RESUMO
In this Article, owing to an error during the production process, the y-axis label of Fig. 2c should read "Number of Tß-syn cells" rather than "Number of T1ß-syn cells" and the left and right panels of Fig. 4 should be labelled 'a' and 'b', respectively. These errors have been corrected online.
RESUMO
The grey matter is a central target of pathological processes in neurodegenerative disorders such as Parkinson's and Alzheimer's diseases. The grey matter is often also affected in multiple sclerosis, an autoimmune disease of the central nervous system. The mechanisms that underlie grey matter inflammation and degeneration in multiple sclerosis are not well understood. Here we show that, in Lewis rats, T cells directed against the neuronal protein ß-synuclein specifically invade the grey matter and that this is accompanied by the presentation of multifaceted clinical disease. The expression pattern of ß-synuclein induces the local activation of these T cells and, therefore, determined inflammatory priming of the tissue and targeted recruitment of immune cells. The resulting inflammation led to significant changes in the grey matter, which ranged from gliosis and neuronal destruction to brain atrophy. In humans, ß-synuclein-specific T cells were enriched in patients with chronic-progressive multiple sclerosis. These findings reveal a previously unrecognized role of ß-synuclein in provoking T-cell-mediated pathology of the central nervous system.
Assuntos
Substância Cinzenta/imunologia , Substância Cinzenta/patologia , Esclerose Múltipla Crônica Progressiva/imunologia , Esclerose Múltipla Crônica Progressiva/patologia , Linfócitos T/imunologia , beta-Sinucleína/imunologia , Animais , Encéfalo/patologia , Movimento Celular/imunologia , Feminino , Regulação da Expressão Gênica , Gliose/patologia , Humanos , Inflamação/imunologia , Inflamação/patologia , Ativação Linfocitária , Contagem de Linfócitos , Masculino , Esclerose Múltipla Crônica Progressiva/sangue , Doenças Neurodegenerativas/imunologia , Doenças Neurodegenerativas/patologia , Neurônios/patologia , Ratos , Ratos Endogâmicos Lew , Linfócitos T/metabolismo , Linfócitos T/patologia , beta-Sinucleína/análise , beta-Sinucleína/genética , beta-Sinucleína/metabolismoRESUMO
Purkinje cells (PCs) are primarily affected in neurodegenerative spinocerebellar ataxias (SCAs). For generating animal models for SCAs, genetic regulatory elements specifically targeting PCs are required, thereby linking pathological molecular effects with impaired function and organismic behavior. Because cerebellar anatomy and function are evolutionary conserved, zebrafish represent an excellent model to study SCAs in vivo We have isolated a 258 bp cross-species PC-specific enhancer element that can be used in a bidirectional manner for bioimaging of transgene-expressing PCs in zebrafish (both sexes) with variable copy numbers for tuning expression strength. Emerging ectopic expression at high copy numbers can be further eliminated by repurposing microRNA-mediated posttranslational mRNA regulation.Subsequently, we generated a transgenic SCA type 13 (SCA13) model, using a zebrafish-variant mimicking a human pathological SCA13R420H mutation, resulting in cell-autonomous progressive PC degeneration linked to cerebellum-driven eye-movement deficits as observed in SCA patients. This underscores that investigating PC-specific cerebellar neuropathologies in zebrafish allows for interconnecting bioimaging of disease mechanisms with behavioral analysis suitable for therapeutic compound testing.SIGNIFICANCE STATEMENT SCA13 patients carrying a KCNC3R420H allele have been shown to display mid-onset progressive cerebellar atrophy, but genetic modeling of SCA13 by expressing this pathogenic mutant in different animal models has not resulted in neuronal degeneration so far; likely because the transgene was expressed in heterologous cell types. We developed a genetic system for tunable PC-specific coexpression of several transgenes to manipulate and simultaneously monitor cerebellar PCs. We modeled a SCA13 zebrafish accessible for bioimaging to investigate disease progression, revealing robust PC degeneration, resulting in impaired eye movement. Our transgenic zebrafish mimicking both neuropathological and behavioral changes manifested in SCA-affected patients will be suitable for investigating causes of cerebellar diseases in vivo from the molecular to the behavioral level.
