Disruption of microtubule network by Alzheimer abnormally hyperphosphorylated tau

Genomic stress and impaired DNA repair in Alzheimer disease

Alzheimer disease (AD) is the most prominent form of dementia and has received considerable attention due to its growing burden on economic, healthcare and basic societal infrastructures. The two major neuropathological hallmarks of AD, i.e., extracellular amyloid beta (Aβ) peptide plaques and intracellular hyperphosphorylated Tau neurofibrillary tangles, have been the focus of much research, with an eye on understanding underlying disease mechanisms and identifying novel therapeutic avenues. One often overlooked aspect of AD is how Aβ and Tau may, through indirect and direct mechanisms, affect genome integrity. Herein, we review evidence that Aβ and Tau abnormalities induce excessive genomic stress and impair genome maintenance mechanisms, events that can promote DNA damage-induced neuronal cell loss and associated brain atrophy.

Potential value of serum prealbumin and serum albumin in the identification of postoperative delirium in patients undergoing knee/hip replacement: an observational study and internal validation study

Background

Postoperative delirium (POD) is a common postoperative neurological complication that can lead to a variety of postoperative complications. At present, the pathogenesis of POD is unclear. This study aims to explore the relationship between serum prealbumin and serum albumin and POD and whether serum prealbumin and serum albumin influence POD through POD core pathology.

Objective

We enrolled 500 Chinese Han patients between September 2020 to January 2023. We analyzed the risk and protective factors of POD using the multivariate logistic regression. We also assessed the predictive power of serum prealbumin, serum albumin, and both in combination with CSF POD biomarkers. We used Stata MP16.0. to examine whether the association between serum prealbumin and serum albumin and POD was mediated by CSF POD biomarkers, and conducted an internal validation study to verify the accuracy of the combination of serum prealbumin + serum albumin + CSF POD biomarkers for predicting POD. The model was visualized using ROC curve and decision curve analysis (DCA). DynNom and Shiny packages were used to create an online calculator. Ten patients who had POD occurring from February 2023 to October 2023 were selected for internal verification.

Results

Finally, a total of 364 patients were included in our study. Levels of serum prealbumin, serum albumin in the POD group were lower than those in the NPOD group. The lever of serum prealbumin, serum albumin were protective factors for POD. The relationship between serum prealbumin, serum albumin and POD was partially mediated by T-tau (12.28%) and P-tau (20.61%). The model combining serum prealbumin and serum albumin and POD biomarkers exhibited a relatively better discriminatory ability to predict POD. DCA also showed that the combination of serum prealbumin and serum albumin and POD biomarkers brought high predictive benefits to patients. The dynamic online calculator can accurately predict the occurrence of POD in the internal validation study.

Conclusion

Preoperative low serum prealbumin and serum albumin levels were the preoperative risk factors for POD, which is partly mediated by T-tau and P-tau. The model combining serum prealbumin and serum albumin and CSF POD biomarkers can accurately predict the occurrence of POD.

Clinical trial registration

http://www.clinicaltrials.gov, identifier ChiCTR2000033439.

Activation of transient receptor potential vanilloid 1 ameliorates tau accumulation-induced synaptic damage and cognitive dysfunction via autophagy enhancement

AIMS

The autophagy-lysosomal pathway is important for maintaining cellular proteostasis, while dysfunction of this pathway has been suggested to drive the aberrant intraneuronal accumulation of tau protein, leading to synaptic damage and cognitive impairment. Previous studies have demonstrated that the activation of transient receptor potential vanilloid 1 (TRPV1) by capsaicin has a positive impact on cognition and AD-related biomarkers. However, the effect and mechanism of TPRV1 activation on neuronal tau homeostasis remain elusive.

METHODS

A mouse model of tauopathy was established by overexpressing full-length human tau in the CA3 area. Mice were fed capsaicin diet (0.0125%) or normal diet for 9 weeks. The cognitive ability, synaptic function, tau phosphorylation levels, and autophagy markers were detected. In vitro, capsaicin-induced alterations in cellular autophagy and tau degradation were characterized using two cell models. Besides, various inhibitors were applied to validate the role of TRPV1-mediated autophagy enhancement in tau clearance.

RESULTS

We observed that TRPV1 activation by capsaicin effectively mitigates hippocampal tau accumulation-induced synaptic damages, gliosis, and cognitive impairment in vivo. Capsaicin promotes the degradation of abnormally accumulated tau through enhancing autophagic function in neurons, which is dependent on TRPV1-mediated activation of AMP-activated protein kinase (AMPK) and subsequent inhibition of the mammalian target of rapamycin (mTOR). Blocking AMPK activation abolishes capsaicin-induced autophagy enhancement and tau degradation in neurons.

CONCLUSION

Our findings reveal that capsaicin-induced TRPV1 activation confers neuroprotection by restoring neuronal tau homeostasis via modulating cellular autophagy and provides additional evidence to support the potential of TRPV1 as a therapeutic target for tauopathies.

A single-domain antibody for the detection of pathological Tau protein in the early stages of oligomerization

BACKGROUND

Soluble oligomeric forms of Tau protein have emerged as crucial players in the propagation of Tau pathology in Alzheimer's disease (AD). Our objective is to introduce a single-domain antibody (sdAb) named 2C5 as a novel radiotracer for the efficient detection and longitudinal monitoring of oligomeric Tau species in the human brain.

METHODS

The development and production of 2C5 involved llama immunization with the largest human Tau isoform oligomers of different maturation states. Subsequently, 2C5 underwent comprehensive in vitro characterization for affinity and specificity via Enzyme-Linked Immunosorbent Assay and immunohistochemistry on human brain slices. Technetium-99m was employed to radiolabel 2C5, followed by its administration to healthy mice for biodistribution analysis.

RESULTS

2C5 exhibited robust binding affinity towards Tau oligomers (Kd = 6.280 nM ± 0.557) and to Tau fibers (Kd = 5.024 nM ± 0.453), with relatively weaker binding observed for native Tau protein (Kd = 1791 nM ± 8.714) and amyloid peptide (Kd > 10,000 nM). Remarkably, this SdAb facilitated immuno-histological labeling of pathological forms of Tau in neurons and neuritic plaques, yielding a high-contrast outcome in AD patients, closely mirroring the performance of reference antibodies AT8 and T22. Furthermore, 2C5 SdAb was successfully radiolabeled with 99mTc, preserving stability for up to 6 h post-radiolabeling (radiochemical purity > 93%). However, following intravenous injection into healthy mice, the predominant uptake occurred in kidneys, amounting to 115.32 ± 3.67, 97.70 ± 43.14 and 168.20 ± 34.52% of injected dose per gram (% ID/g) at 5, 10 and 45 min respectively. Conversely, brain uptake remained minimal at all measured time points, registering at 0.17 ± 0.03, 0.12 ± 0.07 and 0.02 ± 0.01% ID/g at 5, 10 and 45 min post-injection respectively.

