BDNF-TrkB Signaling Research Articles

Brain-derived neurotrophic factor-induced regulation of RNA metabolism in neuronal development and synaptic plasticity.

The neurotrophin brain-derived neurotrophic factor (BDNF) plays multiple roles in the nervous system, including in neuronal development, in long-term synaptic potentiation in different brain regions, and in neuronal survival. Alterations in these regulatory mechanisms account for several diseases of the nervous system. The synaptic effects of BDNF mediated by activation of tropomyosin receptor kinase B (TrkB) receptors are partly mediated by stimulation of local protein synthesis which is now considered a ubiquitous feature in both presynaptic and postsynaptic compartments of the neuron. The capacity to locally synthesize proteins is of great relevance at several neuronal developmental stages, including during neurite development, synapse formation, and stabilization. The available evidence shows that the effects of BDNF-TrkB signaling on local protein synthesis regulate the structure and function of the developing and mature synapses. While a large number of studies have illustrated a wide range of effects of BDNF on the postsynaptic proteome, a growing number of studies also point to presynaptic effects of the neurotrophin in the local regulation of the protein composition at the presynaptic level. Here, we will review the latest evidence on the role of BDNF in local protein synthesis, comparing the effects on the presynaptic and postsynaptic compartments. Additionally, we overview the relevance of BDNF-associated local protein synthesis in neuronal development and synaptic plasticity, at the presynaptic and postsynaptic compartments, and their relevance in terms of disease. This article is categorized under: RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications RNA Export and Localization > RNA Localization.

Utility of 7,8-dihydroxyflavone in preventing astrocytic and synaptic deficits in the hippocampus elicited by PTSD

Astrocytic functions and brain-derived neurotrophic factor (BDNF)-tyrosine kinase receptor B (TrkB) signaling pathways are impaired in stress-related neuropsychiatric diseases. Previous studies have reported neuroprotective effects of 7,8-dihydroxyflavone (7,8-DHF), a TrkB activator. Here, we investigated the molecular mechanisms underlying pathogenesis of post-traumatic stress disorder (PTSD) using a modified single-prolonged stress (SPS&S) model and the potential beneficial effects of 7,8-DHF. SPS&S reduced the hippocampal expression of glial fibrillary acidic protein (GFAP), a marker of astrocytes, and induced morphological changes in astrocytes. From the perspective of synaptic function, the SPS&S model displayed reduced expression of BDNF, p-TrkB, postsynaptic density protein 95 (PSD95), AMPA receptor subunit GluR1 (GluA1), NMDA receptor subunit N2A/N2B ratio, calpain-1, phosphorylated protein kinase B (Akt) and phosphorylated mammalian target of rapamycin (mTOR) and conversely, higher phosphatase and tension homolog (PTEN) expression in the hippocampus. Acute or continuous intraperitoneal administration of 7,8-DHF (5 mg/kg) after SPS&S procedures prevented SPS&S-induced fear memory generalization and anxiety-like behaviors as well as abnormalities of hippocampal oscillations. Most importantly, 7,8-DHF attenuated SPS&S-induced abnormal BDNF-TrkB signaling and calpain-1-dependent cascade of synaptic deficits. Furthermore, treatment with a TrkB inhibitor completely blocked while an mTOR inhibitor partially blocked the effects of 7,8-DHF on behavioral changes of SPS&S model mice. Our collective findings suggest that 7,8-DHF effectively alleviates PTSD-like symptoms, including fear generalization and anxiety-like behavior, potentially by preventing astrocytic and synaptic deficits in the hippocampus through targeting of TrkB.

Chronic Alcohol Exposure-Induced Impairment in Spatial Memory Retention and Sex Specific Changes in BDNF–TrkB Signaling in the Hippocampus

Chronic Alcohol Exposure-Induced Impairment in Spatial Memory Retention and Sex Specific Changes in BDNF–TrkB Signaling in the Hippocampus

Effects of Phototherapy on Learning Memory and BDNF-TrkB Signaling Pathway in Sleep-Deprived Mice

Effects of Phototherapy on Learning Memory and BDNF-TrkB Signaling Pathway in Sleep-Deprived Mice

Analysis of Antidepressant-like Effects and Action Mechanisms of GSB-106, a Small Molecule, Affecting the TrkB Signaling.

