Reduces Tau Pathology Research Articles

Cerebral hypoperfusion reduces tau accumulation

AbstractObjectiveAlzheimer's disease (AD) often coexists with cerebrovascular diseases. However, the impact of cerebrovascular diseases such as stroke on AD pathology remains poorly understood.MethodsThis study examines the correlation between cerebrovascular diseases and AD pathology. The research was carried out using clinical and neuropathological data collected from the National Alzheimer's Coordinating Center (NACC) database and an animal model in which bilateral common carotid artery stenosis surgery was performed, following the injection of tau seeds into the brains of wild‐type mice.ResultsAnalysis of the NACC database suggests that clinical stroke history and lacunar infarcts are associated with lower neurofibrillary tangle pathology. An animal model demonstrates that chronic cerebral hypoperfusion reduces tau pathology, which was observed in not only neurons but also astrocytes, microglia, and oligodendrocytes. Furthermore, we found that astrocytes and microglia were activated in response to tau pathology and chronic cerebral hypoperfusion. Additionally, cerebral hypoperfusion increased a lysosomal enzyme, cathepsin D.InterpretationThese data together indicate that cerebral hypoperfusion reduces tau accumulation likely through an increase in microglial phagocytic activity towards tau and an elevation in degradation through cathepsin D. This study contributes to understanding the relationship between tau pathology and cerebrovascular diseases in older people with multimorbidity.

Co-opting templated aggregation to degrade pathogenic tau assemblies and improve motor function

Protein aggregation causes a wide range of neurodegenerative diseases. Targeting and removing aggregates, but not the functional protein, is a considerable therapeutic challenge. Here, we describe a therapeutic strategy called "RING-Bait," which employs an aggregating protein sequence combined with an E3 ubiquitin ligase. RING-Bait is recruited into aggregates, whereupon clustering dimerizes the RING domain and activates its E3 function, resulting in the degradation of the aggregate complex. We exemplify this concept by demonstrating the specific degradation of tau aggregates while sparing soluble tau. Unlike immunotherapy, RING-Bait is effective against both seeded and cell-autonomous aggregation. RING-Bait removed tau aggregates seeded from Alzheimer's disease (AD) and progressive supranuclear palsy (PSP) brain extracts and was also effective in primary neurons. We used a brain-penetrant adeno-associated virus (AAV) to treat P301S tau transgenic mice, reducing tau pathology and improving motor function. A RING-Bait strategy could be applied to other neurodegenerative proteinopathies by replacing the Bait sequence to match the target aggregate.

TLR2 immunotherapy suppresses neuroinflammation, tau spread, and memory loss in rTg4510 mice

In Alzheimer’s disease, chronic neuroinflammation is accompanied by amyloid and tau pathologies. Especially, aberrant microglial activation is known to precede the regional tau pathology development, but the mechanisms how microglia affect tau spread remain largely unknown. Here, we found that toll-like receptor 2 (TLR2) in microglia recognizes oligomeric tau as a pathogenic ligand and induces inflammatory responses. Knockout of TLR2 reduced tau pathology and microglial activation in rTg4510 tau transgenic mice. Treatment of oligomeric tau induced TLR2 activation and increased inflammatory responses in microglial cells. TLR2 further mediated the tau-induced microglial activation and promoted tau uptake into neurons in neuron-microglia co-culture system and in mouse hippocampus after intracranial tau injection. Importantly, treatment with anti-TLR2 monoclonal antibody Tomaralimab blocked TLR2 activation and inflammatory responses in a dose-dependent manner, and significantly reduced tau spread and memory loss in rTg4510 mice. These results suggest that TLR2 plays a crucial role in tau spread by causing aberrant microglial activation in response to pathological tau, and blocking TLR2 with immunotherapy may ameliorate tau pathogenesis in Alzheimer’s disease.

Proteostasis as a fundamental principle of Tau immunotherapy.

