MAPT isoforms: differential transcriptional profiles related to 3R and 4R splice variants

Herpes simplex virus-1 infection alters microtubule-associated protein Tau splicing and promotes Tau pathology in neural models of Alzheimer's disease

Herpes simplex virus 1 (HSV-1) infection alters critical markers of Alzheimer's disease (AD) in neurons. One key marker of AD is the hyperphosphorylation of Tau, accompanied by altered levels of Tau isoforms. However, an imbalance in these Tau splice variants, specifically resulting from altered 3R to 4R MAPT splicing of exon 10, has yet to be directly associated with HSV-1 infection. To this end, we infected 2D and 3D human neural models with HSV-1 and monitored MAPT splicing and Tau phosphorylation. Further, we transduced SH-SY5Y neurons with HSV-1 ICP27, which alters RNA splicing, to analyze if ICP27 alone is sufficient to induce altered MAPT exon 10 splicing. We show that HSV-1 infection induces altered splicing of MAPT exon 10, increasing 4R-Tau protein levels, Tau hyperphosphorylation, and Tau oligomerization. Our experiments reveal a novel link between HSV-1 infection and the development of cytopathic phenotypes linked with AD progression.

Spliceosome protein alterations differentiate hubs of the default mode connectome during the progression of Alzheimer's disease

Default mode network (DMN) is comprised in part of the frontal (FC), precuneus (PreC), and posterior cingulate (PCC) cortex and displays amyloid and tau pathology in Alzheimer's disease (AD). The PreC hub appears the most resilient to AD pathology, suggesting differential vulnerability within the DMN. However, the mechanisms that underlie this differential pathobiology remain obscure. Here, we investigated changes in RNA polymerase II (RNA pol II) and splicing proteins U1-70K, U1A, SRSF2, and hnRNPA2B1, phosphorylated AT8 tau, 3R and 4Rtau isoforms containing neurons and amyloid plaques in layers III and V-VI in FC, PreC, and PCC obtained from individuals with a preclinical diagnosis of no cognitive impairment (NCI), mild cognitive impairment (MCI), and mild/moderate mAD. We found a significant increase in pS5-RNA pol II levels in FC NCI, U1-70K in PreC MCI and mAD, and hnRNPA2B1 and SRSF2 levels in PCC mAD. 1N3Rtau levels were significantly increased in FC, decreased in PreC in mAD, and unchanged in PCC, whereas 1N4Rtau increased in mAD across the hubs. SRSF2, U1-70K, U1A, and hnRNPA2B1 nuclear optical density (OD), size, and number were unchanged across groups in FC and PCC, while PreC OD hnRNPA2B1 was significantly greater in mAD. Mislocalized U1A and U1-70K tangle-like structures were found in a few PCC cases and colocalized with AT8-bearing neurofibrillary tangles (NFTs). FC pS5-RNA pol II, PreC U1-70K, Pre pS5,2-RNA pol II, and PCC hnRNPA2B1 and SRSF2 protein levels were associated with cognitive decline but not neuropathology across clinical groups. By contrast, splicing protein nuclear OD measures, size, counts, and mislocalized U1-70K and U1A NFT-like structures were not correlated with NFT or plaque density, cognitive domains, and neuropathological criteria in DMN hubs. Findings suggest that RNA splicing protein alterations and U1 mislocalization contribute differentially to DMN pathogenesis and cognitive deterioration in AD.

Amyloid-motif-dependent tau self-assembly is modulated by isoform sequence context

The microtubule-associated protein tau is implicated in neurodegenerative diseases characterized by amyloid formation. Mutations associated with frontotemporal dementia increase tau aggregation propensity and disrupt its endogenous microtubule-binding activity. However, the structural relationship between aggregation propensity and biological activity remains unclear. We employed a multi-disciplinary approach, including computational modeling, NMR, cross-linking mass spectrometry, and cell models to engineer tau sequences that modulate its structural ensemble. Our findings show that substitutions near the conserved 'PGGG' β-turn motif informed by tau isoform context reduce tau aggregation in vitro and cells and can even counteract aggregation induced by turn destabilizing disease-associated proline-to-serine mutations. Engineered tau sequences maintain microtubule binding and explain why 3R isoforms exhibit reduced pathogenesis compared to 4R. We propose a simple mechanism to reduce the formation of pathogenic species while preserving biological function, thus offering insights for therapeutic strategies aimed at reducing tau protein misfolding in neurodegenerative diseases.

Abstract Figure

Ganaxolone Reverses the Effect of Amyloid β-Induced Neurotoxicity by Regulating the Liver X Receptor Expression in APP Transfected SH-SY5Y Cells and Murine Model of Alzheimer's Disease

Inhibiting β-amyloid aggregation and enhancing its clearance are the key strategies in Alzheimer's disease (AD) treatment. Liver X receptors (LXRs) plays a crucial role in cholesterol homeostasis and inflammation, and their activation can clear Aβ aggregates in AD. Allopregnanolone, a neurosteroid, positively influences AD through LXR regulation, while ganaxolone, its synthetic analog, is known for its neuroprotective properties. This study explores the effect of ganaxolone on LXR activation and regulation of genes involved in mitigating Aβ toxicity and tauopathy in SH-SY5Y cells transfected with APP695 Swe/Ind plasmid and an Aβ1-42 induced AD mouse model. Molecular docking stimulations indicated ganaxolone's binding and interaction with LXRβ. Subsequently, transfected neuronal cells exhibited increased mRNA levels of APP, TNF-α and IL-1β, decreased cell viability, reduced MMP and altered protein expression of Aβ, LXR, BCL-2, APOE, ABCA1, along with increased levels of mROS, Bax, and caspase 3 activity. Ganaxolone treatment significantly abrogated Aβ-induced effect in transfected neuronal cells by enhancing LXRβ expression, inducing LXR:RXR colocalization, thereby increasing APOE and ABCA1 expression. It also decreased tau mRNA levels in transfected cells. Importantly, in AD mice, ganaxolone ameliorated cognitive impairment, reduced Aβ toxicity, tau levels, and neuroinflammatory markers, restored mitochondrial function, and decreased neuronal apoptosis. Taken together, these novel results highlight the central role of LXR in mediating Aβ-induced toxicity and provide preclinical evidence for ganaxolone as a potential agent to reduce toxicity in an LXR-dependent manner. This may serve as a promising treatment strategy to slow or prevent neurodegeneration in AD patients.

Development of MAPT S305 mutation human iPSC lines exhibiting elevated 4R tau expression and functional alterations in neurons and astrocytes

Due to the importance of 4R tau (with four microtubule-binding-repeat domains) in the pathogenicity of primary tauopathies, it has been challenging to model these diseases in induced pluripotent stem cell (iPSC)-derived neurons, which express very low levels of 4R tau. To address this, we have developed a panel of isogenic iPSC lines carrying MAPT splice-site mutations, S305S, S305I, or S305N, derived from four different donors. All mutations significantly increase 4R tau expression in iPSC neurons and astrocytes. Functional analyses of S305 mutant neurons reveal shared disruption in synaptic signaling and maturity but divergent effects on mitochondrial bioenergetics. In iPSC astrocytes, S305 mutations promote internalization of exogenous tau that may be a precursor to glial pathology. These lines recapitulate previously characterized tauopathy-relevant phenotypes and highlight functional differences between the wild-type 4R and the mutant 4R proteins in both neurons and astrocytes. As such, these lines enable a more complete understanding of pathogenic mechanisms underlying 4R tauopathies across different cell types.