Induction of BDNF-TrkB signaling is associated with the action mechanisms of conventional and fast-acting antidepressants. GSB-106, developed as a small dimeric dipeptide mimetic of BDNF, was previously shown to produce antidepressant-like effects in the mouse Porsolt test, tail suspension test, Nomura water wheel test, in the chronic social defeat stress model and in the inflammation-induced model of depression. In the present study, we evaluated the effect of chronic per os administration of GSB-106 to Balb/c mice under unpredictable chronic mild stress (UCMS). It was observed for the first time that long term GSB-106 treatment (1 mg/kg, 26 days) during ongoing UCMS procedure ameliorated the depressive-like behaviors in mice as indicated by the Porsolt test. In addition, chronic per os administration of GSB-106 resulted in an increase in BDNF levels, which were found to be decreased in the prefrontal cortex and hippocampus of mice after UCMS. Furthermore, prolonged GSB-106 treatment was accompanied by an increase in the content of pTrkB706/707 in the prefrontal cortex and by a pronounced increase in the level of pTrkB816 in both studied brain structures of mice subjected to UCMS procedure. In summary, the present data show that chronic GSB-106 treatment produces an antidepressant-like effect in the unpredictable chronic mild stress model, which is likely to be associated with the regulation of the BDNF-TrkB signaling.

Brain-derived neurotrophic factor promotes immune reconstitution following radiation injury via activation of bone marrow mesenchymal stem cells.

Brain-derived neurotrophic factor (BDNF) is a member of the nerve growth factor family which has been extensively studied for its roles in neural development, long-term memory, brain injury, and neurodegenerative diseases. BDNF signaling through tropomyosin receptor kinase B (TrkB) stimulates neuronal cell survival. For this reason, small molecule TrkB agonists are under pre-clinical develoment for the treatment of a range of neurodegenerative diseases and injuries. Our laboratory recently reported BDNF is secreted by pro-regenerative endothelial progenitor cells (EPCs) which support hematopoietic reconstitution following total body irradiation (TBI). Here we report BDNF-TrkB signaling plays a novel regenerative role in bone marrow and thymic regeneration following radiation injury. Exogenous administration of BDNF or TrkB agonist 7,8-dihydroxyflavone (7,8-DHF) following myelosuppressive radiation injury promoted faster recovery of mature blood cells and hematopoietic stem cells capable of multi-lineage reconstitution. BDNF promotes hematopoietic regeneration via activation of PDGFRα+ bone marrow mesenchymal stem cells (MSCs) which increase secretion of hematopoietic cytokines interleukin 6 (IL-6) and leukemia inhibitory factor (LIF) in response to TrkB activation. These data suggest pharmacologic activation of the BDNF pathway with either BDNF or 7,8-DHF may be beneficial for treatment of radiation or chemotherapy induced myelosuppression.

Environmental Enrichment Induces Meningeal Niche Remodeling through TrkB-Mediated Signaling.

Neural precursors (NPs) present in the hippocampus can be modulated by several neurogenic stimuli, including environmental enrichment (EE) acting through BDNF-TrkB signaling. We have recently identified NPs in meninges; however, the meningeal niche response to pro-neurogenic stimuli has never been investigated. To this aim, we analyzed the effects of EE exposure on NP distribution in mouse brain meninges. Following neurogenic stimuli, although we did not detect modification of the meningeal cell number and proliferation, we observed an increased number of neural precursors in the meninges. A lineage tracing experiment suggested that EE-induced β3-Tubulin+ immature neuronal cells present in the meninges originated, at least in part, from GLAST+ radial glia cells. To investigate the molecular mechanism responsible for meningeal reaction to EE exposure, we studied the BDNF-TrkB interaction. Treatment with ANA-12, a TrkB non-competitive inhibitor, abolished the EE-induced meningeal niche changes. Overall, these data showed, for the first time, that EE exposure induced meningeal niche remodeling through TrkB-mediated signaling. Fluoxetine treatment further confirmed the meningeal niche response, suggesting it may also respond to other pharmacological neurogenic stimuli. A better understanding of the neurogenic stimuli modulation for meninges may be useful to improve the effectiveness of neurodegenerative and neuropsychiatric treatments.

