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INTRODUCTION: Tropomyosin related kinase B (TrkB) and C (TrkC) receptor signaling promotes synaptic plasticity and interacts with pathways affected by amyloid beta (Aß) toxicity. Upregulating TrkB/C signaling could reduce Alzheimer's disease (AD)-related degenerative signaling, memory loss, and synaptic dysfunction. METHODS: PTX-BD10-2 (BD10-2), a small molecule TrkB/C receptor partial agonist, was orally administered to aged London/Swedish-APP mutant mice (APPL/S) and wild-type controls. Effects on memory and hippocampal long-term potentiation (LTP) were assessed using electrophysiology, behavioral studies, immunoblotting, immunofluorescence staining, and RNA sequencing. RESULTS: In APPL/S mice, BD10-2 treatment improved memory and LTP deficits. This was accompanied by normalized phosphorylation of protein kinase B (Akt), calcium-calmodulin-dependent kinase II (CaMKII), and AMPA-type glutamate receptors containing the subunit GluA1; enhanced activity-dependent recruitment of synaptic proteins; and increased excitatory synapse number. BD10-2 also had potentially favorable effects on LTP-dependent complement pathway and synaptic gene transcription. DISCUSSION: BD10-2 prevented APPL/S/Aß-associated memory and LTP deficits, reduced abnormalities in synapse-related signaling and activity-dependent transcription of synaptic genes, and bolstered transcriptional changes associated with microglial immune response. HIGHLIGHTS: Small molecule modulation of tropomyosin related kinase B (TrkB) and C (TrkC) restores long-term potentiation (LTP) and behavior in an Alzheimer's disease (AD) model. Modulation of TrkB and TrkC regulates synaptic activity-dependent transcription. TrkB and TrkC receptors are candidate targets for translational therapeutics. Electrophysiology combined with transcriptomics elucidates synaptic restoration. LTP identifies neuron and microglia AD-relevant human-mouse co-expression modules.
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Enfermedad de Alzheimer , Microglía , Receptor trkB , Sinapsis , Animales , Masculino , Ratones , Enfermedad de Alzheimer/tratamiento farmacológico , Modelos Animales de Enfermedad , Hipocampo/efectos de los fármacos , Hipocampo/metabolismo , Potenciación a Largo Plazo/efectos de los fármacos , Ratones Transgénicos , Microglía/efectos de los fármacos , Microglía/metabolismo , Plasticidad Neuronal/efectos de los fármacos , Receptor trkB/metabolismo , Receptor trkC/metabolismo , Receptor trkC/genética , Sinapsis/efectos de los fármacos , Transcriptoma/efectos de los fármacosRESUMEN
Introduction: TrkB and TrkC receptor signaling promotes synaptic plasticity and interacts with pathways affected by amyloid-ß (Aß)-toxicity. Upregulating TrkB/C signaling could reduce Alzheimer's disease (AD)-related degenerative signaling, memory loss, and synaptic dysfunction. Methods: PTX-BD10-2 (BD10-2), a small molecule TrkB/C receptor partial agonist, was orally administered to aged London/Swedish-APP mutant mice (APP L/S ) and wild-type controls (WT). Effects on memory and hippocampal long-term potentiation (LTP) were assessed using electrophysiology, behavioral studies, immunoblotting, immunofluorescence staining, and RNA-sequencing. Results: Memory and LTP deficits in APP L/S mice were attenuated by treatment with BD10-2. BD10-2 prevented aberrant AKT, CaMKII, and GLUA1 phosphorylation, and enhanced activity-dependent recruitment of synaptic proteins. BD10-2 also had potentially favorable effects on LTP-dependent complement pathway and synaptic gene transcription. Conclusions: BD10-2 prevented APP L/S /Aß-associated memory and LTP deficits, reduced abnormalities in synapse-related signaling and activity-dependent transcription of synaptic genes, and bolstered transcriptional changes associated with microglial immune response.
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BACKGROUND: Loss of neurotrophic support in the striatum, particularly reduced brain-derived neurotrophic factor (BDNF) levels, contributes importantly to Huntington's disease (HD) pathogenesis. Another neurotrophin (NT), NT-3, is reduced in the cortex of HD patients; however, its role in HD is unknown. BDNF and NT-3 bind with high affinity to the tropomyosin receptor-kinases (Trk) B and TrkC, respectively. Targeting TrkB/TrkC may be an effective HD therapeutic strategy, as multiple links exist between their signaling pathways and HD degenerative mechanisms. We developed a small molecule ligand, LM22B-10, that activates TrkB and TrkC to promote cell survival. OBJECTIVE: This study aimed to determine if upregulating TrkB/TrkC signaling with LM22B-10 would alleviate the HD phenotype in R6/2 and Q140 mice. METHODS: LM22B-10 was delivered by concomitant intranasal-intraperitoneal routes to R6/2 and Q140 mice and then motor performance and striatal pathology were evaluated. RESULTS: NT-3 levels, TrkB/TrkC phosphorylation, and AKT signaling were reduced in the R6/2 striatum; LM22B-10 counteracted these deficits. LM22B-10 also reduced intranuclear huntingtin aggregates, dendritic spine loss, microglial activation, and degeneration of dopamine- and cyclic AMP-regulated phosphoprotein with a molecular weight of 32 kDa (DARPP-32) and parvalbumin-containing neurons in the R6/2 and/or Q140 striatum. Moreover, both HD mouse models showed improved motor performance after LM22B-10 treatment. CONCLUSIONS: These results reveal an NT-3/TrkC signaling deficiency in the striatum of R6/2 mice, support the idea that targeting TrkB/TrkC alleviates HD-related neurodegeneration and motor dysfunction, and suggest a novel, disease-modifying, multi-target strategy for treating HD.