Cellular and pathological functions of tau

Tau protein is involved in various cellular processes, including having a canonical role in binding and stabilization of microtubules in neurons. Tauopathies are neurodegenerative diseases marked by the abnormal accumulation of tau protein aggregates in neurons, as seen, for example, in conditions such as frontotemporal dementia and Alzheimer disease. Mutations in tau coding regions or that disrupt tau mRNA splicing, tau post-translational modifications and cellular stress factors (such as oxidative stress and inflammation) increase the tendency of tau to aggregate and interfere with its clearance. Pathological tau is strongly implicated in the progression of neurodegenerative diseases, and the propagation of tau aggregates is associated with disease severity. Recent technological advancements, including cryo-electron microscopy and disease models derived from human induced pluripotent stem cells, have increased our understanding of tau-related pathology in neurodegenerative conditions. Substantial progress has been made in deciphering tau aggregate structures and the molecular mechanisms that underlie protein aggregation and toxicity. In this Review, we discuss recent insights into the diverse cellular functions of tau and the pathology of tau inclusions and explore the potential for therapeutic interventions.

HSV-1 Infection Alters MAPT Splicing and Promotes Tau Pathology in Neural Models of Alzheimer's Disease

INTRODUCTION

Herpes simplex virus 1 (HSV-1) infection alters critical markers of Alzheimer's Disease (AD) in neurons. One key marker of AD is the hyperphosphorylation of Tau, accompanied by altered levels of Tau isoforms. However, an imbalance in these Tau splice variants, specifically resulting from altered 3R to 4R MAPT splicing of exon 10, has yet to be directly associated with HSV-1 infection.

METHODS

To this end, we infected 2D and 3D human neural models with HSV-1 and monitored MAPT splicing and Tau phosphorylation. Further, we transduced SH-SY5Y-neurons with HSV-1 ICP27 which alters RNA splicing to analyze if ICP27 alone is sufficient to induce altered MAPT exon 10 splicing.

RESULTS

We show that HSV-1 infection induces altered splicing of MAPT exon 10, increasing 4R-Tau protein levels, Tau hyperphosphorylation, and Tau oligomerization.

DISCUSSION

Our experiments reveal a novel link between HSV-1 infection and the development of cytopathic phenotypes linked with AD progression.

HIGHLIGHTS

HSV-1 infection in forebrain organoids reduces the neurite length of MAP2-positive neurons.HSV-1 infection increases Tau hyperphosphorylation in both two-month-old and four-month-old forebrain organoids. HSV-1 infection increases Exon 10 containing (4R) MAPT mRNA and 4R-Tau protein expression in both forebrain organoids and human SH-SY5Y-neurons. HSV-1 ICP27 is both necessary and sufficient to induce increased 4R MAPT mRNA and 4R-Tau protein expression in SH-SY5Y-neurons. HSV-1 infection increases Tau oligomerization in both forebrain organoids and SH-SY5Y-neurons.

Drug repurposing for neurodegenerative diseases

Neurodegenerative diseases (NDDs) are neuronal problems that include the brain and spinal cord and result in loss of sensory and motor dysfunction. Common NDDs include Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), Multiple Sclerosis (MS), and Amyotrophic Lateral Sclerosis (ALS) etc. The occurrence of these diseases increases with age and is one of the challenging problems among elderly people. Though, several scientific research has demonstrated the key pathologies associated with NDDs still the underlying mechanisms and molecular details are not well understood and need to be explored and this poses a lack of effective treatments for NDDs. Several lines of evidence have shown that NDDs have a high prevalence and affect more than a billion individuals globally but still, researchers need to work forward in identifying the best therapeutic target for NDDs. Thus, several researchers are working in the directions to find potential therapeutic targets to alter the disease pathology and treat the diseases. Several steps have been taken to identify the early detection of the disease and drug repurposing for effective treatment of NDDs. Moreover, it is logical that current medications are being evaluated for their efficacy in treating such disorders; therefore, drug repurposing would be an efficient, safe, and cost-effective way in finding out better medication. In the current manuscript we discussed the utilization of drugs that have been repurposed for the treatment of AD, PD, HD, MS, and ALS.

Pathological and physiological functional cross-talks of α-synuclein and tau in the central nervous system

α-Synuclein and tau are abundant multifunctional brain proteins that are mainly expressed in the presynaptic and axonal compartments of neurons, respectively. Previous works have revealed that intracellular deposition of α-synuclein and/or tau causes many neurodegenerative disorders, including Alzheimer's disease and Parkinson's disease. Despite intense investigation, the normal physiological functions and roles of α-synuclein and tau are still unclear, owing to the fact that mice with knockout of either of these proteins do not present apparent phenotypes. Interestingly, the co-occurrence of α-synuclein and tau aggregates was found in post-mortem brains with synucleinopathies and tauopathies, some of which share similarities in clinical manifestations. Furthermore, the direct interaction of α-synuclein with tau is considered to promote the fibrillization of each of the proteins in vitro and in vivo. On the other hand, our recent findings have revealed that α-synuclein and tau are cooperatively involved in brain development in a stage-dependent manner. These findings indicate strong cross-talk between the two proteins in physiology and pathology. In this review, we provide a summary of the recent findings on the functional roles of α-synuclein and tau in the physiological conditions and pathogenesis of neurodegenerative diseases. A deep understanding of the interplay between α-synuclein and tau in physiological and pathological conditions might provide novel targets for clinical diagnosis and therapeutic strategies to treat neurodegenerative diseases.

Ensemble-based design of tau to inhibit aggregation while preserving biological activity

The microtubule-associated protein tau is implicated in neurodegenerative diseases characterized by amyloid formation. Mutations associated with frontotemporal dementia increase tau aggregation propensity and disrupt its endogenous microtubule-binding activity. The structural relationship between aggregation propensity and biological activity remains unclear. We employed a multi-disciplinary approach, including computational modeling, NMR, cross-linking mass spectrometry, and cell models to design tau sequences that stabilize its structural ensemble. Our findings reveal that substitutions near the conserved 'PGGG' beta-turn motif can modulate local conformation, more stably engaging in interactions with the 306VQIVYK311 amyloid motif to decrease aggregation in vitro and in cells. Designed tau sequences maintain microtubule binding and explain why 3R isoforms of tau exhibit reduced pathogenesis over 4R isoforms. We propose a simple mechanism to reduce the formation of pathogenic species while preserving biological function, offering insights for therapeutic strategies aimed at reducing protein misfolding in neurodegenerative diseases.

