Glycogen synthase kinase-3 inhibitors: Rescuers of cognitive impairments

Alcohol drinking exacerbates neural and behavioral pathology in the 3xTg-AD mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that represents the most common cause of dementia in the United States. Although the link between alcohol use and AD has been studied, preclinical research has potential to elucidate neurobiological mechanisms that underlie this interaction. This study was designed to test the hypothesis that nondependent alcohol drinking exacerbates the onset and magnitude of AD-like neural and behavioral pathology. We first evaluated the impact of voluntary 24-h, two-bottle choice home-cage alcohol drinking on the prefrontal cortex and amygdala neuroproteome in C57BL/6J mice and found a striking association between alcohol drinking and AD-like pathology. Bioinformatics identified the AD-associated proteins MAPT (Tau), amyloid beta precursor protein (APP), and presenilin-1 (PSEN-1) as the main modulators of alcohol-sensitive protein networks that included AD-related proteins that regulate energy metabolism (ATP5D, HK1, AK1, PGAM1, CKB), cytoskeletal development (BASP1, CAP1, DPYSL2 [CRMP2], ALDOA, TUBA1A, CFL2, ACTG1), cellular/oxidative stress (HSPA5, HSPA8, ENO1, ENO2), and DNA regulation (PURA, YWHAZ). To address the impact of alcohol drinking on AD, studies were conducted using 3xTg-AD mice that express human MAPT, APP, and PSEN-1 transgenes and develop AD-like brain and behavioral pathology. 3xTg-AD and wild-type mice consumed alcohol or saccharin for 4 months. Behavioral tests were administered during a 1-month alcohol-free period. Alcohol intake induced AD-like behavioral pathologies in 3xTg-AD mice including impaired spatial memory in the Morris Water Maze, diminished sensorimotor gating as measured by prepulse inhibition, and exacerbated conditioned fear. Multiplex immunoassay conducted on brain lysates showed that alcohol drinking upregulated primary markers of AD pathology in 3xTg-AD mice: Aβ 42/40 ratio in the lateral entorhinal and prefrontal cortex and total Tau expression in the lateral entorhinal cortex, medial prefrontal cortex, and amygdala at 1-month post alcohol exposure. Immunocytochemistry showed that alcohol use upregulated expression of pTau (Ser199/Ser202) in the hippocampus, which is consistent with late-stage AD. According to the NIA-AA Research Framework, these results suggest that alcohol use is associated with Alzheimer's pathology. Results also showed that alcohol use was associated with a general reduction in Akt/mTOR signaling via several phosphoproteins (IR, IRS1, IGF1R, PTEN, ERK, mTOR, p70S6K, RPS6) in multiple brain regions including hippocampus and entorhinal cortex. Dysregulation of Akt/mTOR phosphoproteins suggests alcohol may target this pathway in AD progression. These results suggest that nondependent alcohol drinking increases the onset and magnitude of AD-like neural and behavioral pathology in 3xTg-AD mice.

Dietary Polyphenols: A Multifactorial Strategy to Target Alzheimer's Disease

Ageing is an inevitable fundamental process for people and is their greatest risk factor for neurodegenerative disease. The ageing processes bring changes in cells that can drive the organisms to experience loss of nutrient sensing, disrupted cellular functions, increased oxidative stress, loss of cellular homeostasis, genomic instability, accumulation of misfolded protein, impaired cellular defenses and telomere shortening. Perturbation of these vital cellular processes in neuronal cells can lead to life threatening neurological disorders like Alzheimer's Disease, Parkinson's Disease, Huntington's Disease, Lewy body dementia, etc. Alzheimer's Disease is the most frequent cause of deaths in the elderly population. Various therapeutic molecules have been designed to overcome the social, economic and health care burden caused by Alzheimer's Disease. Almost all the chemical compounds in clinical practice have been found to treat symptoms only limiting them to palliative care. The reason behind such imperfect drugs may result from the inefficiencies of the current drugs to target the cause of the disease. Here, we review the potential role of antioxidant polyphenolic compounds that could possibly be the most effective preventative strategy against Alzheimer's Disease.

Intermittent-Excessive and Chronic-Moderate Ethanol Intake during Adolescence Impair Spatial Learning, Memory and Cognitive Flexibility in the Adulthood

Intermittent and excessive ethanol consumption over very short periods of time, known as binge drinking, is common in the adolescence, considered a vulnerable period to the effects of alcohol in terms of cognitive performance. One of the brain functions most drastically affected by ethanol in adolescent individuals seems to be spatial learning and memory dependent on the hippocampus. In the current study we have focused on the long-lasting effects on spatial learning and memory of intermittent and excessive alcohol consumption compared to chronic and moderate alcohol exposure during adolescence. Five-week old male Wistar rats consumed ethanol for 24 days following two different self-administration protocols that differed in the intake pattern. Spatial learning and memory were evaluated in the radial arm maze. Hippocampal synaptic plasticity was assessed by measuring field excitatory postsynaptic potentials. Hippocampal expression of AMPA and NMDA receptor subunits as well as levels of phosphorylated Ser⁹-GSK3β (the inactive form of GSK3β) were also quantified. Our results show that both patterns of ethanol intake during adolescence impair spatial learning, memory and cognitive flexibility in the adulthood in a dose-dependent way. Nevertheless, changes in synaptic plasticity, gene expression and levels of inactive GSK3β depended on the pattern of ethanol intake.

Tadalafil restores long-term memory and synaptic plasticity in mice with hepatic encephalopathy

BACKGROUND AND AIM

Tadalafil displays important neuroprotective effects in experimental models of neurodegenerative diseases, however its mechanisms of action remain poorly understood. The aim of the present study was to investigate the action of Tadalafil on learning and memory, neuroinflammation, glial cell activation and neuroprotection in the experimental model of hepatic encephalopathy (HE) induced by Thioacetamide (TAA) in mice.

METHODS

Mice received intraperitoneal injections of TAA, for 3 consecutive days, reaching the final dose of 600 mg/kg. Tadalafil 15 mg/kg body weight was administered by gavage during 15 days after TAA induction. Mice underwent a Barnes maze for learning and memory evaluation.

RESULTS

Animals with hepatic encephalopathy showed reduced learning and spatial memory in the Barnes Maze, presented astrocyte and microglia activation and increased neuroinflammatory markers such as TNF-α, IL-1β, IL-6, p-p38, p-ERK and p-NF-kB. In addition, the signaling pathway PKA/PKG/CREB/BDNF/NeuN/synaptophysin and glutamate receptors were deregulated by TAA. Tadalafil treatment regulated the inflammation signaling pathways restoring learning and spatial memory.

CONCLUSION

Tadalafil significantly reduced neuroinflammation, promoted neuroprotection and plasticity, regulated the expression of hippocampal glutamate receptor and restored spatial learning ability and memory.

Decoding the PTM-switchboard of Notch

The developmentally indispensable Notch pathway exhibits a high grade of pleiotropism in its biological output. Emerging evidence supports the notion of post-translational modifications (PTMs) as a modus operandi controlling dynamic fine-tuning of Notch activity. Although, the intricacy of Notch post-translational regulation, as well as how these modifications lead to multiples of divergent Notch phenotypes is still largely unknown, numerous studies show a correlation between the site of modification and the output. These include glycosylation of the extracellular domain of Notch modulating ligand binding, and phosphorylation of the PEST domain controlling half-life of the intracellular domain of Notch. Furthermore, several reports show that multiple PTMs can act in concert, or compete for the same sites to drive opposite outputs. However, further investigation of the complex PTM crosstalk is required for a complete understanding of the PTM-mediated Notch switchboard. In this review, we aim to provide a consistent and up-to-date summary of the currently known PTMs acting on the Notch signaling pathway, their functions in different contexts, as well as explore their implications in physiology and disease. Furthermore, we give an overview of the present state of PTM research methodology, and allude to a future with PTM-targeted Notch therapeutics.

