The importance of tau phosphorylation for neurodegenerative diseases

Comparative Analysis of Aducanumab, Zagotenemab and Pioglitazone as Targeted Treatment Strategies for Alzheimer's Disease

Alzheimer’s disease (AD) is the leading cause of dementia that has remained a major medical, sociocultural and economical challenge globally. Previously developed treatments like anticholinesterase inhibitors (AChEIs) and N-methyl-D-aspartate receptor (NMDAR) antagonists only provide short-term symptomatic improvement and do not prevent progression. Repeated setbacks and failures over the past 25 years in AD clinical trials have hindered efforts to develop effective AD treatments. Fortunately, Aducanumab, a specific anti-amyloid β antibody, has shown promising clinical results and was recently approved by the Food and Drug Administration (FDA) through an accelerated approval pathway. This has raised hopes for AD patients; however post-approval trials are necessary to estimate the true scope of its clinical benefits. We have reviewed several AD clinical studies and summarized the experience to date with Aducanumab and two other potential AD drugs including Zagotenemab (an anti-tau antibody) and Pioglitazone (nuclear Peroxisome-Proliferator Activated Receptor γ (PPARγ) agonist). These have shown mixed results so far and the next few years will be critical to elucidate and interpret their broad long-term protective effects. A concerted effort is required to understand and strengthen the translation of pre-clinical findings from these drugs to routine clinical practice.

Targeting tau only extracellularly is likely to be less efficacious than targeting it both intra- and extracellularly

Aggregation of the tau protein is thought to be responsible for the neurodegeneration and subsequent functional impairments in diseases that are collectively named tauopathies. Alzheimer's disease is the most common tauopathy, but the group consists of over 20 different diseases, many of which have tau pathology as their primary feature. The development of tau therapies has mainly focused on preventing the formation of and/or clearing these aggregates. Of these, immunotherapies that aim to either elicit endogenous tau antibodies or deliver exogenous ones are the most common approach in clinical trials. While their mechanism of action can involve several pathways, both extra- and intracellular, pharmaceutical companies have primarily focused on antibody-mediated clearance of extracellular tau. As we have pointed out over the years, this is rather surprising because it is well known that most of pathological tau protein is found intracellularly. It has been repeatedly shown by several groups over the past decades that antibodies can enter neurons and that their cellular uptake can be enhanced by various means, particularly by altering their charge. Here, we will briefly describe the potential extra- and intracellular mechanisms involved in antibody-mediated clearance of tau pathology, discuss these in the context of recent failures of some of the tau antibody trials, and finally provide a brief overview of how the intracellular efficacy of tau antibodies can potentially be further improved by certain modifications that aim to enhance tau clearance via specific intracellular degradation pathways.

Human Induced Pluripotent Stem Cell Models of Frontotemporal Dementia With Tau Pathology

Neurodegenerative dementias are the most common group of neurodegenerative diseases affecting more than 40 million people worldwide. One of these diseases is frontotemporal dementia (FTD), an early onset dementia and one of the leading causes of dementia in people under the age of 60. FTD is a heterogeneous group of neurodegenerative disorders with pathological accumulation of particular proteins in neurons and glial cells including the microtubule-associated protein tau, which is deposited in its hyperphosphorylated form in about half of all patients with FTD. As for other patients with dementia, there is currently no cure for patients with FTD and thus several lines of research focus on the characterization of underlying pathogenic mechanisms with the goal to identify therapeutic targets. In this review, we provide an overview of reported disease phenotypes in induced pluripotent stem cell (iPSC)-derived neurons and glial cells from patients with tau-associated FTD with the aim to highlight recent progress in this fast-moving field of iPSC disease modeling. We put a particular focus on genetic forms of the disease that are linked to mutations in the gene encoding tau and summarize mutation-associated changes in FTD patient cells related to tau splicing and tau phosphorylation, microtubule function and cell metabolism as well as calcium homeostasis and cellular stress. In addition, we discuss challenges and limitations but also opportunities using differentiated patient-derived iPSCs for disease modeling and biomedical research on neurodegenerative diseases including FTD.

Post-translational modifications within tau paired helical filament nucleating motifs perturb microtubule interactions and oligomer formation

Post-translationally modified tau is the primary component of tau neurofibrillary tangles, a pathological hallmark of Alzheimer's disease and other tauopathies. Post-translational modifications within the tau microtubule binding domain (MBD), which encompasses two hexapeptide motifs that act as critical nucleating regions for tau aggregation, can potentially modulate tau aggregation as well as interactions with microtubules (MTs) and membranes. Here we characterize the effects of a recently discovered tau PTM, lysine succinylation, on tau-tubulin interactions, and compare these to the effects of two previously reported MBD modifications, lysine acetylation and tyrosine phosphorylation. As generation of site-specific PTMs in proteins is challenging, we used short synthetic peptides to quantify the effects on tubulin binding of three site-specific PTMs located within the PHF6* (residues 275-280) and PHF6 (residues 306-311) hexapeptide motifs: K280 acetylation, Y310 phosphorylation and K311 succinylation. We compared these effects to those observed for MBD PTM-mimetic point mutations K280Q, Y310E and K311E. Finally, we evaluated the effects of these PTM-mimetic mutations on MBD membrane binding and membrane-induced fibril and oligomer formation. We found that all three PTMs perturb tau MT binding, with Y310 phosphorylation exerting the strongest effect. PTM mimetic mutations partially recapitulated the effects of the PTMs on MT binding and also disrupted tau membrane binding and membrane induced oligomer and fibril formation. These results imply that these PTMs, including the novel and AD-specific succinylation of tau K311, may influence both the physiological and pathological interactions of tau and thus represent targets for therapeutic intervention.

Arginine and Arginine-Rich Peptides as Modulators of Protein Aggregation and Cytotoxicity Associated With Alzheimer's Disease

A substantial body of evidence indicates cationic, arginine-rich peptides (CARPs) are effective therapeutic compounds for a range of neurodegenerative pathologies, with beneficial effects including the reduction of excitotoxic cell death and mitochondrial dysfunction. CARPs, therefore, represent an emergent class of promising neurotherapeutics with multimodal mechanisms of action. Arginine itself is a known chaotrope, able to prevent misfolding and aggregation of proteins. The putative role of proteopathies in chronic neurodegenerative diseases such as Alzheimer's disease (AD) warrants investigation into whether CARPs could also prevent the aggregation and cytotoxicity of amyloidogenic proteins, particularly amyloid-beta and tau. While monomeric arginine is well-established as an inhibitor of protein aggregation in solution, no studies have comprehensively discussed the anti-aggregatory properties of arginine and CARPs on proteins associated with neurodegenerative disease. Here, we review the structural, physicochemical, and self-associative properties of arginine and the guanidinium moiety, to explore the mechanisms underlying the modulation of protein aggregation by monomeric and multimeric arginine molecules. Arginine-rich peptide-based inhibitors of amyloid-beta and tau aggregation are discussed, as well as further modulatory roles which could reduce proteopathic cytotoxicity, in the context of therapeutic development for AD.

The role of pathological tau in synaptic dysfunction in Alzheimer's diseases

Alzheimer’s disease (AD) is a neurodegenerative disease characterized by progressive cognitive decline, accompanied by amyloid-β (Aβ) overload and hyperphosphorylated tau accumulation in the brain. Synaptic dysfunction, an important pathological hallmark in AD, is recognized as the main cause of the cognitive impairments. Accumulating evidence suggests that synaptic dysfunction could be an early pathological event in AD. Pathological tau, which is detached from axonal microtubules and mislocalized into pre- and postsynaptic neuronal compartments, is suggested to induce synaptic dysfunction in several ways, including reducing mobility and release of presynaptic vesicles, decreasing glutamatergic receptors, impairing the maturation of dendritic spines at postsynaptic terminals, disrupting mitochondrial transport and function in synapses, and promoting the phagocytosis of synapses by microglia. Here, we review the current understanding of how pathological tau mediates synaptic dysfunction and contributes to cognitive decline in AD. We propose that elucidating the mechanism by which pathological tau impairs synaptic function is essential for exploring novel therapeutic strategies for AD.

New insights into the role of fibroblast growth factors in Alzheimer's disease

Alzheimer's disease (AD), acknowledged as the most common progressive neurodegenerative disorder, is the leading cause of dementia in the elderly. The characteristic pathologic hallmarks of AD-including the deposition of extracellular senile plaques (SP) formation, intracellular neurofibrillary tangles, and synaptic loss, along with prominent vascular dysfunction and cognitive impairment-have been observed in patients. Fibroblast growth factors (FGFs), originally characterized as angiogenic factors, are a large family of signaling molecules that are implicated in a wide range of biological functions in brain development, maintenance and repair, as well as in the pathogenesis of brain-related disorders including AD. Many studies have focused on the implication of FGFs in AD pathophysiology. In this review, we will provide a summary of recent findings regarding the role of FGFs and their receptors in the pathogenesis of AD, and discuss the possible opportunities for targeting these molecules as novel treatment strategies in AD.

