Tau: Enabler of diverse brain disorders and target of rapidly evolving therapeutic strategies

Irisin inhibits microglial senescence via TFAM-mediated mitochondrial metabolism in a mouse model of tauopathy

BACKGROUND

The accumulation of senescent microglia has been highlighted as a critical contributor to the progression of tauopathies. Irisin, a muscle-derived hormone produced by the proteolytic cleavage of Fibronectin-domain III containing 5 (FNDC5), mediates the pleiotropic effects of exercise on the physical body. Herein, we investigate the potential role of irisin in microglial senescence in tauopathies.

METHODS

To model tauopathies both in vivo and in vitro, we utilized P301S tau transgenic mice and tau K18 fibril-treated microglia BV2 cells, respectively. We first examined the expression of the irisin expression and senescence phenotypes of microglia in tauopathies. Subsequently, we investigated the impact of irisin on microglial senescence and its underlying molecular mechanisms.

RESULT

We observed a reduction in irisin levels and an onset of premature microglial senescence both in vivo and in vitro. Irisin administration was found to counteract microglial senescence and ameliorate cognitive decline in P301S mice. Mechanistically, irisin effectively inhibited microglial senescence by stimulating the expression of mitochondrial transcription factor A (TFAM), a master regulator of mitochondrial respiratory chain biogenesis, thereby enhancing mitochondrial oxidative phosphorylation (OXPHOS). Silencing TFAM eliminated the inhibitory effect of irisin on microglial senescence as well as the restorative effect of irisin on mitochondrial OXPHOS. Furthermore, the SIRT1/PGC1α signaling pathway appeared to be implicated in irisin-mediated upregulation of TFAM.

CONCLUSION

Taken together, our study revealed that irisin mitigated microglial senescence via TFAM-driven mitochondrial biogenesis, suggesting a promising new avenue for therapeutic strategies targeting tauopathies.

Lineage-specific splicing regulation of MAPT gene in the primate brain

Divergence of precursor messenger RNA (pre-mRNA) alternative splicing (AS) is widespread in mammals, including primates, but the underlying mechanisms and functional impact are poorly understood. Here, we modeled cassette exon inclusion in primate brains as a quantitative trait and identified 1,170 (∼3%) exons with lineage-specific splicing shifts under stabilizing selection. Among them, microtubule-associated protein tau (MAPT) exons 2 and 10 underwent anticorrelated, two-step evolutionary shifts in the catarrhine and hominoid lineages, leading to their present inclusion levels in humans. The developmental-stage-specific divergence of exon 10 splicing, whose dysregulation can cause frontotemporal lobar degeneration (FTLD), is mediated by divergent distal intronic MBNL-binding sites. Competitive binding of these sites by CRISPR-dCas13d/gRNAs effectively reduces exon 10 inclusion, potentially providing a therapeutically compatible approach to modulate tau isoform expression. Our data suggest adaptation of MAPT function and, more generally, a role for AS in the evolutionary expansion of the primate brain.

DLK-MAPK Signaling Coupled with DNA Damage Promotes Intrinsic Neurotoxicity Associated with Non-Mutated Tau

Alzheimer's disease (AD) is the most prevalent form of neurodegeneration. Despite the well-established link between tau aggregation and clinical progression, the major pathways driven by this protein to intrinsically damage neurons are incompletely understood. To model AD-relevant neurodegeneration driven by tau, we overexpressed non-mutated human tau in primary mouse neurons and observed substantial axonal degeneration and cell death, a process accompanied by activated caspase 3. Mechanistically, we detected deformation of the nuclear envelope and increased DNA damage response in tau-expressing neurons. Gene profiling analysis further revealed significant alterations in the mitogen-activated protein kinase (MAPK) pathway; moreover, inhibitors of dual leucine zipper kinase (DLK) and c-Jun N-terminal kinase (JNK) were effective in alleviating wild-type human tau-induced neurodegeneration. In contrast, mutant P301L human tau was less toxic to neurons, despite causing comparable DNA damage. Axonal DLK activation induced by wild-type tau potentiated the impact of DNA damage response, resulting in overt neurotoxicity. In summary, we have established a cellular tauopathy model highly relevant to AD and identified a functional synergy between the DLK-MAPK axis and DNA damage response in the neuronal degenerative process.

Research progress on the relationship between epilepsy and circRNA

OBJECTIVE

This review aims to provide a comprehensive summary of the latest research progress regarding the relationship between epilepsy and circular RNA (circRNA).

METHODS

Relevant literature from the PubMed database was meticulously searched and reviewed. The selected articles focused on investigating the association between epilepsy and circRNA, including studies on expression patterns, diagnostic markers, therapeutic targets, and functional mechanisms.

RESULTS

Epilepsy, characterized by recurrent seizures, is a neurological disorder. Numerous studies have demonstrated significant alterations in the expression profiles of circRNA in epileptic brain tissues, animal models, and peripheral blood samples. These differential expressions of circRNA are believed to be closely linked with the occurrence and development of epilepsy. Moreover, circRNA has shown promising potential as diagnostic markers for epilepsy, as well as prognostic indicators for predicting disease outcomes. Furthermore, circRNA has emerged as a potential therapeutic target for epilepsy treatment, offering prospects for gene therapy interventions.

CONCLUSION

The dysregulation of circRNA expression in epilepsy suggests its potential involvement in the pathogenesis and progression of this disorder. Identifying specific circRNA molecules associated with epilepsy may pave the way for novel diagnostic approaches and therapeutic strategies. However, further investigations are imperative to elucidate the precise functional mechanisms of circRNA in epilepsy and validate its clinical utility.

Tau reduction with artificial microRNAs modulates neuronal physiology and improves tauopathy phenotypes in mice

Abnormal tau accumulation is the hallmark of several neurodegenerative diseases, named tauopathies. Strategies aimed at reducing tau in the brain are promising therapeutic interventions, yet more precise therapies would require targeting specific nuclei and neuronal subpopulations affected by disease while avoiding global reduction of physiological tau. Here, we developed artificial microRNAs directed against the human MAPT mRNA to dwindle tau protein by engaging the endogenous RNA interference pathway. In human differentiated neurons in culture, microRNA-mediated tau reduction diminished neuronal firing without affecting neuronal morphology or impairing axonal transport. In the htau mouse model of tauopathy, we locally expressed artificial microRNAs in the prefrontal cortex (PFC), an area particularly vulnerable to initiating tau pathology in this model. Tau knockdown prevented the accumulation of insoluble and hyperphosphorylated tau, modulated firing activity of putative pyramidal neurons, and improved glucose uptake in the PFC. Moreover, such tau reduction prevented cognitive decline in aged htau mice. Our results suggest target engagement of designed tau-microRNAs to effectively reduce tau pathology, providing a proof of concept for a potential therapeutic approach based on local tau knockdown to rescue tauopathy-related phenotypes.

Linking activity dyshomeostasis and sleep disturbances in Alzheimer disease

The presymptomatic phase of Alzheimer disease (AD) starts with the deposition of amyloid-β in the cortex and begins a decade or more before the emergence of cognitive decline. The trajectory towards dementia and neurodegeneration is shaped by the pathological load and the resilience of neural circuits to the effects of this pathology. In this Perspective, I focus on recent advances that have uncovered the vulnerability of neural circuits at early stages of AD to hyperexcitability, particularly when the brain is in a low-arousal states (such as sleep and anaesthesia). Notably, this hyperexcitability manifests before overt symptoms such as sleep and memory deficits. Using the principles of control theory, I analyse the bidirectional relationship between homeostasis of neuronal activity and sleep and propose that impaired activity homeostasis during sleep leads to hyperexcitability and subsequent sleep disturbances, whereas sleep disturbances mitigate hyperexcitability via negative feedback. Understanding the interplay among activity homeostasis, neuronal excitability and sleep is crucial for elucidating the mechanisms of vulnerability to and resilience against AD pathology and for identifying new therapeutic avenues.

