Functions of PI 3-kinase in development of the nervous system

Understanding Glycogen Synthase Kinase-3: A Novel Avenue for Alzheimer's Disease

Alzheimer's Disease (AD) is the most prevalent form of age-related dementia. Even though a century has passed since the discovery of AD, the exact cause of the disease still remains unknown. As a result, this poses a major hindrance in developing effective therapies for treating AD. Glycogen synthase kinase-3 (GSK-3) is one of the kinases that has been investigated recently as a potential therapeutic target for the treatment of AD. It is also known as human tau protein kinase and is a proline-directed serine-threonine kinase. Since dysregulation of this kinase affects all the major characteristic features of the disease, such as tau phosphorylation, amyloid formation, memory, and synaptic function, it is thought to be a major player in the pathogenesis of AD. In this review, we present the most recent information on the role of this kinase in the onset and progression of AD, as well as significant findings that identify GSK-3 as one of the most important targets for AD therapy. We further discuss the potential of treating AD by targeting GSK-3 and give an overview of the ongoing studies aimed at developing GSK-3 inhibitors in preclinical and clinical investigations.

Prenatal stress aggravates age-dependent cognitive decline, insulin signaling dysfunction, and the pro-inflammatory response in the APPNL-F/NL-F mouse model of Alzheimer's disease

Accumulating evidence indicates that early adverse life experiences may be involved in the pathogenesis of Alzheimer's disease (AD). Prenatal stress (PS) can affect brain maturation and neuroimmune and metabolic interactions, leading to age-dependent cognitive deficits in offspring. However, a multi-faceted cause-and-effect impact of PS on the development of cognitive deficits in the process of physiological ageing and in the APP^NL-F/NL-F mouse model of Alzheimer's disease has not yet been evaluated. We have identified age-dependent cognitive learning and memory deficits using male C57BL/6 J (wild type, WT) and the knock-in APP^NL-F/NL-F (KI) aged 12, 15, and 18 months. An increase in the Aβ42/Aβ40 ratio and mouse ApoE levels in the hippocampus and frontal cortex preceded the onset of cognitive deficits in the KI mice. Moreover, dysfunction in insulin signaling, including increased IRS-1 serine phosphorylation in both brain areas and the tyrosine phosphorylation deficit in the frontal cortex, suggested age-dependent insulin/IGF-1 resistance. Resistance was reflected by disturbances in mTOR or ERK1/2 kinase phosphorylation and excessive pro-inflammatory (TNF-α, IL-6, and IL-23) status in the KI mice. Importantly, our study has provided insights into the higher vulnerability to PS-induced exacerbation of age-dependent cognitive deficits and biochemical dysfunction in KI mice than in WT animals. We anticipate our study will lead to future investigation of a multi-faceted cause-and-effect relationship between stress during neurodevelopment and the onset of AD pathology, distinguishing it from changes in the course of dementia during normal ageing.

Screening Traditional Chinese Medicine Combination for Co-Treatment of Alzheimer's Disease and Major Depressive Disorder by Network Pharmacology

Background: Due to their close relationship, the efficacy of major depressive disorder (MDD) drugs in the treatment of Alzheimer's disease (AD) has received widespread attention in recent years. Methods: In this study, we explored the potential therapeutic value of traditional Chinese medicine (TCM) and multitarget components on both MDD and AD by using a comprehensive strategy with network pharmacology and molecular docking technology. Results: In total, 234 MDD-related TCM prescriptions were analyzed and the 10 most commonly used Chinese herbs, correlating to 198 active ingredients, were identified. Through a comparative analysis of 144 prospective ingredient targets, 1095 MDD-related targets, and 1684 AD-related targets, network pharmacology identified 30 common targets, 9 key targets, and 7 representative compounds. The results of GO and KEGG enrichment analysis revealed that common targets were required to regulate multiple pathways related to MDD and AD. In addition, network analysis demonstrated that the combination of Xiangfu (Cyperi Rhizoma)-Gancao (Licorice)-Chaihu (Radix Bupleuri) constituted the major part of the representative ingredients and could be used to treat both diseases. Moreover, ALB, AKT1, ESR1, CASP3, and NOS3 were also chosen as prospective targets for synthetic multitarget ingredient screening. Further docking studies revealed that various natural chemicals exhibited binding affinity with the 5 targets, including quercetin, kaempferol, β-sitosterol, stigmasterol, isorhamnetin, naringenin, and 8-isopentenyl-kaempferol. Conclusion: Taken as a whole, the current study indicates a TCM combination with positive advantages in the combined treatment of AD and MDD.

Towards Kinase Inhibitor Therapies for Fragile X Syndrome: Tweaking Twists in the Autism Spectrum Kinase Signaling Network

Absence of the Fragile X Mental Retardation Protein (FMRP) causes autism spectrum disorders and intellectual disability, commonly referred to as the Fragile X syndrome. FMRP is a negative regulator of protein translation and is essential for neuronal development and synapse formation. FMRP is a target for several post-translational modifications (PTMs) such as phosphorylation and methylation, which tightly regulate its cellular functions. Studies have indicated the involvement of FMRP in a multitude of cellular pathways, and an absence of FMRP was shown to affect several neurotransmitter receptors, for example, the GABA receptor and intracellular signaling molecules such as Akt, ERK, mTOR, and GSK3. Interestingly, many of these molecules function as protein kinases or phosphatases and thus are potentially amendable by pharmacological treatment. Several treatments acting on these kinase-phosphatase systems have been shown to be successful in preclinical models; however, they have failed to convincingly show any improvements in clinical trials. In this review, we highlight the different protein kinase and phosphatase studies that have been performed in the Fragile X syndrome. In our opinion, some of the paradoxical study conclusions are potentially due to the lack of insight into integrative kinase signaling networks in the disease. Quantitative proteome analyses have been performed in several models for the FXS to determine global molecular processes in FXS. However, only one phosphoproteomics study has been carried out in Fmr1 knock-out mouse embryonic fibroblasts, and it showed dysfunctional protein kinase and phosphatase signaling hubs in the brain. This suggests that the further use of phosphoproteomics approaches in Fragile X syndrome holds promise for identifying novel targets for kinase inhibitor therapies.

Maresin 1 promotes nerve regeneration and alleviates neuropathic pain after nerve injury

Background

Peripheral nerve injury (PNI) is a public health concern that results in sensory and motor disorders as well as neuropathic pain and secondary lesions. Currently, effective treatments for PNI are still limited. For example, while nerve growth factor (NGF) is widely used in the treatment of PNI to promote nerve regeneration, it also induces pain. Maresin 1 (MaR1) is an anti-inflammatory and proresolving mediator that has the potential to regenerate tissue. We determined whether MaR1 is able to promote nerve regeneration as well as alleviating neuropathic pain, and to be considered as a putative therapeutic agent for treating PNI.

Methods

PNI models were constructed with 8-week-old adult male ICR mice and treated with NGF, MaR1 or saline by local application, intrathecal injection or intraplantar injection. Behavioral analysis and muscle atrophy test were assessed after treatment. Immunofluorescence assay was performed to examine the expression of ATF-3, GFAP, IBA1, and NF200. The expression transcript levels of inflammatory factors IL1β, IL-6, and TNF-α were detected by quantitative real-time RT-PCR. AKT, ERK, mTOR, PI3K, phosphorylated AKT, phosphorylated ERK, phosphorylated mTOR, and phosphorylated PI3K levels were examined by western blot analysis. Whole-cell patch-clamp recordings were executed to detect transient receptor potential vanilloid 1 (TRPV1) currents.