CONCLUSION

2C5 demonstrates excellent affinity and specificity for pathological Tau oligomers, particularly in their early stages of oligomerization. However, the current limitation of insufficient blood-brain barrier penetration necessitates further modifications before considering its application in nuclear medicine imaging for humans.

Mechanisms of the Beneficial Effects of Exercise on Brain-Derived Neurotrophic Factor Expression in Alzheimer's Disease

Brain-derived neurotrophic factor (BDNF) is a key molecule in promoting neurogenesis, dendritic and synaptic health, neuronal survival, plasticity, and excitability, all of which are disrupted in neurological and cognitive disorders such as Alzheimer's disease (AD). Extracellular aggregates of amyloid-β (Aβ) in the form of plaques and intracellular aggregates of hyperphosphorylated tau protein have been identified as major pathological insults in the AD brain, along with immune dysfunction, oxidative stress, and other toxic stressors. Although aggregated Aβ and tau lead to decreased brain BDNF expression, early losses in BDNF prior to plaque and tangle formation may be due to other insults such as oxidative stress and contribute to early synaptic dysfunction. Physical exercise, on the other hand, protects synaptic and neuronal structure and function, with increased BDNF as a major mediator of exercise-induced enhancements in cognitive function. Here, we review recent literature on the mechanisms behind exercise-induced BDNF upregulation and its effects on improving learning and memory and on Alzheimer's disease pathology. Exercise releases into the circulation a host of hormones and factors from a variety of peripheral tissues. Mechanisms of BDNF induction discussed here are osteocalcin, FNDC5/irisin, and lactate. The fundamental mechanisms of how exercise impacts BDNF and cognition are not yet fully understood but are a prerequisite to developing new biomarkers and therapies to delay or prevent cognitive decline.

Increased G3BP2-Tau interaction in tauopathies is a natural defense against Tau aggregation

Many RNA-binding proteins (RBPs), particularly those associated with RNA granules, promote pathological protein aggregation in neurodegenerative diseases. Here, we demonstrate that G3BP2, a core component of stress granules, directly interacts with Tau and inhibits Tau aggregation. In the human brain, the interaction of G3BP2 and Tau is dramatically increased in multiple tauopathies, and it is independent of neurofibrillary tangle (NFT) formation in Alzheimer's disease (AD). Surprisingly, Tau pathology is significantly elevated upon loss of G3BP2 in human neurons and brain organoids. Moreover, we found that G3BP2 masks the microtubule-binding region (MTBR) of Tau, thereby inhibiting Tau aggregation. Our study defines a novel role for RBPs as a line of defense against Tau aggregation in tauopathies.

Roles of Non-Coding RNA in Alzheimer's Disease Pathophysiology

Alzheimer's disease (AD) is a chronic neurodegenerative disorder that is accompanied by deficits in memory and cognitive functions. The disease is pathologically characterised by the accumulation and aggregation of an extracellular peptide referred to as amyloid-β (Aβ) in the form of amyloid plaques and the intracellular aggregation of a hyperphosphorelated protein tau in the form of neurofibrillary tangles (NFTs) that cause neuroinflammation, synaptic dysfunction, and oxidative stress. The search for pathomechanisms leading to disease onset and progression has identified many key players that include genetic, epigenetic, behavioural, and environmental factors, which lend support to the fact that this is a multi-faceted disease where failure in various systems contributes to disease onset and progression. Although the vast majority of individuals present with the sporadic (non-genetic) form of the disease, dysfunctions in numerous protein-coding and non-coding genes have been implicated in mechanisms contributing to the disease. Recent studies have provided strong evidence for the association of non-coding RNAs (ncRNAs) with AD. In this review, we highlight the current findings on changes observed in circular RNA (circRNA), microRNA (miRNA), short interfering RNA (siRNA), piwi-interacting RNA (piRNA), and long non-coding RNA (lncRNA) in AD. Variations in these ncRNAs could potentially serve as biomarkers or therapeutic targets for the diagnosis and treatment of Alzheimer's disease. We also discuss the results of studies that have targeted these ncRNAs in cellular and animal models of AD with a view for translating these findings into therapies for Alzheimer's disease.

The Contribution of the Locus Coeruleus-Noradrenaline System Degeneration during the Progression of Alzheimer's Disease

Alzheimer's disease (AD), which is characterized by extracellular accumulation of amyloid-beta peptide and intracellular aggregation of hyperphosphorylated tau, is the most common form of dementia. Memory loss, cognitive decline and disorientation are the ultimate consequences of neuronal death, synapse loss and neuroinflammation in AD. In general, there are many brain regions affected but neuronal loss in the locus coeruleus (LC) is one of the earliest indicators of neurodegeneration in AD. Since the LC is the main source of noradrenaline (NA) in the brain, degeneration of the LC in AD leads to decreased NA levels, causing increased neuroinflammation, enhanced amyloid and tau burden, decreased phagocytosis and impairment in cognition and long-term synaptic plasticity. In this review, we summarized current findings on the locus coeruleus-noradrenaline system and consequences of its dysfunction which is now recognized as an important contributor to AD progression.

Single domain antibodies targeting pathological tau protein: Influence of four IgG subclasses on efficacy and toxicity

BACKGROUND

Eleven tau immunoglobulin G (IgG) antibodies have entered clinical trials to treat tauopathies, including Alzheimer's disease, but it is unclear which IgG subclass/subtype has the ideal efficacy and safety profile. Only two subtypes, with or without effector function, have been examined in the clinic and not for the same tau antibody. The few preclinical studies on this topic have only compared two subtypes of one antibody each and have yielded conflicting results.

METHODS

We selected two single domain antibodies (sdAbs) derived from a llama immunized with tau proteins and utilized them to generate an array of Fc-(sdAb)2 subclasses containing identical tau binding domains but differing Fc region. Unmodified sdAbs and their IgG subclasses were tested for efficacy in primary cultures and in vivo microdialysis using JNPL3 tauopathy mice.

FINDINGS

Unmodified sdAbs were non-toxic, blocked tau toxicity and promoted tau clearance. However, the efficacy/safety profile of their Fc-(sdAb)2 subclasses varied greatly within and between sdAbs. For one of them, all its subtypes were non-toxic, only those with effector function cleared tau, and were more effective in vivo than unmodified sdAb. For the other sdAb, all its subtypes were toxic in tauopathy cultures but not in wild-type cells, suggesting that bivalent binding of its tau epitope stabilizes a toxic conformation of tau, with major implications for tau pathogenesis. Likewise, its subclasses were less effective than the unmodified sdAb in clearing tau in vivo.

INTERPRETATION

These findings indicate that tau antibodies with effector function are safe and better at clearing pathological tau than effectorless antibodies, Furthermore, tau antibodies can provide a valuable insight into tau pathogenesis, and some may aggravate it.

FUNDING

Funding for these studies was provided by the National Institute of Health (R01 AG032611, R01 NS077239, RF1 NS120488, R21 AG 069475, R21 AG 058282, T32AG052909), and the NYU Alzheimer's Disease Center Pilot Grant Program (via P30 AG008051).

