Targeting Post-translational Modifications on Tau as a Therapeutic Strategy for Alzheimer's Disease

Heparan sulfate proteoglycans: Mediators of cellular and molecular Alzheimer's disease pathogenic factors via tunnelling nanotubes?

Neurological disorders impact around one billion individuals globally (15 % approx.), with significant implications for disability and mortality with their impact in Australia currently amounts to 6.8 million deaths annually. Heparan sulfate proteoglycans (HSPGs) are complex extracellular molecules implicated in promoting Tau fibril formation resulting in Tau tangles, a hallmark of Alzheimer's disease (AD). HSPG-Tau protein interactions contribute to various AD stages via aggregation, toxicity, and clearance, largely via interactions with the glypican 1 and syndecan 3 core proteins. The tunnelling nanotubes (TNTs) pathway is emerging as a facilitator of intercellular molecule transport, including Tau and Amyloid β proteins, across extensive distances. While current TNT-associated evidence primarily stems from cancer models, their role in Tau propagation and its effects on recipient cells remain unclear. This review explores the interplay of TNTs, HSPGs, and AD-related factors and proposes that HSPGs influence TNT formation in neurodegenerative conditions such as AD.

Monoclonal antibody therapy for Alzheimer's disease focusing on intracerebral targets

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases. Due to the complexity of the disorder and the presence of the blood-brain barrier (BBB), its drug discovery and development are facing enormous challenges, especially after several failures of monoclonal antibody (mAb) trials. Nevertheless, the Food and Drug Administration's approval of the mAb aducanumab has ushered in a new day. As we better understand the disease's pathogenesis and identify novel intracerebral therapeutic targets, antibody-based therapies have advanced over the past few years. The mAb drugs targeting β-amyloid or hyperphosphorylated tau protein are the focus of the current research. Massive neuronal loss and glial cell-mediated inflammation are also the vital pathological hallmarks of AD, signaling a new direction for research on mAb drugs. We have elucidated the mechanisms by which AD-specific mAbs cross the BBB to bind to targets. In order to investigate therapeutic approaches to treat AD, this review focuses on the promising mAbs targeting intracerebral dysfunction and related strategies to cross the BBB.

Modulation of Tau Pathology in Alzheimer's Disease by Dietary Bioactive Compounds

Tau is a microtubule-associated protein essential for microtubule assembly and stability in neurons. The abnormal intracellular accumulation of tau aggregates is a major characteristic of brains from patients with Alzheimer's disease (AD) and other tauopathies. In AD, the presence of neurofibrillary tangles (NFTs), which is composed of hyperphosphorylated tau protein, is positively correlated with the severity of the cognitive decline. Evidence suggests that the accumulation and aggregation of tau cause synaptic dysfunction and neuronal degeneration. Thus, the prevention of abnormal tau phosphorylation and elimination of tau aggregates have been proposed as therapeutic strategies for AD. However, currently tau-targeting therapies for AD and other tauopathies are limited. A number of dietary bioactive compounds have been found to modulate the posttranslational modifications of tau, including phosphorylation, small ubiquitin-like modifier (SUMO) mediated modification (SUMOylation) and acetylation, as well as inhibit tau aggregation and/or promote tau degradation. The advantages of using these dietary components over synthetic substances in AD prevention and intervention are their safety and accessibility. This review summarizes the mechanisms leading to tau pathology in AD and highlights the effects of bioactive compounds on the hyperphosphorylation, aggregation and clearance of tau protein. The potential of using these bioactive compounds for AD prevention and intervention is also discussed.

Traumatic brain injury and the pathways to cerebral tau accumulation

Tau is a protein that has received national mainstream recognition for its potential negative impact to the brain. This review succinctly provides information on the structure of tau and its normal physiological functions, including in hibernation and changes throughout the estrus cycle. There are many pathways involved in phosphorylating tau including diabetes, stroke, Alzheimer's disease (AD), brain injury, aging, and drug use. The common mechanisms for these processes are put into context with changes observed in mild and repetitive mild traumatic brain injury (TBI). The phosphorylation of tau is a part of the progression to pathology, but the ability for tau to aggregate and propagate is also addressed. Summarizing both the functional and dysfunctional roles of tau can help advance our understanding of this complex protein, improve our care for individuals with a history of TBI, and lead to development of therapeutic interventions to prevent or reverse tau-mediated neurodegeneration.

Therapeutic modulation of JAK-STAT, mTOR, and PPAR-γ signaling in neurological dysfunctions

The cytokine-activated Janus kinase (JAK)-signal transducer and activator of transcription (STAT) cascade is a pleiotropic pathway that involves receptor subunit multimerization. The mammalian target of rapamycin (mTOR) is a ubiquitously expressed serine-threonine kinase that perceives and integrates a variety of intracellular and environmental stimuli to regulate essential activities such as cell development and metabolism. Peroxisome proliferator-activated receptor-gamma (PPARγ) is a prototypical metabolic nuclear receptor involved in neural differentiation and axon polarity. The JAK-STAT, mTOR, and PPARγ signaling pathways serve as a highly conserved signaling hub that coordinates neuronal activity and brain development. Additionally, overactivation of JAK/STAT, mTOR, and inhibition of PPARγ signaling have been linked to various neurocomplications, including neuroinflammation, apoptosis, and oxidative stress. Emerging research suggests that even minor disruptions in these cellular and molecular processes can have significant consequences manifested as neurological and neuropsychiatric diseases. Of interest, target modulators have been proven to alleviate neuronal complications associated with acute and chronic neurological deficits. This research-based review explores the therapeutic role of JAK-STAT, mTOR, and PPARγ signaling modulators in preventing neuronal dysfunctions in preclinical and clinical investigations.