Assuntos
Cerebelo/metabolismo , Modelos Animais de Doenças , Células de Purkinje/metabolismo , Ataxias Espinocerebelares/congênito , Animais , Animais Geneticamente Modificados , Cerebelo/crescimento & desenvolvimento , Cerebelo/fisiopatologia , Feminino , Regulação da Expressão Gênica , Masculino , RNA Mensageiro/metabolismo , Elementos Reguladores de Transcrição , Canais de Potássio Shaw/genética , Ataxias Espinocerebelares/genética , Ataxias Espinocerebelares/metabolismo , Peixe-Zebra , Proteínas de Peixe-Zebra/genéticaRESUMO
Dendritic spines are tiny membrane specialization forming the postsynaptic part of most excitatory synapses. They have been suggested to play a crucial role in regulating synaptic transmission during development and in adult learning processes. Changes in their number, size, and shape are correlated with processes of structural synaptic plasticity and learning and memory and also with neurodegenerative diseases, when spines are lost. Thus, their alterations can correlate with neuronal homeostasis, but also with dysfunction in several neurological disorders characterized by cognitive impairment. Therefore, it is important to understand how different stages in the life of a dendritic spine, including formation, maturation, and plasticity, are strictly regulated. In this context, brain-derived neurotrophic factor (BDNF), belonging to the NGF-neurotrophin family, is among the most intensively investigated molecule. This review would like to report the current knowledge regarding the role of BDNF in regulating dendritic spine number, structure, and plasticity concentrating especially on its signaling via its two often functionally antagonistic receptors, TrkB and p75NTR. In addition, we point out a series of open points in which, while the role of BDNF signaling is extremely likely conclusive, evidence is still missing.
Assuntos
Fator Neurotrófico Derivado do Encéfalo/genética , Espinhas Dendríticas/metabolismo , Neurônios/metabolismo , Animais , Humanos , Transdução de SinaisRESUMO
The brain-derived neurotrophic factor (BDNF) plays crucial roles in both the developing and mature brain. Moreover, alterations in BDNF levels are correlated with the cognitive impairment observed in several neurological diseases. Among the different therapeutic strategies developed to improve endogenous BDNF levels is the administration of the BDNF-inducing drug Fingolimod, an agonist of the sphingosine-1-phosphate receptor. Fingolimod treatment was shown to rescue diverse symptoms associated with several neurological conditions (i.e., Alzheimer disease, Rett syndrome). However, the cellular mechanisms through which Fingolimod mediates its BDNF-dependent therapeutic effects remain unclear. We show that Fingolimod regulates the dendritic architecture, dendritic spine density and morphology of healthy mature primary hippocampal neurons. Moreover, the application of Fingolimod upregulates the expression of activity-related proteins c-Fos and pERK1/2 in these cells. Importantly, we show that BDNF release is required for these actions of Fingolimod. As alterations in neuronal structure underlie cognitive impairment, we tested whether Fingolimod application might prevent the abnormalities in neuronal structure typical of two neurodevelopmental disorders, namely Rett syndrome and Cdk5 deficiency disorder. We found a significant rescue in the neurite architecture of developing cortical neurons from Mecp2 and Cdkl5 mutant mice. Our study provides insights into understanding the BDNF-dependent therapeutic actions of Fingolimod.
Assuntos
Fator Neurotrófico Derivado do Encéfalo/metabolismo , Espinhas Dendríticas/metabolismo , Cloridrato de Fingolimode/farmacologia , Células Piramidais/efeitos dos fármacos , Células Piramidais/metabolismo , Animais , Biomarcadores , Imunofluorescência , Expressão Gênica , Regulação da Expressão Gênica , Genes fos , Imunossupressores/farmacologia , Camundongos , Células Piramidais/citologia , Síndrome de Rett/etiologia , Síndrome de Rett/metabolismoRESUMO
Neurotrophins mediate neuronal growth, differentiation, and survival via tropomyosin receptor kinase (Trk) or p75 neurotrophin receptor (p75NTR ) signaling. The p75NTR is not exclusively expressed by neurons but also by certain immune cells, implying a role for neurotrophin signaling in the immune system. In this study, we investigated the effect of p75NTR on innate immune cell behavior and on neuronal morphology upon chronic Toxoplasma gondii (T. gondii) infection-induced neuroinflammation. Characterization of the immune cells in the periphery and central nervous system (CNS) revealed that innate immune cell subsets in the brain upregulated p75NTR upon infection in wild-type mice. Although cell recruitment and phagocytic capacity of p75NTRexonIV knockout (p75-/- ) mice were not impaired, the activation status of resident microglia and recruited myeloid cell subsets was altered. Importantly, recruited mononuclear cells in brains of infected p75-/- mice upregulated the production of the cytokines interleukin (IL)-10, IL-6 as well as IL-1α. Protein levels of proBDNF, known to negatively influence neuronal morphology by binding p75NTR , were highly increased upon chronic infection in the brain of wild-type and p75-/- mice. Moreover, upon infection the activated immune cells contributed to the proBDNF release. Notably, the neuroinflammation-induced changes in spine density were rescued in the p75-/- mice. In conclusion, these findings indicate that neurotrophin signaling via the p75NTR affects innate immune cell behavior, thus, influencing the structural plasticity of neurons under inflammatory conditions.