Ameliorative effects of oyster (Crassostrea hongkongensis) protein hydrolysate on age-induced cognitive impairment via restoring glia cell dysfunction and neuronal injured in zebrafish

• OPU significantly ameliorated the cognitive deficits in aged zebrafish. • OPU enhanced antioxidant and anti-inflammatory effect in aged zebrafish. • OPU restored glial cell function and neuronal injured in aged zebrafish. • OPU regulated neurotrophic level and synaptic function in aged zebrafish. Cognitive impairment caused by aging is a global public health problem. The 5–8 kDa ultrafiltration fraction of oyster ( Crassostrea hongkongensis ) protein hydrolysate (OPU) could ameliorate learning and memory in aged zebrafish, however the mechanism is still unclear. In this paper OPU was applied to explore the mechanism of reducing cognitive impairment of aged zebrafish. The OPU significantly ameliorated behavior in aged zebrafish. It reversed age-induced low antioxidant activity, high lipid peroxidation, microglial activation, and production of inflammatory cytokines, such as IL-1β, TNF-α and CD11b. It could improve age-induced suppressive astrocyte biomarkers and associated BDNF-TrkB signaling because it increased the expression of gfap , bdnf , trkB and psd-95 . OPU consumption could reverse age-induced neuronal loss and apoptosis, increase the neurotransmitters (Ach and r-GABA). The results demonstrated that OPU could ameliorate age-induced cognitive impairment. It may be a good base material to develop a related health food for the elderly.

Ginsenoside Rb1 Produces Antidepressant-Like Effects in a Chronic Social Defeat Stress Model of Depression Through the BDNF–Trkb Signaling Pathway

Ginsenoside Rb1 (Rb1), an important bioactive ingredient of Panax ginseng, has potent neuroprotective effects. The objective of the study is to elucidate the impact of Rb1 treatment on chronic social defeat stress (CSDS)–induced depressive-like behaviors and its related mechanism. According to the obtained results, the daily oral administration of Rb1 (35 and 70 mg/kg) and imipramine (15 mg/kg) for 28 days significantly reversed the social avoidance behavior, anhedonia, and behavioral despair via CSDS exposure, as demonstrated by the considerable elevation in the time in the zone in the social interaction test, consumption of sucrose solution in the sucrose preference test, and decrease in immobility time in the forced swim test. Moreover, Rb1 obviously restored the CSDS-induced decrease in the BDNF signaling pathway and hippocampal neurogenesis. Rb1 significantly increased the hippocampal levels of ERK, AKT, and CREB phosphorylation and increased the number of DCX+ cells in DG. Importantly, the antidepressant effects of Rb1 were completely blocked in mice by using K252a (the nonselective tyrosine kinase B inhibitor). In conclusion, our results indicated that Rb1 exerts promising antidepressant-like effects in mice with CSDS-induced depression, and its effects were facilitated by enhancing the BDNF signaling cascade and upregulation of hippocampal neurogenesis.

Neuronal growth and synaptogenesis are inhibited by prenatal methamphetamine exposure leading to memory impairment in adolescent and adult mice

Synaptogenesis plays critical roles in learning and memory processes and is susceptible to substance abuse toxicity. The present study aimed to elucidate the long-lasting effects of prenatal methamphetamine exposure on synaptogenesis and learning and memory. The involvement of BDNF-TrkB signaling was also investigated. Pregnant mice (C57BL/6 JNc) were administered methamphetamine (5 mg/kg, s.c.) on gestation days 8−15. Primary hippocampal cultures were prepared from fetuses at gestational day 16.5 to study neuronal morphology and synaptogenesis. The expression of synaptic proteins, BDNF and TrkB receptor was determined in postnatal day 14 (PND14), adolescent and adult mice; memory tests were also conducted. MA exposure decreased axon length and diameter, and synaptic areas in the primary cultures. Presynaptic protein was decreased in the hippocampus of PND14 mice prenatally exposed to MA, while increases in postsynaptic protein (PSD-95) were found in MA-exposed adolescent and adult mice. BDNF expression was enhanced in the prefrontal cortex and striatum of MA-exposed PND14 mice. Memory impairment was observed in MA-exposed adolescent and adult mice compared to control mice. Prenatal MA exposure disrupted neuronal growth and synapse formation in the developing brain with only short-term interference of the BDNF-TrkB signaling pathway, resulting in the adaptation of postsynaptic neurons. Alterations in the developing brain and synaptogenesis lead to long-lasting learning and memory impairment.

