RESUMEN
Following spinal cord injury (SCI), astrocytes demonstrate long-lasting reactive changes, which are associated with the persistence of neuropathic pain and motor dysfunction. We previously demonstrated that upregulation of trkB.T1, a truncated isoform of the brain-derived neurotrophic factor receptor (BDNF), contributes to gliosis after SCI, but little is known about the effects of trkB.T1 on the function of astrocytes. As trkB.T1 is the sole isoform of trkB receptors expressed on astrocytes, we examined the function of trkB.T1-driven astrocytes in vitro and in vivo Immunohistochemistry showed that trkB.T1+ cells were significantly upregulated 7 d after injury, with sustained elevation in white matter through 8 weeks. The latter increase was predominantly found in astrocytes. TrkB.T1 was also highly expressed by neurons and microglia/macrophages at 7 d after injury and declined by 8 weeks. RNA sequencing of cultured astrocytes derived from trkB.T1+/+ (WT) and trkB.T1-/- (KO) mice revealed downregulation of migration and proliferation pathways in KO astrocytes. KO astrocytes also exhibited slower migration/proliferation in vitro in response to FBS or BDNF compared with WT astrocytes. Reduced proliferation of astrocytes was also confirmed after SCI in astrocyte-specific trkB.T1 KO mice; using mechanical allodynia and pain-related measurements on the CatWalk, these animals also showed reduced hyperpathic responses, along with improved motor coordination. Together, our data indicate that trkB.T1 in astrocytes contributes to neuropathic pain and neurological dysfunction following SCI, suggesting that trkB.T1 may provide a novel therapeutic target for SCI.SIGNIFICANCE STATEMENT Neuropathic pain after spinal cord injury (SCI) may in part be caused by upregulation of the brain-derived neurotrophic factor (BDNF) receptor trkB.T1, a truncated isoform of BDNF. TrkB.T1 is the only isoform of tropomyosin-related receptor kinase type B (trkB) receptors expressed on astrocytes. Here, we showed that trkB.T1 is significantly increased in the injured mouse spinal cord, where it is predominantly found in astrocytes. RNA sequencing of cultured astrocytes demonstrated downregulation of migration and proliferation pathways in trkB.T1 KO astrocytes. This was validated in vivo, where deletion of trkB.T1 in astrocytes reduced cell proliferation and migration. After SCI, astrocyte-specific trkB.T1 KO mice showed reduced hyperpathic responses and improved motor coordination. Therefore, the trkB.T1 receptor plays a significant pathophysiological role after SCI, and may provide a novel therapeutic target for SCI.
Asunto(s)
Astrocitos/metabolismo , Actividad Motora/fisiología , Neuralgia/metabolismo , Receptor trkB/metabolismo , Traumatismos de la Médula Espinal/metabolismo , Animales , Factor Neurotrófico Derivado del Encéfalo/metabolismo , Movimiento Celular/fisiología , Células Cultivadas , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Neuralgia/fisiopatología , Isoformas de Proteínas/metabolismo , Receptor trkB/deficiencia , Traumatismos de la Médula Espinal/fisiopatologíaRESUMEN
Brain-derived neurotrophic factor (BDNF) and its high affinity receptor, tropomyosin receptor kinase B (TrkB), have important roles in neural plasticity and are required for antidepressant efficacy. Studies examining the role of BDNF-TrkB signaling in depression and antidepressant efficacy have largely focused on the limbic system, leaving it unclear whether this signaling is important in other brain regions. BDNF and TrkB are both highly expressed in the dorsal raphe nucleus (DRN), a brain region that has been suggested to have a role in depression and antidepressant action, although it is unknown whether BDNF and TrkB in the dorsal raphe nucleus are involved in these processes. We combined the adeno-associated virus (AAV) with the Cre-loxP site-specific recombination system to selectively knock down either Bdnf or TrkB in the DRN. These mice were then characterized in several behavioral paradigms including measures of depression-related behavior and antidepressant efficacy. We show that knockdown of TrkB, but not Bdnf, in the DRN results in loss of antidepressant efficacy and increased aggression-related behavior. We also show that knockdown of TrkB or Bdnf in this brain region does not have an impact on weight, activity levels, anxiety, or depression-related behaviors. These data reveal a critical role for TrkB signaling in the DRN in mediating antidepressant responses and normal aggression behavior. The results also suggest a non-cell autonomous role for BDNF in the DRN in mediating antidepressant efficacy.
