Tau immunotherapy has recently shown clinical promise but required high dosing. We developed NIDB-3101, a novel third-generation, high-affinity anti-tau biparatopic antibody designed for superior tau binding, aggregation inhibition, and extended half-life. NIDB-3101 binds tau’s microtubule-binding region and C-terminal domains. Various binding and cellular functional assays using recombinants, but more importantly human AD extracts were used to assess NIDB-3101 benefits. Half-life mutations impact was assessed via FcRn binding and cellular assays recycling. NIDB-3101 exhibited sub-nanomolar affinity, binding a broad spectrum of pathological tau species in AD homogenates, inhibited AD extracts-induced cellular effect compared to benchmark antibodies. Mutations enhanced hFcRn-mediated cellular recycling. NIDB-3101 captures a broad spectrum of pathological tau species leading to strong cellular efficacy using human AD extracts, supporting further clinical development as a potential disease-modifying therapy for AD and related tauopathies.

In Alzheimer's disease, many surviving neurons with tau pathology contain granulovacuolar degeneration bodies (GVBs), neuron-specific lysosomal structures induced by pathological tau assemblies. This could indicate a neuroprotective role for GVBs; however, the mechanism of GVB formation and its functional implications are elusive. Here, we demonstrate that casein kinase 1δ (CK1δ) activity is required for GVB formation. CK1δ is sequestered in the GVB during this process in an autophagy-dependent manner. We show that neurons with GVBs (GVB+) are resilient to tau-induced impairment of global protein synthesis and are protected against tau-mediated neurodegeneration. GVB+ neurons do not exhibit differential activation of transient translational stress responses but have increased ribosomal content. Unlike neurons without GVBs, GVB+ neurons fully retain the capacity to induce long-term potentiation-induced protein synthesis in the presence of tau pathology. Our results have identified CK1δ as a key regulator of GVB formation that confers a protective neuron-specific stress response to tau pathology. These findings provide opportunities for targeting neuronal resilience in tauopathies.

Kufs disease/CLN4 is an autosomal dominant neurodegenerative disorder caused by unknown mechanisms through Leu115Arg and Leu116Δ mutations in the DNAJC5 gene that encodes the synaptic vesicle co-chaperone cysteine string protein α (CSPα/DNAJC5). To investigate the disease mechanisms in vivo, we generated three independent mouse lines overexpressing different versions of CSPα/DNAJC5 under the neuron-specific Thy1 promoter: wild-type (WT), Leu115Arg, and Leu116Δ. Mice expressing mutant Leu115Arg CSPα/DNAJC5 are viable but develop motor deficits. As described in patients with Kufs disease, we observed the pathological lipofuscinosis and intracellular structures resembling granular osmiophilic deposits (GRODs) in the mutant but not in the WT transgenic lines. Microglia engulf lipofuscin and lipofuscin-containing neurons. Notably, conventional or conditional knockout mice lacking CSPα/DNAJC5 did not exhibit any signs of increased lipofuscinosis or GRODs. Our novel mouse models provide a valuable tool to investigate the molecular mechanisms underlying Kufs disease/CLN4. DNAJC5 mutations cause neuronal lipofuscinosis through a cell-autonomous gain of a pathological function of CSPα/DNAJC5.

In Alzheimer’s disease, many surviving neurons with tau pathology contain granulovacuolar degeneration bodies (GVBs), neuron-specific lysosomal structures induced by pathological tau assemblies. This could indicate a neuroprotective role for GVBs, however, the mechanism of GVB formation and its functional implications are elusive. Here, we demonstrate that GVB formation depends on CK1δ activity and basal autophagy. We show that neurons with GVBs (GVB+) are resilient to tau-induced impairment of global protein synthesis and are protected against tau-mediated neurodegeneration. GVB+ neurons have multiple adaptations to counteract the tau pathology-induced decline in protein synthesis, including increased ribosomal content. Importantly, unlike neurons without GVBs, GVB+ neurons fully retain the capacity to induce long-term potentiation-induced protein synthesis in the presence of tau pathology. Our results have identified CK1δ as a key regulator of GVB formation that confers a protective neuron-specific proteostatic stress response to tau pathology. Our findings provide novel opportunities for targeting neuronal resilience in tauopathies. ### Competing Interest Statement The authors have declared no competing interest.

