Tau mRNA Research Articles

Tau accumulation is cleared by the induced expression of VCP via autophagy.

Tauopathy, including frontotemporal lobar dementia and Alzheimer's disease, describes a class of neurodegenerative diseases characterized by the aberrant accumulation of Tau protein due to defects in proteostasis. Upon generating and characterizing a stable transgenic zebrafish that expresses the human TAUP301L mutant in a neuron-specific manner, we found that accumulating Tau protein was efficiently cleared via an enhanced autophagy activity despite constant Tau mRNA expression; apparent tauopathy-like phenotypes were revealed only when the autophagy was genetically or chemically inhibited. We performed RNA-seq analysis, genetic knockdown, and rescue experiments with clinically relevant point mutations of valosin-containing protein (VCP), and showed that induced expression of VCP, an essential cytosolic chaperone for the protein quality system, was a key factor for Tau degradation via its facilitation of the autophagy flux. This novel function of VCP in Tau clearance was further confirmed in a tauopathy mouse model where VCP overexpression significantly decreased the level of phosphorylated and oligomeric/aggregate Tau and rescued Tau-induced cognitive behavioral phenotypes, which were reversed when the autophagy was blocked. Importantly, VCP expression in the brains of human Alzheimer's disease patients was severely downregulated, consistent with its proposed role in Tau clearance. Taken together, these results suggest that enhancing the expression and activity of VCP in a spatiotemporal manner to facilitate the autophagy pathway is a potential therapeutic approach for treating tauopathy.

MAPT haplotype-associated transcriptomic changes in progressive supranuclear palsy

Progressive supranuclear palsy (PSP) is a neurodegenerative movement and cognitive disorder characterized by abnormal accumulation of the microtubule-associated protein tau in the brain. Biochemically, inclusions in PSP are enriched for tau proteoforms with four microtubule-binding domain repeats (4R), an isoform that arises from alternative tau pre-mRNA splicing. While preferential aggregation and reduced degradation of 4R tau protein is thought to play a role in inclusion formation and toxicity, an alternative hypothesis is that altered expression of tau mRNA isoforms plays a causal role. This stems from the observation that PSP is associated with common variation in the tau gene (MAPT) at the 17q21.31 locus which contains low copy number repeats flanking a large recurrent genomic inversion. The complex genomic structural changes at the locus give rise to two dominant haplotypes, termed H1 and H2, that have the potential to markedly influence gene expression. Here, we explored haplotype-dependent differences in gene expression using a bulk RNA-seq dataset derived from human post-mortem brain tissue from PSP (n = 84) and controls (n = 77) using a rigorous computational pipeline, including alternative pre-mRNA splicing. We found 3579 differentially expressed genes in the temporal cortex and 10,011 in the cerebellum. We also found 7214 differential splicing events in the temporal cortex and 18,802 in the cerebellum. In the cerebellum, total tau mRNA levels and the proportion of transcripts encoding 4R tau were significantly increased in PSP compared to controls. In the temporal cortex, the proportion of reads that expressed 4R tau was increased in cases compared to controls. 4R tau mRNA levels were significantly associated with the H1 haplotype in the temporal cortex. Further, we observed a marked haplotype-dependent difference in KANSL1 expression that was strongly associated with H1 in both brain regions. These findings support the hypothesis that sporadic PSP is associated with haplotype-dependent increases in 4R tau mRNA that might play a causal role in this disorder.

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.

Comprehensive analysis of brain injury parameters in a preclinical porcine model of acute liver failure.