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Antidepresivos/farmacología , Conducta Animal/fisiología , Factor Neurotrófico Derivado del Encéfalo/metabolismo , Depresión/metabolismo , Núcleo Dorsal del Rafe/metabolismo , Receptor trkB/metabolismo , Transducción de Señal , Animales , Animales Modificados Genéticamente , Conducta Animal/efectos de los fármacos , Factor Neurotrófico Derivado del Encéfalo/deficiencia , Depresión/tratamiento farmacológico , Modelos Animales de Enfermedad , Núcleo Dorsal del Rafe/efectos de los fármacos , Masculino , Ratones , Receptor trkB/deficienciaRESUMEN
Third trimester-equivalent alcohol exposure causes significant deficits in hippocampal and cortical neuroplasticity, resulting in alterations to dendritic arborization, hippocampal adult neurogenesis, and performance on learning tasks. The current study investigated the impact of neonatal alcohol exposure (postnatal days 4-9, 5.25 g/kg/day) on expression of brain-derived neurotrophic factor (BDNF) and the tropomyosin-related kinase B (TrkB) receptor in the hippocampal and frontal cortex of infant Long-Evans rats. Levels of BDNF protein were increased in the hippocampus, but not frontal cortex, of alcohol-exposed rats 24h after the last dose, when compared with undisturbed (but not sham-intubated) control animals. BDNF protein levels showed a trend toward increase in hippocampus of sham-intubated animals as well, suggesting an effect of the intubation procedure. TrkB protein was increased in the hippocampus of alcohol-exposed animals compared to sham-intubated pups, indicating an alcohol-specific effect on receptor expression. In addition, expression of bdnf total mRNA in alcohol-exposed and sham-intubated pups was enhanced in the hippocampus; however, there was a differential effect of alcohol and intubation stress on exon I- and IV-specific mRNA transcripts. Further, plasma corticosterone was found to be increased in both alcohol-exposed and sham-intubated pups compared to undisturbed animals. Upregulation of BDNF could potentially represent a neuroprotective mechanism activated following alcohol exposure or stress. The results suggest that alcohol exposure and stress have both overlapping and unique effects on BDNF, and highlight the need for the stress of intubation to be taken into consideration in studies that implement this route of drug delivery.
Asunto(s)
Factor Neurotrófico Derivado del Encéfalo/metabolismo , Depresores del Sistema Nervioso Central/efectos adversos , Etanol/efectos adversos , Lóbulo Frontal/efectos de los fármacos , Regulación del Desarrollo de la Expresión Génica/efectos de los fármacos , Hipocampo/efectos de los fármacos , Efectos Tardíos de la Exposición Prenatal/patología , Receptor trkB/metabolismo , Factores de Edad , Animales , Animales Recién Nacidos , Peso Corporal/efectos de los fármacos , Factor Neurotrófico Derivado del Encéfalo/genética , Corticosterona/sangre , Ensayo de Inmunoadsorción Enzimática , Femenino , Lóbulo Frontal/crecimiento & desarrollo , Hipocampo/crecimiento & desarrollo , Masculino , Embarazo , ARN Mensajero/metabolismo , Ratas , Ratas Long-Evans , Receptor trkB/deficiencia , Estrés Psicológico/complicaciones , Estrés Psicológico/patologíaRESUMEN
Activity-dependent brain-derived neurotrophic factor (BDNF) signaling through receptor tyrosine kinase B (TrkB) is required for cued fear memory consolidation and extinction. Although BDNF is primarily secreted from glutamatergic neurons, TrkB is expressed by other genetically defined cells whose contributions to the behavioral effects of BDNF remain poorly understood. Parvalbumin (PV)-positive interneurons, which are highly enriched in TrkB, are emerging as key regulators of fear memory expression. We therefore hypothesized that activity-dependent BDNF signaling in PV-interneurons may modulate emotional learning. To test this hypothesis, we utilized the LoxP/Cre system for conditional deletion of TrkB in PV-positive cells to examine the impact of cell-autonomous BDNF signaling on Pavlovian fear conditioning and extinction. However, behavioral abnormalities indicative of vestibular dysfunction precluded the use of homozygous conditional knockouts in tests of higher cognitive functioning. While vestibular dysfunction was apparent in both sexes, female conditional knockouts exhibited an exacerbated phenotype, including extreme motor hyperactivity and circling behavior, compared to their male littermates. Heterozygous conditional knockouts were spared of vestibular dysfunction. While fear memory consolidation was unaffected in heterozygotes of both sexes, males exhibited impaired extinction consolidation compared to their littermate controls. Our findings complement evidence from human and rodent studies suggesting that BDNF signaling promotes consolidation of extinction and point to PV-positive neurons as a discrete population that mediates these effects in a sex-specific manner.
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Conducta Animal/fisiología , Interneuronas/metabolismo , Parvalbúminas/metabolismo , Fenotipo , Receptor trkB/deficiencia , Caracteres Sexuales , Animales , Proteínas Bacterianas/genética , Proteínas Bacterianas/metabolismo , Encéfalo/citología , Factor Neurotrófico Derivado del Encéfalo/metabolismo , Conducta Exploratoria/fisiología , Extinción Psicológica/fisiología , Femenino , Discapacidades para el Aprendizaje/genética , Proteínas Luminiscentes/genética , Proteínas Luminiscentes/metabolismo , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Parvalbúminas/genética , Receptor trkB/genética , Transducción de Señal/genética , Trastorno de Movimiento Estereotipado/genética , Enfermedades Vestibulares/genéticaRESUMEN
Existing models of Huntington's disease posit that deficits in BDNF delivery to the striatum contribute to atrophy and motor impairment. In this issue of Neuron, Plotkin et al. (2014) show that BDNF delivery is normal but downstream signaling via TrkB and p75 is impaired, leading to corticostriatal synaptic dysfunction.