>Maintenance of protein homeostasis or "proteostasis" is essential for the functioning and viability of cells.This is in particular the case for cells like neurons that cannot self-renew and acquire unique functional properties during their lifetime.Cellular proteostatic stress responses are in place to protect cells from damage in case of proteostatic challenges.The integrated stress response(ISR) is one of the key proteostatic stress responses in the cell(Costa-Mattioli and Walter,

Tau protein hyperphosphorylation and aggregation are key pathological events in neurodegenerative tauopathies such as Alzheimer’s disease. Interestingly, seasonal hibernators show extensive tau hyperphosphorylation during torpor, i.e., the hypothermic and hypometabolic state of hibernation, which is completely reversed during arousal. Torpor-associated mechanisms that reverse tau hyperphosphorylation may be of therapeutic relevance, however, it is currently not known to what extent they apply to human tau. Here we addressed this issue using daily torpor in wildtype mice that express mouse tau (mtau) and in mice that lack mtau expression and instead express human tau (htau). AT8, AT100 and Ser396 immunoblotting and immunohistochemistry were used to assess tau (hyper)phosphorylation at clinically relevant phosphorylation sites. We found that torpor robustly and reversibly increases the levels of phosphorylated tau in both mtau and htau mice. Immunohistochemistry revealed four brain areas that show prominent tau phosphorylation: the hippocampus, posterior parietal cortex, piriform cortex and cortical amygdala. Whereas wildtype mice primarily showed increased levels of diffusely organized hyperphosphorylated tau during torpor, htau mice contained clear somato-dendritic accumulations of AT8 reactivity resembling tau pre-tangles as observed in the Alzheimer brain. Interestingly, AT8-positive accumulations disappeared upon arousal, and tau phosphorylation levels at 24 h after arousal were lower than observed at baseline, suggesting a beneficial effect of torpor-arousal cycles on preexisting hyperphosphorylated tau. In conclusion, daily torpor in mice offers a quick and standardized method to study tau phosphorylation, accumulation and clearance in mouse models relevant for neurodegeneration, as well as opportunities to discover new targets for the treatment of human tauopathies.

AbstractObjectiveMethylation of plasma cell‐free DNA (cfDNA) has potential as a marker of brain damage in neurodegenerative diseases such as frontotemporal dementia (FTD). Here, we study methylation of cfDNA in presymptomatic and symptomatic carriers of genetic FTD pathogenic variants, next to healthy controls.MethodscfDNA was isolated from cross‐sectional plasma of 10 presymptomatic carriers (4 C9orf72, 4 GRN, and 2 MAPT), 10 symptomatic carriers (4 C9orf72, 4 GRN, and 2 MAPT), and 9 healthy controls. Genome‐wide methylation of cfDNA was determined using a high‐resolution sequencing technique (MeD‐seq). Cumulative scores based on the identified differentially methylated regions (DMRs) were estimated for presymptomatic carriers (vs. controls and symptomatic carriers), and reevaluated in a validation cohort (8 presymptomatic: 3 C9orf72, 3 GRN, and 2 MAPT; 26 symptomatic: 7 C9orf72, 6 GRN, 12 MAPT, and 1 TARDBP; 13 noncarriers from genetic FTD families).ResultsPresymptomatic carriers showed a distinctive methylation profile compared to healthy controls and symptomatic carriers. Cumulative DMR scores in presymptomatic carriers enabled to significantly differentiate presymptomatic carriers from healthy controls (p < 0.001) and symptomatic carriers (p < 0.001). In the validation cohort, these scores differentiated presymptomatic carriers from symptomatic carriers (p ≤ 0.007) only. Transcription‐start‐site methylation in presymptomatic carriers, generally associated with gene downregulation, was enriched for genes involved in ubiquitin‐dependent processes, while gene body methylation, generally associated with gene upregulation, was enriched for genes involved in neuronal cell processes.InterpretationA distinctive methylation profile of cfDNA characterizes the presymptomatic stage of genetic FTD, and could reflect neuronal death in this stage.