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Degeneration of basal forebrain cholinergic neurons (BFCNs) in the nucleus basalis of Meynert (NBM) and vertical diagonal band (VDB) along with their connections is a key pathological event leading to memory impairment in Alzheimer's disease (AD). Aberrant neurotrophin signaling via Trks and the p75 neurotrophin receptor (p75NTR) contributes importantly to BFCN dystrophy. While NGF/TrkA signaling has received the most attention in this regard, TrkB and TrkC signaling also provide trophic support to BFCNs and these receptors may be well located to preserve BFCN connectivity. We previously identified a small molecule TrkB/TrkC ligand, LM22B-10, that promotes cell survival and neurite outgrowth in vitro and activates TrkB/TrkC signaling in the hippocampus of aged mice when given intranasally, but shows poor oral bioavailability. An LM22B-10 derivative, PTX-BD10-2, with improved oral bioavailability has been developed and this study examined its effects on BFCN atrophy in the hAPPLond/Swe (APPL/S) AD mouse model. Oral delivery of PTX-BD10-2 was started after appreciable amyloid and cholinergic pathology was present to parallel the clinical context, as most AD patients start treatment at advanced pathological stages. PTX-BD10-2 restored cholinergic neurite integrity in the NBM and VDB, and reduced NBM neuronal atrophy in symptomatic APPL/S mice. Dystrophy of cholinergic neurites in BF target regions, including the cortex, hippocampus, and amygdala, was also reduced with treatment. Finally, PTX-BD10-2 reduced NBM tau pathology and improved the survival of cholinergic neurons derived from human induced pluripotent stem cells (iPSCs) after amyloid-ß exposure. These data provide evidence that targeting TrkB and TrkC signaling with PTX-BD10-2 may be an effective disease-modifying strategy for combating cholinergic dysfunction in AD. The potential for clinical translation is further supported by the compound's reduction of AD-related degenerative processes that have progressed beyond early stages and its neuroprotective effects in human iPSC-derived cholinergic neurons.
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Enfermedad de Alzheimer , Células Madre Pluripotentes Inducidas , Enfermedad de Alzheimer/patología , Animales , Atrofia/patología , Neuronas Colinérgicas/patología , Humanos , Células Madre Pluripotentes Inducidas/patología , Ratones , Factores de Crecimiento Nervioso , Receptor trkC , Receptores de Factor de Crecimiento NerviosoRESUMEN
Huntington's disease (HD) is caused by an expansion of the CAG repeat in the huntingtin gene leading to preferential neurodegeneration of the striatum. Disease-modifying treatments are not yet available to HD patients and their development would be facilitated by translatable pharmacodynamic biomarkers. Multi-modal magnetic resonance imaging (MRI) and plasma cytokines have been suggested as disease onset/progression biomarkers, but their ability to detect treatment efficacy is understudied. This study used the R6/2 mouse model of HD to assess if structural neuroimaging and biofluid assays can detect treatment response using as a prototype the small molecule p75NTR ligand LM11A-31, shown previously to reduce HD phenotypes in these mice. LM11A-31 alleviated volume reductions in multiple brain regions, including striatum, of vehicle-treated R6/2 mice relative to wild-types (WTs), as assessed with in vivo MRI. LM11A-31 also normalized changes in diffusion tensor imaging (DTI) metrics and diminished increases in certain plasma cytokine levels, including tumor necrosis factor-alpha and interleukin-6, in R6/2 mice. Finally, R6/2-vehicle mice had increased urinary levels of the p75NTR extracellular domain (ecd), a cleavage product released with pro-apoptotic ligand binding that detects the progression of other neurodegenerative diseases; LM11A-31 reduced this increase. These results are the first to show that urinary p75NTR-ecd levels are elevated in an HD mouse model and can be used to detect therapeutic effects. These data also indicate that multi-modal MRI and plasma cytokine levels may be effective pharmacodynamic biomarkers and that using combinations of these markers would be a viable and powerful option for clinical trials.