Microtubule-affinity regulating kinase family members distinctively affect tau phosphorylation and promote its toxicity in a Drosophila model

Accumulation of abnormally phosphorylated tau and its aggregation constitute a significant hallmark of Alzheimer's disease (AD). Tau phosphorylation at Ser262 and Ser356 in the KXGS motifs of microtubule-binding repeats plays a critical role in its physiological function and AD disease progression. Major tau kinases to phosphorylate tau at Ser262 and Ser356 belong to the Microtubule Affinity Regulating Kinase family (MARK1-4), which are considered one of the major contributors to tau abnormalities in AD. However, whether and how each member affects tau toxicity in vivo is unclear. We used transgenic Drosophila as a model to compare the effect on tau-induced neurodegeneration among MARKs in vivo. MARK4 specifically promotes tau accumulation and Ser396 phosphorylation, which yields more tau toxicity than was caused by other MARKs. Interestingly, MARK1, 2, and 4 increased tau phosphorylation at Ser262 and Ser356, but only MARK4 caused tau accumulation, indicating that these sites alone did not cause pathological tau accumulation. Our results revealed MARKs are different in their effect on tau toxicity, and also in tau phosphorylation at pathological sites other than Ser262 and Ser356. Understanding the implementation of each MARK into neurodegenerative disease helps to develop more target and safety therapies to overcome AD and related tauopathies.

Acetylated tau exacerbates apoptosis by disturbing mitochondrial dynamics in HEK293 cells

An increase in tau acetylation at K274 and K281 and abnormal mitochondrial dynamics have been observed in the brains of Alzheimer's disease (AD) patients. Here, we constructed three types of tau plasmids, TauKQ (acetylated tau mutant, by mutating its K274/K281 into glutamine to mimic disease-associated lysine acetylation), TauKR (non-acetylated tau mutant, by mutating its K274/K281 into arginine), and TauWT (wild-type human full-length tau). By transfecting these tau plasmids in HEK293 cells, we found that TauWT and TauKR induced mitochondrial fusion by increasing the level of mitochondrial fusion proteins. Conversely, TauKQ induced mitochondrial fission by reducing mitochondrial fusion proteins, exacerbating mitochondrial dysfunction and apoptosis. BGP-15 ameliorated TauKQ-induced mitochondrial dysfunction and apoptosis by improving mitochondrial dynamics. Our findings suggest that acetylation of K274/281 represents an important post-translational modification site regulating mitochondrial dynamics, and that BGP-15 holds potential as a therapeutic agent for mitochondria-associated diseases such as AD.

Novel avenues of tau research

INTRODUCTION

The pace of innovation has accelerated in virtually every area of tau research in just the past few years.

METHODS

In February 2022, leading international tau experts convened to share selected highlights of this work during Tau 2022, the second international tau conference co-organized and co-sponsored by the Alzheimer's Association, CurePSP, and the Rainwater Charitable Foundation.

RESULTS

Representing academia, industry, and the philanthropic sector, presenters joined more than 1700 registered attendees from 59 countries, spanning six continents, to share recent advances and exciting new directions in tau research.

DISCUSSION

The virtual meeting provided an opportunity to foster cross-sector collaboration and partnerships as well as a forum for updating colleagues on research-advancing tools and programs that are steadily moving the field forward.

Quantitative live cell imaging of a tauopathy model enables the identification of a polypharmacological drug candidate that restores physiological microtubule interaction

Tauopathies such as Alzheimer's disease are characterized by aggregation and increased phosphorylation of the microtubule-associated protein tau. Tau's pathological changes are closely linked to neurodegeneration, making tau a prime candidate for intervention. We developed an approach to monitor pathological changes of aggregation-prone human tau in living neurons. We identified 2-phenyloxazole (PHOX) derivatives as putative polypharmacological small molecules that interact with tau and modulate tau kinases. We found that PHOX15 inhibits tau aggregation, restores tau's physiological microtubule interaction, and reduces tau phosphorylation at disease-relevant sites. Molecular dynamics simulations highlight cryptic channel-like pockets crossing tau protofilaments and suggest that PHOX15 binding reduces the protofilament's ability to adopt a PHF-like conformation by modifying a key glycine triad. Our data demonstrate that live-cell imaging of a tauopathy model enables screening of compounds that modulate tau-microtubule interaction and allows identification of a promising polypharmacological drug candidate that simultaneously inhibits tau aggregation and reduces tau phosphorylation.

Targeting glycogen synthase kinase-3β for Alzheimer's disease: Recent advances and future Prospects

Senile plaques induced by β-amyloid (Aβ) abnormal aggregation and neurofibrillary tangles (NFT) caused by tau hyperphosphorylation are important pathological manifestations of Alzheimer's disease (AD). Glycogen synthase kinase-3 (GSK-3) is a conserved kinase; one member GSK-3β is highly expressed in the AD brain and involved in the formation of NFT. Hence, pharmacologically inhibiting GSK-3β activity and expression is a good approach to treat AD. As summarized in this article, multiple GSK-3β inhibitors has been comprehensively summarized over recent five years. However, only lithium carbonate and Tideglusib have been studied in clinical trials of AD. Besides ATP-competitive and non-ATP-competitive inhibitors, peptide inhibitors, allosteric inhibitors and other types of inhibitors have gradually attracted more interest. Moreover, considering the close relationship between GSK-3β and other targets involved in cholinergic hypothesis, Aβ aggregation hypothesis, tau hyperphosphorylation hypothesis, oxidative stress hypothesis, neuro-inflammation hypothesis, etc., diverse multifunctional molecules and multi-target directed ligands (MTDLs) have also been disclosed. We hope that these recent advances and critical perspectives will facilitate the discovery of safe and effective GSK-3β inhibitors for AD treatment.

KIBRA repairs synaptic plasticity and promotes resilience to tauopathy-related memory loss

Synaptic plasticity is obstructed by pathogenic tau in the brain, representing a key mechanism that underlies memory loss in Alzheimer's disease (AD) and related tauopathies. Here, we found that reduced levels of the memory-associated protein KIdney/BRAin (KIBRA) in the brain and increased KIBRA protein levels in cerebrospinal fluid are associated with cognitive impairment and pathological tau levels in disease. We next defined a mechanism for plasticity repair in vulnerable neurons using the C-terminus of the KIBRA protein (CT-KIBRA). We showed that CT-KIBRA restored plasticity and memory in transgenic mice expressing pathogenic human tau; however, CT-KIBRA did not alter tau levels or prevent tau-induced synapse loss. Instead, we found that CT-KIBRA stabilized the protein kinase Mζ (PKMζ) to maintain synaptic plasticity and memory despite tau-mediated pathogenesis. Thus, our results distinguished KIBRA both as a biomarker of synapse dysfunction and as the foundation for a synapse repair mechanism to reverse cognitive impairment in tauopathy.

Neuronal MAPT expression is mediated by long-range interactions with cis-regulatory elements

Tauopathies are a group of neurodegenerative diseases defined by abnormal aggregates of tau, a microtubule-associated protein encoded by MAPT. MAPT expression is near absent in neural progenitor cells (NPCs) and increases during differentiation. This temporally dynamic expression pattern suggests that MAPT expression could be controlled by transcription factors and cis-regulatory elements specific to differentiated cell types. Given the relevance of MAPT expression to neurodegeneration pathogenesis, identification of such elements is relevant to understanding disease risk and pathogenesis. Here, we performed chromatin conformation assays (HiC & Capture-C), single-nucleus multiomics (RNA-seq+ATAC-seq), bulk ATAC-seq, and ChIP-seq for H3K27ac and CTCF in NPCs and differentiated neurons to nominate candidate cis-regulatory elements (cCREs). We assayed these cCREs using luciferase assays and CRISPR interference (CRISPRi) experiments to measure their effects on MAPT expression. Finally, we integrated cCRE annotations into an analysis of genetic variation in neurodegeneration-affected individuals and control subjects. We identified both proximal and distal regulatory elements for MAPT and confirmed the regulatory function for several regions, including three regions centromeric to MAPT beyond the H1/H2 haplotype inversion breakpoint. We also found that rare and predicted damaging genetic variation in nominated CREs was nominally depleted in dementia-affected individuals relative to control subjects, consistent with the hypothesis that variants that disrupt MAPT enhancer activity, and thereby reduced MAPT expression, may be protective against neurodegenerative disease. Overall, this study provides compelling evidence for pursuing detailed knowledge of CREs for genes of interest to permit better understanding of disease risk.

