Lithium treatment of APPSwDI/NOS2-/- mice leads to reduced hyperphosphorylated tau, increased amyloid deposition and altered inflammatory phenotype

Lithium, Inflammation and Neuroinflammation with Emphasis on Bipolar Disorder-A Narrative Review

This narrative review examines lithium's effects on immune function, inflammation and cell survival, particularly in bipolar disorder (BD) in in vitro studies, animal models and clinical studies. In vitro studies show that high lithium concentrations (5 mM, beyond the therapeutic window) reduce interleukin (IL)-1β production in monocytes and enhance T-lymphocyte resistance, suggesting a protective role against cell death. Lithium modulates oxidative stress in lipopolysaccharide (LPS)-activated macrophages by inhibiting nuclear factor (NF)-ƙB activity and reducing nitric oxide production. At therapeutically relevant levels, lithium increased both pro-inflammatory [interferon (INF)-γ, IL-8 and tumor necrosis factor (TNF)-α)] and anti-inflammatory (IL-10) cytokines on whole blood supernatant culture in healthy volunteers, influencing the balance of pro- and anti-inflammatory responses. Animal models reveal lithium's potential to alleviate inflammatory diseases by reducing pro-inflammatory cytokines and enhancing anti-inflammatory responses. It also induces selective macrophage death in atherosclerotic plaques without harming other cells. In primary rat cerebellum cultures (ex vivo), lithium prevents neuronal loss and inhibits astroglial growth, impacting astrocytes and microglia. Clinical studies show that lithium alters cytokine profiles and reduces neuroinflammatory markers in BD patients. Chronic treatment decreases IL-2, IL-6, IL-10 and IFN-γ secretion from peripheral blood leukocytes. Lithium response correlates with TNF-α levels, with poor responders showing higher TNF-α. Overall, these findings elucidate lithium's diverse mechanisms in modulating immune responses, reducing inflammation and promoting cell survival, with significant implications for managing BD and other inflammation-related conditions. Yet, to better understand the drug's impact in BD and other inflammatory/neuroinflammatory conditions, further research is warranted to appreciate lithium's therapeutic potential and its role in immune regulation.

Molecular mechanisms and therapeutic potential of lithium in Alzheimer's disease: repurposing an old class of drugs

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by cognitive decline and memory loss. Despite advances in understanding the pathophysiological mechanisms of AD, effective treatments remain scarce. Lithium salts, recognized as mood stabilizers in bipolar disorder, have been extensively studied for their neuroprotective effects. Several studies indicate that lithium may be a disease-modifying agent in the treatment of AD. Lithium's neuroprotective properties in AD by acting on multiple neuropathological targets, such as reducing amyloid deposition and tau phosphorylation, enhancing autophagy, neurogenesis, and synaptic plasticity, regulating cholinergic and glucose metabolism, inhibiting neuroinflammation, oxidative stress, and apoptosis, while preserving mitochondrial function. Clinical trials have demonstrated that lithium therapy can improve cognitive function in patients with AD. In particular, meta-analyses have shown that lithium may be a more effective and safer treatment than the recently FDA-approved aducanumab for improving cognitive function in patients with AD. The affordability and therapeutic efficacy of lithium have prompted a reassessment of its use. However, the use of lithium may lead to potential side effects and safety issues, which may limit its clinical application. Currently, several new lithium formulations are undergoing clinical trials to improve safety and efficacy. This review focuses on lithium's mechanism of action in treating AD, highlighting the latest advances in preclinical studies and clinical trials. It also explores the side effects of lithium therapy and coping strategies, offering a potential therapeutic strategy for patients with AD.

New Advances in the Pharmacology and Toxicology of Lithium: A Neurobiologically Oriented Overview

Over the last six decades, lithium has been considered the gold standard treatment for the long-term management of bipolar disorder due to its efficacy in preventing both manic and depressive episodes as well as suicidal behaviors. Nevertheless, despite numerous observed effects on various cellular pathways and biologic systems, the precise mechanism through which lithium stabilizes mood remains elusive. Furthermore, there is recent support for the therapeutic potential of lithium in other brain diseases. This review offers a comprehensive examination of contemporary understanding and predominant theories concerning the diverse mechanisms underlying lithium's effects. These findings are based on investigations utilizing cellular and animal models of neurodegenerative and psychiatric disorders. Recent studies have provided additional support for the significance of glycogen synthase kinase-3 (GSK3) inhibition as a crucial mechanism. Furthermore, research has shed more light on the interconnections between GSK3-mediated neuroprotective, antioxidant, and neuroplasticity processes. Moreover, recent advancements in animal and human models have provided valuable insights into how lithium-induced modifications at the homeostatic synaptic plasticity level may play a pivotal role in its clinical effectiveness. We focused on findings from translational studies suggesting that lithium may interface with microRNA expression. Finally, we are exploring the repurposing potential of lithium beyond bipolar disorder. These recent findings on the therapeutic mechanisms of lithium have provided important clues toward developing predictive models of response to lithium treatment and identifying new biologic targets. SIGNIFICANCE STATEMENT: Lithium is the drug of choice for the treatment of bipolar disorder, but its mechanism of action in stabilizing mood remains elusive. This review presents the latest evidence on lithium's various mechanisms of action. Recent evidence has strengthened glycogen synthase kinase-3 (GSK3) inhibition, changes at the level of homeostatic synaptic plasticity, and regulation of microRNA expression as key mechanisms, providing an intriguing perspective that may help bridge the mechanistic gap between molecular functions and its clinical efficacy as a mood stabilizer.