The Mechanism of Two Benzaldehydes from Aspergillus terreus C23-3 Improve Neuroinflammatory and Neuronal Damage to Delay the Progression of Alzheimer's Disease

Alzheimer's disease (AD), a neurodegenerative disease, is the most common cause of dementia in humans worldwide. Although more in-depth research has been carried out on AD, the therapeutic effect of AD is not as expected, and natural active substances are increasingly sought after by scientists. In the present study, we evaluated two benzaldehydes from a coral-derived Aspergillus terreus strain C23-3, their anti-neuroinflammatory activity in microglia (BV-2), and their neuroprotective activity and mechanisms in hippocampal neuronal cells (HT-22). These include the protein expression of iNOS, COX-2, MAPKs pathways, Tau protein-related pathways, caspases family-related signaling pathways. They also include the levels of TNF-α, IL-6, IL-18 and ROS, as well as the level of mitochondrial oxidative stress and neuronal cell apoptosis. The results showed that both benzaldehydes were effective in reducing the secretion of various inflammatory mediators, as well as pro-inflammatory factors. Among these, benzaldehyde 2 inhibited mitochondrial oxidative stress and blocked neuronal cell apoptosis through Tau protein-related pathways and caspases family-related signaling pathways, thereby inhibiting β-amyloid (Aβ)-induced neurological damage. This study reveals that benzaldehyde 2 has potential as a therapeutic agent for Alzheimer's disease, and offers a new approach to the high-value use of marine natural products.

Alzheimer's disease and sleep disorders: Insights into the possible disease connections and the potential therapeutic targets

One of the comorbid conditions in an individual with Alzheimer's disease is a sleep disorder. Clinical features of sleep disorders involve various sleep disturbances such as Obstructive Sleep Apnea (OSAS), Excessive Daytime Sleepiness (EDS), Rapid Eye Movement (REM), Breathing Disorders, Periodic limb movements in sleep (PLMS), etc. The primary tools used for the identification of such disturbances are Polysomnography (PSG) and Wrist actigraphy. This review will highlight and explains the different approaches used in the treatment of sleep disorders. Non-pharmacological treatments include Peter Hauri rules, sleep education program, and light therapy which play a key role in the regulation of sleep-wake cycles. Pharmacological therapy described in this article may be useful in treating sleep destruction in patients with Alzheimer's disease. Along with the Non-pharmacological and pharmacological treatment, here we discuss five commonly recognized plant-based nutraceuticals with hypothesized impact on sleep disorders: caffeine, chamomile, cherries, L-tryptophan, and valerian by the proper emphasis on the known mechanism of their action.

Disease-Modifying Therapies for Alzheimer's Disease: More Questions than Answers

Scientific advances over the last four decades have steadily infused the Alzheimer's disease (AD) field with great optimism that therapies targeting Aβ, amyloid, tau, and innate immune activation states in the brain would provide disease modification. Unfortunately, this optimistic scenario has not yet played out. Though a recent approval of the anti-Aβ aggregate binding antibody, Aduhelm (aducanumab), as a "disease-modifying therapy for AD" is viewed by some as a breakthrough, many remain unconvinced by the data underlying this approval. Collectively, we have not succeeded in changing AD from a largely untreatable, inevitable, and incurable disease to a treatable, preventable, and curable one. Here, I will review the major foci of the AD "disease-modifying" therapeutic pipeline and some of the "open questions" that remain in terms of these therapeutic approaches. I will conclude the review by discussing how we, as a field, might adjust our approach, learning from our past failures to ensure future success.

PIAS3 suppresses damage in an Alzheimer's disease cell model by inducing the STAT3-associated STAT3/Nestin/Nrf2/HO-1 pathway

BACKGROUND

Alzheimer's disease (AD), the most common form of dementia, is caused by the degeneration of the central nervous system (CNS). A previous study reported that signal transducer and activator of transcription 3 (STAT3) is activated during AD development; nonetheless, the related mechanism remains unknown. Thus, this study used a cell model to explore whether and how the protein inhibitor of activated STAT3 (PIAS3) is involved in AD development.

METHODS

Cerebrospinal fluid (CSF) specimens of 30 patients with AD and 10 normal participants were included in this study. SH-SY5Y cells were used to constructed AD model. Relevant indices were then detected and analyzed.

RESULTS

The results showed that compared with the control group, PIAS3 expression was substantially decreased in patients with AD and amyloid beta (Aβ)-treated SH-SY5Y cells. PIAS3 overexpression was able to reverse the detrimental effects of Aβ treatment on cell survival and growth. Further, it could also ameliorate apoptosis and oxidative stress in Aβ-treated SH-SY5Y cells. Additionally, PIAS3 was shown to reduce the activated form of STAT3 and increase the activity of the downstream Nestin/nuclear factor erythroid 2-related factor/heme oxygenase-1 pathway.