A synaptic locus for TrkB signaling underlying ketamine rapid antidepressant action.

SUMMARYKetamine produces rapid antidepressant action in patients with major depression or treatment-resistant depression. Studies have identified brain-derived neurotrophic factor (BDNF) and its receptor, tropomyosin receptor kinase B (TrkB), as necessary for the antidepressant effects and underlying ketamine-induced synaptic potentiation in the hippocampus. Here, we delete BDNF or TrkB in presynaptic CA3 or postsynaptic CA1 regions of the Schaffer collateral pathway to investigate the rapid antidepressant action of ketamine. The deletion of Bdnf in CA3 or CA1 blocks the ketamine-induced synaptic potentiation. In contrast, ablation of TrkB only in postsynaptic CA1 eliminates the ketamine-induced synaptic potentiation. We confirm BDNF-TrkB signaling in CA1 is required for ketamine’s rapid behavioral action. Moreover, ketamine application elicits dynamin1-dependent TrkB activation and downstream signaling to trigger rapid synaptic effects. Taken together, these data demonstrate a requirement for BDNF-TrkB signaling in CA1 neurons in ketamine-induced synaptic potentiation and identify a specific synaptic locus in eliciting ketamine’s rapid antidepressant effects.

Stress Diminishes BDNF-stimulated TrkB Signaling, TrkB-NMDA Receptor Linkage and Neuronal Activity in the Rat Brain

Exposure to intense or repeated stressors can lead to depression or post-traumatic stress disorder (PTSD). Neurological changes induced by stress include impaired neurotrophin signaling, which is known to influence synaptic integrity and plasticity. The present study used an ex vivo approach to examine the impact of acute or repeated stress on BDNF-stimulated TrkB signaling in hippocampus (HIPPO) and prefrontal cortex (PFC). Rats in an acute multiple stressor group experienced five stressors in one day whereas rats in a repeated unpredictable stressor group experienced 20 stressors across 10 days. After stress exposure, slices were incubated with vehicle or BDNF, followed by immunoprecipitation and immunoblot assays to assess protein levels, activation states and protein–protein linkage associated with BDNF-TrkB signaling. Three key findings are (1) exposure to stressors significantly diminished BDNF-stimulated TrkB signaling in HIPPO and PFC such that reductions in TrkB activation, diminished recruitment of adaptor proteins to TrkB, reduced activation of downstream signaling molecules, disruption of TrkB-NMDAr linkage, and changes in basal and BDNF-stimulated Arc expression were observed. (2) After stress, BDNF stimulation enhanced TrkB-NMDAr linkage in PFC, suggestive of compensatory mechanisms in this region. (3) We discovered an uncoupling between TrkB signaling, TrkB-NMDAr linkage and Arc expression in PFC and HIPPO. In addition, a robust surge in pro-inflammatory cytokines was observed in both regions after repeated exposure to stressors. Collectively, these data provide therapeutic targets for future studies that investigate how to reverse stress-induced downregulation of BDNF-TrkB signaling and underscore the need for functional studies that examine stress-related TrkB-NMDAr activities in PFC.

Retraction.

Retraction: "Effects of microRNA-10a on synapse remodeling in hippocampal neurons and neuronal cell proliferation and apoptosis through the BDNF-TrkB signaling pathway in a rat model of Alzheimer's disease," by Bo-Wen Wu, Mi-Shan Wu, Jin-Dong Guo, J Cell Physiol. 2018; 5281-5292: The above article, published online on 07 December 2017 in Wiley Online Library (https://onlinelibrary.wiley.com/doi/10.1002/jcp.26328) has been retracted by agreement between the journal's Editor in Chief, Prof. Dr. Gregg Fields, and Wiley Periodicals LLC. The retraction has been agreed following an investigation based on allegations raised by a third party. Several flaws and inconsistencies between results presented and experimental methods described were found, the editors consider the conclusions of this article to be invalid.