Acute liver failure (ALF) is defined as acute loss of liver function leading to hepatic encephalopathy associated with a high risk of patient death. Brain injury markers in serum and tissue can help detect and monitor ALF-associated brain injury. This study compares different brain injury parameters in plasma and tissue along with the progression of ALF. ALF was induced by performing an 85% liver resection. Following the resection, animals were recovered and monitored for up to 48 h or until reaching the predefined endpoint of receiving standard medical therapy (SMT). Blood and serum samples were taken at Tbaseline, T24, and upon reaching the endpoint (Tend). Control animals were euthanized by exsanguination following plasma sampling. Postmortem brain tissue samples were collected from the frontal cortex (FCTx) and cerebellum (Cb) of all animals. Glial fibrillary acidic protein (GFAP) and tau protein and mRNA levels were quantified using ELISA and qRT-PCR in all plasma and brain samples. Plasma neurofilament light (NFL) was also measured using ELISA. All ALF animals (n = 4) were euthanized upon showing signs of brain herniation. Evaluation of brain injury biomarkers revealed that GFAP was elevated in ALF animals at T24h and Tend, while Tau and NFL concentrations were unchanged. Moreover, plasma glial fibrillary acidic protein (GFAP) levels were negatively correlated with total protein and positively correlated with both aspartate transaminase (AST) and alkaline phosphatase (AP). Additionally, lower GFAP and tau RNA expressions were observed in the FCTx of the ALF group but not in the CB tissue. The current large animal study has identified a strong correlation between GFAP concentration in the blood and markers of ALF. Additionally, the protein and gene expression analyses in the FCTx revealed that this area appears to be susceptible, while the CB is protected from the detrimental impacts of ALF-associated brain swelling. These results warrant further studies to investigate the mechanisms behind this process.

Effects of Exercise Training and L-Arginine Loaded Chitosan Nanoparticles on Hippocampus Histopathology, β-Secretase Enzyme Function, APP, Tau, Iba1and APOE-4 mRNA in Aging Rats.

The objective of this study was to evaluate the combined and independent effects of exercise training and L-Arginine loaded chitosan nanoparticles (LA CNPs) supplementation on hippocampal Tau, App, Iba1, and ApoE gene expression, oxidative stress, β-secretase enzyme activity, and hippocampus histopathology in aging rats. Thirty-five male Wistar rats were randomly assigned to five groups (n = 7 in each): Young (8 weeks old), Old (20 months old), old + L-arginine supplementation (Old Sup), old + exercise (Old Exe) and old + L-arginine supplementation + exercise (Old Sup + Exe). LA CNPs were administered to the supplement groups through gavage at a dosage of 500mg/kg/day for 6-weeks. Exercise groups were subjected to a swimming exercise program five days/week for the same duration. Upon the completion of their interventions, the animals underwent behavioral and open-field task tests and were subsequently sacrificed for hippocampus genetic and histopathological evaluation. For histopathological analysis of brain, Cresyl violet staining was used. Congo Red staining was employed to confirm amyloid plaques in the hippocampus. Expressions of Tau, App, Iba1, and ApoE genes were determined by real-time PCR. In contrast to the Old group, Old Exe and Old Sup + Exe groups spent more time in the central space in the open field task (p < 0.05) and have more live cells in the hippocampus. Old rats (Old, Old Sup and Old Exe groups) exhibited a significant Aβ peptide accumulation and increases in APP, Tau, Iba1, APOE-4 mRNA and MDA, along with decreases in SOD compared to the young group (p < 0.05). However, LA CNPs supplementation, exercise, and their combination (Old Sup, Old Exe and Old Sup + Exe) significantly reduced MDA, Aβ plaque as well as APP, Tau, Iba1, and APOE-4 mRNA compared to the Old group (p < 0.05). Consequently, the administration of LA CNPs supplements and exercise might regulate the risk factors of hippocampus cell and tissue.

Evaluating the efficacy of purchased antisense oligonucleotides to reduce mouse and human tau in vivo.