Recruitment, Retainment, and Biomarkers of Response; A Pilot Trial of Lithium in Humans With Mild Cognitive Impairment

Lithium has been used for decades to treat Bipolar Disorder. Some of its therapeutic benefits may be through inhibition of Glycogen Synthase Kinase (GSK)-3. Enhanced GSK3 activity associates with development of Alzheimer’s disease (AD), therefore lithium is a currently used therapeutic with potential to be repurposed for prevention of Dementia. An important step toward a clinical trial for AD prevention using lithium is to establish the dose of lithium that blocks GSK3 in Mild Cognitive Impairment (MCI), a high-risk condition for progression to AD. We investigated volunteer recruitment, retention, and tolerance in this population, and assessed biomarkers of GSK3 in MCI compared to control and after lithium treatment. Recruitment was close to target, with higher than anticipated interest. Drop out was not related to lithium blood concentration. Indeed, 33% of the withdrawals were in the first week of very low dose lithium. Most made it through to the highest dose of lithium with no adverse events. We analyzed 18 potential biomarkers of GSK3 biology in rat PBMCs, but only four of these gave a robust reproducible baseline signal. The only biomarker that was modified by acute lithium injection in the rat was the inhibitory phosphorylation of Ser9 of GSK3beta (enhanced in PBMCs) and this associated with reduced activity of GSK3beta. In contrast to the rat PBMC preparations the protein quality of the human PBMC preparations was extremely variable. There was no difference between GSK3 biomarkers in MCI and control PBMC preparations and no significant effect of chronic lithium on the robust GSK3 biomarkers, indicating that the dose reached may not be sufficient to modify these markers. In summary, the high interest from the MCI population, and the lack of any adverse events, suggest that it would be relatively straightforward and safe to recruit to a larger clinical trial within this dosing regimen. However, it is clear that we will need an improved PBMC isolation process along with more robust, sensitive, and validated biomarkers of GSK3 function, in order to use GSK3 pathway regulation in human PBMC preparations as a biomarker of GSK3 inhibitor efficacy, within a clinical trial setting.

Reversal of Global Ischemia-Induced Cognitive Dysfunction by Delayed Inhibition of TRPM2 Ion Channels

Hippocampal injury and cognitive impairments are common after cardiac arrest and stroke and do not have an effective intervention despite much effort. Therefore, we developed a new approach aimed at reversing synaptic dysfunction by targeting TRPM2 channels. Cardiac arrest/cardiopulmonary resuscitation (CA/CPR) in mice was used to investigate cognitive deficits and the role of the calcium-permeable ion channel transient receptor potential-M2 (TRPM2) in ischemia-induced synaptic dysfunction. Our data indicates that absence (TRPM2^-/-) or acute inhibition of TRPM2 channels with tatM2NX reduced hippocampal cell death in males only, but prevented synaptic plasticity deficits in both sexes. Remarkably, administration of tatM2NX weeks after injury reversed hippocampal plasticity and memory deficits. Finally, TRPM2-dependent activation of calcineurin-GSK3β pathway contributes to synaptic plasticity impairments. These data suggest persistent TRPM2 activity following ischemia contributes to impairments of the surviving hippocampal network and that inhibition of TRPM2 channels at chronic time points may represent a novel strategy to improve functional recovery following cerebral ischemia that is independent of neuroprotection.

Multitarget-directed cotreatment with cilostazol and aripiprazole for augmented neuroprotection against oxidative stress-induced toxicity in HT22 mouse hippocampal cells

Cerebrovascular dysfunction is crucially associated with cognitive impairment and a high prevalence of psychotic symptoms in the vascular dementia characterized by oxidative stress and multifactorial neurodegeneration. In this study, the significant decrease in BDNF expression in HT22 cells due to H₂O₂ (0.25 mM) was little affected by either aripiprazole (1 μM) or cilostazol (1 μM) alone, but significantly increased by cotreatment with both drugs. Even in the presence of H₂O₂, P-CK2α (Tyr 255), nuclear P-CREB (Ser 133), and nuclear P-β-catenin (Ser 675) levels were significantly increased in a synergistic manner by aripiprazole plus cilostazol cotreatment. Aripiprazole and cilostazol cotreatment synergistically increased P-GSK-3β (Ser 9) level. Nrf2/HO-1 expression was significantly elevated time- and concentration-dependently by either aripiprazole or cilostazol. In line with these, concurrent treatment with aripiprazole (1 μM) plus cilostazol (1 μM) significantly increased Nrf2 and HO-1 expression in a synergistic manner, accompanying with increased ARE luciferase activity, while each drug monotherapy showed little effects. Consequently, this cotreatment synergistically ameliorated the attenuated neurite outgrowth induced by H₂O₂ in the HT22 cells, and these were inhibited by K252A (inhibitor of BDNF receptor), TBCA (CK2 inhibitor), imatinib (β-catenin inhibitor) and ZnPP (inhibitor of HO-1), indicating that BDNF, P-CK2α, β-catenin and HO-1 activation are implicated in the enhanced neurite outgrowth. This study highlights that cotreatment with low concentrations of aripiprazole and cilostazol synergistically elicits neuroprotective effects by overcoming oxidative stress-evoked neurotoxicity associated with increased neurite outgrowth, providing a rationale for the use of this combinatorial treatment in vascular dementia.

The intermittent administration of ethanol during the juvenile period produces changes in the expression of hippocampal genes and proteins and deterioration of spatial memory

BACKGROUND

Binge drinking is a pattern of alcohol intake characterized by excessive and intermittent alcohol consumption over a very short period of time that is more used during adolescence. We aim to compare the lasting effects of a chronic-moderate vs. this intermittent-excessive way of alcohol intake during adolescence in spatial memory and in the expression of glutamatergic receptors and GSK3β activity.

METHODS

Adolescent male Wistar rats were given ethanol/saline i.p. injections in four different groups: High-I (4 g/kg of a 25% (vol/vol) every 3 days), Low-I (1 g/kg of a 5% (vol/vol) every 3 days), M (0.3 g/kg of a 2.5% (vol/vol) daily) and Control (C, sterile isotonic saline daily). Rats received ethanol for up to five 3-day cycles. Spatial memory was measured by spontaneous alternation in the Y-Maze. Gene and protein expression of hippocampal proteins were also analysed.

RESULTS

Both high- and low-intermittent ethanol administration produced spatial memory impairment and changes in glutamatergic receptors gene expression were observed regardless of the pattern of exposure. High doses of intermittent alcohol administration produced an increase of phosphorylation of GSK3β Ser9. Moreover, moderate alcohol administration produced a down-regulation of the AMPAR 2/3 ratio despite lack of spatial memory deficits.

CONCLUSIONS

Excessive and intermittent ethanol exposure during adolescence impaired the spatial memory processes during adulthood regardless of the amount of alcohol administered. Moreover, chronic-moderate and intermittent pattern induced changes in the expression of glutamatergic receptors. In addition, high-intermittent ethanol exposure during adolescence inactivated GSK3β by increasing its phosphorylation in Ser9.