INTRODUCTION:Cerebrospinal fluid (CSF) biomarkers for specific cellular disease processes are lacking for tauopathies. In this translational study we aimed to identify CSF biomarkers reflecting early tau pathology-associated unfolded protein response (UPR) activation.METHODS:We employed mass spectrometry proteomics and targeted immunoanalysis in a combination of biomarker discovery in primary mouse neurons in vitro and validation in patient CSF from two independent large multicentre cohorts (EMIF-AD MBD, n = 310; PRIDE, n = 771).RESULTS:First, we identify members of the protein disulfide isomerase (PDI) family in the neuronal UPR-activated secretome and validate secretion upon tau aggregation in vitro. Next, we demonstrate that PDIA1 and PDIA3 levels correlate with total- and phosphorylated-tau levels in CSF. PDIA1 levels are increased in CSF from AD patients compared to controls and patients with tau-unrelated frontotemporal and Lewy body dementia (LBD).HIGHLIGHTS:Neuronal unfolded protein response (UPR) activation induces the secretion of protein disulfide isomerases (PDIs) in vitro. PDIA1 is secreted upon tau aggregation in neurons in vitro. PDIA1 and PDIA3 levels correlate with total and phosphorylated tau levels in CSF. PDIA1 levels are increased in CSF from Alzheimer's disease (AD) patients compared to controls. PDIA1 levels are not increased in CSF from tau-unrelated frontotemporal dementia (FTD) and Lewy body dementia (LBD) patients.

Tau aggregation is central to the pathogenesis of a large group of neurodegenerative diseases termed tauopathies, but it is still unclear in which way neurons respond to tau pathology and how tau accumulation leads to neurodegeneration. A striking neuron-specific response to tau pathology is presented by granulovacuolar degeneration bodies (GVBs), lysosomal structures that accumulate specific cargo in a dense core. Here we employed different tau aggregation models in primary neurons to investigate which properties of pathological tau assemblies affect GVB accumulation using a combination of confocal microscopy, transmission electron microscopy, and quantitative automated high-content microscopy. Employing GFP-tagged and untagged tau variants that spontaneously form intraneuronal aggregates, we induced pathological tau assemblies with a distinct subcellular localization, morphology, and ultrastructure depending on the presence or absence of the GFP tag. The quantification of the GVB load in the different models showed that an increased GVB accumulation is associated with the untagged tau aggregation model, characterized by shorter and more randomly distributed tau filaments in the neuronal soma. Our data indicate that tau aggregate structure and/or subcellular localization may be key determinants of GVB accumulation.

Communication and contact between neurons and astrocytes is important for proper brain physiology. How neuron/astrocyte crosstalk is affected by intraneuronal tau aggregation in neurodegenerative tauopathies is largely elusive. Human induced pluripotent stem cell (iPSC)-derived neurons provide the opportunity to model tau pathology in a translationally relevant in vitro context. However, current iPSC models inefficiently develop tau aggregates, and co-culture models of tau pathology have thus far utilized rodent astrocytes. In this article, we describe the co-culture of human iPSC-derived neurons with primary human astrocytes in a 96-well format compatible with high-content microscopy. By lentiviral overexpression of different mutated tau variants, this protocol can be flexibly adapted for the efficient induction of seeded or spontaneous tau aggregation. We used this novel co-culture model to identify cell type-specific disease mechanisms and to provide proof of concept for intervention by antisense therapy. These results show that this human co-culture model provides a highly translational tool for target discovery and drug development for human tauopathies. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol: Human neuron/astrocyte co-culture for seeded and spontaneous intraneuronal tau aggregation Support Protocol 1: Human induced pluripotent stem cell culture Support Protocol 2: Human primary astrocyte culture.