Many preclinical and clinical studies support the use of antisense oligonucleotides (ASOs) as effective therapeutic strategies. However, acquiring ASOs for research purposes may be limited by partnerships with the pharmaceutical companies. Our lab previously developed an effective ASO strategy to lower human tau and reverse pathology in aged tauopathy model mice. Testing the efficacy of purchased tau lowering ASOs would provide support for these reagents as broad research tools. Purchased mouse and human tau lowering ASOs were infused or injected intracerebroventricularly into wildtype and tau transgenic mice. Following treatment, brain tissue evaluated for ASO distribution and levels of tau mRNA, protein, and phosphorylated tau. We show that purchased ASOs enter cell types of the brain and effectively decrease mouse or human tau mRNA and protein levels. Human tau lowering ASO treatment in PS19 mice decreased phosphorylated tau and gliosis relative to saline-treated PS19 mice, consistent with our previous study using a non-commercial tau lowering ASO. The results of this study demonstrate the efficacy of purchased tau targeting ASOs in vivo to support their broad use by researchers.

Structural and functional damage to neuronal nuclei caused by extracellular tau oligomers.

Neuronal nuclei are normally smoothly surfaced. In Alzheimer's disease (AD) and other tauopathies, though, they often develop invaginations. We investigated mechanisms and functional consequences of neuronal nuclear invagination in tauopathies. Nuclear invagination was assayed by immunofluorescence in the brain, and in cultured neurons before and after extracellular tau oligomer (xcTauO) exposure. Nucleocytoplasmic transport was assayed in cultured neurons. Gene expression was investigated using nanoString nCounter technology and quantitative reverse transcription polymerase chain reaction. Invaginated nuclei were twice as abundant in human AD as in cognitively normal adults, and were increased in mouse neurodegeneration models. In cultured neurons, nuclear invagination was induced by xcTauOs by an intracellular tau-dependent mechanism. xcTauOs impaired nucleocytoplasmic transport, increased histone H3 trimethylation at lysine 9, and altered gene expression, especially by increasing tau mRNA. xcTauOs may be a primary cause of nuclear invagination in vivo, and by extension, impair nucleocytoplasmic transport and induce pathogenic gene expression changes. Extracellular tau oligomers (xcTauOs) cause neuronal nuclei to invaginate. xcTauOs alter nucleocytoplasmic transport, chromatin structure, and gene expression. The most upregulated gene is MAPT, which encodes tau. xcTauOs may thus drive a positive feedback loop for production of toxic tau.

Determinants of astrocytic pathology in stem cell models of primary tauopathies

Astrocytic tau aggregates are seen in several primary and secondary tauopathies, including progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and chronic traumatic encephalopathy (CTE). In all of these diseases, astrocytic tau consists mostly of the longer (4R) tau isoform, even when adjacent neuronal aggregates consist of a mixture of 3- and 4R tau, as in CTE. Even the rare astrocytic tau aggregates seen in Pick’s disease appear to contain both 3R and 4R tau. The reasons for this, and the mechanisms by which astrocytic tau aggregates form, remain unclear. We used a combination of RNA in situ hybridization and immunofluorescence in post-mortem human brain tissue, as well as tau uptake studies in human stem cell-derived astrocytes, to determine the origins of astrocytic tau in 4R tauopathies. We found no differences in tau mRNA expression between diseases or between tau positive and negative astrocytes within PSP. We then found that stem cell-derived astrocytes preferentially take up long isoform (4R) recombinant tau and that this uptake is impaired by induction of reactivity with inflammatory stimuli or nutritional stress. Astrocytes exposed to either 3R or 4R tau also showed downregulation of genes related to astrocyte differentiation. Our findings suggest that astrocytes preferentially take up neuronal 4R tau from the extracellular space, potentially explaining why 4R tau is the predominant isoform in astrocytic tau aggregates.

Casein Kinase 1δ Phosphorylates TDP-43 and Suppresses Its Function in Tau mRNA Processing.

