with anti-CV2 autoantibodies, together with the exclusive oligodendroglial expression of POP66 in the adult brain, raises the question of the possible involvement of POP66 in neuron survival via neuron/oligodendrocyte interactions.

Adaptive changes of neurotransmitter receptor mechanisms in the central nervous system.

Publisher Summary The concept of adaptive changes in responsiveness to neurotransmitters is not a new one; the processes of hyper- and hyposensitivity of target-cells innervated by the peripheral nervous system have been known for a long time. However, its extension to the CNS awaited the advent of suitable methods to quantify “responses” to neurotransmitters. This chapter describes the various experimental approaches that can be used and discusses, using a few examples provided by studies of the catecholaminergic systems in brain (the most extensively studied ones in the respect), the characters and mechanisms of changes in responsiveness. The chapter shows that these changes are not restricted to catecholaminergic systems in brain and also discusses one functional implication of these adaptative processes.

Is vigor of regeneration a key factor in recovery from peripheral nerve injuries

The nerve-growth-promoting effects of the tricyclic antidepressant, imipramine, were tested on the sympathetic ganglion of chickens and on the sciatic nerve of rats. A powerful neuronotrophic action was observed in vitro, but the utilization of the drug in vivo did not modify the functional recovery from a crush lesion.

Mapping CRMP3 domains involved in dendrite morphogenesis and voltage-gated calcium channel regulation

Summary Although hippocampal neurons are well-distinguished by the morphological characteristics of their dendrites and their structural plasticity, the mechanisms involved in regulating their neurite initiation, dendrite growth, network formation and remodeling are still largely unknown, in part because the key molecules involved remain elusive. Identifying new dendrite-active cues could uncover unknown molecular mechanisms that would add significant understanding to the field and possibly lead to the development of novel neuroprotective therapy because these neurons are impaired in many neuropsychiatric disorders. In our previous studies, we deleted the gene encoding CRMP3 in mice and identified the protein as a new endogenous signaling molecule that shapes diverse features of the hippocampal pyramidal dendrites without affecting axon morphology. We also found that CRMP3 protects dendrites against dystrophy induced by prion peptide PrP106–126. Here, we report that CRMP3 has a profound influence on neurite initiation and dendrite growth of hippocampal neurons in vitro. Our deletional mapping revealed that the C-terminus of CRMP3 probably harbors its dendritogenic capacity and supports an active transport mechanism. By contrast, overexpression of the C-terminal truncated CRMP3 phenocopied the effect of CRMP3 gene deletion with inhibition of neurite initiation or decrease in dendrite complexity, depending on the stage of cell development. In addition, this mutant inhibited the activity of CRMP3, in a similar manner to siRNA. Voltage-gated calcium channel inhibitors prevented CRMP3-induced dendritic growth and somatic Ca2+ influx in CRMP3-overexpressing neurons was augmented largely via L-type channels. These results support a link between CRMP3-mediated Ca2+ influx and CRMP3-mediated dendritic growth in hippocampal neurons.

The altered transcriptome in aging hippocampus

When considering aging, one particularly interesting brain structure to investigate is the hippocampus. The hippocampal formation includes the subiculum, presubiculum, parasubiculum, entorhinal cortex and hippocampus proper. As part of the limbic system, which plays critical roles in information encoding for short and long term memory, intellectual ability, and spatial navigation, the hippocampal formation is involved in a wide spectrum of the physiological and pathological changes of the aging brain. The hippocampus proper is divided into two main areas: