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The role that astrocytes play in central nervous system (CNS) myelination is poorly understood. We investigated the contribution of astrocyte-derived factors to myelination and revealed a substantial overlap in the secretomes of human and rat astrocytes. Using in vitro myelinating co-cultures of primary retinal ganglion cells and cortical oligodendrocyte precursor cells, we discovered that factors secreted by resting astrocytes, but not reactive astrocytes, facilitated myelination. Soluble brevican emerged as a new enhancer of developmental myelination in vivo, CNS and its absence was linked to remyelination deficits following an immune-mediated damage in an EAE mouse model. The observed reduction of brevican expression in reactive astrocytes and human MS lesions suggested a potential link to the compromised remyelination characteristic of neurodegenerative diseases. Our findings suggested brevican's role in myelination may be mediated through interactions with binding partners such as contactin-1 and tenascin-R. Proteomic analysis of resting versus reactive astrocytes highlighted a shift in protein expression profiles, pinpointing candidates that either facilitate or impede CNS repair, suggesting that depending on their reactivity state, astrocytes play a dual role during myelination.
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Epilepsies are multifaceted neurological disorders characterized by abnormal brain activity, e.g. caused by imbalanced synaptic excitation and inhibition. The neural extracellular matrix (ECM) is dynamically modulated by physiological and pathophysiological activity and critically involved in controlling the brain's excitability. We used different epilepsy models, i.e. mice lacking the presynaptic scaffolding protein Bassoon at excitatory, inhibitory or all synapse types as genetic models for rapidly generalizing early-onset epilepsy, and intra-hippocampal kainate injection, a model for acquired temporal lobe epilepsy, to study the relationship between epileptic seizures and ECM composition. Electroencephalogram recordings revealed Bassoon deletion at excitatory or inhibitory synapses having diverse effects on epilepsy-related phenotypes. While constitutive Bsn mutants and to a lesser extent GABAergic neuron-specific knockouts (BsnDlx5/6cKO) displayed severe epilepsy with more and stronger seizures than kainate-injected animals, mutants lacking Bassoon solely in excitatory forebrain neurons (BsnEmx1cKO) showed only mild impairments. By semiquantitative immunoblotting and immunohistochemistry we show model-specific patterns of neural ECM remodeling, and we also demonstrate significant upregulation of the ECM receptor CD44 in null and BsnDlx5/6cKO mutants. ECM-associated WFA-binding chondroitin sulfates were strongly augmented in seizure models. Strikingly, Brevican, Neurocan, Aggrecan and link proteins Hapln1 and Hapln4 levels reliably predicted seizure properties across models, suggesting a link between ECM state and epileptic phenotype.
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Epilepsia , Ácido Caínico , Camundongos , Animais , Matriz Extracelular/metabolismo , Epilepsia/genética , Epilepsia/metabolismo , Neurônios/metabolismo , Convulsões/metabolismoRESUMO
Memory-related functional magnetic resonance imaging (fMRI) activations show age-related differences across multiple brain regions that can be captured in summary statistics like single-value scores. Recently, we described two single-value scores reflecting deviations from prototypical whole-brain fMRI activity of young adults during novelty processing and successful encoding. Here, we investigate the brain-behavior associations of these scores with age-related neurocognitive changes in 153 healthy middle-aged and older adults. All scores were associated with episodic recall performance. The memory network scores, but not the novelty network scores, additionally correlated with medial temporal gray matter and other neuropsychological measures including flexibility. Our results thus suggest that novelty-network-based fMRI scores show high brain-behavior associations with episodic memory and that encoding-network-based fMRI scores additionally capture individual differences in other aging-related functions. More generally, our results suggest that single-value scores of memory-related fMRI provide a comprehensive measure of individual differences in network dysfunction that may contribute to age-related cognitive decline.
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Envelhecimento , Memória Episódica , Pessoa de Meia-Idade , Adulto Jovem , Humanos , Idoso , Envelhecimento/psicologia , Encéfalo/diagnóstico por imagem , Rememoração Mental , Mapeamento Encefálico , Imageamento por Ressonância Magnética/métodos , Testes NeuropsicológicosRESUMO
Human cognitive abilities, and particularly hippocampus-dependent memory performance typically decline with increasing age. Immunosenescence, the age-related disintegration of the immune system, is increasingly coming into the focus of research as a considerable factor contributing to cognitive decline. In the present study, we investigated potential associations between plasma levels of pro- and anti-inflammatory cytokines and learning and memory performance as well as hippocampal anatomy in young and older adults. Plasma concentrations of the inflammation marker CRP as well as the pro-inflammatory cytokines IL-6 and TNF-α and the anti-inflammatory cytokine TGF-ß1 were measured in 142 healthy adults (57 young, 24.47 ± 4.48 years; 85 older, 63.66 ± 7.32 years) who performed tests of explicit memory (Verbal Learning and Memory Test, VLMT; Wechsler Memory Scale, Logical Memory, WMS) with an additional delayed recall test after 24 h. Hippocampal volumetry and hippocampal subfield segmentation were performed using FreeSurfer, based on T1-weighted and high-resolution T2-weighted MR images. When investigating the relationship between memory performance, hippocampal structure, and plasma cytokine levels, we found that TGF-ß1 concentrations were positively correlated with the volumes of the hippocampal CA4-dentate gyrus region in older adults. These volumes were in turn positively associated with better performance in the WMS, particularly in the delayed memory test. Our results support the notion that endogenous anti-inflammatory mechanisms may act as protective factors in neurocognitive aging.
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Citocinas , Fator de Crescimento Transformador beta , Humanos , Idoso , Imageamento por Ressonância Magnética , Testes Neuropsicológicos , Hipocampo/diagnóstico por imagem , Cognição , Anti-InflamatóriosRESUMO
The brain's extracellular matrix (ECM) is assumed to undergo rearrangements in Alzheimer's disease (AD). Here, we investigated changes of key components of the hyaluronan-based ECM in independent samples of post-mortem brains (N = 19), cerebrospinal fluids (CSF; N = 70), and RNAseq data (N = 107; from The Aging, Dementia and TBI Study) of AD patients and non-demented controls. Group comparisons and correlation analyses of major ECM components in soluble and synaptosomal fractions from frontal, temporal cortex, and hippocampus of control, low-grade, and high-grade AD brains revealed a reduction in brevican in temporal cortex soluble and frontal cortex synaptosomal fractions in AD. In contrast, neurocan, aggrecan and the link protein HAPLN1 were up-regulated in soluble cortical fractions. In comparison, RNAseq data showed no correlation between aggrecan and brevican expression levels and Braak or CERAD stages, but for hippocampal expression of HAPLN1, neurocan and the brevican-interaction partner tenascin-R negative correlations with Braak stages were detected. CSF levels of brevican and neurocan in patients positively correlated with age, total tau, p-Tau, neurofilament-L and Aß1-40. Negative correlations were detected with the Aß ratio and the IgG index. Altogether, our study reveals spatially segregated molecular rearrangements of the ECM in AD brains at RNA or protein levels, which may contribute to the pathogenic process.
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Doença de Alzheimer , Neurocam , Humanos , Brevicam/metabolismo , Agrecanas/metabolismo , Neurocam/líquido cefalorraquidiano , Doença de Alzheimer/metabolismo , Matriz Extracelular/metabolismo , Encéfalo/metabolismo , Proteínas tau/metabolismo , Peptídeos beta-Amiloides/metabolismo , Biomarcadores/metabolismoRESUMO
Alterations of the brain extracellular matrix (ECM) can perturb the structure and function of brain networks like the hippocampus, a key region in human memory that is commonly affected in psychiatric disorders. Here, we investigated the potential effects of a genome-wide psychiatric risk variant in the NCAN gene encoding the ECM proteoglycan neurocan (rs1064395) on memory performance, hippocampal function and cortical morphology in young, healthy volunteers. We assessed verbal memory performance in two cohorts (N = 572, 302) and found reduced recall performance in risk allele (A) carriers across both cohorts. In 117 participants, we performed functional magnetic resonance imaging using a novelty-encoding task with visual scenes. Risk allele carriers showed higher false alarm rates during recognition, accompanied by inefficiently increased left hippocampal activation. To assess effects of rs1064395 on brain morphology, we performed voxel-based morphometry in 420 participants from four independent cohorts and found lower grey matter density in the ventrolateral and rostral prefrontal cortex of risk allele carriers. In silico eQTL analysis revealed that rs1064395 SNP is linked not only to increased prefrontal expression of the NCAN gene itself, but also of the neighbouring HAPLN4 gene, suggesting a more complex effect of the SNP on ECM composition. Our results suggest that the NCAN rs1064395 A allele is associated with lower hippocampus-dependent memory function, variation of prefrontal cortex structure and ECM composition. Considering the well-documented hippocampal and prefrontal dysfunction in bipolar disorder and schizophrenia, our results may reflect an intermediate phenotype by which NCAN rs1064395 contributes to disease risk.