Neurofibrillary tangle aggregated from anomalous hyperphosphorylated tau is a hallmark of Alzheimer's disease (AD). Trans-active response DNA-binding protein of 43 kDa (TDP-43) enhances the instability and exon (E) 10 inclusion of tau mRNA. Cytoplasmic inclusion of hyperphosphorylated TDP-43 in the neurons constitutes the third most prevalent proteinopathy of AD. Casein kinase 1δ (CK1δ) is elevated in AD brain and phosphorylates TDP-43 in vitro. To determine the roles of CK1δ in phosphorylation, aggregation, and function of TDP-43 in the processing of tau mRNA. The interaction and colocalization of TDP-43 and CK1δ were analyzed by co-immunoprecipitation and immunofluorescence staining. TDP-43 phosphorylation by CK1δ was determined in vitro and in cultured cells. RIPA-insoluble TDP-43 aggregates obtained by ultracentrifugation were analyzed by immunoblots. The instability and E10 splicing of tau mRNA were studied by using a reporter of green fluorescence protein tailed with 3'-untranslational region of tau mRNA and a mini-tau gene and analyzed by real-time quantitative PCR and reverse transcriptional PCR. We found that CK1δ interacted and co-localized with TDP-43. TDP-43 was phosphorylated by CK1δ at Ser379, Ser403/404, and Ser409/410 in vitro and in cultured cells, which was mutually enhanced. CK1δ overexpression promoted the aggregation of TDP-43 and suppressed its activity in enhancing the instability and E10 inclusion of tau mRNA. CK1δ phosphorylates TDP-43, promotes its aggregation, and inhibits its activity in promoting the instability of tau mRNA and inclusion of tau E10. Elevated CK1δ in AD brain may contribute to TDP-43 and tau pathologies directly or indirectly.

Human microRNA‐298 plays a vital role in maintaining APP and tau homeostasis and IL‐induced inflammation: Implication in Alzheimer’s disease.

AbstractBackgroundAlzheimer’s disease (AD) is marked by neurofibrillary tangles mainly composed of hyperphosphorylated microtubule‐associated protein tau; senile plaques comprising amyloid β (Aβ) peptides; and neuroinflammation. How these pathological changes are regulated remains unclear. Genetic, epigenetic, and environmental factors play important roles in disease progression. MicroRNA (miRNA), a group of small non‐coding RNAs, regulates multiple biological and pathological processes by binding to target mRNAs and altering translation levels. Disrupting this process could contribute to AD pathogenesis. We hypothesize that miR‐298 plays a vital role in maintaining APP and tau homeostasis and IL‐induced inflammation, particularly gliosis.MethodWe performed miR‐298 treatments and blockade by antisense‐miR298 (antagomiRs) in 3’UTR‐reporter clone‐transfected cultures and protein levels from target native mRNAs (Chopra et al‐Mol. Psychiatry‐2021). We transfected human astrocyte cells with miR‐298 mimics or antagomiRs. We analyzed culture media and lysates for protein and mRNA. We performed ELISA and real‐time‐qPCR assays to determine cytokines, APP and tau levels. We analyzed autopsy brain tissues from non‐cognitively impaired (NCI) and AD subjects by measuring levels of miR‐298, target mRNAs and proteins in cortical samples, as we described (Wang et al‐Mol. Psychiatry‐2022).ResultWe identified putative sites for miR‐298 in mRNAs encoding APP, BACE1, MAPT, IL1α, and IL6. Treatment by miR‐298 significantly increased production and secretion of multiple pro‐inflammatory cytokines, specifically IL‐1, IL‐6 and TNF‐α in human astrocyte cultures. Furthermore, treatment by miR‐298 reduced tau, APP and BACE1 protein and mRNA levels in astrocyte cultures. Levels of miR‐298 varied in postmortem human temporal lobe between AD patients and age‐matched NCI controls.ConclusionMiR‐298 induced a variety of pro‐inflammatory cytokines without administration of other challenges. Induction of multiple cytokines may be due to combinations of direct miRNA activity and regulation of upstream signaling pathways. MiR‐298 may play an important biological role in AD by reducing APP, BACE1 and tau expression while increasing the physiologic production of IL cytokines. This apparent paradox is resolved by noting that early‐stage (prodromal) gliosis may contribute to the clearance of toxic aggregates. We plan to test miR‐298 in AD animal models, including human tau‐overexpressing transgenic mice.We appreciate NIH‐NIA grants: (R01AG051086, R21AG056007, R56AG072810, P01AG014449, P30AG072976).