CONCLUSIONS

STAT3 reactivation by colivelin treatment negated the influence of PIAS3 on the survival, growth, apoptosis, and oxidative stress of Aβ-treated SH-SY5Y cells.

Protective Effect of Natural Antioxidant, Curcumin Nanoparticles, and Zinc Oxide Nanoparticles against Type 2 Diabetes-Promoted Hippocampal Neurotoxicity in Rats

Numerous epidemiological findings have repeatedly established associations between Type 2 Diabetes Mellitus (T2DM) and Alzheimer's disease. Targeting different pathways in the brain with T2DM-therapy offers a novel and appealing strategy to treat diabetes-related neuronal alterations. Therefore, here we investigated the capability of a natural compound, curcumin nanoparticle (CurNP), and a biomedical metal, zinc oxide nanoparticle (ZnONP), to alleviate hippocampal modifications in T2DM-induced rats. The diabetes model was induced in male Wistar rats by feeding a high-fat diet (HFD) for eight weeks followed by intraperitoneal injection of streptozotocin (STZ). Then model groups were treated orally with curcumin, zinc sulfate, two doses of CurNP and ZnONP, as well as metformin, for six weeks. HFD/STZ-induced rats exhibited numerous biochemical and molecular changes besides behavioral impairment. Compared with model rats, CurNP and ZnONP boosted learning and memory function, improved redox and inflammation status, lowered Bax, and upregulated Bcl2 expressions in the hippocampus. In addition, the phosphorylation level of the MAPK/ERK pathway was downregulated significantly. The expression of amyloidogenic-related genes and amyloid-beta accumulation, along with tau hyperphosphorylation, were lessened considerably. In addition, both nanoparticles significantly improved histological lesions in the hippocampus. Based on our findings, CurNP and ZnONP appear to be potential neuroprotective agents to mitigate diabetic complications-associated hippocampal toxicity.

The propagation mechanisms of extracellular tau in Alzheimer's disease

Tubulin-associated unit (tau) is an important microtubule-associated protein. The abnormal intracellular aggregation of tau has been strongly associated with Alzheimer's disease (AD). Accumulating evidence has conclusively demonstrated that tau is present in the cytoplasm of neurons and is also actively released into the extracellular space. However, the types of tau species that are released are unclear, as is the mechanism of their release by donor neurons and subsequent uptake by recipient neurons in AD. Understanding the underlying mechanisms of abnormal tau cell-to-cell transmission can provide novel insights into the etiology and pathogenesis of AD and can help identify new targets for the development of AD therapies focused on counteracting neurodegeneration or even preventing it. From this perspective, the present review focuses on recent advances in understanding the mechanisms regulating the levels of extracellular tau and discusses the role of such mechanisms in the propagation of tau-associated pathology.

TTP488 ameliorates NLRP3-associated inflammation, viability, apoptosis, and ROS production in an Alzheimer's disease cell model by mediating the JAK1/STAT3/NFκB/IRF3 pathway

Alzheimer's disease (AD), the most prevalent dementia, is identified as a neurodegenerative disease arising from a degenerative disturbance in the central nervous system. A previous study reported that TTP488 could ameliorate symptoms in patients with mild AD, but the underlying mechanisms need to be studied further. Therefore, the objective of this study was to explore the role of TTP488 in the development of an AD cell model. Administration of TTP448 in an AD cell model reduced the expression of pro-inflammatory cytokines [interleukin (IL)-1β, IL-6, and TNF-α], reversed the inhibitory role of Aβ on cell proliferation and viability, and decreased Aβ-triggered cell apoptosis and reactive oxygen species (ROS) production. Furthermore, Aβ treatment induced activation of JAK1/STAT3/NFκB/IRF3 pathway as well as NLRP3 expression, and TTP488 administration partially reversed the activation of this pathway and NLRP3 expression. Use of WP1160, a STAT3 agonist, re-activated the downstream STAT3/NFκB/IRF3 pathway and NLRP3 expression. Moreover, we found that WP1160 counteracted the role of TTP488 in Aβ-induced SH-SY5Y cells' viability, inflammation, apoptosis, and ROS production. SIGNIFICANCE OF THE STUDY: This study explores the role of TTP488 in the development of an Alzheimer's disease (AD) cell model and confirms that TTP488 administration notably promotes cell proliferation and reduces apoptosis, inflammatory factor expression, and reactive oxygen species generation. Further, this study suggests that the NLRP3-relevant JAK1/STAT3/P65/IRF3 signalling pathway is related to AD pathogenesis.