Asunto(s)
Corteza Cerebral/fisiopatología , Cuerpo Estriado/fisiopatología , Modelos Animales de Enfermedad , Enfermedad de Huntington/fisiopatología , Receptor trkB/deficiencia , Transducción de Señal/genética , AnimalesRESUMEN
Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder. The debilitating choreic movements that plague HD patients have been attributed to striatal degeneration induced by the loss of cortically supplied brain-derived neurotrophic factor (BDNF). Here, we show that in mouse models of early symptomatic HD, BDNF delivery to the striatum and its activation of tyrosine-related kinase B (TrkB) receptors were normal. However, in striatal neurons responsible for movement suppression, TrkB receptors failed to properly engage postsynaptic signaling mechanisms controlling the induction of potentiation at corticostriatal synapses. Plasticity was rescued by inhibiting p75 neurotrophin receptor (p75NTR) signaling or its downstream target phosphatase-and-tensin-homolog-deleted-on-chromosome-10 (PTEN). Thus, corticostriatal synaptic dysfunction early in HD is attributable to a correctable defect in the response to BDNF, not its delivery.
Asunto(s)
Corteza Cerebral/fisiopatología , Cuerpo Estriado/fisiopatología , Modelos Animales de Enfermedad , Enfermedad de Huntington/fisiopatología , Receptor trkB/deficiencia , Transducción de Señal/genética , Animales , Corteza Cerebral/patología , Cuerpo Estriado/patología , Técnicas de Sustitución del Gen , Enfermedad de Huntington/genética , Enfermedad de Huntington/patología , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Técnicas de Cultivo de Órganos , Receptor trkB/antagonistas & inhibidores , Receptor trkB/fisiologíaRESUMEN
BACKGROUND: The high affinity tyrosine kinase receptor, TrkB, is the primary receptor for brain derived neurotrophic factor (BDNF) and plays an important role in development, maintenance and plasticity of the striatal output medium size spiny neuron. The striatal BDNF/TrkB system is thereby implicated in many physiologic and pathophysiologic processes, the latter including mood disorders, addiction, and Huntington's disease. We crossed a mouse harboring a transgene directing cre-recombinase expression primarily to postnatal, dorsal striatal medium spiny neurons, to a mouse containing a floxed TrkB allele (fB) mouse designed for deletion of TrkB to determine its role in the adult striatum. RESULTS: We found that there were sexually dimorphic alterations in behaviors in response to stressful situations and drugs of abuse. Significant sex and/or genotype differences were found in the forced swim test of depression-like behaviors, anxiety-like behaviors on the elevated plus maze, and cocaine conditioned reward. Microarray analysis of dorsal striatum revealed significant dysregulation in individual and groups of genes that may contribute to the observed behavioral responses and in some cases, represent previously unidentified downstream targets of TrkB. CONCLUSIONS: The data point to a set of behaviors and changes in gene expression following postnatal deletion of TrkB in the dorsal striatum distinct from those in other brain regions.
Asunto(s)
Conducta Animal/fisiología , Cuerpo Estriado/metabolismo , Neuronas/metabolismo , Receptor trkB/deficiencia , Receptor trkB/genética , Envejecimiento , Animales , Western Blotting , Femenino , Técnicas de Silenciamiento del Gen , Hibridación in Situ , Masculino , Ratones , Ratones Transgénicos , Análisis de Secuencia por Matrices de Oligonucleótidos , Transducción de Señal/genética , TranscriptomaRESUMEN
Neurotrophins (NTs) play essential roles in the development and survival of neurons in PNS and CNS. In the cochlea, NTs [e.g., NT-3, brain-derived neurotrophic factor (BDNF)] are required for the survival of spiral ganglion neurons (SGNs). Preservation of SGNs in the cochlea of patients suffering sensorineural deafness caused by loss of hair cells is needed for the optimal performance of the cochlear implant. Directly applying exogenous BDNF into the cochlea prevents secondary degeneration of SGNs when hair cells are lost. However, a common translational barrier for in vivo applications of BDNF is the poor pharmacokinetics, which severely limits the efficacy. Here we report that 7,8-dihydroxyflavone and 7,8,3'-trihydroxyflavone, both small-molecule agonists of tyrosine receptor kinase B (TrkB), promoted SGN survival with high potency both in vitro and in vivo. These compounds increased the phosphorylated TrkB and downstream MAPK and protected the SGNs in a TrkB-dependent manner. Their applications in the bulla of conditional connexin26 null mice offered significant protection for SGN survival. The function of survived SGNs was assessed by measuring evoked action potentials (APs) in vitro and electrically evoked auditory brainstem response (eABR) thresholds in vivo. APs were reliably evoked in cultured single SGNs treated with the compounds. In addition, eABR thresholds measured from the treated cochleae were significantly lower than untreated controls. Our findings suggest that these novel small-molecule TrkB agonists are promising in vivo therapeutic agents for preventing degeneration of SGNs.