The microtubule-associated protein Tau is a driver of neuronal dysfunction in Alzheimer's disease and other tauopathies. In this process, Tau initially undergoes subtle changes to its abundance, subcellular localisation and a vast array of post-translational modifications including phosphorylation, that progressively result in the protein's somatodendritic accumulation and dysregulation of multiple Tau-dependent cellular processes. Given the various loss- and gain-of-functions of Tau in disease and the brain-wide changes in the proteome that characterise tauopathies, we asked whether targeting Tau would restore the alterations in proteostasis observed in disease. Therefore, by phage display, we generated a novel pan-Tau antibody, RNJ1, that preferentially binds human Tau and neutralises proteopathic seeding activity in multiple cell lines, and benchmarked it against a clinically tested pan-Tau antibody, HJ8.5 (murine version of tilavonemab). We then evaluated both antibodies, alone and in combination, in the K3 tauopathy mouse model, showing reduced Tau pathology and improvements in neuronal function following 14 weekly treatments, without obtaining synergy for the combination. These effects were more pronounced in female mice. To investigate the molecular mechanisms contributing to improvements in neuronal function, we employed quantitative proteomics, phosphoproteomics and kinase prediction analysis to first establish alterations in K3 mice relative to WT controls at the proteome level. In female K3 mice, we found 342 differentially abundant proteins, which are predominantly involved in metabolic and microtubule-associated processes, strengthening previously reported findings of defects in several functional domains in multiple tauopathy models. We next asked whether antibody-mediated Tau target engagement indirectly affects levels of deregulated proteins in the K3 model. Importantly, both immunotherapies, in particular RNJ1, induced abundance shifts towards a restoration to wild-type levels (proteostasis). A total of 257 of 342 (∼75%) proteins altered in K3 were closer in abundance to WT levels after RNJ1 treatment, and 73% after HJ8.5 treatment. However, the magnitude of these changes was less pronounced than that observed with RNJ1, as reflected by a far smaller number of differentially abundant proteins. Furthermore, analysis of the phosphoproteome showed an even stronger restoration effect with RNJ1, with ∼82% of altered phosphopeptides in K3 showing a shift to WT levels, and 75% with HJ8.5. Gene set over-representation analysis (ORA) further confirmed that proteins undergoing restoration are involved in biological pathways affected in K3 mice. Together, our study suggests that a Tau immunotherapy-induced restoration of proteostasis links target engagement and treatment efficacy.

Anti-acetylated-tau immunotherapy is neuroprotective in tauopathy and brain injury

BackgroundTau is aberrantly acetylated in various neurodegenerative conditions, including Alzheimer’s disease, frontotemporal lobar degeneration (FTLD), and traumatic brain injury (TBI). Previously, we reported that reducing acetylated tau by pharmacologically inhibiting p300-mediated tau acetylation at lysine 174 reduces tau pathology and improves cognitive function in animal models.MethodsWe investigated the therapeutic efficacy of two different antibodies that specifically target acetylated lysine 174 on tau (ac-tauK174). We treated PS19 mice, which harbor the P301S tauopathy mutation that causes FTLD, with anti-ac-tauK174 and measured effects on tau pathology, neurodegeneration, and neurobehavioral outcomes. Furthermore, PS19 mice received treatment post-TBI to evaluate the ability of the immunotherapy to prevent TBI-induced exacerbation of tauopathy phenotypes. Ac-tauK174 measurements in human plasma following TBI were also collected to establish a link between trauma and acetylated tau levels, and single nuclei RNA-sequencing of post-TBI brain tissues from treated mice provided insights into the molecular mechanisms underlying the observed treatment effects.ResultsAnti-ac-tauK174 treatment mitigates neurobehavioral impairment and reduces tau pathology in PS19 mice. Ac-tauK174 increases significantly in human plasma 24 h after TBI, and anti-ac-tauK174 treatment of PS19 mice blocked TBI-induced neurodegeneration and preserved memory functions. Anti-ac-tauK174 treatment rescues alterations of microglial and oligodendrocyte transcriptomic states following TBI in PS19 mice.ConclusionsThe ability of anti-ac-tauK174 treatment to rescue neurobehavioral impairment, reduce tau pathology, and rescue glial responses demonstrates that targeting tau acetylation at K174 is a promising neuroprotective therapeutic approach to human tauopathies resulting from TBI or genetic disease.