Differential regulation of GSK-3β in spinal dorsal horn and in hippocampus mediated by interleukin-1beta contributes to pain hypersensitivity and memory deficits following peripheral nerve injury

Accumulating evidence shows that inhibition of glycogen synthase kinase-3beta (GSK-3β) ameliorates cognitive impairments caused by a diverse array of diseases. Our previous work showed that spared nerve injury (SNI) that induces neuropathic pain causes short-term memory deficits. Here, we reported that GSK-3β activity was enhanced in hippocampus and reduced in spinal dorsal horn following SNI, and the changes persisted for at least 45 days. Repetitive applications of selective GSK-3β inhibitors (SB216763, 5 mg/kg, intraperitoneally, three times or AR-A014418, 400 ng/kg, intrathecally, seven times) prevented short-term memory deficits but did not affect neuropathic pain induced by SNI. Surprisingly, we found that the repetitive SB216763 or AR-A014418 induced a persistent pain hypersensitivity in sham animals. Mechanistically, both β-catenin and brain-derived neurotrophic factor (BDNF) were upregulated in spinal dorsal horn but downregulated in hippocampus following SNI. Injections of SB216763 prevented the BDNF downregulation in hippocampus but enhanced its upregulation in spinal dorsal horn in SNI rats. In sham rats, SB216763 upregulated both β-catenin and BDNF in spinal dorsal horn but affect neither of them in hippocampus. Finally, intravenous injection of interleukin-1beta that induces pain hypersensitivity and memory deficits mimicked the SNI-induced the differential regulation of GSK-3β/β-catenin/BDNF in spinal dorsal horn and in hippocampus. Accordingly, the prolonged opposite changes of GSK-3β activity in hippocampus and in spinal dorsal horn induced by SNI may contribute to memory deficits and neuropathic pain by differential regulation of BDNF in the two regions. GSK-3β inhibitors that treat cognitive disorders may result in a long-lasting pain hypersensitivity.

Curcumin mitigates axonal injury and neuronal cell apoptosis through the PERK/Nrf2 signaling pathway following diffuse axonal injury

Diffuse axonal injury (DAI) accounts for more than 50% of all traumatic brain injury. In response to the mechanical damage associated with DAI, the abnormal proteins produced in the neurons and axons, namely, β-APP and p-tau, induce endoplasmic reticulum (ER) stress. Curcumin, a major component extracted from the rhizome of Curcuma longa, has shown potent anti-inflammatory, antioxidant, anti-infection, and antitumor activity in previous studies. Moreover, curcumin is an activator of nuclear factor-erythroid 2-related factor 2 (Nrf2) and promotes its nuclear translocation. In this study, we evaluated the therapeutic potential of curcumin for the treatment of DAI and investigated the mechanisms underlying the protective effects of curcumin against neural cell death and axonal injury after DAI. Rats subjected to a model of DAI by head rotational acceleration were treated with vehicle or curcumin to evaluate the effect of curcumin on neuronal and axonal injury. We observed that curcumin (20 mg/kg intraperitoneal) administered 1 h after DAI induction alleviated the aggregation of p-tau and β-APP in neurons, reduced ER-stress-related cell apoptosis, and ameliorated neurological deficits. Further investigation showed that the protective effect of curcumin in DAI was mediated by the PERK/Nrf2 pathway. Curcumin promoted PERK phosphorylation, and then Nrf2 dissociated from Keap1 and was translocated to the nucleus, which activated ATF4, an important bZIP transcription factor that maintains intracellular homeostasis, but inhibited the CHOP, a hallmark of ER stress and ER-associated programmed cell death. In summary, we demonstrate for the first time that curcumin confers protection against abnormal proteins and neuronal apoptosis after DAI, that the process is mediated by strengthening of the unfolded protein response to overcome ER stress, and that the protective effect of curcumin against DAI is dependent on the activation of Nrf2.

A Synaptic Perspective of Fragile X Syndrome and Autism Spectrum Disorders

Altered synaptic structure and function is a major hallmark of fragile X syndrome (FXS), autism spectrum disorders (ASDs), and other intellectual disabilities (IDs), which are therefore classified as synaptopathies. FXS and ASDs, while clinically and genetically distinct, share significant comorbidity, suggesting that there may be a common molecular and/or cellular basis, presumably at the synapse. In this article, we review brain architecture and synaptic pathways that are dysregulated in FXS and ASDs, including spine architecture, signaling in synaptic plasticity, local protein synthesis, (m)RNA modifications, and degradation. mRNA repression is a powerful mechanism for the regulation of synaptic structure and efficacy. We infer that there is no single pathway that explains most of the etiology and discuss new findings and the implications for future work directed at improving our understanding of the pathogenesis of FXS and related ASDs and the design of therapeutic strategies to ameliorate these disorders.

LiCl Pretreatment Ameliorates Adolescent Methamphetamine Exposure-Induced Long-Term Alterations in Behavior and Hippocampal Ultrastructure in Adulthood in Mice

BACKGROUND

Adolescent methamphetamine exposure causes a broad range of neurobiological deficits in adulthood. Glycogen synthase kinase-3β is involved in various cognitive and behavioral processes associated with methamphetamine exposure. This study aims to investigate the protective effects of the glycogen synthase kinase-3β inhibitor lithium chloride on adolescent methamphetamine exposure-induced long-term alterations in emotion, cognition, behavior, and molecule and hippocampal ultrastructure in adulthood.

METHODS

A behavioral test battery was used to investigate the protective effects of lithium chloride on adolescent methamphetamine exposure-induced long-term emotional, cognitive, and behavioral impairments in mice. Western blotting and immunohistochemistry were used to detect glycogen synthase kinase-3β activity levels in the medial prefrontal cortex and dorsal hippocampus. Electron microscopy was used to analyze changes in synaptic ultrastructure in the dorsal hippocampus. Locomotor sensitization with a methamphetamine (1 mg/kg) challenge was examined 80 days after adolescent methamphetamine exposure.

RESULTS

Adolescent methamphetamine exposure induced long-term alterations in locomotor activity, novel spatial exploration, and social recognition memory; increases in glycogen synthase kinase-3β activity in dorsal hippocampus; and decreases in excitatory synapse density and postsynaptic density thickness in CA1. These changes were ameliorated by lithium chloride pretreatment. Adolescent methamphetamine exposure-induced working memory deficits in Y-maze spontaneous alternation test and anxiety-like behavior in elevated-plus maze test spontaneously recovered after long-term methamphetamine abstinence. No significant locomotor sensitization was observed after long-term methamphetamine abstinence.

CONCLUSIONS

Hyperactive glycogen synthase kinase-3β contributes to adolescent chronic methamphetamine exposure-induced behavioral and hippocampal impairments in adulthood. Our results suggest glycogen synthase kinase-3β may be a potential target for the treatment of deficits in adulthood associated with adolescent methamphetamine abuse.

Chronic fluoride exposure induces neuronal apoptosis and impairs neurogenesis and synaptic plasticity: Role of GSK-3β/β-catenin pathway

Fluoride is becoming an ineluctable environmental pollutant and its longterm exposure would cause fluorosis and irreversible brain damage, but the molecular mechanisms remain far from fully understood. In the present study, we firstly evaluated the glycogen synthase kinase 3β (GSK-3β)/β-catenin pathway in the hippocampus of rats exposed to fluoride, given the well-established role of GSK-3β/β-catenin pathway in neuronal death and survival. Our data showed that sustained exposure to 50 mg/L and 100 mg/L NaF in drinking water dose-dependently induced neuronal loss and apoptosis in rat hippocampus. Neurogenesis was also weakened by fluoride administration in the hippocampal dentate gyrus region. Additionally, the synaptic markers, synaptophysin (SYP) and post-synaptic density 95 (PSD95) protein levels, were decreased by 100 mg/L NaF treatment, whereas 50 mg/L NaF only reduced SYP expression, indicating a compromised synaptic function. We further demonstrated that NaF, especially the higher dose, induced GSK-3β activity, with decreased inactive phosphorylated GSK-3β levels and increased GSK-3β, the active form of the kinase. Correspondingly, downstream β-catenin signaling was undermined by NaF treatment as evidenced by the fact that both two doses of NaF decreased nucleus β-catenin status and the higher dose of NaF also reduced cytoplasmic β-catenin protein expression. Taken together, the present study firstly showed the aberrant changes of GSK-3β/β-catenin signaling in the fluoride-exposed brain, highlighting the involvement of GSK-3β/β-catenin signaling in the fluoride-induced neurotoxicity.