The PI3K/Akt signaling axis in Alzheimer's disease: a valuable target to stimulate or suppress?

Among the long list of age-related complications, Alzheimer's disease (AD) has the most dreadful impact on the quality of life due to its devastating effects on memory and cognitive abilities. Although a plausible correlation between the phosphatidylinositol 3-kinase (PI3K) signaling and different processes involved in neurodegeneration has been evidenced, few articles reviewed the task. The current review aims to unravel the mechanisms by which the PI3K pathway plays pro-survival roles in normal conditions, and also to discuss the original data obtained from international research laboratories on this topic. Responses to questions on how alterations of the PI3K/Akt signaling pathway affect Tau phosphorylation and the amyloid cascade are given. In addition, we provide a general overview of the association between oxidative stress, neuroinflammation, alterations of insulin signaling, and altered autophagy with aberrant activation of this axis in the AD brain. The last section provides a special focus on the therapeutic possibility of the PI3K/Akt/mTOR modulators, either categorized as chemicals or herbals, in AD. In conclusion, determining the correct timing for the administration of the drugs seems to be one of the most important factors in the success of these agents. Also, the role of the PI3K/Akt signaling axis in the progression or repression of AD widely depends on the context of the cells; generally speaking, while PI3K/Akt activation in neurons and neural stem cells is favorable, its activation in microglia cells may be harmful.

The potential role of glial cells in driving the prion-like transcellular propagation of tau in tauopathies

Dementia is one of the leading causes of death worldwide, with tauopathies, a class of diseases defined by pathology associated with the microtubule-enriched protein, tau, as the major contributor. Although tauopathies, such as Alzheimer's disease and Frontotemporal dementia, are common amongst the ageing population, current effective treatment options are scarce, primarily due to the incomplete understanding of disease pathogenesis. The mechanisms via which aggregated forms of tau are able to propagate from one anatomical area to another to cause disease spread and progression is yet unknown. The prion-like hypothesis of tau propagation proposes that tau can propagate along neighbouring anatomical areas in a similar manner to prion proteins in prion diseases, such as Creutzfeldt-Jacob disease. This hypothesis has been supported by a plethora of studies that note the ability of tau to be actively secreted by neurons, propagated and internalised by neighbouring neuronal cells, causing disease spread. Surfacing research suggests a role of reactive astrocytes and microglia in early pre-clinical stages of tauopathy through their inflammatory actions. Furthermore, both glial types are able to internalise and secrete tau from the extracellular space, suggesting a potential role in tau propagation; although understanding the physiological mechanisms by which this can occur remains poorly understood. This review will discuss the current literature around the prion-like propagation of tau, with particular emphasis on glial-mediated neuroinflammation and the contribution it may play in this propagation process.

Generation and characterization of a tractable C. elegans model of tauopathy

Alzheimer's disease(AD) is an age-associated neurodegenerative disease that results in deterioration of memory and cognitive function. As a currently untreatable disorder, AD has emerged as one of the defining biomedical challenges of our time. Thus, new approaches that can examine the cellular and molecular mechanisms underlying age-related AD pathology are sorely needed. One of the hallmarks of Alzheimer's disease is the hyperphosphorylation of the tau protein. Caenorhabditis elegans have been previously used to study the genetic pathways impacted by tau proteotoxic stress; however, currently, available C. elegans tau models express the human protein solely in neurons, which are unresponsive to global RNA interference (RNAi). This limits powerful RNAi screening methods from being utilized effectively in these disease models. Our goal was to develop a C. elegans tau model that has pronounced tau-induced disease phenotypes in cells that can be modified by feeding RNAi methods. Towards this end, we generated a novel C. elegans transgenic line with codon-optimized human 0N4R V337M tau expressed in the body wall muscle under the myo-3 promoter. Immunoblotting experiments revealed that the expressed tau is phosphorylated on epitopes canonically associated with human AD pathology. The tau line has significantly reduced health metrics, including egg laying, growth rate, paralysis, thrashing frequency, crawling speed, and lifespan. These defects are suppressed by RNAi directed against the tau mRNA. Taken together, our results suggest that this alternative tau genetic model could be a useful tool for uncovering the mechanisms that influence the hyperphosphorylation and toxicity of human tau via RNAi screening and other approaches.

Activity-dependent release of phosphorylated human tau from Drosophila neurons in primary culture

Neuronal activity can enhance tau release and thus accelerate tauopathies. This activity-dependent tau release can be used to study the progression of tau pathology in Alzheimer's disease (AD), as hyperphosphorylated tau is implicated in AD pathogenesis and related tauopathies. However, our understanding of the mechanisms that regulate activity-dependent tau release from neurons and the role that tau phosphorylation plays in modulating activity-dependent tau release is still rudimentary. In this study, Drosophila neurons in primary culture expressing human tau (hTau) were used to study activity-dependent tau release. We found that hTau release was markedly increased by 50 mM KCl treatment for 1 h. A similar level of release was observed using optogenetic techniques, where genetically targeted neurons were stimulated for 30 min using blue light (470 nm). Our results showed that activity-dependent release of phosphoresistant hTauS11A was reduced when compared with wildtype hTau. In contrast, release of phosphomimetic hTauE14 was increased upon activation. We found that released hTau was phosphorylated in its proline-rich and C-terminal domains using phosphorylation site-specific tau antibodies (e.g., AT8). Fold changes in detectable levels of total or phosphorylated hTau in cell lysates or following immunopurification from conditioned media were consistent with preferential release of phosphorylated hTau after light stimulation. This study establishes an excellent model to investigate the mechanism of activity-dependent hTau release and to better understand the role of phosphorylated tau release in the pathogenesis of AD since it relates to alterations in the early stage of neurodegeneration associated with increased neuronal activity.

Exendin-4 Improves Cognitive Function of Diabetic Mice via Increasing Brain Insulin Synthesis

BACKGROUND AND OBJECTIVE

Type 2 diabetes(T2D) patients are more prone to develop Alzheimer's disease (AD). We have previously shown that Glucagon-like peptide-1 receptor agon- ist exendin-4 (Ex-4) reduces tau hyperphosphorylation in T2D animals through upregulating in- sulin signaling, and peripheral injected Ex-4 increases insulin levels in the T2D brain. This study aims to further clarify whether the elevated insulin in the brain is produced by nerve cells under the action of Ex-4.

METHODS

The neuronal cell line-HT22 was treated with Ex-4 under high glucose or normal cultiva- tion, and the number of insulin-positive cells as well as the expression levels of insulin synthesis-re- lated genes were examined. The db/db mice were treated with a peripheral injection of Ex-4 and/or intracerebroventricular (ICV) injection of siRNA to inhibit the expression of insulin synthesis-relat- ed genes and the behavior tests were carried on. Finally, plasma glucose, cerebrospinal fluid (CSF) glucose, CSF insulin, phosphorylation of tau, phosphorylation of AKT and GSK-3β of db/db mice were detected.

RESULTS

We found that Ex-4 promoted the expression of insulin synthesis-related genes and in- duced an obvious increase of insulin-positive HT-22 neuronal cells in a high glucose environment. Peripheral injection of Ex-4 improved the cognitive function of db/db mice and increased brain in- sulin levels which activated brain insulin signaling and subsequently alleviated tau hyperphosphory- lation. However, when siRNA-neurod1 was injected to block insulin synthesis, the cognitive func- tion of db/db mice was not improved under the action of Ex-4 anymore. Moreover, the brain in- sulin levels dropped to an extremely low level, and the phosphorylation level of tau increased signi- ficantly.

CONCLUSION

This study demonstrated that Ex-4 improved cognition function by promoting brain in- sulin synthesis followed by the activation of brain insulin signaling and alleviation of tau hyper- phosphorylation.

Transgenic fluorescent zebrafish lines that have revolutionized biomedical research

Since its debut in the biomedical research fields in 1981, zebrafish have been used as a vertebrate model organism in more than 40,000 biomedical research studies. Especially useful are zebrafish lines expressing fluorescent proteins in a molecule, intracellular organelle, cell or tissue specific manner because they allow the visualization and tracking of molecules, intracellular organelles, cells or tissues of interest in real time and in vivo. In this review, we summarize representative transgenic fluorescent zebrafish lines that have revolutionized biomedical research on signal transduction, the craniofacial skeletal system, the hematopoietic system, the nervous system, the urogenital system, the digestive system and intracellular organelles.