Asunto(s)
Flavonas/uso terapéutico , Degeneración Nerviosa/prevención & control , Neuronas/efectos de los fármacos , Receptor trkB/agonistas , Potenciales de Acción/efectos de los fármacos , Potenciales de Acción/genética , Animales , Animales Recién Nacidos , Antibacterianos/toxicidad , Factor Neurotrófico Derivado del Encéfalo/farmacología , Cóclea/citología , Cóclea/efectos de los fármacos , Conexina 26 , Conexinas/genética , Relación Dosis-Respuesta a Droga , Potenciales Evocados Auditivos del Tronco Encefálico/efectos de los fármacos , Potenciales Evocados Auditivos del Tronco Encefálico/genética , Femenino , Flavonas/farmacología , Gentamicinas/toxicidad , Técnicas In Vitro , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Quinasas de Proteína Quinasa Activadas por Mitógenos/metabolismo , Degeneración Nerviosa/inducido químicamente , Degeneración Nerviosa/genética , Factores de Crecimiento Nervioso/farmacología , Neuritas/efectos de los fármacos , Neuronas/citología , Fosforilación/efectos de los fármacos , Receptor trkB/deficiencia , Receptor trkB/metabolismo , Ganglio Espiral de la Cóclea/citología , Tubulina (Proteína)/metabolismoRESUMEN
Abnormal glucocorticoid and neurotrophin signaling has been implicated in numerous psychiatric disorders. However, the impact of neurotrophic signaling on glucocorticoid receptor (GR)-dependent gene expression is not understood. We therefore examined the impact of brain-derived neurotrophic factor (BDNF) signaling on GR transcriptional regulatory function by gene expression profiling in primary rat cortical neurons stimulated with the selective GR agonist dexamethasone (Dex) and BDNF, alone or in combination. Simultaneous treatment with BDNF and Dex elicited a unique set of GR-responsive genes associated with neuronal growth and differentiation and also enhanced the induction of a large number of Dex-sensitive genes. BDNF via its receptor TrkB enhanced the transcriptional activity of a synthetic GR reporter, suggesting a direct effect of BDNF signaling on GR function. Indeed, BDNF treatment induces the phosphorylation of GR at serine 155 (S155) and serine 287 (S287). Expression of a nonphosphorylatable mutant (GR S155A/S287A) impaired the induction of a subset of BDNF- and Dex-regulated genes. Mechanistically, BDNF-induced GR phosphorylation increased GR occupancy and cofactor recruitment at the promoter of a BDNF-enhanced gene. GR phosphorylation in vivo is sensitive to changes in the levels of BDNF and TrkB as well as stress. Therefore, BDNF signaling specifies and amplifies the GR transcriptome through a coordinated GR phosphorylation-dependent detection mechanism.
Asunto(s)
Factor Neurotrófico Derivado del Encéfalo/metabolismo , Glucocorticoides/metabolismo , Receptores de Glucocorticoides/metabolismo , Animales , Evolución Biológica , Factor Neurotrófico Derivado del Encéfalo/deficiencia , Factor Neurotrófico Derivado del Encéfalo/genética , Células Cultivadas , Secuencia Conservada , Proteína de Unión a Elemento de Respuesta al AMP Cíclico/metabolismo , Dexametasona/farmacología , Glucocorticoides/genética , Células HEK293 , Humanos , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Mutagénesis Sitio-Dirigida , Neuronas/metabolismo , Fosforilación , Regiones Promotoras Genéticas , Ratas , Receptor trkB/deficiencia , Receptor trkB/genética , Receptor trkB/metabolismo , Receptores de Glucocorticoides/deficiencia , Receptores de Glucocorticoides/genética , Transducción de Señal , TranscriptomaRESUMEN
In the adult rodent brain, the olfactory bulb (OB) is continuously supplied with new neurons which survival critically depends on their successful integration into pre-existing networks. Yet, the extracellular signals that determine the selection which neurons will be ultimately incorporated into these circuits are largely unknown. Here, we show that immature neurons express the catalytic form of the brain-derived neurotrophic factor receptor TrkB [full-length TrkB (TrkB-FL)] only after their arrival in the OB, at the time when integration commences. To unravel the role of TrkB signaling in newborn neurons, we conditionally ablated TrkB-FL in mice via Cre expression in adult neural stem and progenitor cells. TrkB-deficient neurons displayed a marked impairment in dendritic arborization and spine growth. By selectively manipulating the signaling pathways initiated by TrkB in vivo, we identified the transducers Shc/PI3K to be required for dendritic growth, whereas the activation of phospholipase C-γ was found to be responsible for spine formation. Furthermore, long-term genetic fate mapping revealed that TrkB deletion severely compromised the survival of new dopaminergic neurons, leading to a substantial reduction in the overall number of adult-generated periglomerular cells (PGCs), but not of granule cells (GCs). Surprisingly, this loss of dopaminergic PGCs was mirrored by a corresponding increase in the number of calretinin+ PGCs, suggesting that distinct subsets of adult-born PGCs may respond differentially to common extracellular signals. Thus, our results identify TrkB signaling to be essential for balancing the incorporation of defined classes of adult-born PGCs and not GCs, reflecting their different mode of integration in the OB.
