BDNF over-expression increases olfactory bulb granule cell dendritic spine density in vivo

Expression profiling of mRNA and functional network analyses of genes regulated by human papilloma virus E6 and E7 proteins in HaCaT cells

Human papillomavirus (HPV) oncogenes E6 and E7 are essential for HPV-related cancer development. Here, we developed a cell line model using lentiviruses for transfection of the HPV16 oncogenes E6 and E7 and investigated the differences in mRNA expression during cell adhesion and chemokine secretion. Subsequently, RNA sequencing (RNA-seq) analysis was performed to explore the differences in mRNA expression. Compared to levels in the control group, 2,905 differentially expressed mRNAs (1,261 downregulated and 1,644 upregulated) were identified in the HaCaT-HPV16E6E7 cell line. To predict the functions of these differentially expressed genes (DEGs) the Gene Ontology and Kyoto Encyclopedia of Genes and Genomes databases were used. Protein–protein interactions were established, and the hub gene was identified based on this network. Real-time quantitative-PCR (RT-qPCR) was conducted to confirm the levels of 14 hub genes, which were consistent with the RNA-seq data. According to this, we found that these DEGs participate in the extracellular matrix (ECM), cell adhesion, immune control, and cancer-related signaling pathways. Currently, an increasing number of clinicians depend on E6/E7mRNA results to make a comprehensive judgment of cervical precancerous lesions. In this study, 14 hub genes closely related to the expression of cell adhesion ability and chemokines were analyzed in HPV16E6E7-stably expressing cell lines, which will open up new research ideas for targeting E6E7 in the treatment of HPV-related cancers.

Changes in Dendritic Spine Morphology and Density of Granule Cells in the Olfactory Bulb of Anguilla anguilla (L., 1758): A Possible Way to Understand Orientation and Migratory Behavior

Simple Summary

The olfactory bulb can process odour cues through granular cells (GCs) and dendritic spines, changing their synaptic plasticity properties and their morphology. The GCs’ dendritic spines density and morphology were analysed in Anguilla anguilla, considering the olfaction as a driver involved in fish orientation and migration. For the head and neck morphology, spines were classified as mushroom, long thin, stubby, and filopodia. Spines’ density decreased from juvenile migrants to no-migrant stages and increased in the adult migrants. Spines’ density was comparable between glass and silver eels as an adaptation to migration, while at non-migrating phases, spines’ density decreased. For its phylogenetic Elopomorph attribution and its complex life cycle, A. anguilla could be recommended as a model species to study the development of dendritic spines in GCs of the olfactory bulb. Considering the role of olfaction in the orientation and migration of A. anguilla, the modification of environmental stimuli (ocean alterations and climate change) could represent contributing factors that threaten this critically endangered species.

Abstract

Olfaction could represent a pivotal process involved in fish orientation and migration. The olfactory bulb can manage olfactive signals at the granular cell (GC) and dendritic spine levels for their synaptic plasticity properties and changing their morphology and structural stability after environmental odour cues. The GCs’ dendritic spine density and morphology were analysed across the life stages of the catadromous Anguilla anguilla. According to the head and neck morphology, spines were classified as mushroom (M), long thin (LT), stubby (S), and filopodia (F). Total spines’ density decreased from juvenile migrants to no-migrant stages, to increase again in the adult migrant stage. Mean spines’ density was comparable between glass and silver eels as an adaptation to migration. At non-migrating phases, spines’ density decreased for M and LT, while M, LT, and S density increased in silver eels. A great dendritic spine development was found in the two migratory phases, regressing in trophic phases, but that could be recreated in adults, tracing the migratory memory of the routes travelled in juvenile phases. For its phylogenetic Elopomorph attribution and its complex life cycle, A. anguilla could be recommended as a model species to study the development of dendritic spines in GCs of the olfactory bulb as an index of synaptic plasticity involved in the modulation of olfactory stimuli. If olfaction is involved in the orientation and migration of A. anguilla and if eels possess a memory, these processes could be influenced by the modification of environmental stimuli (ocean alterations and rapid climate change) contributing to threatening this critically endangered species.