A Tau-Driven Adverse Outcome Pathway Blueprint Toward Memory Loss in Sporadic (Late-Onset) Alzheimer's Disease with Plausible Molecular Initiating Event Plug-Ins for Environmental Neurotoxicants

The worldwide prevalence of sporadic (late-onset) Alzheimer's disease (sAD) is dramatically increasing. Aging and genetics are important risk factors, but systemic and environmental factors contribute to this risk in a still poorly understood way. Within the frame of BioMed21, the Adverse Outcome Pathway (AOP) concept for toxicology was recommended as a tool for enhancing human disease research and accelerating translation of data into human applications. Its potential to capture biological knowledge and to increase mechanistic understanding about human diseases has been substantiated since. In pursuit of the tau-cascade hypothesis, a tau-driven AOP blueprint toward the adverse outcome of memory loss is proposed. Sequences of key events and plausible key event relationships, triggered by the bidirectional relationship between brain cholesterol and glucose dysmetabolism, and contributing to memory loss are captured. To portray how environmental factors may contribute to sAD progression, information on chemicals and drugs, that experimentally or epidemiologically associate with the risk of AD and mechanistically link to sAD progression, are mapped on this AOP. The evidence suggests that chemicals may accelerate disease progression by plugging into sAD relevant processes. The proposed AOP is a simplified framework of key events and plausible key event relationships representing one specific aspect of sAD pathology, and an attempt to portray chemical interference. Other sAD-related AOPs (e.g., Aβ-driven AOP) and a better understanding of the impact of aging and genetic polymorphism are needed to further expand our mechanistic understanding of early AD pathology and the potential impact of environmental and systemic risk factors.

An Overview of the Nrf2/ARE Pathway and Its Role in Neurodegenerative Diseases

Nrf2 is a basic region leucine-zipper transcription factor that plays a pivotal role in the coordinated gene expression of antioxidant and detoxifying enzymes, promoting cell survival in adverse environmental or defective metabolic conditions. After synthesis, Nrf2 is arrested in the cytoplasm by the Kelch-like ECH-associated protein 1 suppressor (Keap1) leading Nrf2 to ubiquitin-dependent degradation. One Nrf2 activation mechanism relies on disconnection from the Keap1 homodimer through the oxidation of cysteine at specific sites of Keap1. Free Nrf2 enters the nucleus, dimerizes with small musculoaponeurotic fibrosarcoma proteins (sMafs), and binds to the antioxidant response element (ARE) sequence of the target genes. Since oxidative stress, next to neuroinflammation and mitochondrial dysfunction, is one of the hallmarks of neurodegenerative pathologies, a molecular intervention into Nrf2/ARE signaling and the enhancement of the transcriptional activity of particular genes are targets for prevention or delaying the onset of age-related and inherited neurogenerative diseases. In this study, we review evidence for the Nrf2/ARE-driven pathway dysfunctions leading to various neurological pathologies, such as Alzheimer’s, Parkinson’s, and Huntington’s diseases, as well as amyotrophic lateral sclerosis, and the beneficial role of natural and synthetic molecules that are able to interact with Nrf2 to enhance its protective efficacy.

Bushen-Huatan-Yizhi formula reduces spatial learning and memory challenges through inhibition of the GSK-3β/CREB pathway in AD-like model rats

BACKGROUND

There is an increase in cases of Alzheimer's disease (AD) stemming from a globally ageing population demographic. Although substantial research efforts were performed for the scope of prophylaxis and therapeutic measure development against AD, based on its pathogenesis, most were unsuccessful. Bushen-Huatan-Yizhi formula (BSHTYZ) is extensively implemented to manage dementia. However, few studies have been carried out to understand how BSHTYZ enhances recovery of spatial learning and memory and how it modulates relevant molecular interplays in order to achieve this.

PURPOSE

To investigate neuroprotective function, ameliorating learning/memory capacity of BSHTYZ via GSK-3β / CREB signaling pathway in rat AD models influenced through Aβ1-42.

METHODS

A total of 60 male SD rats (3 months old) were randomized into six groups and treated with 2.6 μg/μl Aβ1-42 (5 μl) into the lateral ventricle, though the control group (Con) was administered an equivalent volume of vehicle. Consequently, the rat cohorts were administered either BSHTYZ or donepezil hydrochloride or normal saline, by intragastric administration, for four weeks. Spatial learning / memory were detected through the Morris water maze, and possible mechanisms detected by histomorphological examination and Western blot in the rat AD models induced by Aβ1-42.

RESULTS

Spatial learning/memory issues were monitored after Aβ1-42 infusion in rats. Simultaneously, neuron loss in cornuammonis1 (CA1) / dentate gyrus (DG) within hippocampus region were identified, together with enhanced black granule staining within the hippocampus and hyperphosphorylated tau within Ser202 and Ser396 sites. It was also elucidated that Aβ1-42 had the capacity to up-regulate glycogen synthase kinase-3β (GSK-3β) and down-regulate cAMP response element binding protein (CREB). BSHTYZ was found to reverse such molecular interplays.

CONCLUSION

The study suggested BSHTYZ could possibly provide neuroprotective role against learning / memory impairment, which provided a potential therapeutic tool delaying the progression of AD molecular interplays that includes the GSK-3β / CREB signaling pathway.

Icariin ameliorate Alzheimer's disease by influencing SIRT1 and inhibiting Aβ cascade pathogenesis

Of all types of dementia, Alzheimer's disease is the type that has the highest proportion of cases and is the cause of substantial medical and economic burden. The mechanism of Alzheimer's disease is closely associated with the aggregation of amyloid-β protein and causes neurotoxicity and extracellular accumulation in the brain and to intracellular neurofibrillary tangles caused by tau protein hyperphosphorylation in the brain tissue. Previous studies have demonstrated that sirtuin1 downregulation is involved in the pathological mechanism of Alzheimer's disease. The decrease of sirtuin1 level would cause Alzheimer's disease by means of promoting the amyloidogenic pathway to generate amyloid-β species and thereby triggering amyloid-β cascade reaction, such as tau protein hyperphosphorylation, neuron autophagy, neuroinflammation, oxidative stress, and neuron apoptosis. Currently, there is no effective treatment for Alzheimer's disease, it is necessary to develop new treatment strategies. According to the theory of traditional Chinese medicine and based on the mechanism of the disease, tonifying the kidneys is one of the principles for the treatment of Alzheimer's disease and Epimedium is a well-known Chinese medicine for tonifying kidney. Therefore, investigating the influence of the components of Epimedium on the pathological characteristics of Alzheimer's disease may provide a reference for the treatment of Alzheimer's disease in the future. In this article, we summarise the effects and mechanism of icariin, the main ingredient extracted from Epimedium, in ameliorating Alzheimer's disease by regulating sirtuin1 to inhibit amyloid-β protein and improve other amyloid-β cascade pathogenesis.

Metformin protects against neuroinflammation through integrated mechanisms of miR-141 and the NF-ĸB-mediated inflammasome pathway in a diabetic mouse model

The brain responds to diabetic stress by inducing the inflammatory response. Under normal circumstances this process is tightly regulated. However, uncontrolled inflammatory responses lead to compromised function and eventual neurodegeneration. The microRNA (miR)-200 family, specifically miR-141, is differentially expressed in diseased states including cognitive decline, thereby triggering changes in downstream genes. We hypothesised that Metformin (MF) regulates the miR-141/protein phosphatase 2A (PP2A) axis, and associated NF-ĸB-mediated inflammasome expression in diabetic mice brain. Diabetes was induced by intraperitoneal injection of Streptozotocin (STZ), thereafter mice were treated with MF (20 mg/kg BW). Whole brain tissue was harvested for further analysis. In silico analysis showed that Sirt1 and PP2A are prediction targets of miR-141. Selected protein and gene expressions were established through western blotting and qPCR, respectively. Diabetic mice brain tissue demonstrated overexpression of miR-141 and related pro-inflammatory factors as well as decreased PP2A gene expression. MF was able to counteract this by regulating expression of miR-141, PP2A, and p-tau at Ser396 protein expressions. Further experimentation revealed MF's inhibitory action on the inflammasome system by regulating the expression of the upstream controller NLRP3, related cytokines and NF-κB signalling pathway. Collectively, we demonstrate that MF promotes neuroprotection in diabetic mice by dampening inflammatory responses through its inhibitory effects on various signalling pathways. CATEGORIES: Inflammation and Immunopharmacology, Metabolic Disorders and Endocrinology, Neuropharmacology.

Mesenchymal stem cell-derived extracellular vesicles ameliorate Alzheimer's disease-like phenotypes in a preclinical mouse model

Alzheimer's disease (AD) is an irreversible neurodegenerative disorder that affects more than 44 million people worldwide. Despite the high disease burden, there is no effective treatment for people suffering from AD. Mesenchymal stem cells (MSCs) are multipotent stromal cells that have been widely studied due to their therapeutic potential. However, administration of cells has been found to have a multitude of limitations. Recently, extracellular vesicles (EVs) derived from MSCs have been studied as a therapeutic candidate, as they exhibit similar immunoprotective and immunomodulatory abilities as the host human MSCs. Methods: To test the potential therapeutic effects of MSC EVs, human bone-marrow derived MSCs were grown in three-dimensional (3D) cell culture, and small EVs were harvested using differential ultracentrifugation. These small EVs were given to non-transgenic (NT) or 5XFAD (5 familial Alzheimer's disease mutations) mice intranasally (IN) every 4 days for 4 months. The mice were then required to perform a variety of behavioral assays to measure changes in learning and memory. Afterwards, immunohistochemistry was performed on brain slices to measure amyloid beta (Aβ) and glial fibrillary acidic protein (GFAP) levels. Results: The data revealed that 5XFAD mice that received hMSC-EV treatment behaved significantly better in cognitive tests than saline treated 5XFAD mice, with no significant change between EV-treated 5XFAD mice and NT mice. Additionally, we found lower Aβ plaque load in the hippocampus of the EV-treated mice. Finally, less colocalization between GFAP and Aβ plaques was found in the brain of EV-treated mice compared to saline. Conclusions: Taken together, these data suggest that IN administration of MSC-derived EVs can slow down AD pathogenesis.