Results

MaR1 demonstrated a more robust ability to promote sensory and motor function recovery in mice after sciatic nerve crush injury than NGF. Immunohistochemistry analyses showed that the administration of MaR1 to mice with nerve crush injury reduced the number of damaged DRG neurons, promoted injured nerve regeneration and inhibited gastrocnemius muscle atrophy. Western blot analysis of ND7/23 cells cultured with MaR1 or DRG neurons collected from MaR1 treated mice revealed that MaR1 regulated neurite outgrowth through the PI3K–AKT–mTOR signaling pathway. Moreover, MaR1 dose-dependently attenuated the mechanical allodynia and thermal hyperalgesia induced by nerve injury. Consistent with the analgesic effect, MaR1 inhibited capsaicin-elicited TRPV1 currents, repressed the nerve injury-induced activation of spinal microglia and astrocytes and reduced the production of proinflammatory cytokines in the spinal cord dorsal horn in PNI mice.

Conclusions

Application of MaR1 to PNI mice significantly promoted nerve regeneration and alleviated neuropathic pain, suggesting that MaR1 is a promising therapeutic agent for PNI.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02405-1.

Insulin-like Growth Factor 1 Promotes Cell Proliferation by Downregulation of G-Protein-Coupled Receptor 17 Expression via PI3K/Akt/FoxO1 Signaling in SK-N-SH Cells

Insulin-like growth factor 1 (IGF-1) not only regulates neuronal function and development but also is neuroprotective in the setting of acute ischemic stroke. G-protein-coupled receptor 17 (GPR17) expression in brain tissue serves as an indicator of brain damage. As whether IGF-1 regulates GPR17 expression remains unknown, the aim of this study is to investigate how IGF-1 regulates GPR17 expression in vitro. Human neuroblastoma SK-N-SH cells were used. Lentivirus-mediated short hairpin RNA (shRNA) was constructed to mediate the silencing of FoxO1, while adenoviral vectors were used for its overexpression. Verification of the relevant signaling cascade was performed using a FoxO1 inhibitor (AS1842856), a phosphatidylinositol 3-kinase (PI3K) inhibitor (LY294002), and a GPR17 antagonist (cangrelor). Cell proliferation was analyzed using EdU staining; immunofluorescence staining was used to detect the expression and subcellular localization of FoxO1. Chromatin immunoprecipitation was used to analyze the binding of FoxO1 to the GPR17 promoter in SK-N-SH cells. The expression of FoxO1, GPR17, and protein kinase B (also known as Akt) mRNA and protein as well as the levels of FoxO1 and Akt phosphorylation were investigated in this study. IGF-1 was found to downregulate FoxO1 and GPR17 expression in SK-N-SH cells while promoting cell viability and proliferation. Inhibition of FoxO1 and antagonism of GPR17 were found to play a role similar to that of IGF-1. Silencing of FoxO1 by lentivirus-mediated shRNA resulted in the downregulation of FoxO1 and GPR17 expression. The overexpression of FoxO1 via adenoviral vectors resulted in the upregulation of FoxO1 and GPR17 expression. Blocking of PI3K signaling by LY294002 inhibited the effect of IGF-1 on GPR17 suppression. Results from chromatin immunoprecipitation revealed that IGF-1 promotes FoxO1 nuclear export and reduces FoxO1 binding to the GPR17 promoter in SK-N-SH cells. Here, we conclude that IGF-1 enhances cell viability and proliferation in SK-N-SH cells via the promotion of FoxO1 nuclear export and reduction of FoxO1 binding to the GPR17 promoter via PI3K/Akt signaling. Our findings suggest that the enhancement of IGF-1 signaling to antagonize GPR17 serves as a potential therapeutic strategy in the management of acute ischemic stroke.

Structural Plasticity of Dopaminergic Neurons Requires the Activation of the D3R-nAChR Heteromer and the PI3K-ERK1/2/Akt-Induced Expression of c-Fos and p70S6K Signaling Pathway

We have previously shown that the heteromer composed by the dopamine D3 receptor (D3R) and the nicotinic acetylcholine receptor (nAChR) (D3R-nAChR heteromer) is expressed in dopaminergic neurons, activated by nicotine and represents the molecular unit that, in these neurons, contributes to the modulation of critical events such as structural plasticity and neuroprotection. We now extended this study by investigating the D3R-nAChR heteromer properties using various cell models such as transfected HEK293 cells, primary cultures of mouse dopaminergic neurons and human dopaminergic neurons derived from induced pluripotent stem cells.

We found that the D3R-nAChR heteromer is the molecular effector that transduces the remodeling properties not only associated with nicotine but also with D3R agonist stimulation: neither nAChR nor D3R, in fact, when express as monomers, are able to elicit these effects. Moreover, strong and sustained activation of the PI3K-ERK1/2/Akt pathways is coupled with D3R-nAChR heteromer stimulation, leading to the expression of the immediate-early gene c-Fos and to sustained phosphorylation of cytosolic p70 ribosomal S6 kinase (p70S6K), critical for dendritic remodeling. By contrast, while D3R stimulation results in rapid and transient activation of both Erk1/2 and Akt, that is PI3K-dependent, stimulation of nAChR is associated with persistent activation of Erk1/2 and Akt, in a PI3K-independent way. Thus, the D3R-nAChR heteromer and its ability to trigger the PI3K-ERK1/2/Akt signaling pathways may represent a novel target for preserving dopaminergic neurons healthy and for conferring neuronal protection against injuries.

Synergistic gene regulation by thyroid hormone and glucocorticoid in the hippocampus

The hippocampus is considered the center for learning and memory in the brain, and its development and function is greatly affected by the thyroid and stress axes. Thyroid hormone (TH) and glucocorticoids (GC) are known to have a synergistic effect on developmental programs across several vertebrate species, and their effects on hippocampal structure and function are well-documented. However, there are few studies that focus on the processes and genes that are cooperatively regulated by the two hormone axes. Cross-regulation of the thyroid and stress axes in the hippocampus occurs on multiple levels such that TH can regulate the expression of the GC receptor (GR) while GC can modulate tissue sensitivity to TH by controlling the expression of TH receptor (TR) and enzymes involved in TH biosynthesis. Thyroid hormone and GC are also known to synergistically regulate the transcription of genes associated with neuronal function and development. Synergistic gene regulation by TH and GC may occur through the direct, cooperative action of TR and GR on common target genes, or by indirect mechanisms involving gene regulatory cascades activated by TR and GR. In this chapter, we describe the known physiological effects and underlying molecular mechanisms of TH and GC synergistic gene regulation in the hippocampus.

Nyap1 Regulates Multipolar-Bipolar Transition and Morphology of Migrating Neurons by Fyn Phosphorylation during Corticogenesis

The coordination of cytoskeletal regulation is a prerequisite for proper neuronal migration during mammalian corticogenesis. Neuronal tyrosine-phosphorylated adaptor for the phosphoinositide 3-kinase 1 (Nyap1) is a member of the Nyap family of phosphoproteins, which has been studied in neuronal morphogenesis and is involved in remodeling of the actin cytoskeleton. However, the precise role of Nyap1 in neuronal migration remains unknown. Here, overexpression and knockdown of Nyap1 in the embryonic neocortex of mouse by in utero electroporation-induced abnormal morphologies and multipolar-bipolar transitions of migrating neurons. The level of phosphorylated Nyap1 was crucial for neuronal migration and morphogenesis in neurons. Furthermore, Nyap1 regulated neuronal migration as a downstream target of Fyn, a nonreceptor protein-tyrosine kinase that is a member of the Src family of kinases. Importantly, Nyap1 mediated the role of Fyn in the multipolar-bipolar transition of migrating neurons. Taken together, these results suggest that cortical radial migration is regulated by a molecular hierarchy of Fyn via Nyap1.