Rescue of synaptosomal glutamate release defects in tau transgenic mice by the tau aggregation inhibitor hydromethylthionine

Glutamatergic neurotransmission, important for learning and memory, is disrupted in different ways in patients with Alzheimer's disease (AD) and frontotemporal dementia (FTD) tauopathies. We have previously reported that two tau transgenic mouse models, L1 and L66, produce different phenotypes resembling AD and FTD, respectively. The AD-like L1 model expresses the truncated core aggregation domain of the AD paired helical filament (PHF) form of tau (tau296–390) whereas the FTD-like L66 model expresses full-length tau carrying two mutations at P301S/G335D. We have used synaptosomes isolated from these mice to investigate K+-evoked glutamate release and, if abnormal, to determine responsiveness to hydromethylthionine, a tau aggregation inhibitor previously shown to reduce tau pathology in these models. We report that the transgenes in these two mouse lines cause opposite abnormalities in glutamate release. Over-expression of the core tau unit in L1 produces a significant reduction in glutamate release and a loss of Ca2+-dependency compared with wild-type control mice. Full-length mutant tau produces an increase in glutamate release that retains normal Ca2+-dependency. Chronic pre-treatment with hydromethylthionine normalises both reduced (L1) and excessive glutamate (L66) and restores normal Ca2+-dependency in L1 mice. This implies that both patterns of impairment are the result of tau aggregation, but that the direction and Ca2+-dependency of the abnormality is determined by expression of the disease-specific transgene. Our results lead to the conclusion that the tauopathies need not be considered a single entity in terms of the downstream effects of pathological aggregation of tau protein. In this case, directionally opposite abnormalities in glutamate release resulting from different types of tau aggregation in the two mouse models can be corrected by hydromethylthionine. This may help to explain the activity of hydromethylthionine on cognitive decline and brain atrophy in both AD and behavioural-variant FTD.

Virus-like particle (VLP)-based vaccine targeting tau phosphorylated at Ser396/Ser404 (PHF1) site outperforms phosphorylated S199/S202 (AT8) site in reducing tau pathology and restoring cognitive deficits in the rTg4510 mouse model of tauopathy.

Tauopathies, including Alzheimer's disease (AD) and Frontotemporal Dementia (FTD), are histopathologically defined by the aggregation of hyperphosphorylated pathological tau (pTau) as neurofibrillary tangles in the brain. Site-specific phosphorylation of tau occurs early in the disease process and correlates with progressive cognitive decline, thus serving as targetable pathological epitopes for immunotherapeutic development. Previously, we developed a vaccine (Qβ-pT181) displaying phosphorylated Thr181 tau peptides on the surface of a Qβ bacteriophage virus-like particle (VLP) that induced robust antibody responses, cleared pathological tau, and rescued memory deficits in a transgenic mouse model of tauopathy. Here we report the characterization and comparison of two additional Qβ VLP-based vaccines targeting the dual phosphorylation sites Ser199/Ser202 (Qβ-AT8) and Ser396/Ser404 (Qβ-PHF1). Both Qβ-AT8 and Qβ-PHF1 vaccines elicited high-titer antibody responses against their pTau epitopes. However, only Qβ-PHF1 rescued cognitive deficits, reduced soluble and insoluble pathological tau, and reactive microgliosis in a 4-month rTg4510 model of FTD. Both sera from Qβ-AT8 and Qβ-PHF1 vaccinated mice were specifically reactive to tau pathology in human AD post-mortem brain sections. These studies further support the use of VLP-based immunotherapies to target pTau in AD and related tauopathies and provide potential insight into the clinical efficacy of various pTau epitopes in the development of immunotherapeutics.

5-HT4 receptor agonists treatment reduces tau pathology and behavioral deficit in the PS19 mouse model of tauopathy.