PEGylated-liposomal astaxanthin ameliorates Aβ neurotoxicity and Alzheimer-related phenotypes by scavenging formaldehyde

Alzheimer's disease (AD), which is a prevailing type of dementia, presents a significant global health concern. The current therapies do not meet clinical expectations. Amyloid-beta (Aβ) has been found to induce endogenous formaldehyde (FA) accumulation by inactivating FA dehydrogenase (FDH); in turn, excessive FA triggers Aβ aggregation that eventually leads to AD onset. Hence, scavenging FA by astaxanthin (ATX, a strong exogenous antioxidant) may be pursued as a promising disease-modifying approach. Here, we report that liposomal nanoparticles coupled with PEG (PEG-ATX@NPs) could enhance water-solubility of ATX and alleviate cognitive impairments by scavenging FA and reducing Aβ deposition. To enable drug delivery to the brain, liposomes were used to encapsulate ATX and then coupled with PEG, which produced liposomal nanoparticles (PEGATX@NPs) with a diameter of <100 nm. The PEG-ATX@NPs reduced Aβ neurotoxicity by both degrading FA and reducing FA-induced Aβ assembly in vitro. Intraperitoneal administration of PEG-ATX@NPs in APPswe/PS1dE9 mice (APP/PS1, a familial model of AD), not only decreased the levels of brain FA and malondialdehyde (MDA, a typical product of oxidative stress), but also attenuated both intracellular Aβ oligomerization and extracellular Aβ-related senile plaque (SP) formation. These pathological changes were accompanied by rescued ability of spatial learning and memory. Collectively, PEG-ATX@NPs improved the water-solubility, bioavailability, and effectiveness of ATX. Thus, it has the potential to be developed as a safe and effective strategy for treating AD.

Top 100 most-cited articles on tau protein: a bibliometric analysis and evidence mapping

Background

Tau, a microtubule-associated protein extensively distributed within the central nervous system (CNS), exhibits close associations with various neurodegenerative disorders. Here, we aimed to conduct a qualitative and quantitative bibliometric study of the top 100 most-cited publications on tau protein and reveal the current research hotspots and future perspectives.

Methods

The relevant literature was retrieved from the Web of Science Core Collection. CiteSpace (v6.2.R4) and VOSviewer (1.6.19) were adopted for bibliometric analysis with statistical and visual analysis.

Results

Citations per article ranged from 615 to 3,123, with a median number of 765.5 times. "Neuroscience" emerged as the most extensively researched subject in this field. The USA has emerged as the leading country, with a publication record (n = 65), total citations (n = 66,543), strong centrality (0.29), and extensive international collaborations. Harvard University (n = 11) and the University of California, San Francisco (n = 11) were the top two institutions in terms of publications. Neuron dominated with 13 articles in the 37 high-quality journals. M. Goedert from the MRC Laboratory of Molecular Biology was the most productive (n = 9) and top co-cited (n = 179) author. The most frequently studied keywords were Alzheimer's disease (n = 38). Future research is anticipated to intensify its focus on the pathogenesis of various tau-related diseases, emphasizing the phosphorylation and structural alterations of tau protein, particularly in Alzheimer's disease.

Conclusion

The pathogenesis of various tau-related diseases, including the phosphorylation and structural alterations of the tau protein, will be the primary focus of future research, with particular emphasis on Alzheimer's disease as a central area of investigation.

Immunoproteasome deficiency results in age-dependent development of epilepsy

The immunoproteasome is a central protease complex required for optimal antigen presentation. Immunoproteasome activity is also associated with facilitating the degradation of misfolded and oxidized proteins, which prevents cellular stress. While extensively studied during diseases with increasing evidence suggesting a role for the immunoproteasome during pathological conditions including neurodegenerative diseases, this enzyme complex is believed to be mainly not expressed in the healthy brain. In this study, we show an age-dependent increase in polyubiquitination in the brains of wild-type mice, accompanied by an induction of immunoproteasomes, which was most prominent in neurons and microglia. In contrast, mice completely lacking immunoproteasomes (triple-knockout mice), displayed a strong increase in polyubiquitinated proteins already in the young brain and developed spontaneous epileptic seizures, beginning at the age of 6 months. Injections of kainic acid led to high epilepsy-related mortality of aged triple-knockout mice, confirming increased pathological hyperexcitability states. Notably, the expression of the immunoproteasome was reduced in the brains of patients suffering from epilepsy. In addition, the aged triple-knockout mice showed increased anxiety, tau hyperphosphorylation and degeneration of Purkinje cell population with the resulting ataxic symptoms and locomotion alterations. Collectively, our study suggests a critical role for the immunoproteasome in the maintenance of a healthy brain during ageing.

Interaction Between a High-Fat Diet and Tau Pathology in Mice: Implications for Alzheimer's Disease

BACKGROUND

Obesity is a modifiable risk factor for Alzheimer's disease (AD). However, its relation with tau pathology (i.e., aberrant tau protein behavior in tauopathies such as AD) has been inconclusive.

OBJECTIVE

This study investigated the interaction between a high-fat diet (HFD) and tau pathology in adult male mice.

METHODS

Transgenic mice overexpressing human P301S Tau (those with the pathology) and wild-type (WT) littermates were subjected to behavioral tests, functional magnetic resonance imaging (fMRI), diffusion tensor imaging (DTI), and western blotting analysis to investigate the effects of prolonged HFD versus regular diet during adulthood.

RESULTS

HFD increased body weight in both WT and P301S mice but had minimal effect on blood glucose levels. The brain response to HFD was tau genotype-specific. WT mice exhibited decreased recognition memory and enhanced network connectivity in fMRI, while P301S mice exhibited white matter tract disorganization in DTI as the sole significant finding. The reduction of insulin receptor β, insulin downstream signaling, neuronal nuclear protein, CD68-positive phagocytic activity, and myelin basic protein level were confined to the cortex of WT mice. In contrast to P301S mice, WT mice showed significant changes in the tau protein and its phosphorylation levels along with increased soluble neurofilament light levels in the hippocampus.

CONCLUSIONS

HFD-induced brain dysfunction and pathological changes were blunted in mice with the pathology and more profound in healthy mice. Our findings highlight the need to consider this interaction between obesity and tau pathology when tailoring treatment strategies for AD and other tauopathies.

Reevaluating tau reduction as a therapeutic approach for tauopathies: Insights and perspectives

Tau, one of the most abundant microtubule-associated protein in neurons plays a role in regulating microtubule dynamics in axons, as well as shaping the overall morphology of the axon. Recent studies challenge the traditional view of tau as a microtubule stabilizer and shed new light on the complexity of its role in regulating various properties of the microtubule. While reducing tau levels shows therapeutic promise for early tauopathies, efficacy wanes in later stages due to resilient toxic tau aggregates and neurofibrillary tangles. Notably, tauopathies involve factors beyond toxic tau alone, necessitating a broader therapeutic approach. Overexpression of human tau in mouse models, although useful for answering some questions, may not accurately reflect disease mechanisms in patients with tauopathies. Furthermore, the interplay between tau and MAP6, another microtubule-associated protein, adds complexity to tau's regulation of microtubule dynamics. Tau promotes the formation and elongation of labile microtubule domains, vital for cellular processes, while MAP6 stabilizes microtubules. A delicate balance between these proteins is important for neuronal function. Therefore, tau reduction therapies require a comprehensive understanding of disease progression, considering functional tau loss, toxic aggregates, and microtubule dynamics. Stage-dependent application and potential unintended consequences must be carefully evaluated. Restoring microtubule dynamics in late-stage tauopathies may necessitate alternative strategies. This knowledge is valuable for developing effective and safe treatments for tauopathies.