Class I HDAC Inhibitor Improves Synaptic Proteins and Repairs Cytoskeleton Through Regulating Synapse-Related Genes In vitro and In vivo

β-amyloid (Aβ) is an important protein molecule in the pathology of Alzheimer’s disease (AD). Accumulation of Aβ leads to the loss of dendritic spines and synapses. These impairments can be ameliorated by histone deacetylase inhibitors (HDACI). However, the mechanisms of HDACIs underlying the effect on synapse are not fully understood. In this study, we examined the relationship between HDAC activity and synapse-related genes and proteins by the administration of a class I HDAC inhibitor, BG45, in the exogenous Aβ-treated cells and mice. Our studies showed that the treatment of HF-488-Aβ_1–42 to SH-SY5Y cells first increased the expression of the postsynaptic dendritic protein (PSD), then decreased it after 36 h. BG45 can alleviate the reduction of the expression of PSD-95 as well as spinophilin and cytoskeletal protein induced by HF-488-Aβ^1–42 aggregation in SH-SY5Y cells. Similar to the results in vitro, PSD-95 in the hippocampus was temporarily increased in the early days of intravenous injection HF-488-Aβ_1–40 to the mice, followed by the decreased expression of PSD-95 on the 9th day. In further studies, for the mice treated with Aβ for 9 days, we found that BG45 decreased the expression of HDAC1 and 2, increased the expression of PSD-95, spinophilin, and synaptophysin (SYP). Our data also showed that BG45 upregulated levels of three synapse-related genes and proteins GRIK2, SCN3B, and SYNPR. These findings suggest that the exogenous Aβ may stimulate transiently the expression of PSD-95 at an early stage, but subsequently contribute to synaptic defects. HDAC1 and 2 are involved in synaptic defects, and BG45 may improve the expression of synaptic and cytoskeletal proteins and repair cytoskeletal damage by specifically inhibiting HDAC1 and 2, thereby modulating synapse-related genes. BG45 might be a potential therapeutic agent for the treatment of an early stage of Aβ-related neurodegenerative disease.

Endoplasmic Reticulum Stress in Tauopathies: Contrasting Human Brain Pathology with Cellular and Animal Models

The accumulation and spreading of protein tau in the human brain are major features of neurodegenerative disorders known as tauopathies. In addition to several subcellular abnormalities, tau aggregation within neurons seems capable of triggering endoplasmic reticulum (ER) stress and the consequent unfolded protein response (UPR). In metazoans, full activation of a complex ER-UPR network may restore proteostasis and ER function or, if stress cannot be solved, commit cells to apoptosis. Due to these alternative outcomes (survival or death), the pharmacological manipulation of ER-UPR has become the focus of potential therapies in many human diseases, including tauopathies. Here we update and analyze the experimental data from human brain, cellular, and animal models linking tau accumulation and ER-UPR. We further discuss mechanistic aspects and put the ER-UPR into perspective as a possible therapeutic target in this group of diseases.

MicroRNA-107 Ameliorates Damage in a Cell Model of Alzheimer's Disease by Mediating the FGF7/FGFR2/PI3K/Akt Pathway

Alzheimer's disease (AD), the most prevalent representation of dementia, is a neurodegenerative disease resulting from the degenerative disturbance of the central nervous system. Previous studies have indicated that miR-107 is reduced in the brain neocortex of patients with AD; however, its underlying mechanism is not clear. Therefore, the objective of this study was to explore the question of whether miR-107 participates in AD development. The study confirmed that the miR-107 expression levels were dramatically decreased in patients with AD and in beta-amyloid (Aβ) (Aβ)-treated SH-SY5Y cells compared with control groups. Upregulation of miR-107 reversed the inhibitory role of Aβ on cell proliferation and viability. In addition, miR-107 upregulation also ameliorated the Aβ-induced inflammation and apoptosis of SH-SY5Y cells. Furthermore, using bioinformatic prediction, dual-luciferase reporter assay (DLRA), quantitative polymerase chain reaction (qPCR), and Western blot (WB), miR-107 was confirmed to reduce the expression level of FGF7, and it subsequently deactivated the FGFR2/PI3K/Akt pathway. Moreover, FGF7 overexpression counteracted the role of miR-107 in the viability, proliferation, inflammation, and apoptosis of Aβ-induced SH-SY5Y cells.

Oligomerization and Conformational Change Turn Monomeric β-Amyloid and Tau Proteins Toxic: Their Role in Alzheimer's Pathogenesis

The structural polymorphism and the physiological and pathophysiological roles of two important proteins, β-amyloid (Aβ) and tau, that play a key role in Alzheimer's disease (AD) are reviewed. Recent results demonstrate that monomeric Aβ has important physiological functions. Toxic oligomeric Aβ assemblies (AβOs) may play a decisive role in AD pathogenesis. The polymorph fibrillar Aβ (fAβ) form has a very ordered cross-β structure and is assumed to be non-toxic. Tau monomers also have several important physiological actions; however, their oligomerization leads to toxic oligomers (TauOs). Further polymerization results in probably non-toxic fibrillar structures, among others neurofibrillary tangles (NFTs). Their structure was determined by cryo-electron microscopy at atomic level. Both AβOs and TauOs may initiate neurodegenerative processes, and their interactions and crosstalk determine the pathophysiological changes in AD. TauOs (perhaps also AβO) have prionoid character, and they may be responsible for cell-to-cell spreading of the disease. Both extra- and intracellular AβOs and TauOs (and not the previously hypothesized amyloid plaques and NFTs) may represent the novel targets of AD drug research.