The relationship between mild cognitive impairment and postoperative delirium undergoing total knee arthroplasty: The PNDABLE study

Background

Patients undergoing surgery are at a higher risk of developing postoperative delirium (POD) as a result of anesthesia and surgical procedures. This study examined the association between POD and mild cognitive impairment (MCI) and whether MCI influences POD through the core pathology of POD.

Methods

We enrolled Chinese Han patients undergoing unilateral total knee arthroplasty (aged 50–90, weighing 50–80 kg, and using ASAI-II), combined with epidural anesthesia between October 2020 and June 2021. All the participants were assessed using Winblad's criteria for diagnosing MCI on pre-operation and using the Confusion Assessment Method (CAM) and the Memorial Delirium Assessment Scale (MDAS) postoperative 1–7 days (or before discharge) for diagnosing POD by an anesthesiologist. Cerebrospinal fluid (CSF) biomarkers of POD were measured by enzyme-linked immunosorbent assay (ELISA). To examine the mechanism by which POD pathologies affect cognition, causal mediation analyses were performed.

Results

POD incidence was 20.2%, including 32.5% in the MCI group and 12.4% in the non-mild cognitive impairment (NMCI) group. The MCI and CSF levels of T-tau and P-tau were risk factors, and the CSF levels of Aβ₄₂, Aβ₄₂/ T-tau, and Aβ₄₂/ P-tau were protective factors in POD (p < 0.05). Part of the effects of MCI on cognition can be attributed to amyloid pathology and tau.

Conclusion

MCI may be a reasonably good prognostic factor in POD development. Overall, amyloid pathology and tau protein might partially mediate the influence of MCI on POD.

Clinical trial registration

www.clinicaltrials.gov, identifier: ChiCTR2000033439.

Antimicrobial, Polarizing Light, and Paired Helical Filament Properties of Fragmented Tau Peptides of Selected Putative Gingipains

BACKGROUND

Tau is an established substrate for gingipains secreted by Porphyromonas gingivalis. Hyperphosphorylation of tau and neurofibrillary tangle (NFT) formation is a defining lesion of Alzheimer's disease (AD) where NFT distribution is related to Braak stage and disease severity.

OBJECTIVE

To assess gingipains'-fragmented tau peptides for their antimicrobial properties and for the likelihood of paired helical/straight filament (PHF/SF) formation with implications for the NFT lesion.

METHODS

Seven non-phosphorylated (A-G) and three phosphorylated (A-C) tau peptides, were tested for antimicrobial properties against P. gingivalis. Polarizing light properties were determined using Congo Red staining. Secondary and tertiary structures of peptides B-F were determined using transmission electron microscopy (TEM) and circular dichroism (CD) was undertaken for the soluble peptides A in phosphorylated and non-phosphorylated states.

RESULTS

Phosphorylated tau peptide A displayed a significant effect against planktonic P. gingivalis. The CD results demonstrated that both peptides A, in phosphorylated and non-phosphorylated states, in aqueous solution, adopted mainly β-type structures. Non-phosphorylated peptides B-F and phosphorylated peptides B-C were insoluble and fibrillar under the TEM. The secondary and tertiary structures of the non-phosphorylated peptide B demonstrated fewer helical twists, whereas peptide C displayed significantly more helical twists along the whole fiber(s) length following its phosphorylation.

CONCLUSION

Phosphorylated peptide A reduced P. gingivalis viability. CD spectroscopy demonstrated the phosphorylated and the non-phosphorylated peptide A predominantly formed from β-sheet structures in aqueous solution with potential antimicrobial activity. Phosphorylation of tau peptides physically changed their tertiary structure into PHFs with potential for self-aggregation and binding to the NFT lesion.

Association of periodontitis and oral microbiomes with Alzheimer’s disease: A narrative systematic review

Background/purpose

Alzheimer’s disease (AD) is a neurodegenerative disorder and the most common form of dementia. The etiology for AD includes age, genetic susceptibility, neuropathology, and infection. Periodontitis is an infectious and inflammatory disease which mainly causes alveolar bone destruction and tooth loss. The evidence of a link between AD and periodontitis remains controversial. Thus far, studies reviewing the association between AD and periodontal disease have been insufficient from the viewpoint of the oral microbiome. The aim of this review was to focus on studies that have explored the relationship between the oral microbiome and AD development by using the next-generation sequencing technique.

Materials and methods

A comprehensive electronic search of MEDLINE via PubMed, EMBASE, Scopus, and Google Scholar was conducted. The keywords included dementia, Alzheimer’s disease, cognitive impairment, periodontitis, periodontal disease, and oral microbiome.

Results

This review included 26 articles based on the eligibility criteria. Epidemiologic researches and post-mortem studies showed that the presence of periodontitis is associated with cognitive decline, suggesting a possible role of periodontal pathogens in the pathogenesis of AD. The reported microbiome was inconsistent with those in gene sequencing studies. Nevertheless, Gram-negative species may be possible candidates.

Conclusion

This review suggests that periodontal infection is associated with AD. The contributing microbiome remains unconfirmed, possibly because of different microbiome sampling sites or methods. Additional large-scale studies with periodontal intervention and longitudinal follow-up are warranted to clarify the relationship between periodontal disease and AD.

FTD-associated mutations in Tau result in a combination of dominant and recessive phenotypes

Although mutations in the microtubules-associated protein Tau have long been connected with several neurodegenerative diseases, the underlying molecular mechanisms causing these tauopathies are still not fully understood. Studies in various models suggested that dominant gain-of-function effects underlie the pathogenicity of these mutants; however, there is also evidence that the loss of normal physiological functions of Tau plays a role in tauopathies. Previous studies on Tau in Drosophila involved expressing the human Tau protein in the background of the endogenous Tau gene in addition to inducing high expression levels. To study Tau pathology in more physiological conditions, we recently created Drosophila knock-in models that express either wildtype human Tau (hTau^WT) or disease-associated mutant hTau (hTau^V337M and hTau^K369I) in place of the endogenous Drosophila Tau (dTau). Analyzing these flies as homozygotes, we could therefore detect recessive effects of the mutations while identifying dominant effects in heterozygotes. Using memory, locomotion and sleep assays, we found that homozygous mutant hTau flies showed deficits already when quite young whereas in heterozygous flies, disease phenotypes developed with aging. Homozygotes also revealed an increase in microtubule diameter, suggesting that changes in the cytoskeleton underlie the axonal degeneration we observed in these flies. In contrast, heterozygous mutant hTau flies showed abnormal axonal targeting and no detectable changes in microtubules. However, we previously showed that heterozygosity for hTau^V337M interfered with synaptic homeostasis in central pacemaker neurons and we now show that heterozygous hTau^K369I flies have decreased levels of proteins involved in the release of synaptic vesicles. Taken together, our results demonstrate that both mutations induce a combination of dominant and recessive disease-related phenotypes that provide behavioral and molecular insights into the etiology of Tauopathies.