Lithium and disease modification: A systematic review and meta-analysis in Alzheimer's and Parkinson's disease

The role of lithium as a possible therapeutic strategy for neurodegenerative diseases has generated scientific interest. We systematically reviewed and meta-analyzed pre-clinical and clinical studies that evidenced the neuroprotective effects of lithium in Alzheimer's (AD) and Parkinson's disease (PD). We followed the PRISMA guidelines and performed the systematic literature search using PubMed, EMBASE, Web of Science, and Cochrane Library. A total of 32 articles were identified. Twenty-nine studies were performed in animal models and 3 studies were performed on human samples of AD. A total of 17 preclinical studies were included in the meta-analysis. Our analysis showed that lithium treatment has neuroprotective effects in diseases. Lithium treatment reduced amyloid-β and tau levels and significantly improved cognitive behavior in animal models of AD. Lithium increased the tyrosine hydroxylase levels and improved motor behavior in the PD model. Despite fewer clinical studies on these aspects, we evidenced the positive effects of lithium in AD patients. This study lends further support to the idea of lithium's therapeutic potential in neurodegenerative diseases.

Tau, tau kinases, and tauopathies: An updated overview

Tau is a macrotubule-associated protein primarily involved in the stabilization of the cytoskeleton. Under normal conditions, phosphorylation reduces the affinity of tau for tubulin, allowing the protein to detach from microtubules and ensuring the system dynamics in neuronal cells. However, hyperphosphorylated tau aggregates into paired helical filaments, the main constituents of neurofibrillary tangles found in the brains of patients with Alzheimer's disease and other tauopathies. In this review, we provide an overview of the structure of tau and the pathophysiological roles of tau phosphorylation. We also evaluate the major protein kinases involved and discuss the progress made in the development of drug therapies aimed at inhibiting tau kinases.

Lithium beyond psychiatric indications: the reincarnation of a new old drug

Lithium has been used in the treatment of bipolar disorders for decades, but the exact mechanisms of action remain elusive to this day. Recent evidence suggests that lithium is critically involved in a variety of signaling pathways affecting apoptosis, inflammation, and neurogenesis, all of which contributing to the complex pathophysiology of various neurological diseases. As a matter of fact, preclinical work reports both acute and long-term neuroprotection in distinct neurological disease models such as Parkinson’s disease, traumatic brain injury, Alzheimer’s disease, and ischemic stroke. Lithium treatment reduces cell injury, decreases α-synuclein aggregation and Tau protein phosphorylation, modulates inflammation and even stimulates neuroregeneration under experimental conditions of Parkinson’s disease, traumatic brain injury, and Alzheimer’s disease. The therapeutic impact of lithium under conditions of ischemic stroke was also studied in numerous preclinical in vitro and in vivo studies, giving rise to a randomized double-blind clinical stroke trial. The preclinic data revealed a lithium-induced upregulation of anti-apoptotic proteins such as B-cell lymphoma 2, heat shock protein 70, and activated protein 1, resulting in decreased neuronal cell loss. Lithium, however, does not only yield postischemic neuroprotection but also enhances endogenous neuroregeneration by stimulating neural stem cell proliferation and by regulating distinct signaling pathways such as the RE1-silencing transcription factor. In line with this, lithium treatment has been shown to modulate postischemic cytokine secretion patterns, diminishing microglial activation and stabilizing blood-brain barrier integrity yielding reduced levels of neuroinflammation. The aforementioned observations culminated in a first clinical trial, which revealed an improved motor recovery in patients with cortical stroke after lithium treatment. Beside its well-known psychiatric indications, lithium is thus a promising neuroprotective candidate for the aforementioned neurological diseases. A detailed understanding of the lithium-induced mechanisms, however, is important for prospective clinical trials which may pave the way for a successful bench-to-bedside translation in the future. In this review, we will give an overview of lithium-induced neuroprotective mechanisms under various pathological conditions, with special emphasis on ischemic stroke.

Is There Justification to Treat Neurodegenerative Disorders by Repurposing Drugs? The Case of Alzheimer's Disease, Lithium, and Autophagy

Lithium is the prototype mood-stabilizer used for acute and long-term treatment of bipolar disorder. Cumulated translational research of lithium indicated the drug's neuroprotective characteristics and, thereby, has raised the option of repurposing it as a drug for neurodegenerative diseases. Lithium's neuroprotective properties rely on its modulation of homeostatic mechanisms such as inflammation, mitochondrial function, oxidative stress, autophagy, and apoptosis. This myriad of intracellular responses are, possibly, consequences of the drug's inhibition of the enzymes inositol-monophosphatase (IMPase) and glycogen-synthase-kinase (GSK)-3. Here we review lithium's neurobiological properties as evidenced by its neurotrophic and neuroprotective properties, as well as translational studies in cells in culture, in animal models of Alzheimer's disease (AD) and in patients, discussing the rationale for the drug's use in the treatment of AD.