Total alkaloids from the seed embryo of Nelumbo nucifera Gaertn. improve cognitive impairment in APP/PS1 mice and protect Aβ-damaged PC12 cells

The seed embryo of Nelumbo nucifera Gaertn. is a famous traditional Chinese medicine and food which is considered conducive to the prevention of Alzheimer's disease (AD). In this study, the effect and mechanism of TASENN (total alkaloids from the seed embryo of Nelumbo nucifera Gaertn.) on AD mice and amyloid-β (Aβ) injured PC12 cells were evaluated. HPLC-UV analysis showed that the extracted TASENN (purity = 95.6%) mainly contains Liensinine, Isoliensinine, and Neferine (purity was 23.01, 28.02, and 44.57%, respectively). In vivo, oral treatment with TASENN (50 mg/kg/day for 28 days) improved the learning and memory functions of APP/PS1 transgenic mice, ameliorated the histopathological changes of cortical and hippocampal neurons, and inhibited neuronal apoptosis. We found that TASENN reduced the phosphorylation of Tau and the formation of neurofibrillary tangles (NFTs) in APP/PS1 mouse brain. Moreover, TASENN down-regulated the expression of APP and BACE1, ameliorated Aβ deposition, and inhibited microglial proliferation and aggregation. The elevated protein expression of CaM and p-CaMKII in APP/PS1 mouse brain was also reduced by TASENN. In vitro, TASENN inhibited the apoptosis of PC12 cells injured by Aβ25-35 and increased the cell viability. Aβ25-35-induced increase of cytosolic free Ca2+ level and high expression of CaM, p-CaMKII, and p-Tau were decreased by TASENN. Our findings indicate that TASENN has a potential therapeutic effect on AD mice and a protective effect on PC12 cells. The anti-AD activity of TASENN may be closely related to its negative regulation of the CaM pathway.

Preclinical Evidence for the Role of the Yin/Yang Angiotensin System Components in Autism Spectrum Disorder: A Therapeutic Target of Astaxanthin

Autism spectrum disorder (ASD) prevalence is emerging with an unclear etiology, hindering effective therapeutic interventions. Recent studies suggest potential renin-angiotensin system (RAS) alterations in different neurological pathologies. However, its implications in ASD are unexplored. This research fulfills the critical gap by investigating dual arms of RAS and their interplay with Notch signaling in ASD, using a valproic acid (VPA) model and assessing astaxanthin's (AST) modulatory impacts. Experimentally, male pups from pregnant rats receiving either saline or VPA on gestation day 12.5 were divided into control and VPA groups, with subsequent AST treatment in a subset (postnatal days 34-58). Behavioral analyses, histopathological investigations, and electron microscopy provided insights into the neurobehavioral and structural changes induced by AST. Molecular investigations of male pups' cortices revealed that AST outweighs the protective RAS elements with the inhibition of the detrimental arm. This established the neuroprotective and anti-inflammatory axes of RAS (ACE2/Ang1-7/MasR) in the ASD context. The results showed that AST's normalization of RAS components and Notch signaling underscore a novel therapeutic avenue in ASD, impacting neuronal integrity and behavioral outcomes. These findings affirm the integral role of RAS in ASD and highlight AST's potential as a promising treatment intervention, inviting further neurological research implications.

APOE4-promoted gliosis and degeneration in tauopathy are ameliorated by pharmacological inhibition of HMGB1 release

Apolipoprotein E4 (APOE4) is an important driver of Tau pathology, gliosis, and degeneration in Alzheimer's disease (AD). Still, the mechanisms underlying these APOE4-driven pathological effects remain elusive. Here, we report in a tauopathy mouse model that APOE4 promoted the nucleocytoplasmic translocation and release of high-mobility group box 1 (HMGB1) from hippocampal neurons, which correlated with the severity of hippocampal microgliosis and degeneration. Injection of HMGB1 into the hippocampus of young APOE4-tauopathy mice induced considerable and persistent gliosis. Selective removal of neuronal APOE4 reduced HMGB1 translocation and release. Treatment of APOE4-tauopathy mice with HMGB1 inhibitors effectively blocked the intraneuronal translocation and release of HMGB1 and ameliorated the development of APOE4-driven gliosis, Tau pathology, neurodegeneration, and myelin deficits. Single-nucleus RNA sequencing revealed that treatment with HMGB1 inhibitors diminished disease-associated and enriched disease-protective subpopulations of neurons, microglia, and astrocytes in APOE4-tauopathy mice. Thus, HMGB1 inhibitors represent a promising approach for treating APOE4-related AD.

Multivalent Tau/PSD-95 interactions arrest in vitro condensates and clusters mimicking the postsynaptic density

Alzheimer's disease begins with mild memory loss and slowly destroys memory and thinking. Cognitive impairment in Alzheimer's disease has been associated with the localization of the microtubule-associated protein Tau at the postsynapse. However, the correlation between Tau at the postsynapse and synaptic dysfunction remains unclear. Here, we show that Tau arrests liquid-like droplets formed by the four postsynaptic density proteins PSD-95, GKAP, Shank, Homer in solution, as well as NMDA (N-methyl-D-aspartate)-receptor-associated protein clusters on synthetic membranes. Tau-mediated condensate/cluster arrest critically depends on the binding of multiple interaction motifs of Tau to a canonical GMP-binding pocket in the guanylate kinase domain of PSD-95. We further reveal that competitive binding of a high-affinity phosphorylated peptide to PSD-95 rescues the diffusional dynamics of an NMDA truncated construct, which contains the last five amino acids of the NMDA receptor subunit NR2B fused to the C-terminus of the tetrameric GCN4 coiled-coil domain, in postsynaptic density-like condensates/clusters. Taken together, our findings propose a molecular mechanism where Tau modulates the dynamic properties of the postsynaptic density.

Accelerating Alzheimer's therapeutic development: The past and future of clinical trials

Alzheimer's disease (AD) research has entered a new era with the recent positive phase 3 clinical trials of the anti-Aβ antibodies lecanemab and donanemab. Why did it take 30 years to achieve these successes? Developing potent therapies for reducing fibrillar amyloid was key, as was selection of patients at relatively early stages of disease. Biomarkers of the target pathologies, including amyloid and tau PET, and insights from past trials were also critical to the recent successes. Moving forward, the challenge will be to develop more efficacious therapies with greater efficiency. Novel trial designs, including combination therapies and umbrella and basket protocols, will accelerate clinical development. Better diversity and inclusivity of trial participants are needed, and blood-based biomarkers may help to improve access for medically underserved groups. Incentivizing innovation in both academia and industry through public-private partnerships, collaborative mechanisms, and the creation of new career paths will be critical to build momentum in these exciting times.

The therapeutic landscape of tauopathies: challenges and prospects

Tauopathies are a group of neurodegenerative disorders characterized by the aggregation of the microtubule-associated protein tau. Aggregates of misfolded tau protein are believed to be implicated in neuronal death, which leads to a range of symptoms including cognitive decline, behavioral change, dementia, and motor deficits. Currently, there are no effective treatments for tauopathies. There are four clinical candidates in phase III trials and 16 in phase II trials. While no effective treatments are currently approved, there is increasing evidence to suggest that various therapeutic approaches may slow the progression of tauopathies or improve symptoms. This review outlines the landscape of therapeutic drugs (indexed through February 28, 2023) that target tau pathology and describes drug candidates in clinical development as well as those in the discovery and preclinical phases. The review also contains information on notable therapeutic programs that are inactive or that have been discontinued from development.

Randomized Phase II Study of the Safety and Efficacy of Semorinemab in Participants With Mild-to-Moderate Alzheimer Disease: Lauriet

BACKGROUND AND OBJECTIVES

Accumulation of tau pathology in Alzheimer disease (AD) correlates with cognitive decline. Anti-tau immunotherapies were proposed as potential interventions in AD. While antibodies targeting N-terminal tau failed to demonstrate clinical efficacy in prodromal-to-mild AD, their utility at other disease stages was not evaluated in prior studies. Lauriet is a phase 2 study of an anti-tau monoclonal antibody, semorinemab, in patients with mild-to-moderate AD.

METHODS

The phase 2 Lauriet study included a randomized, placebo-controlled, double-blind period, during which participants with mild-to-moderate AD received 4,500 mg of IV semorinemab or placebo every 4 weeks for 48 or 60 weeks. Participants who chose to continue in the subsequent optional open-label extension received 4,500 mg of semorinemab every 4 weeks for up to 96 weeks. Coprimary efficacy endpoints were change from baseline to week 49 or 61 on the 11-item version of the Alzheimer's Disease Assessment Scale-Cognitive Subscale (ADAS-Cog11) and the Alzheimer's Disease Cooperative Study-Activities of Daily Living (ADCS-ADL) scale. Secondary efficacy endpoints included change from baseline on the Mini-Mental State Examination (MMSE) and Clinical Dementia Rating-Sum of Boxes (CDR-SB). Safety, pharmacokinetics, and pharmacodynamic effects were also evaluated.