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Enfermedad de Huntington/diagnóstico por imagen , Enfermedad de Huntington/metabolismo , Isoleucina/análogos & derivados , Morfolinas/metabolismo , Morfolinas/uso terapéutico , Neuroimagen/métodos , Receptores de Factor de Crecimiento Nervioso/metabolismo , Animales , Biomarcadores/sangre , Biomarcadores/orina , Estudios Transversales , Evaluación Preclínica de Medicamentos/métodos , Femenino , Enfermedad de Huntington/tratamiento farmacológico , Isoleucina/metabolismo , Isoleucina/farmacología , Isoleucina/uso terapéutico , Masculino , Ratones , Ratones Endogámicos CBA , Ratones Transgénicos , Morfolinas/farmacologíaRESUMEN
AIM: To evaluate the impact of ultra-rapid FLASH mouse whole brain irradiation on hippocampal dendritic spines and neuroinflammation, factors associated with cognitive impairment after brain irradiation. METHODS: We administered 30â¯Gy whole brain irradiation to C57BL6/J mice in sub-second (FLASH) vs. 240â¯s conventional delivery time keeping all other parameters constant, using a custom configured clinical linac. Ten weeks post-irradiation, we evaluated spatial and non-spatial object recognition using novel object location and object recognition testing. We measured dendritic spine density by tracing Golgi-stained hippocampal neurons and evaluated neuroinflammation by CD68 immunostaining, a marker of activated microglia, and expression of 10 pro-inflammatory cytokines using a multiplex immunoassay. RESULTS: At ten weeks post-irradiation, compared to unirradiated controls, conventional delivery time irradiation significantly impaired novel object location and recognition tasks whereas the same dose given in FLASH delivery did not. Conventional delivery time, but not FLASH, was associated with significant loss of dendritic spine density in hippocampal apical dendrites, with a similar non-significant trend in basal dendrites. Conventional delivery time was associated with significantly increased CD68-positive microglia compared to controls whereas FLASH was not. Conventional delivery time was associated with significant increases in 5 of 10 pro-inflammatory cytokines in the hippocampus (and non-significant increases in another 3), whereas FLASH was associated with smaller increases in only 3. CONCLUSION: Reduced cognitive impairment and associated neurodegeneration were observed with FLASH compared to conventional delivery time irradiation, potentially through decreased induction of neuroinflammation, suggesting a promising approach to increasing therapeutic index in radiation therapy of brain tumors.
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Disfunción Cognitiva/prevención & control , Irradiación Craneana , Espinas Dendríticas/efectos de la radiación , Hipocampo/efectos de la radiación , Inflamación/prevención & control , Animales , Espinas Dendríticas/patología , Hipocampo/patología , Masculino , Ratones , Ratones Endogámicos C57BL , Dosificación RadioterapéuticaRESUMEN
Huntington's disease (HD) is an inherited neurodegenerative disorder that has no cure. HD therapeutic development would benefit from a non-invasive translatable biomarker to track disease progression and treatment response. A potential biomarker is using positron emission tomography (PET) imaging with a translocator protein 18 kDa (TSPO) radiotracer to detect microglial activation, a key contributor to HD pathogenesis. The ability of TSPO-PET to identify microglial activation in HD mouse models, essential for a translatable biomarker, or therapeutic efficacy in HD patients or mice is unknown. Thus, this study assessed the feasibility of utilizing PET imaging with the TSPO tracer, [18F]PBR06, to detect activated microglia in two HD mouse models and to monitor response to treatment with LM11A-31, a p75NTR ligand known to reduce neuroinflammation in HD mice. [18F]PBR06-PET detected microglial activation in striatum, cortex and hippocampus of vehicle-treated R6/2 mice at a late disease stage and, notably, also in early and mid-stage symptomatic BACHD mice. After oral administration of LM11A-31 to R6/2 and BACHD mice, [18F]PBR06-PET discerned the reductive effects of LM11A-31 on neuroinflammation in both HD mouse models. [18F]PBR06-PET signal had a spatial distribution similar to ex vivo brain autoradiography and correlated with microglial activation markers: increased IBA-1 and TSPO immunostaining/blotting and striatal levels of cytokines IL-6 and TNFα. These results suggest that [18F]PBR06-PET is a useful surrogate marker of therapeutic efficacy in HD mice with high potential as a translatable biomarker for preclinical and clinical HD trials.
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Corteza Cerebral/diagnóstico por imagen , Enfermedad de Huntington/diagnóstico por imagen , Receptores de GABA/administración & dosificación , Receptores de Factor de Crecimiento Nervioso/genética , Animales , Corteza Cerebral/metabolismo , Corteza Cerebral/fisiopatología , Modelos Animales de Enfermedad , Progresión de la Enfermedad , Fluorodesoxiglucosa F18/administración & dosificación , Fluorodesoxiglucosa F18/química , Hipocampo/diagnóstico por imagen , Hipocampo/metabolismo , Hipocampo/fisiopatología , Humanos , Enfermedad de Huntington/tratamiento farmacológico , Enfermedad de Huntington/genética , Enfermedad de Huntington/patología , Isoleucina/administración & dosificación , Isoleucina/análogos & derivados , Masculino , Ratones , Microglía/efectos de los fármacos , Morfolinas/administración & dosificación , Tomografía de Emisión de Positrones , Unión Proteica , Receptores de GABA/química , Receptores de GABA/genéticaRESUMEN
Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder caused by CAG repeat expansions in the IT15 gene which encodes the huntingtin (HTT) protein. Currently, no treatments capable of preventing or slowing disease progression exist. Disease modifying therapeutics for HD would be expected to target a comprehensive set of degenerative processes given the diverse mechanisms contributing to HD pathogenesis including neuroinflammation, excitotoxicity, and transcription dysregulation. A major contributor to HD-related degeneration is mutant HTT-induced loss of neurotrophic support. Thus, neurotrophin (NT) receptors have emerged as therapeutic targets in HD. The considerable overlap between NT signaling networks and those dysregulated by mutant HTT provides strong theoretical support for this approach. This review will focus on the contributions of disrupted NT signaling in HD-related neurodegeneration and how targeting NT receptors to augment pro-survival signaling and/or to inhibit degenerative signaling may combat HD pathologies. Therapeutic strategies involving NT delivery, peptidomimetics, and the targeting of specific NT receptors (e.g., Trks or p75NTR), particularly with small molecule ligands, are discussed.
