Role of Nerve Growth Factor in Plasticity of Forebrain Cholinergic Neurons

Enhancement of neural regeneration as a therapeutic strategy for Alzheimer's disease (Review)

Alzheimer's disease (AD), the most common cause of dementia worldwide, has gradually become a global health concern for society and individuals with the process of global ageing. Although extensive research has been carried out on AD, the etiology and pathological mechanism of the disease are still unclear, and there is no specific drug to cure or delay AD progression. The exploration of enhancing nerve regeneration in AD has gradually attracted increasing attention. In the current review, the existing therapeutic strategies were summarized to induce nerve regeneration which can increase the number of neurons, and improve the survival of neurons, the plasticity of synapses and synaptic activity. The strategies include increasing neurotrophic expression (such as brain-derived neurotrophic factor and nerve growth factor), inhibiting acetylcholinesterase (such as donepezil, tacrine, rivastigmine and galanthamine), elevating histone deacetylase levels (such as RGFP-966, Tasquinimod, CM-414 and 44B), stimulating the brain by physiotherapy (such as near-infrared light, repetitive transcranial magnetic stimulation, and transcranial direct current stimulation) and transplanting exogenous neural stem cells. However, further evaluations need to be performed to determine the optimal treatment. The present study reviews recent interventions for enhancing adult neurogenesis and attempts to elucidate their mechanisms of action, which may provide a theoretical basis for inducing nerve regeneration to fight against AD.

Targeting Persistent Changes in Neuroimmune and Epigenetic Signaling in Adolescent Drinking to Treat Alcohol Use Disorder in Adulthood

Studies universally find early age of drinking onset is linked to lifelong risks of alcohol problems and alcohol use disorder (AUD). Assessment of the lasting effect of drinking during adolescent development in humans is confounded by the diversity of environmental and genetic factors that affect adolescent development, including emerging personality disorders and progressive increases in drinking trajectories into adulthood. Preclinical studies using an adolescent intermittent ethanol (AIE) exposure rat model of underage binge drinking avoid the human confounds and support lifelong changes that increase risks. AIE increases adult alcohol drinking, risky decision-making, reward-seeking, and anxiety as well as reductions in executive function that all increase risks for the development of an AUD. AIE causes persistent increases in brain neuroimmune signaling high-mobility group box 1 (HMGB1), Toll-like receptor, receptor for advanced glycation end products, and innate immune genes that are also found to be increased in human AUD brain. HMGB1 is released from cells by ethanol, both free and within extracellular vesicles, that act on neurons and glia, shifting transcription and cellular phenotype. AIE-induced decreases in adult hippocampal neurogenesis and loss of basal forebrain cholinergic neurons are reviewed as examples of persistent AIE-induced pathology. Both are prevented and reversed by anti-inflammatory and epigenetic drugs. Findings suggest AIE-increased HMGB1 signaling induces the RE-1 silencing transcript blunting cholinergic gene expression, shifting neuronal phenotype. Inhibition of HMGB1 neuroimmune signaling, histone methylation enzymes, and galantamine, the cholinesterase inhibitor, both prevent and reverse AIE pathology. These findings provide new targets that may reverse AUD neuropathology as well as other brain diseases linked to neuroimmune signaling. SIGNIFICANCE STATEMENT: Adolescent underage binge drinking studies find that earlier adolescent drinking is associated with lifelong alcohol problems including high levels of lifetime alcohol use disorder (AUD). Preclinical studies find the underage binge drinking adolescent intermittent ethanol (AIE) model causes lasting changes in adults that increase risks of developing adult alcohol problems. Loss of hippocampal neurogenesis and loss of basal forebrain cholinergic neurons provide examples of how AIE-induced epigenetic and neuroimmune signaling provide novel therapeutic targets for adult AUD.

Nerve Growth Factor (NGF) Encourages the Neuroinvasive Potential of Pancreatic Cancer Cells by Activating the Warburg Effect and Promoting Tumor Derived Exosomal miRNA-21 Expression

Background

It has been reported that signaling from the nerve growth factor (NGF) pathway associated with peripheral nerves is able to contribute to perineural invasion (PNI) of pancreatic cancer (PC). Nevertheless, the underlying mechanism by which NGF leads to PNI remained poorly understood.

Methods

Western blotting was employed to determine NGF level in PC and paracarcinoma tissues and in PC cell lines as well as pancreatic ductal epithelial cells. MiaPaCa-2 and CFPAC-1 cells were treated with 100 ng/ml of NGF or the NGF inhibitor Tanezumab for 24 h, CCK-8 and Transwell assays were employed to test cell proliferation, invasion, and migration, respectively. TrkA expression was knocked down in MiaPaCa-2 and dorsal root ganglion (DRG) cells treated with NGF to determine its effect on the Warburg effect. To reveal that the NGF-TrkA signaling pathway was closely associated with PC PNI, in vitro neuroinvasion model was established by using MiaPaCa-2 cells via coculturing DRG cells in Matrigel. Further, exosomes were extracted from PC cells and identified by examining the levels of specific markers for exosomes. Then RT-qPCR was applied to test miR-21-5p level in tumor derived exosomal (TDE-miR-21-5p). RIP assay was performed to validate NGF and miR-21 binding ability in MiaPaCa-2 cells. Rescue experiments were performed by using coprocessing of Tanezumab and miR-21-5p mimic on MiaPaCa-2 cells, followed by coculture with DRG cells. Subsequently, we used a model of neuroinvasion in nude mice to assess the effect of NGF in vivo on tumor nerve invasion as well as on nociceptive transmission.