Therapeutic Trem2 activation ameliorates amyloid-beta deposition and improves cognition in the 5XFAD model of amyloid deposition

BACKGROUND

Triggering receptor expressed on myeloid cell-2 (TREM2) is a lipid and lipoprotein binding receptor expressed by cells of myeloid origin. Homozygous TREM2 mutations cause early onset progressive presenile dementia while heterozygous, point mutations triple the risk of Alzheimer's disease (AD). Although human genetic findings support the notion that loss of TREM2 function exacerbates neurodegeneration, it is not clear whether activation of TREM2 in a disease state would result in therapeutic benefits. To determine the viability of TREM2 activation as a therapeutic strategy, we sought to characterize an agonistic Trem2 antibody (AL002a) and test its efficacy and mechanism of action in an aggressive mouse model of amyloid deposition.

METHODS

To determine whether agonism of Trem2 results in therapeutic benefits, we designed both intracranial and systemic administration studies. 5XFAD mice in the intracranial administration study were assigned to one of two injection groups: AL002a, a Trem2-agonizing antibody, or MOPC, an isotype-matched control antibody. Mice were then subject to a single bilateral intracranial injection into the frontal cortex and hippocampus and euthanized 72 h later. The tissue from the left hemisphere was histologically examined for amyloid-beta and microglia activation, whereas the tissue from the right hemisphere was used for biochemical analyses. Similarly, mice in the systemic administration study were randomized to one of the aforementioned injection groups and the assigned antibody was administered intraperitoneally once a week for 14 weeks. Mice underwent behavioral assessment between the 12- and 14-week timepoints and were euthanized 24 h after their final injection. The tissue from the left hemisphere was used for histological analyses whereas the tissue from the right hemisphere was used for biochemical analyses.

RESULTS

Here, we show that chronic activation of Trem2, in the 5XFAD mouse model of amyloid deposition, leads to reversal of the amyloid-associated gene expression signature, recruitment of microglia to plaques, decreased amyloid deposition, and improvement in spatial learning and novel object recognition memory.

CONCLUSIONS

These findings indicate that Trem2 activators may be effective for the treatment of AD and possibly other neurodegenerative disorders.

Time course of neuropathological events in hyperhomocysteinemic amyloid depositing mice reveals early neuroinflammatory changes that precede amyloid changes and cerebrovascular events

BACKGROUND

Vascular contributions to cognitive impairment and dementia (VCID) are the second leading cause of dementia behind only Alzheimer's disease (AD); however, VCID is commonly found as a co-morbidity with sporadic AD. We have previously established a mouse model of VCID by inducing hyperhomocysteinemia in both wild-type and amyloid depositing mice. While we have shown the time course of neuropathological events in the wild-type mice with hyperhomocysteinemia, the effect of amyloid deposition on this time course remains unknown; therefore, in this study, we determined the time course of neuropathological changes in our mouse model of hyperhomocysteinemia-induced VCID in amyloid depositing mice.

METHODS

APP/PS1 mice were placed on either a diet deficient in folate and vitamins B6 and B12 and enriched in methionine to induce hyperhomocysteinemia or a control diet for 2, 6, 10, 14, or 18 weeks. Immunohistochemistry and gene expression analysis were used to determine neuroinflammatory changes. Microhemorrhages and amyloid deposition were analyzed using histology and, finally, behavior was assessed using the 2-day radial arm water maze.

RESULTS

Neuroinflammation, specifically a pro-inflammatory phenotype, was the first pathological change to occur. Specifically, we see a significant increase in gene expression of tumor necrosis factor alpha, interleukin 1 beta, interleukin 6, and interleukin 12a by 6 weeks. This was followed by cognitive deficits starting at 10 weeks. Finally, there is a significant increase in the number of microhemorrhages at 14 weeks on diet as well as redistribution of amyloid from the parenchyma to the vasculature.

CONCLUSIONS

The time course of these pathologies points to neuroinflammation as the initial, key player in homocysteine-induced VCID co-morbid with amyloid deposition and provides a possible therapeutic target and time points.

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.

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.

Hyperhomocysteinemia-Induced Gene Expression Changes in the Cell Types of the Brain

High plasma levels of homocysteine, termed hyperhomocysteinemia, are a risk factor for vascular cognitive impairment and dementia, which is the second leading cause of dementia. While hyperhomocysteinemia induces microhemorrhages and cognitive decline in mice, the specific effect of hyperhomocysteinemia on each cell type remains unknown. We took separate cultures of astrocytes, microglia, endothelial cells, and neuronal cells and treated each with moderate levels of homocysteine for 24, 48, 72, and 96 hr. We then determined the gene expression changes for cell-specific markers and neuroinflammatory markers including the matrix metalloproteinase 9 system. Astrocytes had decreased levels of several astrocytic end feet genes, such as aquaporin 4 and an adenosine triphosphate (ATP)-sensitive inward rectifier potassium channel at 72 hr, as well as an increase in matrix metalloproteinase 9 at 48 hr. Gene changes in microglia indicated a peak in proinflammatory markers at 48 hr followed by a peak in the anti-inflammatory marker, interleukin 1 receptor antagonist, at 72 hr. Endothelial cells had reduced occludin expression at 72 hr, while kinases and phosphatases known to alter tau phosphorylation states were increased in neuronal cells. This suggests that hyperhomocysteinemia induces early proinflammatory changes in microglia and astrocytic changes relevant to their interaction with the vasculature. Overall, the data show how hyperhomocysteinemia could impact Alzheimer’s disease and vascular cognitive impairment and dementia.