Structure and Regulation of Glycogen Synthase in the Brain

Brain glycogen synthesis is a regulated, multi-step process that begins with glucose transport across the blood brain barrier and culminates with the actions of glycogen synthase and the glycogen branching enzyme to elongate glucose chains and introduce branch points in a growing glycogen molecule. This review focuses on the synthesis of glycogen in the brain, with an emphasis on glycogen synthase, but draws on salient studies in mammalian muscle and liver as well as baker's yeast, with the goal of providing a more comprehensive view of glycogen synthesis and highlighting potential areas for further study in the brain. In addition, deficiencies in the glycogen biosynthetic enzymes which lead to glycogen storage diseases in humans are discussed, highlighting effects on the brain and discussing findings in genetically modified animal models that recapitulate these diseases. Finally, implications of glycogen synthesis in neurodegenerative and other diseases that impact the brain are presented.

GSK-3 Inhibitors: From the Brain to the Retina and Back Again

Enzyme glycogen synthase kinase-3 (GSK-3) is a candidate pharmacological target for the treatment of neurodegenerative diseases of the brain. Given the many molecular, cellular, and functional features shared by the brain and the retina in both physiological and pathological processes, drugs originally designed to treat neurodegenerative diseases of the brain could be useful candidates for the treatment of retinal degenerative pathologies. Moreover, the accessibility of the eye to noninvasive, quantitative diagnostic techniques allows for easier evaluation of the efficacy of candidate therapies in clinical trials. In this chapter, we discuss the potential of GSK-3 inhibitors in the treatment of retinal degeneration.

Comprehensive review of mechanisms of pathogenesis involved in Alzheimer's disease and potential therapeutic strategies

AD is a progressive neurodegenerative disorder and a leading cause of dementia in an aging population worldwide. The enormous challenge which AD possesses to global healthcare makes it as urgent as ever for the researchers to develop innovative treatment strategies to fight this disease. An in-depth analysis of the extensive available data associated with the AD is needed for a more comprehensive understanding of underlying molecular mechanisms and pathophysiological pathways associated with the onset and progression of the AD. The currently understood pathological and biochemical manifestations include cholinergic, Aβ, tau, excitotoxicity, oxidative stress, ApoE, CREB signaling pathways, insulin resistance, etc. However, these hypotheses have been criticized with several conflicting reports for their involvement in the disease progression. Several issues need to be addressed such as benefits to cost ratio with cholinesterase therapy, the dilemma of AChE selectivity over BChE, BBB permeability of peptidic BACE-1 inhibitors, hurdles related to the implementation of vaccination and immunization therapy, and clinical failure of candidates related to newly available targets. The present review provides an insight to the different molecular mechanisms involved in the development and progression of the AD and potential therapeutic strategies, enlightening perceptions into structural information of conventional and novel targets along with the successful applications of computational approaches for the design of target-specific inhibitors.

Targeting GSK3 signaling as a potential therapy of neurodegenerative diseases and aging

INTRODUCTION

Glycogen synthase kinase 3 (GSK3) is at the center of cellular signaling and controls various aspects of brain functions, including development of the nervous system, neuronal plasticity and onset of neurodegenerative disorders. Areas covered: In this review, recent efforts in elucidating the roles of GSK3 in neuronal plasticity and development of brain pathologies; Alzheimer's and Parkinson's disease, schizophrenia, and age-related neurodegeneration are described. The effect of microglia and astrocytes on development of the pathological states is also discussed. Expert opinion: GSK3β and its signaling pathway partners hold great promise as therapeutic target(s) for a multitude of neurological disorders. Activity of the kinase is often elevated in brain disorders. However, due to the wide range of GSK3 cellular targets, global inhibition of the kinase leads to severe side-effects and GSK3 inhibitors rarely reach Phase-2 clinical trials. Thus, a selective modulation of a specific cellular pool of GSK3 or specific down- or upstream partners of the kinase might provide more efficient anti-neurodegenerative therapies.

Glycans and glycosaminoglycans in neurobiology: key regulators of neuronal cell function and fate

The aim of the present study was to examine the roles of l-fucose and the glycosaminoglycans (GAGs) keratan sulfate (KS) and chondroitin sulfate/dermatan sulfate (CS/DS) with selected functional molecules in neural tissues. Cell surface glycans and GAGs have evolved over millions of years to become cellular mediators which regulate fundamental aspects of cellular survival. The glycocalyx, which surrounds all cells, actuates responses to growth factors, cytokines and morphogens at the cellular boundary, silencing or activating downstream signaling pathways and gene expression. In this review, we have focused on interactions mediated by l-fucose, KS and CS/DS in the central and peripheral nervous systems. Fucose makes critical contributions in the area of molecular recognition and information transfer in the blood group substances, cytotoxic immunoglobulins, cell fate-mediated Notch-1 interactions, regulation of selectin-mediated neutrophil extravasation in innate immunity and CD-34-mediated new blood vessel development, and the targeting of neuroprogenitor cells to damaged neural tissue. Fucosylated glycoproteins regulate delivery of synaptic neurotransmitters and neural function. Neural KS proteoglycans (PGs) were examined in terms of cellular regulation and their interactive properties with neuroregulatory molecules. The paradoxical properties of CS/DS isomers decorating matrix and transmembrane PGs and the positive and negative regulatory cues they provide to neurons are also discussed.

Endoplasmic reticulum stress induces spatial memory deficits by activating GSK-3

Endoplasmic reticulum (ER) stress is involved in Alzheimer's disease (AD), but the mechanism is not fully understood. Here, we injected tunicamycin (TM), a recognized ER stress inducer, into the brain ventricle of Sprague-Dawley (SD) rats to induce the unfolded protein response (UPR), demonstrated by the enhanced phosphorylation of pancreatic ER kinase (PERK), inositol-requiring enzyme-1 (IRE-1) and activating transcription factor-6 (ATF-6). We observed that UPR induced spatial memory deficits and impairments of synaptic plasticity in the rats. After TM treatment, GSK-3β was activated and phosphorylation of cAMP response element binding protein at Ser129 (pS129-CREB) was increased with an increased nuclear co-localization of pY126-GSK-3β and pS129-CREB. Simultaneous inhibition of GSK-3β by hippocampal infusion of SB216763 (SB) attenuated TM-induced UPR and spatial memory impairment with restoration of pS129-CREB and synaptic plasticity. We concluded that UPR induces AD-like spatial memory deficits with mechanisms involving GSK-3β/pS129-CREB pathway.

Degradation or aggregation: the ramifications of post-translational modifications on tau

Tau protein is encoded in the microtubule-associated protein tau (MAPT) gene and contributes to the stability of microtubules in axons. Despite of its basic isoelectric point and high solubility, tau is often found in intraneuronal filamentous inclusions such as paired helical filaments (PHFs), which are the primary constituent of neurofibrillary tangles (NFTs). This pathological feature is the nosological entity termed "tauopathies" which notably include Alzheimer's disease (AD). A proteinaceous signature of all tauopathies is hyperphosphorylation of the accumulated tau, which has been extensively studied as a major pharmacological target for AD therapy. However, in addition to phosphorylation events, tau undergoes a number of diverse posttranslational modifications (PTMs) which appear to be controlled by complex crosstalk. It remains to be elucidated which of the PTMs or their combinations have pro-aggregation or anti-aggregation properties. In this review, we outline the consequences of and communications between several key PTMs of tau, such as acetylation, phosphorylation, and ubiquitination, focusing on their roles in aggregation and degradation. We place emphasis on the structure of tau protofilaments from the human AD brain, which may be good targets to modulate etiological PTMs which cause tau aggregation. [BMB Reports 2018; 51(6): 265-273].