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Células Madre Adultas/fisiología , Células-Madre Neurales/fisiología , Neurogénesis/fisiología , Bulbo Olfatorio/citología , Bulbo Olfatorio/crecimiento & desarrollo , Receptor trkB/fisiología , Transducción de Señal/fisiología , Factores de Edad , Animales , Animales Recién Nacidos , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , ARN Mensajero/biosíntesis , ARN Mensajero/genética , Receptor trkB/deficiencia , Receptor trkB/genéticaRESUMEN
Neurotrophin growth factors support neuronal survival and function. In this study, we show that the expression of the neurotrophin receptor TrkB is induced on astrocytes in white matter lesions in multiple sclerosis (MS) patients and mice with experimental autoimmune encephalomyelitis (EAE). Surprisingly, mice lacking TrkB specifically in astrocytes were protected from EAE-induced neurodegeneration. In an in vitro assay, astrocytes stimulated with the TrkB agonist brain-derived neurotrophic factor (BDNF) released nitric oxide (NO), and conditioned medium from activated astrocytes had detrimental effects on the morphology and survival of neurons. This neurodegenerative process was amplified by NO produced by neurons. NO synthesis in the central nervous system during EAE depended on astrocyte TrkB. Together, these findings suggest that TrkB expression on astrocytes may represent a new target for neuroprotective therapies in MS.
Asunto(s)
Astrocitos/metabolismo , Astrocitos/patología , Degeneración Nerviosa/etiología , Óxido Nítrico/biosíntesis , Receptor trkB/metabolismo , Adulto , Anciano , Animales , Astrocitos/efectos de los fármacos , Factor Neurotrófico Derivado del Encéfalo/metabolismo , Factor Neurotrófico Derivado del Encéfalo/farmacología , Estudios de Casos y Controles , Células Cultivadas , Encefalomielitis Autoinmune Experimental/metabolismo , Encefalomielitis Autoinmune Experimental/patología , Femenino , Humanos , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Persona de Mediana Edad , Esclerosis Múltiple/metabolismo , Esclerosis Múltiple/patología , Degeneración Nerviosa/metabolismo , Degeneración Nerviosa/patología , Receptor de Factor de Crecimiento Nervioso/metabolismo , Receptor trkB/deficiencia , Receptor trkB/genética , Regulación hacia ArribaRESUMEN
Brain-derived neurotrophic factor (BDNF) signalling through its receptor, TrkB is known to regulate GABAergic function and glutamic acid decarboxylase (GAD) 67 expression in neurons. Alterations in BDNF signalling have been implicated in the pathophysiology of schizophrenia and as a result, they are a potential therapeutic target. Interestingly, heterozygous reeler mice (HRM) have decreased GAD67 expression in the frontal cortex and hippocampus and they exhibit many behavioural and neurochemical abnormalities similar to schizophrenia. In this study, we evaluated the potential of cysteamine, a neuroprotective compound to improve the deficits in GAD67 expression and cognitive function in HRM. We found that cysteamine administration (150 mg/kg.d, through drinking water) for 30 d significantly ameliorated the decreases in GAD67, mature BDNF and full-length TrkB protein levels found in frontal cortex and hippocampus of HRM. A significant attenuation of the increased levels of truncated BDNF in frontal cortex and hippocampus, as well as truncated TrkB in frontal cortex of HRM was also observed following cysteamine treatment. In behavioural studies, HRM were impaired in a Y-maze spatial recognition memory task, but not in a spontaneous alternation task or a sensorimotor, prepulse inhibition (PPI) procedure. Cysteamine improved Y-maze spatial recognition in HRM to the level of wide-type controls and it improved PPI in both wild-type and HRM. Finally, mice deficient in TrkB, showed a reduced response to cysteamine in GAD67 expression suggesting that TrkB signalling plays an important role in GAD67 regulation by cysteamine.