Untangling Tau: Molecular Insights into Neuroinflammation, Pathophysiology, and Emerging Immunotherapies

Neuroinflammation, a core pathological feature observed in several neurodegenerative diseases, including Alzheimer's disease (AD), is rapidly gaining attention as a target in understanding the molecular underpinnings of these disorders. Glial cells, endothelial cells, peripheral immune cells, and astrocytes produce a variety of pro-inflammatory mediators that exacerbate the disease progression. Additionally, microglial cells play a complex role in AD, facilitating the clearance of pathological amyloid-beta peptide (Aβ) plaques and aggregates of the tau protein. Tau proteins, traditionally associated with microtubule stabilization, have come under intense scrutiny for their perturbed roles in neurodegenerative conditions. In this narrative review, we focus on recent advances from molecular insights that have revealed aberrant tau post-translational modifications, such as phosphorylation and acetylation, serving as pathological hallmarks. These modifications also trigger the activation of CNS-resident immune cells, such as microglia and astrocytes substantially contributing to neuroinflammation. This intricate relationship between tau pathologies and neuroinflammation fosters a cascading impact on neural pathophysiology. Furthermore, understanding the molecular mechanisms underpinning tau's influence on neuroinflammation presents a frontier for the development of innovative immunotherapies. Neurodegenerative diseases have been relatively intractable to conventional pharmacology using small molecules. We further comprehensively document the many alternative approaches using immunotherapy targeting tau pathological epitopes and structures with a wide array of antibodies. Clinical trials are discussed using these therapeutic approaches, which have both promising and disappointing outcomes. Future directions for tau immunotherapies may include combining treatments with Aβ immunotherapy, which may result in more significant clinical outcomes for neurodegenerative diseases.

IM-MS and ECD-MS/MS Provide Insight into Modulation of Amyloid Proteins Self-Assembly by Peptides and Small Molecules

Neurodegenerative proteinopathies are characterized by formation and deposition of misfolded, aggregated proteins in the nervous system leading to neuronal dysfunction and death. It is widely believed that metastable oligomers of the offending proteins, preceding the fibrillar aggregates found in the tissue, are the proximal neurotoxins. There are currently almost no disease-modifying therapies for these diseases despite an active pipeline of preclinical development and clinical trials for over two decades, largely because studying the metastable oligomers and their interaction with potential therapeutics is notoriously difficult. Mass spectrometry (MS) is a powerful analytical tool for structural investigation of proteins, including protein-protein and protein-ligand interactions. Specific MS tools have been useful in determining the composition and conformation of abnormal protein oligomers involved in proteinopathies and the way they interact with drug candidates. Here, we analyze critically the utilization of ion-mobility spectroscopy-MS (IM-MS) and electron-capture dissociation (ECD) MS/MS for analyzing the oligomerization and conformation of multiple amyloidogenic proteins. We also discuss IM-MS investigation of their interaction with two classes of compounds developed by our group over the last two decades: C-terminal fragments derived from the 42-residue form of amyloid β-protein (Aβ42) and molecular tweezers. Finally, we review the utilization of ECD-MS/MS for elucidating the binding sites of the ligands on multiple proteins. These approaches are readily applicable to future studies addressing similar questions and hold promise for facilitating the development of successful disease-modifying drugs against neurodegenerative proteinopathies.

Deregulated Transcription and Proteostasis in Adult mapt Knockout Mouse

Transcriptomics and phosphoproteomics were carried out in the cerebral cortex of B6.Cg-Mapttm1(EGFP)Klt (tau knockout: tau-KO) and wild-type (WT) 12 month-old mice to learn about the effects of tau ablation. Compared with WT mice, tau-KO mice displayed reduced anxiety-like behavior and lower fear expression induced by aversive conditioning, whereas recognition memory remained unaltered. Cortical transcriptomic analysis revealed 69 downregulated and 105 upregulated genes in tau-KO mice, corresponding to synaptic structures, neuron cytoskeleton and transport, and extracellular matrix components. RT-qPCR validated increased mRNA levels of col6a4, gabrq, gad1, grm5, grip2, map2, rab8a, tubb3, wnt16, and an absence of map1a in tau-KO mice compared with WT mice. A few proteins were assessed with Western blotting to compare mRNA expression with corresponding protein levels. Map1a mRNA and protein levels decreased. However, β-tubulin III and GAD1 protein levels were reduced in tau-KO mice. Cortical phosphoproteomics revealed 121 hypophosphorylated and 98 hyperphosphorylated proteins in tau-KO mice. Deregulated phosphoproteins were categorized into cytoskeletal (n = 45) and membrane proteins, including proteins of the synapses and vesicles, myelin proteins, and proteins linked to membrane transport and ion channels (n = 84), proteins related to DNA and RNA metabolism (n = 36), proteins connected to the ubiquitin-proteasome system (UPS) (n = 7), proteins with kinase or phosphatase activity (n = 21), and 22 other proteins related to variegated pathways such as metabolic pathways, growth factors, or mitochondrial function or structure. The present observations reveal a complex altered brain transcriptome and phosphoproteome in tau-KO mice with only mild behavioral alterations.

Using Optogenetics to Model Cellular Effects of Alzheimer's Disease

Across the world a dementia case is diagnosed every three seconds. Alzheimer's disease (AD) causes 50-60% of these cases. The most prominent theory for AD correlates the deposition of amyloid beta (Aβ) with the onset of dementia. Whether Aβ is causative remains unclear due to findings such as the recently approved drug Aducanumab showing effective clearance of Aβ, but not improving cognition. New approaches for understanding Aβ function, are therefore necessary. Here we discuss the application of optogenetic techniques to gain insight into AD. Optogenetics, or genetically encoded, light-dependent on/off switches, provides precise spatiotemporal control to regulate cellular dynamics. This precise control over protein expression and oligomerization or aggregation could provide a better understanding of the etiology of AD.

Chronic Stress, Depression, and Alzheimer's Disease: The Triangle of Oblivion

Chronic stress and high levels of the main stress hormones, and glucocorticoids (GC), are implicated in susceptibility to brain pathologies such as depression and Alzheimer's disease (AD), as they promote neural plasticity damage and glial reactivity, which can lead to dendritic/synaptic loss, reduced neurogenesis, mood deficits, and impaired cognition. Moreover, depression is implicated in the development of AD with chronic stress being a potential link between both disorders via common neurobiological underpinnings. Hereby, we summarize and discuss the clinical and preclinical evidence related to the detrimental effect of chronic stress as a precipitator of AD through the activation of pathological mechanisms leading to the accumulation of amyloid β (Aβ) and Tau protein. Given that the modern lifestyle increasingly exposes individuals to high stress loads, it is clear that understanding the mechanistic link(s) between chronic stress, depression, and AD pathogenesis may facilitate the treatment of AD and other stress-related disorders.