Assuntos
Leucócitos Mononucleares/fisiologia , Neurônios/fisiologia , Receptor de Fator de Crescimento Neural/fisiologia , Toxoplasma , Toxoplasmose/imunologia , Animais , Feminino , Imunidade Inata/fisiologia , Inflamação/imunologia , Inflamação/patologia , Leucócitos Mononucleares/patologia , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Camundongos Transgênicos , Toxoplasmose/patologiaRESUMO
Nogo-A restricts long-term potentiation (LTP) at the Schaffer collateral-CA1 pathway in the adult hippocampus via 2 extracellular domains: Nogo-A-Δ20 and Nogo-66. Nogo-66 signals via Nogo Receptor 1 (NgR1) to regulate synaptic function. Whether the NgR1 coreceptors Lingo1 and p75NTR are involved in the signaling in this context is still not known. Moreover, the intracellular cascade mediating the activity of Nogo-66 in restricting LTP is unexplored. We combine electrophysiology and biochemistry in acute hippocampal slices and demonstrate that a loss of function for Lingo1 results in a significant increase in LTP levels at the Schaffer collateral-CA1 pathway, and that Lingo1 is the NgR1 coreceptor mediating the role of Nogo-66 in restricting LTP. Our data show that p75NTR is not involved in mediating the Nogo-66 effect on LTP. Moreover, loss of function for p75NTR and NgR1 equally attenuate LTD, suggesting that p75NTR might mediate the NgR1-dependent regulation of LTD, independently of Nogo-66. Finally, our results indicate that Nogo-66 signaling limits LTP via the ROCK2-Cofilin pathway to control the dynamics of the actin cytoskeleton. The present results elucidate the signaling pathway activated by Nogo-66 to control LTP and contribute to the understanding of how Nogo-A stabilizes the neural circuits to limit activity-dependent plasticity events in the mature hippocampus.
Assuntos
Fatores de Despolimerização de Actina/metabolismo , Actinas/metabolismo , Plasticidade Neuronal/fisiologia , Proteínas Nogo/metabolismo , Transdução de Sinais/fisiologia , Quinases Associadas a rho/metabolismo , Fatores de Despolimerização de Actina/genética , Amidas/farmacologia , Animais , Biofísica , Estimulação Elétrica , Inibidores Enzimáticos/farmacologia , Feminino , Hipocampo , Técnicas In Vitro , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Plasticidade Neuronal/efeitos dos fármacos , Proteínas Nogo/antagonistas & inibidores , Proteínas Nogo/química , Técnicas de Patch-Clamp , Peptídeos/farmacologia , Fosforilação/efeitos dos fármacos , Fosforilação/fisiologia , Piridinas/farmacologia , Receptor de Fator de Crescimento Neural/deficiência , Receptor de Fator de Crescimento Neural/genética , Transdução de Sinais/efeitos dos fármacos , Fatores de Tempo , Quinases Associadas a rho/antagonistas & inibidores , Quinases Associadas a rho/genéticaRESUMO
When excited with rotating linear polarized light, differently oriented fluorescent dyes emit periodic signals peaking at different times. We show that measurement of the average orientation of fluorescent dyes attached to rigid sample structures mapped to regularly defined (50 nm)(2) image nanoareas can provide subdiffraction resolution (super resolution by polarization demodulation, SPoD). Because the polarization angle range for effective excitation of an oriented molecule is rather broad and unspecific, we narrowed this range by simultaneous irradiation with a second, de-excitation, beam possessing a polarization perpendicular to the excitation beam (excitation polarization angle narrowing, ExPAN). This shortened the periodic emission flashes, allowing better discrimination between molecules or nanoareas. Our method requires neither the generation of nanometric interference structures nor the use of switchable or blinking fluorescent probes. We applied the method to standard wide-field microscopy with camera detection and to two-photon scanning microscopy, imaging the fine structural details of neuronal spines.