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Transtorno Bipolar , Hipocampo , Neurocam/genética , Esquizofrenia , Mapeamento Encefálico , Proteoglicanas de Sulfatos de Condroitina/genética , Hipocampo/diagnóstico por imagem , Hipocampo/fisiologia , Humanos , Lectinas Tipo C/genética , Imageamento por Ressonância Magnética , Memória , Proteínas do Tecido Nervoso/genéticaRESUMO
Older adults and particularly those at risk for developing dementia typically show a decline in episodic memory performance, which has been associated with altered memory network activity detectable via functional magnetic resonance imaging (fMRI). To quantify the degree of these alterations, a score has been developed as a putative imaging biomarker for successful aging in memory for older adults (Functional Activity Deviations during Encoding, FADE; Düzel et al., Hippocampus, 2011; 21: 803-814). Here, we introduce and validate a more comprehensive version of the FADE score, termed FADE-SAME (Similarity of Activations during Memory Encoding), which differs from the original FADE score by considering not only activations but also deactivations in fMRI contrasts of stimulus novelty and successful encoding, and by taking into account the variance of young adults' activations. We computed both scores for novelty and subsequent memory contrasts in a cohort of 217 healthy adults, including 106 young and 111 older participants, as well as a replication cohort of 117 young subjects. We further tested the stability and generalizability of both scores by controlling for different MR scanners and gender, as well as by using different data sets of young adults as reference samples. Both scores showed robust age-group-related differences for the subsequent memory contrast, and the FADE-SAME score additionally exhibited age-group-related differences for the novelty contrast. Furthermore, both scores correlate with behavioral measures of cognitive aging, namely memory performance. Taken together, our results suggest that single-value scores of memory-related fMRI responses may constitute promising biomarkers for quantifying neurocognitive aging.
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Encéfalo/fisiologia , Envelhecimento Cognitivo/fisiologia , Neuroimagem Funcional/métodos , Hipocampo/fisiologia , Memória Episódica , Adolescente , Adulto , Fatores Etários , Idoso , Idoso de 80 Anos ou mais , Encéfalo/diagnóstico por imagem , Feminino , Hipocampo/diagnóstico por imagem , Humanos , Imageamento por Ressonância Magnética , Masculino , Pessoa de Meia-Idade , Adulto JovemRESUMO
Dopaminergic neurotransmission plays a pivotal role in appetitively motivated behavior in mammals, including humans. Notably, action and valence are not independent in motivated tasks, and it is particularly difficult for humans to learn the inhibition of an action to obtain a reward. We have previously observed that the carriers of the DRD2/ANKK1 TaqIA A1 allele, that has been associated with reduced striatal dopamine D2 receptor expression, showed a diminished learning performance when required to learn response inhibition to obtain rewards, a finding that was replicated in two independent cohorts. With our present study, we followed two aims: first, we aimed to replicate our finding on the DRD2/ANKK1 TaqIA polymorphism in a third independent cohort (N = 99) and to investigate the nature of the genetic effects more closely using trial-by-trial behavioral analysis and computational modeling in the combined dataset (N = 281). Second, we aimed to assess a potentially modulatory role of prefrontal dopamine availability, using the widely studied COMT Val108/158Met polymorphism as a proxy. We first report a replication of the above mentioned finding. Interestingly, after combining all three cohorts, exploratory analyses regarding the COMT Val108/158Met polymorphism suggest that homozygotes for the Met allele, which has been linked to higher prefrontal dopaminergic tone, show a lower learning bias. Our results corroborate the importance of genetic variability of the dopaminergic system in individual learning differences of action-valence interaction and, furthermore, suggest that motivational learning biases are differentially modulated by genetic determinants of striatal and prefrontal dopamine function.