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Cisteamina/farmacología , Regulación de la Expresión Génica/efectos de los fármacos , Glutamato Descarboxilasa/metabolismo , Memoria/efectos de los fármacos , Percepción Espacial/efectos de los fármacos , Estimulación Acústica/efectos adversos , Análisis de Varianza , Animales , Lóbulo Frontal/efectos de los fármacos , Lóbulo Frontal/metabolismo , Regulación de la Expresión Génica/genética , Glutamato Descarboxilasa/genética , Heterocigoto , Hipocampo/efectos de los fármacos , Hipocampo/metabolismo , Masculino , Aprendizaje por Laberinto/efectos de los fármacos , Ratones , Ratones Noqueados , Ratones Mutantes Neurológicos , Receptor trkB/deficiencia , Receptor trkB/metabolismo , Filtrado Sensorial/efectos de los fármacos , Filtrado Sensorial/genética , Factores de TiempoRESUMEN
Neurotrophin-dependent activation of the tyrosine kinase receptor trkB.FL modulates neuromuscular synapse maintenance and function; however, it is unclear what role the alternative splice variant, truncated trkB (trkB.T1), may have in the peripheral neuromuscular axis. We examined this question in trkB.T1 null mice and demonstrate that in vivo neuromuscular performance and nerve-evoked muscle tension are significantly increased. In vitro assays indicated that the gain-in-function in trkB.T1(-/-) animals resulted specifically from an increased muscle contractility, and increased electrically evoked calcium release. In the trkB.T1 null muscle, we identified an increase in Akt activation in resting muscle as well as a significant increase in trkB.FL and Akt activation in response to contractile activity. On the basis of these findings, we conclude that the trkB signaling pathway might represent a novel target for intervention across diseases characterized by deficits in neuromuscular function.
Asunto(s)
Contracción Muscular/genética , Unión Neuromuscular/genética , Receptor trkB/deficiencia , Receptor trkB/genética , Animales , Calcio/metabolismo , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Actividad Motora/genética , Actividad Motora/fisiología , Contracción Muscular/fisiología , Unión Neuromuscular/fisiología , Receptor trkB/fisiologíaRESUMEN
Although brain-derived neurotrophic factor (BDNF) is known to regulate circuit development and synaptic plasticity, its exact role in neuronal network activity remains elusive. Using mutant mice (TrkB-PV(-/-)) in which the gene for the BDNF receptor, tyrosine kinase B receptor (trkB), has been specifically deleted in parvalbumin-expressing, fast-spiking GABAergic (PV+) interneurons, we show that TrkB is structurally and functionally important for the integrity of the hippocampal network. The amplitude of glutamatergic inputs to PV+ interneurons and the frequency of GABAergic inputs to excitatory pyramidal cells were reduced in the TrkB-PV(-/-) mice. Functionally, rhythmic network activity in the gamma-frequency band (30-80 Hz) was significantly decreased in hippocampal area CA1. This decrease was caused by a desynchronization and overall reduction in frequency of action potentials generated in PV+ interneurons of TrkB-PV(-/-) mice. Our results show that the integration of PV+ interneurons into the hippocampal microcircuit is impaired in TrkB-PV(-/-) mice, resulting in decreased rhythmic network activity in the gamma-frequency band.
Asunto(s)
Región CA1 Hipocampal/fisiología , Interneuronas/fisiología , Receptor trkB/fisiología , Potenciales de Acción , Animales , Factor Neurotrófico Derivado del Encéfalo/fisiología , Región CA1 Hipocampal/citología , Recuento de Células , Dendritas/fisiología , Neuronas GABAérgicas/fisiología , Ratones , Ratones Noqueados , Red Nerviosa/citología , Red Nerviosa/fisiología , Parvalbúminas/metabolismo , Receptor trkB/deficiencia , Receptor trkB/genética , Transducción de Señal , Transmisión Sináptica/fisiologíaRESUMEN
The pathological hallmark of Parkinson's disease (PD) is a selective and progressive loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNc). In the vast majority of cases the appearance of PD is sporadic, and its etiology remains unknown. Several postmortem studies demonstrate reduced levels of brain-derived neurotrophic factor (BDNF) in the SNc of PD patients. Application of BDNF promotes the survival of DA neurons in PD animal models. Here we show that BDNF signaling via its TrkB receptor tyrosine kinase is important for survival of nigrostriatal DA neurons in aging brains. Immunohistochemistry revealed that the TrkB receptor was expressed in DA neurons located in the SNc and ventral tegmental area (VTA). However, a significant loss of DA neurons occurred at 12-24 months of age only in the SNc but not in the VTA of TrkB hypomorphic mice in which the TrkB receptor was expressed at a quarter to a third of the normal amount. The neuronal loss was accompanied by a decrease in dopaminergic axonal terminals in the striatum and by gliosis in both the SNc and striatum. Furthermore, nigrostriatal DA neurons in the TrkB mutant mice were hypersensitive to the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a mitochondrial complex I inhibitor that selectively kills DA neurons. These results suggest that BDNF-to-TrkB signaling plays an important role in the long-term maintenance of the nigrostriatal system and that its deficiency may contribute to the progression of PD.