Assuntos
Polarização de Fluorescência/métodos , Microscopia de Fluorescência/métodos , Nanotecnologia/métodos , Algoritmos , Animais , Células Cultivadas , Simulação por Computador , Células Epiteliais/metabolismo , Desenho de Equipamento , Corantes Fluorescentes/química , Proteínas de Fluorescência Verde/metabolismo , Microtúbulos/ultraestrutura , Modelos Teóricos , Nanosferas/química , Distribuição Normal , Fótons , Potoroidae , SoftwareRESUMO
Behavioral learning has been shown to involve changes in the function and structure of synaptic connections of the central nervous system (CNS). On the other hand, the neuronal circuitry in the mature brain is characterized by a high degree of stability possibly providing a correlate for long-term storage of information. This observation indicates the requirement for a set of molecules inhibiting plasticity and promoting stability thereby providing temporal and spatial specificity to plastic processes. Indeed, signaling of Nogo-A via its receptors has been shown to play a crucial role in restricting activity-dependent functional and structural plasticity in the adult CNS. However, whether Nogo-A controls learning and memory formation and what are the cellular and molecular mechanisms underlying this function is still unclear. Here we show that Nogo-A signaling controls spatial learning and reference memory formation upon training in the Morris water maze and negatively modulates structural changes at spines in the mouse hippocampus. Learning processes and the correlated structural plasticity have been shown to involve changes in excitatory as well as in inhibitory neuronal connections. We show here that Nogo-A is highly expressed not only in excitatory, but also in inhibitory, Parvalbumin positive neurons in the adult hippocampus. By this means our current and previous data indicate that Nogo-A loss-of-function positively influences spatial learning by priming the neuronal structure to a higher plasticity level. Taken together our results link the role of Nogo-A in negatively regulating plastic processes to a physiological function in controlling learning and memory processes in the mature hippocampus and open the interesting possibility that it might mainly act by controlling the function of the hippocampal inhibitory circuitry.
Assuntos
Hipocampo/metabolismo , Memória/fisiologia , Plasticidade Neuronal/fisiologia , Proteínas Nogo/metabolismo , Aprendizagem Espacial/fisiologia , Animais , Cognição/fisiologia , Espinhas Dendríticas/metabolismo , Masculino , Camundongos , Camundongos Knockout , Inibição Neural/fisiologia , Proteínas Nogo/genética , Parvalbuminas/metabolismoRESUMO
Nogo-A is a membrane protein of the central nervous system (CNS) restricting neurite growth and synaptic plasticity via two extracellular domains: Nogo-66 and Nogo-A-Δ20. Receptors transducing Nogo-A-Δ20 signaling remained elusive so far. Here we identify the G protein-coupled receptor (GPCR) sphingosine 1-phosphate receptor 2 (S1PR2) as a Nogo-A-Δ20-specific receptor. Nogo-A-Δ20 binds S1PR2 on sites distinct from the pocket of the sphingolipid sphingosine 1-phosphate (S1P) and signals via the G protein G13, the Rho GEF LARG, and RhoA. Deleting or blocking S1PR2 counteracts Nogo-A-Δ20- and myelin-mediated inhibition of neurite outgrowth and cell spreading. Blockade of S1PR2 strongly enhances long-term potentiation (LTP) in the hippocampus of wild-type but not Nogo-A(-/-) mice, indicating a repressor function of the Nogo-A/S1PR2 axis in synaptic plasticity. A similar increase in LTP was also observed in the motor cortex after S1PR2 blockade. We propose a novel signaling model in which a GPCR functions as a receptor for two structurally unrelated ligands, a membrane protein and a sphingolipid. Elucidating Nogo-A/S1PR2 signaling platforms will provide new insights into regulation of synaptic plasticity.