TRPV4 mRNA is elevated in the caudate nucleus with NPH but not in Alzheimer's disease.

Symptoms of normal pressure hydrocephalus (NPH) and Alzheimer's disease (AD) are somewhat similar, and it is common to misdiagnose these two conditions. Although there are fluid markers detectable in humans with NPH and AD, determining which biomarker is optimal in representing genetic characteristics consistent throughout species is poorly understood. Here, we hypothesize that NPH can be differentiated from AD with mRNA biomarkers of unvaried proximity to telomeres. We examined human caudate nucleus tissue samples for the expression of transient receptor potential cation channel subfamily V member 4 (TRPV4) and amyloid precursor protein (APP). Using the genome data viewer, we analyzed the mutability of TRPV4 and other genes in mice, rats, and humans through matching nucleotides of six genes of interest and one house keeping gene with two factors associated with high mutation rate: 1) proximity to telomeres or 2) high adenine and thymine (A + T) content. We found that TRPV4 and microtubule associated protein tau (MAPT) mRNA were elevated in NPH. In AD, mRNA expression of TRPV4 was unaltered unlike APP and other genes. In mice, rats, and humans, the nucleotide size of TRPV4 did not vary, while in other genes, the sizes were inconsistent. Proximity to telomeres in TRPV4 was <50Mb across species. Our analyses reveal that TRPV4 gene size and mutability are conserved across three species, suggesting that TRPV4 can be a potential link in the pathophysiology of chronic hydrocephalus in aged humans (>65years) and laboratory rodents at comparable ages.

Electroacupuncture improves learning-memory ability by down-regulating expression of hippocampal Aβ1-42 and Tau and NF-κB proteins in diabetic rats with cognitive impairment

To observe the effect of electroacupuncture(EA) on the expression of nuclear transcription factors κB (NF-κB) and Tau protein and content of amyloid (Aβ) in diabetic rats with cognitive impairment, so as to explore its mechanism underlying improvement of learning-memory ability. Male SD rats were randomly divided into normal control (n=9), model (n=9) and EA (n=9) groups. The diabetic mellitus model was established by feeding the rats with high fat and high sugar for 1 month and intraperitoneal injection of STZ (25 mg·kg-1·d-1) for 2 days. EA was applied to "Zusanli"(ST36) and "Neiting"(ST44) for 20 min, alternatively on both side every day, and "Yishu"(EX-B3) was stimulated by twirling the acupuncture needle with uniform reinforcing-reducing method for 1 min, followed by retaining it for 20 min. The treatment was conducted 6 times a week for 4 weeks. The learning-memory ability was evaluated by using Morris water maze swimming test. The blood glucose level was randomly detected by using a glucometer, the content of Aβ1-42 in the hippocampal tissue was detected by ELISA, and the relative expression levels of hippocampal Tau and NF-κB p65 proteins and mRNAs were determined by Western blot and fluorescence quantitative real-time PCR, separately. After modeling, the blood glucose, escape latency, Aβ1-42 content and the expression levels of Tau and NF-κB p65 proteins and mRNAs in the model group were significantly increased (P<0.01, P<0.05) in comparison with the normal control group. Following EA intervention, the modeling induced increase of blood glucose, escape latency, Aβ1-42 content and the expression levels of Tau and NF-κB p65 proteins and mRNAs were reversed (P<0.05, P<0.01). EA can improve the learning-memory ability in rats with diabetic cognitive impairment, which may be related to its function in down-regulating the levels of hippocampal Aβ1-42, Tau and NF-κB proteins.