Background Intraneuronal tau aggregation is the major pathological hallmark of neurodegenerative tauopathies. It is now generally acknowledged that tau aggregation also affects astrocytes in a cell non-autonomous manner. However, mechanisms involved are unclear, partly because of the lack of models that reflect the situation in the human tauopathy brain. To accurately model neuron-astrocyte interaction in tauopathies, there is a need for a model that contains both human neurons and human astrocytes, intraneuronal tau pathology and mimics the three-dimensional architecture of the brain. Results Here we established a novel 100–200 µm thick 3D human neuron/astrocyte co-culture model of tau pathology, comprising homogenous populations of hiPSC-derived neurons and primary human astrocytes in microwell format. Using confocal, electron and live microscopy, we validate the procedures by showing that neurons in the 3D co-culture form pre- and postsynapses and display spontaneous calcium transients within 4 weeks. Astrocytes in the 3D co-culture display bipolar and stellate morphologies with extensive processes that ensheath neuronal somas, spatially align with axons and dendrites and can be found perisynaptically. The complex morphology of astrocytes and the interaction with neurons in the 3D co-culture mirrors that in the human brain, indicating the model’s potential to study physiological and pathological neuron-astrocyte interaction in vitro . Finally, we successfully implemented a methodology to introduce seed-independent intraneuronal tau aggregation in the 3D co-culture, enabling study of neuron-astrocyte interaction in early tau pathogenesis. Conclusions Altogether, these data provide proof-of-concept for the utility of this rapid, miniaturized, and standardized 3D model for cell type-specific manipulations, such as the intraneuronal pathology that is associated with neurodegenerative disorders.

Progressive aggregation of tau protein in neurons is associated with neurodegeneration in tauopathies. Cell non-autonomous disease mechanisms in astrocytes may be important drivers of the disease process but remain largely elusive. Here, we studied cell type-specific responses to intraneuronal tau aggregation prior to neurodegeneration. To this end, we developed a fully human co-culture model of seed-independent intraneuronal tau pathology, which shows no neuron and synapse loss. Using high-content microscopy, we show that intraneuronal tau aggregation induces oxidative stress accompanied by activation of the integrated stress response specifically in astrocytes. This requires the direct co-culture with neurons and is not related to neurodegeneration or extracellular tau levels. Tau-directed antisense therapy reduced intraneuronal tau levels and aggregation and prevented the cell non-autonomous responses in astrocytes. These data identify the astrocytic integrated stress response as a novel disease mechanism activated by intraneuronal tau aggregation. In addition, our data provide the first evidence for the efficacy of tau-directed antisense therapy to target cell autonomous and cell non-autonomous disease pathways in a fully human model of tau pathology.

ABSTRACT Kufs disease/CLN4 is an autosomal dominant neurodegenerative disorder that affects young adults, caused by mutations in the DNAJC5 gene that encodes the synaptic vesicle co-chaperone Cysteine String Protein α (CSPα/DNAJC5). The Leu115Arg and Leu116Δ mutations in humans are known to independently cause the disease, although the underlying mechanisms are unknown. To investigate the disease mechanisms in vivo, we generated three independent mouse lines overexpressing different versions of CSPα/DNAJC5 under the neuron-specific Thy1 promoter: wild-type (WT), Leu115Arg, and Leu116Δ. Mice expressing mutant CSPα/DNAJC5 are viable and do not show any significant increase in morbidity or mortality. However, we observed the presence of pathological lipofuscinosis in the mutants, indicated by autofluorescent punctate structures labeled with antibodies against ATP synthase subunit C, which were absent in the WT transgenic line. Additionally, transmission electron microscopy revealed intracellular structures resembling granular osmiophilic deposits (GRODs), observed in Kufs disease patients, in the mutants but not in non-transgenic controls or the WT transgenic mice. Notably, conventional, or conditional knockout mice lacking CSPα/DNAJC5 did not exhibit any signs of increased lipofuscinosis or GRODs. Our novel mouse models thus provide a valuable tool to investigate the molecular mechanisms underlying Kufs disease/CLN4. We conclude that DNAJC5 mutations cause neuronal lipofuscinosis through a cell-autonomous gain of a novel but pathological function of CSPα/DNAJC5.