Reduced Efficacy of Anti-Aβ Immunotherapy in a Mouse Model of Amyloid Deposition and Vascular Cognitive Impairment Comorbidity

Vascular cognitive impairment and dementia (VCID) is the second most common form of dementia behind Alzheimer's disease (AD). It is estimated that 40% of AD patients also have some form of VCID. One promising therapeutic for AD is anti-Aβ immunotherapy, which uses antibodies against Aβ to clear it from the brain. While successful in clearing Aβ and improving cognition in mice, anti-Aβ immunotherapy failed to reach primary cognitive outcomes in several different clinical trials. We hypothesized that one potential reason the anti-Aβ immunotherapy clinical trials were unsuccessful was due to this high percentage of VCID comorbidity in the AD population. We used our unique model of VCID-amyloid comorbidity to test this hypothesis. We placed 9-month-old wild-type and APP/PS1 mice on either a control diet or a diet that induces hyperhomocysteinemia (HHcy). After being placed on the diet for 3 months, the mice then received intraperotineal injections of either IgG2a control or 3D6 for another 3 months. While we found that treatment of our comorbidity model with 3D6 resulted in decreased total Aβ levels, there was no cognitive benefit of the anti-Aβ immunotherapy in our AD/VCID mice. Further, microhemorrhages were increased by 3D6 in the APP/PS1/control but further increased in an additive fashion when 3D6 was administered to the APP/PS1/HHcy mice. This suggests that the use of anti-Aβ immunotherapy in patients with both AD and VCID would be ineffective on cognitive outcomes.

SIGNIFICANCE STATEMENT

Despite significant mouse model data demonstrating both pathological and cognitive efficacy of anti-Aβ immunotherapy for the treatment of Alzheimer's disease, clinical trial outcomes have been underwhelming, failing to meet any primary endpoints. We show here that vascular cognitive impairment and dementia (VCID) comorbidity eliminates cognitive efficacy of anti-Aβ immunotherapy, despite amyloid clearance. Further, cerebrovascular adverse events of the anti-Aβ immunotherapy are significantly exacerbated by the VCID comorbidity. These data suggest that VCID comorbidity with Alzheimer's disease may mute the response to anti-Aβ immunotherapy.

LISPRO mitigates β-amyloid and associated pathologies in Alzheimer's mice

Lithium has been marketed in the United States of America since the 1970s as a treatment for bipolar disorder. More recently, studies have shown that lithium can improve cognitive decline associated with Alzheimer’s disease (AD). However, the current United States Food and Drug Administration-approved lithium pharmaceutics (carbonate and citrate chemical forms) have a narrow therapeutic window and unstable pharmacokinetics that, without careful monitoring, can cause serious adverse effects. Here, we investigated the safety profile, pharmacokinetics, and therapeutic efficacy of LISPRO (ionic co-crystal of lithium salicylate and l-proline), lithium salicylate, and lithium carbonate (Li₂CO₃). We found that LISPRO (8-week oral treatment) reduces β-amyloid plaques and phosphorylation of tau by reducing neuroinflammation and inactivating glycogen synthase kinase 3β in transgenic Tg2576 mice. Specifically, cytokine profiles from the brain, plasma, and splenocytes suggested that 8-week oral treatment with LISPRO downregulates pro-inflammatory cytokines, upregulates anti-inflammatory cytokines, and suppresses renal cyclooxygenase 2 expression in transgenic Tg2576 mice. Pharmacokinetic studies indicated that LISPRO provides significantly higher brain lithium levels and more steady plasma lithium levels in both B6129SF2/J (2-week oral treatment) and transgenic Tg2576 (8-week oral treatment) mice compared with Li₂CO₃. Oral administration of LISPRO for 28 weeks significantly reduced β-amyloid plaques and tau-phosphorylation. In addition, LISPRO significantly elevated pre-synaptic (synaptophysin) and post-synaptic protein (post synaptic density protein 95) expression in brains from transgenic 3XTg-AD mice. Taken together, our data suggest that LISPRO may be a superior form of lithium with improved safety and efficacy as a potential new disease modifying drug for AD.

Haloperidol inactivates AMPK and reduces tau phosphorylation in a tau mouse model of Alzheimer's disease

INTRODUCTION

The use of antipsychotic medications in Alzheimer's disease has been associated with an increased risk of mortality in clinical trials. However, an older postmortem literature suggests that those with schizophrenia treated in an era of exclusively conventional antipsychotic medications had a surprisingly low incidence of tau pathology. No previously published studies have investigated the impact of conventional antipsychotic exposure on tau outcomes in a tau mouse model of AD.

METHODS

In two experiments, transgenic rTg (tauP301L) 4510 tau mice were treated with either haloperidol or vehicle and phosphotau epitopes were quantified using high-sensitivity tau ELISA.

RESULTS

After treatments of 2 and 6 week's duration, mice treated with haloperidol evidenced a significant reduction in tau phosphorylation associated with an inactivation of the tau kinase AMPK.