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Catecol O-Metiltransferase , Dopamina , Animais , Viés , Catecol O-Metiltransferase/genética , Corpo Estriado , Genótipo , Humanos , Aprendizagem , Polimorfismo de Nucleotídeo Único/genética , Proteínas Serina-Treonina Quinases/genéticaRESUMO
Anxiety disorders are common and debilitating conditions with higher prevalence in women. However, factors that predispose women to anxiety phenotypes are not clarified. Here we investigated potential contribution of the single nucleotide polymorphism rs2236418 in GAD2 gene to changes in regional inhibition/excitation balance, anxiety-like traits, and related neural activity in both sexes. One hundred and five healthy individuals were examined with high-field (7T) multimodal magnetic resonance imaging (MRI); including resting-state functional MRI in combination with assessment of GABA and glutamate (Glu) levels via MR spectroscopy. Regional GABA/Glu levels in anterior cingulate cortex (ACC) subregions were assessed as mediators of gene-personality interaction for the trait harm avoidance and moderation by sex was tested. In AA homozygotes, with putatively lower GAD2 promoter activity, we observed increased intrinsic neuronal activity and higher inhibition/excitation balance in pregenual ACC (pgACC) compared with G carriers. The pgACC drove a significant interaction of genotype, region, and sex, where inhibition/excitation balance was significantly reduced only in female AA carriers. This finding was specific for rs2236418 as other investigated single nucleotide polymorphisms of the GABA synthesis related enzymes (GAD1, GAD2, and GLS) were not significant. Furthermore, only in women there was a negative association of pgACC GABA/Glu ratios with harm avoidance. A moderated-mediation model revealed that pgACC GABA/Glu also mediated the association between the genotype variant and level of harm avoidance, dependent on sex. Our data thus provide new insights into the neurochemical mechanisms that control emotional endophenotypes in humans and constitute predisposing factors for the development of anxiety disorders in women.SIGNIFICANCE STATEMENT Anxiety disorders are among the most common and burdensome psychiatric disorders, with higher prevalence rates in women. The causal mechanisms are, however, poorly understood. In this study we propose a neurobiological basis that could help to explain female bias of anxiety endophenotypes. Using magnetic resonance brain imaging and personality questionnaires we show an interaction of the genetic variation rs2236418 in the GAD2 gene and sex on GABA/glutamate (Glu) balance in the pregenual anterior cingulate cortex (pgACC), a region previously connected to affect regulation and anxiety disorders. The GAD2 gene polymorphism further influenced baseline neuronal activity in the pgACC. Importantly, GABA/Glu was shown to mediate the relationship between the genetic variant and harm avoidance, however, only in women.
Assuntos
Aprendizagem da Esquiva/fisiologia , Glutamato Descarboxilase/genética , Giro do Cíngulo/fisiologia , Polimorfismo Genético/genética , Adulto , Mapeamento Encefálico , Feminino , Genótipo , Humanos , Imageamento por Ressonância Magnética , Masculino , Personalidade , Polimorfismo de Nucleotídeo Único , Regiões Promotoras Genéticas , Adulto JovemRESUMO
The past 20 years have resulted in unprecedented progress in understanding brain energy metabolism and its role in health and disease. In this review, which was initiated at the 14th International Society for Neurochemistry Advanced School, we address the basic concepts of brain energy metabolism and approach the question of why the brain has high energy expenditure. Our review illustrates that the vertebrate brain has a high need for energy because of the high number of neurons and the need to maintain a delicate interplay between energy metabolism, neurotransmission, and plasticity. Disturbances to the energetic balance, to mitochondria quality control or to glia-neuron metabolic interaction may lead to brain circuit malfunction or even severe disorders of the CNS. We cover neuronal energy consumption in neural transmission and basic ('housekeeping') cellular processes. Additionally, we describe the most common (glucose) and alternative sources of energy namely glutamate, lactate, ketone bodies, and medium chain fatty acids. We discuss the multifaceted role of non-neuronal cells in the transport of energy substrates from circulation (pericytes and astrocytes) and in the supply (astrocytes and microglia) and usage of different energy fuels. Finally, we address pathological consequences of disrupted energy homeostasis in the CNS.
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Encéfalo/metabolismo , Metabolismo Energético/fisiologia , Neuroquímica/educação , Estudantes , Animais , Astrócitos/metabolismo , Congressos como Assunto/tendências , Humanos , Neuroglia/metabolismo , Neurônios/metabolismoRESUMO
Activation of parietal cortex structures like the precuneus is commonly observed during explicit memory retrieval, but the role of parietal cortices in encoding has only recently been appreciated and is still poorly understood. Considering the importance of the precuneus in human visual attention and imagery, we aimed to assess a potential role for the precuneus in the encoding of visuospatial representations into long-term memory. We therefore investigated the acquisition of constant versus repeatedly shuffled configurations of icons on background images over five subsequent days in 32 young, healthy volunteers. Functional magnetic resonance imaging was conducted on Days 1, 2, and 5, and persistent memory traces were assessed by a delayed memory test after another 5 days. Constant compared to shuffled configurations were associated with significant improvement of position recognition from Day 1 to 5 and better delayed memory performance. Bilateral dorsal precuneus activations separated constant from shuffled configurations from Day 2 onward, and coactivation of the precuneus and hippocampus dissociated recognized and forgotten configurations, irrespective of condition. Furthermore, learning of constant configurations elicited increased functional coupling of the precuneus with dorsal and ventral visual stream structures. Our results identify the precuneus as a key brain structure in the acquisition of detailed visuospatial information by orchestrating a parieto-occipito-temporal network.