Isoform-specific patterns of tau burden and neuronal degeneration in MAPT-associated frontotemporal lobar degeneration

Frontotemporal lobar degeneration with MAPT pathogenic variants (FTLD-MAPT) has heterogeneous tau pathological inclusions postmortem, consisting of three-repeat (3R) or four-repeat (4R) tau isoforms, or a combination (3R + 4R). Here, we studied grey matter tau burden, its relation to neuronal degeneration, and regional patterns of pathology in different isoform groups of FTLD-MAPT. We included 38 FTLD-MAPT autopsy cases with 10 different MAPT pathogenic variants, grouped based on predominant tau isoform(s). In up to eleven regions (ten cortical and one striatal), we quantified grey matter tau burden using digital histopathological analysis and assigned semi-quantitative ratings for neuronal degeneration (i.e. 0-4) and separate burden of glial and neuronal tau inclusions (i.e. 0-3). We used mixed modelling to compare pathology measures (1) across the entire cohort and (2) within isoform groups. In the total cohort, tau burden and neuronal degeneration were positively associated and most severe in the anterior temporal, anterior cingulate and transentorhinal cortices. Isoform groups showed distinctive features of tau burden and neuronal degeneration. Across all regions, the 3R isoform group had lower tau burden compared to the 4R group (p = 0.008), while at the same time showing more severe neuronal degeneration than the 4R group (p = 0.002). The 3R + 4R group had an intermediate profile with relatively high tau burden along with relatively severe neuronal degeneration. Neuronal tau inclusions were most frequent in the 4R group (p < 0.001 vs. 3R), while cortical glial tau inclusions were most frequent in the 3R + 4R and 4R groups (p ≤ 0.009 vs. 3R). Regionally, neuronal degeneration was consistently most severe in the anterior temporal cortex within each isoform group. In contrast, the regions with the highest tau burden differed in isoform groups (3R: striatum; 3R + 4R: striatum, inferior parietal lobule, middle frontal cortex, anterior cingulate cortex; 4R: transentorhinal cortex, anterior temporal cortex, fusiform gyrus). We conclude that FTLD-MAPT isoform groups show distinctive features of overall neuronal degeneration and regional tau burden, but all share pronounced anterior temporal neuronal degeneration. These data suggest that distinct isoform-related mechanisms of genetic tauopathies, with slightly divergent tau distribution, may share similar regional vulnerability to neurodegeneration within the frontotemporal paralimbic networks.

Redox signaling and metabolism in Alzheimer's disease

Reduction and oxidation reactions are essential for biochemical processes. They are part of metabolic pathways and signal transduction. Reactive oxygen species (ROS) as second messengers and oxidative modifications of cysteinyl (Cys) residues are key to transduce and translate intracellular and intercellular signals. Dysregulation of cellular redox signaling is known as oxidative distress, which has been linked to various pathologies, including neurodegeneration. Alzheimer's disease (AD) is a neurodegenerative pathology linked to both, abnormal amyloid precursor protein (APP) processing, generating Aβ peptide, and Tau hyperphosphorylation and aggregation. Signs of oxidative distress in AD include: increase of ROS (H2O2, O2 •-), decrease of the levels or activities of antioxidant enzymes, abnormal oxidation of macromolecules related to elevated Aβ production, and changes in mitochondrial homeostasis linked to Tau phosphorylation. Interestingly, Cys residues present in APP form disulfide bonds that are important for intermolecular interactions and might be involved in the aggregation of Aβ. Moreover, two Cys residues in some Tau isoforms have been shown to be essential for Tau stabilization and its interaction with microtubules. Future research will show the complexities of Tau, its interactome, and the role that Cys residues play in the progression of AD. The specific modification of cysteinyl residues in redox signaling is also tightly connected to the regulation of various metabolic pathways. Many of these pathways have been found to be altered in AD, even at very early stages. In order to analyze the complex changes and underlying mechanisms, several AD models have been developed, including animal models, 2D and 3D cell culture, and ex-vivo studies of patient samples. The use of these models along with innovative, new redox analysis techniques are key to further understand the importance of the redox component in Alzheimer's disease and the identification of new therapeutic targets in the future.

Structure-Activity Relationship in the Leucettine Family of Kinase Inhibitors

The protein kinase DYRK1A is involved in Alzheimer's disease, Down syndrome, diabetes, viral infections, and leukemia. Leucettines, a family of 2-aminoimidazolin-4-ones derived from the marine sponge alkaloid Leucettamine B, have been developed as pharmacological inhibitors of DYRKs (dual specificity, tyrosine phosphorylation regulated kinases) and CLKs (cdc2-like kinases). We report here on the synthesis and structure-activity relationship (SAR) of 68 Leucettines. Leucettines were tested on 11 purified kinases and in 5 cellular assays: (1) CLK1 pre-mRNA splicing, (2) Threonine-212-Tau phosphorylation, (3) glutamate-induced cell death, (4) autophagy and (5) antagonism of ligand-activated cannabinoid receptor CB1. The Leucettine SAR observed for DYRK1A is essentially identical for CLK1, CLK4, DYRK1B, and DYRK2. DYRK3 and CLK3 are less sensitive to Leucettines. In contrast, the cellular SAR highlights correlations between inhibition of specific kinase targets and some but not all cellular effects. Leucettines deserve further development as potential therapeutics against various diseases on the basis of their molecular targets and cellular effects.

In Vivo 18 F-APN-1607 Tau Positron Emission Tomography Imaging in MAPT Mutations: Cross-Sectional and Longitudinal Findings

BACKGROUND

Frontotemporal lobar degeneration with tauopathy caused by MAPT (microtubule-associated protein tau) mutations is a highly heterogenous disorder. The ability to visualize and longitudinally monitor tau deposits may be beneficial to understand disease pathophysiology and predict clinical trajectories.

OBJECTIVE

The aim of this study was to investigate the cross-sectional and longitudinal ¹⁸ F-APN-1607 positron emission tomography/computed tomography (PET/CT) imaging findings in MAPT mutation carriers.

METHODS

Seven carriers of MAPT mutations (six within exon 10 and one outside of exon 10) and 15 healthy control subjects were included. All participants underwent ¹⁸ F-APN-1607 PET/CT at baseline. Three carriers of exon 10 mutations received follow-up ¹⁸ F-APN-1607 PET/CT scans. Standardized uptake value ratio (SUVR) maps were obtained using the cerebellar gray matter as the reference region. SUVR values observed in MAPT mutation carriers were normalized to data from healthy control subjects. A regional SUVR z score ≥ 2 was used as the criterion to define positive ¹⁸ F-APN-1607 PET/CT findings.

RESULTS

Although the seven study patients had heterogenous clinical phenotypes, all showed a significant ¹⁸ F-APN-1607 uptake characterized by high-contrast signals. However, the anatomical localization of tau deposits differed in patients with distinct clinical symptoms. Follow-up imaging data, which were available for three patients, demonstrated worsening trends in patterns of tau accumulation over time, which were paralleled by a significant clinical deterioration.

CONCLUSIONS

Our data represent a promising step in understanding the usefulness of ¹⁸ F-APN-1607 PET/CT imaging for detecting tau accumulation in MAPT mutation carriers. Our preliminary follow-up data also suggest the potential value of ¹⁸ F-APN-1607 PET/CT for monitoring the longitudinal trajectories of frontotemporal lobar degeneration caused by MAPT mutations. © 2021 International Parkinson and Movement Disorder Society.