Treatment with the GSK3-beta inhibitor Tideglusib improves hippocampal development and memory performance in juvenile, but not adult, Cdkl5 knockout mice

Cyclin-dependent kinase-like 5 (CDKL5) disorder is a severe neurodevelopmental disorder characterized by early-onset epileptic seizures, severe developmental delay, and intellectual disability. To date, no effective pharmacological treatments are available to improve the neurological phenotype that is due to mutations in the CDKL5 gene. Murine models of CDKL5 disorder have recently been generated, making the preclinical testing of pharmacological interventions possible. Using a Cdkl5 knockout (KO) mouse model, we recently demonstrated that deficiency of Cdkl5 causes defects in postnatal hippocampal development and hippocampus-dependent learning and memory. These defects were accompanied by an increased activity of GSK3β, an important inhibitory regulator of many neuronal functions. Pharmacological inhibition of GSK3β activity was able to recover hippocampal defects and cognitive performance in juvenile Cdkl5 KO mice, suggesting that GSK3β inhibitors might be a potential therapeutic option for CDKL5 disorder. As GSK3β inhibitors have been shown to have differential medication responses in young people and adults, this study was designed to examine whether GSK3β is a possible therapeutic target both in juvenile and in adult CDKL5 patients. We found that treatment with the GSK3β inhibitor Tideglusib during the juvenile period improved hippocampal development and hippocampus-dependent behaviors in Cdkl5 KO mice, while treatment later on in adulthood had no positive effects. These results suggest that pharmacological interventions aimed at normalizing impaired GSK3β activity might have different age-dependent outcomes in CDKL5 disorder. This is of utmost importance in the development of therapeutic approaches in CDKL5 patients and in the design of rational clinical trials.

Liver carbohydrates metabolism: A new islet-neogenesis associated protein peptide (INGAP-PP) target

Islet-Neogenesis Associated Protein-Pentadecapeptide (INGAP-PP) increases β-cell mass and enhances glucose and amino acids-induced insulin secretion. Our aim was to demonstrate its effect on liver metabolism. For that purpose, adult male Wistar rats were injected twice-daily (10 days) with saline solution or INGAP-PP (250 μg). Thereafter, serum glucose, triglyceride and insulin levels were measured and homeostasis model assessment (HOMA-IR) and hepatic insulin sensitivity (HIS) were determined. Liver glucokinase and glucose-6-phosphatase (G-6-Pase) expression and activity, phosphoenolpyruvate carboxykinase (PEPCK) expression, phosphofructokinase-2 (PFK-2) protein content, P-Akt/Akt and glycogen synthase kinase-3β (P-GSK3/GSK3) protein ratios and glycogen deposit were also determined. Additionally, glucokinase activity and G-6-Pase and PEPCK gene expression were also determined in isolated hepatocytes from normal rats incubated with INGAP-PP (5 μg/ml). INGAP-PP administration did not modify any of the serum parameters tested but significantly increased activity of liver glucokinase and the protein level of its cytosolic activator, PFK-2. Conversely, INGAP-PP treated rats decreased gene expression and enzyme activity of gluconeogenic enzymes, G-6-Pase and PEPCK. They also showed a higher glycogen deposit and P-GSK3/GSK3 and P-Akt/Akt ratio. In isolated hepatocytes, INGAP-PP increased GK activity and decreased G-6-Pase and PEPCK expression. These results demonstrate a direct effect of INGAP-PP on the liver acting through P-Akt signaling pathway. INGAP-PP enhances liver glucose metabolism and deposit and reduces its production/output, thereby contributing to maintain normal glucose homeostasis. These results reinforce the concept that INGAP-PP might become a useful tool to treat people with impaired islet/liver glucose metabolism as it occurs in T2D.

The Role of Insulin/IGF-1/PI3K/Akt/GSK3β Signaling in Parkinson's Disease Dementia

Dementia, a condition that frequently afflicts patients in advanced stages of Parkinson's disease (PD), results in decreased quality of life and survival time. Nevertheless, the pathological mechanisms underlying Parkinson's disease dementia (PDD) are not completely understood. The symptoms characteristic of PDD may be the result of functional and structural deficiencies. The present study implicates the accumulation of Lewy bodies in the cortex and limbic system as a potent trigger in the development of PDD. In addition, significant Alzheimer-type pathologies, including amyloid-β (Aβ) plaques and NFTs, are observed in almost half of PDD patients. Interestingly, links between PDD pathogenesis and the mechanisms underlying the development of insulin resistance have begun to emerge. Furthermore, previous studies have demonstrated that insulin treatment reduces amyloid plaques in Alzheimer's disease (AD), and normalizes the production and functionality of dopamine and ameliorates motor impairments in 6-OHDA-induced rat PD models. GSK3β, a downstream substrate of PI3K/Akt signaling following induction by insulin and IGF-1, exerts an influence on AD and PD physiopathology. The genetic overexpression of GSK3β in cortex and hippocampus results in signs of neurodegeneration and spatial learning deficits in in vivo models (Lucas et al., 2001), whereas its inhibition results in improvements in cognitive impairment in these rodents, including AD and PD. Accordingly, insulin- or IGF-1-activated PI3K/Akt/GSK3β signaling may be involved in PDD pathogenesis, at least in the pathology of PD-type + AD-type.

Microglia Polarization, Gene-Environment Interactions and Wnt/β-Catenin Signaling: Emerging Roles of Glia-Neuron and Glia-Stem/Neuroprogenitor Crosstalk for Dopaminergic Neurorestoration in Aged Parkinsonian Brain

Neuroinflammatory processes are recognized key contributory factors in Parkinson's disease (PD) physiopathology. While the causes responsible for the progressive loss of midbrain dopaminergic (mDA) neuronal cell bodies in the subtantia nigra pars compacta are poorly understood, aging, genetics, environmental toxicity, and particularly inflammation, represent prominent etiological factors in PD development. Especially, reactive astrocytes, microglial cells, and infiltrating monocyte-derived macrophages play dual beneficial/harmful effects, via a panel of pro- or anti-inflammatory cytokines, chemokines, neurotrophic and neurogenic transcription factors. Notably, with age, microglia may adopt a potent neurotoxic, pro-inflammatory “primed” (M1) phenotype when challenged with inflammatory or neurotoxic stimuli that hamper brain's own restorative potential and inhibit endogenous neurorepair mechanisms. In the last decade we have provided evidence for a major role of microglial crosstalk with astrocytes, mDA neurons and neural stem progenitor cells (NSCs) in the MPTP- (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-) mouse model of PD, and identified Wnt/β-catenin signaling, a pivotal morphogen for mDA neurodevelopment, neuroprotection, and neuroinflammatory modulation, as a critical actor in glia-neuron and glia-NSCs crosstalk. With age however, Wnt signaling and glia-NSC-neuron crosstalk become dysfunctional with harmful consequences for mDA neuron plasticity and repair. These findings are of importance given the deregulation of Wnt signaling in PD and the emerging link between most PD related genes, Wnt signaling and inflammation. Especially, in light of the expanding field of microRNAs and inflammatory PD-related genes as modulators of microglial-proinflammatory status, uncovering the complex molecular circuitry linking PD and neuroinflammation will permit the identification of new druggable targets for the cure of the disease. Here we summarize recent findings unveiling major microglial inflammatory and oxidative stress pathways converging in the regulation of Wnt/β-catenin signaling, and reciprocally, the ability of Wnt signaling pathways to modulate microglial activation in PD. Unraveling the key factors and conditons promoting the switch of the proinflammatory M1 microglia status into a neuroprotective and regenerative M2 phenotype will have important consequences for neuroimmune interactions and neuronal outcome under inflammatory and/or neurodegenerative conditions.