Disruption of postnatal neurogenesis and adult-stage suppression of synaptic plasticity in the hippocampal dentate gyrus after developmental exposure to sterigmatocystin in rats

Exposure to sterigmatocystin (STC) raises concerns on developmental neurological disorders. The present study investigated the effects of maternal oral STC exposure on postnatal hippocampal neurogenesis of offspring in rats. Dams were exposed to STC (1.7, 5.0, and 15.0 ppm in diet) from gestational day 6 until day 21 post-delivery (weaning), and offspring were maintained without STC exposure until adulthood on postnatal day (PND) 77, in accordance with OECD chemical testing guideline Test No. 426. On PND 21, 15.0-ppm STC decreased type-3 neural progenitor cell numbers in the subgranular zone (SGZ) due to suppressed proliferation. Increased γ-H2AX-immunoreactive (+) cell numbers in the SGZ and Ercc1 upregulation and Brip1 downregulation in the dentate gyrus suggested induction of DNA double-strand breaks in SGZ cells. Upregulation of Apex1 and Ogg1 and downregulation of antioxidant genes downstream of NRF2-Keap1 signaling suggested induction of oxidative DNA damage. Increased p21WAF1/CIP1+ SGZ cell numbers and suppressed cholinergic signaling through CHRNB2-containing receptors in GABAergic interneurons suggested potential neurogenesis suppression mechanisms. Multiple mechanisms involving N-methyl-d-aspartate (NMDA) receptor-mediated glutamatergic signaling and various GABAergic interneuron subpopulations, including CHRNA7-expressing somatostatin+ interneurons activated by BDNF-TrkB signaling, may be involved in ameliorating the neurogenesis. Upregulation of Arc, Ptgs2, and genes encoding NMDA receptors and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors suggested synaptic plasticity facilitation. On PND 77, ARC+ granule cells decreased, and Nos2 was upregulated following 15.0 ppm STC exposure, suggesting oxidative stress-mediated synaptic plasticity suppression. Inverse pattern in gene expression changes in vesicular glutamate transporter isoforms, Slc17a7 and Slc17a6, from weaning might also be responsible for the synaptic plasticity suppression. The no-observed-adverse-effect level of maternal oral STC exposure for offspring neurogenesis was determined to be 5.0 ppm, translating to 0.34–0.85 mg/kg body weight/day.

HGG-21. MALIGNANT SYNAPTIC PLASTICITY IN PEDIATRIC HIGH-GRADE GLIOMAS

Pediatric high-grade gliomas (pHGG) are a devastating group of diseases that urgently require novel therapeutic options. We have previously demonstrated that pHGGs directly synapse onto neurons and the subsequent tumor cell depolarization, mediated by calcium-permeable AMPA channels, promotes their proliferation. The regulatory mechanisms governing these postsynaptic connections are unknown. Here, we investigated the role of BDNF-TrkB signaling in modulating the plasticity of the malignant synapse. BDNF ligand activation of its canonical receptor, TrkB (which is encoded for by the gene NTRK2), has been shown to be one important modulator of synaptic regulation in the normal setting. Electrophysiological recordings of glioma cell membrane properties, in response to acute neurotransmitter stimulation, demonstrate in an inward current resembling AMPA receptor (AMPAR) mediated excitatory neurotransmission. Extracellular BDNF increases the amplitude of this glutamate-induced tumor cell depolarization and this effect is abrogated in NTRK2 knockout glioma cells. Upon examining tumor cell excitability using in situ calcium imaging, we found that BDNF increases the intensity of glutamate-evoked calcium transients in GCaMP6s expressing glioma cells. Western blot analysis indicates the tumors AMPAR properties are altered downstream of BDNF induced TrkB activation in glioma. We find that BDNF-TrkB signaling promotes neuron-to-glioma synaptogenesis as measured by high-resolution confocal and electron microscopy in culture and tumor xenografts. Our analysis of published pHGG transcriptomic datasets, together with brain slice conditioned medium experiments in culture, indicate the tumor microenvironment as the chief source of BDNF ligand. Disruption of the BDNF-TrkB pathway in patient-derived orthotopic glioma xenograft models, both genetically and pharmacologically, results in an increased overall survival and reduced tumor proliferation rate. These findings suggest that gliomas leverage mechanisms of plasticity to modulate the excitatory channels involved in synaptic neurotransmission and they reveal the potential to target the regulatory components of glioma circuit dynamics as a therapeutic strategy for these lethal cancers.

Mechanism of miR-365 in regulating BDNF-TrkB signal axis of HFD/STZ induced diabetic nephropathy fibrosis and renal function.