Targeting PI3K-AKT/mTOR signaling in the prevention of autism

PI3K-AKT/mTOR signaling pathway represents an essential signaling mechanism for mammalian enzyme-related receptors in transducing signals or biological processes such as cell development, differentiation, cell survival, protein synthesis, and metabolism. Upregulation of the PI3K-AKT/mTOR signaling pathway involves many human brain abnormalities, including autism and other neurological dysfunctions. Autism is a neurodevelopmental disorder associated with behavior and psychiatric illness. This research-based review discusses the functional relationship between the neuropathogenic factors associated with PI3K-AKT/mTOR signaling pathway. Ultimately causes autism-like conditions associated with genetic alterations, neuronal apoptosis, mitochondrial dysfunction, and neuroinflammation. Therefore, inhibition of the PI3K-AKT/mTOR signaling pathway may have an effective therapeutic value for autism treatment. The current review also summarizes the involvement of PI3K-AKT/mTOR signaling pathway inhibitors in the treatment of autism and other neurodegenerative disorders.

Effects of Long-Term Endurance Exercise and Lithium Treatment on Neuroprotective Factors in Hippocampus of Obese Rats

To investigate the effects of long-term lithium treatment and low intensity endurance exercise on brain-derived neurotrophic factor (BDNF) expression and glycogen synthase kinase 3 beta (GSK3β) activity in the hippocampus of obese rats. Fifty 10-week-old male Sprague-Dawley rats were selected. There was a control group of 10 rats (chow control group) while the other forty rats were fed on a high-fat diet for eight weeks to induce obesity. Rats were then assigned into four random groups. The rats were given 10 mg/kg lithium chloride (LiCl) dissolved in 1 mL sterile distilled water once a day, 5 times a week. The rats did 20 min of treadmill walking with an exercise intensity of 40% maximal oxygen uptake (VO₂ max) (12 m/min, slope 0%). This was performed for 20 min a day, 3 days a week. Twelve weeks of lithium treatment or endurance exercise significantly reduced body weight and body fat mass in obese rats, without showing additive effects when the treatments were given in parallel or significant toxic responses in alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels in blood and kidney and liver tissues. BDNF expression in the hippocampus was significantly increased both in exercise and lithium groups with synergistic effects found in the group where both exercise and lithium treatments were given in parallel. On the other hand, the decrease in GSK3β activity was shown only in the lithium treatment group, without showing additive effects when the treatments were given in parallel. Lithium and low-intensity endurance exercise for 12 weeks increased the expression of BDNF, a neuroprotective factor in the hippocampus of obese mice. Lithium treatment alone inhibited the activity of GSK3β. This can be interpreted as a positive indication of applicability of the two factors in the prevention of neurodegenerative diseases.

Excess active P13K rescues huntingtin-mediated neuronal cell death but has no effect on axonal transport defects

High levels of oxidative stress is detected in neurons affected by many neurodegenerative diseases, including huntington's disease. Many of these diseases also show neuronal cell death and axonal transport defects. While nuclear inclusions/accumulations likely cause cell death, we previously showed that cytoplasmic axonal accumulations can also contribute to neuronal death. However, the cellular mechanisms responsible for activating cell death is unclear. One possibility is that perturbations in normal axonal transport alter the function of the phosphatidylinositol 3-kinase (PI3K)-protein kinase B (AKT)-pathway, a signal transduction pathway that promotes survival/growth in response to extracellular signals. To test this proposal in vivo, we expressed active PI3K in the context of pathogenic huntingtin (HTT-138Q) in Drosophila larval nerves, which show axonal transport defects and neuronal cell death. We found that excess expression of active P13K significantly suppressed HTT-138Q-mediated neuronal cell death, but had no effect on HTT-138Q-mediated axonal transport defects. Expression of active PI3K also rescued Paraquat-mediated cell death. Further, increased levels of pSer9 (inactive) glycogen synthase kinase 3β was seen in HTT-138Q-mediated larval brains, and in dynein loss of function mutants, indicating the modulation of the pro-survival pathway. Intriguingly, proteins in the PI3K/AKT-pathway showed functional interactions with motor proteins. Taken together our observations suggest that proper axonal transport is likely essential for the normal function of the pro-survival PI3K/AKT-signaling pathway and for neuronal survival in vivo. These results have important implications for targeting therapeutics to early insults during neurodegeneration and death.

Wnt signalling pathway and tau phosphorylation: A comprehensive study on known connections

The Wnt pathway is the most important cascade in the nervous system; evidence has indicated that deregulation of the Wnt pathway induced pathogenic hallmarks of neurodegenerative diseases. Glycogen synthase kinase-3β (GSK-3β) as the main member of the Wnt pathway increases tau inclusions, the main marker in the neurodegenerative diseases. Phosphorylated tau is observed in the pre-tangle of the neurons in the early stage of neurodegenerative diseases. The researchers always try to improve pharmacological approaches of new therapeutic strategies to the treatment of neurodegenerative diseases that are required to represent a significant entry point by understanding the theoretical interactions of the molecular pathways. In this review, we have discussed the recent knowledge about the canonical and non-canonical Wnt signalling pathway, GSK-3β, Wnt/β-catenin antagonists, tau phosphorylation, and their important roles in the neurodegenerative diseases.

Neuroprotective Approach of Anti-Cancer Microtubule Stabilizers Against Tauopathy Associated Dementia: Current Status of Clinical and Preclinical Findings

Neuronal microtubule (MT) tau protein provides cytoskeleton to neuronal cells and plays a vital role including maintenance of cell shape, intracellular transport, and cell division. Tau hyperphosphorylation mediates MT destabilization resulting in axonopathy and neurotransmitter deficit, and ultimately causing Alzheimer’s disease (AD), a dementing disorder affecting vast geriatric populations worldwide, characterized by the existence of extracellular amyloid plaques and intracellular neurofibrillary tangles in a hyperphosphorylated state. Pre-clinically, streptozotocin stereotaxically mimics the behavioral and biochemical alterations similar to AD associated with tau pathology resulting in MT assembly defects, which proceed neuropathological cascades. Accessible interventions like cholinesterase inhibitors and NMDA antagonist clinically provides only symptomatic relief. Involvement of microtubule stabilizers (MTS) prevents tauopathy particularly by targeting MT oriented cytoskeleton and promotes polymerization of tubulin protein. Multiple in vitro and in vivo research studies have shown that MTS can hold substantial potential for the treatment of AD-related tauopathy dementias through restoration of tau function and axonal transport. Moreover, anti-cancer taxane derivatives and epothiolones may have potential to ameliorate MT destabilization and prevent the neuronal structural and functional alterations associated with tauopathies. Therefore, this current review strictly focuses on exploration of various clinical and pre-clinical features available for AD to understand the neuropathological mechanisms as well as introduce pharmacological interventions associated with MT stabilization. MTS from diverse natural sources continue to be of value in the treatment of cancer, suggesting that these agents have potential to be of interest in the treatment of AD-related tauopathy dementia in the future.

Beyond Trophic Factors: Exploiting the Intrinsic Regenerative Properties of Adult Neurons

Injuries and diseases of the peripheral nervous system (PNS) are common but frequently irreversible. It is often but mistakenly assumed that peripheral neuron regeneration is robust without a need to be improved or supported. However, axonal lesions, especially those involving proximal nerves rarely recover fully and injuries generally are complicated by slow and incomplete regeneration. Strategies to enhance the intrinsic growth properties of reluctant adult neurons offer an alternative approach to consider during regeneration. Since axons rarely regrow without an intimately partnered Schwann cell (SC), approaches to enhance SC plasticity carry along benefits to their axon partners. Direct targeting of molecules that inhibit growth cone plasticity can inform important regenerative strategies. A newer approach, a focus of our laboratory, exploits tumor suppressor molecules that normally dampen unconstrained growth. However several are also prominently expressed in stable adult neurons. During regeneration their ongoing expression “brakes” growth, whereas their inhibition and knockdown may enhance regrowth. Examples have included phosphatase and tensin homolog deleted on chromosome ten (PTEN), a tumor suppressor that inhibits PI3K/pAkt signaling, Rb1, the protein involved in retinoblastoma development, and adenomatous polyposis coli (APC), a tumor suppressor that inhibits β-Catenin transcriptional signaling and its translocation to the nucleus. The identification of several new targets to manipulate the plasticity of regenerating adult peripheral neurons is exciting. How they fit with canonical regeneration strategies and their feasibility require additional work. Newer forms of nonviral siRNA delivery may be approaches for molecular manipulation to improve regeneration.