Investigation of the Molecular Role of Brain-Derived Neurotrophic Factor in Alzheimer's Disease

Brain-derived neurotrophic factor (BDNF), or abrineurin, is a member of the neurotrophin family of growth factors that acts on both the central and peripheral nervous systems. BDNF is also well known for its cardinal role in normal neural maturation. It binds to at least two receptors at the cell surface known as tyrosine kinase B (TrkB) and p75^NTR. Additional neurotrophins that are anatomically linked with BDNF include neurotrophin-3 (NT-3), neurotrophin-4 (NT-4), and nerve growth factor (NGF). It is evident that BDNF levels in patients with Alzheimer's disease (AD) are altered. AD is a progressive disorder and a form of dementia, where the mental function of an elderly person is disrupted. It is associated with a progressive decline in cognitive function, which mainly targets the thinking, memory, and behavior of the person. The degeneration of neurons occurs in the cerebral cortex region of brain. The two major sources responsible for neuronal degeneration are protein fragment amyloid-beta (Aβ), which builds up in the spaces between the nerve cells, known as plaques, disrupting the neuron signaling pathway and leading to dementia, and neurofibrillary tangles (NFTs), which are the twisted fibers of proteins that build up inside the cells. AD is highly prevalent, with recent data indicating nearly 5.8 million Americans aged 65 and older with AD in 2020, and with 80% of patients 75 and older. AD is recognized as the sixth leading cause of death in the USA, and its prevalence is predicted to increase exponentially in the coming years. As AD worsens over time, it becomes increasingly important to understand the exact pathophysiology, biomarkers, and treatment. In this article, we focus primarily on the controversial aspect of BDNF in AD, including its influence on various other proteins and enzymes and the current treatments associated with BDNF, along with future perspectives.

Ultrasound Combined With Microbubbles Loading BDNF Retrovirus to Open BloodBrain Barrier for Treatment of Alzheimer's Disease

Background: Brain-derived nerve growth factor (BDNF) is a promising effective target for the treatment of Alzheimer's disease (AD). BDNF, which has a high molecular weight, has difficulty in crossing the blood-brain barrier (BBB). The study aimed to prepare microbubbles loading brain-derived nerve growth factor (BDNF) retrovirus (MpLXSN-BDNF), to verify the characteristics of the microbubbles, and to study the therapeutic effect of the microbubbles combined with ultrasound on the opening of the blood-brain barrier in an AD rat model. Methods: 32 adult male SD rats were randomly divided into four groups: control group, ultrasound + pLXSN-EGFP microbubble group (U + MpLXSN-BDNF), ultrasound + pLXSN-BDNF microbubble group, and ultrasound + microbubble + pLXSN-BDNF virus group (U + MpLXSN-BDNF), with eight rats in each group. At the same time, the left hippocampus of rats was irradiated with low-frequency focused ultrasound guided by MRI to open the blood-brain barrier (BBB). The effects of BDNF overexpression on AD rats were evaluated behaviorally before and 1 month after the treatment. The number of acetylcholinesterase (ChAT)-positive cells and the content of acetylcholine (ACh) in brain tissues were determined by immunohistochemistry and high-performance liquid chromatography (HPLC), respectively. IF staining of synaptic spines and Western blot of synaptophysin presented herein detected synaptic density recovery. Results: Signal intensity enhancement at the BBB disruption sites could be observed on the MR images. The behavioral evaluation showed that the times of crossing the original platform in the U + MpLXSN-BDNF group increased significantly after treatment. Immunohistochemistry and HPLC revealed that the number of ChAT-positive neurons and the contents of ACh in the brain were significantly decreased in the treated groups compared with the controls. IF staining of synaptic spines and Western blot data of synaptophysin showed that the U + MpLXSN-BDNF group can recover the synaptic loss better by BDNF supplementation than the other treatment groups. Conclusion: Ultrasound combined with viral microbubbles carrying BDNF can increase the transfection efficiency of brain neurons, promote the high expression of exogenous gene BDNF, and play a therapeutic role in the AD model rats.