Diabetic nephropathy (DN) is one of the most serious complications of diabetes that leads to decline of renal function. Although numerous studies have revealed that microRNAs (miRNAs) play essential roles in the progression of DN, whether miR-365 is involved remains elusive. The successful construction of DN model was confirmed by ELSIA, hematoxylin-eosin (HE) and Masson staining assay. The expression of miR-365 was detected through RT-qPCR. The levels of BDNF, p-TrkB, α-smooth muscle actin (SMA), collagen IV (Col.IV), transforming growth factor-β1 (TGF-β1), tumor necrosis factor α (TNF-α), and interleukin-6 (IL-6) were evaluated by western blot, IF or ELISA assays. Luciferase reporter assay was used to detect the interaction between miR-365 and BDNF. The DN mice model was induced by streptozotocin (STZ). Then miR-365 expression was found to upregulate in tissues of DN rat. Furthermore, elevated expression of miR-365 was found in high glucose (HG)-treated HK-2 cells. Silencing of miR-365 suppressed the accumulation of ECM components and secretion of inflammatory cytokines in HK-2 cells. In addition, it was demonstrated that miR-365 could target BDNF. The protein levels of BDNF and p-TrkB were negatively regulated by miR-365 in HK-2 cells. Moreover, inhibition of miR-365 suppressed the levels of SMA, Col.IV, TGF-β1, TNF-α, and IL-6, indicating the renal fibrosis was inhibited by miR-365 knockdown. MiR-365 could regulate BDNF-TrkB signal axis in STZ induced DN fibrosis and renal function. The results of the current study might provide a promising biomarker for the treatment of DN in the future.

Induction of cellular senescence as a late effect and BDNF-TrkB signaling-mediated ameliorating effect on disruption of hippocampal neurogenesis after developmental exposure to lead acetate in rats

Lead (Pb) exposure causes cognitive deficits in children. The present study investigated the effect of developmental exposure to Pb acetate (PbAc) on postnatal hippocampal neurogenesis. Pregnant rats were administered drinking water containing 0, 2000, or 4000 ppm PbAc from gestational day 6 until day 21 post-delivery (weaning), and offspring were maintained without PbAc exposure until adulthood on postnatal day (PND) 77. There was a dose-related accumulation of Pb in the offspring brain at weaning, while Pb was mainly excreted in adulthood. In the hippocampus, metallothionein I/II immunoreactive (+) glia were increased through adulthood as a neuroprotective response to accumulated Pb, accompanied by increased astrocyte and microglia numbers in adulthood, suggesting sustained neural damage. Gene expression changes suggested elevated oxidative stress at weaning and suppression of the antioxidant system in adulthood, as well as continued neuroinflammatory responses. At weaning, granule cell apoptosis was increased and numbers of type-3 neural progenitor cells (NPCs) were decreased. By contrast, type-2a and type-2b NPCs were increased, suggesting suppressed differentiation to type-3 NPCs. In adulthood, there were increased numbers of immature granule cells. In the hilus of the dentate gyrus, somatostatin+ interneurons were increased at weaning, while calbindin-D-29K+ interneurons were increased throughout adulthood, suggesting a strengthened interneuron regulatory system against the suppressed differentiation at weaning. In the dentate gyrus, Bdnf, Ntrk2, and Chrna7 gene expression were upregulated and numbers of hilar TrkB+ interneurons increased at weaning. These findings suggest activation of BDNF-TrkB signaling to increase somatostatin+ interneurons and promote cholinergic signaling, thus increasing later production of immature granule cells. In adulthood, Pcna and Apex1 gene expression were downregulated and Chek1 and cyclin-dependent kinase inhibitor expression were upregulated. Furthermore, there was an increase in γ-H2AX+ SGZ cells, suggesting induction of cellular senescence of SGZ cells due to Pb genotoxicity.

Depletion of TrkB Receptors From Adult Serotonergic Neurons Increases Brain Serotonin Levels, Enhances Energy Metabolism and Impairs Learning and Memory.