Assuntos
Hipocampo/metabolismo , Córtex Motor/metabolismo , Proteínas da Mielina/genética , Plasticidade Neuronal/genética , Receptores de Lisoesfingolipídeo/genética , Animais , Proliferação de Células , Subunidades alfa G12-G13 de Proteínas de Ligação ao GTP/genética , Subunidades alfa G12-G13 de Proteínas de Ligação ao GTP/metabolismo , Regulação da Expressão Gênica , Hipocampo/citologia , Potenciação de Longa Duração , Lisofosfolipídeos/metabolismo , Camundongos , Camundongos Knockout , Córtex Motor/citologia , Proteínas da Mielina/deficiência , Bainha de Mielina/genética , Bainha de Mielina/metabolismo , Neuritos/metabolismo , Proteínas Nogo , Pró-Proteína Convertases/genética , Pró-Proteína Convertases/metabolismo , Receptores de Lisoesfingolipídeo/antagonistas & inibidores , Receptores de Lisoesfingolipídeo/metabolismo , Serina Endopeptidases/genética , Serina Endopeptidases/metabolismo , Transdução de Sinais , Esfingosina/análogos & derivados , Esfingosina/metabolismo , Receptores de Esfingosina-1-Fosfato , Sinapses/metabolismo , Proteínas rho de Ligação ao GTP/genética , Proteínas rho de Ligação ao GTP/metabolismo , Proteína rhoA de Ligação ao GTPRESUMO
Nogo-A and its receptors have been shown to control synaptic plasticity, including negatively regulating long-term potentiation (LTP) in the cortex and hippocampus at a fast time scale and restraining experience-dependent turnover of dendritic spines over days. However, the molecular mechanisms and the precise time course mediating these actions of Nogo-A are largely unexplored. Here we show that Nogo-A signaling in the adult nervous system rapidly modulates the spine actin cytoskeleton within minutes to control structural plasticity at dendritic spines of CA3 pyramidal neurons. Indeed, acute Nogo-A loss-of-function transiently increases F-actin stability and results in an increase in dendritic spine density and length. In addition, Nogo-A acutely restricts AMPAR insertion and mEPSC amplitude at hippocampal synaptic sites. These data indicate a crucial function of Nogo-A in modulating the very tight balance between plasticity and stability of the neuronal circuitry underlying learning processes and the ability to store long-term information in the mature CNS. © 2016 Wiley Periodicals, Inc.
Assuntos
Actinas/metabolismo , Espinhas Dendríticas/metabolismo , Proteínas Nogo/metabolismo , Animais , Região CA3 Hipocampal/metabolismo , Células Cultivadas , Potenciais Pós-Sinápticos Excitadores/fisiologia , Camundongos Endogâmicos C57BL , Potenciais Pós-Sinápticos em Miniatura/fisiologia , Plasticidade Neuronal/fisiologia , Células Piramidais/fisiologia , Ratos Wistar , Receptores de AMPA/metabolismo , Técnicas de Cultura de TecidosRESUMO
The membrane protein Nogo-A is known as an inhibitor of axonal outgrowth and regeneration in the CNS. However, its physiological functions in the normal adult CNS remain incompletely understood. Here, we investigated the role of Nogo-A in cortical synaptic plasticity and motor learning in the uninjured adult rodent motor cortex. Nogo-A and its receptor NgR1 are present at cortical synapses. Acute treatment of slices with function-blocking antibodies (Abs) against Nogo-A or against NgR1 increased long-term potentiation (LTP) induced by stimulation of layer 2/3 horizontal fibers. Furthermore, anti-Nogo-A Ab treatment increased LTP saturation levels, whereas long-term depression remained unchanged, thus leading to an enlarged synaptic modification range. In vivo, intrathecal application of Nogo-A-blocking Abs resulted in a higher dendritic spine density at cortical pyramidal neurons due to an increase in spine formation as revealed by in vivo two-photon microscopy. To investigate whether these changes in synaptic plasticity correlate with motor learning, we trained rats to learn a skilled forelimb-reaching task while receiving anti-Nogo-A Abs. Learning of this cortically controlled precision movement was improved upon anti-Nogo-A Ab treatment. Our results identify Nogo-A as an influential molecular modulator of synaptic plasticity and as a regulator for learning of skilled movements in the motor cortex.