Results

NGF level was preeminently higher in PC tissues and cell lines than in paracarcinoma tissues and normal pancreatic epithelial cell lines. NGF promoted MiaPaCa-2 and CFPAC-1 cell invasion and migration, while Tanezumab treatment showed the opposite results. Besides, NGF binding to TrkA receptors encouraged the intracellular Warburg effect in PC and DRG cells. TrkA blocking-up could restrain NGF induced PC cell migration and neural invasion. Mechanistically, NGF could upregulate TDE-miR-21-5p levels, and DRG cells took up TDE to activate the Warburg effect and stimulate nociceptor gene expression. miR-21-5p inhibitor could abolish the facilitative effect of NGF on PNI in MiaPaCa-2 cells. In vivo tumorigenesis experiments, Tanezumab markedly alleviated nerve invasion of PC cells as well as relieved nociceptive conduction in animal models.

Conclusions

These findings displayed that NGF/TrkA encouraged the neuroinvasive potential of PC cells by activating the Warburg effect in DRG cells through upregulation of TDE-miR-21-5p expression.

A Microglial Function for the Nerve Growth Factor: Predictions of the Unpredictable

Microglia are the only immune cell population present in the brain parenchyma. Their vantage position in the central nervous system (CNS) enables these myeloid cells to perform the most disparate of tasks: from the classical immune functions of fighting infections and surveilling the extracellular space for pathogens and damage, to sculpting the neuronal circuitry by pruning unnecessary synapses and assisting neurons in spine formation, aiding in the maintenance of brain homeostasis. The neurotrophin field has always been dominated by the neurocentric view that the primary target of these molecules must be neurons: this holds true even for the Nerve Growth Factor (NGF), which owes its popularity in the neuroscience community to its trophic and tropic activity towards sensory and sympathetic neurons in the peripheral nervous system, and cholinergic neurons in the CNS. The increasing evidence that microglia are an integral part of neuronal computation calls for a closer look as to whether these glial cells are capable of responding directly to NGF. In this review, we will first outline evidence in support of a role for NGF as a molecule mediating neuroimmune communication. Then, we will illustrate some of those non-immune features that have made microglial cells one of the hottest topics of this last decade. In conclusion, we will discuss evidence in support of a microglial function for NGF.

Protective Effects of a synthetic glycosaminoglycan mimetic (OTR4132) in a rat immunotoxic lesion model of septohippocampal cholinergic degeneration

Using a partial hippocampal cholinergic denervation model, we assessed the effects of the RGTA^® named OTR4132, a synthetic heparan-mimetic biopolymer with neuroprotective/neurotrophic properties. Long-Evans male rats were injected with the cholinergic immunotoxin 192 IgG-saporin into the medial septum/diagonal band of Broca (0.37 µg); vehicle injections served as controls. Immediately after surgery, OTR4132 was injected into the lateral ventricles (0.25 µg/5 µl/rat) or intramuscularly (1.5 mg/kg). To determine whether OTR4132 reached the lesion site, some rats received intracerebroventricular (ICV) or intramuscular (I.M.) injections of fluorescent OTR4132. Rats were sacrificed at 4, 10, 20, or 60 days post-lesion (DPL). Fluorescein-labeled OTR4132 injected ICV or I.M. was found in the lesion from 4 to 20 DPL. Rats with partial hippocampal cholinergic denervation showed decreases in hippocampal acetylcholinesterase reaction products and in choline acetyltransferase-positive neurons in the medial septum. These lesions were the largest at 10 DPL and then remained stable until 60 DPL. Both hippocampal acetylcholinesterase reaction products and choline acetyltransferase-positive neurons in the medial septum effects were significantly attenuated in OTR4132-treated rats. These effects were not related to competition between OTR4132 and 192 IgG-saporin for the neurotrophin receptor P75 (p75^NTR), as OTR4132 treatment did not alter the internalization of Cy3-labelled 192 IgG. OTR4132 was more efficient at reducing the acetylcholinesterase reaction products and choline acetyltransferase-positive neurons than a comparable heparin dose used as a comparator. Using the slice superfusion technique, we found that the lesion-induced decrease in muscarinic autoreceptor sensitivity was abolished by intramuscular OTR4132. After partial cholinergic damage, OTR4132 was able to concentrate at the brain lesion site possibly due to the disruption of the blood-brain barrier and to exert structural and functional effects that hold promises for neuroprotection/neurotrophism.

Neuroprotective Effects of Physical Activity via the Adaptation of Astrocytes

The multifold benefits of regular physical exercise have been largely demonstrated in human and animal models. Several studies have reported the beneficial effects of physical activity, both in peripheral tissues and in the central nervous system (CNS). Regular exercise improves cognition, brain plasticity, neurogenesis and reduces the symptoms of neurodegenerative diseases, making timeless the principle of “mens sana in corpore sano” (i.e., a healthy mind in a healthy body). Physical exercise promotes morphological and functional changes in the brain, acting not only in neurons but also in astrocytes, which represent the most numerous glial cells in the brain. The multiple effects of exercise on astrocytes comprise the increased number of new astrocytes, the maintenance of basal levels of catecholamine, the increase in glutamate uptake, the major release of trophic factors and better astrocytic coverage of cerebral blood vessels. The purpose of this review is to highlight the effects of exercise on brain function, emphasize the role of astrocytes in the healthy CNS, and provide an update for a better understanding of the effects of physical exercise in the modulation of astrocyte function.

Beneficial Effects of Choline Alphoscerate on Amyloid-β Neurotoxicity in an In vitro Model of Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is the most common form of neurodegenerative disorder characterized by cognitive impairment, which represents an urgent public health concern. Given the worldwide impact of AD, there is a compelling need for effective therapies to slow down or halt this disorder.