Distinct Effects of BDNF and NT-3 on the Dendrites and Presynaptic Boutons of Developing Olfactory Bulb GABAergic Interneurons In Vitro

Brain-derived neurotrophic factor (BDNF) and neurotrophin 3 (NT-3) are known to regulate neuronal morphology and the formation of neural circuits, yet the neuronal targets of each neurotrophin are still to be defined. To address how these neurotrophins regulate the morphological and synaptic differentiation of developing olfactory bulb (OB) GABAergic interneurons, we analyzed the effect of BDNF and NT-3 on GABA⁺-neurons and on different subtypes of these neurons: tyrosine hydroxylase (TH⁺); calretinin (Calr⁺); calbindin (Calb⁺); and parvalbumin (PVA⁺). These cells were generated from cultured embryonic mouse olfactory bulb neural stem cells (eOBNSCs) and after 14 days in vitro (DIV), when the neurons expressed TrkB and/or TrkC receptors, BDNF and NT-3 did not significantly change the number of neurons. However, long-term BDNF treatment did produce a longer total dendrite length and/or more dendritic branches in all the interneuron populations studied, except for PVA⁺-neurons. Similarly, BDNF caused an increase in the cell body perimeter in all the interneuron populations analyzed, except for PVA⁺-neurons. GABA⁺- and TH⁺-neurons were also studied at 21 DIV, when BDNF produced significantly longer neurites with no clear change in their number. Notably, these neurons developed synaptophysin⁺ boutons at 21 DIV, the size of which augmented significantly following exposure to either BDNF or NT-3. Our results show that in conditions that maintain neuronal survival, BDNF but not NT-3 promotes the morphological differentiation of developing OB interneurons in a cell-type-specific manner. In addition, our findings suggest that BDNF and NT-3 may promote synapse maturation by enhancing the size of synaptic boutons.

Intervention of Brain-Derived Neurotrophic Factor and Other Neurotrophins in Adult Neurogenesis

Cell survival during adult neurogenesis and the modulation of each step, namely, proliferation, lineage differentiation, migration, maturation, and functional integration of the newborn cells into the existing circuitry, is regulated by intrinsic and extrinsic factors. Transduction of extracellular niche signals triggers the activation of intracellular mechanisms that regulate adult neurogenesis by affecting gene expression. While the intrinsic factors include transcription factors and epigenetic regulators, the extrinsic factors are molecular signals that are present in the neurogenic niche microenvironment. These include morphogens, growth factors, neurotransmitters, and signaling molecules secreted as soluble factors or associated to the extracellular matrix. Among these molecular mechanisms are neurotrophins and neurotrophin receptors which have been implicated in the regulation of adult neurogenesis at different levels, with brain-derived neurotrophic factor (BDNF) being the most studied neurotrophin. In this chapter, we review the current knowledge about the role of neurotrophins in the regulation of adult neurogenesis in both the subventricular zone (SVZ) and the hippocampal subgranular zone (SGZ).

Genetic Increases in Olfactory Bulb BDNF Do Not Enhance Survival of Adult-Born Granule Cells