Lower novelty-related locus coeruleus function is associated with Aβ-related cognitive decline in clinically healthy individuals

Animal and human imaging research reported that the presence of cortical Alzheimer’s Disease’s (AD) neuropathology, beta-amyloid and neurofibrillary tau, is associated with altered neuronal activity and circuitry failure, together facilitating clinical progression. The locus coeruleus (LC), one of the initial subcortical regions harboring pretangle hyperphosphorylated tau, has widespread connections to the cortex modulating cognition. Here we investigate whether LC’s in-vivo neuronal activity and functional connectivity (FC) are associated with cognitive decline in conjunction with beta-amyloid. We combined functional MRI of a novel versus repeated face-name paradigm, beta-amyloid-PET and longitudinal cognitive data of 128 cognitively unimpaired older individuals. We show that LC activity and LC-FC with amygdala and hippocampus was higher during novelty. We also demonstrated that lower novelty-related LC activity and LC-FC with hippocampus and parahippocampus were associated with steeper beta-amyloid-related cognitive decline. Our results demonstrate the potential of LC’s functional properties as a gauge to identify individuals at-risk for AD-related cognitive decline.

Older individuals exhibiting diminished function of the locus coeruleus while learning new information show faster cognitive decline that is typical for Alzheimer’s disease.

The Role of Non-coding RNAs in Alzheimer's Disease: From Regulated Mechanism to Therapeutic Targets and Diagnostic Biomarkers

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder. AD is characterized by the production and aggregation of beta-amyloid (Aβ) peptides, hyperphosphorylated tau proteins that form neurofibrillary tangles (NFTs), and subsequent neuroinflammation, synaptic dysfunction, autophagy and oxidative stress. Non-coding RNAs (ncRNAs) can be used as potential therapeutic targets and biomarkers due to their vital regulatory roles in multiple biological processes involved in disease development. The involvement of ncRNAs in the pathogenesis of AD has been increasingly recognized. Here, we review the ncRNAs implicated in AD and elaborate on their main regulatory pathways, which might have contributions for discovering novel therapeutic targets and drugs for AD.

Liquid-liquid phase separation of tau: From molecular biophysics to physiology and disease

Biomolecular condensation via liquid-liquid phase separation (LLPS) of intrinsically disordered proteins/regions (IDPs/IDRs), with and without nucleic acids, has drawn widespread interest due to the rapidly unfolding role of phase-separated condensates in a diverse range of cellular functions and human diseases. Biomolecular condensates form via transient and multivalent intermolecular forces that sequester proteins and nucleic acids into liquid-like membrane-less compartments. However, aberrant phase transitions into gel-like or solid-like aggregates might play an important role in neurodegenerative and other diseases. Tau, a microtubule-associated neuronal IDP, is involved in microtubule stabilization, regulates axonal outgrowth and transport in neurons. A growing body of evidence indicates that tau can accomplish some of its cellular activities via LLPS. However, liquid-to-solid transition resulting in the abnormal aggregation of tau is associated with neurodegenerative diseases. The physical chemistry of tau is crucial for governing its propensity for biomolecular condensation which is governed by various intermolecular and intramolecular interactions leading to simple one-component and complex multi-component condensates. In this review, we aim at capturing the current scientific state in unveiling the intriguing molecular mechanism of phase separation of tau. We particularly focus on the amalgamation of existing and emerging biophysical tools that offer unique spatiotemporal resolutions on a wide range of length- and time-scales. We also discuss the link between quantitative biophysical measurements and novel biological insights into biomolecular condensation of tau. We believe that this account will provide a broad and multidisciplinary view of phase separation of tau and its association with physiology and disease.

The extracellular HDAC6 ZnF UBP domain modulates the actin network and post-translational modifications of Tau

BACKGROUND

Microtubule-associated protein Tau undergoes aggregation in Alzheimer`s disease (AD) and a group of other related diseases collectively known as Tauopathies. In AD, Tau forms aggregates, which are deposited intracellularly as neurofibrillary tangles. Histone deacetylase-6 (HDAC6) plays an important role in aggresome formation, where it recruits polyubiquitinated aggregates to the motor protein dynein.

METHODS

Here, we have studied the effects of HDAC6 ZnF UBP on Tau phosphorylation, ApoE localization, GSK-3β regulation and cytoskeletal organization in neuronal cells by immunocytochemical analysis. This analysis reveals that the cell exposure to the UBP-type zinc finger domain of HDAC6 (HDAC6 ZnF UBP) can modulate Tau phosphorylation and actin cytoskeleton organization.

RESULTS

HDAC6 ZnF UBP treatment to cells did not affect their viability and resulted in enhanced neurite extension and formation of structures similar to podosomes, lamellipodia and podonuts suggesting the role of this domain in actin re-organization. Also, HDAC6 ZnF UBP treatment caused increase in nuclear localization of ApoE and tubulin localization in microtubule organizing centre (MTOC). Therefore, our studies suggest the regulatory role of this domain in different aspects of neurodegenerative diseases. Upon HDAC6 ZnF UBP treatment, inactive phosphorylated form of GSK-3β increases without any change in total GSK-3β level.

CONCLUSIONS

HDAC6 ZnF UBP was found to be involved in cytoskeletal re-organization by modulating actin dynamics and tubulin localization. Overall, our study suggests that ZnF domain of HDAC6 performs various regulatory functions apart from its classical function in aggresome formation in protein misfolding diseases. Video abstract.

Nasal Extracts from Patients with Alzheimer's Disease Induce Tau Aggregates in a Cellular Model of Tau Propagation

Background:

Emerging evidence indicates that the misfolded tau protein can propagate aggregates between cells in a prion-like manner. This prion activity has been typically studied in brain extracts of patients with Alzheimer’s disease (AD), but not in the olfactory region that can be a potential biomarker in AD.

Objective:

To investigate the prion seeding activity of tau in nasal mucosa tissues using a cell culture model of tau propagation.

Methods:

Brain and nasal mucosa homogenates were added to HEK293T cells expressing three repeat or four-repeat domains of tau with the L266V, V337M (3RD^*VM) and P301L and V377M mutations (4RD^*LM) fused to the enhanced green fluorescence protein (EGFP) respectively. We also measured the level of phosphorylated tau (p-tau), total tau (t-tau), and p-tau/t-tau ratio and performed correlation analysis between tau prion activity and the level of tau.

Results:

We found that brain and nasal tissue homogenates from patients with AD significantly induced tau aggregation in HEK293T cells either expressing tau 3RD^*VM-EGFP or 4RD^*LM-EGFP compared with control brain and nasal tissue homogenates. The levels of p-tau and p-tau/t-tau ratio were significantly increased in the brain of patients with AD; however, no significant difference was found in nasal tissue compared with their respective control tissue homogenates.