The Synaptic Vesicle Protein 2A Interacts With Key Pathogenic Factors in Alzheimer's Disease: Implications for Treatment

Alzheimer’s disease (AD), a serious neurodegenerative disease, is pathologically characterized by synaptic loss and dysfunction. Synaptic vesicle protein 2A (SV2A) is an indispensable vesicular protein specifically expressed in synapses and can be used as a biomarker for synaptic density. We found that the expression of SV2A was down-regulated in the hippocampus of AD patients, yet the relation of SV2A to other hallmarks of AD pathology such as amyloid precursor protein (APP), β-amyloid (Aβ), and Tau protein is not thoroughly clear. In addition, SV2A colocalized with APP and was down-regulated at Aβ deposition. Moreover, we found that SV2A deficiency leads to a simultaneous increase in Aβ and Tau hyperphosphorylation, while SV2A overexpression was associated with downregulation of β-site APP cleaving enzyme 1 and apolipoprotein E genes. In addition, evidence gained in the study points to the phosphatidylinositol 3-kinase signaling pathway as a possible mediator in SV2A regulation influencing the incidence and development of AD. With limited effective diagnostic methods for AD, a close interplay between SV2A and AD-related proteins demonstrated in our study may provide novel and innovative diagnostic and therapeutic opportunities.

Intravenous administration of mesenchymal stem cells reduces Tau phosphorylation and inflammation in the 3xTg-AD mouse model of Alzheimer's disease

Mesenchymal stem cell (MSC) administration is a novel and promising therapeutic approach for Alzheimer's disease (AD). Focusing on an intervention easily translatable into clinical practice, we administered allogeneic bone marrow-derived MSCs intravenously in a mouse model of AD (3xTg-AD). We systematically evaluated the effects of a single-dose and multiple-doses of MSCs in young and old mice (5 or 10 months old), comparing the short-term and long-term effects after 1, 2, or 7 months of treatment. A single dose of MSCs in young mice attenuated neuroinflammation 1 and 7 months after injection, whereas multiple-doses did not show any effect. Multiple-doses of MSCs (administered at 5 to 12 mo, or 10 to 12 mo) reduced the β-secretase cleavage of the amyloid precursor protein, although levels of Aβ-42 did not change. Most interestingly, multiple doses of MSCs affected tau hyperphosphorylation. MSCs administered in young mice for 7 months decreased the pathological tau phosphorylation at T205, S214, and T231. MSCs administered in old mice for 2 months decreased tau phosphorylation at S396. Our findings show how different timing and frequency of MSC injections can affect and modulate several aspects of the AD-like neuropathology in the 3xTg-AD mouse model, strengthening the concept of fine-tuning MSC therapy for Alzheimer's disease.

The Association between Tau Protein Level in Cerebrospinal Fluid and Cognitive Status: A Large-Scale Analysis of GAAIN Database

Alzheimer’s disease (AD) and the associated neurodegenerative dementia have become of increasing concern in healthcare. The tau protein has been considered a key hallmark of progressive neurodegeneration. In this paper, a large-scale analysis of five datasets (more than 2500 people) from the Global Alzheimer’s Association Interactive Network (GAAIN) databases was performed to investigate the association between the level of tau protein, including total tau and phosphorylated tau (p-tau), in cerebrospinal fluid (CSF) and cognitive status. Statistically significant (or marginally significant) high total tau or p-tau concentrations in CSF were observed in dementia patients compared with healthy people in all datasets. There is also a statistically significant (or marginally significant) negative correlation between p-tau concentrations in CSF and Folstein Mini-Mental State Examination (MMSE) scores. In addition, transcriptomic data derived from mouse microglial cells showed multiple genes upregulated in Toll-like receptor signaling and Alzheimer’s disease pathways, including TNF, TLR2, IL-1β, and COX subunits, suggesting that the mechanism of action that relates p-tau and MMSE scores may be through overactivation of pro-inflammatory microglial activity by Aβ peptides, TNF-mediated hyperphosphorylation of tau, and the infectious spread of pathological tau across healthy neurons. Our results not only confirmed the association between tau protein level and cognitive status in a large population but also provided useful information for the understanding of the role of tau in neurodegeneration and the development of dementia.

Oral (-)-Epicatechin Inhibits Progressive Tau Pathology in rTg4510 Mice Independent of Direct Actions at GSK3β

Aggregation of the microtubule-associated protein tau into paired helical filaments (PHFs) and neurofibrillary tangles is a defining characteristic of Alzheimer’s Disease. Various plant polyphenols disrupt tau aggregation in vitro but display poor bioavailability and low potency, challenging their therapeutic translation. We previously reported that oral administration of the flavonoid (−)-epicatechin (EC) reduced Amyloid-β (Aβ) plaque pathology in APP/PS1 transgenic mice. Here, we investigated whether EC impacts on tau pathology, independent of actions on Aβ, using rTg4510 mice expressing P301L mutant tau. 4 and 6.5 months old rTg4510 mice received EC (∼18 mg/day) or vehicle (ethanol) via drinking water for 21 days and the levels of total and phosphorylated tau were assessed. At 4 months, tau appeared as two bands of ∼55 kDa, phosphorylated at Ser262 and Ser396 and was unaffected by exposure to EC. At 6.5 months an additional higher molecular weight form of tau was detected at ∼64 kDa which was phosphorylated at Ser262, Ser396 and additionally at the AT8 sites, indicative of the presence of PHFs. EC consumption reduced the levels of the ∼64 kDa tau species and inhibited phosphorylation at Ser262 and AT8 phosphoepitopes. Regulation of the key tau kinase glycogen synthase kinase 3β (GSK3β) by phosphorylation at Ser9 was not altered by exposure to EC in mice or primary neurons. Furthermore, EC did not significantly inhibit GSK3β activity at physiologically-relevant concentrations in a cell free assay. Therefore, a 21-day intervention with EC inhibits or reverses the development of tau pathology in rTg4510 mice independently of direct inhibition of GSK3β.

Interplay of isoform 1N4R tau protein and amyloid-β peptide fragment 25-35 in reducing and non-reducing conditions

Amyloid-β (Aβ) peptide and tau protein are two hallmark proteins in Alzheimer's disease (AD); however, the parameters, which mediate the abnormal aggregation of Aβ and tau, have not been fully discovered. Here, we have provided an optimum method to purify tau protein isoform 1N4R by using nickel-nitrilotriacetic acid agarose chromatography under denaturing condition. The biochemical and biophysical properties of the purified protein were further characterized using in vitro tau filament assembly, tubulin polymerization assay, circular dichroism (CD) spectroscopy and atomic force microscopy. Afterwards, we investigated the effect of tau protein on aggregation of Aβ (25-35) peptide using microscopic imaging and cell viability assay. Incubation of tau at physiologic and supra-physiologic concentrations with Aβ25-35 for 40 days under reducing and non-reducing conditions revealed formation of two types of aggregates with distinct morphologies and dimensions. In non-reducing condition, the co-incubated sample showed granular aggregates, while in reducing condition, they formed annular protofibrils. Results from cell viability assay revealed the increased cell viability for the co-incubated sample. Therefore, the disassembling action shown by tau protein on Aβ25-35 suggests the possibility that tau may have a protective role in preventing Aβ peptide from acquiring the cytotoxic, aggregated form against oxidative stress damages.