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Enfermedad de Huntington/tratamiento farmacológico , Enfermedad de Huntington/metabolismo , Receptores de Factor de Crecimiento Nervioso/metabolismo , Animales , Humanos , Transducción de Señal/efectos de los fármacosRESUMEN
Effective non-genetic disease modifying treatments for Huntington's disease (HD) will necessarily target multiple diverse neurodegenerative processes triggered by mutant huntingtin. Neurotrophin receptors are well-positioned for this task as they regulate signaling pathways that largely overlap with signaling networks contributing to HD-related synaptic dysfunction, glial activation, excitotoxicity, and other degenerative processes. This review will discuss the contributions of disrupted neurotrophin receptor-related signaling to primary HD neuropathologies, and prospects for harnessing this signaling to develop therapeutics to counteract HD degenerative mechanisms. Application of the native protein ligands has been challenging pharmacologically, but progress has been made with the advent of small molecule compounds that can selectively bind to and activate specific Trk receptors or p75NTR to promote trophic and/or inhibit degenerative signaling in cell populations preferentially affected in HD.
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Enfermedad de Huntington/metabolismo , Enfermedad de Huntington/terapia , Receptores de Factor de Crecimiento Nervioso/metabolismo , Transducción de Señal/fisiología , Animales , Factor Neurotrófico Derivado del Encéfalo/metabolismo , Humanos , Ligandos , Transducción de Señal/efectos de los fármacosRESUMEN
Neurotrophin (NT) receptors are coupled to numerous signaling networks that play critical roles in neuronal survival and plasticity. Several non-peptide small molecule ligands have recently been reported that bind to and activate specific tropomyosin-receptor kinase (Trk) NT receptors, stimulate their downstream signaling, and cause biologic effects similar to, though not completely overlapping, those of the native NT ligands. Here, in silico screening, coupled with low-throughput neuronal survival screening, identified a compound, LM22B-10, that, unlike prior small molecule Trk ligands, binds to and activates TrkB as well as TrkC. LM22B-10 increased cell survival and strongly accelerated neurite outgrowth, superseding the effects of brain-derived neurotrophic factor (BDNF), NT-3 or the two combined. Additionally, unlike the NTs, LM22B-10 supported substantial early neurite outgrowth in the presence of inhibiting glycoproteins. Examination of the mechanisms of these actions suggested contributions of the activation of both Trks and differential interactions with p75(NTR), as well as a requirement for involvement of the Trk extracellular domain. In aged mice, LM22B-10 activated hippocampal and striatal TrkB and TrkC, and their downstream signaling, and increased hippocampal dendritic spine density. Thus, LM22B-10 may constitute a new tool for the study of TrkB and TrkC signaling and their interactions with p75(NTR), and provides groundwork for the development of ligands that stimulate unique combinations of Trk receptors and activity patterns for application to selected neuronal populations and deficits present in various disease states.