DISCUSSION

The data suggest that D2 receptor blockade reduces tau phosphorylation in vivo. Future studies are necessary to investigate the impact of this reduction on tau neuropathology.

Oral Triphenylmethane Food Dye Analog, Brilliant Blue G, Prevents Neuronal Loss in APPSwDI/NOS2-/- Mouse Model

Reducing amyloid-β (Aβ) accumulation is a promising strategy for developing Alzheimer's Disease (AD) therapeutics. We recently reported that a triphenylmethane food dye analog, Brilliant Blue G (BBG), is a dose-dependent modulator of in vitro amyloid-β aggregation and cytotoxicity in cell-based assays. Following up on this recent work, we sought to further evaluate this novel modulator in a therapeutically-relevant AD transgenic mouse model. BBG was orally administered to APPSwDI/NOS2-/- mice for three months in order to assess its biocompatibility, its permeability across the blood-brain barrier, and its efficacy at rescuing AD pathology. The results showed that BBG was well-tolerated, caused no significant weight change/unusual behavior, and was able to significantly cross the AD blood-brain barrier in APPSwDI/NOS2-/- mice. Immunohistochemical and electron microscopic analysis of the brain sections revealed that BBG was able to significantly prevent neuronal loss and reduce intracellular APP/Aβ in hippocampal neurons. This is the first report of 1) the effect of Brilliant Blue G on neuronal loss in a transgenic animal model of AD, 2) oral administration of BBG to affect a protein conformation/aggregation disease, and 3) electron microscopic ultrastructural analysis of AD pathology in APPSwDI/NOS2-/- mice.

The cytoskeleton as a novel therapeutic target for old neurodegenerative disorders

Cytoskeleton defects, including alterations in microtubule stability, in axonal transport as well as in actin dynamics, have been characterized in several unrelated neurodegenerative conditions. These observations suggest that defects of cytoskeleton organization may be a common feature contributing to neurodegeneration. In line with this hypothesis, drugs targeting the cytoskeleton are currently being tested in animal models and in human clinical trials, showing promising effects. Drugs that modulate microtubule stability, inhibitors of posttranslational modifications of cytoskeletal components, specifically compounds affecting the levels of tubulin acetylation, and compounds targeting signaling molecules which regulate cytoskeleton dynamics, constitute the mostly addressed therapeutic interventions aiming at preventing cytoskeleton damage in neurodegenerative disorders. In this review, we will discuss in a critical perspective the current knowledge on cytoskeleton damage pathways as well as therapeutic strategies designed to revert cytoskeleton-related defects mainly focusing on the following neurodegenerative disorders: Alzheimer's Disease, Parkinson's Disease, Huntington's Disease, Amyotrophic Lateral Sclerosis and Charcot-Marie-Tooth Disease.

Glycogen synthase kinase-3 beta (GSK-3β) signaling: Implications for Parkinson's disease

Glycogen synthase kinase 3 (GSK-3) dysregulation plays an important role in the pathogenesis of numerous disorders, affecting the central nervous system (CNS) encompassing both neuroinflammation and neurodegenerative diseases. Several lines of evidence have illustrated a key role of the GSK-3 and its cellular and molecular signaling cascades in the control of neuroinflammation. Glycogen synthase kinase 3 beta (GSK-3β), one of the GSK-3 isomers, plays a major role in neuronal apoptosis and its inhibition decreases expression of alpha-Synuclein (α-Synuclein), which make this kinase an attractive therapeutic target for neurodegenerative disorders. Parkinson's disease (PD) is a chronic neurodegenerative movement disorder characterized by the progressive and massive loss of dopaminergic neurons by neuronal apoptosis in the substantia nigra pars compacta and depletion of dopamine in the striatum, which lead to pathological and clinical abnormalities. Thus, understanding the role of GSK-3β in PD will enhance our knowledge of the basic mechanisms underlying the pathogenesis of this disorder and facilitate the identification of new therapeutic avenues. In recent years, GSK-3β has been shown to play essential roles in modulating a variety of cellular functions, which have prompted efforts to develop GSK-3β inhibitors as therapeutics. In this review, we summarize GSK-3 signaling pathways and its association with neuroinflammation. Moreover, we highlight the interaction between GSK-3β and several cellular processes involved in the pathogenesis of PD, including the accumulation of α-Synuclein aggregates, oxidative stress and mitochondrial dysfunction. Finally, we discuss about GSK-3β inhibitors as a potential therapeutic strategy in PD.

Determining the role of IL-4 induced neuroinflammation in microglial activity and amyloid-β using BV2 microglial cells and APP/PS1 transgenic mice

Background

Microglia are considered the resident immune cells of the central nervous system (CNS). In response to harmful stimuli, an inflammatory reaction ensues in which microglia are activated in a sequenced spectrum of pro- and antiinflammatory phenotypes that are akin to the well-characterized polarization states of peripheral macrophages. A “classically” activated M1 phenotype is known to eradicate toxicity. The transition to an “alternatively” activated M2 phenotype encompasses neuroprotection and repair. In recent years, inflammation has been considered an accompanying pathology in response to the accumulation of extracellular amyloid-β (Aβ) in Alzheimer’s disease (AD). This study aimed to drive an M2a-biased immune phenotype with IL-4 in vitro and in vivo and to determine the subsequent effects on microglial activation and Aβ pathology.