Accumulation of tau in synapses in the early stages of Alzheimer's disease (AD) has been shown to cause synaptic damage, synaptic loss, and the spread of tau pathology through trans-synaptically connected neurons. Moreover, synaptic loss correlates with a decline in cognitive function, providing an opportunity to investigate therapeutic strategies to target synapses and synaptic tau to rescue or prevent cognitive decline in AD. One of the promising synaptic targets is the 5-HT4 serotonergic receptor present postsynaptically in the brain structures involved in the memory processes. 5-HT4R stimulation exerts synaptogenic and pro-cognitive effects involving synapse-to-nucleus signaling essential for synaptic plasticity. However, it is not known whether 5-HT4R activation has a therapeutic effect on tau pathology. The goal of this study was to investigate the impact of chronic stimulation of 5-HT4R by two agonists, prucalopride and RS-67333, in PS19 mice, a model of tauopathy. We utilized gradient assays to isolate pre- and post-synaptic compartments, followed by biochemical analyses for tau species and ubiquitinated proteins in the synaptic compartments and total brain tissue. Next, we performed kinetic assays to test the proteasome's hydrolysis capacity in treatment conditions. Moreover, behavioral tests such as the open field and non-maternal nest-building tests were used to evaluate anxiety-like behaviors and hippocampal-related cognitive functioning in the treatment paradigm. Our results show that 5-HT4R agonism reduced tauopathy, reduced synaptic tau, increased proteasome activity, and improved cognitive functioning in PS19 mice. Our data suggest that enhanced proteasome activity by synaptic mediated signaling leads to the enhanced turnover of tau initially within synapses where the receptors are localized, and over time, the treatment attenuated the accumulation of tau aggregation and improved cognitive functioning of the PS19 mice. Therefore, stimulation of 5-HT4R offers a promising therapy to rescue synapses from the accumulation of toxic synaptic tau, evident in the early stages of AD.

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

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

Pediococcus acidilactici reduces tau pathology and ameliorates behavioral deficits in models of neurodegenerative disorders

BackgroundAlzheimer’s disease (AD), affecting many elders worldwide, is characterized by A-beta and tau-related cognitive decline. Accumulating evidence suggests that brain iron accumulation is an important characteristic of AD. However, the function and mechanism of the iron-mediated gut-brain axis on AD is still unclear.MethodsA Caenorhabditis elegans model with tau-overexpression and a high-Fe diet mouse model of cognitive impairment was used for probiotic function evaluation. With the use of qPCR, and immunoblotting, the probiotic regulated differential expression of AD markers and iron related transporting genes was determined. Colorimetric kits, IHC staining, and immunofluorescence have been performed to explore the probiotic mechanism on the development of gut-brain links and brain iron accumulation.ResultsIn the present study, a high-Fe diet mouse model was used for evaluation in which cognitive impairment, higher A-beta, tau and phosphorylated (p)-tau expression, and dysfunctional phosphate distribution were observed. Considering the close crosstalk between intestine and brain, probiotics were then employed to delay the process of cognitive impairment in the HFe mouse model. Pediococcus acidilactici (PA), but not Bacillus subtilis (BN) administration in HFe-fed mice reduced brain iron accumulation, enhanced global alkaline phosphatase (AP) activity, accelerated dephosphorylation, lowered phosphate levels and increased brain urate production. In addition, because PA regulated cognitive behavior in HFe fed mice, we used the transgenic Caenorhabditis elegans with over-expressed human p-tau for model, and then PA fed worms became more active and longer lived than E.coli fed worms, as well as p-tau was down-regulated. These results suggest that brain iron accumulation influences AD risk proteins and various metabolites. Furthermore, PA was shown to reverse tau-induced pathogenesis via iron transporters and AP-urate interaction.ConclusionsPA administration studies demonstrate that PA is an important mediator of tau protein reduction, p-tau expression and neurodegenerative behavior both in Caenorhabditis elegans and iron-overload mice. Finally, our results provide candidates for AP modulation strategies as preventive tools for promoting brain health.1zXKqRd2u82F96nqb8MmwuVideo

Cell type-specific regulation of m6 A modified RNAs in the aging Drosophila brain.

The aging brain is highly vulnerable to cellular stress, and neurons employ numerous mechanisms to combat neurotoxic proteins and promote healthy brain aging. The RNA modification m6 A is highly enriched in the Drosophila brain and is critical for the acute heat stress response of the brain. Here we examine m6 A in the fly brain with the chronic stresses of aging and degenerative disease. m6 A levels dynamically increased with both age and disease in the brain, marking integral neuronal identity and signaling pathway transcripts that decline in level with age and disease. Unexpectedly, there is opposing impact of m6 A transcripts in neurons versus glia, which conferred different outcomes on animal health span upon Mettl3 knockdown to reduce m6 A: whereas Mettl3 function is normally beneficial to neurons, it is deleterious to glia. Moreover, knockdown of Mettl3 in glial tauopathy reduced tau pathology and increased animal survival. These findings provide mechanistic insight into regulation of m6 A modified transcripts with age and disease, highlighting an overall beneficial function of Mettl3 in neurons in response to chronic stresses, versus a deleterious impact in glia.