Background In Alzheimer’s disease (AD), amyloid-β 1–42 (Aβ42) neurotoxicity stems mostly from its soluble oligomeric aggregates. Studies of such aggregates have been hampered by the lack of oligomer-specific research tools and their intrinsic instability and heterogeneity. Here, we developed a monoclonal antibody with a unique oligomer-specific binding profile (ALZ-201) using oligomer-stabilising technology. Subsequently, we assessed the etiological relevance of the Aβ targeted by ALZ-201 on physiologically derived, toxic Aβ using extracts from post-mortem brains of AD patients and controls in primary mouse neuron cultures. Methods Mice were immunised with stable oligomers derived from the Aβ42 peptide with A21C/A30C mutations (AβCC), and ALZ-201 was developed using hybridoma technology. Specificity for the oligomeric form of the Aβ42CC antigen and Aβ42 was confirmed using ELISA, and non-reactivity against plaques by immunohistochemistry (IHC). The antibody’s potential for cross-protective activity against pathological Aβ was evaluated in brain tissue samples from 10 individuals confirmed as AD ( n =7) and non-AD ( n =3) with IHC staining for Aβ and phosphorylated tau (p-Tau) aggregates. Brain extracts were prepared and immunodepleted using the positive control 4G8 antibody, ALZ-201 or an isotype control to ALZ-201. Fractions were biochemically characterised, and toxicity assays were performed in primary mouse neuronal cultures using automated high-content microscopy. Results AD brain extracts proved to be more toxic than controls as demonstrated by neuronal loss and morphological determinants (e.g. synapse density and measures of neurite complexity). Immunodepletion using 4G8 reduced Aβ levels in both AD and control samples compared to ALZ-201 or the isotype control, which showed no significant difference. Importantly, despite the differential effect on the total Aβ content, the neuroprotective effects of 4G8 and ALZ-201 immunodepletion were similar, whereas the isotype control showed no effect. Conclusions ALZ-201 depletes a toxic species in post-mortem AD brain extracts causing a positive physiological and protective impact on the integrity and morphology of mouse neurons. Its unique specificity indicates that a low-abundant, soluble Aβ42 oligomer may account for much of the neurotoxicity in AD. This critical attribute identifies the potential of ALZ-201 as a novel drug candidate for achieving a true, clinical therapeutic effect in AD.

Proteostasis is essential for cellular survival and particularly important for highly specialised post‐mitotic cells such as neurons. Transient reduction in protein synthesis by protein kinase R‐like endoplasmic reticulum (ER) kinase (PERK)‐mediated phosphorylation of eukaryotic translation initiation factor 2α (p‐eIF2α) is a major proteostatic survival response during ER stress. Paradoxically, neurons are remarkably tolerant to PERK dysfunction, which suggests the existence of cell type‐specific mechanisms that secure proteostatic stress resilience. Here, we demonstrate that PERK‐deficient neurons, unlike other cell types, fully retain the capacity to control translation during ER stress. We observe rescaling of the ATF4 response, while the reduction in protein synthesis is fully retained. We identify two molecular pathways that jointly drive translational control in PERK‐deficient neurons. Haem‐regulated inhibitor (HRI) mediates p‐eIF2α and the ATF4 response and is complemented by the tRNA cleaving RNase angiogenin (ANG) to reduce protein synthesis. Overall, our study elucidates an intricate back‐up mechanism to ascertain translational control during ER stress in neurons that provides a mechanistic explanation for the thus far unresolved observation of neuronal resilience to proteostatic stress.

Granulovacuolar degeneration bodies (GVBs) are intracellular vesicular structures that commonly accompany pathological tau accumulations in neurons of patients with tauopathies. Recently, we developed the first model for GVBs in primary neurons, that requires exogenous tau seeds to elicit tau aggregation. This model allowed the identification of GVBs as proteolytically active lysosomes induced by tau pathology. GVBs selectively accumulate cargo in a dense core, that shows differential and inconsistent immunopositivity for (phosphorylated) tau epitopes. Despite the strong evidence connecting GVBs to tau pathology, these structures have been reported in neurons without apparent pathology in brain tissue of tauopathy patients. Additionally, GVBs and putative GVBs have also been reported in the brain of patients with non-tau proteinopathies. Here, we investigated the connection between pathological protein assemblies and GVBs in more detail. This study combined newly developed primary neuron models for tau and α-synuclein pathology with observations in human brain tissue from tauopathy and Parkinson’s disease patients. Immunolabeling and imaging techniques were employed for extensive characterisation of pathological proteins and GVBs. Quantitative data were obtained by high-content automated microscopy as well as single-cell analysis of confocal images. Employing a novel seed-independent neuronal tau/GVB model, we show that in the context of tauopathy, GVBs are inseparably associated with the presence of cytosolic pathological tau and that intracellular tau aggregation precedes GVB formation, strengthening the causal relationship between pathological accumulation of tau and GVBs. We also report that GVBs are inseparably associated with pathological tau at the single-cell level in the hippocampus of tauopathy patients. Paradoxically, we demonstrate the presence of GVBs in the substantia nigra of Parkinson’s disease patients and in a primary neuron model for α-synuclein pathology. GVBs in this newly developed α-synuclein/GVB model are induced in the absence of cytosolic pathological tau accumulations. GVBs in the context of tau or α-synuclein pathology showed similar immunoreactivity for different phosphorylated tau epitopes. The phosphorylated tau immunoreactivity signature of GVBs is therefore independent of the presence of cytosolic tau pathology. Our data identify the emergence of GVBs as a more generalised response to cytosolic protein pathology.