Alzheimer's disease: pathogenesis, diagnostics, and therapeutics

Currently, 47 million people live with dementia globally, and it is estimated to increase more than threefold (~131 million) by 2050. Alzheimer's disease (AD) is one of the major causative factors to induce progressive dementia. AD is a neurodegenerative disease, and its pathogenesis has been attributed to extracellular aggregates of amyloid β (Aβ) plaques and intracellular neurofibrillary tangles made of hyperphosphorylated τ-protein in cortical and limbic areas of the human brain. It is characterized by memory loss and progressive neurocognitive dysfunction. The anomalous processing of APP by β-secretases and γ-secretases leads to production of Aβ40 and Aβ42 monomers, which further oligomerize and aggregate into senile plaques. The disease also intensifies through infectious agents like HIV. Additionally, during disease pathogenesis, the presence of high concentrations of Aβ peptides in central nervous system initiates microglial infiltration. Upon coming into vicinity of Aβ, microglia get activated, endocytose Aβ, and contribute toward their clearance via TREM2 surface receptors, simultaneously triggering innate immunoresponse against the aggregation. In addition to a detailed report on causative factors leading to AD, the present review also discusses the current state of the art in AD therapeutics and diagnostics, including labeling and imaging techniques employed as contrast agents for better visualization and sensing of the plaques. The review also points to an urgent need for nanotechnology as an efficient therapeutic strategy to increase the bioavailability of drugs in the central nervous system.

Endo-lysosomal pathway and ubiquitin-proteasome system dysfunction in Alzheimer's disease pathogenesis

Several lines of evidence have shown that defects in the endo-lysosomal autophagy degradation pathway and the ubiquitin-proteasome system play a role in Alzheimer's Disease (AD) pathogenesis and pathophysiology. Early pathological changes, such as marked enlargement of endosomal compartments, gradual accumulation of autophagic vacuoles (AVs) and lysosome dyshomeostasis, are well-recognized in AD. In addition to these pathological indicators, many genetic variants of key regulators in the endo-lysosomal autophagy networks and the ubiquitin-proteasome system have been found to be associated with AD. Furthermore, altered expression levels of key proteins in these pathways have been found in AD human brain tissues, primary cells and AD mouse models. In this review, we discuss potential disease mechanisms underlying the dysregulation of protein homeostasis governing systems. While the importance of two major protein degradation pathways in AD pathogenesis has been highlighted, targeted therapy at key components of these pathways has great potential in developing novel therapeutic interventions for AD. Future investigations are needed to define molecular mechanisms by which these complex regulatory systems become malfunctional at specific stages of AD development and progression, which will facilitate future development of novel therapeutic interventions. It is also critical to investigate all key components of the protein degradation pathways, both upstream and downstream, to improve our abilities to manipulate transport pathways with higher efficacy and less side effects.

It's all about tau

Tau is a protein that is highly enriched in neurons and was originally defined by its ability to bind and stabilize microtubules. However, it is now becoming evident that the functions of tau extend beyond its ability to modulate microtubule dynamics. Tau plays a role in mediating axonal transport, synaptic structure and function, and neuronal signaling pathways. Although tau plays important physiological roles in neurons, its involvement in neurodegenerative diseases, and most prominently in the pathogenesis of Alzheimer disease (AD), has directed the majority of tau studies. However, a thorough knowledge of the physiological functions of tau and its post-translational modifications under normal conditions are necessary to provide the foundation for understanding its role in pathological settings. In this review, we will focus on human tau, summarizing tau structure and organization, as well as its posttranslational modifications associated with physiological processes. We will highlight possible mechanisms involved in mediating the turnover of tau and finally discuss newly elucidated tau functions in a physiological context.

Pharmacological Inhibition of O-GlcNAcase Enhances Autophagy in Brain through an mTOR-Independent Pathway

The glycosylation of nucleocytoplasmic proteins with O-linked N-acetylglucosamine residues (O-GlcNAc) is conserved among metazoans and is particularly abundant within brain. O-GlcNAc is involved in diverse cellular processes ranging from the regulation of gene expression to stress response. Moreover, O-GlcNAc is implicated in various diseases including cancers, diabetes, cardiac dysfunction, and neurodegenerative diseases. Pharmacological inhibition of O-GlcNAcase (OGA), the sole enzyme that removes O-GlcNAc, reproducibly slows neurodegeneration in various Alzheimer's disease (AD) mouse models manifesting either tau or amyloid pathology. These data have stimulated interest in the possibility of using OGA-selective inhibitors as pharmaceuticals to alter the progression of AD. The mechanisms mediating the neuroprotective effects of OGA inhibitors, however, remain poorly understood. Here we show, using a range of methods in neuroblastoma N2a cells, in primary rat neurons, and in mouse brain, that selective OGA inhibitors stimulate autophagy through an mTOR-independent pathway without obvious toxicity. Additionally, OGA inhibition significantly decreased the levels of toxic protein species associated with AD pathogenesis in the JNPL3 tauopathy mouse model as well as the 3×Tg-AD mouse model. These results strongly suggest that OGA inhibitors act within brain through a mechanism involving enhancement of autophagy, which aids the brain in combatting the accumulation of toxic protein species. Our study supports OGA inhibition being a feasible therapeutic strategy for hindering the progression of AD and other neurodegenerative diseases. Moreover, these data suggest more targeted strategies to stimulate autophagy in an mTOR-independent manner may be found within the O-GlcNAc pathway. These findings should aid the advancement of OGA inhibitors within the clinic.