Syntaxin-1/TI-VAMP SNAREs interact with Trk receptors and are required for neurotrophin-dependent outgrowth

SNARE proteins are essential components of the machinery that regulates vesicle trafficking and exocytosis. Their role is critical for the membrane-fusion processes that occur during neurotransmitter release. However, research in the last decade has also unraveled the relevance of these proteins in membrane expansion and cytoskeletal rearrangements during developmental processes such as neuronal migration and growth cone extension and attraction. Neurotrophins are neurotrophic factors that are required for many cellular functions throughout the brain, including neurite outgrowth and guidance, synaptic formation, and plasticity. Here we show that neurotrophin Trk receptors form a specific protein complex with the t-SNARE protein Syntaxin 1, both in vivo and in vitro. We also demonstrate that blockade of Syntaxin 1 abolishes neurotrophin-dependent growth of axons in neuronal cultures and decreases exocytotic events at the tip of axonal growth cones. 25-kDa soluble N-ethylmaleimide-sensitive factor attachment protein and Vesicle-associated membrane protein 2 do not participate in the formation of this SNARE complex, while tetanus neurotoxin-insensitive vesicle-associated membrane protein interacts with Trk receptors; knockdown of this (v) SNARE impairs Trk-dependent outgrowth. Taken together, our results support the notion that an atypical SNARE complex comprising Syntaxin 1 and tetanus neurotoxin-insensitive vesicle-associated membrane protein is required for axonal neurotrophin function.

Escitalopram attenuates β-amyloid-induced tau hyperphosphorylation in primary hippocampal neurons through the 5-HT1A receptor mediated Akt/GSK-3β pathway

Tau hyperphosphorylation is an important pathological feature of Alzheimer's disease (AD). To investigate whether escitalopram could inhibit amyloid-β (Aβ)-induced tau hyperphosphorylation and the underlying mechanisms, we treated the rat primary hippocampal neurons with Aβ1-42 and examined the effect of escitalopram on tau hyperphosphorylation. Results showed that escitalopram decreased Aβ1-42-induced tau hyperphosphorylation. In addition, escitalopram activated the Akt/GSK-3β pathway, and the PI3K inhibitor LY294002 blocked the attenuation of tau hyperphosphorylation induced by escitalopram. Moreover, the 5-HT1A receptor agonist 8-OH-DPAT also activated the Akt/GSK-3β pathway and decreased Aβ1-42-induced tau hyperphosphorylation. Furthermore, the 5-HT1A receptor antagonist WAY-100635 blocked the activation of Akt/GSK-3β pathway and the attenuation of tau hyperphosphorylation induced by escitalopram. Finally, escitalopram improved Aβ1-42 induced impairment of neurite outgrowth and spine density, and reversed Aβ1-42 induced reduction of synaptic proteins. Our results demonstrated that escitalopram attenuated Aβ1-42-induced tau hyperphosphorylation in primary hippocampal neurons through the 5-HT1A receptor mediated Akt/GSK-3β pathway.

In retinitis pigmentosa TrkC.T1-dependent vectorial Erk activity upregulates glial TNF-α, causing selective neuronal death

In some diseases the TrkC.T1 isoform is upregulated in glia, associated with glial TNF-α production and neuronal death. What remains unknown are the activating signals in glia, and how paracrine signals may be selective for a targeted neuron while sparing other proximate neurons. We studied these questions in the retina, where Müller glia contacts photoreceptors on one side and retinal ganglion cells on the other. In a mutant Rhodopsin mouse model of retinitis pigmentosa (RP) causing progressive photoreceptor death—but sparing retinal ganglion cells—TrkC.T1 and NT-3 ligand are upregulated in Müller glia. TrkC.T1 activity generates p-Erk, which causes increased TNF-α. These sequential events take place predominantly in Müller fibers contacting stressed photoreceptors, and culminate in selective death. Each event and photoreceptor death can be prevented by reduction of TrkC.T1 expression, by pharmacological antagonism of TrkC or by pharmacological inhibition Erk. Unmasking the sequence of non-cell autologous events and mechanisms causing selective neuronal death may help rationalize therapies.

Functional integration of complex miRNA networks in central and peripheral lesion and axonal regeneration

New players are emerging in the game of peripheral and central nervous system injury since their physiopathological mechanisms remain partially elusive. These mechanisms are characterized by several molecules whose activation and/or modification following a trauma is often controlled at transcriptional level. In this scenario, microRNAs (miRNAs/miRs) have been identified as main actors in coordinating important molecular pathways in nerve or spinal cord injury (SCI). miRNAs are small non-coding RNAs whose functionality at network level is now emerging as a new level of complexity. Indeed they can act as an organized network to provide a precise control of several biological processes. Here we describe the functional synergy of some miRNAs in case of SCI and peripheral damage. In particular we show how several small RNAs can cooperate in influencing simultaneously the molecular pathways orchestrating axon regeneration, inflammation, apoptosis and remyelination. We report about the networks for which miRNA-target bindings have been experimentally demonstrated or inferred based on target prediction data: in both cases, the connection between one miRNA and its downstream pathway is derived from a validated observation or is predicted from the literature. Hence, we discuss the importance of miRNAs in some pathological processes focusing on their functional structure as participating in a cooperative and/or convergence network.

Neuroprotective Role of the PI3 Kinase/Akt Signaling Pathway in Zebrafish

Neuronal survival and growth in the embryo is controlled partly by trophic factors. For most trophic factors (such as Insulin-like growth factor-1), the ability to regulate cell survival has been attributed to the phosphoinositide 3-kinase (PI3K)/Akt kinase cascade. This study presents data illustrating the role of PI3K/Akt in attainment of normal brain size during zebrafish embryogenesis. Blocking PI3K with inhibitor LY294002 caused a significant reduction in brain size (in addition to global growth retardation) during zebrafish embryogenesis. This PI3 Kinase inhibition-induced brain size decrease was recovered by the overexpression of myristoylated Akt (myr-Akt), a constitutive form of Akt. Further analysis reveals that expressing exogenous myr-Akt significantly augmented brain size. Whole mount in situ hybridization analysis of several marker genes showed that myr-Akt overexpression did not alter brain patterning. Furthermore, the expression of myr-Akt was found to protect neuronal cells from apoptosis induced by heat shock and UV light, suggesting that inhibition of neuronal cell death may be part of the underlying cause of the increased brain size. These data provide a foundation for addressing the role of PI3K/Akt in brain growth during zebrafish embryogenesis.

Hydrogen sulfide down-regulates BACE1 and PS1 via activating PI3K/Akt pathway in the brain of APP/PS1 transgenic mouse

BACKGROUND

Endogenous hydrogen sulfide (H2S) may have multiple physiological functions in brain. Our previous study showed that H2S improved spatial memory impairment and decreased the production of Aβ in APP/PS1 transgenic mice. However, many of the underlying mechanisms are not still being elucidated. The aim of the present study is to investigate the neuroprotective mechanisms of H2S involving in the activity of β-secretase (BACE1), γ-secretase (PS1) and α-secretase (ADAM17).

METHODS

Morris water maze was used to measure the behavior change. The levels of Aβ40 and Aβ42 were quantified using colorimetric ELISA kits and immunohistochemical analysis. The levels of BACE1, PS1, ADAM17, pAkt, pp38MAPK, pERK and pJNK were tested by Western blot analysis in normal mice, APP/PS1 transgenic mice and 50μmol/kg-NaHS-treated transgenic mice. On the basis of exogenous H2S treatment, LY294002 (inhibitors of PI3K/Akt) or PD98059 (inhibitors of MAPK/ERK) was injected into lateral cerebral ventricle.