Assuntos
Aprendizagem/fisiologia , Potenciação de Longa Duração/fisiologia , Córtex Motor/fisiologia , Destreza Motora/fisiologia , Proteínas da Mielina/metabolismo , Animais , Masculino , Córtex Motor/metabolismo , Proteínas da Mielina/genética , Proteínas Nogo , Ratos , Ratos Sprague-Dawley , Sinapses/metabolismo , Sinapses/fisiologiaRESUMO
Whereas the role of NogoA in limiting axonal fiber growth and regeneration following an injury of the mammalian central nervous system (CNS) is well known, its physiological functions in the mature uninjured CNS are less well characterized. NogoA is mainly expressed by oligodendrocytes, but also by subpopulations of neurons, in particular in plastic regions of the CNS, e.g., in the hippocampus where it is found at synaptic sites. We analyzed synaptic transmission as well as long-term synaptic plasticity (long-term potentiation, LTP) in the presence of function blocking anti-NogoA or anti-Nogo receptor (NgR) antibodies and in NogoA KO mice. Whereas baseline synaptic transmission, short-term plasticity and long-term depression were not affected by either approach, long-term potentiation was significantly increased following NogoA or NgR1 neutralization. Synaptic potentiation thus seems to be restricted by NogoA. Surprisingly, synaptic weakening was not affected by interfering with NogoA signaling. Mechanistically of interest is the observation that by blockade of the GABA(A) receptors normal synaptic strengthening reoccurred in the absence of NogoA signaling. The present results show a unique role of NogoA expressed in the adult hippocampus in restricting physiological synaptic plasticity on a very fast time scale. NogoA could thus serve as an important negative regulator of functional and structural plasticity in mature neuronal networks.
Assuntos
Hipocampo/metabolismo , Potenciação de Longa Duração/fisiologia , Proteínas da Mielina/metabolismo , Plasticidade Neuronal/fisiologia , Oligodendroglia/metabolismo , Sinapses/metabolismo , Animais , Anticorpos Bloqueadores/farmacologia , Hipocampo/citologia , Potenciação de Longa Duração/efeitos dos fármacos , Camundongos , Camundongos Knockout , Proteínas da Mielina/antagonistas & inibidores , Proteínas da Mielina/genética , Plasticidade Neuronal/efeitos dos fármacos , Proteínas Nogo , Oligodendroglia/citologia , Transdução de Sinais/efeitos dos fármacos , Transdução de Sinais/fisiologia , Sinapses/genéticaRESUMO
Two profilin isoforms (PFN1 and PFN2a) are expressed in the mammalian brain. Although profilins are essential for regulating actin dynamics in general, the specific role of these isoforms in neurons has remained elusive. We show that knockdown of the neuron-specific PFN2a results in a significant reduction in dendrite complexity and spine numbers of hippocampal neurons. Overexpression of PFN1 in PFN2a-deficient neurons prevents the loss of spines but does not restore dendritic complexity. Furthermore, we show that profilins are involved in differentially regulating actin dynamics downstream of the pan-neurotrophin receptor (p75(NTR)), a receptor engaged in modulating neuronal morphology. Overexpression of PFN2a restores the morphological changes in dendrites caused by p75(NTR) overexpression, whereas PFN1 restores the normal spine density. Our data assign specific functions to the two PFN isoforms, possibly attributable to different affinities for potent effectors also involved in actin dynamics, and suggest that they are important for the signal-dependent fine-tuning of neuronal architecture.
Assuntos
Neurônios/citologia , Profilinas/fisiologia , Isoformas de Proteínas/fisiologia , Animais , Sequência de Bases , Técnicas de Silenciamento de Genes , Imuno-Histoquímica , Camundongos , Profilinas/genética , Isoformas de Proteínas/genética , Interferência de RNA , Transdução de SinaisRESUMO
Introduction: Alzheimer's disease (AD), is characterized by a gradual cognitive decline associated with the accumulation of Amyloid beta (Aß)-oligomers, progressive neuronal degeneration and chronic neuroinflammation. Among the receptors shown to bind and possibly transduce the toxic effects of Aß-oligomers is the p75 neurotrophin receptor (p75NTR). Interestingly, p75NTR mediates several crucial processes in the nervous system, including neuronal survival and apoptosis, maintenance of the neuronal architecture, and plasticity. Furthermore, p75NTR is also expressed in microglia, the resident immune cells of the brain, where it is markedly increased under pathological conditions. These observations indicate p75NTR as a potential candidate for mediating Aß-induced toxic effects at the interface between the nervous and the immune system, thereby potentially participating in the crosstalk between these two systems. Methods: Here we used APP/PS1 transgenic mice (APP/PS1tg) and compared the Aß-induced alterations in neuronal function, chronic inflammation as well as their cognitive consequences between 10 months old APP/PS1tg and APP/PS1tg x p75NTRexonIV knockout mice. Results: Electrophysiological recordings show that a loss of p75NTR rescues the impairment in long-term potentiation at the Schaffer collaterals in the hippocampus of APP/PS1tg mice. Interestingly, however loss of p75NTR does not influence the severity of neuroinflammation, microglia activation or the decline in spatial learning and memory processes observed in APP/PS1tg mice. Conclusion: Together these results indicate that while a deletion of p75NTR rescues the synaptic defect and the impairment in synaptic plasticity, it does not affect the progression of the neuroinflammation and the cognitive decline in a mouse model for AD.