RESULTS

Between December 3, 2018, and February 27, 2020, 624 individuals were screened, 272 participants were randomized, and 238 were included in the modified intent-to-treat population (received ≥1 dose(s) of study medication and underwent baseline and ≥1 postbaseline assessment(s)). Baseline characteristics were well balanced. At week 49, the semorinemab arm demonstrated a 42.2% reduction (-2.89 points, 95% CI -4.56 to -1.21, p = 0.0008) in decline on the ADAS-Cog11 (coprimary endpoint) relative to the placebo arm. However, no treatment effects were observed on the ADCS-ADL scale (coprimary endpoint; absolute difference between the 2 treatment arms in the ADCS-ADL score change from baseline of -0.83 points, 95% CI -3.39 to 1.72, p = 0.52) or on the MMSE or CDR-SB (secondary endpoints). Semorinemab was safe and well tolerated.

DISCUSSION

Based on the results of the prespecified coprimary endpoints, this study was negative. While semorinemab had a significant effect on cognition measured by the ADAS-Cog11, this effect did not extend to improved functional or global outcomes. These results may warrant further exploration of semorinemab or other anti-tau therapies in mild-to-moderate AD.

CLASSIFICATION OF EVIDENCE

This study provides Class I evidence that semorinemab does not slow functional decline in patients with mild-to-moderate AD.

TRIAL REGISTRATION INFORMATION

The Lauriet study is registered on ClinicalTrials.gov, NCT03828747, and EudraCT 2018-003398-87.

Preclinical characterization and IND-enabling safety studies for PNT001, an antibody that recognizes cis-pT231 tau

BACKGROUND

The cis-conformer of tau phosphorylated at threonine-231 (cis-pT231 tau) is hypothesized to contribute to tauopathies. PNT001 is a humanized, monoclonal antibody that recognizes cis-pT231 tau. PNT001 was characterized to assess clinical development readiness.

METHODS

Affinity and selectivity were assessed by surface plasmon resonance and enzyme-linked immunosorbent assay. Immunohistochemistry (IHC) was performed with brain sections from human tauopathy patients and controls. Real-time quaking-induced conversion (RT-QuIC) was used to assess whether PNT001 reduced tau seeds from Tg4510 transgenic mouse brain. Murine PNT001 was evaluated in vivo in the Tg4510 mouse.

RESULTS

The affinity of PNT001 for a cis-pT231 peptide was 0.3 to 3 nM. IHC revealed neurofibrillary tangle-like structures in tauopathy patients with no detectable staining in controls. Incubation of Tg4510 brain homogenates with PNT001 lowered seeding in RT-QuIC. Multiple endpoints were improved in the Tg4510 mouse. No adverse findings attributable to PNT001 were detected in Good Laboratory Practice safety studies.

DISCUSSION

The data support clinical development of PNT001 in human tauopathies.

Treatment of Alzheimer's Disease: Beyond Symptomatic Therapies

In an ever-increasing aged world, Alzheimer's disease (AD) represents the first cause of dementia and one of the first chronic diseases in elderly people. With 55 million people affected, the WHO considers AD to be a disease with public priority. Unfortunately, there are no final cures for this pathology. Treatment strategies are aimed to mitigate symptoms, i.e., acetylcholinesterase inhibitors (AChEI) and the N-Methyl-D-aspartate (NMDA) antagonist Memantine. At present, the best approaches for managing the disease seem to combine pharmacological and non-pharmacological therapies to stimulate cognitive reserve. Over the last twenty years, a number of drugs have been discovered acting on the well-established biological hallmarks of AD, deposition of β-amyloid aggregates and accumulation of hyperphosphorylated tau protein in cells. Although previous efforts disappointed expectations, a new era in treating AD has been working its way recently. The Food and Drug Administration (FDA) gave conditional approval of the first disease-modifying therapy (DMT) for the treatment of AD, aducanumab, a monoclonal antibody (mAb) designed against Aβ plaques and oligomers in 2021, and in January 2023, the FDA granted accelerated approval for a second monoclonal antibody, Lecanemab. This review describes ongoing clinical trials with DMTs and non-pharmacological therapies. We will also present a future scenario based on new biomarkers that can detect AD in preclinical or prodromal stages, identify people at risk of developing AD, and allow an early and curative treatment.

Function and regulation of cis P-tau in the pathogenesis and treatment of conventional and nonconventional tauopathies

Conventional tauopathies are a group of disease characterized by tau inclusions in the brains, including Alzheimer's disease (AD), Pick's disease (PiD), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and certain types of frontotemporal dementia (FTD), among which AD is the most prevalent. Extensive post-translational modifications, especially hyperphosphorylation, and abnormal aggregation of tau protein underlie tauopathy. Cis-trans isomerization of protein plays an important role in protein folding, function, and degradation, which is regulated by peptidyl-proline isomerases (PPIases). Peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (Pin1), the only PPIase found to isomerize Pro following phosphorylated Ser or Thr residues, alters phosphorylated tau protein conformation at pT231-P motif. The cis P-tau but not trans P-tau serves as an early driver of multiple neurodegenerative disease, encompassing AD, traumatic brain injury (TBI), chronic traumatic encephalopathy (CTE), and vascular contributions to cognitive impairment and dementia (VCID). Cis but not trans P-tau is resistant to protein dephosphorylation and degradation, and also prone to protein aggregation. Cis P-tau loses its ability to stabilize microtubule, causing and spreading tauopathy mainly in axons, a pathological process called cistauosis. The conformation-specific monoclonal antibody that targets only the cis P-tau serves as a very early diagnosis method and a potential treatment of not only conventional tauopathies but also nonconventional tauopathies such as VCID, with clinical trials ongoing. Notably, cis P-tau antibody is the only clinical-stage Alzheimer's therapeutic that has shown the efficacy in animal models of not only AD but also TBI and stroke, which are very early stages of dementia. Here we review the identification and pathological consequences of cis pt231-tau, the role of its regulator Pin1, as well as the clinical implication of cis pt231-tau conformation-specific antibody in conventional and nonconventional tauopathies.

Neuronal apoE4 induces early hyperexcitability in select populations of hippocampal neurons by altering Nell2 expression

The impact of apolipoprotein E4 (apoE4), the strongest genetic risk factor for Alzheimer's disease (AD), on neuronal function remains unclear. We investigated this by examining excitatory neurons in the hippocampus of young and aged human apoE4 knock-in (apoE4-KI) and apoE3-KI mice using electrophysiology and single-nucleus RNA-sequencing (snRNA-seq). In young apoE4-KI mice, we identified region-specific subpopulations of excitatory neurons with hyperexcitability underlain by reduced cell size, which were eliminated by selective removal of neuronal apoE4. Aged apoE4-KI mice showed an increased fraction of hyperexcitable granule cells, a pronounced inhibitory deficit, and E/I imbalance in the dentate gyrus, contributing to network dysfunction. snRNA-seq analysis revealed neuron type-specific and age-dependent transcriptomic changes, identifying Nell2 overexpression in apoE4-KI mice. Reducing Nell2 expression in specific neuronal types of apoE4-KI mice with CRISPRi rescued their morphological and excitability phenotypes, supporting Nell2 overexpression as a cause for apoE4-induced neuronal dysfunction. Our findings highlight the early transcriptomic and morpho-electric alterations behind the apoE4-induced neuronal dysfunction in AD.

HIGHLIGHTS

ApoE4 causes hyperexcitability of select hippocampal neurons in young apoE4 mice.ApoE4 causes dentate hyperexcitability and inhibitory deficit in aged apoE4 mice.snRNA-seq reveals apoE genotype-, cell type-, and age-dependent transcriptomic changes.Nell2 overexpression identified as a cause of apoE4-induced neuronal hyperexcitability.