Dendritic distribution of CDK5 mRNA and p35 mRNA, and a glutamate-responsive increase of CDK5/p25 complex contribute to tau hyperphosphorylation

BackgroundIn Alzheimer's disease (AD), abnormally phosphorylated tau in the somatodendrite compartment of brain neurons causes synaptic loss, resulting in neuron death. Although the mechanism by which hyperphosphorylated tau appears in dendrites remains unclear, we have previously reported that local translation of tau mRNA and GSK3β mRNA in response to glutamatergic stimulation triggers an increase of tau protein and initiation of a cycle for amplification of reactivated preexisting GSK3β, respectively. In this study, we investigated the mechanism responsible for neural excitation-dependent activation of another major tau kinase, CDK5, within dendrites. MethodsPrimary hippocampal neurons were treated with glutamate and examined by in situ hybridization, immunocytochemistry and Western blotting. ResultsThe mRNAs for both CDK5 and its neural-specific activator, p35, were found to be constitutively distributed in dendrites. Glutamate treatment induced immediate local dendritic translation of these proteins as well as conversion of p35 to p25, which forms the hyper-activated CDK5/p25 complex. This neural excitation-dependent tau phosphorylation by CDK5 was suppressed in the presence of a calpain inhibitor or a NMDA receptor antagonist. ConclusionOur results indicate that in addition to an increase of dendritic tau and reactivation of preexisting GSK3β, increase and hyper-activation of CDK5 are evoked by translation of dendrite-distributed mRNAs upon NMDA receptor-mediated neural excitation. General significanceHyperphosphorylated tau with AD epitopes is locally produced in dendrites via translational activation of dendrite-distributed mRNAs in response to glutamatergic stimulation. Therefore, tau hyperphosphorylation may play a crucial role in synaptic transduction.

Abstract WP24: Pharmacological Hypothermia (PH) Promotes Plasticity Through RNA Binding Motif 3 (RBM3)-Mediated Cold Shock Pathway Following Ischemic Stroke

Background: Phenothiazine, including chlorpromazine and promethazine (C+P), induce hypothermia and neuroprotection after stroke. Immediately after stroke onset, there is a neuroplasticity window within which rehabilitation is especially effective. Recent studies have indicated that hypothermia-induced neuroplasticity involves the RBM3-mediated cold shock pathway, but it is unknown whether this pathway participates in neuroprotection and neuroplasticity in the context of pharmacological hypothermia (PH) induced by C+P after stroke. Methods: Adult Sprague-Dawley rats were divided in 3 groups: (1) sham; (2) stroke; (3) stroke treated with C+P before reperfusion. Long-term functional outcomes were determined by grid walk tests, rota-rod tests, beam balance tests, forelimb placing tests, adhesive tape touch and adhesive tape removal at 7 through 28 days. mRNA and protein quantities of cold shock pathway [RBM3, eukaryotic initiation factor 2 alpha (eIF2α), and reticulon 3 (RTN3)] and neuroplasticity [synaptophysin (SYN), post-synaptic density protein-95 (PSD-95), Tau, and recombinant growth associated protein 43 (GAP43)] were assessed by real-time PCR and western blot at day 1, 7 and 28 after reperfusion. Additionally, expression of RTN3 and eIF2α, and the co-localization of SYN and PSD95 was measured in primary neurons which subjected to oxygen/glucose deprivation (OGD) with RBM3 knockdown. Results: PH significantly improved functional outcomes at day 7 and 28. At day 1, mRNA and protein expression of RBM3 and RTN3 were significantly increased, and eIF2α was dephosphorylated by PH after stroke. mRNA and protein levels of SYN, Tau and GAP43 were all increased by PH at day 7 and 28. Furthermore, in OGD with shRBM3 group, levels of RTN3 and eIF2α dephosphorylation were significantly decreased, and the co-localization of SYN and PSD95 were significantly reduced compared with OGD group at 24 h without shRBM3. Conclusion: Our study has provided evidence, for the first time, for a novel mechanism underlying hypothermia in which the neuroplasticity and rehabilitation were achieved after ischemic stroke. Our findings suggest that the RBM3-induce cold shock pathway is a potential target of hypothermia for neuroprotection and neurorehabilitation.