RESULTS

The levels of BACE1, PS1 and pp38MAPK were increased and ADAM17 were decreased in the APP/PS1 transgenic mice. After intraperitoneal administration of an H2S donor (NaHS) into APP/PS1 mice, the levels of BACE1, PS1 and pp38MAPK were reduced and ADAM17 increased. The level of pp38 MAPKs, pAkt and pERK1/2 was increased in APP/PS1 transgenic mice compared with normal mice (p<0.05). There was no difference in the expression of pJNK between AD transgenic mice and normal mice (p>0.05). These results demonstrated that LY294002 inhibited the effect of H2S on decreasing the BACE1 and PS1, reducing the level of Aβ and improving memory impairment in APP/PS1 transgenic mice. PD98059 had no influence on the expression of BACE1 and PS1.

CONCLUSIONS

H2S inhibits the expression of BACE1 and PS1 by activating PI3K/Akt pathway in AD.

Protective effects of butyrate-based compounds on a mouse model for spinal muscular atrophy

Proximal spinal muscular atrophy (SMA) is a childhood-onset degenerative disease resulting from the selective loss of motor neurons in the spinal cord. SMA is caused by the loss of SMN1 (survival motor neuron 1) but retention of SMN2. The number of copies of SMN2 modifies disease severity in SMA patients as well as in mouse models, making SMN2 a target for therapeutics development. Sodium butyrate (BA) and its analog (4PBA) have been shown to increase SMN2 expression in SMA cultured cells. In this study, we examined the effects of BA, 4PBA as well as two BA prodrugs-glyceryl tributyrate (BA3G) and VX563-on the phenotype of SMNΔ7 SMA mice. Treatment with 4PBA, BA3G and VX563 but not BA beginning at PND04 significantly improved the lifespan and delayed disease end stage, with administration of VX563 also improving the growth rate of these mice. 4PBA and VX563 improved the motor phenotype of SMNΔ7 SMA mice and prevented spinal motor neuron loss. Interestingly, neither 4PBA nor VX563 had an effect on SMN expression in the spinal cords of treated SMNΔ7 SMA mice; however, they inhibited histone deacetylase (HDAC) activity and restored the normal phosphorylation states of Akt and glycogen synthase kinase 3β, both of which are altered by SMN deficiency in vivo. These observations show that BA-based compounds with favorable pharmacokinetics ameliorate SMA pathology possibly by modulating HDAC and Akt signaling.

Functions of the neuron-specific protein ADAP1 (centaurin-α1) in neuronal differentiation and neurodegenerative diseases, with an overview of structural and biochemical properties of ADAP1

Eukaryotic cells express numerous ArfGAPs (ADP-ribosylation factor GTPase-activating proteins). There is increasing knowledge about the function of the brain-specific protein ADAP1 [ArfGAP with dual pleckstrin homology (PH) domain] as well as about its biochemical properties. The ADAP subfamily, also designated centaurin-α, has an N-terminal ArfGAP domain followed by two PH domains. The mammalian ADAP subfamily consists of two identified isoforms, ADAP1 and ADAP2 (centaurin-α1 and -α2). ADAP1 is highly expressed in neurons. We highlight the functional roles of ADAP1 in neuronal differentiation and neurodegeneration. Because of interactions with different proteins and phosphoinositol-lipids, ADAP1 can function as a scaffolding protein in several signal transduction pathways. Firstly, ADAP1 mediates cytoskeletal crosstalk. This is indicated by multiple interactions of ADAP1 with components of the actin and microtubule cytoskeleton. Secondly, regulation of neuronal polarity formation and axon specification by ADAP1 is suggested by crystal structural data obtained for human ADAP1, and the complexes of ADAP1-Ins(1,3,4,5)P4 and/or the forkhead-associated domain of the kinesin KIF13B. These structures support the concept that a KIF13B-ADAP1 complex enhances the local accumulation of PtdIns(3,4,5)P3 at the tips of neurites, and thus favors neuronal polarity. Thirdly, recent evidence unravels a pathological role of ADAP1 because upregulation of ADAP1 by amyloid β-peptide causes ADAP1-Ras-ERK-dependent translocation of Elk-1 to mitochondria. This impairs mitochondrial functions with subsequent synaptic dysfunction and exacerbates neurodegeneration, as in Alzheimer's disease.

Aberrant insulin signaling in Alzheimer's disease: current knowledge

Alzheimer's disease (AD) is the most common form of dementia affecting elderly people. AD is a multifaceted pathology characterized by accumulation of extracellular neuritic plaques, intracellular neurofibrillary tangles (NFTs) and neuronal loss mainly in the cortex and hippocampus. AD etiology appears to be linked to a multitude of mechanisms that have not been yet completely elucidated. For long time, it was considered that insulin signaling has only peripheral actions but now it is widely accepted that insulin has neuromodulatory actions in the brain. Insulin signaling is involved in numerous brain functions including cognition and memory that are impaired in AD. Recent studies suggest that AD may be linked to brain insulin resistance and patients with diabetes have an increased risk of developing AD compared to healthy individuals. Indeed insulin resistance, increased inflammation and impaired metabolism are key pathological features of both AD and diabetes. However, the precise mechanisms involved in the development of AD in patients with diabetes are not yet fully understood. In this review we will discuss the role played by aberrant brain insulin signaling in AD. In detail, we will focus on the role of insulin signaling in the deposition of neuritic plaques and intracellular NFTs. Considering that insulin mitigates beta-amyloid deposition and phosphorylation of tau, pharmacological strategies restoring brain insulin signaling, such as intranasal delivery of insulin, could have significant therapeutic potential in AD treatment.

Association between AKT1 gene polymorphisms and depressive symptoms in the Chinese Han population with major depressive disorder

For this study, 461 Chinese Han patients with depressive disorder were recruited. The AKT1 genotype and allele distribution were determined by PCR amplification and direct sequencing. UNPHASED software was used to analyze associations between the 17-item Hamilton Depression Rating Scale, total score, four factors and the AKT1 rs2494746 and rs3001371 polymorphisms. The results indicate that there is a significant association between suicidal ideation and anxiety symptoms in depressed patients and the rs2494746 polymorphism. The other AKT1 polymorphism, rs3001371, was significantly associated with work and activities. Patients with the rs3001371-A allele had a significantly more severe illness compared to patients with the rs3001371-G allele. Thus, AKT1 polymorphisms appear to be associated with depression severity, anxiety symptoms, work and activities, and suicide attempts in patients with depressive disorder.

Hypoxic conditioned medium from rat cerebral cortical cells enhances the proliferation and differentiation of neural stem cells mainly through PI3-K/Akt pathways

Purpose

To investigate the effects of hypoxic conditioned media from rat cerebral cortical cells on the proliferation and differentiation of neural stem cells (NSCs) in vitro, and to study the roles of PI3-K/Akt and JNK signal transduction pathways in these processes.

Methods

Cerebral cortical cells from neonatal Sprague–Dawley rat were cultured under hypoxic and normoxic conditions; the supernatant was collected and named ‘hypoxic conditioned medium’ (HCM) and ‘normoxic conditioned medium’ (NCM), respectively. We detected the protein levels (by ELISA) of VEGF and BDNF in the conditioned media and mRNA levels (by RT-PCR) in cerebral cortical cells. The proliferation (number and size of neurospheres) and differentiation (proportion of neurons and astrocytes over total cells) of NSCs was assessed. LY294002 and SP600125, inhibitors of PI3-K/Akt and JNK, respectively, were applied, and the phosphorylation levels of PI3-K, Akt and JNK were measured by western blot.