OBJECTIVE

Choline alphoscerate (α-GPC) represents a potentially effective cholinergic neurotrans- mission enhancing agent with an interesting clinical profile in cognitive dysfunctions improve- ment, although only scanty data are available about the mechanisms underlying such beneficial ef- fects.

METHOD

The SH-SY5Y neuronal cell line, differentiated for 1 week with 10 μm of all-trans-reti- noic acid (RA), to achieve a switch towards a cholinergic phenotype, was used as an in vitro model of AD. SH-SY5Y cells were pre-treated for 1h with α-GPC (100nM) and treated for 72 h with Aβ25-35 (10μM).

RESULTS

α-GPC was able to antagonize Aβ25-35 mediated neurotoxicity and attenuate the Aβ-in- duced phosphorylation of the Tau protein. Moreover, α-GPC exerted its beneficial effects by em- ploying the NGF/TrkA system, knocked down in AD and, consequently, by sustaining the expres- sion level of synaptic vesicle proteins, such as synaptophysin.

CONCLUSION

Taken together, our data suggest that α-GPC can have a role in neuroprotection in the course of toxic challenges with Aβ. Thus, a deeper understanding of the mechanism underlying its beneficial effect, could provide new insights into potential future pharmacological applications of its functional cholinergic enhancement, with the aim to mitigate AD and could represent the basis for innovative therapy.Recent Advances in Anti-Infective Drug Discovery.

Elevated Levels of miR-144-3p Induce Cholinergic Degeneration by Impairing the Maturation of NGF in Alzheimer's Disease

Cholinergic degeneration is one of the key pathological hallmarks of Alzheimer’s disease (AD), a condition that is characterized by synaptic disorders and memory impairments. Nerve growth factor (NGF) is secreted in brain regions that receive projections from the basal forebrain cholinergic neurons. The trophic effects of NGF rely on the appropriate maturation of NGF from its precursor, proNGF. The ratio of proNGF/NGF is known to be increased in patients with AD; however, the mechanisms that underlie this observation have yet to be elucidated. Here, we demonstrated that levels of miR-144-3p are increased in the hippocampi and the medial prefrontal cortex of an APP/PS1 mouse model of AD. These mice also exhibited cholinergic degeneration (including the loss of cholinergic fibers, the repression of choline acetyltransferase (ChAT) activity, the reduction of cholinergic neurons, and an increased number of dystrophic neurites) and synaptic/memory deficits. The elevated expression of miR-144-3p specifically targets the mRNA of tissue plasminogen activator (tPA) and reduces the expression of tPA, thus resulting in the abnormal maturation of NGF. The administration of miR-144-3p fully replicated the cholinergic degeneration and synaptic/memory deficits observed in the APP/PS1 mice. The injection of an antagomir of miR-144-3p into the hippocampi partially rescued cholinergic degeneration and synaptic/memory impairments by restoring the levels of tPA protein and by correcting the ratio of proNGF/NGF. Collectively, our research revealed potential mechanisms for the disturbance of NGF maturation and cholinergic degeneration in AD and identified a potential therapeutic target for AD.

NGF-Induced Nav1.7 Upregulation Contributes to Chronic Post-surgical Pain by Activating SGK1-Dependent Nedd4-2 Phosphorylation

At present, chronic post-surgical pain (CPSP) is difficult to prevent and cure clinically because of our lack of understanding of its mechanisms. Surgical injury induces the upregulation of voltage-gated sodium channel Nav1.7 in dorsal root ganglion (DRG) neurons, suggesting that Nav1.7 is involved in the development of CPSP. However, the mechanism leading to persistent dysregulation of Nav1.7 is largely unknown. Given that nerve growth factor (NGF) induces a long-term increase in the neuronal hyperexcitability after injury, we hypothesized that NGF might cause the long-term dysregulation of Nav1.7. In this study, we aimed to investigate whether Nav1.7 regulation by NGF is involved in CPSP and thus contributes to the specific mechanisms involved in the development of CPSP. Using conditional nociceptor-specific Nav1.7 knockout mice, we confirmed the involvement of Nav1.7 in NGF-induced pain and identified its role in the maintenance of pain behavior during long-term observations (up to 14 days). Using western blot analyses and immunostaining, we showed that NGF could trigger the upregulation of Nav1.7 expression and thus support the development of CPSP in rats. Using pharmacological approaches, we showed that the increase of Nav1.7 might be partly regulated by an NGF/TrkA-SGK1-Nedd4-2-mediated pathway. Furthermore, reversing the upregulation of Nav1.7 in DRG could alleviate spinal sensitization. Our results suggest that the maintained upregulation of Nav1.7 triggered by NGF contributes to the development of CPSP. Attenuating the dysregulation of Nav1.7 in peripheral nociceptors may be a strategy to prevent the transition from acute post-surgical pain to CPSP.

Gene and cell therapy for the nucleus basalis of Meynert with NGF in Alzheimer's disease

There is currently no effective treatment for the most common of the dementia disorders, Alzheimer's disease (AD). It has been known for decades that the central cholinergic system is important for memory. The cholinergic neurons in the basal forebrain with its cortical and hippocampal projections degenerate in AD and thus contribute to the cognitive decline characteristic of AD. This knowledge led to the development of the currently approved treatment for AD, with inhibitors of acetylcholine-esterase targeting the cholinergic system with beneficial but mild effects. In recent years, other approaches to influence the degenerating cholinergic system in AD focusing on nerve growth factor (NGF) have been undertaken. NGF is required for the survival and function of the basal forebrain cholinergic neurons, the most important being the nucleus basalis of Meynert (nbM). Since there is a lack of NGF and its receptors in the AD forebrain, the hypothesis is that local delivery of NGF to the nbM could revive the cholinergic circuitry and thereby restore cognitive functions. Since NGF does not pass through the blood-brain barrier, approaches involving cerebral injections of genetically modified cells or viral vectors or implantation of encapsulated cells in the nbM in AD patients have been used. These attempts have been partially successful but also have limitations, which are presented and discussed here. In conclusion, these trials point to the importance of further development of NGF-related therapies in AD.

