TDP-43 Pathology in Alzheimer's Disease

CSF α-synuclein aggregation is associated with APOE ε4 and progressive cognitive decline in Alzheimer's disease

At autopsy, around half of the Alzheimer's disease (AD) brains exhibit Lewy body pathology, and the main component of Lewy body pathology is α-synuclein aggregates. This study investigated the prevalence of cerebrospinal fluid (CSF) α-synuclein aggregation and its association with demographic factors and cognitive decline among 1619 participants from the Alzheimer's Disease Neuroimaging Initiative (ADNI), with the test for α-synuclein aggregation by seed amplification assay (SAA). This cohort consisted of 595 cognitively normal (CN) individuals, 765 with mild cognitive impairment (MCI), and 259 with AD dementia. The results showed a higher prevalence of positive α-synuclein aggregation status in the AD dementia group (37.07 %) and the MCI group (22.75 %) compared to CN controls (16.13 %). Additionally, APOE ε4 carriers exhibited a higher prevalence of α-synuclein aggregation compared to non-carriers: 20.12 % for APOE ε4-/- (non-carriers), 24.82 % for APOE ε4 + /-, and 30.92 % for APOE ε4 + /+ . Longitudinally, positive CSF α-synuclein aggregation associated with accelerated cognitive decline, especially in the MCI and AD groups. Notably, positive aggregation status did not significantly affect cognitive trajectories in CN individuals. Moreover, APOE ε4 carriers with positive CSF α-synuclein aggregation experienced more pronounced cognitive decline. This study provides evidence that CSF α-synuclein aggregation is associated with cognitive function and the APOE ε4 allele. These findings suggest that CSF α-synuclein SAA, in combination with APOE ε4 status, could serve as biomarkers for predicting cognitive decline in AD.

Structural insights and milestones in TDP-43 research: A comprehensive review of its pathological and therapeutic advances

Transactive response (TAR) DNA-binding protein 43 (TDP-43) is a critical RNA/DNA-binding protein involved in various cellular processes, including RNA splicing, transcription regulation, and RNA stability. Mislocalization and aggregation of TDP-43 in the cytoplasm are key features of the pathogenesis of several neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), and Alzheimer's disease (AD). This review provides a comprehensive retrospective and prospective analysis of TDP-43 research, highlighting structural insights, significant milestones, and the evolving understanding of its physiological and pathological functions. We delineate five major stages in TDP-43 research, from its initial discovery as a pathological hallmark in neurodegeneration to the recent advances in understanding its liquid-liquid phase separation (LLPS) behavior and interactions with cellular processes. Furthermore, we assess therapeutic strategies targeting TDP-43 pathology, categorizing approaches into direct and indirect interventions, alongside modulating aberrant TDP-43 LLPS. We propose that future research will focus on three critical areas: targeting TDP-43 structural polymorphisms for disease-specific therapeutics, exploring dual temporal-spatial modulation of TDP-43, and advancing nano-therapy. More importantly, we emphasize the importance of understanding TDP-43's functional repertoire at the mesoscale, which bridges its molecular functions with broader cellular processes. This review offers a foundational framework for advancing TDP-43 research and therapeutic development.

TDP-43 seeding activity in the olfactory mucosa of patients with amyotrophic lateral sclerosis

BACKGROUND

In recent years, the seed amplification assay (SAA) has enabled the identification of pathological TDP-43 in the cerebrospinal fluid (CSF) and olfactory mucosa (OM) of patients with genetic forms of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). Here, we investigated the seeding activity of TDP-43 in OM samples collected from patients with sporadic ALS.