Identification of image genetic biomarkers of Alzheimer's disease by orthogonal structured sparse canonical correlation analysis based on a diagnostic information fusion

Alzheimer's disease (AD) is an irreversible neurodegenerative disease, and its incidence increases yearly. Because AD patients will have cognitive impairment and personality changes, it has caused a heavy burden on the family and society. Image genetics takes the structure and function of the brain as a phenotype and studies the influence of genetic variation on the structure and function of the brain. Based on the structural magnetic resonance imaging data and transcriptome data of AD and healthy control samples in the Alzheimer's Disease Neuroimaging Disease database, this paper proposed the use of an orthogonal structured sparse canonical correlation analysis for diagnostic information fusion algorithm. The algorithm added structural constraints to the region of interest (ROI) of the brain. Integrating the diagnostic information of samples can improve the correlation performance between samples. The results showed that the algorithm could extract the correlation between the two modal data and discovered the brain regions most affected by multiple risk genes and their biological significance. In addition, we also verified the diagnostic significance of risk ROIs and risk genes for AD. The code of the proposed algorithm is available at https://github.com/Wanguangyu111/OSSCCA-DIF.

Tau deficiency inhibits classically activated macrophage polarization and protects against collagen-induced arthritis in mice

BACKGROUND

Tau protein serves a pro-inflammatory function in neuroinflammation. However, the role of tau in other inflammatory disorders such as rheumatoid arthritis (RA) is less explored. This study is to investigate the role of endogenous tau and the potential mechanisms in the pathogenesis of inflammatory arthritis.

METHODS

We established collagen-induced arthritis (CIA) model in wild-type and Tau-/- mice to compare the clinical score and arthritis incidence. Micro-CT analysis was used to evaluate bone erosion of ankle joints. Histological analysis was performed to assess inflammatory cell infiltration, cartilage damage, and osteoclast activity in the ankle joints. Serum levels of pro-inflammatory cytokines were measured by ELISA. The expression levels of macrophage markers were determined by immunohistochemistry staining and quantitative real-time PCR.

RESULTS

Tau expression was upregulated in joints under inflammatory condition. Tau deletion in mice exhibited milder inflammation and protected against the progression of CIA, evidenced by reduced serum levels of pro-inflammatory cytokines and attenuated bone loss, inflammatory cell infiltration, cartilage damage, and osteoclast activity in the ankle joints. Furthermore, tau deficiency led to the inhibition of classically activated type 1 (M1) macrophage polarization in the synovium.

CONCLUSION

Tau is a previously unrecognized critical regulator in the pathogenesis of RA and may provide a potential therapeutic target for autoimmune and inflammatory joint diseases.

Single-cell RNA-seq reveals alterations in peripheral CX3CR1 and nonclassical monocytes in familial tauopathy

BACKGROUND

Emerging evidence from mouse models is beginning to elucidate the brain's immune response to tau pathology, but little is known about the nature of this response in humans. In addition, it remains unclear to what extent tau pathology and the local inflammatory response within the brain influence the broader immune system.

METHODS

To address these questions, we performed single-cell RNA sequencing (scRNA-seq) of peripheral blood mononuclear cells (PBMCs) from carriers of pathogenic variants in MAPT, the gene encoding tau (n = 8), and healthy non-carrier controls (n = 8). Primary findings from our scRNA-seq analyses were confirmed and extended via flow cytometry, droplet digital (dd)PCR, and secondary analyses of publicly available transcriptomics datasets.

RESULTS

Analysis of ~ 181,000 individual PBMC transcriptomes demonstrated striking differential expression in monocytes and natural killer (NK) cells in MAPT pathogenic variant carriers. In particular, we observed a marked reduction in the expression of CX3CR1-the gene encoding the fractalkine receptor that is known to modulate tau pathology in mouse models-in monocytes and NK cells. We also observed a significant reduction in the abundance of nonclassical monocytes and dysregulated expression of nonclassical monocyte marker genes, including FCGR3A. Finally, we identified reductions in TMEM176A and TMEM176B, genes thought to be involved in the inflammatory response in human microglia but with unclear function in peripheral monocytes. We confirmed the reduction in nonclassical monocytes by flow cytometry and the differential expression of select biologically relevant genes dysregulated in our scRNA-seq data using ddPCR.

CONCLUSIONS

Our results suggest that human peripheral immune cell expression and abundance are modulated by tau-associated pathophysiologic changes. CX3CR1 and nonclassical monocytes in particular will be a focus of future work exploring the role of these peripheral signals in additional tau-associated neurodegenerative diseases.

Sut-6/NIPP1 modulates tau toxicity

Neurodegenerative diseases exhibiting the pathological accumulation of tau such as Alzheimer's disease and related disorders still have no disease-modifying treatments and the molecular mechanisms of neurodegeneration remain unclear. To discover additional suppressor of tauopathy (sut) genes that mediate or modulate the toxicity of pathological tau, we performed a classical genetic screen using a tau transgenic Caenorhabditis elegans model. From this screen, we identified the suppressing mutation W292X in sut-6, the C. elegans homolog of human NIPP1, which truncates the C-terminal RNA-binding domain. Using CRISPR-based genome editing approaches, we generated null and additional C-terminally truncated alleles in sut-6 and found that loss of sut-6 or sut-6(W292X) suppresses tau-induced behavioral locomotor deficits, tau protein accumulation and neuron loss. The sut-6(W292X) mutation showed stronger and semi-dominant suppression of tau toxicity while sut-6 deletion acted recessively. Neuronal overexpression of SUT-6 protein did not significantly alter tau toxicity, but neuronal overexpression of SUT-6 W292X mutant protein reduced tau-mediated deficits. Epistasis studies showed tauopathy suppression by sut-6 occurs independent of other known nuclear speckle-localized suppressors of tau such as sut-2, aly-1/aly-3 and spop-1. In summary, we have shown that sut-6/NIPP1 modulates tau toxicity and found a dominant mutation in the RNA-binding domain of sut-6 which strongly suppresses tau toxicity. This suggests that altering RNA-related functions of SUT-6/NIPP1 instead of complete loss of SUT-6/NIPP1 will provide the strongest suppression of tau.

Disrupting pathologic phase transitions in neurodegeneration

Solid-like protein deposits found in aged and diseased human brains have revealed a relationship between insoluble protein accumulations and the resulting deficits in neurologic function. Clinically diverse neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, frontotemporal lobar degeneration, and amyotrophic lateral sclerosis, exhibit unique and disease-specific biochemical protein signatures and abnormal protein depositions that often correlate with disease pathogenesis. Recent evidence indicates that many pathologic proteins assemble into liquid-like protein phases through the highly coordinated process of liquid-liquid phase separation. Over the last decade, biomolecular phase transitions have emerged as a fundamental mechanism of cellular organization. Liquid-like condensates organize functionally related biomolecules within the cell, and many neuropathology-associated proteins reside within these dynamic structures. Thus, examining biomolecular phase transitions enhances our understanding of the molecular mechanisms mediating toxicity across diverse neurodegenerative diseases. This Review explores the known mechanisms contributing to aberrant protein phase transitions in neurodegenerative diseases, focusing on tau and TDP-43 proteinopathies and outlining potential therapeutic strategies to regulate these pathologic events.

CRISPR screens in iPSC-derived neurons reveal principles of tau proteostasis

A hallmark of age-associated neurodegenerative diseases is the aggregation of proteins. Aggregation of the protein tau defines tauopathies, which include Alzheimer's disease and frontotemporal dementia. Specific neuronal subtypes are selectively vulnerable to the accumulation of tau aggregates, and subsequent dysfunction and death. The mechanisms underlying cell type-selective vulnerability are unknown. To systematically uncover the cellular factors controlling the accumulation of tau aggregates in human neurons, we conducted a genome-wide CRISPRi-based modifier screen in iPSC-derived neurons. The screen uncovered expected pathways, including autophagy, but also unexpected pathways including UFMylation and GPI anchor synthesis, that control tau oligomer levels. We identify the E3 ubiquitin ligase CUL5 as a tau interactor and potent modifier of tau levels. In addition, disruption of mitochondrial function increases tau oligomer levels and promotes proteasomal misprocessing of tau. These results reveal new principles of tau proteostasis in human neurons and pinpoint potential therapeutic targets for tauopathies.