Phosphorylation of huntingtin at residue T3 is decreased in Huntington's disease and modulates mutant huntingtin protein conformation

Posttranslational modifications can have profound effects on the biological and biophysical properties of proteins associated with misfolding and aggregation. However, their detection and quantification in clinical samples and an understanding of the mechanisms underlying the pathological properties of misfolding- and aggregation-prone proteins remain a challenge for diagnostics and therapeutics development. We have applied an ultrasensitive immunoassay platform to develop and validate a quantitative assay for detecting a posttranslational modification (phosphorylation at residue T3) of a protein associated with polyglutamine repeat expansion, namely Huntingtin, and characterized its presence in a variety of preclinical and clinical samples. We find that T3 phosphorylation is greatly reduced in samples from Huntington's disease models and in Huntington's disease patients, and we provide evidence that bona-fide T3 phosphorylation alters Huntingtin exon 1 protein conformation and aggregation properties. These findings have significant implications for both mechanisms of disease pathogenesis and the development of therapeutics and diagnostics for Huntington's disease.

Application of Chitosan, Chitooligosaccharide, and Their Derivatives in the Treatment of Alzheimer's Disease

Classic hypotheses of Alzheimer's disease (AD) include cholinergic neuron death, acetylcholine (ACh) deficiency, metal ion dynamic equilibrium disorder, and deposition of amyloid and tau. Increased evidence suggests neuroinflammation and oxidative stress may cause AD. However, none of these factors induces AD independently, but they are all associated with the formation of Aβ and tau proteins. Current clinical treatments based on ACh deficiency can only temporarily relieve symptoms, accompanied with many side-effects. Hence, searching for natural neuroprotective agents, which can significantly improve the major symptoms and reverse disease progress, have received great attention. Currently, several bioactive marine products have shown neuroprotective activities, immunomodulatory and anti-inflammatory effects with low toxicity and mild side effects in laboratory studies. Recently, chitosan (CTS), chitooligosaccharide (COS) and their derivatives from exoskeletons of crustaceans and cell walls of fungi have shown neuroprotective and antioxidative effects, matrix metalloproteinase inhibition, anti-HIV and anti-inflammatory properties. With regards to the hypotheses of AD, the neuroprotective effect of CTS, COS, and their derivatives on AD-like changes in several models have been reported. CTS and COS exert beneficial effects on cognitive impairments via inhibiting oxidative stress and neuroinflammation. They are also a new type of non-toxic β-secretase and AChE inhibitor. As neuroprotective agents, they could reduce the cell membrane damage caused by copper ions and decrease the content of reactive oxygen species. This review will focus on their anti-neuroinflammation, antioxidants and their inhibition of β-amyloid, acetylcholinesterase and copper ions adsorption. Finally, the limitations and future work will be discussed.

Chronic administration of SUMO‑1 has negative effects on novel object recognition memory as well as cell proliferation and neuroblast differentiation in the mouse dentate gyrus

Post‑translational modifications have been associated with developmental and aging processes, as well as in the pathogenesis of certain diseases. The present study aimed to investigate the effects of small ubiquitin‑like modifier 1 (SUMO‑1) on hippocampal dependent memory function, cell proliferation and neuroblast differentiation. To facilitate the delivery of SUMO‑1 into hippocampal neurons, a transactivator of transcription (Tat)‑SUMO‑1 fusion protein was constructed and mice were divided into two groups: A vehicle (Tat peptide)‑treated group and a Tat‑SUMO‑1‑treated group. The vehicle or Tat‑SUMO‑1 was administered intraperitoneally to 7‑week‑old mice once daily for 3 weeks, and a novel object recognition test was conducted following the final treatment; the animals were sacrificed 2 h following the test for further analysis. Administration of Tat‑SUMO‑1 significantly decreased exploration of a new object in a novel object recognition test compared with mice in the vehicle‑treated group. In addition, cell proliferation and neuroblast differentiation analyses (based on Ki67 and doublecortin immunohistochemistry, respectively) revealed that the administration of Tat‑SUMO‑1 significantly reduced cell proliferation and neuroblast differentiation in the dentate gyrus. These results suggested that chronic supplementation of Tat‑SUMO‑1 affects hippocampal functions by decreasing cell proliferation and neuroblast differentiation in the mouse dentate gyrus.

Therapeutic strategies for the treatment of tauopathies: Hopes and challenges

A group of neurodegenerative diseases referred to as tauopathies are characterized by the presence of brain cells harboring inclusions of pathological species of the tau protein. These disorders include Alzheimer's disease and frontotemporal lobar degeneration due to tau pathology, including progressive supranuclear palsy, corticobasal degeneration, and Pick's disease. Tau is normally a microtubule (MT)-associated protein that appears to play an important role in ensuring proper axonal transport, but in tauopathies tau becomes hyperphosphorylated and disengages from MTs, with consequent misfolding and deposition into inclusions that mainly affect neurons but also glia. A body of experimental evidence suggests that the development of tau inclusions leads to the neurodegeneration observed in tauopathies, and there is a growing interest in developing tau-directed therapeutic agents. The following review provides a summary of strategies under investigation for the potential treatment of tauopathies, highlighting both the promises and challenges associated with these various therapeutic approaches.