Lithium Inhibits GSK3β and Augments GluN2A Receptor Expression in the Prefrontal Cortex

Glycogen synthase kinase 3β (GSK3β) is a highly conserved serine/threonine kinase that has been implicated in both psychiatric and neurodegenerative diseases including schizophrenia, bipolar disorder, and Alzheimer's disease; therefore regulating its activity has become an important strategy for treatment of cognitive impairments in these disorders. This study examines the effects of lithium on GSK3β and its interaction with β-catenin and NMDA receptors within the prefrontal cortex. Lithium, a clinically relevant drug commonly prescribed as a mood stabilizer for psychiatric disorders, significantly increased levels of phosphorylated GSK3β serine 9, an inhibitory phosphorylation site, and decreased β-catenin ser33/37/thr41 phosphorylation in vitro, indicating GSK3β inhibition and reduced β-catenin degradation. GluN2A subunit levels were concurrently increased following lithium treatment. Similar alterations were also demonstrated in vivo; lithium administration increased GSK3β serine 9 phosphorylation and GluN2A levels, suggesting a reduced GSK3β activity and augmented GluN2A expression. Correspondingly, we observed that the amplitudes of evoked GluN2A-mediated excitatory postsynaptic currents in mPFC pyramidal neurons were significantly increased following lithium administration. Our data suggest that GSK3β activity negatively regulates GluN2A expression, likely by mediating upstream β-catenin phosphorylation, in prefrontal cortical neurons. Furthermore, our biochemical and electrophysiological experiments demonstrate that lithium mediates a specific increase in GluN2A subunit expression, ultimately augmenting GluN2A-mediated currents in the prefrontal cortex.

The GSK3 kinase inhibitor lithium produces unexpected hyperphosphorylation of β-catenin, a GSK3 substrate, in human glioblastoma cells

Lithium salt is a classic glycogen synthase kinase 3 (GSK3) inhibitor. Beryllium is a structurally related inhibitor that is more potent but relatively uncharacterized. This study examined the effects of these inhibitors on the phosphorylation of endogenous GSK3 substrates. In NIH-3T3 cells, both salts caused a decrease in phosphorylated glycogen synthase, as expected. GSK3 inhibitors produce enhanced phosphorylation of Ser9 of GSK3β via a positive feedback mechanism, and both salts elicited this enhancement. Another GSK3 substrate is β-catenin, which has a central role in Wnt signaling. In A172 human glioblastoma cells, lithium treatment caused a surprising increase in phospho-Ser33/Ser37-β-catenin, which was quantified using an antibody-coupled capillary electrophoresis method. The β-catenin hyperphosphorylation was unaffected by p53 RNAi knockdown, indicating that p53 is not involved in the mechanism of this response. Lithium caused a decrease in the abundance of axin, a component of the β-catenin destruction complex that has a role in coordinating β-catenin ubiquitination and protein turnover. The axin and phospho-β-catenin results were reproduced in U251 and U87MG glioblastoma cell lines. These observations run contrary to the conventional view of the canonical Wnt signaling pathway, in which a GSK3 inhibitor would be expected to decrease, not increase, phospho-β-catenin levels.

This article has an associated First Person interview with the first author of the paper.

Summary: GSK3 inhibitors have potential use against Alzheimer's disease and other conditions. In this study, a classic inhibitor produced unexpected molecular effects on key components of the Wnt signaling pathway.

Alzheimer's disease pathology and the unfolded protein response: prospective pathways and therapeutic targets

Many vital interdependent cellular functions including proteostasis, lipogenesis and Ca homeostasis are executed by the endoplasmic reticulum (ER). Exogenous insults can impair ER performance: this must be rapidly corrected or cell death will ensue. Protective adaptations can boost the functional capacity of the ER and form the basis of the unfolded protein response (UPR). Activated in response to the accumulation of misfolded proteins, the UPR can halt protein translation while increasing protein-handling chaperones and the degradation of erroneous proteins through a conserved three-tier molecular cascade. However, prolonged activation of the UPR can result in the maladaptation of the system, resulting in the activation of inflammatory and apoptotic effectors. Recently, UPR and its involvement in neurodegenerative disease has attracted much interest and numerous potentially 'drugable' points of crosstalk are now emerging. Here, we summarize the functions of the ER and UPR, and highlight evidence for its potential role in the pathogenesis of Alzheimer's disease, before discussing several key targets with therapeutic potential.

Inhibition of hippocampal long-term potentiation by high-fat diets: is it related to an effect of palmitic acid involving glycogen synthase kinase-3?

High-fat diets (HFD) impair hippocampal-dependent learning and memory and produce important changes in synaptic transmission by enhancing glutamate uptake, decreasing synaptic efficacy, and inhibiting plasticity mechanisms such as N-methyl-D-aspartate-mediated long-term depression (LTD) within the hippocampus. Adolescent animals seem to be particularly susceptible to the detrimental effect of HFD as dietary treatments carried out between weaning and early adulthood are much more efficient in terms of hippocampal damage that those carried out during the adult period. As palmitic acid is the most abundant saturated fatty acid in HFD, its effect on hippocampal function needs to be studied. However, glycogen synthase kinase-3 (GSK-3), a pleiotropic enzyme highly expressed in the central nervous system, modulates both hippocampal long-term potentiation (LTP) and LTD, and has been implicated in neurological disorders including Alzheimer's disease. In this study, we have characterized in mice hippocampus the effect of (i) a 48 h HFD intervention and (ii) in-vitro palmitic acid, as well as the possible involvement of GSK-3 in the above-mentioned plasticity mechanisms. Our results show that both 48 h HFD and palmitic acid inhibit LTP in hippocampal slices, whereas no effect on LTD was observed. Moreover, tideglusib, an ATP-noncompetitive inhibitor of GSK-3, induced hippocampal LTP and partially reversed the impairment of LTP induced by palmitic acid.

Perspective Insights into Disease Progression, Diagnostics, and Therapeutic Approaches in Alzheimer's Disease: A Judicious Update

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the progressive accumulation of β-amyloid fibrils and abnormal tau proteins in and outside of neurons. Representing a common form of dementia, aggravation of AD with age increases the morbidity rate among the elderly. Although, mutations in the ApoE4 act as potent risk factors for sporadic AD, familial AD arises through malfunctioning of APP, PSEN-1, and−2 genes. AD progresses through accumulation of amyloid plaques (Aβ) and neurofibrillary tangles (NFTs) in brain, which interfere with neuronal communication. Cellular stress that arises through mitochondrial dysfunction, endoplasmic reticulum malfunction, and autophagy contributes significantly to the pathogenesis of AD. With high accuracy in disease diagnostics, Aβ deposition and phosphorylated tau (p-tau) are useful core biomarkers in the cerebrospinal fluid (CSF) of AD patients. Although five drugs are approved for treatment in AD, their failures in achieving complete disease cure has shifted studies toward a series of molecules capable of acting against Aβ and p-tau. Failure of biologics or compounds to cross the blood-brain barrier (BBB) in most cases advocates development of an efficient drug delivery system. Though liposomes and polymeric nanoparticles are widely adopted for drug delivery modules, their use in delivering drugs across the BBB has been overtaken by exosomes, owing to their promising results in reducing disease progression.