Synaptic proteins associated with cognitive performance and neuropathology in older humans revealed by multiplexed fractionated proteomics

Alzheimer's disease (AD) is defined by the presence of abundant amyloid-β (Aβ) and tau neuropathology. While this neuropathology is necessary for AD diagnosis, it is not sufficient for causing cognitive impairment. Up to one third of community dwelling older adults harbor intermediate to high levels of AD neuropathology at death yet demonstrate no significant cognitive impairment. Conversely, there are individuals who exhibit dementia with no gross explanatory neuropathology. In prior studies, synapse loss correlated with cognitive impairment. To understand how synaptic composition changes in relation to neuropathology and cognition, multiplexed liquid chromatography mass-spectrometry was used to quantify enriched synaptic proteins from the parietal association cortex of 100 subjects with contrasting levels of AD pathology and cognitive performance. 123 unique proteins were significantly associated with diagnostic category. Functional analysis showed enrichment of serotonin release and oxidative phosphorylation categories in normal (cognitively unimpaired, low neuropathology) and "resilient" (unimpaired despite AD pathology) individuals. In contrast, frail individuals, (low pathology, impaired cognition) showed a metabolic shift towards glycolysis and increased presence of proteasome subunits.

[Progressive supranuclear palsy]

Progressive supranuclear palsy (PSP) is a heterogeneous progressive neurodegenerative disease characterized by onset after 50 years old, Parkinson's syndrome, early development of postural instability, absence or transient reaction to levodopa drugs, neuropsychological disorders, dysphagia and dysarthria and eye movement disorders. The review provides an analysis of modern data on etiology, clinical presentation, differential diagnosis of the disease. The morphological picture and neuroimaging features, as well as modern ideas about treatment, are described. A great clinical polymorphism of the disease, as well as its similarity to other neurodegenerative diseases, manifested by Parkinson's syndrome, complicates the diagnosis of PSP. Establishing an accurate diagnosis makes it possible to determine the prognosis and further tactics of patient management.

Splicing alterations in healthy aging and disease

Alternative RNA splicing is a key step in gene expression that allows generation of numerous messenger RNA transcripts encoding proteins of varied functions from the same gene. It is thus a rich source of proteomic and functional diversity. Alterations in alternative RNA splicing are observed both during healthy aging and in a number of human diseases, several of which display premature aging phenotypes or increased incidence with age. Age-associated splicing alterations include differential splicing of genes associated with hallmarks of aging, as well as changes in the levels of core spliceosomal genes and regulatory splicing factors. Here, we review the current known links between alternative RNA splicing, its regulators, healthy biological aging, and diseases associated with aging or aging-like phenotypes. This article is categorized under: RNA in Disease and Development > RNA in Disease RNA Processing > Splicing Regulation/Alternative Splicing.

Splicing alterations in healthy aging and disease

Alternative RNA splicing is a key step in gene expression that allows generation of numerous messenger RNA transcripts encoding proteins of varied functions from the same gene. It is thus a rich source of proteomic and functional diversity. Alterations in alternative RNA splicing are observed both during healthy aging and in a number of human diseases, several of which display premature aging phenotypes or increased incidence with age. Age-associated splicing alterations include differential splicing of genes associated with hallmarks of aging, as well as changes in the levels of core spliceosomal genes and regulatory splicing factors. Here, we review the current known links between alternative RNA splicing, its regulators, healthy biological aging, and diseases associated with aging or aging-like phenotypes. This article is categorized under: RNA in Disease and Development > RNA in Disease RNA Processing > Splicing Regulation/Alternative Splicing.

Robustness during Aging-Molecular Biological and Physiological Aspects

Understanding the process of aging is still an important challenge to enable healthy aging and to prevent age-related diseases. Most studies in age research investigate the decline in organ functionality and gene activity with age. The focus on decline can even be considered a paradigm in that field. However, there are certain aspects that remain surprisingly stable and keep the organism robust. Here, we present and discuss various properties of robust behavior during human and animal aging, including physiological and molecular biological features, such as the hematocrit, body temperature, immunity against infectious diseases and others. We examine, in the context of robustness, the different theories of how aging occurs. We regard the role of aging in the light of evolution.

Tau affects P53 function and cell fate during the DNA damage response

Cells are constantly exposed to DNA damaging insults. To protect the organism, cells developed a complex molecular response coordinated by P53, the master regulator of DNA repair, cell division and cell fate. DNA damage accumulation and abnormal cell fate decision may represent a pathomechanism shared by aging-associated disorders such as cancer and neurodegeneration. Here, we examined this hypothesis in the context of tauopathies, a neurodegenerative disorder group characterized by Tau protein deposition. For this, the response to an acute DNA damage was studied in neuroblastoma cells with depleted Tau, as a model of loss-of-function. Under these conditions, altered P53 stability and activity result in reduced cell death and increased cell senescence. This newly discovered function of Tau involves abnormal modification of P53 and its E3 ubiquitin ligase MDM2. Considering the medical need with vast social implications caused by neurodegeneration and cancer, our study may reform our approach to disease-modifying therapies.

Martina Sola, Claudia Magrin et al. study the relation between Tau and P53 in response to DNA damage. They uncover an important role for Tau in regulating the stability, and activity of P53 post translationally. Their findings provide insights to potentially common pathways in neurodegenerative disease and cancer.

Exploring the RNA Gap for Improving Diagnostic Yield in Primary Immunodeficiencies

Challenges in diagnosing primary immunodeficiency are numerous and diverse, with current whole-exome and whole-genome sequencing approaches only able to reach a molecular diagnosis in 25–60% of cases. We assess these problems and discuss how RNA-focused analysis has expanded and improved in recent years and may now be utilized to gain an unparalleled insight into cellular immunology. We review how investigation into RNA biology can give information regarding the differential expression, monoallelic expression, and alternative splicing—which have important roles in immune regulation and function. We show how this information can inform bioinformatic analysis pipelines and aid in the variant filtering process, expediting the identification of causal variants—especially those affecting splicing—and enhance overall diagnostic ability. We also demonstrate the challenges, which remain in the design of this type of investigation, regarding technological limitation and biological considerations and suggest potential directions for the clinical applications.

Astrocyte senescence may drive alterations in GFAPα, CDKN2A p14ARF, and TAU3 transcript expression and contribute to cognitive decline

The accumulation of senescent cells in tissues is causally linked to the development of several age-related diseases; the removal of senescent glial cells in animal models prevents Tau accumulation and cognitive decline. Senescent cells can arise through several distinct mechanisms; one such mechanism is dysregulation of alternative splicing. In this study, we characterised the senescent cell phenotype in primary human astrocytes in terms of SA-β-Gal staining and SASP secretion, and then assessed splicing factor expression and candidate gene splicing patterns. Finally, we assessed associations between expression of dysregulated isoforms and premature cognitive decline in 197 samples from the InCHIANTI study of ageing, where expression was present in both blood and brain. We demonstrate here that senescent astrocytes secrete a modified SASP characterised by increased IL8, MMP3, MMP10, and TIMP2 but decreased IL10 levels. We identified significant changes in splicing factor expression for 10/20 splicing factors tested in senescent astrocytes compared with early passage cells, as well as dysregulation of isoform levels for 8/13 brain or senescence genes tested. Finally, associations were identified between peripheral blood GFAPα, TAU3, and CDKN2A (P14^ARF) isoform levels and mild or severe cognitive decline over a 3–7-year period. Our data are suggestive that some of the features of cognitive decline may arise from dysregulated splicing of important genes in senescent brain support cells, and that defects in alternative splicing or splicing regulator expression deserve exploration as points of therapeutic intervention in the future.