Nerve Growth Factor in Alcohol Use Disorders

The nerve growth factor (NGF) belongs to the family of neurotrophic factors. Initially discovered as a signaling molecule involved in the survival, protection, differentiation, and proliferation of sympathetic and peripheral sensory neurons, it also participates in the regulation of the immune system and endocrine system. NGF biological activity is due to the binding of two classes of receptors: the tropomyosin-related kinase A (TrkA) and the low-affinity NGF pan-neurotrophin receptor p75. Alcohol Use Disorders (AUD) are one of the most frequent mental disorders in developed countries, characterized by heavy drinking, despite the negative effects of alcohol on brain development and cognitive functions that cause individual’s work, medical, legal, educational, and social life problems. In addition, alcohol consumption during pregnancy disrupts the development of the fetal brain causing a wide range of neurobehavioral outcomes collectively known as fetal alcohol spectrum disorders (FASD). The rationale of this review is to describe crucial findings on the role of NGF in humans and animals, when exposed to prenatal, chronic alcohol consumption, and on binge drinking.

GK-2 Reduces Death of Cultured Granule Neurons in Cerebellum Induced by the Toxic Effects of Zinc Ions

Peptide mimetic of nerve growth factor GK-2 in a dose of 1-2 mg/liter improves survival of cultured rat cerebellar granule neurons exposed to the cytotoxic effect of zinc ions, but has no protective effect against copper ion cytotoxicity. Experiments on cultured rat hippocampal slices demonstrated that GK-2 did not affect reactivity of pyramidal neurons and long-term potentiation in the hippocampal field CA1 and the probability of glutamate release from presynaptic terminals in the synapses of the CA3-CA1 fields. The results suggest that GK-2 does not affect the functional properties of synaptic transmission under normal conditions, but protects neurons from the toxic effects of zinc, which creates prerequisites for GK-12 use in the treatment of neurodegenerative diseases.

Neuroimmune and epigenetic involvement in adolescent binge ethanol-induced loss of basal forebrain cholinergic neurons: Restoration with voluntary exercise

Binge drinking and alcohol abuse are common during adolescence and cause lasting pathology. Preclinical rodent studies using the adolescent intermittent ethanol (AIE; 5.0 g/kg, i.g., 2‐day on/2‐day off from postnatal day [P]25 to P55) model of human adolescent binge drinking report decreased basal forebrain cholinergic (ie, ChAT+) neurons that persist into adulthood (ie, P56‐P220). Recent studies link AIE‐induced neuroimmune activation to cholinergic pathology, but the underlying molecular mechanisms contributing to the persistent loss of basal forebrain ChAT+ neurons are unknown. We report here that the AIE‐induced loss of cholinergic neuron markers (ie, ChAT, TrkA, and p75^NTR), cholinergic neuron shrinkage, and increased expression of the neuroimmune marker pNF‐κB p65 are restored by exercise exposure from P56 to P95 after AIE. Our data reveal that persistently reduced expression of cholinergic neuron markers following AIE is because of the loss of the cholinergic neuron phenotype most likely through an epigenetic mechanism involving DNA methylation and histone 3 lysine 9 dimethylation (H3K9me2). Adolescent intermittent ethanol caused a persistent increase in adult H3K9me2 and DNA methylation at promoter regions of Chat and H3K9me2 of Trka, which was restored by wheel running. Exercise also restored the AIE‐induced reversal learning deficits on the Morris water maze. Together, these data suggest that AIE‐induced adult neuroimmune signaling and cognitive deficits are linked to suppression of Chat and Trka gene expression through epigenetic mechanisms that can be restored by exercise. Exercise restoration of the persistent AIE‐induced phenotypic loss of cholinergic neurons via epigenetic modifications is novel mechanism of neuroplasticity.

Cornel iridoid glycoside ameliorates cognitive deficits in APP/PS1/tau triple transgenic mice by attenuating amyloid-beta, tau hyperphosphorylation and neurotrophic dysfunction

Background

Targeted proteinopathy is involved in creating pharmacological agents that protect against Alzheimer disease (AD). Cornel iridoid glycoside (CIG) is an effective component derived from Cornus officinalis. The present study aimed to determine the effects of CIG on β-amyloid (Aβ) and tau pathology and the underlying mechanisms in APP/PS1/tau triple transgenic (3×Tg) model mice.

Methods

We intragastrically administered 16-month-old 3×Tg mice with CIG (100 and 200 mg/kg) daily for two months. Learning and memory abilities were determined using the Morris water maze (MWM) and object recognition tests (ORT). Amyloid plaques and Aβ40/42 and the expression of related proteins in the cerebral cortex and hippocampus of mice was determined by western blotting

Results

CIG improved learning and memory impairment in 3×Tg model mice, decreased amyloid plaque deposition, Aβ40/42 and the expression of full-length amyloid precursor protein, and increased levels of ADAM-10 (α-secretase), neprilysin (NEP), and insulin degrading enzyme (IDE) in the brains of the model mice. CIG also reduced tau hyperphosphorylation, and elevated phosphorylation level of GSK-3β at Ser9 and methylation of PP2A catalytic subunit C in the model mice. Moreover, CIG increased the expression of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and phosphorylated cAMP-responsive element binding protein (p-CREB) in the brain of 3×Tg mice.