Methods

In vitro, exogenous IL-4 was applied to BV2 microglial cell cultures to evaluate the temporal progression of microglial responses. In vivo, intracranial injections of an adeno-associate-virus (AAV) viral vector were performed to assess long-term expression of IL-4 in the frontal cortex and hippocampus of Aβ-depositing, APP/PS1 transgenic mice. Quantitative real-time PCR was used to assess the fold change in expression of biomarkers representing each of the microglial phenotypes in both the animal tissue and the BV2 cells. ELISAs quantified IL-4 expression and Aβ levels. Histological staining permitted quantification of microglial and astrocytic activity.

Results

Both in vitro and in vivo models showed an enhanced M2a phenotype, and the in vivo model revealed a trend toward a decreased trend in Aβ deposition.

Conclusions

In summary, this study offers insight into the therapeutic potential of microglial immune response in AD.

Illite improves memory impairment and reduces Aβ level in the Tg-APPswe/PS1dE9 mouse model of Alzheimer׳s disease through Akt/CREB and GSK-3β phosphorylation in the brain

ETHNOPHARMACOLOGICAL RELEVANCE

The use of illite in Korean medicine has a long history as a therapeutic agent for various cerebrovascular diseases. According to Dongui Bogam, illite can be used for Qi-tonifying, phlegm dispersing and activation of blood circulation which is an important principle for the treatment of brain-associated diseases.

AIM OF THE STUDY

This study was undertaken to evaluate beneficial effects of illite on the neurodegenerative diseases such as Alzheimer׳s disease (AD).

MATERIAL AND METHODS

The transgenic mice of AD, Tg-APPswe/PS1dE9, were fed with 1% or 3% of illite for 3 months. Behavioral, immunological and ELISA analyses were used to assess memory impairment with additional measurement of Aβ accumulation and plaque deposition in the brain. Other in vitro studies were performed to examine whether illite inhibits the Aβ-induced neurotoxicity in human neuroblastoma cell line, SH-SY5Y cells.

RESULTS

Illite treatment rescued Aβ-induced neurotoxicity on SH-SY5Y cells, which was dependent on the PI3K/Akt activation. Intake of illite improved the Aβ-induced memory impairment and suppressed Aβ levels and plaque deposition in the brain of Tg-APPswe/PS1dE9 mice. Illite increased CREB, Akt, and GSK-3β phosphorylation and suppressed tau phosphorylation in the AD-like brains. Moreover, 1% of illite reduced weight gain and suppressed glucose level in the blood.

CONCLUSION

The present study suggests that illite has the potential to be a useful adjunct as a therapeutic drug for the treatment of AD.

Glycogen synthase kinase-3 as a therapeutic target for cognitive dysfunction in neuropsychiatric disorders

The serine/threonine kinase glycogen synthase kinase-3 (GSK-3) is involved in a broad range of cellular processes including cell proliferation, apoptosis and inflammation. It is now also increasingly acknowledged as having a role to play in cognitive-related processes such as neurogenesis, synaptic plasticity and neural cell survival. Cognitive impairment represents a major debilitating feature of many neurodegenerative and psychiatric disorders, including Alzheimer's disease, mood disorders, schizophrenia and fragile X syndrome, as well as being a result of traumatic brain injury or cranial irradiation. Accordingly, GSK-3 has been identified as an important therapeutic target for cognitive impairment, and recent preclinical studies have yielded important evidence demonstrating that GSK-3 inhibitors may be useful therapeutic interventions for restoring cognitive function in some of these brain disorders. The current review summarises the role of GSK-3 as a regulator of cognitive-dependent functions, examines current preclinical and clinical evidence of the potential of GSK-3 inhibitors as therapeutic agents for cognitive impairments in neuropsychiatric disorders, and offers some insight into the current obstacles that are impeding the clinical use of selective GSK-3 inhibitors in the treatment of cognitive impairment.

Neuroinflammation in Alzheimer's disease; A source of heterogeneity and target for personalized therapy

Neuroinflammation has long been known as an accompanying pathology of Alzheimer's disease. Microglia surrounding amyloid plaques in the brain of Auguste D were described in the original publication of Alois Alzheimer. It is only quite recently, however, that we have a more complete appreciation for the diverse roles of neuroinflammation in neurodegenerative disorders such as Alzheimer's. While gaps in our knowledge remain, and conflicting data are abound in the field, our understanding of the complexities and heterogeneous functions of the inflammatory response in Alzheimer's is vastly improved. This review article will discuss some of the roles of neuroinflammation in Alzheimer's disease, in particular, how understanding heterogeneity in the individual inflammatory response can be used in therapeutic development and as a mechanism of personalizing our treatment of the disease.

Transition from an M1 to a mixed neuroinflammatory phenotype increases amyloid deposition in APP/PS1 transgenic mice

Background

The polarization to different neuroinflammatory phenotypes has been described in early Alzheimer’s disease, yet the impact of these phenotypes on amyloid-beta (Aβ) pathology remains unknown. Short-term studies show that induction of an M1 neuroinflammatory phenotype reduces Aβ, but long-term studies have not been performed that track the neuroinflammatory phenotype.