Results

The protein levels and mRNA expressions of VEGF and BDNF in 4% HCM and 1% HCM were both higher than that of those in NCM. The efficiency and speed of NSCs proliferation was enhanced in 4% HCM compared with 1% HCM. The highest percentage of neurons and lowest percentage of astrocytes was found in 4% HCM. However, the enhancement of NSCs proliferation and differentiation into neurons accelerated by 4% HCM was inhibited by LY294002 and SP600125, with LY294002 having a stronger inhibitory effect. The increased phosphorylation levels of PI3-K, Akt and JNK in 4% HCM were blocked by LY294002 and SP600125.

Conclusions

4%HCM could promote NSCs proliferation and differentiation into high percentage of neurons, these processes may be mainly through PI3-K/Akt pathways.

Differential effects of antidepressant drugs on mTOR signalling in rat hippocampal neurons

Recent studies suggest that ketamine produces antidepressant actions via stimulation of mammalian target of rapamycin (mTOR), leading to increased levels of synaptic proteins in the prefrontal cortex. Thus, mTOR activation may be related to antidepressant action. However, the mTOR signalling underlying antidepressant drug action has not been well investigated. The aim of the present study was to determine whether alterations in mTOR signalling were observed following treatment with antidepressant drugs, using ketamine as a positive control. Using Western blotting, we measured changes in the mTOR-mediated proteins and synaptic proteins in rat hippocampal cultures. Dendritic outgrowth was determined by neurite assay. Our findings demonstrated that escitalopram, paroxetine and tranylcypromine significantly increased levels of phospho-mTOR and its down-stream regulators (phospho-4E-BP-1 and phospho-p70S6K); fluoxetine, sertraline and imipramine had no effect. All drugs tested increased up-stream regulators (phospho-Akt and phospho-ERK) levels. Increased phospho-mTOR induced by escitalopram, paroxetine or tranylcypromine was significantly blocked in the presence of specific PI3K, MEK or mTOR inhibitors, respectively. All drugs tested also increased hippocampal dendritic outgrowth and synaptic proteins levels. The mTOR inhibitor, rapamycin, significantly blocked these effects on escitalopram, paroxetine and tranylcypromine whereas fluoxetine, sertraline and imipramine effects were not affected. The effects of escitalopram, paroxetine and tranylcypromine paralleled those of ketamine. This study presents novel in vitro evidence indicating that some antidepressant drugs promote dendritic outgrowth and increase synaptic protein levels through mTOR signalling; however, other antidepressant drugs seem to act via a different pathway. mTOR signalling may be a promising target for the development of new antidepressant drugs.

Hydrogen sulfide-induced processing of the amyloid precursor protein in SH-SY5Y human neuroblastoma cells involves the PI3-K/Akt signaling pathway

Hydrogen sulfide (H2S) has been recently categorized as a gasotransmitter, and it may be involved in the pathology of Alzheimer's disease. However, whether H2S induces amyloid precursor protein (APP) processing remains unknown. In the present study, we tested the ability of H2S to mediate APP processing in SH-SY5Y human neuroblastoma cells. We treated SH-SY5Y human neuroblastoma cells with a range of sodium hydrosulfide (H2S donor) concentrations. Western blot analysis showed that H2S increased the generation of C83 and decreased the production of C99. Meanwhile, H2S increased the levels of a disintegrin and metalloprotease 10 (ADAM10) mRNA and protein, but had no effect on TNF-α-converting enzyme (TACE, also known as ADAM17) mRNA and protein levels. H2S also induced a significant decrease of extracellular amyloid-β42 (Aβ42). Furthermore, SH-SY5Y human neuroblastoma cells were assayed for activation of the phosphoinositide 3-kinase (PI3-K) pathway. H2S activated the PI3-K pathway. Using specific inhibitor of PI3-K, we determined that the effects of H2S on APP processing and Aβ42 were blocked by LY 294002 (PI3-K inhibitor). These data indicate that H2S can induce APP processing, and this effect is dependent on activation of the PI3-K signaling pathway.

Phosphatase-mediated intracellular signaling contributes to neuroprotection by flavonoids of Iris tenuifolia

A variety of flavonoids are suggested to be useful for the treatment of brain-related disorders, including dementia and depression. An investigation on the characteristics of the extracted compounds of Iris tenuifolia Pall. (IT) is of much interest, as this plant has been used as a traditional medicine. In the present study, we examined the effect of total flavonoids obtained from IT on cultured cortical neurons under oxidative-stress and found that pretreatment with IT flavonoids significantly inhibited H 2 O 2-induced cell death in cortical neurons. Such a survival-promoting effect by IT flavonoids was partially blocked by inhibitors for extracellular signal-regulated kinase (ERK) and phosphoinositide 3-kinase/Akt (PI3K/Akt) cascades, both of which are known as survival-promoting signaling molecules. Furthermore, the phosphorylation of Src homology-2 (SH2) domain-containing phosphatase2 (Shp2) was induced by IT flavonoids, and the protective effect of IT flavonoids was abolished by NSC87877, an inhibitor for Shp2, suggesting the involvement of Shp2-mediated intracellular signaling in flavonoid-dependent neuroprotection.

Effect of Tenuifoliside A isolated from Polygala tenuifolia on the ERK and PI3K pathways in C6 glioma cells

Tenuifoliside A (TFSA) is a bioactive oligosaccharide ester component of Polygala tenuifolia Wild, a traditional Chinese medicine which was used to manage mental disorders effectively. The neuroprotective and anti-apoptotic effects of TFSA have been demonstrated in our previous studies. The present work was designed to study the molecular mechanism of TFSA on promoting the viability of rat glioma cells C6. We exposed C6 cells to TFSA (or combined with ERK, PI3K and TrkB inhibitors) to examine the effects of TFSA on the cell viability and the expression and phosphorylation of key proteins in the ERK and PI3K signaling pathway. TFSA increased levels of phospho-ERK and phospho-Akt, enhanced release of BDNF, which were blocked by ERK and PI3K inhibitors, respectively (U0126 and LY294002). Moreover, the TFSA caused the enhanced phosphorylation of cyclic AMP response element binding protein (CREB) at Ser133 site, the effect was revoked by U0126, LY294002 and K252a. Furthermore, when C6 cells were pretreated with K252a, a TrkB antagonist, known to significantly inhibit the activity of brain-derived neurotrophic factor (BDNF), blocked the levels of phospho-ERK, phospho-Akt and phosphor-CREB. Taking these results together, we suggested the neuroprotection of TFSA might be mediated through BDNF/TrkB-ERK/PI3K-CREB signaling pathway in C6 glioma cells.

Diabetes mellitus and disturbances in brain connectivity: a bidirectional relationship?

Diabetes mellitus (DM) is associated with deficits across multiple cognitive domains. The observed impairments in cognitive function are hypothesized to be subserved by alterations in brain structure and function. Several lines of evidence indicate that alterations in glial integrity and function, as well as abnormal synchrony within brain circuits and associated networks, are observed in adults with DM. Microangiopathy and alterations in insulin homeostasis appear to be principal effector systems, although a unitary explanation subsuming the complex etiopathology of white matter in DM is unavailable. A contemporary model of disease pathophysiology for several mental disorders, including but not limited to mood disorders, posits abnormalities in the synchronization of cellular systems in circuits. The observation that similar abnormalities occur in diabetic populations provides the basis for hypothesizing the convergence of pathoetiological factors. Herein, we propose that abnormal structure, function and chemical composition as well as synchrony within and between circuits is an accompaniment of DM and is shared in common with several mental disorders.