A novel DYRK1a inhibitor, DYR533, reduces tau pathology and TNF alpha in the 3xTg‐AD and PS19 mouse models

AbstractBackgroundDual specificity tyrosine phosphorylation kinase 1a (DYRK1a) directly phosphorylates tau and amyloid precursor protein and is upregulated in postmortem brain tissue of patients with disorders including Alzheimer’s (AD) and Picks disease (a tauopathy). Our lab has shown that treatment with a DYRK1a inhibitor (DYR219) reduced Aβ plaque deposition and decreased phosphorylated tau at Serine 396 (pTauSer396) in the 3xTg‐AD mouse model. Here, we developed and tested a novel DYRK1a inhibitor (DYR533), which has an increased half‐life and bioavailability, in 3xTg‐AD mice that develop both Aβ and pathological tau, and PS19 mice that develop solely pathological tau.MethodWe dosed eight‐month‐old 3xTg‐AD and four‐month‐old PS19 mice daily with either 1.0‐, 2.5‐, or 5.0‐mg/kg DYR533 or a vehicle dose for two or four months respectively per model. Treatment start age occurred at the onset of neuropathology. Mice underwent rotarod testing to assess motor function and water maze testing to assess spatial learning and memory, with testing starting 2 weeks prior to the end of treatment. Blood and brain tissue were collected for neuropathology assessment. We assessed Aβ 40‐42 in the 3xTg‐AD mice, and pTauSer396 and the pro‐inflammatory cytokine tumor necrosis factor (Tnf)α in the hippocampus of both models. Blood plasma was extracted and analyzed for Tnfα levels.ResultIn both 3xTg‐AD and PS19 mice, DYR533 reduced soluble and insoluble fractions of pTau Ser396 in a dose dependent manner. Notably, DYR533 in 3xTg‐AD mice reduced pTau at threonine 217, which was recently identified as an early marker of AD progression. Soluble cortical Aβ42 levels were significantly reduced in the 1.0 mg/kg and 5.0 mg/kg 3xTg‐AD groups. DYR533 significantly reduced the levels of Tnfα in blood plasma and the hippocampus of both 3xTg‐AD and PS19 mice.ConclusionIn conclusion, the DYRK1a inhibitor, DYR533, reduces pTauSer396, as well as blood plasma and hippocampal levels of Tnf α in both 3xTg‐AD and PS19 models. Ongoing efforts include testing the effects of DYR533 in a rodent model of Down syndrome (Ts65Dn), which harbors three copies of DYRK1a, and completion of 3xTg‐AD and PS19 experiments. Thus far, these results support DYR533 as a potential therapeutic for AD and the tauopathies.

The relationship between ApoE4 and lipid dysregulation in glia of the PS19 mouse model of tauopathy

AbstractBackgroundApolipoprotein E4 (apoE), the major lipoprotein in the brain, plays an essential role in brain`s lipid homeostasis; furthermore, the presence of the apoE4 allele is the strongest genetic risk factor for developing late‐onset AD compared to most common apoE3 and protective apoE2 alleles. Recent studies in iPSC microglia and astrocytes demonstrate that apoE modulates cholesterol dysfunction and inflammatory responses in an isoform‐specific fashion. However, it is not known if lipid accumulation in glia mediates toxic effects in vivo in the context of tauopathy and neurodegeneration.MethodIn this work we used the combination unbiased lipidomics coupled with immunostainings to dissect the role of apoE and apoE isoforms in glial lipid metabolism of tauopathy P301S tau transgenic mice with a targeted replacement of murine apoE with human ApoE4, ApoE3, or ApoE KO. We further treated the P301S/ApoE4 mice with the LXR agonist GW3965 to test if promoting cholesterol efflux in P301S mice would reduce tau pathology and neurodegeneration in this model.ResultsBy performing unbiased lipidomic analysis of forebrain samples, we demonstrate that P301S/ApoE KI mice accumulate significant amounts of specific cholesteryl esters, oxidized sterols and endolysosomal BMP lipids in an ApoE‐isoform and Tau‐dependent manner. We further show that microglia from aged 9.5 months old P301S/ApoE4 mice accumulate significant amounts of neutral BODIPY‐positive lipid inclusions within lysosomes. Next, we demonstrate that the oral administration of the LXR agonist GW3965 for 3 months significantly reduces p‐tau‐positive AT8 immunostaining in cortex and hippocampus, protects from associated brain neurodegeneration, and improves nesting behavior in 9.5 months old P301S/ApoE4 mice. Using bulk RNA sequencing and immunostaining, we show that LXR agonist diet induces changes in cholesterol biosynthesis and metabolism that result in a significant reduction of neuroinflammatory responses in aged P301S/ApoE4 mice. Lastly, using unbiased lipidomics of forebrain tissues we demonstrate that P301S/ApoE4 mice on LXR diet exhibit significantly lower levels of cholesterol esters when compared to tau transgenic animals on control diet.ConclusionsTogether, we demonstrate that ApoE4 promotes lipid accumulation in glia in the setting of tauopathy and that reducing the accumulation of these lipids by LXR activation is neuroprotective.