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Aprendizagem por Associação/fisiologia , Memória/fisiologia , Lobo Parietal/fisiologia , Percepção Espacial/fisiologia , Percepção Visual/fisiologia , Adulto , Mapeamento Encefálico , Feminino , Hipocampo/diagnóstico por imagem , Hipocampo/fisiologia , Humanos , Estudos Longitudinais , Imageamento por Ressonância Magnética , Masculino , Rede Nervosa/diagnóstico por imagem , Rede Nervosa/fisiologia , Lobo Parietal/diagnóstico por imagem , Estimulação Luminosa , Desempenho Psicomotor , Adulto JovemRESUMO
KEY POINTS: The proteoglycan brevican is a major component of the extracellular matrix of perineuronal nets and is highly enriched in the perisynaptic space suggesting a role for synaptic transmission. We have introduced the calyx of Held in the auditory brainstem as a model system to study the impact of brevican on dynamics and reliability of synaptic transmission. In vivo extracellular single-unit recordings at the calyx of Held in brevican-deficient mice yielded a significant increase in the action potential (AP) transmission delay and a prolongation of pre- and postsynaptic APs. The changes in dynamics of signal transmission were accompanied by the reduction of presynaptic vGlut1 and ultrastructural changes in the perisynaptic space. These data show that brevican is an important mediator of fast synaptic transmission at the calyx of Held. ABSTRACT: The extracellular matrix is an integral part of the neural tissue. Its most conspicuous manifestation in the brain are the perineuronal nets (PNs) which surround somata and proximal dendrites of distinct neuron types. The chondroitin sulfate proteoglycan brevican is a major component of PNs. In contrast to other PN-comprising proteoglycans (e.g. aggrecan and neurocan), brevican is mainly expressed in the perisynaptic space closely associated with both the pre- and postsynaptic membrane. This specific localization prompted the hypothesis that brevican might play a role in synaptic transmission. In the present study we specifically investigated the role of brevican in synaptic transmission at a central synapse, the calyx of Held in the medial nucleus of the trapezoid body, by the use of in vivo electrophysiology, immunohistochemistry, biochemistry and electron microscopy. In vivo extracellular single-unit recordings were acquired in brevican-deficient mice and the dynamics and reliability of synaptic transmission were compared to wild-type littermates. In knockout mice, the speed of pre-to-postsynaptic action potential (AP) transmission was reduced and the duration of the respective pre- and postsynaptic APs increased. The reliability of signal transmission, however, was not affected by the lack of brevican. The changes in dynamics of signal transmission were accompanied by the reduction of (i) presynaptic vGlut1 and (ii) the size of subsynaptic cavities. The present results suggest an essential role of brevican for the functionality of high-speed synaptic transmission at the calyx of Held.
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Brevicam/fisiologia , Transmissão Sináptica/fisiologia , Corpo Trapezoide/fisiologia , Estimulação Acústica , Potenciais de Ação , Animais , Brevicam/genética , Transportador 2 de Aminoácido Excitatório/metabolismo , Matriz Extracelular , Feminino , Transportador de Glucose Tipo 1/metabolismo , Transportador de Glucose Tipo 2/metabolismo , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Sinapses/fisiologia , Corpo Trapezoide/metabolismoRESUMO
Formation, maintenance, and activity of excitatory and inhibitory synapses are essential for neuronal network function. Cell adhesion molecules (CAMs) are crucially involved in these processes. The CAM neuroplastin-65 (Np65) highly expressed during periods of synapse formation and stabilization is present at the pre- and postsynaptic membranes. Np65 can translocate into synapses in response to electrical stimulation and it interacts with subtypes of GABAA receptors in inhibitory synapses. Here, we report that in the murine hippocampus and in hippocampal primary culture, neurons of the CA1 region and the dentate gyrus (DG) express high Np65 levels, whereas expression in CA3 neurons is lower. In neuroplastin-deficient (Np(-/-)) mice the number of excitatory synapses in CA1 and DG, but not CA3 regions is reduced. Notably this picture is mirrored in mature Np(-/-) hippocampal cultures or in mature CA1 and DG wild-type (Np(+/+)) neurons treated with a function-blocking recombinant Np65-Fc extracellular fragment. Although the number of GABAergic synapses was unchanged in Np(-/-) neurons or in mature Np65-Fc-treated Np(+/+) neurons, the ratio of excitatory to inhibitory synapses was significantly lower in Np(-/-) cultures. Furthermore, GABAA receptor composition was altered at inhibitory synapses in Np(-/-) neurons as the α1 to α2 GABAA receptor subunit ratio was increased. Changes of excitatory and inhibitory synaptic function in Np(-/-) neurons were confirmed evaluating the presynaptic release function and using patch clamp recording. These data demonstrate that Np65 is an important regulator of the number and function of synapses in the hippocampus.