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Supervivencia Celular/efectos de los fármacos , Proyección Neuronal/efectos de los fármacos , Neuronas/efectos de los fármacos , Fármacos Neuroprotectores/farmacología , Animales , Factor Neurotrófico Derivado del Encéfalo/metabolismo , Supervivencia Celular/fisiología , Cuerpo Estriado/citología , Cuerpo Estriado/efectos de los fármacos , Cuerpo Estriado/metabolismo , Células HEK293 , Hipocampo/citología , Hipocampo/efectos de los fármacos , Hipocampo/metabolismo , Humanos , Masculino , Ratones , Ratones Endogámicos C57BL , Células 3T3 NIH , Proyección Neuronal/fisiología , Neuronas/citología , Neuronas/metabolismo , Ratas , Receptor trkB/agonistas , Receptor trkB/genética , Receptor trkB/metabolismo , Receptor trkC/agonistas , Receptor trkC/genética , Receptor trkC/metabolismo , Receptores de Factor de Crecimiento Nervioso/genética , Receptores de Factor de Crecimiento Nervioso/metabolismoRESUMEN
Decreases in the ratio of neurotrophic versus neurodegenerative signalling play a critical role in Huntington's disease (HD) pathogenesis and recent evidence suggests that the p75 neurotrophin receptor (NTR) contributes significantly to disease progression. p75NTR signalling intermediates substantially overlap with those promoting neuronal survival and synapse integrity and with those affected by the mutant huntingtin (muHtt) protein. MuHtt increases p75NTR-associated deleterious signalling and decreases survival signalling suggesting that p75NTR could be a valuable therapeutic target. This hypothesis was investigated by examining the effects of an orally bioavailable, small molecule p75NTR ligand, LM11A-31, on HD-related neuropathology in HD mouse models (R6/2, BACHD). LM11A-31 restored striatal AKT and other pro-survival signalling while inhibiting c-Jun kinase (JNK) and other degenerative signalling. Normalizing p75NTR signalling with LM11A-31 was accompanied by reduced Htt aggregates and striatal cholinergic interneuron degeneration as well as extended survival in R6/2 mice. The p75NTR ligand also decreased inflammation, increased striatal and hippocampal dendritic spine density, and improved motor performance and cognition in R6/2 and BACHD mice. These results support small molecule modulation of p75NTR as an effective HD therapeutic strategy. LM11A-31 has successfully completed Phase I safety and pharmacokinetic clinical trials and is therefore a viable candidate for clinical studies in HD.
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Enfermedad de Huntington/tratamiento farmacológico , Isoleucina/análogos & derivados , Morfolinas/farmacología , Receptores de Factor de Crecimiento Nervioso/metabolismo , Animales , Modelos Animales de Enfermedad , Proteína Huntingtina/genética , Proteína Huntingtina/metabolismo , Enfermedad de Huntington/genética , Enfermedad de Huntington/metabolismo , Isoleucina/farmacología , Ligandos , Masculino , Ratones , Ratones Transgénicos , Terapia Molecular Dirigida , Fenotipo , Unión Proteica , Distribución Aleatoria , Receptores de Factor de Crecimiento Nervioso/genética , Transducción de Señal/efectos de los fármacosRESUMEN
Degeneration of basal forebrain cholinergic neurons contributes significantly to the cognitive deficits associated with Alzheimer's disease (AD) and has been attributed to aberrant signaling through the neurotrophin receptor p75 (p75NTR). Thus, modulating p75NTR signaling is considered a promising therapeutic strategy for AD. Accordingly, our laboratory has developed small molecule p75NTR ligands that increase survival signaling and inhibit amyloid-ß-induced degenerative signaling in in vitro studies. Previous work found that a lead p75NTR ligand, LM11A-31, prevents degeneration of cholinergic neurites when given to an AD mouse model in the early stages of disease pathology. To extend its potential clinical applications, we sought to determine whether LM11A-31 could reverse cholinergic neurite atrophy when treatment begins in AD mouse models having mid- to late stages of pathology. Reversing pathology may have particular clinical relevance as most AD studies involve patients that are at an advanced pathological stage. In this study, LM11A-31 (50 or 75 mg/kg) was administered orally to two AD mouse models, Thy-1 hAPPLond/Swe (APPL/S) and Tg2576, at age ranges during which marked AD-like pathology manifests. In mid-stage male APPL/S mice, LM11A-31 administered for 3 months starting at 6-8 months of age prevented and/or reversed atrophy of basal forebrain cholinergic neurites and cortical dystrophic neurites. Importantly, a 1 month LM11A-31 treatment given to male APPL/S mice (12-13 months old) with late-stage pathology reversed the degeneration of cholinergic neurites in basal forebrain, ameliorated cortical dystrophic neurites, and normalized increased basal forebrain levels of p75NTR. Similar results were seen in female Tg2576 mice. These findings suggest that LM11A-31 can reduce and/or reverse fundamental AD pathologies in late-stage AD mice. Thus, targeting p75NTR is a promising approach to reducing AD-related degenerative processes that have progressed beyond early stages.
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Enfermedad de Alzheimer/patología , Neuronas Colinérgicas/efectos de los fármacos , Isoleucina/análogos & derivados , Morfolinas/farmacología , Degeneración Nerviosa/prevención & control , Sustancias Protectoras/farmacología , Receptor de Factor de Crecimiento Nervioso/metabolismo , Transducción de Señal , Péptidos beta-Amiloides/genética , Péptidos beta-Amiloides/metabolismo , Precursor de Proteína beta-Amiloide/genética , Precursor de Proteína beta-Amiloide/metabolismo , Animales , Modelos Animales de Enfermedad , Progresión de la Enfermedad , Evaluación Preclínica de Medicamentos , Femenino , Humanos , Isoleucina/farmacología , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , NeuritasRESUMEN
As human lifespan increases, a greater fraction of the population is suffering from age-related cognitive impairments, making it important to elucidate a means to combat the effects of aging. Here we report that exposure of an aged animal to young blood can counteract and reverse pre-existing effects of brain aging at the molecular, structural, functional and cognitive level. Genome-wide microarray analysis of heterochronic parabionts--in which circulatory systems of young and aged animals are connected--identified synaptic plasticity-related transcriptional changes in the hippocampus of aged mice. Dendritic spine density of mature neurons increased and synaptic plasticity improved in the hippocampus of aged heterochronic parabionts. At the cognitive level, systemic administration of young blood plasma into aged mice improved age-related cognitive impairments in both contextual fear conditioning and spatial learning and memory. Structural and cognitive enhancements elicited by exposure to young blood are mediated, in part, by activation of the cyclic AMP response element binding protein (Creb) in the aged hippocampus. Our data indicate that exposure of aged mice to young blood late in life is capable of rejuvenating synaptic plasticity and improving cognitive function.