Dichotomous role of microtubule associated protein tau as a biomarker of response to and a target for increasing efficacy of taxane treatment in cancers of epithelial origin

Cancer is the second leading cause of death worldwide, and the World Health Organization estimates that one in six deaths globally is due to cancer. Chemotherapy is one of the major modalities used to treat advanced cancers and their metastasis. However, the existence of acquired and intrinsic resistance to anti-cancer drugs often diminishes their therapeutic effect. In order to pre-select patients who could benefit the most from these treatments, the efforts of many research groups have been focused on identification of biomarkers of therapy response. Taxanes paclitaxel (Taxol) and docetaxel (Taxotere) have been introduced as chemotherapy for treatment of cancers of ovary in 1992 and breast in 1996, respectively. Since then, clinical use of taxanes has expanded to include lung, prostate, gastric, head and neck, esophageal, pancreatic, and cervical cancers, as well as Kaposi sarcoma. Several independent molecular mechanisms have been shown to support taxane chemoresistance. One such mechanism is dependent on microtubule associated protein tau. Tau binds to the same site on the inner side of the microtubules that is also occupied by paclitaxel or docetaxel, and several studies have demonstrated that low/no tau expression significantly correlated with better response to the taxane treatment, suggesting that levels of tau expression could have a predictive value in pre-selecting patient cohorts that are likely to benefit from the treatment. However, several other studies have found no correlation between tau expression and taxane response, introducing a controversy and precluding its wide use as a predictive biomarker. Based on the knowledge of tau biology accumulated thus far, in this review we attempt to critically analyze the studies that evaluated tau as a biomarker of taxane response. Further, we identify yet unknown aspects of tau biology understanding of which is necessary for improvement of development of tau as a biomarker of response and a target for increasing response to taxane treatment.

Inclusion of the C-Terminal Domain in the β-Sheet Core of Heparin-Fibrillized Three-Repeat Tau Protein Revealed by Solid-State Nuclear Magnetic Resonance Spectroscopy

Many neurodegenerative diseases such as Alzheimer's disease are characterized by pathological β-sheet filaments of the tau protein, which spread in a prion-like manner in patient brains. To date, high-resolution structures of tau filaments obtained from patient brains show that the β-sheet core only includes portions of the microtubule-binding repeat domains and excludes the C-terminal residues, indicating that the C-terminus is dynamically disordered. Here, we use solid-state NMR spectroscopy to identify the β-sheet core of full-length 0N3R tau fibrillized using heparin. Assignment of 13C and 15N chemical shifts of the rigid core of the protein revealed a single predominant β-sheet conformation, which spans not only the R3, R4, R' repeats but also the entire C-terminal domain (CT) of the protein. This massive β-sheet core qualitatively differs from all other tau fibril structures known to date. Using long-range correlation NMR experiments, we found that the R3 and R4 repeats form a β-arch, similar to that seen in some of the brain-derived tau fibrils, but the R1 and R3 domains additionally stack against the CT, reminiscent of previously reported transient interactions of the CT with the microtubule-binding repeats. This expanded β-sheet core structure suggests that the CT may have a protective effect against the formation of pathological tau fibrils by shielding the amyloidogenic R3 and R4 domains, preventing side-on nucleation. Truncation and post-translational modification of the CT in vivo may thus play an important role in the progression of tauopathies.

Graph Models of Pathology Spread in Alzheimer's Disease: An Alternative to Conventional Graph Theoretic Analysis

Background: Graph theory and connectomics are new techniques for uncovering disease-induced changes in the brain's structural network. Most prior studied have focused on network statistics as biomarkers of disease. However, an emerging body of work involves exploring how the network serves as a conduit for the propagation of disease factors in the brain and has successfully mapped the functional and pathological consequences of disease propagation. In Alzheimer's disease (AD), progressive deposition of misfolded proteins amyloid and tau is well-known to follow fiber projections, under a "prion-like" trans-neuronal transmission mechanism, through which misfolded proteins cascade along neuronal pathways, giving rise to network spread. Methods: In this review, we survey the state of the art in mathematical modeling of connectome-mediated pathology spread in AD. Then we address several open questions that are amenable to mathematically precise parsimonious modeling of pathophysiological processes, extrapolated to the whole brain. We specifically identify current formal models of how misfolded proteins are produced, aggregate, and disseminate in brain circuits, and attempt to understand how this process leads to stereotyped progression in Alzheimer's and other related diseases. Conclusion: This review serves to unify current efforts in modeling of AD progression that together have the potential to explain observed phenomena and serve as a test-bed for future hypothesis generation and testing in silico. Impact statement Graph theory is a powerful new approach that is transforming the study of brain processes. There do not exist many focused reviews of the subfield of graph modeling of how Alzheimer's and other dementias propagate within the brain network, and how these processes can be mapped mathematically. By providing timely and topical review of this subfield, we fill a critical gap in the community and present a unified view that can serve as an in silico test-bed for future hypothesis generation and testing. We also point to several open and unaddressed questions and controversies that future practitioners can tackle.

Alzheimer's Disease Animal Models: Elucidation of Biomarkers and Therapeutic Approaches for Cognitive Impairment

Alzheimer’s disease (AD) is an age-related and progressive neurodegenerative disorder. It is widely accepted that AD is mainly caused by the accumulation of extracellular amyloid β (Aβ) and intracellular neurofibrillary tau tangles. Aβ begins to accumulate years before the onset of cognitive impairment, suggesting that the benefit of currently available interventions would be greater if they were initiated in the early phases of AD. To understand the mechanisms of AD pathogenesis, various transgenic mouse models with an accelerated accumulation of Aβ and tau tangles have been developed. However, none of these models exhibit all pathologies present in human AD. To overcome these undesirable phenotypes, APP knock-in mice, which were presented with touchscreen-based tasks, were developed to better evaluate the efficacy of candidate therapeutics in mouse models of early-stage AD. This review assesses several AD mouse models from the aspect of biomarkers and cognitive impairment and discusses their potential as tools to provide novel AD therapeutic approaches.

Prolonged arsenic exposure increases tau phosphorylation in differentiated SH-SY5Y cells: The contribution of GSK3 and ERK1/2

Arsenic is a metalloid that has been hypothesized to be an environmental risk factor for Alzheimer's disease (AD), a disease having hyperphosphorylated tau aggregate as a marker. The present study demonstrated that prolonged exposure to sodium arsenite at low micromolar range (1-10 μM) reduced Tau 1 (recognizing dephosphorylated tau at residues 189-207) and elevated pS202 tau in differentiated human neuroblastoma SH-SY5Y cells indicating that arsenic increases tau phosphorylation in neurons. Sodium arsenite elevated GSK3β kinase activity, while GSK3 inhibitors, BIO, SB216763, and lithium, reversed the Tau 1 reduction by sodium arsenite. Additionally, sodium arsenite increased levels of active phosphorylation of ERK1/2, and inhibition of ERK1/2 by U0126 partially improved the Tau1 reduction. These results suggest that arsenic may cause tau hyperphosphorylation in neurons through the activation of GSK3 and ERK1/2. Furthermore, sodium arsenite augmented tau phosphorylation in the membrane and cytosolic fractions. Inductions of GSK3 activity by sodium arsenite treatment were observed in the membrane fraction, as evidenced by a reduction of β-catenin, a protein signaled for degradation following phosphorylation by GSK3. An enhancement of ERK1/2 phosphorylation by sodium arsenite was also witnessed in the cytosol. Additionally, sodium arsenite increased insoluble tau aggregation. These results suggest that arsenic induces tau hyperphosphorylation in the membrane fraction which may lead to its redistribution from the membrane fraction to the cytosol, where it promotes neurofibrillary formation. Collectively, we demonstrate that prolonged arsenic exposure increases tau phosphorylation, partly through GSK3 and ERK1/2 activation, and insoluble tau aggregates, hence possibly contributing to the development of sporadic AD.

High-fat diet-induced activation of SGK1 promotes Alzheimer's disease-associated tau pathology

Type 2 diabetes mellitus (T2DM) has long been considered a risk factor for Alzheimer’s disease (AD). However, the molecular links between T2DM and AD remain obscure. Here, we reported that serum-/glucocorticoid-regulated kinase 1 (SGK1) is activated by administering a chronic high-fat diet (HFD), which increases the risk of T2DM, and thus promotes Tau pathology via the phosphorylation of tau at Ser214 and the activation of a key tau kinase, namely, GSK-3ß, forming SGK1-GSK-3ß-tau complex. SGK1 was activated under conditions of elevated glucocorticoid and hyperglycemia associated with HFD, but not of fatty acid–mediated insulin resistance. Elevated expression of SGK1 in the mouse hippocampus led to neurodegeneration and impairments in learning and memory. Upregulation and activation of SGK1, SGK1-GSK-3ß-tau complex were also observed in the hippocampi of AD cases. Our results suggest that SGK1 is a key modifier of tau pathology in AD, linking AD to corticosteroid effects and T2DM.