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Potenciais Pós-Sinápticos Excitadores , Potenciais Pós-Sinápticos Inibidores , Glicoproteínas de Membrana/metabolismo , Receptores de GABA-A/metabolismo , Sinapses/metabolismo , Animais , Região CA1 Hipocampal/citologia , Contagem de Células , Giro Denteado/citologia , Regulação da Expressão Gênica , Ácido Glutâmico/metabolismo , Glicoproteínas de Membrana/deficiência , Camundongos , Neurônios/citologia , Neurônios/metabolismo , Subunidades Proteicas/metabolismo , Transporte Proteico , RatosRESUMO
New episodic memory traces represent a record of the ongoing neocortical processing engaged during memory formation (encoding). Thus, during encoding, deep (semantic) processing typically establishes more distinctive and retrievable memory traces than does shallow (perceptual) processing, as assessed by later episodic memory tests. By contrast, the hippocampus appears to play a processing-independent role in encoding, because hippocampal lesions impair encoding regardless of level of processing. Here, we clarified the neural relationship between processing and encoding by examining hippocampal-cortical connectivity during deep and shallow encoding. Participants studied words during functional magnetic resonance imaging and freely recalled these words after distraction. Deep study processing led to better recall than shallow study processing. For both levels of processing, successful encoding elicited activations of bilateral hippocampus and left prefrontal cortex, and increased functional connectivity between left hippocampus and bilateral medial prefrontal, cingulate and extrastriate cortices. Successful encoding during deep processing was additionally associated with increased functional connectivity between left hippocampus and bilateral ventrolateral prefrontal cortex and right temporoparietal junction. In the shallow encoding condition, on the other hand, pronounced functional connectivity increases were observed between the right hippocampus and the frontoparietal attention network activated during shallow study processing. Our results further specify how the hippocampus coordinates recording of ongoing neocortical activity into long-term memory, and begin to provide a neural explanation for the typical advantage of deep over shallow study processing for later episodic memory.
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Córtex Cerebral/fisiologia , Hipocampo/fisiologia , Memória Episódica , Vias Neurais/fisiologia , Adolescente , Adulto , Algoritmos , Análise de Variância , Mapeamento Encefálico , Interpretação Estatística de Dados , Feminino , Lateralidade Funcional/fisiologia , Humanos , Processamento de Imagem Assistida por Computador , Imageamento por Ressonância Magnética , Masculino , Rememoração Mental/fisiologia , Modelos Estatísticos , Estimulação Luminosa , Desempenho Psicomotor/fisiologia , Psicofisiologia , Tempo de Reação/fisiologia , Leitura , Adulto JovemRESUMO
Action potential initiation and propagation requires clustered Na(+) (voltage-gated Na(+) [Nav]) channels at axon initial segments (AIS) and nodes of Ranvier. In addition to ion channels, these domains are characterized by cell adhesion molecules (CAMs; neurofascin-186 [NF-186] and neuron glia-related CAM [NrCAM]), cytoskeletal proteins (ankyrinG and betaIV spectrin), and the extracellular chondroitin-sulfate proteoglycan brevican. Schwann cells initiate peripheral nervous system node formation by clustering NF-186, which then recruits ankyrinG and Nav channels. However, AIS assembly of this protein complex does not require glial contact. To determine the AIS assembly mechanism, we silenced expression of AIS proteins by RNA interference. AnkyrinG knockdown prevented AIS localization of all other AIS proteins. Loss of NF-186, NrCAM, Nav channels, or betaIV spectrin did not affect other neuronal AIS proteins. However, loss of NF-186 blocked assembly of the brevican-based AIS extracellular matrix, and NF-186 overexpression caused somatodendritic brevican clustering. Thus, NF-186 assembles and links the specialized brevican-containing AIS extracellular matrix to the intracellular cytoskeleton.