Conclusions

CIG ameliorated learning and memory deficit via reducing Aβ content and, tau hyperphosphorylation and increasing neurotrophic factors in the brain of 3×Tg mice. These results suggest that CIG may be beneficial for AD therapy.

Centella asiatica L. Phytosome Improves Cognitive Performance by Promoting Bdnf Expression in Rat Prefrontal Cortex

A wide range of people in the world use natural remedies as primary approaches against illnesses. Accordingly, understanding the mechanisms of action of phytochemicals has become of great interest. In this context, Centella asiatica L. is extensively used, not only as anti-inflammatory or antioxidant agent but also as brain tonic. On this basis, the purpose of this study was to evaluate whether the chronic administration of C. asiatica L. to adult male rats was able to improve the expression of Bdnf, one of the main mediators of brain plasticity. Moreover, we assessed whether the treatment could affect the cognitive performance in the novel object recognition (NOR) test. We confirmed the presence of the main compounds in the plasma. Furthermore, C. asiatica L. administration induced an increase of Bdnf in the prefrontal cortex, and the administration of the higher dose of the extract was able to improve cognitive performance. Finally, the increase in the preference index in the NOR test was paralleled by a further increase in Bdnf expression. Overall, we highlight the ability of C. asiatica L. to affect brain functions by increasing Bdnf expression and by enhancing the cognitive performance.

NGF protects neuroblastoma cells against β-amyloid-induced apoptosis via the Nrf2/HO-1 pathway

As one of the main neurotrophic factors, nerve growth factor (NGF) participates in various processes related to viability, plasticity, and neuronal growth. NGF is known to protect against cell death and toxicity triggered by β‐amyloid (Aβ), but the underlying mechanism remains unclear. Here, we investigated this process in SKNSH neuroblastoma, in which NGF reduced cell death induced by Aβ25–35. Furthermore, NGF suppressed the production of reactive oxygen species (ROS) and promoted antioxidant function via Aβ25–35. Additionally, we demonstrated that NGF impaired the activation of the JNK/c‐Jun signaling pathway and significantly increased Nrf2 nuclear translocation and HO‐1 expression. Nrf2 elimination abolished the protective effect of NGF‐1 on Aβ25–35‐induced ROS generation, apoptosis, and activation of the JNK/c‐Jun pathway. The results of our study indicate that NGF protects neuroblastoma against injury triggered by Aβ25–35 via suppression of ROS–JNK/c‐Jun pathway stimulation through the Nrf2/HO‐1 pathway.

Nerve growth factor (NGF) promotes the nuclear translocation of Nrf2 and subsequently upregulates HO‐1 expression. This reduces the levels of reactive oxygen species (ROS), which attenuates the activation of JNK/c‐Jun pathway and eventually contributes to deceased cell apoptosis. The present discovery of this novel NGF/Nrf2/HO‐1 pathway and ROS–JNK/c‐Jun pathway identifies new clinical targets for therapeutic intervention of Alzheimer's disease.

AVP(4-8) Improves Cognitive Behaviors and Hippocampal Synaptic Plasticity in the APP/PS1 Mouse Model of Alzheimer's Disease

Memory deficits with aging are related to the neurodegeneration in the brain, including a reduction in arginine vasopressin (AVP) in the brain of patients with Alzheimer's disease (AD). AVP(4-8), different from its precursor AVP, plays memory enhancement roles in the CNS without peripheral side-effects. However, it is not clear whether AVP(4-8) can improve cognitive behaviors and synaptic plasticity in the APP/PS1 mouse model of AD. Here, we investigated for the first time the neuroprotective effects of AVP(4-8) on memory behaviors and in vivo long-term potentiation (LTP) in APP/PS1-AD mice. The results showed that: (1) APP/PS1-AD mice had lower spontaneous alternation in the Y-maze than wild-type (WT) mice, and this was significantly reversed by AVP(4-8); (2) the prolonged escape latency of APP/PS1-AD mice in the Morris water maze was significantly decreased by AVP(4-8), and the decreased swimming time in target quadrant recovered significantly after AVP(4-8) treatment; (3) in vivo hippocampal LTP induced by high-frequency stimulation had a significant deficit in the AD mice, and this was partly rescued by AVP(4-8); (4) AVP(4-8) significantly up-regulated the expression levels of postsynaptic density 95 (PSD95) and nerve growth factor (NGF) in the hippocampus of AD mice. These results reveal the beneficial effects of AVP(4-8) in APP/PS1-AD mice, showing that the intranasal administration of AVP(4-8) effectively improved the working memory and long-term spatial memory of APP/PS1-AD mice, which may be associated with the elevation of PSD95 and NGF levels in the brain and the maintenance of hippocampal synaptic plasticity.