KIBRA repairs synaptic plasticity and promotes resilience to tauopathy-related memory loss

Synaptic plasticity is obstructed by pathogenic tau in the brain, representing a key mechanism that underlies memory loss in Alzheimer's disease (AD) and related tauopathies. Here, we define a mechanism for plasticity repair in vulnerable neurons using the C-terminus of the KIdney/BRAin (KIBRA) protein (CT-KIBRA). We show that CT-KIBRA restores plasticity and memory in transgenic mice expressing pathogenic human tau; however, CT-KIBRA did not alter tau levels or prevent tau-induced synapse loss. Instead, we find that CT-KIBRA binds to and stabilizes protein kinase Mζ (PKMζ) to maintain synaptic plasticity and memory despite tau-mediated pathogenesis. In humans we find that reduced KIBRA in brain and increased KIBRA in cerebrospinal fluid are associated with cognitive impairment and pathological tau levels in disease. Thus, our results distinguish KIBRA both as a novel biomarker of synapse dysfunction in AD and as the foundation for a synapse repair mechanism to reverse cognitive impairment in tauopathy.

Does modulation of tau hyperphosphorylation represent a reasonable therapeutic strategy for Alzheimer's disease? From preclinical studies to the clinical trials

Protein kinases (PKs) have emerged as one of the most intensively investigated drug targets in current pharmacological research, with indications ranging from oncology to neurodegeneration. Tau protein hyperphosphorylation was the first pathological post-translational modification of tau protein described in Alzheimer's disease (AD), highlighting the role of PKs in neurodegeneration. The therapeutic potential of protein kinase inhibitors (PKIs)) and protein phosphatase 2 A (PP2A) activators in AD has recently been explored in several preclinical and clinical studies with variable outcomes. Where a number of preclinical studies demonstrate a visible reduction in the levels of phospho-tau in transgenic tauopathy models, no reduction in neurofibrillary lesions is observed. Amongst the few PKIs and PP2A activators that progressed to clinical trials, most failed on the efficacy front, with only a few still unconfirmed and potential positive trends. This suggests that robust preclinical and clinical data is needed to unequivocally evaluate their efficacy. To this end, we take a systematic look at the results of preclinical and clinical studies of PKIs and PP2A activators, and the evidence they provide regarding the utility of this approach to evaluate the potential of targeting tau hyperphosphorylation as a disease modifying therapy.

Focusing on oligomeric tau as a therapeutic target in Alzheimer's disease and other tauopathies

INTRODUCTION

Tau has commanded much attention as a potential therapeutic target in neurodegenerative diseases. Tau pathology is a hallmark of primary tauopathies, such as progressive supranuclear palsy (PSP), corticobasal syndrome (CBS), and subtypes of frontotemporal dementia (FTD), as well as secondary tauopathies, such as Alzheimer's disease (AD). The development of tau therapeutics must reconcile with the structural complexity of the tau proteome, as well as an incomplete understanding of the role of tau in both physiology and disease.

AREAS COVERED

This review offers a current perspective on tau biology, discusses key barriers to the development of effective tau-based therapeutics, and promotes the idea that pathogenic (as opposed to merely pathological) tau should be at the center of drug development efforts.

EXPERT OPINION

An efficacious tau therapeutic will exhibit several primary features: 1) selectivity for pathogenic tau versus other tau species; 2) blood-brain barrier and cell membrane permeability, enabling access to intracellular tau in disease-relevant brain regions; and 3) minimal toxicity. Oligomeric tau is proposed as a major pathogenic form of tau and a compelling drug target in tauopathies.

Big Tau: What We Know, and We Need to Know

Tau is a microtubule-associated protein (MAP) that has multiple isoforms generated by alternative splicing of the MAPT gene at a range of 45-60 kDa [low-molecular-weight (LMW) tau] as well as a unique isoform termed Big tau containing an additional exon 4a encoding a large projecting domain of ∼250 aa to form a protein of 110 kDa. Big tau is expressed in adult PNS neurons such as DRG neurons and specific regions of CNS such as the cerebellum in a developmental transition from LMW tau to Big tau during the postnatal period. Despite a conserved size of the 4a exons across the vertebrate phylogeny, there is no sequence homology among different species outside the Mammalia class, which underscores the focus on structural preservation of Big tau. Despite the original discovery of Big tau in the early 1990s, there has been little progress elucidating its physiological properties and pathologic implications. We propose that Big tau may be able to improve axonal transport in projecting axons and speculate on the potential protective properties in preventing tau aggregation in pathologic conditions. This perspective highlights the importance and benefits of understanding of the role of Big tau in neuronal health and disease.

AdipoRon mitigates tau pathology and restores mitochondrial dynamics via AMPK-related pathway in a mouse model of Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is a complicated and refractory neurodegenerative disease that is typically characterized by memory loss and multiple cognitive impairments. Multiple neuropathology including hyperphosphorylated tau formation and accumulation, dysregulated mitochondrial dynamics, and synaptic damage have been well implicated in the progression of AD. So far, there are few valid and effective therapeutic modalities for treatment. AdipoRon, a specific adiponectin (APN) receptor agonist, is reported to be associated with cognitive deficits improvement. In the present study, we attempt to explore the potential therapeutic effects of AdipoRon on tauopathy and related molecular mechanisms.

METHODS

In this study, P301S tau transgenic mice were used. The plasma level of APN was detected by ELISA. The level of APN receptors was qualified by western blot and immunofluorescence. 6-month-old mice were treated with AdipoRon or vehicle by oral administration daily for 4 months. The benefits of AdipoRon on tau hyperphosphorylation, mitochondrial dynamics, and synaptic function were detected by western blot, immunohistochemistry, immunofluorescence, Golgi staining and transmission electron microscopy. Morris water maze test and novel object recognition test were conducted to explore memory impairments.

RESULTS

Compared with wild-type mice, the expression of APN in plasma in 10-month-old P301S mice was obviously decreased. APN receptors in the hippocampus were increased in the hippocampus. AdipoRon treatment significantly rescued memory deficits in P301S mice. Besides, AdipoRon treatment was also detected to improve synaptic function, enhance mitochondrial fusion, and mitigate hyperphosphorylated tau accumulation in P301S mice and SY5Y cells. Mechanistically, AMPK/SIRT3 and AMPK/GSK3β signaling pathways are demonstrated to be involved in AdipoRon-mediated benefits on mitochondrial dynamics and tau accumulation, respectively, and inhibition of AMPK related pathways showed counteracted effects.

CONCLUSION

Our results demonstrated that AdipoRon treatment could significantly mitigate tau pathology, improve synaptic damage, and restore mitochondrial dynamics via the AMPK-related pathway, which provides a novel potential therapeutic approach to retard the progression of AD and other tauopathies diseases.

Tubulin polyglutamylation differentially regulates microtubule-interacting proteins

Tubulin posttranslational modifications have been predicted to control cytoskeletal functions by coordinating the molecular interactions between microtubules and their associating proteins. A prominent tubulin modification in neurons is polyglutamylation, the deregulation of which causes neurodegeneration. Yet, the underlying molecular mechanisms have remained elusive. Here, using in-vitro reconstitution, we determine how polyglutamylation generated by the two predominant neuronal polyglutamylases, TTLL1 and TTLL7, specifically modulates the activities of three major microtubule interactors: the microtubule-associated protein Tau, the microtubule-severing enzyme katanin and the molecular motor kinesin-1. We demonstrate that the unique modification patterns generated by TTLL1 and TTLL7 differentially impact those three effector proteins, thus allowing for their selective regulation. Given that our experiments were performed with brain tubulin from mouse models in which physiological levels and patterns of polyglutamylation were altered by the genetic knockout of the main modifying enzymes, our quantitative measurements provide direct mechanistic insight into how polyglutamylation could selectively control microtubule interactions in neurons.

Aberrant serotonergic signaling contributes to the hyperexcitability of CA1 pyramidal neurons in a mouse model of Alzheimer's disease

Hyperactivity of pyramidal neurons (PNs) in CA1 is an early event in Alzheimer's disease. However, factors accounting for the hyperactivity of CA1 PNs remain to be completely investigated. In the present study, we report that the serotonergic signaling is abnormal in the hippocampus of hAPP-J20 mice. Interestingly, chemogenetic activation of serotonin (5-hydroxytryptamine; 5-HT) neurons in the median raphe nucleus (MRN) attenuates the activity of CA1 PNs in hAPP-J20 mice by regulating the intrinsic properties or inhibitory synaptic transmission of CA1 PNs through 5-HT3aR and/or 5-HT1aR. Furthermore, activating MRN 5-HT neurons improves memory in hAPP-J20 mice, and this effect is mediated by 5-HT3aR and 5-HT1aR. Direct activation of 5-HT3aR and 5-HT1aR with their selective agonists also improves the memory of hAPP-J20 mice. Together, we identify the impaired 5-HT/5-HT3aR and/or 5-HT/5-HT1aR signaling as pathways contributing to the hyperexcitability of CA1 PNs and the impaired cognition in hAPP-J20 mice.