A role for hippocampal PSA-NCAM and NMDA-NR2B receptor function in flavonoid-induced spatial memory improvements in young rats

The increase in incidence and prevalence of neurodegenerative diseases highlights the need for a more comprehensive understanding of how food components may affect neural systems. In particular, flavonoids have been recognized as promising agents capable of influencing different aspects of synaptic plasticity resulting in improvements in memory and learning in both animals and humans. Our previous studies highlight the efficacy of flavonoids in reversing memory impairments in aged rats, yet little is known about the effects of these compounds in healthy animals, particularly with respect to the molecular mechanisms by which flavonoids might alter the underlying synaptic modifications responsible for behavioral changes. We demonstrate that a 3-week intervention with two dietary doses of flavonoids (Dose I: 8.7 mg/day and Dose II: 17.4 mg/day) facilitates spatial memory acquisition and consolidation (24 recall) (p < 0.05) in young healthy rats. We show for the first time that these behavioral improvements are linked to increased levels in the polysialylated form of the neural adhesion molecule (PSA-NCAM) in the dentate gyrus (DG) of the hippocampus, which is known to be required for the establishment of durable memories. We observed parallel increases in hippocampal NMDA receptors containing the NR2B subunit for both 8.7 mg/day (p < 0.05) and 17.4 mg/day (p < 0.001) doses, suggesting an enhancement of glutamate signaling following flavonoid intervention. This is further strengthened by the simultaneous modulation of hippocampal ERK/CREB/BDNF signaling and the activation of the Akt/mTOR/Arc pathway, which are crucial in inducing changes in the strength of hippocampal synaptic connections that underlie learning. Collectively, the present data supports a new role for PSA-NCAM and NMDA-NR2B receptor on flavonoid-induced improvements in learning and memory, contributing further to the growing body of evidence suggesting beneficial effects of flavonoids in cognition and brain health.

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We have identified novel targets for the flavonoid actions in the brain.

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Flavonoid ingestion facilitates hippocampal-dependent learning in healthy animals.

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Flavonoids regulate hippocampal PSA-NCAM in the Dentate Gyrus of the hippocampus.

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Flavonoids modulate the levels of hippocampal glutamate receptors (NMDA-NR2B).

Neuron-NG2 cell synapses: novel functions for regulating NG2 cell proliferation and differentiation

NG2 cells are a population of CNS cells that are distinct from neurons, mature oligodendrocytes, astrocytes, and microglia. These cells can be identified by their NG2 proteoglycan expression. NG2 cells have a highly branched morphology, with abundant processes radiating from the cell body, and express a complex set of voltage-gated channels, AMPA/kainate, and GABA receptors. Neurons notably form classical and nonclassical synapses with NG2 cells, which have varied characteristics and functions. Neuron-NG2 cell synapses could fine-tune NG2 cell activities, including the NG2 cell cycle, differentiation, migration, and myelination, and may be a novel potential therapeutic target for NG2 cell-related diseases, such as hypoxia-ischemia injury and periventricular leukomalacia. Furthermore, neuron-NG2 cell synapses may be correlated with the plasticity of CNS in adulthood with the synaptic contacts passing onto their progenies during proliferation, and synaptic contacts decrease rapidly upon NG2 cell differentiation. In this review, we highlight the characteristics of classical and nonclassical neuron-NG2 cell synapses, the potential functions, and the fate of synaptic contacts during proliferation and differentiation, with the emphasis on the regulation of the NG2 cell cycle by neuron-NG2 cell synapses and their potential underlying mechanisms.

Specific induction of Akt3 in spinal cord motor neurons is neuroprotective in a mouse model of familial amyotrophic lateral sclerosis

Evidence is accumulating that an imbalance between pathways for degeneration or survival in motor neurons may play a central role in mechanisms that lead to neurodegeneration in amyotrophic lateral sclerosis (ALS). We and other groups have observed that downregulation, or lack of induction, of the PI3K/Akt prosurvival pathway may be responsible for defective response of motor neurons to injury and their consequent cellular demise. Some of the neuroprotective effects mediated by growth factors may involve activation of Akt, but a proof of concept of Akt as a target for therapy is lacking. We demonstrate that specific expression of constitutively activated Akt3 in motor neurons through the use of the promoter of homeobox gene Hb9 prevents neuronal loss induced by SOD1.G93A both in vitro (in mixed neuron/astrocyte cocultures) and in vivo (in a mouse model of ALS). Inhibition of ASK1 and GSK3beta was involved in the neuroprotective effects of activated Akt3, further supporting the hypothesis that induction of Akt3 may be a key step in activation of pathways for survival in the attempt to counteract motor neuronal degeneration in ALS.

Neurotoxicity of developmental hypothyroxinemia and hypothyroidism in rats: Impairments of long-term potentiation are mediated by phosphatidylinositol 3-kinase signaling pathway

Neurotoxicity of iodine deficiency-induced hypothyroidism during developmental period results in serious impairments of brain function, such as learning and memory. These impairments are largely irreversible, and the underlying mechanisms remain unclear. In addition to hypothyroidism, iodine deficiency may cause hypothyroxinemia, a relatively subtle form of thyroid hormone deficiency. Neurotoxicity of developmental hypothyroxinemia also potentially impairs learning and memory. However, more direct evidence of the associations between developmental hypothyroxinemia and impairments of learning and memory should be provided, and the underlying mechanisms remain to be elucidated. Thus, in the present study, we investigated the effects of developmental hypothyroxinemia and hypothyroidism on long-term potentiation (LTP), a widely accepted cellular model of learning and memory, in the hippocampal CA1 region. The activation of the phosphatidylinositol 3-kinase (PI3K) signaling pathway - a pathway closely associated with synaptic plasticity and learning and memory - was also investigated. Wistar rats were treated with iodine deficient diet or methimazole (MMZ) to induce developmental hypothyroxinemia or hypothyroidism. The results showed that developmental hypothyroxinemia caused by mild iodine deficiency and developmental hypothyroidism caused by severe iodine deficiency or MMZ significantly reduced the field-excitatory postsynaptic potential (f-EPSP) slope and the population spike (PS) amplitude. Decreased activation of the PI3K signaling pathway was also observed in rats subjected to developmental hypothyroxinemia or hypothyroidism. Our results may support the hypothesis that neurotoxicity of both developmental hypothyroxinemia and hypothyroidism causes damages to learning and memory. Our results also suggest that decreased activation of the PI3K signaling pathway may contribute to impairments of LTP caused by neurotoxicity of both developmental hypothyroxinemia and hypothyroidism.

The essential role of endothelial nitric oxide synthase activation in insulin-mediated neuroprotection against ischemic stroke in diabetes

BACKGROUND

Stroke patients with diabetes have a higher mortality rate, worse neurologic outcome, and more severe disability than those without diabetes. Results from clinical trials comparing the outcomes of stroke seen with intensive glycemic control in diabetic individuals are conflicting. Therefore, the present study was aimed to identify the key factor involved in the neuroprotective action of insulin beyond its hypoglycemic effects in streptozotocin-diabetic rats with ischemic stroke.

METHODS

Long-Evans male rats were divided into three groups (control, diabetes, and diabetes treated with insulin) and subjected to focal cerebral ischemia-reperfusion (FC I/R) injury.

RESULTS

Hyperglycemia aggravated FC I/R injuries with an increase in cerebral infarction and neurologic deficits, inhibition of glucose uptake and membrane-trafficking activity of glucose transporter 1, and reduction of Akt and endothelial nitric oxide synthase (eNOS) phosphorylation in the cerebrum. Insulin treatment alleviated hyperglycemia and the symptoms of diabetes in streptozotocin-diabetic rats. Insulin administration also significantly decreased cerebral infarction and neurologic deficits and increased phosphorylation of Akt and eNOS protein in the cerebrum of FC I/R-injured diabetic rats. However, the glucose uptake and membrane trafficking activity of glucose transporter 1 in the cerebrum were not restored by insulin treatment. Coadministration of the eNOS inhibitor, N-iminoethyl-L-ornithine, with insulin abrogated beneficial effects of insulin on cerebral infarct volume and neurologic deficits in FC I/R-injured diabetic rats without affecting the hypoglycemic action of insulin.