Enriched environment modulates behavior, myelination and augments molecules governing the plasticity in the forebrain region of rats exposed to chronic immobilization stress

Recently, several reports on chronic stress have shown that prolonged exposure to stress contributes to psychological and neurological complications. However, the impact of stress-induced alterations in myelination remains to be unexplored. Therefore, in the current study, the rats were subjected to immobilization stress (IS) followed by enriched environment (EE) and the behavioral, neurochemical changes pertaining to neuronal survival pathway, in addition, to the ultrastructural changes in myelin in forebrain (FB) region of rats were analyzed. Immobilization stress-exposed rats (4 h/day IS, for 28 days) exhibited increased anhedonia, anxiety, immobility, and reduced social interaction, which could be reflected in increased levels of corticosterone. In contrast, exposure to EE (4 h IS+2 h EE/day, for 28 days) was found to minimize anhedonic state, supress the depressive-like features, enhance social interaction and also reduce the levels of corticosterone. The ultrastructural changes in the FB region of the brain revealed that IS group showed enhanced g-ratio indicating decreased myelin thickness, while EE group exhibited reduced g-ratio manifesting increased myelination. Further, the study revealed that IS exposed group showed decreased levels of NGF, TrkA, PI3K, AKT, ERK, CREB, and MBP in FB regions whereas EE group could preserve normal protein and mRNA levels of these neuronal survival molecules. The results from this study suggest that EE exerts a positive impact by improving myelination in rats exposed to chronic immobilization stress.

Synapse formation: from cellular and molecular mechanisms to neurodevelopmental and neurodegenerative disorders

The precise patterns of neuronal assembly during development determine all functional outputs of a nervous system; these may range from simple reflexes to learning, memory, cognition, etc. To understand how brain functions and how best to repair it after injury, disease, or trauma, it is imperative that we first seek to define fundamental steps mediating this neuronal assembly. To acquire the sophisticated ensemble of highly specialized networks seen in a mature brain, all proliferated and migrated neurons must extend their axonal and dendritic processes toward targets, which are often located at some distance. Upon contact with potential partners, neurons must undergo dramatic structural changes to become either a pre- or a postsynaptic neuron. This connectivity is cemented through specialized structures termed synapses. Both structurally and functionally, the newly formed synapses are, however, not static as they undergo consistent changes in order for an animal to meet its behavioral needs in a changing environment. These changes may be either in the form of new synapses or an enhancement of their synaptic efficacy, referred to as synaptic plasticity. Thus, synapse formation is not restricted to neurodevelopment; it is a process that remains active throughout life. As the brain ages, either the lack of neuronal activity or cell death render synapses dysfunctional, thus giving rise to neurodegenerative disorders. This review seeks to highlight salient steps that are involved in a neuron's journey, starting with the establishment, maturation, and consolidation of synapses; we particularly focus on identifying key players involved in the synaptogenic program. We hope that this endeavor will not only help the beginners in this field to understand how brain networks are assembled in the first place but also shed light on various neurodevelopmental, neurological, neurodegenerative, and neuropsychiatric disorders that involve synaptic inactivity or dysfunction.

Innovative Therapy for Alzheimer's Disease-With Focus on Biodelivery of NGF

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder associated with abnormal protein modification, inflammation and memory impairment. Aggregated amyloid beta (Aβ) and phosphorylated tau proteins are medical diagnostic features. Loss of memory in AD has been associated with central cholinergic dysfunction in basal forebrain, from where the cholinergic circuitry projects to cerebral cortex and hippocampus. Various reports link AD progression with declining activity of cholinergic neurons in basal forebrain. The neurotrophic molecule, nerve growth factor (NGF), plays a major role in the maintenance of cholinergic neurons integrity and function, both during development and adulthood. Numerous studies have also shown that NGF contributes to the survival and regeneration of neurons during aging and in age-related diseases such as AD. Changes in neurotrophic signaling pathways are involved in the aging process and contribute to cholinergic and cognitive decline as observed in AD. Further, gradual dysregulation of neurotrophic factors like NGF and brain derived neurotrophic factor (BDNF) have been reported during AD development thus intensifying further research in targeting these factors as disease modifying therapies against AD. Today, there is no cure available for AD and the effects of the symptomatic treatment like cholinesterase inhibitors (ChEIs) and memantine are transient and moderate. Although many AD treatment studies are being carried out, there has not been any breakthrough and new therapies are thus highly needed. Long-term effective therapy for alleviating cognitive impairment is a major unmet need. Discussion and summarizing the new advancements of using NGF as a potential therapeutic implication in AD are important. In summary, the intent of this review is describing available experimental and clinical data related to AD therapy, priming to gain additional facts associated with the importance of NGF for AD treatment, and encapsulated cell biodelivery (ECB) as an efficient tool for NGF delivery.

Rs7219 Regulates the Expression of GRB2 by Affecting miR-1288-Mediated Inhibition and Contributes to the Risk of Schizophrenia in the Chinese Han Population

In the present study, we examined a potential genetic association between the variant rs7219 within the 3'-UTR of GRB2 and the susceptibility to schizophrenia (SCZ) and bipolar disorder (BD) in the Chinese Han population. A genetic association study, including 548 SCZ patients, 512 BD patients, and 598 normal controls, was conducted in the Chinese Han population. Genotyping was performed through the Sequenom MassARRAY technology platform. The expression of GRB2 was detected using quantitative real-time polymerase chain reaction (qRT-PCR). A dual-luciferase reporter assay was performed to determine whether miR-1288 could bind to the 3'-UTR region of GRB2 containing rs7219. We found that rs7219 was significantly associated with the susceptibility to SCZ under different genetic models, including additive [OR (95% CI) = 1.24 (1.02-1.49), P = 0.027], dominant [OR (95% CI) = 1.31 (1.04-1.66), P = 0.025], and allelic models[OR (95% CI) = 1.24 (1.03-1.49), P = 0.027]. However, no significant associations were found between rs7219 and the risk for BD (all P > 0.05). Moreover, we observed that the expression of GRB2 significantly decreased in SCZ patients compared with the controls (P = 0.004). The dual-luciferase reporter assay showed that the minor allele C of rs7219 significantly decreased the luciferase activity by binding miR-1288 (P < 0.001). In summary, we are the first to reveal that rs7219 is significantly associated with the susceptibility to SCZ in the Chinese Han population. Moreover, the minor allele C of rs7219 is identified as a risk allele for SCZ because it generates a binding site for miR-1288, thereby resulting in decreased expression of GRB2 and ultimately increasing the risk of SCZ.