Neuronal targeting of tau using a mRNA‐encoded tau‐specific antibody fragment

AbstractBackgroundA promising target for the treatment of Alzheimer’s disease and related tauopathies is intraneuronal tau. We have generated conventional tau‐specific monoclonal antibodies, as well as engineered antibody fragments, and demonstrated their ability to reduce tau pathology in the brains of tau transgenic mice (Nisbet et al., Brain 2017, Bajracharya, Brici et al., ANC 2021, Bajracharya et al. JCR 2022). Therapeutic efficacy is limited, however, by the inability of these antibodies to readily cross the blood‐brain barrier (BBB) and neuronal membrane to target intraneuronal tau. The SARS‐CoV‐2 pandemic revealed the potential of mRNA technology as an accessible and affordable strategy for delivering exogenous proteins, such as antibodies, to cells. The aim of this study was to explore the potential of utilizing mRNA to improve the intraneuronal delivery of our lead‐candidate tau‐specific monoclonal antibody in a single chain variable fragment (scFv) format.MethodThe cDNA encoding the tau scFv was cloned into an expression plasmid with a T7 promotor. The plasmid DNA was linearized, and in vitro transcription was conducted. The resulting mRNA was capped at the 5’ end with anti‐reverse cap analogue (ARCA), and possessed a 3’ poly (A) tail. The mRNA was then loaded into synthetic and biological nanoparticles and cellular uptake of the encapsulated mRNA and expression of the scFv was determined using mouse primary hippocampal neurons and human neuroblastoma SH‐SY5Y cells. Finally, binding of the expressed scFv to cytoplasmic tau was determined using a GFP‐pulldown assay.ResultHighly‐pure synthetic mRNA encoding a tau scFv was successfully generated and encapsulated into synthetic and biological nanocarriers. Upon treatment of cells with the encapsulated mRNA in vitro, the tau scFv was expressed and capable of engaging intracellular tau.ConclusionCollectively, our results validate the use of mRNA encoding tau‐specific antibodies as an effective and economic alternative to conventional antibodies for specific targeting of intracellular antigens such as tau.

Importance of functional outcome measures when evaluating the efficacy of tau immunotherapies

AbstractBackgroundTau immunotherapies are promising approaches to treat Alzheimer’s disease and other tauopathies. Using in vivo two‐photon calcium imaging, we have observed altered neuronal calcium activity in behaving JNPL3 tauopathy mice at both early and advanced stage of tauopathy. We have also shown that two mouse monoclonal antibodies, targeting phosphorylated tau‐Ser396/Ser404, partially restored these neuronal deficits (Wu Q et al Neurobiol Dis 2021, Ji C et al Alzheimers Dement AAIC 2022). Recently, we reported that novel single domain antibodies (sdAbs) and their divalent derivatives conjugated to Fc fragment showed varied efficacy to reduce tau pathology in culture, and to clear tau in brain interstitial fluid by in vivo microdialysis. Whether these sdAbs restore tauopathy‐induced neuronal deficits warrants further evaluation.MethodSomatic calcium activity in the motor cortex of homozygous 6‐month‐old JNPL3 mice was imaged by two‐photon microscopy when animals were either quiet or running. Two doses (100 µg each) of a tau IgG1‐(sdAb)2 or a control IgG1 were administered intravenously four days apart after the first imaging session. Somatic calcium activity was assessed again four days later, and compared to profile before treatment. Tau pathology was then analyzed in the mouse brain lysates by immunoblotting.ResultAbnormal cortical calcium activity was observed in resting and running JNPL3 mice at 6 months of age. Acute treatment with the tau IgG1‐(sdAb)2 did not normalize the frequency, amplitude or total activity of calcium transients in motor cortical neurons. Littermate mice treated with control IgG1 showed worsening of the tauopathy‐induced calcium dysfunction in the resting condition, and no improvement in the running condition. Interestingly, tau IgG1‐(sdAb)2 treatment decreased soluble phosphorylated tau in the treated mice, although it did not improve neuronal function. Additional analyses are ongoing, including of antibody target engagement.ConclusionThese findings confirmed neuronal calcium dysregulation in young JNPL3 mice. The failure of this particular acute tau antibody treatment to restore neuronal function is in contrast to our prior findings on two other tau antibodies targeting a different epitope, although all reduced soluble phospho‐tau. Therefore, these results highlight the importance of including a functional readout during preclinical development of tau antibodies.