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Envejecimiento/fisiología , Transfusión Sanguínea/métodos , Trastornos del Conocimiento/fisiopatología , Trastornos del Conocimiento/terapia , Plasticidad Neuronal/fisiología , Factores de Edad , Envejecimiento/patología , Animales , Western Blotting , Línea Celular , Proteína de Unión a Elemento de Respuesta al AMP Cíclico/metabolismo , Cartilla de ADN/genética , Hipocampo/metabolismo , Inmunohistoquímica , Ratones , Ratones Endogámicos C57BL , Análisis por Micromatrices , Parabiosis/métodos , Reacción en Cadena de la PolimerasaRESUMEN
Loss of neurotrophic support in the striatum caused by reduced brain-derived neurotrophic factor (BDNF) levels plays a critical role in Huntington's disease (HD) pathogenesis. BDNF acts via TrkB and p75 neurotrophin receptors (NTR), and restoring its signaling is a prime target for HD therapeutics. Here we sought to determine whether a small molecule ligand, LM22A-4, specific for TrkB and without effects on p75(NTR), could alleviate HD-related pathology in R6/2 and BACHD mouse models of HD. LM22A-4 was administered to R6/2 mice once daily (5-6 d/week) from 4 to 11 weeks of age via intraperitoneal and intranasal routes simultaneously to maximize brain levels. The ligand reached levels in the R6/2 forebrain greater than the maximal neuroprotective dose in vitro and corrected deficits in activation of striatal TrkB and its key signaling intermediates AKT, PLCγ, and CREB. Ligand-induced TrkB activation was associated with a reduction in HD pathologies in the striatum including decreased DARPP-32 levels, neurite degeneration of parvalbumin-containing interneurons, inflammation, and intranuclear huntingtin aggregates. Aggregates were also reduced in the cortex. Notably, LM22A-4 prevented deficits in dendritic spine density of medium spiny neurons. Moreover, R6/2 mice given LM22A-4 demonstrated improved downward climbing and grip strength compared with those given vehicle, though these groups had comparable rotarod performances and survival times. In BACHD mice, long-term LM22A-4 treatment (6 months) produced similar ameliorative effects. These results support the hypothesis that targeted activation of TrkB inhibits HD-related degenerative mechanisms, including spine loss, and may provide a disease mechanism-directed therapy for HD and other neurodegenerative conditions.
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Benzamidas/uso terapéutico , Enfermedad de Huntington/tratamiento farmacológico , Trastornos del Movimiento/tratamiento farmacológico , Receptor trkB/efectos de los fármacos , Animales , Conducta Animal/efectos de los fármacos , Conducta Animal/fisiología , Benzamidas/farmacocinética , Western Blotting , Peso Corporal/efectos de los fármacos , Factor Neurotrófico Derivado del Encéfalo/fisiología , Espinas Dendríticas/fisiología , Humanos , Proteína Huntingtina , Enfermedad de Huntington/patología , Enfermedad de Huntington/fisiopatología , Inmunohistoquímica , Ligandos , Masculino , Ratones , Ratones Mutantes Neurológicos , Ratones Transgénicos , Trastornos del Movimiento/patología , Trastornos del Movimiento/fisiopatología , Proteínas del Tejido Nervioso/metabolismo , Equilibrio Postural/efectos de los fármacos , ARN/biosíntesis , ARN/genética , Reacción en Cadena en Tiempo Real de la Polimerasa , Receptor trkB/fisiología , Transducción de Señal/efectos de los fármacos , SobrevidaRESUMEN
The p75 neurotrophin receptor (p75(NTR)) is associated with multiple mechanisms linked to Alzheimer's disease (AD); hence, modulating its function might confer therapeutic effects. In previous in vitro work, we developed small molecule p75(NTR) ligands that inhibited amyloid-ß-induced degenerative signaling and prevented neurite degeneration. In the present study, a prototype p75(NTR) ligand, LM11A-31, was administered orally to the Thy-1 hAPP(Lond/Swe) (APP(L/S)) AD mouse model. LM11A-31 reached brain concentrations known to inhibit degenerative signaling without toxicity or induction of hyperalgesia. It prevented deficits in novel object recognition after 2.5 months and, in a separate cohort, deficits in Y-maze performance after 3 months of treatment. Stereology studies found that the number and size of basal forebrain cholinergic neurons, which are normal in APP(L/S) mice, were unaffected. Neuritic dystrophy, however, was readily apparent in the basal forebrain, hippocampus and cortex, and was significantly reduced by LM11A-31, with no effect on amyloid levels. These studies reveal that p75(NTR) is an important and tractable in vivo drug target for AD, with LM11A-31 representing a novel class of therapeutic candidates.