Adult-born neurons produced in the dentate gyrus subgranular zone (SGZ) develop as excitatory hippocampal granule cells (GCs), while those from the subventricular zone (SVZ) migrate to the olfactory bulb (OB), where most develop as GABAergic olfactory GCs. Both types of neurons express TrkB as they mature. Normally ~50% of new olfactory GCs survive, but survival declines if sensory drive is reduced. Increases in endogenous brain-derived neurotrophic factor (BDNF) in hippocampus, particularly with wheel running, enhance dentate GC survival. Whether survival of new olfactory GCs is impacted by augmenting BDNF in the OB, where they mature and integrate, is not known. Here, we determined if increasing OB BDNF expression enhances survival of new GCs, and if it counters their loss under conditions of reduced sensory activity. Neurogenesis was assessed under normal conditions, and following unilateral naris occlusion, in mice overexpressing BDNF in the granule cell layer (GCL). OB BDNF levels were significantly higher in transgenic mice compared to controls, and this was maintained following sensory deprivation. Bromodeoxyuridine (BrdU) cell birth dating showed that at 12-14 days post-BrdU, numbers of new GCs did not differ between genotypes, indicating normal recruitment to the OB. At later intervals, transgenic and control mice showed levels of GC loss in deprived and nondeprived animals that were indistinguishable, as was the incidence of apoptotic cells in the GCL. These results demonstrate that, in contrast to new dentate GCs, elevations in endogenous BDNF do not enhance survival of adult-born olfactory GCs.

Impairment of Dendrodendritic Inhibition in the Olfactory Bulb of APP/PS1 Mice

Olfactory dysfunction is an early event in Alzheimer’s disease (AD). However, the mechanism underlying the AD-related changes in the olfactory bulb (OB) remains unknown. Granule cells (GCs) in the OB regulate the activity of mitral cells (MCs) through reciprocal dendrodendritic synapses, which is crucial for olfactory signal processing and odor discrimination. Nevertheless, the relationships between the morphological and functional changes of dendrodendritic synapses, particularly the local field potentials (LFPs) as a consequence of olfactory disorders in patients with AD have not been investigated. Here, we studied the morphological and functional changes induced by dendrodendritic inhibition in GCs onto MCs in the OB of amyloid precursor protein (APP)/PS1 mice and age-matched control mice during aging, particular, we focused on the effects of olfactory disorder in the dendrodendritic synaptic structures and the LFPs. We found that olfactory disorder was associated with increased amyloid-β (Aβ) deposits in the OB of APP/PS1 mice, and those mice also exhibited abnormal changes in the morphology of GCs and MCs, a decreased density of GC dendritic spines and impairments in the synaptic interface of dendrodendritic synapses between GCs and MCs. In addition, the aberrant enhancements in the γ oscillations and firing rates of MCs in the OB of APP/PS1 mice were recorded by multi-electrode arrays (MEAs). The local application of a GABA_AR agonist nearly abolished the aberrant increase in γ oscillations in the external plexiform layer (EPL) at advanced stages of AD, whereas a GABA_AR antagonist aggravated the γ oscillations. Based on our findings, we concluded that the altered morphologies of the synaptic structures of GCs, the dysfunction of reciprocal dendrodendritic synapses between MCs and GCs, and the abnormal γ oscillations in the EPL might contribute to olfactory dysfunction in AD.

Kinase activity in the olfactory bulb is required for odor memory consolidation

Long-term fear memory formation in the hippocampus and neocortex depends upon brain-derived neurotrophic factor (BDNF) signaling after acquisition. Incremental, appetitive odor discrimination learning is thought to depend substantially on the differentiation of adult-born neurons within the olfactory bulb (OB)—a process that is closely associated with BDNF signaling. We sought to elucidate the role of neurotrophin signaling within the OB on odor memory consolidation. Male mice were trained on odor–reward associative discriminations after bilateral infusion of the kinase inhibitor K252a, or vehicle control, into the OB. K252a is a partially selective inhibitor of tyrosine kinase (Trk) receptors, including the TrkB receptor for BDNF, though it also inhibits other plasticity-related kinases such as PKC and CaMKII/IV. K252a infusion into the OB did not impair odor acquisition or short-term (2 h) memory for the learned discriminations, but significantly impaired long-term (48 h) odor memory (LTM). This LTM deficit also was associated with reduced selectivity for the conditioned odorant in a reward-seeking digging task. Infusions of K252a immediately prior to testing did not impair LTM recall. These results indicate that kinase activation in the OB is required for the consolidation of odor memory of incrementally acquired information.