Untold New Beginnings: Adult Hippocampal Neurogenesis and Alzheimer's Disease

Neurogenesis occurs in a limited number of brain regions during adulthood. Of these, the hippocampus has attracted great interest due to its involvement in memory processing. Moreover, both the hippocampus and the main area that innervates this structure, namely the entorhinal cortex, show remarkable atrophy in patients with Alzheimer's disease (AD). Adult hippocampal neurogenesis is a process that continuously gives rise to newborn granule neurons in the dentate gyrus. These cells coexist with developmentally generated granule neurons in this structure, and both cooperative and competition phenomena regulate the communication between these two types of cells. Importantly, it has been revealed that GSK-3β and tau proteins, which are two of the main players driving AD pathology, are cornerstones of adult hippocampal neurogenesis regulation. We have shown that alterations either promoting or impeding the actions of these two proteins have detrimental effects on the structural plasticity of granule neurons. Of note, these impairments occur both under basal conditions and in response to detrimental and neuroprotective stimuli. Thus, in order to achieve the full effectiveness of future therapies for AD, we propose that attention be turned toward identifying the pathological and physiological actions of the proteins involved in the pathogenesis of this condition.

Genetically Engineered iPSC-Derived FTDP-17 MAPT Neurons Display Mutation-Specific Neurodegenerative and Neurodevelopmental Phenotypes

Tauopathies such as frontotemporal dementia (FTD) remain incurable to date, partially due to the lack of translational in vitro disease models. The MAPT gene, encoding the microtubule-associated protein tau, has been shown to play an important role in FTD pathogenesis. Therefore, we used zinc finger nucleases to introduce two MAPT mutations into healthy donor induced pluripotent stem cells (iPSCs). The IVS10+16 mutation increases the expression of 4R tau, while the P301S mutation is pro-aggregant. Whole-transcriptome analysis of MAPT IVS10+16 neurons reveals neuronal subtype differences, reduced neural progenitor proliferation potential, and aberrant WNT/SHH signaling. Notably, these neurodevelopmental phenotypes could be recapitulated in neurons from patients carrying the MAPT IVS10+16 mutation. Moreover, the additional pro-aggregant P301S mutation revealed additional phenotypes, such as an increased calcium burst frequency, reduced lysosomal acidity, tau oligomerization, and neurodegeneration. This series of iPSCs could serve as a platform to unravel a potential link between pathogenic 4R tau and FTD.

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Analysis of ZFN-engineered MAPT IVS10+16 with or without additional P301S mutation

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Neurodevelopmental phenotypes in ZFN and patient-derived MAPT IVS10+16 neurons

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Neurodegenerative phenotypes in MAPT IVS10+16/P301S double-mutant neurons

Neurofibrillary tangles mediated human neuronal tauopathies: insights from fly models

Tauopathies represent a group of neurodegenerative disorder which are characterized by the presence of tau positive specialized argyrophilic and insoluble intraneuronal and glial fibrillar lesions known as neurofibrillary tangles (NFTs). Tau is a neuron specific microtubule binding protein which is required for the integrity and functioning of neuronal cells, and hyperphosphorylation of tau and its subsequent aggregation and paired helical filaments (PHFs) and NFTs has emerged as one of the major pathogenic mechanisms of tauopathies in human and mammalian model systems. Modeling of human tauopathies in Drosophila results in manifestation of associated phenotypes, and a recent study has demonstrated that similar to human and mammalian models, accumulation of insoluble tau aggregates in the form of typical neurotoxic NFTs triggers the pathogenesis of tauopathies in fly models. In view of the availability of remarkable genetic tools, Drosophila tau models could be extremely useful for in-depth analysis of the role of NFTs in neurodegeneration and tau aetiology, and also for the screening of novel gene(s) and molecule(s) which suppress the toxicity of tau aggregates.

Anti-aggregant tau mutant promotes neurogenesis

BACKGROUND

The microtubule-associated protein Tau plays a role in neurodegeneration as well as neurogenesis. Previous work has shown that the expression of the pro-aggregant mutant Tau repeat domain causes strong aggregation and pronounced neuronal loss in the hippocampus whereas the anti-aggregant form has no deleterious effects. These two proteins differ mainly in their propensity to form ß structure and hence to aggregate.

METHODS

To elucidate the basis of these contrasting effects, we analyzed organotypic hippocampal slice cultures (OHSCs) from transgenic mice expressing the repeat domain (RD) of Tau with the anti-aggregant mutation (Tau^RDΔKPP) and compared them with slices containing pro-aggregant Tau^RDΔK. Transgene expression in the hippocampus was monitored via a sensitive bioluminescence reporter gene assay (luciferase).

RESULTS

The expression of the anti-aggregant Tau^RDΔKPP leads to a larger volume of the hippocampus at a young age due to enhanced neurogenesis, resulting in an increase in neuronal number. There were no signs of activation of microglia and astrocytes, indicating the absence of an inflammatory reaction. Investigation of signaling pathways showed that Wnt-5a was strongly decreased whereas Wnt3 was increased. A pronounced increase in hippocampal stem cell proliferation (seen by BrdU) was observed as early as P8, in the CA regions where neurogenesis is normally not observed. The increase in neurons persisted up to 16 months of age.

CONCLUSION

The data suggest that the expression of anti-aggregant Tau^RDΔKPP enhances hippocampal neurogenesis mediated by the canonical Wnt signaling pathway, without an inflammatory reaction. This study points to a role of tau in brain development and neurogenesis, in contrast to its detrimental role in neurodegeneration at later age.

Chronic traumatic encephalopathy-integration of canonical traumatic brain injury secondary injury mechanisms with tau pathology

In recent years, a new neurodegenerative tauopathy labeled Chronic Traumatic Encephalopathy (CTE), has been identified that is believed to be primarily a sequela of repeated mild traumatic brain injury (TBI), often referred to as concussion, that occurs in athletes participating in contact sports (e.g. boxing, American football, Australian football, rugby, soccer, ice hockey) or in military combatants, especially after blast-induced injuries. Since the identification of CTE, and its neuropathological finding of deposits of hyperphosphorylated tau protein, mechanistic attention has been on lumping the disorder together with various other non-traumatic neurodegenerative tauopathies. Indeed, brains from suspected CTE cases that have come to autopsy have been confirmed to have deposits of hyperphosphorylated tau in locations that make its anatomical distribution distinct for other tauopathies. The fact that these individuals experienced repetitive TBI episodes during their athletic or military careers suggests that the secondary injury mechanisms that have been extensively characterized in acute TBI preclinical models, and in TBI patients, including glutamate excitotoxicity, intracellular calcium overload, mitochondrial dysfunction, free radical-induced oxidative damage and neuroinflammation, may contribute to the brain damage associated with CTE. Thus, the current review begins with an in depth analysis of what is known about the tau protein and its functions and dysfunctions followed by a discussion of the major TBI secondary injury mechanisms, and how the latter have been shown to contribute to tau pathology. The value of this review is that it might lead to improved neuroprotective strategies for either prophylactically attenuating the development of CTE or slowing its progression.