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Enfermedad de Alzheimer/tratamiento farmacológico , Enfermedad de Alzheimer/patología , Encéfalo/patología , Isoleucina/análogos & derivados , Morfolinas/uso terapéutico , Degeneración Nerviosa/prevención & control , Neuritas/patología , Receptores de Factor de Crecimiento Nervioso/fisiología , Administración Oral , Péptidos beta-Amiloides/metabolismo , Animales , Encéfalo/metabolismo , Trastornos del Conocimiento/prevención & control , Modelos Animales de Enfermedad , Femenino , Isoleucina/administración & dosificación , Isoleucina/farmacología , Isoleucina/uso terapéutico , Ligandos , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Endogámicos , Terapia Molecular Dirigida , Morfolinas/administración & dosificación , Morfolinas/farmacologíaRESUMEN
Brain-derived neurotrophic factor (BDNF) has emerged as a possible broad-spectrum treatment for the plasticity losses found in rodent models of human conditions associated with memory and cognitive deficits. We have tested this strategy in the particular case of ovariectomy. The actin polymerization in spines normally found after patterned afferent stimulation was greatly reduced, along with the stabilization of long-term potentiation, in hippocampal slices prepared from middle-aged ovariectomized rats. Both effects were fully restored by a 60-minute infusion of 2 nM BDNF. Comparable rescue results were obtained after elevating endogenous BDNF protein levels in hippocampus with 4 daily injections of a short half-life ampakine (positive modulator of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate [AMPA]-type glutamate receptors). These results provide the first evidence that minimally invasive, mechanism-based drug treatments can ameliorate defects in spine plasticity caused by depressed estrogen levels.
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Factor Neurotrófico Derivado del Encéfalo/farmacología , Hipocampo/citología , Hipocampo/efectos de los fármacos , Sinapsis/efectos de los fármacos , Regulación hacia Arriba/efectos de los fármacos , Animales , Estimulación Eléctrica , Estradiol/farmacología , Estrógenos/farmacología , Agonistas de Aminoácidos Excitadores/farmacología , Femenino , Técnicas In Vitro , Potenciación a Largo Plazo/efectos de los fármacos , Potenciación a Largo Plazo/fisiología , Ovariectomía , Ratas , Ratas Long-EvansRESUMEN
Two clusters of forebrain neurons-one in the posterodorsal preoptic nucleus (PdPN) and one in the lateral part of the posterodorsal medial amygdala (MeApd)-are activated at ejaculation in male rats and gerbils as seen with Fos immunocytochemistry. To understand the functions of these cells and how they respond synchronously, it may be useful to identify their neurotransmitters. Nitric oxide (NO) was of interest because its levels in the preoptic area affect ejaculation, and it could synchronize clustered neurons through paracrine/volume transmission. Thus, we determined whether the ejaculation-related cells produce NO by assessing Fos co-localization with NO synthase (NOS) in recently mated male gerbils. We also studied NOS-Fos co-localization in the medial part of the medial preoptic nucleus (MPNm), where half of the neurons that express Fos after mating reflect ejaculation. We also quantified NOS co-localization with androgen receptor (AR) and NOS sensitivity to androgens at these sites. Without quantification, we extended these analyses throughout the hypothalamus and amygdala. Many mating-activated PdPN, lateral MeApd, and MPNm cells contained NOS (32-54%), and many NOS neurons at these sites expressed Fos (34-51%) or AR (25-69%). PdPN and MPNm NOS cells were sensitive to testosterone but not its androgenic metabolite dihydrotestosterone. The overall distribution of NOS and NOS-AR cells was similar to that in rats. These data suggest that NO may help to synchronize the activation of PdPN and lateral MeApd neurons at ejaculation and that NOS in PdPN and MPNm cells is regulated by testosterone acting via estradiol or without undergoing metabolism.