RESUMO
Signaling of BDNF via its TrkB receptor is crucial in regulating several critical aspects of the architecture and function of neurons both during development and in the adult central nervous system. Indeed, several neurological conditions, such as neurodevelopmental and neurodegenerative disorders are associated with alterations both in the expression levels of BDNF and TrkB, and in their intracellular signaling. Thus, the possibility of promoting BDNF/TrkB signaling has become relevant as a potential therapeutic intervention for neurological disorders. However, the clinical potential of BDNF itself has been limited due to its restricted diffusion rate in biological tissue, poor bioavailability and pharmacological properties, as well as the potential for unwanted side effects due to its ability to also signal via the p75NTR pathway. Several small molecule and biologic drug candidate TrkB agonists have been developed and are reported to have effects in rescuing both the pathological alterations and disease related symptoms in mouse models of several neurological diseases. However, recent side-by-side comparative studies failed to show their specificity for activating TrkB signaling cascades, suggesting the need for the generation and validation of improved candidates. In the present study, we examine the ability of the novel, fully human TrkB agonist antibody ZEB85 to modulate the architecture, activity and synaptic plasticity of hippocampal murine neurons under physiological conditions. Moreover, we show here that ZEB85 prevents ß-amyloid toxicity in cultured hippocampal neurons, in a manner which is comparable to BDNF.
RESUMO
Although the role of myelin-derived Nogo-A as an inhibitor of axonal regeneration after CNS injury has been thoroughly described, its physiological function in the adult, uninjured CNS is less well known. We address this question in the hippocampus, where Nogo-A is expressed by neurons as well as oligodendrocytes. We used 21 d in vitro slice cultures of neonatal hippocampus where we applied different approaches to interfere with Nogo-A signaling and expression and analyze their effects on the dendritic and axonal architecture of pyramidal cells. Neutralization of Nogo-A by function-blocking antibodies induced a major alteration in the dendrite structure of hippocampal pyramidal neurons. Although spine density was not influenced by Nogo-A neutralization, spine type distribution was shifted toward a more immature phenotype. Axonal complexity and length were greatly increased. Nogo-A KO mice revealed a weak dendritic phenotype resembling the effect of the antibody treatment. To discriminate a possible cell-autonomous role of Nogo-A from an environmental, receptor-mediated function, we studied the effects of short hairpin RNA-induced knockdown of Nogo-A or NgR1, a prominent Nogo-A receptor, within individual neurons. Knockdown of Nogo-A reproduced part of the dendritic and none of the spine or axon alterations. However, downregulation of NgR1 replicated the dendritic, the axonal, and the spine alterations observed after Nogo-A neutralization. Together, our results demonstrate that Nogo-A plays a major role in stabilizing and maintaining the architecture of hippocampal pyramidal neurons. Mechanistically, although the majority of the activity of Nogo-A relies on a receptor-mediated mechanism involving NgR1, its cell-autonomous function plays a minor role.
Assuntos
Hipocampo/citologia , Hipocampo/crescimento & desenvolvimento , Proteínas da Mielina/fisiologia , Animais , Diferenciação Celular/genética , Forma Celular/genética , Células Cultivadas , Condicionamento Operante/fisiologia , Dendritos/metabolismo , Hipocampo/metabolismo , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Modelos Neurológicos , Proteínas da Mielina/antagonistas & inibidores , Proteínas da Mielina/metabolismo , Proteínas Nogo , Técnicas de Cultura de Órgãos , Estabilidade Proteica , Células Piramidais/citologia , Células Piramidais/metabolismo , Potenciais Sinápticos/genéticaRESUMO
Although brain-derived neurotrophic factor (BDNF) is linked with an increasing number of conditions causing brain dysfunction, its role in the postnatal CNS has remained difficult to assess. This is because the bdnf-null mutation causes the death of the animals before BDNF levels have reached adult levels. In addition, the anterograde axonal transport of BDNF complicates the interpretation of area-specific gene deletion. The present study describes the generation of a new conditional mouse mutant essentially lacking BDNF throughout the CNS. It shows that BDNF is not essential for prolonged postnatal survival, but that the behavior of such mutant animals is markedly altered. It also reveals that BDNF is not a major survival factor for most CNS neurons and for myelination of their axons. However, it is required for the postnatal growth of the striatum, and single-cell analyses revealed a marked decreased in dendritic complexity and spine density. In contrast, BDNF is dispensable for the growth of the hippocampus and only minimal changes were observed in the dendrites of CA1 pyramidal neurons in mutant animals. Spine density remained unchanged, whereas the proportion of the mushroom-type spine was moderately decreased. In line with these in vivo observations, we found that BDNF markedly promotes the growth of cultured striatal neurons and of their dendrites, but not of those of hippocampal neurons, suggesting that the differential responsiveness to BDNF is part of a neuron-intrinsic program.