SH-SY5Y-derived neurons: a human neuronal model system for investigating TAU sorting and neuronal subtype-specific TAU vulnerability

The microtubule-associated protein (MAP) TAU is mainly sorted into the axon of healthy brain neurons. Somatodendritic missorting of TAU is a pathological hallmark of many neurodegenerative diseases, including Alzheimer's disease (AD). Cause, consequence and (patho)physiological mechanisms of TAU sorting and missorting are understudied, in part also because of the lack of readily available human neuronal model systems. The human neuroblastoma cell line SH-SY5Y is widely used for studying TAU physiology and TAU-related pathology in AD and related tauopathies. SH-SY5Y cells can be differentiated into neuron-like cells (SH-SY5Y-derived neurons) using various substances. This review evaluates whether SH-SY5Y-derived neurons are a suitable model for (i) investigating intracellular TAU sorting in general, and (ii) with respect to neuron subtype-specific TAU vulnerability. (I) SH-SY5Y-derived neurons show pronounced axodendritic polarity, high levels of axonally localized TAU protein, expression of all six human brain isoforms and TAU phosphorylation similar to the human brain. As SH-SY5Y cells are highly proliferative and readily accessible for genetic engineering, stable transgene integration and leading-edge genome editing are feasible. (II) SH-SY5Y-derived neurons display features of subcortical neurons early affected in many tauopathies. This allows analyzing brain region-specific differences in TAU physiology, also in the context of differential vulnerability to TAU pathology. However, several limitations should be considered when using SH-SY5Y-derived neurons, e.g., the lack of clearly defined neuronal subtypes, or the difficulty of mimicking age-related tauopathy risk factors in vitro. In brief, this review discusses the suitability of SH-SY5Y-derived neurons for investigating TAU (mis)sorting mechanisms and neuron-specific TAU vulnerability in disease paradigms.

Knockdown of long non-coding RNA SOX21-AS1 attenuates amyloid-β-induced neuronal damage by sponging miR-107

BACKGROUND

Alzheimer's disease (AD), which has no effective drugs to delay or prevent its progression, is a multifactorial complex neurodegenerative disease. Long non-coding RNA SOX21 antisense RNA1 (SOX21-AS1) is associated with the development of AD, but the underlying molecular mechanism of SOX21-AS1 in AD is still largely unclear.

METHODS

To construct the AD model, SH-SY5Y and SK-N-SH cells were treated with amyloid-β1-42 (Aβ1-42). Quantitative real-time polymerase chain reaction (qRT-PCR) was executed to detect the expression of SOX21-AS1 and miRNA-107. Western blot analysis was utilized to assess the levels of phosphorylated Tau (p-Tau). 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) or flow cytometry assay was employed to determine the viability and apoptosis of SH-SY5Y and SK-N-SH cells. The relationship between SOX21-AS1 and miRNA-107 was verified with the dual-luciferase reporter assay.

RESULTS

SOX21-AS1 expression was augmented while miR-107 expression was decreased in Aβ1-42-treated SH-SY5Y and SK-N-SH cells. Moreover, Aβ1-42 elevated the levels of p-Tau and impeded viability and induced apoptosis of SH-SY5Y and SK-N-SH cells. Also, SOX21-AS1 silencing attenuated Aβ1-42 mediated the levels of p-Tau, viability, and apoptosis of SH-SY5Y and SK-N-SH cells. Importantly, SOX21-AS1 acted as a sponge for miR-107 in SH-SY5Y and SK-N-SH cells. Furthermore, the increase in p-Tau levels and apoptosis and the repression of viability of Aβ1-42-treated SH-SY5Y and SK-N-SH cells mediated by miR-107 inhibition were partly recovered by SOX21-AS1 depletion.

CONCLUSION

SOX21-AS1 silencing could attenuate Aβ1-42-induced neuronal damage by sponging miR-107, which provided a possible strategy for the treatment of AD.

GSK-3 and Tau: A Key Duet in Alzheimer's Disease

Glycogen synthase kinase-3 (GSK-3) is a ubiquitously expressed serine/threonine kinase with a plethora of substrates. As a modulator of several cellular processes, GSK-3 has a central position in cell metabolism and signaling, with important roles both in physiological and pathological conditions. GSK-3 has been associated with a number of human disorders, such as neurodegenerative diseases including Alzheimer’s disease (AD). GSK-3 contributes to the hyperphosphorylation of tau protein, the main component of neurofibrillary tangles (NFTs), one of the hallmarks of AD. GSK-3 is further involved in the regulation of different neuronal processes that are dysregulated during AD pathogenesis, such as the generation of amyloid-β (Aβ) peptide or Aβ-induced cell death, axonal transport, cholinergic function, and adult neurogenesis or synaptic function. In this review, we will summarize recent data about GSK-3 involvement in these processes contributing to AD pathology, mostly focusing on the crucial interplay between GSK-3 and tau protein. We further discuss the current development of potential AD therapies targeting GSK-3 or GSK-3-phosphorylated tau.

A common theme for axonopathies? The dependency cycle of local axon homeostasis

The number of acquired or inherited conditions leading to axon degeneration (from now on referred to as axonopathies) is vast. To diagnose patients, clinicians use a range of indicators including physiology, morphology, family and patient history, as well as genetics, with the specific location of the lesion within the nervous system being a prominent feature. For the neurobiologist, these criteria are often unsatisfactory, and key questions remain unanswered. For example, does it make sense that different axonopathies affect distinct neuron groups through distinct mechanisms? Would it not be more likely that there are common routes to axon degeneration? In this opinion piece, I shall pose this fundamental question and try to find answers that are hopefully thought-provoking and trigger some conceptual rethinking in the field. I will conclude by describing the 'dependency cycle of axon homeostasis' as a new approach to make sense of the intricate connections of axon biology and physiology, also suggesting that different axonopathies might share common paths to axon degeneration.

Cognitive Improvement and Safety Assessment of a Dietary Supplement Containing Propolis Extract in Elderly Japanese: A Placebo-Controlled, Randomized, Parallel-Group, Double-Blind Human Clinical Study

Objectives. This study aimed to evaluate the effect of propolis on cognitive function in elderly Japanese with a placebo-controlled design. Material and Methods. This study was performed on 79 elderly Japanese. Participants orally received either a placebo or dietary supplement containing propolis extract for 24 weeks. Cognitive function assessed by Cognitrax and various blood or urine markers were measured at pre- and postadministration. Results and Conclusion. Eligible data from 68 subjects (placebo: 33, propolis: 35) who completed the study were analyzed. Compared to the placebo group, the propolis group showed significant improvement in verbal memory in Cognitrax (P=0.028). Total cholesterol, LDL cholesterol, urea nitrogen, creatinine, and uric acid were significantly improved in the propolis group compared to the placebo group (P = 0.011, P = 0.004, P = 0.048, P = 0.045, and P = 0.005, respectively). However, urea nitrogen, creatinine, and uric acid fluctuated within the normal level. Furthermore, a subgroup analysis was performed on those with higher than 100 of the standardized score of the neurocognitive index indicated by the overall Cognitrax score. Significant improvements in the propolis group compared to placebo were confirmed in verbal memory (P = 0.007) and processing speed as indications for information processing ability, complex attention, and concentration (P = 0.029). No side effects were observed in any of the groups. This study demonstrates that propolis is effective in improving cognitive functions such as memory, information processing, complex attention, and concentration in elderly Japanese.

Conformational fingerprinting of tau variants and strains by Raman spectroscopy

Tauopathies are a group of disorders in which the deposition of abnormally folded tau protein accompanies neurodegeneration. The development of methods for detection and classification of pathological changes in protein conformation are desirable for understanding the factors that influence the structural polymorphism of aggregates in tauopathies. We have previously demonstrated the utility of Raman spectroscopy for the characterization and discrimination of different protein aggregates, including tau, based on their unique conformational signatures. Building on this, in the present study, we assess the utility of Raman spectroscopy for characterizing and distinguishing different conformers of the same protein which in the case of tau are unique tau strains generated in vitro. We now investigate the impact of aggregation environment, cofactors, post-translational modification and primary sequence on the Raman fingerprint of tau fibrils. Using quantitative conformational fingerprinting and multivariate statistical analysis, we found that the aggregation of tau in different buffer conditions resulted in the formation of distinct fibril strains. Unique spectral markers were identified for tau fibrils generated using heparin or RNA cofactors, as well as for phosphorylated tau. We also determined that the primary sequence of the tau monomer influenced the conformational signature of the resulting tau fibril, including 2N4R, 0N3R, K18 and P301S tau variants. These results highlight the conformational polymorphism of tau fibrils, which is reflected in the wide range of associated neurological disorders. Furthermore, the analyses presented in this study provide a benchmark for the Raman spectroscopic characterization of tau strains, which may shed light on how the aggregation environment, cofactors and post-translational modifications influence tau conformation in vivo in future studies.