Methods

Wild-type and APP/PS1 transgenic mice aged 3 to 4 months received a bilateral intracranial injection of adeno-associated viral (AAV) vectors expressing IFNγ or green fluorescent protein in the frontal cortex and hippocampus. Mice were sacrificed 4 or 6 months post-injection. ELISA measurements were used for IFNγ protein levels and biochemical levels of Aβ. The neuroinflammatory phenotype was determined through quantitative PCR. Microglia, astrocytes, and Aβ levels were assessed with immunohistochemistry.

Results

AAV expressing IFNγ induced an M1 neuroinflammatory phenotype at 4 months and a mixed phenotype along with an increase in Aβ at 6 months. Microglial staining was increased at 6 months and astrocyte staining was decreased at 4 and 6 months in mice receiving AAV expressing IFNγ.

Conclusions

Expression of IFNγ through AAV successfully induced an M1 phenotype at 4 months that transitioned to a mixed phenotype by 6 months. This transition also appeared with an increase in amyloid burden suggesting that a mixed phenotype, or enhanced expression of M2a and M2c markers, could contribute to increasing amyloid burden and disease progression.

GSK-3β, a pivotal kinase in Alzheimer disease

Alzheimer disease (AD) is the most common form of age-related dementia. The etiology of AD is considered to be multifactorial as only a negligible percentage of cases have a familial or genetic origin. Glycogen synthase kinase-3 (GSK-3) is regarded as a critical molecular link between the two histopathological hallmarks of the disease, namely senile plaques and neurofibrillary tangles. In this review, we summarize current data regarding the involvement of this kinase in several aspects of AD development and progression, as well as key observations highlighting GSK-3 as one of the most relevant targets for AD treatment.

Glycogen synthase kinase-3 inhibitors: Rescuers of cognitive impairments

Impairment of cognitive processes is a devastating outcome of many diseases, injuries, and drugs affecting the central nervous system (CNS). Most often, very little can be done by available therapeutic interventions to improve cognitive functions. Here we review evidence that inhibition of glycogen synthase kinase-3 (GSK3) ameliorates cognitive deficits in a wide variety of animal models of CNS diseases, including Alzheimer's disease, Fragile X syndrome, Down syndrome, Parkinson's disease, spinocerebellar ataxia type 1, traumatic brain injury, and others. GSK3 inhibitors also improve cognition following impairments caused by therapeutic interventions, such as cranial irradiation for brain tumors. These findings demonstrate that GSK3 inhibitors are able to ameliorate cognitive impairments caused by a diverse array of diseases, injury, and treatments. The improvements in impaired cognition instilled by administration of GSK3 inhibitors appear to involve a variety of different mechanisms, such as supporting long-term potentiation and diminishing long-term depression, promotion of neurogenesis, reduction of inflammation, and increasing a number of neuroprotective mechanisms. The potential for GSK3 inhibitors to repair cognitive deficits associated with many conditions warrants further investigation of their potential for therapeutic interventions, particularly considering the current dearth of treatments available to reduce loss of cognitive functions.

In vivo modification of Abeta plaque toxicity as a novel neuroprotective lithium-mediated therapy for Alzheimer's disease pathology

Background

Alzheimer’s disease (AD) is characterized by the abnormal accumulation of extracellular beta-amyloid (Abeta) plaques, intracellular hyperphosphorylated tau, progressive synaptic alterations, axonal dystrophies, neuronal loss and the deterioration of cognitive capabilities of patients. However, no effective disease-modifying treatment has been yet developed. In this work we have evaluated whether chronic lithium treatment could ameliorate the neuropathology evolution of our well characterized PS1M146LxAPPSwe-London mice model.

Results

Though beneficial effects of lithium have been previously described in different AD models, here we report a novel in vivo action of this compound that efficiently ameliorated AD-like pathology progression and rescued memory impairments by reducing the toxicity of Abeta plaques. Transgenic PS1M146LxAPPSwe-London mice, treated before the pathology onset, developed smaller plaques characterized by higher Abeta compaction, reduced oligomeric-positive halo and therefore with attenuated capacity to induce neuronal damage. Importantly, neuronal loss in hippocampus and entorhinal cortex was fully prevented. Our data also demonstrated that the axonal dystrophic area associated with lithium-modified plaques was highly reduced. Moreover, a significant lower accumulation of phospho-tau, LC3-II and ubiquitinated proteins was detected in treated mice. Our study highlights that this switch of plaque quality by lithium could be mediated by astrocyte activation and the release of heat shock proteins, which concentrate in the core of the plaques.

Conclusions

Our data demonstrate that the pharmacological in vivo modulation of the extracellular Abeta plaque compaction/toxicity is indeed possible and, in addition, might constitute a novel promising and innovative approach to develop a disease-modifying therapeutic intervention against AD.