Neuronal ApoE4 stimulates C/EBPβ activation, promoting Alzheimer’s disease pathology in a mouse model

ApoE4 is a major genetic risk determinant for Alzheimer's disease (AD) and drives its pathogenesis via Aβ-dependent and -independent pathways. C/EBPβ, a proinflammatory cytokine-activated transcription factor, is upregulated in AD patients and increases cytokines and δ-secretase expression. Under physiological conditions, ApoE is mainly expressed in glial cells, but its neuronal expression is highly elevated under pathological stresses. However, how neuronal ApoE4 mediates AD pathologies remains incompletely understood. Here we show that ApoE4 activates C/EBPβ that subsequently regulates APP, Tau and BACE1 mRNA expression in mouse neurons, driving AD-like pathogenesis. To interrogate the pathological roles of both human ApoE4 and C/EBPβ elevation in neurons in the aged brain, we develop neuronal specific Thy1-ApoE4/C/EBPβ double transgenic mice. Neuronal ApoE4 strongly activates C/EBPβ and augmented δ-secretase subsequently cleaves increased mouse APP and Tau, promoting AD-like pathologies. Notably, Thy1-ApoE4/C/EBPβ mice develop amyloid deposits, Tau aggregates and neurodegeneration in an age-dependent manner, leading to synaptic dysfunction and cognitive disorders. Thus, our findings demonstrate that neuronal ApoE4 triggers AD pathogenesis via activating the crucial regulator C/EBPβ.

Tau mRNA Metabolism in Neurodegenerative Diseases: A Tangle Journey.

Tau proteins are known to be mainly involved in regulation of microtubule dynamics. Besides this function, which is critical for axonal transport and signal transduction, tau proteins also have other roles in neurons. Moreover, tau proteins are turned into aggregates and consequently trigger many neurodegenerative diseases termed tauopathies, of which Alzheimer’s disease (AD) is the figurehead. Such pathological aggregation processes are critical for the onset of these diseases. Among the various causes of tau protein pathogenicity, abnormal tau mRNA metabolism, expression and dysregulation of tau post-translational modifications are critical steps. Moreover, the relevance of tau function to general mRNA metabolism has been highlighted recently in tauopathies. In this review, we mainly focus on how mRNA metabolism impacts the onset and development of tauopathies. Thus, we intend to portray how mRNA metabolism of, or mediated by, tau is associated with neurodegenerative diseases.

Results of the first‐in‐human, randomized, double‐blind, placebo‐controlled phase 1b study of lumbar intrathecal bolus administrations of antisense oligonucleotide (ISIS 814907; BIIB080) targeting tau mRNA in patients with mild Alzheimer’s disease

AbstractBackgroundISIS 814907 (BIIB080) is an antisense oligonucleotide (ASO) that hybridizes to a complementary nucleotide sequence of mRNA of the human microtubule‐associated protein tau (MAPT) gene, preventing production of tau protein. Accumulation of hyperphosphorylated tau is associated with cognitive decline and brain atrophy in Alzheimer’s Disease (AD). The placebo controlled period of the Phase 1b multiple ascending dose (MAD) study of ISIS 814907 in patients with mild AD is complete and the open‐label long term extension (LTE) is ongoing in the UK, Canada, Germany, Sweden, Netherlands and Finland (EudraCT: 2016‐002713‐22; NCT03186989).MethodsThe study is divided into 2 parts. Part 1 is the MAD study, comprising a 3‐month Treatment Evaluation (TE) Period and a 6‐month Post‐Treatment (PT) Period. Part 2 is the open‐label LTE, comprising a 12‐month TE Period and a 4‐ or 6‐month PT Period. Four ascending dose cohorts were enrolled sequentially and randomized 3:1 to intrathecal (IT) bolus administrations of ISIS 814907 or placebo. Male or female patients aged 50‐74 years with mild AD and confirmed amyloid positivity (via CSF) at Screening were considered eligible. The primary objective was to assess safety and tolerability of multiple IT bolus administrations of ISIS 814907. The secondary objective was to evaluate CSF pharmacokinetics (PK). Exploratory objectives include assessment of plasma PK, target engagement and disease biomarkers, genotype and clinical endpoints relevant to AD.ResultsAll subjects (N=46) completed the MAD TE Period and 43 subjects completed the PT Period. All AEs were mild/moderate in severity. No serious AEs occurred in subjects receiving ISIS 814907. Dose‐dependent mean reduction from baseline in CSF total tau and phospho‐tau was observed in the TE period and continued in the PT period. CSF total tau and phospho‐tau reductions were comparable.ConclusionsIT bolus administration of multiple ascending doses of ISIS 814907 over 3 months was well‐tolerated in patients with mild AD. The robust lowering of CSF total tau and phospho‐tau warrants further investigation for the treatment of AD.