Impact of chronic hyperglycemia on Small Heat Shock Proteins in diabetic rat brain

Small heat shock proteins (sHsps) are a family of proteins. Some are induced in response to multiple stimuli and others are constitutively expressed. They are involved in fundamental cellular processes, including protein folding, apoptosis, and maintenance of cytoskeletal integrity. Hyperglycemia created during diabetes leads to neuronal derangements in the brain. In this study, we investigated the impact of chronic hyperglycemia on the expression of sHsps and heat shock transcription factors (HSFs), solubility and aggregation of sHsps and amyloidogenic proteins, and their role in neuronal apoptosis in a diabetic rat model. Diabetes was induced in Sprague-Dawley rats with streptozotocin and hyperglycemia was maintained for 16 weeks. Expressions of sHsps and HSFs were analyzed by qRT-PCR and immunoblotting in the cerebral cortex. Solubility of sHsps and amyloidogenic proteins, including α-synuclein and Tau, was analyzed by the detergent soluble assay. Neuronal cell death was analyzed by TUNEL staining and apoptotic markers. The interaction of sHsps with amyloidogenic proteins and Bax was assessed using co-immunoprecipitation. Hyperglycemia decreased Hsp27 and HSF1, and increased αBC, Hsp22, and HSF4 levels at transcript and protein levels. Diabetes induced the aggregation of αBC, Hsp22, α-synuclein, and pTau, as their levels were higher in the insoluble fraction. Additionally, diabetes impaired the interaction of αBC with α-synuclein and pTau. Furthermore, diabetes reduced the interaction of αBC with Bax, which may possibly contribute to neuronal apoptosis. Together, these results indicate that chronic hyperglycemia induces differential responses of sHsps by altering their expression, solubility, interaction, and roles in apoptosis.

Imaging Techniques in Alzheimer's Disease: A Review of Applications in Early Diagnosis and Longitudinal Monitoring

BACKGROUND

Alzheimer's disease (AD) is a progressive neurodegenerative disorder affecting many individuals worldwide with no effective treatment to date. AD is characterized by the formation of senile plaques and neurofibrillary tangles, followed by neurodegeneration, which leads to cognitive decline and eventually death.

INTRODUCTION

In AD, pathological changes occur many years before disease onset. Since disease-modifying therapies may be the most beneficial in the early stages of AD, biomarkers for the early diagnosis and longitudinal monitoring of disease progression are essential. Multiple imaging techniques with associated biomarkers are used to identify and monitor AD.

AIM

In this review, we discuss the contemporary early diagnosis and longitudinal monitoring of AD with imaging techniques regarding their diagnostic utility, benefits and limitations. Additionally, novel techniques, applications and biomarkers for AD research are assessed.

FINDINGS

Reduced hippocampal volume is a biomarker for neurodegeneration, but atrophy is not an AD-specific measure. Hypometabolism in temporoparietal regions is seen as a biomarker for AD. However, glucose uptake reflects astrocyte function rather than neuronal function. Amyloid-β (Aβ) is the earliest hallmark of AD and can be measured with positron emission tomography (PET), but Aβ accumulation stagnates as disease progresses. Therefore, Aβ may not be a suitable biomarker for monitoring disease progression. The measurement of tau accumulation with PET radiotracers exhibited promising results in both early diagnosis and longitudinal monitoring, but large-scale validation of these radiotracers is required. The implementation of new processing techniques, applications of other imaging techniques and novel biomarkers can contribute to understanding AD and finding a cure.

CONCLUSIONS

Several biomarkers are proposed for the early diagnosis and longitudinal monitoring of AD with imaging techniques, but all these biomarkers have their limitations regarding specificity, reliability and sensitivity. Future perspectives. Future research should focus on expanding the employment of imaging techniques and identifying novel biomarkers that reflect AD pathology in the earliest stages.

Kinase Signaling in Dendritic Development and Disease

Dendrites undergo extensive growth and remodeling during their lifetime. Specification of neurites into dendrites is followed by their arborization, maturation, and functional integration into synaptic networks. Each of these distinct developmental processes is spatially and temporally controlled in an exquisite fashion. Protein kinases through their highly specific substrate phosphorylation regulate dendritic growth and plasticity. Perturbation of kinase function results in aberrant dendritic growth and synaptic function. Not surprisingly, kinase dysfunction is strongly associated with neurodevelopmental and psychiatric disorders. Herein, we review, (a) key kinase pathways that regulate dendrite structure, function and plasticity, (b) how aberrant kinase signaling contributes to dendritic dysfunction in neurological disorders and (c) emergent technologies that can be applied to dissect the role of protein kinases in dendritic structure and function.

Preclinical and clinical biomarker studies of CT1812: A novel approach to Alzheimer's disease modification

INTRODUCTION

Amyloid beta (Aβ) oligomers are one of the most toxic structural forms of the Aβ protein and are hypothesized to cause synaptotoxicity and memory failure as they build up in Alzheimer's disease (AD) patients' brain tissue. We previously demonstrated that antagonists of the sigma-2 receptor complex effectively block Aβ oligomer toxicity. CT1812 is an orally bioavailable, brain penetrant small molecule antagonist of the sigma-2 receptor complex that appears safe and well tolerated in healthy elderly volunteers. We tested CT1812's effect on Aβ oligomer pathobiology in preclinical AD models and evaluated CT1812's impact on cerebrospinal fluid (CSF) protein biomarkers in mild to moderate AD patients in a clinical trial (ClinicalTrials.gov NCT02907567).

METHODS

Experiments were performed to measure the impact of CT1812 versus vehicle on Aβ oligomer binding to synapses in vitro, to human AD patient post mortem brain tissue ex vivo, and in living APP_Swe /PS1dE9 transgenic mice in vivo. Additional experiments were performed to measure the impact of CT1812 versus vehicle on Aβ oligomer-induced deficits in membrane trafficking rate, synapse number, and protein expression in mature hippocampal/cortical neurons in vitro. The impact of CT1812 on cognitive function was measured in transgenic Thy1 huAPP^Swe/Lnd+ and wild-type littermates. A multicenter, double-blind, placebo-controlled parallel group trial was performed to evaluate the safety, tolerability, and impact on protein biomarker expression of CT1812 or placebo given once daily for 28 days to AD patients (Mini-Mental State Examination 18-26). CSF protein expression was measured by liquid chromatography with tandem mass spectrometry or enzyme-linked immunosorbent assay in samples drawn prior to dosing (Day 0) and at end of dosing (Day 28) and compared within each patient and between pooled treated versus placebo-treated dosing groups.

RESULTS

CT1812 significantly and dose-dependently displaced Aβ oligomers bound to synaptic receptors in three independent preclinical models of AD, facilitated oligomer clearance into the CSF, increased synaptic number and protein expression in neurons, and improved cognitive performance in transgenic mice. CT1812 significantly increased CSF concentrations of Aβ oligomers in AD patient CSF, reduced concentrations of synaptic proteins and phosphorylated tau fragments, and reversed expression of many AD-related proteins dysregulated in CSF.

DISCUSSION

These preclinical studies demonstrate the novel disease-modifying mechanism of action of CT1812 against AD and Aβ oligomers. The clinical results are consistent with preclinical data and provide evidence of target engagement and impact on fundamental disease-related signaling pathways in AD patients, supporting further development of CT1812.

Similarities and Differences in the Pattern of Tau Hyperphosphorylation in Physiological and Pathological Conditions: Impacts on the Elaboration of Therapies to Prevent Tau Pathology

Tau protein, a neuronal microtubule-associated protein, becomes hyperphosphorylated in several neurodegenerative diseases called tauopathies. Hyperphosphorylation of tau is correlated to its redistribution from the axon to the somato-dendritic compartment at early stages of tauopathies. Interestingly, tau hyperphosphorylation begins in different regions of the brain in each tauopathy. In some regions, both neurons and glial cells develop tau hyperphosphorylation. Tau hyperphosphorylation is also observed in physiological conditions such as hibernation and brain development. In the first section of present article, we will review the spatiotemporal and cellular distribution of hyperphosphorylated tau in the most frequent tauopathies. In the second section, we will compare the pattern of tau hyperphosphorylation in physiological and pathological conditions and discuss the sites that could play a pivotal role in the conversion of non-toxic to toxic forms of hyperphosphorylated tau. Furthermore, we will discuss the role of hyperphosphorylated tau in physiological and pathological conditions and the fact that tau hyperphosphorylation is reversible in physiological conditions but not in a pathological ones. In the third section, we will speculate how the differences and similarities between hyperphosphorylated tau in physiological and pathological conditions could impact the elaboration of therapies to prevent tau pathology. In the fourth section, the different therapeutic approaches using tau as a direct or indirect therapeutic target will be presented.

Tau Post-translational Modifications: Dynamic Transformers of Tau Function, Degradation, and Aggregation

Post-translational modifications (PTMs) on tau have long been recognized as affecting protein function and contributing to neurodegeneration. The explosion of information on potential and observed PTMs on tau provides an opportunity to better understand these modifications in the context of tau homeostasis, which becomes perturbed with aging and disease. Prevailing views regard tau as a protein that undergoes abnormal phosphorylation prior to its accumulation into the toxic aggregates implicated in Alzheimer's disease (AD) and other tauopathies. However, the phosphorylation of tau may, in fact, represent part of the normal but interrupted function and catabolism of the protein. In addition to phosphorylation, tau undergoes another forms of post-translational modification including (but not limited to), acetylation, ubiquitination, glycation, glycosylation, SUMOylation, methylation, oxidation, and nitration. A holistic appreciation of how these PTMs regulate tau during health and are potentially hijacked in disease remains elusive. Recent studies have reinforced the idea that PTMs play a critical role in tau localization, protein-protein interactions, maintenance of levels, and modifying aggregate structure. These studies also provide tantalizing clues into the possibility that neurons actively choose how tau is post-translationally modified, in potentially competitive and combinatorial ways, to achieve broad, cellular programs commensurate with the distinctive environmental conditions found during development, aging, stress, and disease. Here, we review tau PTMs and describe what is currently known about their functional impacts. In addition, we classify these PTMs from the perspectives of protein localization, electrostatics, and stability, which all contribute to normal tau function and homeostasis. Finally, we assess the potential impact of tau PTMs on tau solubility and aggregation. Tau occupies an undoubtedly important position in the biology of neurodegenerative diseases. This review aims to provide an integrated perspective of how post-translational modifications actively, purposefully, and dynamically remodel tau function, clearance, and aggregation. In doing so, we hope to enable a more comprehensive understanding of tau PTMs that will positively impact future studies.