Imaging Multimodalities for Dissecting Alzheimer's Disease: Advanced Technologies of Positron Emission Tomography and Fluorescence Imaging

The rapid progress in advanced imaging technologies has expanded our toolbox for monitoring a variety of biological aspects in living subjects including human. In vivo radiological imaging using small chemical tracers, such as with positron emission tomography, represents an especially vital breakthrough in the efforts to improve our understanding of the complicated cascade of neurodegenerative disorders including Alzheimer's disease (AD), and it has provided the most reliable visible biomarkers for enabling clinical diagnosis. At the same time, in combination with genetically modified animal model systems, the most recent innovation of fluorescence imaging is helping establish diverse applications in basic neuroscience research, from single-molecule analysis to animal behavior manipulation, suggesting the potential utility of fluorescence technology for dissecting the detailed molecular-based consequence of AD pathophysiology. In this review, our primary focus is on a current update of PET radiotracers and fluorescence indicators beneficial for understanding the AD cascade, and discussion of the utility and pitfalls of those imaging modalities for future translational research applications. We will also highlight current cutting-edge genetic approaches and discuss how to integrate individual technologies for further potential innovations.

The Human Tau Interactome: Binding to the Ribonucleoproteome, and Impaired Binding of the Proline-to-Leucine Mutant at Position 301 (P301L) to Chaperones and the Proteasome

The tau protein is central to the etiology of several neurodegenerative diseases, including Alzheimer's disease, a subset of frontotemporal dementias, progressive supranuclear palsy and dementia following traumatic brain injury, yet the proteins it interacts with have not been studied using a systematic discovery approach. Here we employed mild in vivo crosslinking, isobaric labeling, and tandem mass spectrometry to characterize molecular interactions of human tau in a neuroblastoma cell model. The study revealed a robust association of tau with the ribonucleoproteome, including major protein complexes involved in RNA processing and translation, and documented binding of tau to several heat shock proteins, the proteasome and microtubule-associated proteins. Follow-up experiments determined the relative contribution of cellular RNA to the tau interactome and mapped interactions to N- or C-terminal tau domains. We further document that expression of P301L mutant tau disrupts interactions of the C-terminal half of tau with heat shock proteins and the proteasome. The data are consistent with a model whereby a higher propensity of P301L mutant tau to aggregate may reflect a perturbation of its chaperone-assisted stabilization and proteasome-dependent degradation. Finally, using a global proteomics approach, we show that heterologous expression of a tau construct that lacks the C-terminal domain, including the microtubule binding domain, does not cause a discernible shift of the proteome except for a significant direct correlation of steady-state levels of tau and cystatin B.

Genetics pathway-based imaging approaches in Chinese Han population with Alzheimer's disease risk

The tau hypothesis has been raised with regard to the pathophysiology of Alzheimer's disease (AD). Mild cognitive impairment (MCI) is associated with a high risk for developing AD. However, no study has directly examined the brain topological alterations based on combined effects of tau protein pathway genes in MCI population. Forty-three patients with MCI and 30 healthy controls underwent resting-state functional magnetic resonance imaging (fMRI) in Chinese Han, and a tau protein pathway-based imaging approaches (7 candidate genes: 17 SNPs) were used to investigate changes in the topological organisation of brain activation associated with MCI. Impaired regional activation is related to tau protein pathway genes (5/7 candidate genes) in patients with MCI and likely in topologically convergent and divergent functional alterations patterns associated with genes, and combined effects of tau protein pathway genes disrupt the topological architecture of cortico-cerebellar loops. The associations between the loops and behaviours further suggest that tau protein pathway genes do play a significant role in non-episodic memory impairment. Tau pathway-based imaging approaches might strengthen the credibility in imaging genetic associations and generate pathway frameworks that might provide powerful new insights into the neural mechanisms that underlie MCI.

Age-related changes of protein SUMOylation balance in the AβPP Tg2576 mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a complex disorder that affects the central nervous system causing a severe neurodegeneration. This pathology affects an increasing number of people worldwide due to the overall aging of the human population. In recent years SUMO protein modification has emerged as a possible cellular mechanism involved in AD. Some of the proteins engaged in the physiopathological process of AD, like BACE1, GSK3-β tau, AβPP, and JNK, are in fact subject to protein SUMO modifications or interactions. Here, we have investigated the SUMO/deSUMOylation balance and SUMO-related proteins during the onset and progression of the pathology in the Tg2576 mouse model of AD. We examined four age-stages (1.5, 3, 6, 17 months old) and observed shows an increase in SUMO-1 protein conjugation at 3 and 6 months in transgenic mice with respect to WT in both cortex and hippocampus. Interestingly this is paralleled by increased expression levels of Ubc9 and SENP1 in both brain regions. At 6 months of age also the SUMO-1 mRNA resulted augmented. SUMO-2-ylation was surprisingly decreased in old transgenic mice and was unaltered in the other time windows. The fact that alterations in SUMO/deSUMOylation equilibrium occur from the early phases of AD suggests that global posttranslational modifications may play an important role in the mechanisms underlying disease pathogenesis, thus providing potential targets for pharmacological interventions.