METHODS

OM samples were collected from patients with (a) sporadic motor neuron diseases (MND), including spinal ALS (n = 35), bulbar ALS (n = 18), primary lateral sclerosis (n = 10), and facial onset sensory and motor neuronopathy (n = 2); (b) genetic MND, including carriers of C9orf72exp (n = 6), TARDBP (n = 4), SQSTM1 (n = 3), C9orf72exp + SQSTM1 (n = 1), OPTN (n = 1), GLE1 (n = 1), FUS (n = 1) and SOD1 (n = 4) mutations; (c) other neurodegenerative disorders (OND), including Alzheimer's disease (n = 3), dementia with Lewy bodies (n = 8) and multiple system atrophy (n = 6); and (d) control subjects (n = 22). All samples were subjected to SAA analysis for TDP-43 (TDP-43_SAA). Plasmatic levels of TDP-43 and neurofilament-light chain (NfL) were also assessed in a selected number of patients.

RESULTS

TDP-43_SAA was positive in 29/65 patients with sporadic MND, 9/21 patients with genetic MND, 6/17 OND patients and 3/22 controls. Surprisingly, one presymptomatic individual also tested positive. As expected, OM of genetic non-TDP-43-related MND tested negative. Interestingly, fluorescence values from non-MND samples that tested positive were consistently and significantly lower than those obtained with sporadic and genetic MND. Furthermore, among TDP-43-positive samples, the lag phase observed in MND patients was significantly longer than that in non-MND patients. Plasma TDP-43 levels were significantly higher in sporadic MND patients compared to controls and decreased as the disease progressed. Similarly, plasma NfL levels were higher in both sporadic and genetic MND patients and positively correlated with disease progression rate (ΔFS). No significant correlations were detected between TDP-43_SAA findings and the biological, clinical, or neuropsychological parameters considered.

CONCLUSIONS

The OM of a subset of patients with sporadic MND can trigger seeding activity for TDP-43, as previously observed in genetic MND. Thus, TDP-43_SAA analysis of OM can improve the clinical characterization of ALS across different phenotypes and enhance our understanding of these diseases. Finally, plasma TDP-43 could serve as a potential biomarker for monitoring disease progression. However, further research is needed to confirm and expand these findings.

Neurotoxic Implications of Human Coronaviruses in Neurodegenerative Diseases: A Perspective from Amyloid Aggregation

Human coronaviruses (HCoVs) include seven species: HCoV-229E, HCoV-NL63, HCoV-OC43, HCoV-HKU1, MERS-CoV, SARS-CoV-1, and SARS-CoV-2. The last three, classified as Betacoronaviruses, are highly transmissible and have caused severe pandemics. HCoV infections primarily affect the respiratory system, leading to symptoms such as dry cough, fever, and breath shortness, which can progress to acute respiratory failure and death. Beyond respiratory effects, increasing evidence links HCoVs to neurological dysfunction. However, distinguishing direct neural complications from preexisting disorders, particularly in the elderly, remains challenging. This study examines the association between HCoVs and neurodegenerative diseases like Alzheimer disease, Parkinson disease, Lewy body dementia, amyotrophic lateral sclerosis, and Creutzfeldt-Jakob disease. It also presents the long-term neurological effects of HCoV infections and their differential impact across age groups and sexes. A key aspect of this study is the investigation of the sequence and structural similarities between amyloidogenic and HCoV spike proteins, which can provide insights into potential neuropathomechanisms.

Cross-Interaction with Amyloid-β Drives Pathogenic Structural Transformation within the Amyloidogenic Core Region of TDP-43