Immunotherapy against tau pathology in mouse models requires cytosolic Fc receptor TRIM21

AbstractBackgroundThe passive transfer of monoclonal antibodies reduces tau pathology in mouse models and is under evaluation as a potential immunotherapeutic strategy against Alzheimer’s disease and other tauopathies. The mechanisms that drive therapeutic protection of anti‐tau antibodies are not well understood.MethodP301S tau transgenic animals were treated with antibodies against pS422 and analysed for tau pathology by biochemical fractionation. Organotypic hippocampal slice cultures were used as a model of tau seeding and neutralisation. AAV serotypes were used to deliver tau‐selective degraders.ResultGenetic deletion of the cytosolic antibody receptor and E3 ubiquitin ligase TRIM21 rendered tau immunotherapy ineffective in animal models. In organotypic slices, expression of TRIM21 was essential for protection against seeded aggregation of tau. Cytosolic antibody‐tau complexes were visible inside neurons in complex with TRIM21 shortly after application of tau assemblies and antibodies to the cell exterior. Nanobody‐based degraders were developed using TRIM21 and found to protect against tau pathology.ConclusionAnti‐tau antibodies can engage extracellular tau seeds and enter neurons as a complex. Following cytosolic entry, TRIM21 engages the antibodies and mediates neutralisation of tau seeding activity. The results reveal a mechanism that can be optimised for future immunotherapeutics. In this direction, AAV‐delivered degraders reveal a route by which tau aggregates may be selectively removed from the brain.

The type-I interferon response potentiates seeded tau aggregation and exacerbates tau pathology.

Signatures of a type-I interferon (IFN-I) response are observed in the post mortem brain in Alzheimer's disease (AD) and other tauopathies. However, the effect of the IFN-I response on pathological tau accumulation remains unclear. We examined the effects of IFN-I signaling in primary neural culture models of seeded tau aggregation and P301S-tau transgenic mouse models in the context of genetic deletion of the IFN-I receptor (IFNAR). Polyinosinic:polycytidylic acid (PolyI:C), a synthetic analog of viral nucleic acids, evoked a potent cytokine response that enhanced seeded aggregation of tau in an IFN-I-dependent manner. IFN-I-induced vulnerability could be pharmacologically prevented and was intrinsic to neurons. Aged P301S-tau mice lacking Ifnar1 had significantly reduced tau pathology compared to mice with intact IFN signaling. We identify a critical role for IFN-I in potentiating tau aggregation. IFN-I is therefore identified as a potential therapeutic target in AD and other tauopathies. Type-I IFN (IFN-I) promotes seeded tau aggregation in neural cultures. IFNAR inhibition prevents IFN-I driven sensitivity to tau aggregation. IFN-I driven vulnerability is intrinsic to neurons. Tau pathology is significantly reduced in aged P301S-tau mice lacking IFNAR.

Therapeutic Implications of Probiotics in the Gut Microbe-Modulated Neuroinflammation and Progression of Alzheimer's Disease.