Focus on Alzheimer's Disease: The Role of Fibroblast Growth Factor 21 and Autophagy

Alzheimer's disease (AD) is a disorder of the central nervous system that is typically marked by progressive cognitive impairment and memory loss. Amyloid β plaque deposition and neurofibrillary tangles with hyperphosphorylated tau are the two hallmark pathologies of AD. In mammalian cells, autophagy clears aberrant protein aggregates, thus maintaining proteostasis as well as neuronal health. Autophagy affects production and metabolism of amyloid β and accumulation of phosphorylated tau proteins, whose malfunction can lead to the progression of AD. On the other hand, defective autophagy has been found to induce the production of the neuroprotective factor fibroblast growth factor 21 (FGF21), although the underlying mechanism is unclear. In this review, we highlight the significance of aberrant autophagy in the pathogenesis of AD, discuss the possible mechanisms by which defective autophagy induces FGF21 production, and analyze the potential of FGF21 in the treatment of AD. The findings provide some insights into the potential role of FGF21 and autophagy in the pathogenesis of AD.

Jiedu Yizhi Formula Improves Cognitive Function by Regulating the Gut Dysbiosis and TLR4/NF-κB Signaling Pathway

OBJECTIVE

The objective of this study was to explore the neuroprotective mechanism of JDYZF in treating AD from the perspective of inflammation and intestinal microflora.

METHODS

A total of 24 APP/PS1 mice were randomly divided into four groups: model (n = 6), JDYZF low-dose (n = 6), JDYZF high-dose (n = 6), and positive drug (n = 6), six C57 mice were used as the control group. The body weights and diets of all mice were examined daily. After 8 weeks of administration, the learning and memory of mice were evaluated by the Morris water maze test. The histopathological changes of hippocampus, liver and kidney in mice were observed by HE staining after being euthanized. The expression of p-tau in hippocampus tissue was detected by immunohistochemistry. After that, 16S rDNA sequencing was used to investigate the relationship between JDYZF and intestinal microbiota. Finally, a comparison of TLR4, p65, p-p65, iκB, p-iκB, and IL-1β protein expression in the hippocampus tissue of mice in each group was measured by Western blot.

RESULTS

The results showed that APP/PS1 mice taking JDYZF orally were generally in good condition. Compared with the control group, JDYZF significantly improved learning and memory ability in ethology. Histology showed that JDYZF improved the hippocampal structure of mice and inhibited the deposition of p-tau. JDYZF treatment could regulate the gut microbiota of APP/PS1 mice by increasing the richness of Lachnospiraceae, Ruminococcaceae, and Actinobacteria and reducing that of Alistipes and Muribaculaceae. It also significantly inhibited the activation of the TLR4/NF-κB signaling pathway in the brain. In addition, no obvious toxic reactions were found in the liver and kidney of APP/PS1 mice after taking JDYZF for 8 weeks.

CONCLUSION

The findings revealed that JDYZF improved cognitive ability and alleviated the TLR4/NF-κB signaling pathway in APP/PS1 mice, and the modulating the gut microbiota presented here may help illuminate its activation mechanism.

Tau protein plays a role in the mechanism of cognitive disorders induced by anesthetic drugs

Cognitive disorders are mental health disorders that can affect cognitive ability. Surgery and anesthesia have been proposed to increase the incidence of cognitive dysfunction, including declines in memory, learning, attention and executive function. Tau protein is a microtubule-associated protein located in the axons of neurons and is important for microtubule assembly and stability; its biological function is mainly regulated by phosphorylation. Phosphorylated tau protein has been associated with cognitive dysfunction mediated by disrupting the stability of the microtubule structure. There is an increasing consensus that anesthetic drugs can cause cognitive impairment. Herein, we reviewed the latest literature and compared the relationship between tau protein and cognitive impairment caused by different anesthetics. Our results substantiated that tau protein phosphorylation is essential in cognitive dysfunction caused by anesthetic drugs, and the possible mechanism can be summarized as "anesthetic drugs-kinase/phosphatase-p-Tau-cognitive impairment".

Evolutionary perspective of Big tau structure: 4a exon variants of MAPT

The MAPT gene encoding the microtubule-associated protein tau can generate multiple isoforms by alternative splicing giving rise to proteins which are differentially expressed in specific areas of the nervous system and at different developmental stages. Tau plays important roles in modulating microtubule dynamics, axonal transport, synaptic plasticity, and DNA repair, and has also been associated with neurodegenerative diseases (tauopathies) including Alzheimer's disease and frontotemporal dementia. A unique high-molecular-weight isoform of tau, originally found to be expressed in the peripheral nervous system and projecting neurons, has been termed Big tau and has been shown to uniquely contain the large exon 4a that significantly increases the size and 3D structure of tau. With little progress since the original discovery of Big tau, more than 25 years ago, we have now completed a comprehensive comparative study to analyze the structure of the MAPT gene against available databases with respect to the composition of the tau exons as they evolved from early vertebrates to primates and human. We focused the analysis on the evolution of the 4a exon variants and their homology relative to humans. We discovered that the 4a exon defining Big tau appears to be present early in vertebrate evolution as a large insert that dramatically changed the size of the tau protein with low sequence conservation despite a stable size range of about 250aa, and in some species a larger 4a-L exon of 355aa. We suggest that 4a exon variants evolved independently in different species by an exonization process using new alternative splicing to address the growing complexities of the evolving nervous systems. Thus, the appearance of a significantly larger isoform of tau independently repeated itself multiple times during evolution, accentuating the need across vertebrate species for an elongated domain that likely endows Big tau with novel physiological functions as well as properties related to neurodegeneration.

Heparan Sulfate Proteoglycans in Tauopathy

Tauopathies are a class of neurodegenerative diseases, including Alzheimer's disease, and are characterized by intraneuronal tau inclusion in the brain and the patient's cognitive decline with obscure pathogenesis. Heparan sulfate proteoglycans, a major type of extracellular matrix, have been believed to involve in tauopathies. The heparan sulfate proteoglycans co-deposit with tau in Alzheimer's patient brain, directly bind to tau and modulate tau secretion, internalization, and aggregation. This review summarizes the current understanding of the functions and the modulated molecular pathways of heparan sulfate proteoglycans in tauopathies, as well as the implication of dysregulated heparan sulfate proteoglycan expression in tau pathology and the potential of targeting heparan sulfate proteoglycan-tau interaction as a novel therapeutic option.

Prenatal PM2.5 exposure contributes to neuronal tau lesion in male offspring mice through mitochondrial dysfunction-mediated insulin resistance

The epidemiological evidence has linked prenatal exposure to fine particulate matter (PM_2.5) pollution with neurological diseases in offspring. However, the biological process and toxicological mechanisms remain unclear. Tau protein is a neuronal microtubule-associated protein expressed in fetal brain and plays a critical role in mediating neuronal development. Aberrant expression of tau is associated with adverse neurodevelopmental outcomes. To study whether prenatal exposure to PM_2.5 pollution induce tau lesion in mice offspring and elucidate the underlying pathogenic mechanism, we exposed pregnant mice to PM_2.5 (3 mg/kg b.w.) by oropharyngeal aspiration every other day. The results indicate that prenatal PM_2.5 exposure induced hyperphosphorylation of tau in the cortex of postnatal male offspring, which was accompanied by insulin resistance through the IRS-1/PI3K/AKT signaling pathway. Importantly, we further found that prenatal PM_2.5 exposure induced mitochondrial dysfunction by disrupting mitochondrial ultrastructure and decreasing the expression of rate-limiting enzymes (CS, IDH2 and FH) in the Krebs cycle and the subunits of mitochondrial complex IV and V (CO1, CO4, ATP6, and ATP8) during postnatal neurodevelopment. The findings suggest that prenatal PM_2.5 exposure could induce tauopathy-like changes in male offspring, in which mitochondrial dysfunction-induced insulin resistance might play an important role.