Assuntos
Fator Neurotrófico Derivado do Encéfalo/metabolismo , Hipocampo/crescimento & desenvolvimento , Neostriado/crescimento & desenvolvimento , Animais , Contagem de Células , Células Cultivadas , Dendritos/metabolismo , Dendritos/ultraestrutura , Feminino , Hipocampo/citologia , Imuno-Histoquímica , Masculino , Camundongos , Camundongos Knockout , Neostriado/ultraestrutura , Neurônios/citologia , Neurônios/ultraestrutura , Oligodendroglia/citologia , Oligodendroglia/ultraestrutura , Nervo Óptico/crescimento & desenvolvimento , Nervo Óptico/ultraestrutura , Proteínas tau/metabolismoRESUMO
A tight regulation of the balance between inhibitory and excitatory synaptic transmission is a prerequisite for synaptic plasticity in neuronal networks. In this context, the neurite growth inhibitor membrane protein Nogo-A modulates synaptic plasticity, strength, and neurotransmitter receptor dynamics. However, the molecular mechanisms underlying these actions are unknown. We show that Nogo-A loss-of-function in primary mouse hippocampal cultures by application of a function-blocking antibody leads to higher excitation following a decrease in GABAARs at inhibitory and an increase in the GluA1, but not GluA2 AMPAR subunit at excitatory synapses. This unbalanced regulation of AMPAR subunits results in the incorporation of Ca2+-permeable GluA2-lacking AMPARs and increased intracellular Ca2+ levels due to a higher Ca2+ influx without affecting its release from the internal stores. Increased neuronal activation upon Nogo-A loss-of-function prompts the phosphorylation of the transcription factor CREB and the expression of c-Fos. These results contribute to the understanding of the molecular mechanisms underlying the regulation of the excitation/inhibition balance and thereby of plasticity in the brain.
Assuntos
Cálcio/metabolismo , Hipocampo/metabolismo , Neurônios/metabolismo , Proteínas Nogo/metabolismo , Animais , Potenciais Pós-Sinápticos Excitadores/fisiologia , Feminino , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Plasticidade Neuronal/fisiologia , Receptores de AMPA/metabolismo , Sinapses/metabolismo , Transmissão Sináptica/fisiologiaRESUMO
Synapse and dendritic spine loss induced by amyloid-ß oligomers is one of the main hallmarks of the early phases of Alzheimer's disease (AD) and is directly correlated with the cognitive decline typical of this pathology. The p75 neurotrophin receptor (p75NTR) binds amyloid-ß oligomers in the nM range. While it was shown that µM concentrations of amyloid-ß mediate cell death, the role and intracellular signaling of p75NTR for dendritic spine pathology induced by sublethal concentrations of amyloid-ß has not been analyzed. We describe here p75NTR as a crucial binding partner in mediating effects of soluble amyloid-ß oligomers on dendritic spine density and structure in non-apoptotic hippocampal neurons. Removing or over-expressing p75NTR in neurons rescues or exacerbates the typical loss of dendritic spines and their structural alterations observed upon treatment with nM concentrations of amyloid-ß oligomers. Moreover, we show that binding of amyloid-ß oligomers to p75NTR activates the RhoA/ROCK signaling cascade resulting in the fast stabilization of the actin spinoskeleton. Our results describe a role for p75NTR and downstream signaling events triggered by binding of amyloid-ß oligomers and causing dendritic spine pathology. These observations further our understanding of the molecular mechanisms underlying one of the main early neuropathological hallmarks of AD.