Conclusion:

These results suggest that the nasal tissues contain tau seeds, similar to the brain, albeit without changes in the levels of p-tau and t-tau. Therefore, a cellular bioassay using nasal tissues would have great potential as an AD biomarker because of the usefulness of nasal tissue biopsy.

Hyperphosphorylation Renders Tau Prone to Aggregate and to Cause Cell Death

Alzheimer's disease (AD) is a neurodegenerative disorder without a cure or prevention to date. Hyperphosphorylated tau forms the neurofibrillary tangles (NFTs) that correlate well with the progression of cognitive impairments. Animal studies demonstrated the pathogenic role of hyperphosphorylated tau. Understanding how abnormal phosphorylation renders a normal tau prone to form toxic fibrils is key to delineating molecular pathology and to developing efficacious drugs for AD. Production of a tau bearing the disease-relevant hyperphosphorylation and molecular characters is a pivotal step. Here, we report the preparation and characterization of a recombinant hyperphosphorylated tau (p-tau) with strong relevance to disease. P-tau generated by the PIMAX approach resulted in phosphorylation at multiple epitopes linked to the progression of AD neuropathology. In stark contrast to unmodified tau that required an aggregation inducer, and which had minimal effects on cell functions, p-tau formed inducer-free fibrils that triggered a spike of mitochondrial superoxide, induced apoptosis, and caused cell death at sub-micromolar concentrations. P-tau-induced apoptosis was suppressed by inhibitors for reactive oxygen species. Hyperphosphorylation apparently caused rapid formation of a disease-related conformation. In both aggregation and cytotoxicity, p-tau exhibited seeding activities that converted the unmodified tau into a cytotoxic species with an increased propensity for fibrillization. These characters of p-tau are consistent with the emerging view that hyperphosphorylation causes tau to become an aggregation-prone and cytotoxic species that underlies diffusible pathology in AD and other tauopathies. Our results further suggest that p-tau affords a feasible tool for Alzheimer's disease mechanistic and drug discovery studies.

Cornel Iridoid Glycoside Suppresses Tau Hyperphosphorylation and Aggregation in a Mouse Model of Tauopathy through Increasing Activity of PP2A

BACKGROUND

rTg4510 mice are transgenic mice expressing P301L mutant tau and have been developed as an animal model of tauopathy including Alzheimer's Disease (AD). Cornel Iridoid Glycoside (CIG) is an active ingredient extracted from Cornus officinalis, a traditional Chinese herb. The purpose of the present study was to investigate the effects of CIG on tau pathology and underlying mechanisms using rTg4510 mice.

METHODS

The cognitive functions were detected by Morris water maze and objective recognition tests. Western blotting and immunofluorescence were conducted to measure the levels of phosphorylated tau and related proteins. Serine/threonine phosphatase assay was applied to detect the activity of protein phosphatase 2A (PP2A).

RESULTS

Intragastric administration of CIG for 3 months improved learning and memory abilities, prevented neuronal and synapse loss, halted brain atrophy, elevated levels of synaptic proteins, protected cytoskeleton, reduced tau hyperphosphorylation and aggregation in the brain of rTg4510 mice. In the mechanism studies, CIG increased the activity of PP2A, elevated the methylation of PP2A catalytic C (PP2Ac) at leucine 309, decreased the phosphorylation of PP2Ac at tyrosine 307, and increased protein expression of leucine carboxyl methyltransferase 1 (LCMT-1), protein tyrosine phosphatase 1B (PTP1B), and protein phosphatase 2A phosphatase activator (PTPA) in the brain of rTg4510 mice.

CONCLUSION

CIG might have the potential to treat tauopathy such as AD via activating PP2A.

S-Adenosylmethionine Rescues Cognitive Deficits in the rTg4510 Animal Model by Stabilizing Protein Phosphatase 2A and Reducing Phosphorylated Tau

Background: Alterations in the methionine cycle and abnormal tau phosphorylation are implicated in many neurodegenerative diseases, including Alzheimer’s disease and frontotemporal dementia. rTg4510 mice express mutant human P301L tau and are a model of tau hyperphosphorylation. The cognitive deficit seen in these animals correlates with a burden of hyperphosphorylated tau and is a model to test therapies aimed at lowering phosphorylated tau. Objective: This study aimed to increase protein phosphatase 2A activity through supplementation of S-adenosylmethionine and analyze the effect on spatial memory and tau in treated animals. Methods: 6-month-old rTg4510 mice were treated with 100 mg/kg S-adenosylmethionine by oral gavage for 3 weeks. Spatial recognition memory was tested in the Y-maze. Alterations to phosphorylated tau and protein phosphatase 2A were explored using immunohistochemistry, western blot, and enzyme-linked immunosorbent assays. Results: Treatment with S-adenosylmethionine increased the Y-maze novel arm exploration time and increased both the expression and activity of protein phosphatase 2A. Furthermore, treatment reduced the number of AT8 positive neurons and reduced the expression of phosphorylated tau (Ser202/Thr205). S-adenosylmethionine contributes to multiple pathways in neuronal homeostasis and neurodegeneration. Conclusion: This study shows that supplementation with S-adenosylmethionine stabilizes the heterotrimeric form of PP2A resulting in an increase the enzymatic activity, a reduced level of pathological tau, and improved cognition.

Extensive Plasmid Library to Prepare Tau Protein Variants and Study Their Functional Biochemistry

Tau neurofibrillary tangles are key pathological features of Alzheimer's disease and other tauopathies. Recombinant protein technology is vital for studying the structure and function of tau in physiology and aggregation in pathophysiology. However, open-source and well-characterized plasmids for efficiently expressing and purifying different tau variants are lacking. We generated 44 sequence-verified plasmids including those encoding full length (FL) tau-441, its four-repeat microtubule-binding (K18) fragment, and their respective selected familial pathological variants (N279K, V337M, P301L, C291R, and S356T). Moreover, plasmids for expressing single (C291A), double (C291A/C322A), and triple (C291A/C322A/I260C) cysteine-modified variants were generated to study alterations in cysteine content and locations. Furthermore, protocols for producing representative tau forms were developed. We produced and characterized the aggregation behavior of the triple cysteine-modified tau-K18, often used in real-time cell internalization and aggregation studies because it can be fluorescently labeled on a cysteine outside the microtubule-binding core. Similar to the wild type (WT), triple cysteine-modified tau-K18 aggregated by progressive β-sheet enrichment, albeit at a slower rate. On prolonged incubation, cysteine-modified K18 formed paired helical filaments similar to those in Alzheimer's disease, sharing morphological phenotypes with WT tau-K18 filaments. Nonetheless, cysteine-modified tau-K18 filaments were significantly shorter (p = 0.002) and mostly wider than WT filaments, explainable by their different principal filament elongation pathways: vertical (end-to-end) and lateral growth for WT and cysteine-modified, respectively. Cysteine rearrangement may therefore induce filament polymorphism. Together, the plasmid library, the protein production methods, and the new insights into cysteine-dependent aggregation should facilitate further studies and the design of antiaggregation agents.