Thiamine and benfotiamine improve cognition and ameliorate GSK-3β-associated stress-induced behaviours in mice

Thiamine (vitamin B1) deficiency in the brain has been implicated in the development of dementia and symptoms of depression. Indirect evidence suggests that thiamine may contribute to these pathologies by controlling the activities of glycogen synthase kinase (GSK)-3β. While decreased GSK-3β activity appears to impair memory, increased GSK-3β activity is associated with the distressed/depressed state. However, hitherto direct evidence for the effects of thiamine on GSK-3β function has not been reported. Here, we administered thiamine or, the more bioavailable precursor, benfotiamine at 200mg/kg/day for 2weeks to C57BL/6J mice, to determine whether treatment might affect behaviours that are known to be sensitive to GSK-3β activity and whether such administration impacts on GSK-3β expression within the brain. The mice were tested in models of contextual conditioning and extinction, a 5-day rat exposure stress test, and a modified swim test with repeated testing. The tricyclic antidepressant imipramine (7.5mg/kg/day), was administered as a positive control for the effects of thiamine or benfotiamine. As for imipramine, both compounds inhibited the upregulation of GSK-3β induced by predator stress or repeated swimming, and reduced floating scores and the predator stress-induced behavioural changes in anxiety and exploration. Coincident, thiamine and benfotiamine improved learning and extinction of contextual fear, and the acquisition of the step-down avoidance task. Our data indicate that thiamine and benfotiamine have antidepressant/anti-stress effects in naïve animals that are associated with reduced GSK-3β expression and conditioning of adverse memories. Thus thiamine and benfotiamine may modulate GSK-3β functions in a manner that is dependent on whether the contextual conditioning is adaptive or maladaptive.

Intranasal siRNA administration reveals IGF2 deficiency contributes to impaired cognition in Fragile X syndrome mice

Molecular mechanisms underlying learning and memory remain imprecisely understood, and restorative interventions are lacking. We report that intranasal administration of siRNAs can be used to identify targets important in cognitive processes and to improve genetically impaired learning and memory. In mice modeling the intellectual deficiency of Fragile X syndrome, intranasally administered siRNA targeting glycogen synthase kinase-3β (GSK3β), histone deacetylase-1 (HDAC1), HDAC2, or HDAC3 diminished cognitive impairments. In WT mice, intranasally administered brain-derived neurotrophic factor (BDNF) siRNA or HDAC4 siRNA impaired learning and memory, which was partially due to reduced insulin-like growth factor-2 (IGF2) levels because the BDNF siRNA- or HDAC4 siRNA-induced cognitive impairments were ameliorated by intranasal IGF2 administration. In Fmr1^-/- mice, hippocampal IGF2 was deficient, and learning and memory impairments were ameliorated by IGF2 intranasal administration. Therefore intranasal siRNA administration is an effective means to identify mechanisms regulating cognition and to modulate therapeutic targets.

ROS Production and ERK Activity Are Involved in the Effects of d-β-Hydroxybutyrate and Metformin in a Glucose Deficient Condition

Hypoglycemia, a complication of insulin or sulfonylurea therapy in diabetic patients, leads to brain damage. Furthermore, glucose replenishment following hypoglycemic coma induces neuronal cell death. In this study, we investigated the molecular mechanism underlying glucose deficiency-induced cytotoxicity and the protective effect of d-β-hydroxybutyrate (D-BHB) using SH-SY5Y cells. The cytotoxic mechanism of metformin under glucose deficiency was also examined. Cell viability under 1 mM glucose (glucose deficiency) was significantly decreased which was accompanied by increased production of reactive oxygen species (ROS) and decreased phosphorylation of extracellular signal-regulated kinase (ERK) and glycogen synthase 3 (GSK3β). ROS inhibitor reversed the glucose deficiency-induced cytotoxicity and restored the reduced phosphorylation of ERK and GSK3β. While metformin did not alter cell viability in normal glucose media, it further increased cell death and ROS production under glucose deficiency. However, D-BHB reversed cytotoxicity, ROS production, and the decrease in phosphorylation of ERK and GSK3β induced by the glucose deficiency. ERK inhibitor reversed the D-BHB-induced increase in cell viability under glucose deficiency, whereas GSK3β inhibitor did not restore glucose deficiency-induced cytotoxicity. Finally, the protective effect of D-BHB against glucose deficiency was confirmed in primary neuronal cells. We demonstrate that glucose deficiency-induced cytotoxicity is mediated by ERK inhibition through ROS production, which is attenuated by D-BHB and intensified by metformin.

Kinase targets in CNS drug discovery

Originally thought to be nondruggable, kinases represent attractive drug targets for pharmaceutical companies and academia. To date, there are over 40 kinase inhibitors approved by the US FDA, with 32 of these being small molecules, in addition to the three mammalian target of rapamycin inhibitor macrolides (sirolimus, temsirolimus and everolimus). Despite the rapid development of kinase inhibitors for cancer, presently none of these agents are approved for CNS indications. This mini perspective highlights selected kinase targets for CNS disorders, of which brain-permeable small-molecule inhibitors are reported, with demonstrated preclinical proof-of-concept efficacy. This is followed by a brief discussion on the key challenges of blood–brain barrier penetration and selectivity profiles in developing kinase inhibitors for CNS disorders.

Synthesis, Docking Study and Kinase Inhibitory Activity of a Number of New Substituted Pyrazolo[3,4-c]pyridines

A series of new pyrazolo[3,4-c]pyridines bearing various 1, 3, 5 or 1, 3, 7 pattern substitutions, were designed and synthesized. Some of them showed interesting inhibitory activity mainly against glycogen synthase kinase 3 (GSK3)α/β as well as against cdc2-like kinases 1 (CLK1) and dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A), with good selectivity and remarkable structure-activity relationships (SARs), without being cytotoxic. Molecular simulations in correlation with biological data revealed the importance of the existence of N1-H as well as the absence of a bulky 7-substituent.

Glycogen Synthase Kinase-3β: Variation over Time and the Possible Association with Mood and Cognition in Healthy Individuals

Evidence indicates a role for glycogen synthase kinase-3β (GSK-3β) in the pathophysiology of mood disorders and in cognitive disturbances; however, the natural variation in GSK-3β activity over time is unknown. We aimed to investigate GSK-3β activity over time and its possible correlation with emotional lability, subjective mood fluctuations and cognitive function in healthy individuals. Thirty-seven healthy subjects were evaluated with neuropsychological tests and blood samples at baseline and 12-week follow-up. Total GSK-3β and serine-9-phosphorylated GSK-3β in peripheral blood mononuclear cells were quantitated using enzyme immunometric assays. The activity of GSK-3β (serine-9-phosphorylated GSK-3β/total GSK-3β) was lower at baseline compared with follow-up. No significant mean change over time was observed in levels of total GSK-3β and serine-9-phosphorylated GSK-3β. Exploratory analysis revealed lower activity of GSK-3β in spring and summer compared with the fall season. No correlation was observed between GSK-3β activity and emotional lability, subjective mood fluctuations or cognitive function. The results suggest that intra- and interindividual variation in GSK-3β activity over time could contribute to the heterogeneity of findings in clinical studies. The stability of GSK-3β activity and the role of potential moderators of GSK-3β activity warrant further investigation. Clinical studies of GSK-3β should consider including repeated measures of both cases and healthy individuals.

GSK3β Hyperactivity during an Early Critical Period Impairs Prefrontal Synaptic Plasticity and Induces Lasting Deficits in Spine Morphology and Working Memory

Schizophrenia (SZ) is a neurodevelopmental disorder in which the emergence of cognitive symptoms occurs during early adolescence. Glycogen synthase kinase-3β (GSK3β) plays a critical role in synaptic plasticity during development and is highly implicated in the etiology of SZ. However, how GSK3β activity affects synaptic plasticity and working memory function in the prefrontal cortex (PFC) during development remains unknown. Here we show a GSK3β hyperactivity during the early postnatal period in a neurodevelopmental rat SZ model that receives gestational exposure (E17) to the neurotoxin methylazoxymethanol (MAM). Accompanied with this change, adult MAM rats exhibited a significant decrease in spine density as well as impaired working memory, which was rescued by treatment with a GSK3β inhibitor during the juvenile period. Furthermore, the age-dependent hyperactive GSK3β caused a significant deficit in long-term potentiation (LTP) and facilitated long-term depression (LTD) in PFC pyramidal neurons. Notably, these changes in synaptic plasticity occurred only during the late juvenile period and were efficiently reversed by application of GSK3β inhibitors. Because the balance of LTP and LTD plays a critical role in activity-dependent synaptic stabilization and elimination during cortical development, the transient hyperactive GSK3β likely accounts for the cortical spine loss and PFC-dependent cognitive deficits in adulthood. These results highlight the importance of the postnatal trajectory of GSK3β for spine development and PFC function, and may shed light on the prophylactic treatment of cognitive symptoms in the SZ.