Neonatal Hyperoxia Perturbs Neuronal Development in the Cerebellum

Impaired postnatal brain development of preterm infants often results in neurological deficits. Besides pathologies of the forebrain, maldeveolopment of the cerebellum is increasingly recognized to contribute to psychomotor impairments of many former preterm infants. However, causes are poorly defined. We used a hyperoxia model to define neonatal damage in cerebellar granule cell precursors (GCPs) and in Purkinje cells (PCs) known to be essential for interaction with GCPs during development. We exposed newborn rats to 24 h 80% O₂ from age P6 to P7 to identify postnatal and long-term damage in cerebellar GCPs at age P7 after hyperoxia and also after recovery in room air thereafter until P11 and P30. We determined proliferation and apoptosis of GCPs and immature neurons by immunohistochemistry, quantified neuronal damage by qPCR and Western blots for neuronal markers, and measured dendrite outgrowth of PCs by CALB1 immunostainings and by Sholl analysis of Golgi stainings. After hyperoxia, proliferation of PAX6+ GCPs was decreased at P7, while DCX + CASP3+ cells were increased at P11. Neuronal markers Pax6, Tbr2, and Prox1 were downregulated at P11 and P30. Neuronal damage was confirmed by reduced NeuN protein expression at P30. Sonic hedgehog (SHH) was significantly decreased at P7 and P11 after hyperoxia and coincided with lower CyclinD2 and Hes1 expression at P7. The granule cell injury was accompanied by hampered PC maturation with delayed dendrite formation and impaired branching. Neonatal injury induced by hyperoxia inhibits PC functioning and impairs granule cell development. As a conclusion, maldevelopment of the cerebellar neurons found in preterm infants could be caused by postnatal oxygen toxicity.

Adult neurogenesis and neurodegenerative diseases: A systems biology perspective

New neurons are generated throughout adulthood in two regions of the brain, the olfactory bulb and dentate gyrus of the hippocampus, and are incorporated into the hippocampal network circuitry; disruption of this process has been postulated to contribute to neurodegenerative diseases including Alzheimer's disease and Parkinson's disease. Known modulators of adult neurogenesis include signal transduction pathways, the vascular and immune systems, metabolic factors, and epigenetic regulation. Multiple intrinsic and extrinsic factors such as neurotrophic factors, transcription factors, and cell cycle regulators control neural stem cell proliferation, maintenance in the adult neurogenic niche, and differentiation into mature neurons; these factors act in networks of signaling molecules that influence each other during construction and maintenance of neural circuits, and in turn contribute to learning and memory. The immune system and vascular system are necessary for neuronal formation and neural stem cell fate determination. Inflammatory cytokines regulate adult neurogenesis in response to immune system activation, whereas the vasculature regulates the neural stem cell niche. Vasculature, immune/support cell populations (microglia/astrocytes), adhesion molecules, growth factors, and the extracellular matrix also provide a homing environment for neural stem cells. Epigenetic changes during hippocampal neurogenesis also impact memory and learning. Some genetic variations in neurogenesis related genes may play important roles in the alteration of neural stem cells differentiation into new born neurons during adult neurogenesis, with important therapeutic implications. In this review, we discuss mechanisms of and interactions between these modulators of adult neurogenesis, as well as implications for neurodegenerative disease and current therapeutic research. © 2016 Wiley Periodicals, Inc.

Cortical Plasticity and Olfactory Function in Early Blindness

Over the last decade, functional brain imaging has provided insight to the maturation processes and has helped elucidate the pathophysiological mechanisms involved in brain plasticity in the absence of vision. In case of congenital blindness, drastic changes occur within the deafferented “visual” cortex that starts receiving and processing non visual inputs, including olfactory stimuli. This functional reorganization of the occipital cortex gives rise to compensatory perceptual and cognitive mechanisms that help blind persons achieve perceptual tasks, leading to superior olfactory abilities in these subjects. This view receives support from psychophysical testing, volumetric measurements and functional brain imaging studies in humans, which are presented here.