Understanding the Immunologic Characteristics of Neurologic Manifestations of SARS-CoV-2 and Potential Immunological Mechanisms

Similar to its predecessors, coronavirus disease 2019 (COVID-19) exhibits neurotrophic properties, which lead to progression of neurologic sequelae. Besides direct viral invasion to the central nervous system (CNS), indirect CNS involvement through viral-mediated immune response is plausible. Aberrant immune pathways such as extreme release of cytokines (cytokine storm), autoimmunity mediated by cross-reactivity between CNS components and viral particles, and microglial activation propagate CNS damage in these patients. Here, we review the currently available evidence to discuss the plausible immunologic pathways that may contribute to the development of COVID-19 neurological complications, namely Alzheimer’s disease, Parkinson’s disease, stroke, multiple sclerosis, Guillain-Barre syndrome, seizure, and brainstem involvement.

Prenatal to early postnatal neurotrophic treatment prevents Alzheimer-like behavior and pathology in mice

BACKGROUND

Alzheimer's disease (AD) is a progressive neurodegenerative disorder of middle-aged to old individuals. The pathophysiological process of AD is believed to begin many years before the emergence of clinical symptoms. The important influence of congenital genetic aberrations on the development of AD provides a novel opportunity to initiate prenatal to early postnatal pharmacological treatment to address the role of this critical period of brain development in the disease.

METHODS

We investigated for the first time the effect of oral treatment during prenatal to early postnatal development with a neurotrophic compound, P021 (Ac-DGGL^AG-NH2), on neurobehavior and AD-like pathology in 3xTg-AD, a transgenic mouse model of AD. The transgenic and control wild-type female mice were treated from prenatal day 8 to postnatal day 21 with a custom-made diet containing P021 or a vehicle diet, followed by a standard diet. AD-type cognitive function and pathological features were studied during adulthood and old age.

RESULTS

The P021 treatment rescued cognitive deficits at 4 months, reduced abnormal hyperphosphorylation and accumulation of tau at known major AD neurofibrillary pathology-associated sites, and decreased Aβ plaque load at 22 months in 3xTg-AD mice. Prenatal to early postnatal treatment with P021 also ameliorated certain markers of postsynaptic deficits, including PSD-95 levels and CREB activity, and decreased one measure of neuroinflammation, GFAP level in the brain at 4 and 22 months in 3xTg mice.

CONCLUSIONS

These findings suggest that neurotrophic impairment during early development can be one of the etiopathogenic factors of AD and that the neurotrophic peptide mimetic is a potential early prevention strategy for this disease.

Methylene Blue Inhibits Formation of Tau Fibrils but not of Granular Tau Oligomers: A Plausible Key to Understanding Failure of a Clinical Trial for Alzheimer's Disease

Alzheimer's disease pathology is characterized by extracellular deposits of amyloid-β (Aβ) and intracellular inclusions of hyperphosphorylated tau. Although genetic studies of familial Alzheimer's disease suggest a causal link between Aβ and disease symptoms, the failure of various Aβ-targeted strategies to slow or halt disease progression has led to consideration of the idea that inhibition of tau aggregation might be a more promising therapeutic approach. Methylene blue (MB), which inhibits tau aggregation and rescue memory deficits in a mouse model of tauopathy, however, lacked efficacy in a recent Phase III clinical trial. In order to gain insight into this failure, the present study was designed to examine the mechanism through which MB inhibits tau aggregation. We found that MB inhibits heparin-induced tau aggregation in vitro, as measured by thioflavin T fluorescence. Further, MB reduced the amount of tau in precipitants recovered after ultracentrifugation of the aggregation mixture. Atomic force microscopy revealed that MB reduces the number of tau fibrils but increases the number of granular tau oligomers. The latter result was confirmed by sucrose gradient centrifugation: MB treatment was associated with higher levels of granular tau oligomers (fraction 3) and lower levels of tau fibrils (fractions 5 and 6). We previously demonstrated that the formation of granular tau oligomers, rather than tau fibrils, is essential for neuronal death. Thus, the fact that MB actions are limited to inhibition of tau fibril formation provides a mechanistic explanation for the poor performance of MB in the recent Phase III clinical trial.

Tau and Alpha Synuclein Synergistic Effect in Neurodegenerative Diseases: When the Periphery Is the Core

In neuronal cells, tau is a microtubule-associated protein placed in axons and alpha synuclein is enriched at presynaptic terminals. They display a propensity to form pathologic aggregates, which are considered the underlying cause of Alzheimer's and Parkinson's diseases. Their functional impairment induces loss of axonal transport, synaptic and mitochondrial disarray, leading to a "dying back" pattern of degeneration, which starts at the periphery of cells. In addition, pathologic spreading of alpha-synuclein from the peripheral nervous system to the brain through anatomical connectivity has been demonstrated for Parkinson's disease. Thus, examination of the extent and types of tau and alpha-synuclein in peripheral tissues and their relation to brain neurodegenerative diseases is of relevance since it may provide insights into patterns of protein aggregation and neurodegeneration. Moreover, peripheral nervous tissues are easily accessible in-vivo and can play a relevant role in the early diagnosis of these conditions. Up-to-date investigations of tau species in peripheral tissues are scant and have mainly been restricted to rodents, whereas, more evidence is available on alpha synuclein in peripheral tissues. Here we aim to review the literature on the functional role of tau and alpha synuclein in physiological conditions and disease at the axonal level, their distribution in peripheral tissues, and discuss possible commonalities/diversities as well as their interaction in proteinopathies.

Bayesian integrative analysis of epigenomic and transcriptomic data identifies Alzheimer's disease candidate genes and networks

Biomedical research studies have generated large multi-omic datasets to study complex diseases like Alzheimer’s disease (AD). An important aim of these studies is the identification of candidate genes that demonstrate congruent disease-related alterations across the different data types measured by the study. We developed a new method to detect such candidate genes in large multi-omic case-control studies that measure multiple data types in the same set of samples. The method is based on a gene-centric integrative coefficient quantifying to what degree consistent differences are observed in the different data types. For statistical inference, a Bayesian hierarchical model is used to study the distribution of the integrative coefficient. The model employs a conditional autoregressive prior to integrate a functional gene network and to share information between genes known to be functionally related. We applied the method to an AD dataset consisting of histone acetylation, DNA methylation, and RNA transcription data from human cortical tissue samples of 233 subjects, and we detected 816 genes with consistent differences between persons with AD and controls. The findings were validated in protein data and in RNA transcription data from two independent AD studies. Finally, we found three subnetworks of jointly dysregulated genes within the functional gene network which capture three distinct biological processes: myeloid cell differentiation, protein phosphorylation and synaptic signaling. Further investigation of the myeloid network indicated an upregulation of this network in early stages of AD prior to accumulation of hyperphosphorylated tau and suggested that increased CSF1 transcription in astrocytes may contribute to microglial activation in AD. Thus, we developed a method that integrates multiple data types and external knowledge of gene function to detect candidate genes, applied the method to an AD dataset, and identified several disease-related genes and processes demonstrating the usefulness of the integrative approach.