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Eyaculación/fisiología , Neuronas/metabolismo , Óxido Nítrico/metabolismo , Prosencéfalo/citología , Receptores Androgénicos/metabolismo , Conducta Sexual Animal/fisiología , Testosterona/metabolismo , Andrógenos/metabolismo , Andrógenos/farmacología , Animales , Castración , Femenino , Gerbillinae/anatomía & histología , Gerbillinae/fisiología , Masculino , Neuronas/citología , Neuronas/efectos de los fármacos , Óxido Nítrico Sintasa de Tipo I/metabolismo , Prosencéfalo/fisiología , Proteínas Proto-Oncogénicas c-fos/metabolismo , RatasRESUMEN
The posterodorsal preoptic nucleus (PdPN), lateral part of the posterodorsal medial amygdala (MeApd) and medial part of the medial preoptic nucleus (MPNm) are activated at ejaculation in male gerbils as assessed by Fos expression. We sought to immunocytochemically visualize substance P (SP), cholecystokinin (CCK), oxytocin, vasopressin and tyrosine hydroxylase (TH), a catecholaminergic marker, in the mating-activated cells, but the need for colchicine precluded behavioral testing. Instead, we detailed distributions of cells containing these molecules in the medial amygdala, caudal preoptic area and caudal bed nuclei of the stria terminalis (BST) and quantified their densities in the PdPN, MPNm and lateral MeApd for comparison to densities previously assessed for mating-activated efferents from these sites. TH cells were as dense in the PdPN and lateral MeApd as activated efferents to the anteroventral periventricular nucleus. In the lateral MeApd, TH cells were grouped where cells activated at ejaculation are clustered and where CCK cells form a ball. Lateral MeApd CCK cells and PdPN SP cells were as dense as activated efferents to the principal BST. Oxytocinergic PdPN cells and SP cells in the MPNm were as dense as mating-activated efferents to the lateral MeApd. If some oxytocin cells in the PdPN project to the neurohypophysis, as in rats, they could be a source of the oxytocin secreted at ejaculation. Since gerbils are monogamous and biparental, it was also interesting that, unlike monogamous prairie voles, they had few TH cells in the MeApd or dorsal BST, resembling promiscuous rats, hamsters and meadow voles.
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Amígdala del Cerebelo/citología , Eyaculación/fisiología , Hipotálamo/citología , Área Preóptica/citología , Núcleos Septales/citología , Amígdala del Cerebelo/química , Amígdala del Cerebelo/metabolismo , Animales , Arvicolinae , Núcleo Celular/metabolismo , Colecistoquinina/análisis , Colecistoquinina/metabolismo , Femenino , Gerbillinae , Hipotálamo/química , Hipotálamo/metabolismo , Inmunohistoquímica , Masculino , Oxitocina/análisis , Oxitocina/metabolismo , Área Preóptica/química , Área Preóptica/metabolismo , Núcleos Septales/química , Núcleos Septales/metabolismo , Sustancia P/análisis , Sustancia P/metabolismo , Tirosina 3-Monooxigenasa/análisis , Tirosina 3-Monooxigenasa/metabolismo , Vasopresinas/análisis , Vasopresinas/metabolismoRESUMEN
Daily, systemic injections of a positive AMPA-type glutamate receptor modulator (ampakine) have been shown to reduce synaptic plasticity defects in rodent models of aging and early-stage Huntington's disease (HD). Here we report that long-term ampakine treatment markedly slows the progression of striatal neuropathology and locomotor dysfunction in the R6/2 HD mouse model. Remarkably, these effects were produced by an ampakine, CX929, with a short half-life. Injected once daily for 4-7 weeks, the compound increased protein levels of brain-derived neurotrophic factor (BDNF) in the neocortex and striatum of R6/2 but not wild-type mice. Moreover, ampakine treatments prevented the decrease in total striatal area, blocked the loss of striatal DARPP-32 immunoreactivity and reduced by 36% the size of intra-nuclear huntingtin aggregates in R6/2 striatum. The CX929 treatments also markedly improved motor performance of R6/2 mice on several measures (rotarod, vertical pole descent) but did not influence body weight or lifespan. These findings describe a minimally invasive, pharmacologically plausible strategy for treatment of HD and, potentially, other neuropathological diseases.
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Antidiscinéticos/farmacología , Cuerpo Estriado/efectos de los fármacos , Agonistas de Aminoácidos Excitadores/farmacología , Enfermedad de Huntington/tratamiento farmacológico , Fenotipo , Receptores AMPA/agonistas , Ácido alfa-Amino-3-hidroxi-5-metil-4-isoxazol Propiónico/farmacología , Animales , Antidiscinéticos/química , Antidiscinéticos/uso terapéutico , Cuerpo Estriado/patología , Modelos Animales de Enfermedad , Progresión de la Enfermedad , Agonistas de Aminoácidos Excitadores/uso terapéutico , Humanos , Enfermedad de Huntington/genética , Enfermedad de Huntington/patología , Masculino , Ratones , Ratones Transgénicos , Receptores AMPA/fisiología , Resultado del TratamientoRESUMEN
Cognitive problems occur in asymptomatic gene carriers of Huntington's disease (HD), and mouse models of the disease exhibit impaired learning and substantial deficits in the cytoskeletal changes that stabilize long-term potentiation (LTP). The latter effects may be related to the decreased production of brain-derived neurotrophic factor (BDNF) associated with the HD mutation. This study asked whether up-regulating endogenous BDNF levels with an ampakine, a positive modulator of AMPA-type glutamate receptors, rescues plasticity and reduces learning problems in HD (CAG140) mice. Twice-daily injections of a short half-life ampakine normalized BDNF levels, activity-driven actin polymerization in dendritic spines, and LTP stabilization in 8-week-old mutants. Comparable results were obtained in 16-week-old HD mice with more severe LTP deficits. Ampakine treatments had no measurable effect on the decreased locomotor activity observed in the mutants but offset their impairments in long-term memory. Given that ampakines are well tolerated in clinical trials and were effective in this study after brief exposures, these results suggest a novel strategy for chronic treatment of the cognitive difficulties that occur in the early stages of HD.