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Cuerpo Estriado/metabolismo , Dopamina/metabolismo , Degeneración Nerviosa/metabolismo , Receptor trkB/deficiencia , Transducción de Señal/genética , Sustancia Negra/metabolismo , Animales , Cuerpo Estriado/patología , Ratones , Ratones de la Cepa 129 , Ratones Endogámicos C57BL , Ratones Mutantes Neurológicos , Degeneración Nerviosa/patología , Enfermedad de Parkinson/metabolismo , Enfermedad de Parkinson/patología , Distribución Aleatoria , Receptor trkB/biosíntesis , Sustancia Negra/patología , Factores de TiempoRESUMEN
Head and neck squamous cell carcinoma (HNSCC) remains a significant public health problem, accounting for over 5% of all cancer-related deaths, and these deaths primarily result from metastatic disease. The molecular processes involved in HNSCC pathogenesis and progression are poorly understood, and here we present experimental evidence for a direct role of the cell surface receptor tyrosine kinase, TrkB, in HNSCC tumor progression. Using immunohistochemical analysis and transcriptional profiling of archival HNSCC tumor specimens, we found that TrkB and its secreted ligand, brain-derived neurotrophic factor (BDNF), are expresses in greater than 50% of human HNSCC tumors, but not in normal upper aerodigestive tract (UADT) epithelia. Studies with HNSCC cell lines reveal that in vitro stimulation with BDNF, the ligand for TrkB, upregulates the migration and invasion of HNSCC cells, and both transient and stable suppressions of TrkB result in significant abrogation of constitutive and ligand-mediated migration and invasion. Furthermore, enforced overexpression of TrkB results in altered expression of molecular mediators of epithelial-to-mesenchymal transition (EMT), including downregulation of E-cadherin and upregulation of Twist. Using an in vivo mouse model of HNSCC, we were able to show that downregulation of TrkB suppresses tumor growth. These results directly implicate TrkB in EMT and the invasive behavior of HNSCC, and correlate with the in vivo overexpression of TrkB in human HNSCC. Taken together, these data suggest that the TrkB receptor may be a critical component in the multi-step tumor progression of HNSCC, and may be an attractive target for much needed new therapies for this disease.
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Carcinoma de Células Escamosas/patología , Transformación Celular Neoplásica , Células Epiteliales/patología , Neoplasias de Cabeza y Cuello/patología , Mesodermo/patología , Receptor trkB/metabolismo , Animales , Factor Neurotrófico Derivado del Encéfalo/metabolismo , Carcinoma de Células Escamosas/genética , Carcinoma de Células Escamosas/metabolismo , Diferenciación Celular , Línea Celular Tumoral , Quimiotaxis , Progresión de la Enfermedad , Regulación hacia Abajo , Activación Enzimática , Regulación Neoplásica de la Expresión Génica , Técnicas de Silenciamiento del Gen , Neoplasias de Cabeza y Cuello/genética , Neoplasias de Cabeza y Cuello/metabolismo , Humanos , Ligandos , Masculino , Ratones , Invasividad Neoplásica , Proteínas Proto-Oncogénicas c-akt/metabolismo , Receptor trkB/deficiencia , Receptor trkB/genética , Transducción de Señal , Regulación hacia ArribaRESUMEN
TrkB is an important receptor for brain-derived neurotrophic factor and NT4, members of the neurotrophin family. TrkB signaling is crucial in many activity-dependent and activity-independent processes of neural development. Here, we investigate the role of trkB signaling in the development of two distinct, organizational features of retinal projections--the segregation of crossed and uncrossed retinal inputs along the "lines of projection" that represent a single point in the visual field and the "retinotopic" mapping of retinofugal axons within their cerebral targets. Using anterograde tracing, we obtained quantitative measures of the distribution of retinal projections in the dorsal nucleus of the lateral geniculate body (LGd) and superior colliculus (SC) of wild-type mice and mice homozygous for constitutive null mutation (knockout) of the full-length trkB receptor (trkB(FL)(-/-)). In trkB(FL)(-/-) mice, uncrossed retinal projections cluster normally but there is a topographic expansion in the distribution of these clusters across the SC. By contrast, the absence of trkB signaling has no significant effect on the segregation of crossed and uncrossed retinal projections along the lines of projection in LGd or SC. We conclude that the normal topographic organization of uncrossed retinal projections depends upon trkB signaling, whereas the segregation of crossed and uncrossed retinal projections is trkB-independent. We also found that in trkB(FL)(-/-) mice, neuronal number was reduced in the LGd and SC and in the caudate-putamen. Previous studies by ourselves and others have shown that the number of retinal ganglion cells (RGCs) is unchanged in trkB(FL)(-/-) mice. Together, these results demonstrate that there is no matching of the numbers of RGCs with neuronal numbers in the LGd or SC.