Subchronic exposure to acrylamide caused behaviour disorders and related pathological and molecular changes in rat cerebellum

Acrylamide (ACR) is a neurotoxin with moderate acute toxicity. Significant level of ACR exists in diet and drinking water. Occupational exposure causes motor function impairment, but the underlying mechanisms remain poorly defined. This study aims to explore whether microtubule-associated protein tau phosphorylation, excessive activation of protein kinase RNA-like endoplasmic reticulum kinase (PERK) signaling pathway and BDNF decline are involved in cerebellar neuron lesions and motor dysfunction after subchronic ACR exposure. The present results displayed that ACR caused gait abnormality and hind foot splay in rats. The HE and Nissl staining results revealed that ACR exposure aggravated cerebellar neuron lesions especially in purkinje cell layer. ACR markedly increased tau phosphorylation at Ser262 and Ser396/404 and inhibited the level of phosphorylation of glycogen synthase kinase 3β (P-GSK3β) at Ser9. The PERK-eukaryotic initiation factor-2α (eIF2α)-activating transcription factor 4 (ATF4) pathway was activated to promote CHOP expression and then to accelerate neuron lesions. Furthermore, ACR significantly decreased P-CREB at Ser133 and BDNF expression, which might be related to the inhibition of upstream signals from extracellular signal-related kinase (ERK) and protein kinase B (Akt). This work helps to elucidate the underlying mechanisms of ACR-induced neurotoxicity and present a potential target for prevention against the neurotoxicity.

Journey on Naphthoquinone and Anthraquinone Derivatives: New Insights in Alzheimer's Disease

Alzheimer’s disease (AD) is a progressive neurodegenerative disease that is characterized by memory loss, cognitive impairment, and functional decline leading to dementia and death. AD imposes neuronal death by the intricate interplay of different neurochemical factors, which continue to inspire the medicinal chemist as molecular targets for the development of new agents for the treatment of AD with diverse mechanisms of action, but also depict a more complex AD scenario. Within the wide variety of reported molecules, this review summarizes and offers a global overview of recent advancements on naphthoquinone (NQ) and anthraquinone (AQ) derivatives whose more relevant chemical features and structure-activity relationship studies will be discussed with a view to providing the perspective for the design of viable drugs for the treatment of AD. In particular, cholinesterases (ChEs), β-amyloid (Aβ) and tau proteins have been identified as key targets of these classes of compounds, where the NQ or AQ scaffold may contribute to the biological effect against AD as main unit or significant substructure. The multitarget directed ligand (MTDL) strategy will be described, as a chance for these molecules to exhibit significant potential on the road to therapeutics for AD.

Multifunctional compounds for the treatment of Alzheimer’s disease

Alzheimer’s disease (AD) is the most common form of dementia, and the prevalence of this currently untreatable disease is expected to rise in step with increased global life expectancy. AD is a multifaceted disorder commonly characterized by extracellular amyloid–beta (Aβ) aggregates, oxidative stress, metal ion dysregulation, and intracellular neurofibrillary tangles. This review will focus on medicinal inorganic chemistry strategies to target AD, with a focus on the Aβ peptide and its relation to metal ion dysregulation and oxidative stress. Multifunctional compounds designed to target multiple disease processes have emerged as promising therapeutic options, and recent reports detailing multifunctional metal-binding compounds, as well as discrete metal complexes, will be discussed.

Relevance of 5-HT2A Receptor Modulation of Pyramidal Cell Excitability for Dementia-Related Psychosis: Implications for Pharmacotherapy

Psychosis occurs across a wide variety of dementias with differing etiologies, including Alzheimer's dementia, Parkinson's dementia, Lewy body dementia, frontotemporal dementia, and vascular dementia. Pimavanserin, a selective serotonin 5-HT_2A receptor (5-HT_2AR) inverse agonist, has shown promising results in clinical trials by reducing the frequency and/or severity of hallucinations and delusions and the risk of relapse of these symptoms in patients with dementia-related psychosis. A literature review was conducted to identify mechanisms that explain the role of 5-HT_2ARs in both the etiology and treatment of dementia-related psychosis. This review revealed that most pathological changes commonly associated with neurodegenerative diseases cause one or more of the following events to occur: reduced synaptic contact of gamma aminobutyric acid (GABA)-ergic interneurons with glutamatergic pyramidal cells, reduced cortical innervation from subcortical structures, and altered 5-HT_2AR expression levels. Each of these events promotes increased pyramidal cell hyperexcitability and disruption of excitatory/inhibitory balance, facilitating emergence of psychotic behaviors. The brain regions affected by these pathological changes largely coincide with areas expressing high levels of 5-HT_2ARs. At the cellular level, 5-HT_2ARs are most highly expressed on cortical glutamatergic pyramidal cells, where they regulate pyramidal cell excitability. The common effects of different neurodegenerative diseases on pyramidal cell excitability together with the close anatomical and functional connection of 5-HT_2ARs to pyramidal cell excitability may explain why suppressing 5-HT_2AR activity could be an effective strategy to treat dementia-related psychosis.

Disrupted ubiquitin proteasome system underlying tau accumulation in Alzheimer's disease

Accumulation of phosphorylated tau (p-tau) has long been an underappreciated hallmark of Alzheimer's disease. Tau is one of the major components of microtubule networks in neurons, and its abnormal phosphorylation and aggregation are closely related to the impairment of axonal transport. Abnormalities in axonal transport can impede autophagy in neurons, interrupting the autophagic clearance of amyloid beta. The ubiquitin proteasome system (UPS) maintains intracellular proteostasis by degrading abnormal or redundant proteins. Ever-mounting evidence suggests that UPS deficits contribute to p-tau accumulation. And targeting UPS attenuates tau pathology. This review endeavors to exam the potential role of UPS in p-tau aggregation, and how pathogenic tau may inflict other abnormalities such as amyloid beta accumulation in Alzheimer's disease.

Tauopathies: Deciphering Disease Mechanisms to Develop Effective Therapies

Tauopathies are neurodegenerative diseases characterized by the pathological accumulation of microtubule-associated protein tau (MAPT) in the form of neurofibrillary tangles and paired helical filaments in neurons and glia, leading to brain cell death. These diseases include frontotemporal dementia (FTD) and Alzheimer's disease (AD) and can be sporadic or inherited when caused by mutations in the MAPT gene. Despite an incredibly high socio-economic burden worldwide, there are still no effective disease-modifying therapies, and few tau-focused experimental drugs have reached clinical trials. One major hindrance for therapeutic development is the knowledge gap in molecular mechanisms of tau-mediated neuronal toxicity and death. For the promise of precision medicine for brain disorders to be fulfilled, it is necessary to integrate known genetic causes of disease, i.e., MAPT mutations, with an understanding of the dysregulated molecular pathways that constitute potential therapeutic targets. Here, the growing understanding of known and proposed mechanisms of disease etiology will be reviewed, together with promising experimental tau-directed therapeutics, such as recently developed tau degraders. Current challenges faced by the fields of tau research and drug discovery will also be addressed.

Targeting Tau to Treat Clinical Features of Huntington's Disease

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder characterized by severe motor, cognitive and psychiatric impairments. While motor deficits often confirm diagnosis, cognitive dysfunctions usually manifest early in the disease process and are consistently ranked among the leading factors that impact the patients' quality of life. The genetic component of HD, a mutation in the huntingtin (HTT) gene, is traditionally presented as the main contributor to disease pathology. However, accumulating evidence suggests the implication of the microtubule-associated tau protein to the pathogenesis and therefore, proposes an alternative conceptual framework where tau and mutant huntingtin (mHTT) act conjointly to drive neurodegeneration and cognitive dysfunction. This perspective on disease etiology offers new avenues to design therapeutic interventions and could leverage decades of research on Alzheimer's disease (AD) and other tauopathies to rapidly advance drug discovery. In this mini review, we examine the breadth of tau-targeting treatments currently tested in the preclinical and clinical settings for AD and other tauopathies, and discuss the potential application of these strategies to HD.