Tau-dependent suppression of adult neurogenesis in the stressed hippocampus

Stress, a well-known sculptor of brain plasticity, is shown to suppress hippocampal neurogenesis in the adult brain; yet, the underlying cellular mechanisms are poorly investigated. Previous studies have shown that chronic stress triggers hyperphosphorylation and accumulation of the cytoskeletal protein Tau, a process that may impair the cytoskeleton-regulating role(s) of this protein with impact on neuronal function. Here, we analyzed the role of Tau on stress-driven suppression of neurogenesis in the adult dentate gyrus (DG) using animals lacking Tau (Tau-knockout; Tau-KO) and wild-type (WT) littermates. Unlike WTs, Tau-KO animals exposed to chronic stress did not exhibit reduction in DG proliferating cells, neuroblasts and newborn neurons; however, newborn astrocytes were similarly decreased in both Tau-KO and WT mice. In addition, chronic stress reduced phosphoinositide 3-kinase (PI3K)/mammalian target of rapamycin (mTOR)/glycogen synthase kinase-3β (GSK3β)/β-catenin signaling, known to regulate cell survival and proliferation, in the DG of WT, but not Tau-KO, animals. These data establish Tau as a critical regulator of the cellular cascades underlying stress deficits on hippocampal neurogenesis in the adult brain.

The Microtubule-Associated Protein Tau and Its Relevance for Pancreatic Beta Cells

Structural and biochemical alterations of the microtubule-associated protein tau (MAPT) are associated with degenerative disorders referred to as tauopathies. We have previously shown that MAPT is present in human islets of Langerhans, human insulinomas, and pancreatic beta-cell line models, with biophysical similarities to the pathological MAPT in the brain. Here, we further studied MAPT in pancreatic endocrine tissue to better understand the mechanisms that lead to functional dysregulation of pancreatic beta cells. We found upregulation of MAPT protein expression in human insulinomas when compared to human pancreatic islets of Langerhans and an imbalance between MAPT isoforms in insulinomas tissue. We cloned one 3-repeat domain MAPT and transduced this into a beta-cell derived rodent cell line Rin-5F. Proliferation experiments showed higher growth rates and metabolic activities of cells overexpressing MAPT protein. We observed that a MAPT overexpressing cell line demonstrates altered insulin transcription, translation, and insulin secretion rates. We found the relative insulin secretion rates were significantly decreased in a MAPT overexpressing cell line and these findings could be confirmed using partial MAPT knock-down cell lines. Our findings support that MAPT may play an important role in insulin granule trafficking and indicate the importance of balanced MAPT phosphorylation and dephosphorylation for adequate insulin release.

Temperature and toxic Tau in Alzheimer's disease: new insights

Alzheimer's disease (AD), the most common dementia in the elderly, is characterized by cognitive impairment and severe autonomic symptoms such as disturbance in core body temperature (Tc), which may be predictors or early events in AD onset. Inclusions of phosphorylated Tau (p-Tau) are a hallmark of AD and other neurodegenerative disorders called “Tauopathies.” Animal and human studies show that anesthesia augments p-Tau levels through reduction of Tc, with implications for AD. Additionally, hypothermia impairs memory and cognitive function. The molecular networks related to Tc that are associated with AD remain poorly characterized. Under physiological conditions, Tau binds microtubules, promoting their assembly and stability. The dynamically regulated Tau-microtubule interaction plays an important role in structural remodeling of the cytoskeleton, having important functions in neuronal plasticity and memory in the hippocampus. Hypothermia-induced increases in p-Tau levels are significant, with an 80% increase for each degree Celsius below normothermic conditions. Although the effects of temperature on Tau phosphorylation are evident, its effects on p-Tau degradation remain poorly understoodWe review information concerning the mechanisms of Tau regulation of neuron plasticity via its effects on microtubule dynamics, with focus on pathways regulating the abundance of phosphorylated Tau species.  We highlight the effects of temperature on molecular mechanisms influencing the development of Tau-related diseases. Specifically, we argue that cold might preferentially affects central nervous system structures that are highly reliant upon plasticity, such as the hippocampus, and that the effect of cold on Tau phosphorylation may constitute a pathology-initiating trigger leading to neurodegeneration.

Human tau expression reduces adult neurogenesis in a mouse model of tauopathy

Accumulation of hyperphosphorylated and aggregated microtubule-associated protein tau (MAPT) is a central feature of a class of neurodegenerative diseases termed tauopathies. Notably, there is increasing evidence that tauopathies, including Alzheimer's disease, are also characterized by a reduction in neurogenesis, the birth of adult neurons. However, the exact relationship between hyperphosphorylation and aggregation of MAPT and neurogenic deficits remains unclear, including whether this is an early- or late-stage disease marker. In the present study, we used the genomic-based hTau mouse model of tauopathy to examine the temporal and spatial regulation of adult neurogenesis during the course of the disease. Surprisingly, hTau mice exhibited reductions in adult neurogenesis in 2 different brain regions by as early as 2 months of age, before the development of robust MAPT pathology in this model. This reduction was found to be due to reduced proliferation and not because of enhanced apoptosis in the hippocampus. At these same time points, hTau mice also exhibited altered MAPT phosphorylation with neurogenic precursors. To examine whether the effects of MAPT on neurogenesis were cell autonomous, neurospheres prepared from hTau animals were examined in vitro, revealing a growth deficit when compared with non-transgenic neurosphere cultures. Taken together, these studies provide evidence that altered adult neurogenesis is a robust and early marker of altered, cell-autonomous function of MAPT in the hTau mouse mode of tauopathy and that altered adult neurogenesis should be examined as a potential marker and therapeutic target for human tauopathies.

Mitochondrial complex 1 inhibition increases 4-repeat isoform tau by SRSF2 upregulation

Progressive Supranuclear Palsy (PSP) is a neurodegenerative disorder characterised by intracellular aggregation of the microtubule-associated protein tau. The tau protein exists in 6 predominant isoforms. Depending on alternative splicing of exon 10, three of these isoforms have four microtubule-binding repeat domains (4R), whilst the others only have three (3R). In PSP there is an excess of the 4R tau isoforms, which are thought to contribute significantly to the pathological process. The cause of this 4R increase is so far unknown. Several lines of evidence link mitochondrial complex I inhibition to the pathogenesis of PSP. We demonstrate here for the first time that annonacin and MPP⁺, two prototypical mitochondrial complex I inhibitors, increase the 4R isoforms of tau in human neurons. We show that the splicing factor SRSF2 is necessary to increase 4R tau with complex I inhibition. We also found SRSF2, as well as another tau splicing factor, TRA2B, to be increased in brains of PSP patients. Thereby, we provide new evidence that mitochondrial complex I inhibition may contribute as an upstream event to the pathogenesis of PSP and suggest that splicing factors may represent an attractive therapeutic target to intervene in the disease process.