Recent technological advances have led to a new generation of studies that interrogate multiple molecular levels in the same target tissue of a set of subjects, generating complex multi-omic datasets with which to study disease mechanism. These datasets of genetic, epigenomic, transcriptomic, and other data have the potential to reveal novel biological insights; however, integrative analyses remain challenging and require new computational methods. We developed an integrative Bayesian approach to detect genes with consistent differences between case and control samples across multiple data types. The method further integrates prior knowledge about gene function in the form of a gene functional similarity network to improve statistical inference by sharing information between related genes. We applied our method to an Alzheimer’s disease dataset of epigenomic and transcriptomic data and detected and then validated several novel and known candidate genes as well as three major disease-related biological processes. One of these processes reflected microglial activation and included the cytokine CSF1. Single-nucleus data revealed that CSF1 was primarily upregulated in astrocytes, implicating the involvement of this cell type in microglial activation. Hence, we demonstrated that integrative analysis approaches to multi-omic datasets can improve candidate gene detection and thereby generate new insights into complex diseases.

Beclin 1 Complex and Neurodegenerative Disorders

Beclin1 is the mammalian orthologue of yeast Atg6/vacuolar protein sorting-30 (VPS30). Beclin1 interacts with various biological macromolecules like ATG14, BIF-1, NRBF2, RUBICON, UVRAG, AMBRA1, HMGB1, PINK1, and PARKIN. Such interactions promote Beclin1-PI3KC3 complex formation. Autophagy is blocked in apoptosis owing to the breakdown of Beclin1 by caspase whereas autophagy induction inhibits effector caspase degradation, therefore, blocks apoptosis. Thus, the Beclin1 is an essential biomolecular species for cross-regulation between autophagy and apoptosis. Various studies carried out in neurodegenerative animal models associated with aggregated proteins have confirmed that multifunctional Beclin1 protein is necessary for neuronal integrity. The role of Beclin1 protein has been investigated and was reported in various human neurodegeneration disorders. This chapter aims to provide an insight into the role of Beclin1 in the development of neurodegenerative disorders.

Tau Misfolding Efficiently Propagates between Individual Intact Hippocampal Neurons

Neurofibrillary tangles, formed of misfolded, hyperphosphorylated tau protein, are a pathological hallmark of several neurodegenerations, including Alzheimer's disease. Tau pathology spreads between neurons and propagates misfolding in a prion-like manner throughout connected neuronal circuits. Tauopathy is accompanied by significant neuronal death, but the relationships between initial tau misfolding, propagation across connected neurons and cytotoxicity remain unclear. In particular the immediate functional consequence of tau misfolding for the individual neuron is not well understood. Here, using microfluidic devices to recreate discretely organized neuronal connections, we show that the spread and propagation of misfolded tau between individual murine neurons is rapid and efficient; it occurs within days. The neurons containing and propagating tau pathology display selective axonal transport deficits but remain viable and electrically competent. Therefore, we demonstrate that seed-competent misfolded tau species do not acutely cause cell death, but instead initiate discrete cellular dysfunctions.SIGNIFICANCE STATEMENT Public awareness of progressive neurodegenerations such as dementias associated with aging or repetitive head trauma is rising. Protein misfolding underlies many neurodegenerative diseases including tauopathies, where the misfolded tau protein propagates pathology through connected brain circuits in a prion-like manner. Clinically, these diseases progress over the course of years. Here we show that the underlying protein misfolding propagates rapidly between individual neurons. Presence of misfolded tau is not directly cytotoxic to the neuron; the cells remain viable with limited deficits. This suggests that neurons with tau pathology could be rescued with a therapeutic disease modifier and highlights an under-appreciated time window for such therapeutic intervention.

Exosomes in Pathogenesis, Diagnosis, and Treatment of Alzheimer's Disease

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by the accumulation of β-amyloid peptide 1-42 and phosphorylation of tau protein in the brain. Thus far, the transfer mechanism of these cytotoxic proteins between nerve cells remains unclear. Recent studies have shown that nanoscale extracellular vesicles (exosomes) originating from cells may play important roles in this transfer process. In addition, several genetic materials and proteins are also involved in intercellular communication by the secretion of the exosomes. That proposes novel avenues for early diagnosis and biological treatment in AD, based on exosome detection and intervention. In this review, exosome-related pathways of cytotoxic protein intercellular transfer in AD, and the effect of membrane proteins on exosomes targeting cells are first introduced. The advances in exosome-related biomarker detection in AD are summarized. Finally, the advantages and challenges of reducing cytotoxic protein accumulation via exosomal intervention for AD treatment are discussed. It is envisaged that future research in exosomes may well provide new insights into the pathogenesis, diagnosis, and treatment of AD.

The elusive tau molecular structures: can we translate the recent breakthroughs into new targets for intervention?

Insights into tau molecular structures have advanced significantly in recent years. This field has been the subject of recent breakthroughs, including the first cryo-electron microscopy structures of tau filaments from Alzheimer’s and Pick’s disease inclusions, as well as the structure of the repeat regions of tau bound to microtubules. Tau structure covers various species as the tau protein itself takes many forms. We will here address a range of studies that help to define the many facets of tau protein structures and how they translate into pathogenic forms. New results shed light on previous data that need now to be revisited in order to up-date our knowledge of tau molecular structure. Finally, we explore how these data can contribute the important medical aspects of this research - diagnosis and therapeutics.

Free d-aspartate triggers NMDA receptor-dependent cell death in primary cortical neurons and perturbs JNK activation, Tau phosphorylation, and protein SUMOylation in the cerebral cortex of mice lacking d-aspartate oxidase activity

In mammals, free d-aspartate (D-Asp) is abundant in the embryonic brain, while levels remain very low during adulthood as a result of the postnatal expression and activity of the catabolizing enzyme d-aspartate oxidase (DDO). Previous studies have shown that long-lasting exposure to nonphysiological, higher D-Asp concentrations in Ddo knockout (Ddo^-/-) mice elicits a precocious decay of synaptic plasticity and cognitive functions, along with a dramatic age-dependent expression of active caspase 3, associated with increased cell death in different brain regions, including hippocampus, prefrontal cortex, and substantia nigra pars compacta. Here, we investigate the yet unclear molecular and cellular events associated with the exposure of abnormally high D-Asp concentrations in cortical primary neurons and in the brain of Ddo^-/- mice. For the first time, our in vitro findings document that D-Asp induces in a time-, dose-, and NMDA receptor-dependent manner alterations in JNK and Tau phosphorylation levels, associated with pronounced cell death in primary cortical neurons. Moreover, observations obtained in Ddo^-/- animals confirmed that high in vivo levels of D-Asp altered cortical JNK signaling, Tau phosphorylation and enhanced protein SUMOylation, indicating a robust indirect role of DDO activity in regulating these biochemical NMDA receptor-related processes. Finally, no gross modifications in D-Asp concentrations and DDO mRNA expression were detected in the cortex of patients with Alzheimer's disease when compared to age-matched healthy controls.