Alzheimer's disease (AD) is characterized by the accumulation of specific proteins in the brain. A recent study revealed that manipulating gut microbiota (GM) significantly reduced tau pathology and neurodegeneration in an apolipoprotein E isoform-dependent manner. The resilience of a healthy microbiota protects it from a variety of dysbiosis-related pathologies. Convincing evidence has demonstrated the roles of GM in the pathogenesis of AD, which are partly mediated by modified microglial activity in the brain. Therefore, modulation of GM may be a promising therapeutic option for AD prevention. In addition to providing the cells with energy and affecting microglial maturation, these microbial metabolites appear to influence neuronal function. One of the potential therapeutic approaches targeting GM may involve using probiotics. Additionally, human GM and its metabolites have also become potential therapeutic targets for developing interventions for the prevention of disorders. Synbiotics and postbiotics can also be used to treat AD by modulating GM. In addition, physical activity, exercise, and physical fitness are being considered as potential nonpharmacological therapies to reduce signaling pathways related to neuroinflammation. Therefore, interventions targeting GM might be promising strategies for health promotion.

The Crystal Structure of the Hsp90-LA1011 Complex and the Mechanism by Which LA1011 May Improve the Prognosis of Alzheimer's Disease.

Functional changes in chaperone systems play a major role in the decline of cognition and contribute to neurological pathologies, such as Alzheimer's disease (AD). While such a decline may occur naturally with age or with stress or trauma, the mechanisms involved have remained elusive. The current models suggest that amyloid-β (Aβ) plaque formation leads to the hyperphosphorylation of tau by a Hsp90-dependent process that triggers tau neurofibrillary tangle formation and neurotoxicity. Several co-chaperones of Hsp90 can influence the phosphorylation of tau, including FKBP51, FKBP52 and PP5. In particular, elevated levels of FKBP51 occur with age and stress and are further elevated in AD. Recently, the dihydropyridine LA1011 was shown to reduce tau pathology and amyloid plaque formation in transgenic AD mice, probably through its interaction with Hsp90, although the precise mode of action is currently unknown. Here, we present a co-crystal structure of LA1011 in complex with a fragment of Hsp90. We show that LA1011 can disrupt the binding of FKBP51, which might help to rebalance the Hsp90-FKBP51 chaperone machinery and provide a favourable prognosis towards AD. However, without direct evidence, we cannot completely rule out effects on other Hsp90-co-chaprone complexes and the mechanisms they are involved in, including effects on Hsp90 client proteins. Nonetheless, it is highly significant that LA1011 showed promise in our previous AD mouse models, as AD is generally a disease affecting older patients, where slowing of disease progression could result in AD no longer being life limiting. The clinical value of LA1011 and its possible derivatives thereof remains to be seen.

TREM2 Agonism with a Monoclonal Antibody Attenuates Tau Pathology and Neurodegeneration.

TREM2 is a membrane receptor expressed on microglia that plays a pivotal role in the organization and function of these innate immune cell components within the neurodegenerated brain. Whereas TREM2 deletion has been studied extensively in experimental beta-amyloid and Tau-based models of Alzheimer's disease, its engagement, and subsequent agonism have not been tested in the context of Tau pathology. Herein, we explored the effects of Ab-T1, an agonistic TREM2 monoclonal antibody on Tau uptake, phosphorylation, seeding, and spreading as well as its therapeutic efficacy in a Tauopathy model. Ab-T1 enhanced the uptake of misfolded Tau to microglia and induced a non-cell autonomous attenuation of spontaneous Tau seeding and phosphorylation in primary neurons from human Tau transgenic mice. Ex vivo, incubation with Ab-T1 led to a significant reduction in the seeding of Tau pathology in the hTau murine organoid brain system. Systemic administration of Ab-T1 resulted in reduced Tau pathology and propagation when hTau was stereotactically injected into the hemispheres of hTau mice. Intraperitoneal treatment with Ab-T1 lead to attenuation of cognitive decline in the hTau mice that was associated with reduced neurodegeneration and synaptic preservation with amelioration of the global neuroinflammatory program. Collectively, these observations show that TREM2 engagement with an agonistic antibody result in reduced Tau burden concomitant with attenuated neurodegeneration ascribed to the education of resident microglia. These results may suggest that despite the opposing results with regard to the effect of TREM2 knockout in experimental Tau-based model systems, receptor engagement and activation by Ab-T1 appears to possess beneficial effects with respect to the various mechanisms mediating Tau-driven neurodegeneration.