A unique type of GSK-3 inhibitor brings new opportunities to the clinic

A substrate peptide that the kinase GSK-3 converts into its own inhibitor improves symptoms and cognitive function in an Alzheimer’s disease model.

Cotinine administration improves impaired cognition in the mouse model of Fragile X syndrome

Cotinine is the major metabolite of nicotine and has displayed some capacity for improving cognition in mouse models following chronic administration. We tested if acute cotinine treatment is capable of improving cognition in the mouse model of Fragile X syndrome, Fmr1^-/- knockout mice, and if this is related to inhibition by cotinine treatment of glycogen synthase kinase-3β (GSK3β), which is abnormally active in Fmr1^-/- mice. Acute cotinine treatment increased the inhibitory serine-phosphorylation of GSK3β and the activating phosphorylation of AKT, which can mediate serine-phosphorylation of GSK3β, in both wild-type and Fmr1^-/- mouse hippocampus. Acute cotinine treatment improved cognitive functions of Fmr1^-/- mice in coordinate and categorical spatial processing, novel object recognition, and temporal ordering. However, cotinine failed to restore impaired cognition in GSK3β knockin mice, in which a serine9-to-alanine9 mutation blocks the inhibitory serine phosphorylation of GSK3β, causing GSK3β to be hyperactive. These results indicate that acute cotinine treatment effectively repairs impairments of these four cognitive tasks in Fmr1^-/- mice, and suggest that this cognition-enhancing effect of cotinine is linked to its induction of inhibitory serine-phosphorylation of GSK3. Taken together, these results show that nicotinic receptor agonists can act as cognitive enhancers in a mouse model of Fragile X syndrome and highlight the potential role of inhibiting GSK3β in mediating the beneficial effects of cotinine on memory.

Lithium posttreatment confers neuroprotection through glycogen synthase kinase-3β inhibition in intracerebral hemorrhage rats

OBJECTIVE Inflammation and apoptosis are two key factors contributing to secondary brain injury after intracerebral hemorrhage (ICH). The objective of this study was to evaluate the effects of lithium posttreatment on behavior, brain atrophy, inflammation, and perihematomal cell death. Furthermore, the authors aimed to determine the role of the pro-apoptotic glycogen synthase kinase-3β (GSK-3β) after experimental ICH. METHODS Male Sprague-Dawley rats (n = 108) were subjected to intracerebral infusion of semicoagulated autologous blood. Window of opportunity and dose optimization studies of lithium on ICH-induced injury were performed by measuring neurological deficits. Animals with ICH received vehicle administration or lithium posttreatment (60 mg/kg) for up to 21 days. Hemispheric atrophy was evaluated. Perihematomal cell death was quantified through terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL). The number of myeloperoxidase (MPO)-positive neutrophils and OX42-positive microglia in the perihematomal areas were calculated. Western blotting was used for the quantification of GSK-3β, heat shock protein 70 (HSP70), nuclear factor-κB p65 (NF-κB p65), and cy-clooxygenase-2 (COX-2). RESULTS Lithium, at a dose of 60 mg/kg initiated from 2 hours after injury, exhibited the best effects of improving neurological outcomes 3, 5, 7, 14, 21, and 28 days after ICH, reduced the hemispheric atrophy at 42 days after surgery, and reduced the number of TUNEL-positive cells, MPO-positive neutrophils, and OX42-positive microglia in the perihematomal areas. Furthermore, lithium posttreatment modulated GSK-3β, increased HSP70, and decreased NF-κB p65 and COX-2 expression in the ipsilateral hemisphere. CONCLUSIONS Lithium posttreatment at a dose of 60 mg/kg, initiated beginning 2 hours after injury, improves functional and morphological outcomes, and inhibits inflammation and perihematomal cell death in a rat model of semicoagulated autologous blood ICH through inactivation of GSK-3β.

Small GSK-3 Inhibitor Shows Efficacy in a Motor Neuron Disease Murine Model Modulating Autophagy

Amyotrophic lateral sclerosis (ALS) is a progressive motor neuron degenerative disease that has no effective treatment up to date. Drug discovery tasks have been hampered due to the lack of knowledge in its molecular etiology together with the limited animal models for research. Recently, a motor neuron disease animal model has been developed using β-N-methylamino-L-alanine (L-BMAA), a neurotoxic amino acid related to the appearing of ALS. In the present work, the neuroprotective role of VP2.51, a small heterocyclic GSK-3 inhibitor, is analysed in this novel murine model together with the analysis of autophagy. VP2.51 daily administration for two weeks, starting the first day after L-BMAA treatment, leads to total recovery of neurological symptoms and prevents the activation of autophagic processes in rats. These results show that the L-BMAA murine model can be used to test the efficacy of new drugs. In addition, the results confirm the therapeutic potential of GSK-3 inhibitors, and specially VP2.51, for the disease-modifying future treatment of motor neuron disorders like ALS.

Retroviral induction of GSK-3β expression blocks the stimulatory action of physical exercise on the maturation of newborn neurons

Adult hippocampal neurogenesis (AHN) is a key process for certain types of hippocampal-dependent learning. Alzheimer's disease (AD) is accompanied by memory deficits related to alterations in AHN. Given that the increased activity of GSK-3β has been related to alterations in the population of hippocampal granule neurons in AD patients, we designed a novel methodology by which to induce selective GSK-3β overexpression exclusively in newborn granule neurons. To this end, we injected an rtTA-IRES-EGFP-expressing retrovirus into the hippocampus of tTO-GSK-3β mice. Using this novel retroviral strategy, we found that GSK-3β caused a cell-autonomous impairment of the morphological and synaptic maturation of newborn neurons. In addition, we examined whether GSK-3β overexpression in newborn neurons limits the effects of physical activity. While physical exercise increased the number of dendritic spines, the percentage of mushroom spines, and the head diameter of the same in tet-OFF cells, these effects were not triggered in tet-ON cells. This observation suggests that GSK-3β blocks the stimulatory actions of exercise. Given that the activity of GSK-3β is increased in the brains of individuals with AD, these data may be relevant for non-pharmacological therapies for AD.

The central role of heat shock factor 1 in synaptic fidelity and memory consolidation

Networks of neuronal synapses are the fundamental basis for making and retaining memory. Reduced synapse number and quality correlates with loss of memory in dementia. Heat shock factor 1 (HSF1), the major transcription factor regulating expression of heat shock genes, plays a central role in proteostasis, in establishing and sustaining synaptic fidelity and function, and in memory consolidation. Support for this thesis is based on these observations: (1) heat shock induces improvements in synapse integrity and memory consolidation; (2) synaptic depolarization activates HSF1; (3) activation of HSF1 alone (independent of the canonical heat shock response) augments formation of essential synaptic elements-neuroligands, vesicle transport, synaptic scaffolding proteins, lipid rafts, synaptic spines, and axodendritic synapses; (4) HSF1 coalesces and activates memory receptors in the post-synaptic dendritic spine; (5) huntingtin or α-synuclein accumulation lowers HSF1 while HSF1 lowers huntingtin and α-synuclein aggregation-a potential vicious cycle; and (6) HSF1 agonists (including physical activity) can improve cognitive function in dementia models. Thus, via direct gene expression of synaptic elements, production of HSPs that assure high protein fidelity, and activation of other neuroprotective signaling pathways, HSF1 agonists could provide breakthrough therapy for dementia-associated disease.