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

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

Phosphorylation of trans-active response DNA-binding protein-of 43kDa promotes its cytoplasmic aggregation and modulates its function in tau mRNA stability and exon 10 alternative splicing.

Trans-active response DNA-binding protein of 43kDa (TDP-43) promotes tau mRNA instability and tau exon 10 inclusion. Aggregation of phosphorylated TDP-43 is associated with amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration. Casein kinase 1ε (CK1ε) phosphorylates TDP-43 at multiple sites, enhances its cytoplasmic aggregation, and modulates its function in tau mRNA processing. To determine roles of TDP-43 site-specific phosphorylation in its localization, aggregation, and function in tau mRNA processing, TDP-43 was mutated to alanine or aspartic acid at Ser379, Ser403/404, or Ser409/410 to block or mimic phosphorylation. Site-specific phosphorylation of TDP-43 and its mutants by CK1ε was studied in vitro and in cultured cells. Cytoplasmic and nuclear TDP-43 and phospho-TDP-43 were analyzed by western blots. Aggregation of TDP-43 was assessed by immunostaining and level of radioimmunoprecipitation assay buffer-insoluble TDP-43. Green florescent protein tailed with tau 3'-untranslated region and mini-tau gene pCI/SI9-LI10 were used to study tau mRNA stability and alternative splicing of tau exon 10. We found that phospho-blocking mutations of TDP-43 at Ser379, Ser403/404, or Ser409/410 were not effectively phosphorylated by CK1ε. Compared with TDP-43, higher level of phosphorylated TDP-43 in the cytoplasm was observed. Phospho-mimicking mutations at these sites enhanced cytoplasmic aggregation of TDP-43. Green florescent protein expression was not inhibited by phospho-blocking mutants of TDP-43, but tau exon 10 inclusion was further enhanced by phospho-blocking mutations at Ser379 and Ser403/404. Phosphorylation of TDP-43 at Ser379, Ser403/404, or Ser409/410 primes its phosphorylation by CK1ε, promotes TDP-43 cytoplasmic aggregation, and modulates its function in tau mRNA processing in site-specific manner.

Tau Exon 10 Inclusion by PrPC through Downregulating GSK3β Activity.

Tau protein is largely responsible for tauopathies, including Alzheimer’s disease (AD), where it accumulates in the brain as insoluble aggregates. Tau mRNA is regulated by alternative splicing, and inclusion or exclusion of exon 10 gives rise to the 3R and 4R isoforms respectively, whose balance is physiologically regulated. In this sense, one of the several factors that regulate alternative splicing of tau is GSK3β, whose activity is inhibited by the cellular prion protein (PrPC), which has different physiological functions in neuroprotection and neuronal differentiation. Moreover, a relationship between PrPC and tau expression levels has been reported during AD evolution. For this reason, in this study we aimed to analyze the role of PrPC and the implication of GSK3β in the regulation of tau exon 10 alternative splicing. We used AD human samples and mouse models of PrPC ablation and tau overexpression. In addition, we used primary neuronal cultures to develop functional studies. Our results revealed a paralleled association between PrPC expression and tau 4R isoforms in all models analyzed. In this sense, reduction or ablation of PrPC levels induces an increase in tau 3R/4R balance. More relevantly, our data points to GSK3β activity downstream from PrPC in this phenomenon. Our results indicate that PrPC plays a role in tau exon 10 inclusion through the inhibitory capacity of GSK3β.