Increased O-GlcNAcylation reduces pathological tau without affecting its normal phosphorylation in a mouse model of tauopathy

Neurofibrillary tangles (NFT), mainly consisting of fibrillar aggregates of hyperphosphorylated tau, are a defining pathological feature of Alzheimer's Disease and other tauopathies. Progressive accumulation of tau into NFT is considered to be a toxic cellular event causing neurodegeneration. Tau is subject to O-linked N-acetylglucosamine (O-GlcNAc) modification and O-GlcNAcylation of tau has been suggested to regulate tau phosphorylation. We tested if an increase in tau O-GlcNAcylation affected tau phosphorylation and aggregation in the rTg4510 tau transgenic mouse model. Acute treatment of rTg4510 mice with an O-GlcNAcase inhibitor transiently reduced tau phosphorylation at epitopes implicated in tau pathology. More importantly, long-term inhibitor treatment strongly increased tau O-GlcNAcylation, reduced the number of dystrophic neurons, and protected against the formation of pathological tau species without altering the phosphorylation of non-pathological tau. This indicates that O-GlcNAcylation prevents the aggregation of tau in a manner that does not affect its normal phosphorylation state. Collectively, our results support O-GlcNAcase inhibition as a potential therapeutic strategy for the treatment of Alzheimer's Disease and other tauopathies.

GWAS of cerebrospinal fluid tau levels identifies risk variants for Alzheimer's disease

Cerebrospinal fluid (CSF) tau, tau phosphorylated at threonine 181 (ptau), and Aβ₄₂ are established biomarkers for Alzheimer's disease (AD) and have been used as quantitative traits for genetic analyses. We performed the largest genome-wide association study for cerebrospinal fluid (CSF) tau/ptau levels published to date (n = 1,269), identifying three genome-wide significant loci for CSF tau and ptau: rs9877502 (p = 4.89 × 10⁻⁹ for tau) located at 3q28 between GEMC1 and OSTN, rs514716 (p = 1.07 × 10⁻⁸ and p = 3.22 × 10⁻⁹ for tau and ptau, respectively), located at 9p24.2 within GLIS3 and rs6922617 (p = 3.58 × 10⁻⁸ for CSF ptau) at 6p21.1 within the TREM gene cluster, a region recently reported to harbor rare variants that increase AD risk. In independent data sets, rs9877502 showed a strong association with risk for AD, tangle pathology, and global cognitive decline (p = 2.67 × 10⁻⁴, 0.039, 4.86 × 10⁻⁵, respectively) illustrating how this endophenotype-based approach can be used to identify new AD risk loci.

Intracerebral propagation of Alzheimer's disease: strengthening evidence of a herpes simplex virus etiology

BACKGROUND

A faulty human protein, abnormally phosphorylated tau, was recently publicized to spread "like a virus" from neuron to neuron in Alzheimer's patients' brains. For several decades, we have been amassing arguments showing that herpes simplex virus type 1 (HSV-1), not p-tau, propagates this interneuronal, transsynaptic pathologic cascade.

METHODS

We reiterate convincing data from our own (and other) laboratories, reviewing the first anatomic foothold neurofibrillary tangles gain in brainstem and/or entorhinal cortex; the chronic immunosurveillance cellularity of the trigeminal ganglia wherein HSV-1 awakens from latency to reactivate; the inabilities of p-tau protein's physical properties to promote it to jump synapses; the amino acid homology between human p-tau and VP22, a key target for phosphorylation by HSV serine/threonine-protein kinase UL13; and the exosomic secretion of HSV-1-infected cells' L-particles, attesting to the cell-to-cell passage of microRNAs of herpesviruses.

RESULTS

The now-maturing construct that reactivated HSV-1 best accounts for the intracerebral propagation of AD changes in the human brain should at last seem highly attractive. This hypothesis might even explain statins' apparent mechanism in some studies for lowering AD incidence.

CONCLUSION

Provided that funding agencies will quickly ignite a new realm of investigation, the rejuvenated enthusiasm for testing this optimistic construct holds incalculable potential for rapid, efficacious clinical application, through already available and relatively safe antiviral therapeutics.

Increasing O-GlcNAc slows neurodegeneration and stabilizes tau against aggregation

Oligomerization of tau is a key process contributing to the progressive death of neurons in Alzheimer's disease. Tau is modified by O-linked N-acetylglucosamine (O-GlcNAc), and O-GlcNAc can influence tau phosphorylation in certain cases. We therefore speculated that increasing tau O-GlcNAc could be a strategy to hinder pathological tau-induced neurodegeneration. Here we found that treatment of hemizygous JNPL3 tau transgenic mice with an O-GlcNAcase inhibitor increased tau O-GlcNAc, hindered formation of tau aggregates and decreased neuronal cell loss. Notably, increases in tau O-GlcNAc did not alter tau phosphorylation in vivo. Using in vitro biochemical aggregation studies, we found that O-GlcNAc modification, on its own, hinders tau oligomerization. O-GlcNAc also inhibits thermally induced aggregation of an unrelated protein, TAK-1 binding protein, suggesting that a basic biochemical function of O-GlcNAc may be to prevent protein aggregation. These results also suggest O-GlcNAcase as a potential therapeutic target that could hinder progression of Alzheimer's disease.