Nerve growth factor metabolic dysfunction contributes to sevoflurane-induced cholinergic degeneration and cognitive impairments

General anesthesia with sevoflurane is associated with an increased incidence of postoperative cognitive dysfunction. Previous studies have shown that sevoflurane anesthesia can affect the integrity and function of basal forebrain cholinergic neurons (BFCNs) which are essential for learning and memory. However, the underlying mechanisms remain largely unknown. Here, we demonstrated that exposure to 2.5% sevoflurane induced significant loss of BFCNs and caused impairments of the spatial and the fear memory. Further, sevoflurane exposure significantly reduced the level of nerve growth factor (NGF), an important factor for the survival and phenotype maintenance of BFCNs, by disrupting its synthesis pathways in the brain. More importantly, NGF administration not only prevented the loss of BFCNs but also ameliorated the cognitive impairments in sevoflurane-treated mice. Our findings indicate that NGF metabolic dysfunction contributes to sevoflurane-associated BFCNs degeneration and subsequent cognitive deficits.

Nerve Growth Factor Is Responsible for Exercise-Induced Recovery of Septohippocampal Cholinergic Structure and Function

Exercise has been shown to improve or rescue cognitive functioning in both humans and rodents, and the augmented actions of neurotrophins within the hippocampus and associated regions play a significant role in the improved neural plasticity. The septohippocampal circuit is modified by exercise. Beyond an enhancement of spatial working memory and a rescue of hippocampal activity-dependent acetylcholine (ACh) efflux, the re-emergence of the cholinergic/nestin neuronal phenotype within the medial septum/diagonal band (MS/dB) is observed following exercise (Hall and Savage, 2016). To determine which neurotrophin, brain-derived neurotrophic factor (BDNF) or nerve growth factor (NGF), is critical for exercise-induced cholinergic improvements, control and amnestic rats had either NGF or BDNF sequestered by TrkA-IgG or TrkB-IgG coated microbeads placed within the dorsal hippocampus. Hippocampal ACh release within the hippocampus during spontaneous alternation was measured and MS/dB cholinergic neuronal phenotypes were assessed. Sequestering NGF, but not BDNF, abolished the exercise-induced recovery of spatial working memory and ACh efflux. Furthermore, the re-emergence of the cholinergic/nestin neuronal phenotype within the MS/dB following exercise was also selectively dependent on the actions of NGF. Thus, exercise-induced enhancement of NGF within the septohippocampal pathway represents a key avenue for aiding failing septo-hippocampal functioning and therefore has significant potential for the recovery of memory and cognition in several neurological disorders.

Adolescent binge ethanol-induced loss of basal forebrain cholinergic neurons and neuroimmune activation are prevented by exercise and indomethacin

Basal forebrain cholinergic neurons mature in adolescence coinciding with development of adult cognitive function. Preclinical studies using the rodent model of adolescent intermittent ethanol (AIE; 5.0 g/kg, i.g., 2-days on/2-days off from postnatal day [P]25 to P55) reveal persistent increases of brain neuroimmune genes that are associated with cognitive dysfunction. Adolescent intermittent ethanol exposure also reduces basal forebrain expression of choline acetyltransferase (ChAT), an enzyme critical for acetylcholine synthesis in cholinergic neurons similar to findings in the post-mortem human alcoholic basal forebrain. We report here that AIE decreases basal forebrain ChAT+IR neurons in both adult female and male Wistar rats following early or late adolescent ethanol exposure. In addition, we find reductions in ChAT+IR somal size as well as the expression of the high-affinity nerve growth factor (NGF) receptor tropomyosin receptor kinase A (TrkA) and the low-affinity NGF receptor p75NTR, both of which are expressed on cholinergic neurons. The decrease in cholinergic neuron marker expression was accompanied by increased phosphorylation of NF-κB p65 (pNF-κB p65) consistent with increased neuroimmune signaling. Voluntary wheel running from P24 to P80 prevented AIE-induced cholinergic neuron shrinkage and loss of cholinergic neuron markers (i.e., ChAT, TrkA, and p75NTR) as well as the increase of pNF-κB p65 in the adult basal forebrain. Administration of the anti-inflammatory drug indomethacin (4.0 mg/kg, i.p prior to each ethanol exposure) during AIE also prevented the loss of basal forebrain cholinergic markers and the concomitant increase of pNF-κB p65. In contrast, treatment with the proinflammatory immune activator lipopolysaccharide (1.0 mg/kg, i.p. on P70) caused a loss of cholinergic neuron markers that was paralleled by increased pNF-κB p65 in the basal forebrain. These novel findings are consistent with AIE causing lasting activation of the neuroimmune system that contributes to the persistent loss of basal forebrain cholinergic neurons in adulthood.

Increase in Blood Levels of Growth Factors Involved in the Neuroplasticity Process by Using an Extremely Low Frequency Electromagnetic Field in Post-stroke Patients

Background: Neuroplasticity ensures the improvement of functional status in patients after stroke. The aim of this study was to evaluate the effect of extremely low-frequency electromagnetic field therapy (ELF-EMF) on brain plasticity in the rehabilitation of patients after stroke.