Asunto(s)
Mapeo Encefálico , Lateralidad Funcional/fisiología , Receptor trkB/deficiencia , Receptor trkB/genética , Retina/fisiología , Vías Visuales/fisiología , Animales , Animales Recién Nacidos , Recuento de Células/métodos , Toxina del Cólera/metabolismo , Cuerpos Geniculados/citología , Cuerpos Geniculados/fisiología , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Microscopía Confocal , Colículos Superiores/citología , Colículos Superiores/fisiologíaRESUMEN
Pathological or in vitro overexpression of the truncated TrkB (TrkB.T1) receptor inhibits signaling through the full-length TrkB (TrkB.FL) tyrosine kinase receptor. However, to date, the role of endogenous TrkB.T1 is still unknown. By studying mice lacking the truncated TrkB.T1 isoform but retaining normal spatiotemporal expression of TrkB.FL, we have analyzed TrkB.T1-specific physiological functions and its effect on endogenous TrkB kinase signaling in vivo. We found that TrkB.T1-deficient mice develop normally but show increased anxiety in association with morphological abnormalities in the length and complexity of neurites of neurons in the basolateral amygdala. However, no behavioral abnormalities were detected in hippocampal-dependent memory tasks, which correlated with lack of any obvious hippocampal morphological deficits or alterations in basal synaptic transmission and long-term potentiation. In vivo reduction of TrkB signaling by removal of one BDNF allele could be partially rescued by TrkB.T1 deletion, which was revealed by an amelioration of the enhanced aggression and weight gain associated with BDNF haploinsufficiency. Our results suggest that, at the physiological level, TrkB.T1 receptors are important regulators of TrkB.FL signaling in vivo. Moreover, TrkB.T1 selectively affects dendrite complexity of certain neuronal populations.
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Encéfalo/anomalías , Encéfalo/anatomía & histología , Mutación , Neuronas/fisiología , Receptor trkB/genética , Animales , Peso Corporal/genética , Encéfalo/ultraestructura , Factor Neurotrófico Derivado del Encéfalo/genética , Condicionamiento Psicológico/fisiología , Conducta Exploratoria/fisiología , Miedo , Hipocampo/citología , Técnicas In Vitro , Aprendizaje por Laberinto/fisiología , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Receptor trkB/deficiencia , Tinción con Nitrato de Plata/métodosRESUMEN
Adult hippocampal neurogenesis is stimulated by chronic administration of antidepressants (ADs) and by voluntary exercise. Neural progenitor cells (NPCs) in the dentate gyrus (DG) that are capable of continuous proliferation and neuronal differentiation are the source of such structural plasticity. Here we report that mice lacking the receptor tyrosine kinase TrkB in hippocampal NPCs have impaired proliferation and neurogenesis. When exposed to chronic ADs or wheel-running, no increase in proliferation or neurogenesis is observed. Ablation of TrkB also renders these mice behaviorally insensitive to antidepressive treatment in depression- and anxiety-like paradigms. In contrast, mice lacking TrkB only in differentiated DG neurons display typical neurogenesis and respond normally to chronic ADs. Thus, our data establish an essential cell-autonomous role for TrkB in regulating hippocampal neurogenesis and behavioral sensitivity to antidepressive treatments, and support the notion that impairment of the neurogenic niche is an etiological factor for refractory responses to an antidepressive regimen.
Asunto(s)
Antidepresivos/farmacología , Diferenciación Celular/efectos de los fármacos , Proliferación Celular/efectos de los fármacos , Hipocampo/citología , Neuronas/efectos de los fármacos , Receptor trkB/fisiología , Células Madre Adultas , Animales , Animales Recién Nacidos , Conducta Animal , Factor Neurotrófico Derivado del Encéfalo/metabolismo , Ensayo de Inmunoadsorción Enzimática/métodos , Antagonistas de Estrógenos/farmacología , Citometría de Flujo/métodos , Proteínas Fluorescentes Verdes/biosíntesis , Proteínas Fluorescentes Verdes/genética , Proteínas de Filamentos Intermediarios/genética , Proteínas de Filamentos Intermediarios/metabolismo , Ratones , Ratones Transgénicos , Actividad Motora/efectos de los fármacos , Actividad Motora/genética , Proteínas del Tejido Nervioso/genética , Proteínas del Tejido Nervioso/metabolismo , Nestina , Receptor trkB/deficiencia , Tamoxifeno/farmacologíaRESUMEN
BDNF signaling through its TrkB receptor plays a pivotal role in activity-dependent refinement of synaptic connectivity of retinal ganglion cells. Additionally, studies using TrkB knockout mice have suggested that BDNF/TrkB signaling is essential for the development of photoreceptors and for synaptic communication between photoreceptors and second order retinal neurons. Thus the action of BDNF on refinement of synaptic connectivity of retinal ganglion cells could be a direct effect in the inner retina, or it could be secondary to its proposed role in rod maturation and in the formation of rod to bipolar cell synaptic transmission. To address this matter we have conditionally eliminated TrkB within the retina. We find that rod function and synaptic transmission to bipolar cells is not compromised in these conditional knockout mice. Consistent with previous work, we find that inner retina neural development is regulated by retinal BDNF/TrkB signaling. Specifically we show here also that the complexity of neuronal processes of dopaminergic cells is reduced in conditional TrkB knockout mice. We conclude that retinal BDNF/TrkB signaling has its primary role in the development of inner retinal neuronal circuits, and that this action is not a secondary effect due to the loss of visual signaling in the outer retina.