Neurotrophin brain-derived neurotrophic factor (BDNF) and neurotransmitter serotonin (5-HT) regulate each other and have been implicated in several neuronal mechanisms, including neuroplasticity. We have investigated the effects of BDNF on serotonergic neurons by deleting BDNF receptor TrkB from serotonergic neurons in the adult brain. The transgenic mice show increased 5-HT and Tph2 levels with abnormal behavioral phenotype. In spite of increased food intake, the transgenic mice are significantly leaner than their wildtype littermates, which may be due to increased metabolic activity. Consistent with increased 5-HT, the proliferation of hippocampal progenitors is significantly increased, however, long-term survival of newborn cells is unchanged. Our data indicates that BDNF-TrkB signaling regulates the functional phenotype of 5-HT neurons with long-term behavioral consequences.

The Effects of Serum Removal on Gene Expression and Morphological Plasticity Markers in Differentiated SH-SY5Y Cells

Despite the widespread use of the SH-SY5Y human neuroblastoma cell line in modeling human neurons in vitro, protocols for growth, differentiation and experimentation differ considerably across the literature. Many studies fully differentiate SH-SY5Y cells before experimentation, to investigate plasticity measures in a mature, human neuronal-like cell model. Prior to experimentation, serum is often removed from cell culture media, to arrest the cell growth cycle and synchronize cells. However, the exact effect of this serum removal before experimentation on mature, differentiated SH-SY5Y cells has not yet been described. In studies using differentiated SH-SY5Y cells, any effect of serum removal on plasticity markers may influence results. The aim of the current study was to systematically characterize, in differentiated, neuronal-like SH-SY5Y cells, the potentially confounding effects of complete serum removal in terms of morphological and gene expression markers of plasticity. We measured changes in commonly used morphological markers and in genes related to neuroplasticity and synaptogenesis, particularly in the BDNF-TrkB signaling pathway. We found that complete serum removal from already differentiated SH-SY5Y cells increases neurite length, neurite branching, and the proportion of cells with a primary neurite, as well as proportion of βIII-Tubulin and MAP2 expressing cells. Gene expression results also indicate increased expression of PSD95 and NTRK2 expression 24 h after serum removal. We conclude that serum deprivation in differentiated SH-SY5Y cells affects morphology and gene expression and can potentially confound plasticity-related outcome measures, having significant implications for experimental design in studies using differentiated SH-SY5Y cells as a model of human neurons.

Preservation of spatial memory and neuroprotection by the fatty acid amide hydrolase inhibitor URB597 in a rat model of vascular dementia.

BackgroundChronic cerebral hypoperfusion (CCH) is a major risk factor for vascular dementia (VaD). There are currently no broadly effective prevention or treatment strategies for VaD, but recent studies have reported promising results following vascular bypass surgery and pharmacomodulation of the brain endocannabinoid system (ECS). In this study, early effects of encephalomyosynangiosis (EMS) bypass surgery and augmented endocannabinoid signaling on CCH-induced cognitive dysfunction and neuronal damage were investigated.MethodsAn animal model of VaD was established by bilateral common carotid artery occlusion (BCCAO). Cannabinoid signaling was upregulated by treatment with the fatty acid amide hydrolase inhibitor URB597 (URB). Spatial learning and memory, cerebral blood flow (CBF), revascularization, brain-derived neurotrophic factor (BDNF)-tropomyosin receptor kinase B (TrkB) signaling, and apoptosis were compared among Sham, BCCAO, BCCAO + EMS, BCCAO + URB, and BCCAO + URB + EMS groups. Spatial learning and memory were evaluated using the Morris water maze (MWM). The CBF in cortex and hippocampus was evaluated by 3-dimensional arterial spin labeling. The neovascularization was visualized by CD34 immunofluorescence staining, and BDNF-TrkB signaling protein expression levels were assessed by Western blotting.ResultsTreatment with URB597 but not EMS alone reversed the spatial learning and memory deficits induced by BCCAO. Neovascularization was enhanced after EMS surgery but not by URB597. Alternatively, there were no significant differences in CBF among treatment groups. Expression levels of BDNF and TrkB were significantly reduced by CCH compared to Sham treatment, and downregulation of both proteins was reversed by URB597 treatment but not EMS. BCCAO enhanced neuronal apoptosis, which was also reversed by URB597.ConclusionsAugmentation of endogenous cannabinoid signaling but not EMS protects against CCH-induced neurodegeneration and preserves spatial learning and memory, possibly by activating BDNF-TrkB signaling.