Intracranial injection of Gammagard, a human IVIg, modulates the inflammatory response of the brain and lowers Aβ in APP/PS1 mice along a different time course than anti-Aβ antibodies

Gammagard IVIg is a therapeutic approach to treat Alzheimer's disease currently in phase 3 clinical trials. Despite the reported efficacy of the approach the mechanism of action is poorly understood. We have previously shown that intracranial injection of anti-Aβ antibodies into the frontal cortex and hippocampus reveals important information regarding the time course of events once the agent is in the brain. In the current study we compared IVIg, mouse-pooled IgG, and the anti-Aβ antibody 6E10 injected intracranially into the frontal cortex and hippocampus of 7-month-old APP/PS1 mice. We established a time course of events ranging from 1 to 21 d postinjection. IVIg and pooled mouse IgG both significantly reduced Aβ deposition to the same degree as the 6E10 anti-Aβ antibody; however, the clearance was much slower to occur, happening between the 3 and 7 d time points. In contrast, as we have previously shown, Aβ reductions were apparent with the 6E10 anti-Aβ group at the 1 d time point. Also, neuroinflammatory profiles were significantly altered by the antibody treatments. APP/PS1 transgenic mice at 7 months of age typically exhibit an M2a inflammatory phenotype. All antibody treatments stimulated an M2b response, yet anti-Aβ antibody was a more rapid change. Because the neuroinflammatory switch occurs before the detectable reductions in amyloid deposition, we hypothesize that the IVIg and pooled mouse IgG act as immune modulators and this immune modulation is responsible for the reductions in amyloid pathology.

The p38α MAPK regulates microglial responsiveness to diffuse traumatic brain injury

Neuropathology after traumatic brain injury (TBI) is the result of both the immediate impact injury and secondary injury mechanisms. Unresolved post-traumatic glial activation is a secondary injury mechanism that contributes to a chronic state of neuroinflammation in both animal models of TBI and human head injury patients. We recently demonstrated, using in vitro models, that p38α MAPK signaling in microglia is a key event in promoting cytokine production in response to diverse disease-relevant stressors and subsequent inflammatory neuronal dysfunction. From these findings, we hypothesized that the p38α signaling pathway in microglia could be contributing to the secondary neuropathologic sequelae after a diffuse TBI. Mice where microglia were p38α-deficient (p38α KO) were protected against TBI-induced motor deficits and synaptic protein loss. In wild-type (WT) mice, diffuse TBI produced microglia morphological activation that lasted for at least 7 d; however, p38α KO mice failed to activate this response. Unexpectedly, we found that the peak of the early, acute phase cytokine and chemokine levels was increased in injured p38α KO mice compared with injured WT mice. The increased cytokine levels in the p38α KO mice could not be accounted for by more infiltration of macrophages or neutrophils, or increased astrogliosis. By 7 d after injury, the cytokine and chemokine levels remained elevated in injured WT mice but not in p38α KO mice. Together, these data suggest that p38α balances the inflammatory response by acutely attenuating the early proinflammatory cytokine surge while perpetuating the chronic microglia activation after TBI.

Induction of hyperhomocysteinemia models vascular dementia by induction of cerebral microhemorrhages and neuroinflammation

Vascular dementia (VaD) is the second leading cause of dementia behind Alzheimer's disease (AD) and is a frequent comorbidity with AD, estimated to occur in as many as 40% of AD patients. The causes of VaD are varied and include chronic cerebral hypoperfusion, microhemorrhages, hemorrhagic infarcts, or ischemic infarcts. We have developed a model of VaD by inducing hyperhomocysteinemia (HHcy) in wild-type mice. By placing wild-type mice on a diet deficient in folate, B6, and B12 and supplemented with excess methionine, we induced a moderate HHcy (plasma level homocysteine 82.93 ± 3.561 μmol). After 11 weeks on the diet, the hyperhomocysteinemic mice showed a spatial memory deficit as assessed by the 2-day radial-arm water maze. Also, magnetic resonance imaging and subsequent histology revealed significant microhemorrhage occurrence. We found neuroinflammation induced in the hyperhomocysteinemic mice as determined by elevated interleukin (IL)-1β, tumor necrosis factor (TNF)α, and IL-6 in brain tissue. Finally, we found increased expression and increased activity of the matrix metalloproteinase 2 (MMP2) and MMP9 systems that are heavily implicated in the pathogenesis of cerebral hemorrhage. Overall, we have developed a dietary model of VaD that will be valuable for studying the pathophysiology of VaD and also for studying the comorbidity of VaD with other dementias and other neurodegenerative disorders.

Neuroinflammatory phenotype in early Alzheimer's disease

Alzheimer's disease (AD) involves progressive neurodegeneration in the presence of misfolded proteins and poorly-understood inflammatory changes. However, research has shown that AD is genetically, clinically, and pathologically heterogeneous. In frozen brain samples of frontal cortex (diseased) and cerebellum (nondiseased) from the University of Kentucky Alzheimer's Disease Center autopsy cohort, we performed gene expression analysis for genes categorizing inflammatory states (termed M1 and M2) from early and late stage AD, and age-matched nondemented controls. We performed analysis of the serum samples for a profile of inflammatory proteins and examined the neuropathologic data on these samples. Striking heterogeneity was found in early AD. Specifically, early-stage AD brain samples indicated apparent polarization toward either the M1 or M2 brain inflammatory states when compared with age-matched nondisease control tissue. This polarization was observed in the frontal cortex and not in cerebellar tissue. We were able to detect differences in AD neuropathology, and changes in serum proteins that distinguished the individuals with apparent M1 versus M2 brain inflammatory polarization.