Gain of BDNF Function in Engrafted Neural Stem Cells Promotes the Therapeutic Potential for Alzheimer's Disease

Stem cell-based therapy is a potential treatment for neurodegenerative diseases, but its application to Alzheimer’s disease (AD) remains limited. Brain-derived neurotrophic factor (BDNF) is critical in the pathogenesis and treatment of AD. Here, we present a novel therapeutic approach for AD treatment using BDNF-overexpressing neural stem cells (BDNF-NSCs). In vitro, BDNF overexpression was neuroprotective to beta-amyloid-treated NSCs. In vivo, engrafted BDNF-NSCs-derived neurons not only displayed the Ca²⁺-response fluctuations, exhibited electrophysiological properties of mature neurons and integrated into local brain circuits, but recovered the cognitive deficits. Furthermore, BDNF overexpression improved the engrafted cells’ viability, neuronal fate, neurite complexity, maturation of electrical property and the synaptic density. In contrast, knockdown of the BDNF in BDNF-NSCs diminished stem cell-based therapeutic efficacy. Together, our findings indicate BDNF overexpression improves the therapeutic potential of engrafted NSCs for AD via neurogenic effects and neuronal replacement, and further support the feasibility of NSC-based ex vivo gene therapy for AD.

Increased Olfactory Bulb BDNF Expression Does Not Rescue Deficits in Olfactory Neurogenesis in the Huntington's Disease R6/2 Mouse

Huntington's disease (HD) is an inherited neurodegenerative disorder caused by expansion of CAG trinucleotide repeats in the huntingtin gene. Mutant huntingtin protein (mhtt) interferes with the actions of brain-derived neurotrophic factor (BDNF), and BDNF signaling is reduced in the diseased striatum. Loss of this trophic support is thought to contribute to loss of striatal medium spiny neurons in HD. Increasing BDNF in the adult striatum or ventricular ependyma slows disease progression in HD mouse models, and diverts subventricular zone (SVZ)-derived neuroblasts from their normal destination, the olfactory bulb, to the striatum, where some survive and develop features of mature neurons. Most neuroblasts that migrate to the olfactory bulb differentiate as granule cells, with approximately half surviving whereas others undergo apoptosis. In the R6/2 HD mouse model, survival of adult-born granule cells is reduced. Newly maturing cells express the BDNF receptor TrkB, suggesting that mhtt may interfere with normal BDNF trophic activity, increasing their loss. To determine if augmenting BDNF counteracts this, we examined granule cell survival in R6/2 mice that overexpress BDNF in olfactory bulb. Although we detected a decline in apoptosis, increased BDNF was not sufficient to normalize granule cell survival within their normal target in R6/2 mice.

Molecular Mechanisms Regulating the Dendritic Development of Newborn Olfactory Bulb Interneurons in a Sensory Experience-Dependent Manner

Inhibitory interneurons in the olfactory bulb are generated continuously throughout life in the subventricular zone and differentiate into periglomerular and granule cells. Neural circuits that undergo reorganization by newborn olfactory bulb interneurons are necessary for odor detection, odor discrimination, olfactory memory, and innate olfactory responses. Although sensory experience has been shown to regulate development in a variety of species and in various structures, including the retina, cortex, and hippocampus, little is known about how sensory experience regulates the dendritic development of newborn olfactory bulb interneurons. Recent studies revealed that the 5T4 oncofetal trophoblast glycoprotein and the neuronal Per/Arnt/Sim domain protein 4 (Npas4) transcription factor regulate dendritic branching and dendritic spine formation, respectively, in olfactory bulb interneurons. Here, we summarize the molecular mechanisms that underlie the sensory input-dependent development of newborn interneurons and the formation of functional neural circuitry in the olfactory bulb.