Tau aggregation is the major pathological hallmark of neurodegenerative tauopathies and strongly correlates with neurodegeneration. Yet, the mechanism by which tau pathology leads to neuronal dysfunction and how astrocytes contribute to disease pathogenesis is largely elusive, partly due to the lack of suitable human co-culture models. We established a novel human neuron/astrocyte co-culture model in 96-well format, compatible with high-content automated microscopy analysis. Ngn2-iPSC differentiated neurons and primary human astrocytes were used in combination with a spontaneously aggregating tau variant. Neurons with a morphologically mature synapse pattern were obtained within 4 weeks. Introduction of a spontaneously aggregating tau variant induces progressive intraneuronal accumulation of pathologically phosphorylated, insoluble tau. Intraneuronal tau accumulation progressively induces oxidative stress and activation of the integrated stress response in co-cultured human astrocytes. This novel human co-culture model recapitulates key features of human tau pathology and enables the identification of cell autonomous and non-autonomous disease mechanisms, giving a unique opportunity for future target identification and intervention studies in a translationally relevant in vitro context.

Accumulating evidence suggests that the efficacy of cancer immunotherapies, such as immune checkpoint blockade, is to a large extent driven by T-cells that recognize cancer neoantigens – T-cell antigens that arise as a result of patient-specific nonsynonymous tumor mutations. Based on these data, a major effort has been initiated to develop approaches that can be used to specifically boost the activity of neoantigen-reactive CD8+ and CD4+ T-cells in individual patients. However, tumor mutations and their associated neoantigens are, with few exceptions, unique to individual cancer patients, underscoring the need for technologies that enable the comprehensive discovery of both CD4+ and CD8+ T-cell-recognized neoantigens in a truly personalized fashion. We present HANSolo (HLA-Agnostic Neoantigen Screening), a high-throughput genetic platform for the personalized identification of CD4+ and CD8+ T-cell-recognized (neo)antigens. In this method, patient-matched, Bcl-6/xL-immortalized B cell lines are engineered to express large libraries of minigenes that encode candidate T-cell antigens. As the resulting B cells are fully MHC class I and class II proficient, this enables the unbiased screening of T-cell specificities across the complete MHC class I and class II genotypes of individual patients. To this purpose, antigen library-expressing B cells are co-incubated with patient T-cells, and antigen hits are identified by next-generation sequencing to measure the depletion of those B cells that express T-cell-recognized epitopes. We benchmark the feasibility and sensitivity of our genetic screening method, and illustrate the potential of our approach by profiling the neoantigen-specificities of patient-derived T-cell populations in a setting in which neoantigen-specific T-cells represent only a minor fraction of the T-cell population. Collectively, these data demonstrate the feasibility of personalized and HLA-agnostic discovery of CD4+ and CD8+ T-cell neoantigens from large genetic libraries. Thus, this technology should facilitate the development of personalized neoantigen-based cancer immunotherapies, such as neoantigen vaccines or neoantigen TCR gene therapies.

In Alzheimer’s disease (AD), the neurotoxicity of amyloid‐β 1‐42 (Aβ42) stems mostly from soluble oligomeric aggregates of this peptide. However, the study of these aggregates has been hampered by their unstable and elusive nature, thus questioning the very definition of them as distinct targets for drug development. Here, we assess the toxicity of physiologically‐derived Aβ using extracts from deceased patients and controls in primary neuron cultures. By using a monoclonal antibody with a unique binding profile, ALZ‐201, we demonstrate that all of the Aβ toxicity observed in human‐derived brain extracts stem from soluble Aβ42 aggregates.