Assuntos
Axônios , Moléculas de Adesão Celular/metabolismo , Matriz Extracelular/metabolismo , Fatores de Crescimento Neural/metabolismo , Animais , Anquirinas/genética , Anquirinas/metabolismo , Axônios/metabolismo , Axônios/ultraestrutura , Brevicam , Moléculas de Adesão Celular/genética , Células Cultivadas , Proteoglicanas de Sulfatos de Condroitina/metabolismo , Citoesqueleto/metabolismo , Matriz Extracelular/química , Hipocampo/citologia , Lectinas Tipo C/metabolismo , Fatores de Crescimento Neural/genética , Proteínas do Tecido Nervoso/metabolismo , RNA/genética , RNA/metabolismo , Interferência de RNA , Nós Neurofibrosos/metabolismo , Nós Neurofibrosos/ultraestrutura , Ratos , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , Canais de Sódio/genética , Canais de Sódio/metabolismo , Espectrina/genética , Espectrina/metabolismoRESUMO
Upon postsynaptic glutamate receptor activation, the cytosolic Ca2+ concentration rises and initiates signaling and plasticity in spines. The plasma membrane Ca2+ ATPase (PMCA) is a major player to limit the duration of cytosolic Ca2+ signals. It forms complexes with the glycoprotein neuroplastin (Np) isoforms Np55 and Np65 and functionally interplays with N-methyl-D-aspartate (NMDA)-type ionotropic glutamate receptors (iGluNRs). Moreover, binding of the Np65-specific extracellular domain to Ca2+-permeable GluA1-containing α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)-type ionotropic glutamate receptors (iGluA1Rs) was found to be required for long-term potentiation (LTP). However, the link between PMCA and iGluRs function to regulate cytosolic Ca2+ signals remained unclear. Here, we report that Np65 coordinates PMCA and iGluRs' functions to modulate the duration and amplitude of cytosolic Ca2+ transients in dendrites and spines of hippocampal neurons. Using live-cell Ca2+ imaging, acute pharmacological treatments, and GCaMP5G-expressing hippocampal neurons, we discovered that endogenous or Np65-promoted PMCA activity contributes to the restoration of basal Ca2+ levels and that this effect is dependent on iGluR activation. Super-resolution STED and confocal microscopy revealed that electrical stimulation increases the abundance of synaptic neuroplastin-PMCA complexes depending on iGluR activation and that low-rate overexpression of Np65 doubled PMCA levels and decreased cell surface levels of GluN2A and GluA1 in dendrites and Shank2-positive glutamatergic synapses. In neuroplastin-deficient hippocampi, we observed reduced PMCA and unchanged GluN2B levels, while GluN2A and GluA1 levels were imbalanced. Our electrophysiological data from hippocampal slices argues for an essential interplay of PMCA with GluN2A- but not with GluN2B-containing receptors upon induction of synaptic plasticity. Accordingly, we conclude that Np65 may interconnect PMCA with core players of glutamatergic neurotransmission to fine-tune the Ca2+ signal regulation in basal synaptic function and plasticity.
Assuntos
Adenosina Trifosfatases , Receptores Ionotrópicos de Glutamato , Adenosina Trifosfatases/metabolismo , Hipocampo/metabolismo , Plasticidade Neuronal , Neurônios/metabolismo , Receptores Ionotrópicos de Glutamato/metabolismo , Receptores de N-Metil-D-Aspartato/metabolismo , Sinapses/metabolismoRESUMO
The neural extracellular matrix (ECM) composition shapes the neuronal microenvironment and undergoes substantial changes upon development and aging, but also due to cerebral pathologies. In search for potential biomarkers, cerebrospinal fluid (CSF) and serum concentrations of brain ECM molecules have been determined recently to assess ECM changes during neurological conditions including Alzheimer's disease or vascular dementia. Here, we measured the levels of two signature proteoglycans of brain ECM, neurocan and brevican, in the CSF and serum of 96 neurological patients currently understudied regarding ECM alterations: 16 cases with amyotrophic lateral sclerosis (ALS), 26 epilepsy cases, 23 cerebral small vessel disease (CSVD) patients and 31 controls. Analysis of total brevican and neurocan was performed via sandwich Enzyme-linked immunosorbent assays (ELISAs). Major brevican and neurocan cleavage products were measured in the CSF using semiquantitative immunoblotting. Total brevican and neurocan concentrations in serum and CSF did not differ between groups. The 60 kDa brevican fragment resulting from cleavage by the protease ADAMTS-4 was also found unchanged among groups. The presumably intracellularly generated 150 kDa C-terminal neurocan fragment, however, was significantly increased in ALS as compared to all other groups. This group also shows the highest correlation between cleaved and total neurocan in the CSF. Brevican and neurocan levels strongly correlated with each other across all groups, arguing for a joint but yet unknown transport mechanism from the brain parenchyma into CSF. Conclusively our findings suggest an ALS-specific pattern of brain ECM remodeling and may thus contribute to new diagnostic approaches for this disorder.