Hypoxia alters expression of zebrafish microtubule-associated protein tau (mapta, maptb) gene transcripts

BACKGROUND

Microtubule-associated protein tau (MAPT) is abundant in neurons and functions in assembly and stabilization of microtubules to maintain cytoskeletal structure. Human MAPT transcripts undergo alternative splicing to produce 3R and 4R isoforms normally present at approximately equal levels in the adult brain. Imbalance of the 3R-4R isoform ratio can affect microtubule binding and assembly and may promote tau hyperphosphorylation and neurofibrillary tangle formation as seen in neurodegenerative diseases such as frontotemporal dementia (FTD) and Alzheimer's disease (AD). Conditions involving hypoxia such as cerebral ischemia and stroke can promote similar tau pathology but whether hypoxic conditions cause changes in MAPT isoform formation has not been widely explored. We previously identified two paralogues (co-orthologues) of MAPT in zebrafish, mapta and maptb.

RESULTS

In this study we assess the splicing of transcripts of these genes in adult zebrafish brain under hypoxic conditions. We find hypoxia causes increases in particular mapta and maptb transcript isoforms, particularly the 6R and 4R isoforms of mapta and maptb respectively. Expression of the zebrafish orthologue of human TRA2B, tra2b, that encodes a protein binding to MAPT transcripts and regulating splicing, was reduced under hypoxic conditions, similar to observations in AD brain.

CONCLUSION

Overall, our findings indicate that hypoxia can alter splicing of zebrafish MAPT co-orthologues promoting formation of longer transcripts and possibly generating Mapt proteins more prone to hyperphosphorylation. This supports the use of zebrafish to provide insight into the mechanisms regulating MAPT transcript splicing under conditions that promote neuronal dysfunction and degeneration.

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

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

Mechanisms of disease in frontotemporal lobar degeneration: gain of function versus loss of function effects

Frontotemporal lobar degeneration (FTLD) is clinically, pathologically and genetically heterogeneous. Three major proteins are implicated in its pathogenesis. About half of cases are characterized by depositions of the microtubule associated protein, tau (FTLD-tau). In most of the remaining cases, deposits of the transactive response (TAR) DNA-binding protein with Mw of 43 kDa, known as TDP-43 (FTLD-TDP), are seen. Lastly, about 5-10 % of cases are characterized by abnormal accumulations of a third protein, fused in sarcoma (FTLD-FUS). Depending on the protein concerned, the signature accumulations can take the form of inclusion bodies (neuronal cytoplasmic inclusions and neuronal intranuclear inclusions) or dystrophic neurites, in the cerebral cortex, hippocampus and subcortex. In some instances, glial cells are also affected by inclusion body formation. In motor neurone disease (MND), TDP-43 or FUS inclusions can present within motor neurons of the brain stem and spinal cord. This present paper attempts to critically examine the role of such proteins in the pathogenesis of FTLD and MND as to whether they might exert a direct pathogenetic effect (gain of function), or simply act as relatively innocent witnesses to a more fundamental loss of function effect. We conclude that although there is strong evidence for both gain and loss of function effects in respect of each of the proteins concerned, in reality, it is likely that each is a single face of either side of the coin, and that both will play separate, though complementary, roles in driving the damage which ultimately leads to the downfall of neurons and clinical expression of disease.

Lessons from tau-deficient mice

Both Alzheimer's disease (AD) and frontotemporal dementia (FTD) are characterized by the deposition of hyperphosphorylated forms of the microtubule-associated protein tau in neurons and/or glia. This unifying pathology led to the umbrella term “tauopathies” for these conditions, also emphasizing the central role of tau in AD and FTD. Generation of transgenic mouse models expressing human tau in the brain has contributed to the understanding of the pathomechanistic role of tau in disease. To reveal the physiological functions of tau in vivo, several knockout mouse strains with deletion of the tau-encoding MAPT gene have been established over the past decade, using different gene targeting constructs. Surprisingly, when initially introduced tau knockout mice presented with no overt phenotype or malformations. The number of publications using tau knockout mice has recently markedly increased, and both behavioural changes and motor deficits have been identified in aged mice of certain strains. Moreover, tau knockout mice have been instrumental in identifying novel functions of tau, both in cultured neurons and in vivo. Importantly, tau knockout mice have significantly contributed to the understanding of the pathophysiological interplay between Aβ and tau in AD. Here, we review the literature that involves tau knockout mice to summarize what we have learned so far from depleting tau in vivo.

Structural and functional characterization of H2 haplotype MAPT promoter: unique neurospecific domains and a hypoxia-inducible element would enhance rationally targeted tauopathy research for Alzheimer's disease

Alzheimer's disease (AD) is the leading cause of dementia in the elderly. Extraneuronal plaque comprising mostly the amyloid β peptide and intraneuronal tangles of hyperphosphorylated microtubule-associated τ protein (τ, gene MAPT) are typical of AD. Misfolded τ is also implicated in Parkinson's disease and frontotemporal dementia. We aim to understand the regulation of the human MAPT promoter by mapping its functional domains. We subcloned a 4868 base pair (bp) fragment from human BAC RPCI-11 100C5. Sequence analysis revealed an H2 haplotype MAPT promoter, 5'-UTR, and intronal fragment. Database analysis of the fragment showed 50%-75% homology with mouse and >90% with rhesus monkey. Comparison with human H1 sequences revealed differences that crossed predicted transcription factor sites. DNA-protein interaction studies by electrophoretic mobility shift assay suggested hypoxia response and an active specificity protein 1 (SP1) site in the 5'-untranslated region. Transfection of a series of MAPT promoter deletions revealed unique functional domains. The distal-most had different activities in neuronal vs. non-neuronal cells. We have cloned, sequenced, and functionally characterized a 4868bp fragment of the human MAPT 5'-flanking region, including the core promoter region (-302/+4), neurospecific domains (-4364/-1992 and +293/+504, relative to +1 TSS), and a hypoxia-inducible element (+60/+84). Our work extended functional analysis of the MAPT sequence further upstream, and explores cell-type specificity of MAPT promoter activity. Finally, we provided direct comparison of likely transcription factor binding sites, which are useful to understand differences between H1/H2 pathogenic associations.

Human aging is characterized by focused changes in gene expression and deregulation of alternative splicing

Aging is a major risk factor for chronic disease in the human population, but there are little human data on gene expression alterations that accompany the process. We examined human peripheral blood leukocyte in-vivo RNA in a large-scale transcriptomic microarray study (subjects aged 30-104 years). We tested associations between probe expression intensity and advancing age (adjusting for confounding factors), initially in a discovery set (n= 58), following-up findings in a replication set (n=240). We confirmed expression of key results by real-time PCR. Of 16,571 expressed probes, only 295 (2%) were robustly associated with age. Just six probes were required for a highly efficient model for distinguishing between young and old (area under the curve in replication set; 95%). The focused nature of age-related gene expression may therefore provide potential biomarkers of aging. Similarly, only 7 of 1065 biological or metabolic pathways were age-associated, in gene set enrichment analysis, notably including the processing of messenger RNAs (mRNAs); [P<0.002, false discovery rate (FDR) q<0.05]. This is supported by our observation of age-associated disruption to the balance of alternatively expressed isoforms for selected genes, suggesting that modification of mRNA processing may be a feature of human aging.