Prionoid Proteins in the Pathogenesis of Neurodegenerative Diseases

There is a growing body of evidence that prionoid protein behaviors are a core element of neurodegenerative diseases (NDs) that afflict humans. Common elements in pathogenesis, pathological effects and protein-level behaviors exist between Alzheimer's Disease (AD), Parkinson's Disease (PD), Huntington's Disease (HD) and Amyotrophic Lateral Sclerosis (ALS). These extend beyond the affected neurons to glial cells and processes. This results in a complicated system of disease progression, which often takes advantage of protective processes to promote the propagation of pathological protein aggregates. This review article provides a current snapshot of knowledge on these proteins and their intrinsic role in the pathogenesis and disease progression seen across NDs.

Genesis of Neuroprotective Peptoid from Aβ30-34 Inhibits Aβ Aggregation and AChE Activity

Aβ peptide and hyper-phosphorylated microtubule associated protein (Tau) aggregation causes severe damage to both the neuron membrane and key signal processing microfilament (microtubule) in Alzheimer's disease (AD) brains. To date, the key challenge is to develop nontoxic, proteolytically stable amyloid inhibitors, which can simultaneously target multiple pathways involved in AD. Various attempts have been made in this direction; however, clinical outcomes of those attempts have been reported to be poor. Thus, we choose development of peptoid (N-substituted glycine oligomers)-based leads as potential AD therapeutics, which are easy to synthesize, found to be proteolytically stable, and exhibit excellent bioavailability. In this paper, we have designed and synthesized a new short peptoid for amyloid inhibition from 30-34 hydrophobic pocket of amyloid beta (Aβ) peptide. The peptoid selectively binds with 17-21 hydrophobic region of Aβ and inhibits Aβ fibril formation. Various in vitro assays suggested that our AI peptoid binds with tubulin/microtubule and promotes its polymerization and stability. This peptoid also inhibits AChE-induced Aβ fibril formation and provides significant neuroprotection against toxicity generated by nerve growth factor (NGF) deprived neurons derived from rat adrenal pheochromocytoma (PC12) cell line. Moreover, this peptoid shows serum stability and is noncytotoxic to primary rat cortical neurons.

Autophagy in Age-Associated Neurodegeneration

The elimination of abnormal and dysfunctional cellular constituents is an essential prerequisite for nerve cells to maintain their homeostasis and proper function. This is mainly achieved through autophagy, a process that eliminates abnormal and dysfunctional cellular components, including misfolded proteins and damaged organelles. Several studies suggest that age-related decline of autophagy impedes neuronal homeostasis and, subsequently, leads to the progression of neurodegenerative disorders due to the accumulation of toxic protein aggregates in neurons. Here, we discuss the involvement of autophagy perturbation in neurodegeneration and present evidence indicating that upregulation of autophagy holds potential for the development of therapeutic interventions towards confronting neurodegenerative diseases in humans.

The direct and indirect effects of α-synuclein on microtubule stability in the pathogenesis of Parkinson's disease

Despite decades of research, the mechanism of Parkinson's disease pathogenesis remains unclear. Studies have focused heavily on the protein α-synuclein, which is the primary component of Lewy bodies, the pathologic inclusions that are the hallmark of Parkinson's on the cellular level. While the roles of α-synuclein in causing mitochondrial dysfunction and disruptions to the proteasomal system have been well documented, recently, its role in effecting microtubule dynamics has been investigated as a potential source of pathogenicity. Here, we evaluate the evidence for and against the role of α-synuclein in destabilizing microtubules, causing axonal transport deficits and eventually neurodegeneration. We present evidence for a model where α-synuclein has both a direct and indirect effect on microtubule stability. Directly, it may act as a microtubule-associated protein, binding to microtubules and directly effecting their dynamics. Indirectly, it may promote the hyperphosphorylation of the microtubule stabilizing protein, tau, leading to tau aggregation with other microtubule stabilizing proteins, hence indirectly causing microtubule destabilization. This model provides insights into the function of α-synuclein and tau in Parkinson's disease pathogenesis and raises the possibility that this role that may also be conserved in Alzheimer's disease.

CNS Injury: Posttranslational Modification of the Tau Protein as a Biomarker

The ideal biomarker for central nervous system (CNS) trauma in patients would be a molecular marker specific for injured nervous tissue that would provide a consistent and reliable assessment of the presence and severity of injury and the prognosis for recovery. One candidate biomarker is the protein tau, a microtubule-associated protein abundant in the axonal compartment of CNS neurons. Following axonal injury, tau becomes modified primarily by hyperphosphorylation of its various amino acid residues and cleavage into smaller fragments. These posttrauma products can leak into the cerebrospinal fluid or bloodstream and become candidate biomarkers of CNS injury. This review examines the primary molecular changes that tau undergoes following traumatic brain injury and spinal cord injury, and reviews the current literature in traumatic CNS biomarker research with a focus on the potential for hyperphosphorylated and cleaved tau as sensitive biomarkers of injury.

O-GlcNAcylation: A regulator of tau pathology and neurodegeneration

O-GlcNAcylation is the posttranslational modification of intracellular proteins by O-linked β-N-acetylglucosamine (O-GlcNAc). The discovery of O-GlcNAc modification of tau and its impact on tau phosphorylation has attracted recent research interest in O-GlcNAc studies in the Alzheimer's disease (AD) field. Modification of proteins by O-GlcNAc occurs extensively in the brain. The expressions and activities of the enzymes catalyzing O-GlcNAc cycling are several-fold higher in the brain than in the peripheral tissues. The O-GlcNAcylation levels of brain proteins including tau are decreased in AD brain, probably due to decreased brain glucose metabolism. The reduction of brain O-GlcNAcylation appears to mediate the molecular mechanism by which decreased brain glucose metabolism contributes to neurodegeneration. Studies on mouse models of tauopathies suggest a neuroprotective role of pharmacological elevation of brain O-GlcNAc, which could potentially be a promising approach for treating AD and other neurodegenerative diseases.

New insights into Alzheimer's disease pathogenesis: the involvement of neuroligins in synaptic malfunction

Synaptic damage is a key hallmark of Alzheimer's disease and the best correlate with cognitive decline ante mortem. Signature protein combinations arrayed at tightly apposed pre- and post-synaptic sites characterize different types of synapse. Neuroligins are postsynaptic cell adhesion molecules that interact with neurexins across the synaptic cleft. These pairings recruit receptors, channels and signal transduction molecules to the synapse, and help mediate trans-synaptic transmission. Dysfunction in the neuroligin family can disrupt neuronal networks and leads to neurodegeneration and other diseases. The extracellular domain of neuroligins is homologous with acetylcholinesterase but lacks residues required for enzymatic activity. This domain may interact pathogenically with β-amyloid. Here we summarize research over the last decade on the potential involvement of neuroligins in Alzheimer's disease.