RESUMO
NMDA (N-methyl-D-aspartate) receptors and calcium can exert multiple and very divergent effects within neuronal cells, thereby impacting opposing occurrences such as synaptic plasticity and neuronal degeneration. The neuronal Ca2+ sensor Caldendrin is a postsynaptic density component with high similarity to calmodulin. Jacob, a recently identified Caldendrin binding partner, is a novel protein abundantly expressed in limbic brain and cerebral cortex. Strictly depending upon activation of NMDA-type glutamate receptors, Jacob is recruited to neuronal nuclei, resulting in a rapid stripping of synaptic contacts and in a drastically altered morphology of the dendritic tree. Jacob's nuclear trafficking from distal dendrites crucially requires the classical Importin pathway. Caldendrin binds to Jacob's nuclear localization signal in a Ca2+-dependent manner, thereby controlling Jacob's extranuclear localization by competing with the binding of Importin-alpha to Jacob's nuclear localization signal. This competition requires sustained synapto-dendritic Ca2+ levels, which presumably cannot be achieved by activation of extrasynaptic NMDA receptors, but are confined to Ca2+ microdomains such as postsynaptic spines. Extrasynaptic NMDA receptors, as opposed to their synaptic counterparts, trigger the cAMP response element-binding protein (CREB) shut-off pathway, and cell death. We found that nuclear knockdown of Jacob prevents CREB shut-off after extrasynaptic NMDA receptor activation, whereas its nuclear overexpression induces CREB shut-off without NMDA receptor stimulation. Importantly, nuclear knockdown of Jacob attenuates NMDA-induced loss of synaptic contacts, and neuronal degeneration. This defines a novel mechanism of synapse-to-nucleus communication via a synaptic Ca2+-sensor protein, which links the activity of NMDA receptors to nuclear signalling events involved in modelling synapto-dendritic input and NMDA receptor-induced cellular degeneration.
Assuntos
Proteínas de Ligação ao Cálcio/metabolismo , Núcleo Celular/metabolismo , Receptores de N-Metil-D-Aspartato/metabolismo , Transdução de Sinais , Animais , Sequência de Bases , Western Blotting , Proteínas de Ligação ao Cálcio/genética , Cromatografia de Afinidade , Primers do DNA , DNA Complementar , Imuno-Histoquímica , Sinais de Localização Nuclear , Ligação Proteica , Ratos , Técnicas do Sistema de Duplo-HíbridoRESUMO
Correct brain wiring depends on reliable synapse formation. Nevertheless, signaling codes promoting synaptogenesis are not fully understood. Here, we report a spinogenic mechanism that operates during neuronal development and is based on the interaction of tumor necrosis factor receptor-associated factor 6 (TRAF6) with the synaptic cell adhesion molecule neuroplastin. The interaction between these proteins was predicted in silico and verified by co-immunoprecipitation in extracts from rat brain and co-transfected HEK cells. Binding assays show physical interaction between neuroplastin's C-terminus and the TRAF-C domain of TRAF6 with a K d value of 88 µM. As the two proteins co-localize in primordial dendritic protrusions, we used young cultures of rat and mouse as well as neuroplastin-deficient mouse neurons and showed with mutagenesis, knock-down, and pharmacological blockade that TRAF6 is required by neuroplastin to promote early spinogenesis during in vitro days 6-9, but not later. Time-framed TRAF6 blockade during days 6-9 reduced mEPSC amplitude, number of postsynaptic sites, synapse density and neuronal activity as neurons mature. Our data unravel a new molecular liaison that may emerge during a specific window of the neuronal development to determine excitatory synapse density in the rodent brain.