CONCLUSIONS

These results suggest that eNOS activation is required for the neuroprotection of insulin against ischemic stroke in patients with diabetes.

The Role of Neurotrophins in Major Depressive Disorder

Neurotrophins and other growth factors have been advanced as critical modulators of depressive behavior. Support for this model is based on analyses of knockout and transgenic mouse models, human genetic studies, and screens for gene products that are regulated by depressive behavior and/or antidepressants. Even subtle alteration in the regulated secretion of brain-derived neurotrophic factor (BDNF), for example, due to a single nucleotide polymorphism (SNP)-encoded Val-Met substitution in proBDNF that affects processing and sorting, impacts behavior and cognition. Alterations in growth factor expression result in changes in neurogenesis as well as structural changes in neuronal cytoarchitecture, including effects on dendritic length and spine density, in the hippocampus, nucleus accumbens, and prefrontal cortex. These changes have the potential to impact the plasticity and stability of synapses in the CNS, and the complex brain circuitry that regulates behavior. Here we review the role that neurotrophins play in the modulation of depressive behavior, and the downstream signaling targets they regulate that potentially mediate these behavioral pro-depressant and antidepressant effects.

Synaptic changes in Alzheimer's disease and its models

Alzheimer's disease (AD) is a highly prevalent neurodegenerative disorder characterized by a progressive loss of cognition and the presence of two hallmark lesions, senile plaques (SP) and neurofibrillary tangles (NFT), which result from the accumulation and deposition of the β-amyloid peptide (Aβ) and the aggregation of hyperphosphorylated tau protein, respectively. Initially, it was thought that Aβ fibrils, which make up SP, were the root cause of the massive neurodegeneration usual found in AD brains. Over time, the longstanding emphasis on fibrillar Aβ deposits and neuronal death slowly gave way to a new paradigm involving soluble oligomeric forms of Aβ, which play a prominent role in triggering the cognitive deficits by specifically targeting synapses and disrupting synaptic signaling pathways. While this paradigm is widely accepted today in the AD field, the molecular details have not been fully elucidated. In this review, we address some of the important evidence, which has led to the Aβ oligomer-centric hypothesis as well as some of the key findings concerning the effects of Aβ oligomers on synapses at a morphological and functional level. Understanding how Aβ oligomers target synapses provides an important framework for ongoing AD research, which can lead to the development of successful therapeutic strategies designed to alter or perhaps reverse the course of the disease.

Natural polyphenols against neurodegenerative disorders: potentials and pitfalls

Within the last years, a rapidly growing number of polyphenolic compounds with neuroprotective effects have been described. Many efforts have been made to explore the mechanisms behind the neuroprotective action of polyphenols. However, many pathways and mechanisms considered for mediating these effects are rather general than specific. Moreover, despite the beneficial effects of polyphenols in experimental treatment of neurodegeneration, little has been achieved in bringing them into routine clinical applications. In this review, we have summarized the protective effects of polyphenols against neurodegeneration, and we have also discussed some of the barricades in translating these biochemical compounds, into relevant therapeutics for neurodegenerative diseases.

Changes in vascular endothelial growth factor (VEGF) induced by the Morris water maze task

The present study was undertaken to evaluate the effects on hippocampal vascular endothelial growth factor (VEGF) levels in rats when they experience hippocampal-dependent spatial learning via the Morris water maze (MWM) task. Rats underwent one of two different versions of the MWM: weak or intensive. After one day of intensive training, a highly sensitive enzyme-linked immunosorbent assay (ELISA) was used to measure VEGF protein levels in the hippocampus, cortex, and serum, and higher levels were found in the trained group compared to a naive control group. VEGF levels also increased in rats that swam only for durations equal to the intensive training periods. In contrast, rats trained under the weaker MWM paradigm for five days showed a decrease in hippocampal VEGF protein level. Mimicking increases in neuronal VEGF in the hippocampus by direct infusion of VEGF into CA1 resulted in up-regulation of the phosphorylation of the cAMP response element-binding (CREB) protein and the Ca2+/calmodulin-dependent protein kinases II (CaMKII). These results suggest that VEGF may be a physiological parameter involved in learning procedures that include physical activity.

Insulin dysfunction and allostatic load in bipolar disorder

Bipolar disorder (BD) is associated with substantial morbidity, as well as premature mortality. Available evidence indicates that 'stress-sensitive' chronic medical disorders, such as cardiovascular disease, obesity and Type 2 diabetes mellitus, are critical mediators and/or moderators of BD. Changes in physiologic systems implicated in allostasis have been proposed to impact brain structures and neurocognition, as well as medical comorbidity in this population. For example, abnormalities in insulin physiology, for example, insulin resistance, hyperinsulinemia and central insulinopenia, are implicated as effectors of allostatic load in BD. Insulin's critical role in CNS physiological (e.g., neurotrophism and synaptic plasticity) and pathophysiological (e.g., neurocognitive deficits, pro-apoptosis and amyloid deposition) processes is amply documented. This article introduces the concept that insulin is a mediator of allostatic load in the BD and possibly a therapeutic target.

NYAP: a phosphoprotein family that links PI3K to WAVE1 signalling in neurons

The phosphoinositide 3-kinase (PI3K) pathway has been extensively studied in neuronal function and morphogenesis. However, the precise molecular mechanisms of PI3K activation and its downstream signalling in neurons remain elusive. Here, we report the identification of the Neuronal tYrosine-phosphorylated Adaptor for the PI 3-kinase (NYAP) family of phosphoproteins, which is composed of NYAP1, NYAP2, and Myosin16/NYAP3. The NYAPs are expressed predominantly in developing neurons. Upon stimulation with Contactin5, the NYAPs are tyrosine phosphorylated by Fyn. Phosphorylated NYAPs interact with PI3K p85 and activate PI3K, Akt, and Rac1. Moreover, the NYAPs interact with the WAVE1 complex which mediates remodelling of the actin cytoskeleton after activation by PI3K-produced PIP(3) and Rac1. By simultaneously interacting with PI3K and the WAVE1 complex, the NYAPs bridge a PI3K-WAVE1 association. Disruption of the NYAP genes in mice affects brain size and neurite elongation. In conclusion, the NYAPs activate PI3K and concomitantly recruit the downstream effector WAVE complex to the close vicinity of PI3K and regulate neuronal morphogenesis.

Adult subependymal neural precursors, but not differentiated cells, undergo rapid cathodal migration in the presence of direct current electric fields

BACKGROUND

The existence of neural stem and progenitor cells (together termed neural precursor cells) in the adult mammalian brain has sparked great interest in utilizing these cells for regenerative medicine strategies. Endogenous neural precursors within the adult forebrain subependyma can be activated following injury, resulting in their proliferation and migration toward lesion sites where they differentiate into neural cells. The administration of growth factors and immunomodulatory agents following injury augments this activation and has been shown to result in behavioural functional recovery following stroke.

METHODS AND FINDINGS

With the goal of enhancing neural precursor migration to facilitate the repair process we report that externally applied direct current electric fields induce rapid and directed cathodal migration of pure populations of undifferentiated adult subependyma-derived neural precursors. Using time-lapse imaging microscopy in vitro we performed an extensive single-cell kinematic analysis demonstrating that this galvanotactic phenomenon is a feature of undifferentiated precursors, and not differentiated phenotypes. Moreover, we have shown that the migratory response of the neural precursors is a direct effect of the electric field and not due to chemotactic gradients. We also identified that epidermal growth factor receptor (EGFR) signaling plays a role in the galvanotactic response as blocking EGFR significantly attenuates the migratory behaviour.

CONCLUSIONS

These findings suggest direct current electric fields may be implemented in endogenous repair paradigms to promote migration and tissue repair following neurotrauma.