Methods: Forty-eight patients were divided into two groups underwent the same rehabilitation program, but in the study group, the patients additionally were exposed to a standard series of 10 ELF-EMF treatments. To determine the level of neuroplasticity, we measured the plasma level of the brain-derived neurotrophic factor (BDNF), the vascular-endothelial growth factor, as well as BDNF mRNA expression. Additionally, we determined the molecule levels for hepatocyte growth factor, stem cell factor, stromal cell-derived factor 1α, nerve growth factor β, and leukemia inhibitory factor, using 5plex cytokine panel in plasma. After 4 weeks, during which patients had undergone neurorehabilitation and neurological examinations, we assessed functional recovery using the Barthel Index, Mini-Mental State Examination (MMSE), Geriatric Depression Scale, National Institutes of Health Stroke Scale (NIHSS), and the modified Rankin Scale (mRS).

Results: We observed that ELF-EMF significantly increased growth factors and cytokine levels involved in neuroplasticity, as well as promoted an enhancement of functional recovery in post-stroke patients. Additionally, we presented evidence that these effects could be related to the increase of gene expression on the mRNA level. Moreover, a change of BDNF plasma level was positively correlated with the Barthel Index, MMSE, and negatively correlated with GDS.

Conclusion: Extremely low-frequency electromagnetic field therapy improves the effectiveness of rehabilitation of post-stroke patients by improving neuroplasticity processes.

The Regulatory Effects of Acetyl-CoA Distribution in the Healthy and Diseased Brain

Brain neurons, to support their neurotransmitter functions, require a several times higher supply of glucose than non-excitable cells. Pyruvate, the end product of glycolysis, through pyruvate dehydrogenase complex reaction, is a principal source of acetyl-CoA, which is a direct energy substrate in all brain cells. Several neurodegenerative conditions result in the inhibition of pyruvate dehydrogenase and decrease of acetyl-CoA synthesis in mitochondria. This attenuates metabolic flux through TCA in the mitochondria, yielding energy deficits and inhibition of diverse synthetic acetylation reactions in all neuronal sub-compartments. The acetyl-CoA concentrations in neuronal mitochondrial and cytoplasmic compartments are in the range of 10 and 7 μmol/L, respectively. They appear to be from 2 to 20 times lower than acetyl-CoA Km values for carnitine acetyltransferase, acetyl-CoA carboxylase, aspartate acetyltransferase, choline acetyltransferase, sphingosine kinase 1 acetyltransferase, acetyl-CoA hydrolase, and acetyl-CoA acetyltransferase, respectively. Therefore, alterations in acetyl-CoA levels alone may significantly change the rates of metabolic fluxes through multiple acetylation reactions in brain cells in different physiologic and pathologic conditions. Such substrate-dependent alterations in cytoplasmic, endoplasmic reticulum or nuclear acetylations may directly affect ACh synthesis, protein acetylations, and gene expression. Thereby, acetyl-CoA may regulate the functional and adaptative properties of neuronal and non-neuronal brain cells. The excitotoxicity-evoked intracellular zinc excess hits several intracellular targets, yielding the collapse of energy balance and impairment of the functional and structural integrity of postsynaptic cholinergic neurons. Acute disruption of brain energy homeostasis activates slow accumulation of amyloid-β_1-42 (Aβ). Extra and intracellular oligomeric deposits of Aβ affect diverse transporting and signaling pathways in neuronal cells. It may combine with multiple neurotoxic signals, aggravating their detrimental effects on neuronal cells. This review presents evidences that changes of intraneuronal levels and compartmentation of acetyl-CoA may contribute significantly to neurotoxic pathomechanisms of different neurodegenerative brain disorders.

The delayed protective effect of GK-2, а dipeptide mimetic of Nerve Growth Factor, in a model of rat traumatic brain injury

The delayed protective effect of GK-2, a dipeptide mimetic of Nerve Growth Factor, was investigated on the model of focal one-sided traumatic brain injury (TBI) of the sensorimotor cortex region on the 180th day after the injury. TBI caused a reliably disruption of the functions of the limbs contralateral to injury focus. The intraperitoneal administration of GK-2 (1 mg/kg) from 1st to 4th and from 7th to 10th days after TBI reduced the impairment of the motor functions of the limbs. This therapeutic effect significant manifested itself from the 7th day and continued until the end of the experiment - on the 180th day after TBI. Morphological studies of the animal brains on the 180th day after TBI demonstrated a decrease in the number of neurons in the V layer of the cerebral cortex and a decrease in the thickness of the corpus callosum. The treatment of animals with GK-2 after TBI statistically significant prevented a decrease in the density of neurons in the ipsilateral hemisphere and a decrease in the thickness of the corpus callosum in the contralateral hemisphere in comparison with untreated animals. Additionally, we showed in vitro that GK-2 exhibits neuroprotective properties under oxidative stress in primary hippocampal cultures. Our results demonstrate that the use of GK-2 at the early stages of development of traumatic brain damage can prevent such delayed damage as neuronal and axonal degeneration as well as reduce TBI-related disruptions of brain functions.

Molecular Mechanisms of Neuroplasticity: An Expanding Universe

Biochemical processes in synapses and other neuronal compartments underlie neuroplasticity (functional and structural alterations in the brain enabling adaptation to the environment, learning, memory, as well as rehabilitation after brain injury). This basic molecular level of brain plasticity covers numerous specific proteins (enzymes, receptors, structural proteins, etc.) participating in many coordinated and interacting signal and metabolic processes, their modulation forming a molecular basis for brain plasticity. The articles in this issue are focused on different "hot points" in the research area of biochemical mechanisms supporting neuroplasticity.