Alzheimer's disease (AD) is the world's most prevalent neurodegenerative disorder, characterized neuropathologically by senile plaques and neurofibrillary tangles formed by amyloid-β (Aβ) and tau, respectively. Notably, a subset of AD patients also exhibits pathological aggregates composed of TAR DNA-Binding Protein 43 (TDP-43). Clinically, the presence of TDP-43 copathology in AD correlates with more severe cognitive decline and faster disease progression. While previous studies have shown that TDP-43 can exacerbate Aβ toxicity and modulate its assembly dynamics by delaying fibrillization and promoting oligomer formation, the impact of the Aβ interaction on the structural dynamics and aggregation of TDP-43 remains unclear. Here, we employed all-atom discrete molecular dynamics simulations to study the direct interaction between Aβ42, the more amyloidogenic isoform of Aβ, and the amyloidogenic core region (ACR) of TDP-43, which spans residues 311-360 and is critical for TDP-43 aggregation. We found that monomeric Aβ42 could strongly bind to the ACR, establishing sustained contact through intermolecular hydrogen bonding. In contrast, simulation of ACR dimerization revealed a transient helix-helix interaction, experimentally known to drive the phase separation behavior of TDP-43. The binding of the ACR to an Aβ42 fibril seed resulted in significant structural transformation, with the complete unfolding of the helical region being observed. Furthermore, interaction with the Aβ42 fibril seed catalyzed the formation of a parallel, in-register intermolecular β-sheet between two ACR monomers. Collectively, our computational study provides important theoretical insights into TDP-43 pathology in AD, demonstrating that Aβ42, especially in its fibrillar form, may catalyze the pathogenic structural transformation within the TDP-43 ACR that initiates its aberrant aggregation.

Hippocampal sclerosis in senile dementia of the neurofibrillary tangle type

INTRODUCTION

Senile dementia of the neurofibrillary tangle type (SD-NFT) is a subset of dementia in elderly individuals. Recent studies have reported a correlation between hippocampal sclerosis (HS) and aging. This study aimed to investigate the relationship between HS and SD-NFT.

METHODS

We conducted a clinical and neuropathological review of Japanese patients diagnosed with SD-NFT. Hematoxylin-eosin and Klüver-Barrera staining, Gallyas silver impregnation, and immunohistochemistry were employed. Pathological assessments focused on identifying HS, neuritic plaques, and phosphorylated transactive response DNA-binding protein 43 (p-TDP-43)-positive inclusions. Additionally, we quantified the densities of neurofibrillary tangles (NFTs) and ghost tangles (GTs) within the hippocampal CA1 region.

RESULTS

Nine patients met the criteria for SD-NFT from the patients who underwent consecutive autopsies from 1994 to 2022 at our institute. The mean ages at onset and death were 84.0 ± 6.8 years (range, 76-94 years) and 91.0 ± 7.0 years (range, 79-101 years), respectively. The mean dementia duration was 7.0 ± 4.0 years (range, 1-13 years). All patients exhibited memory loss although none were diagnosed with SD-NFT during their lifetime. The mean brain weight was 1124.2 ± 132.1 g (range, 980-1390 g). Three patients displayed HS. NFT and GT densities were significantly higher in patients with HS than in those without HS. No significant correlation was found between HS and p-TDP-43 inclusions in the medial temporal lobe.

CONCLUSION

In SD-NFT, NFTs are more strongly associated with HS. This finding enhances our understanding of the pathological underpinnings of HS in SD-NFT.

Rare Diseases, Spotlighting Amyotrophic Lateral Sclerosis, Huntington's Disease, and Myasthenia Gravis: Insights from Landscape Analysis of Current Research

Rare diseases are a diverse group of disorders that, despite each individual condition's rarity, collectively affect a significant portion of the global population. Currently approximately 10,000 rare diseases exist globally, with 80% of these diseases being identified as having genetic origins. In this Review, we examine data from the CAS Content Collection to summarize scientific progress in the area of rare diseases. We examine the publication landscape in the area in an effort to provide insights into current advances and developments. We then discuss the evolution of key concepts in the field, genetic associations, as well as the major technologies and development pipelines of rare disease treatments. We focus our attention on three specific rare diseases: (i) amyotrophic lateral sclerosis, a terminal neurodegenerative disease affecting the central nervous system resulting in progressive loss of motor neurons that control voluntary muscles; (ii) Huntington's disease, another terminal neurodegenerative disease that causes progressive degeneration of nerve cells in the brain, with a wide impact on a person's functional abilities; and (iii) myasthenia gravis, a chronic autoimmune synaptopathy leading to skeletal muscle weakness. While the pathogenesis of these rare diseases is being elucidated, there is neither a cure nor preventative treatment available, only symptomatic treatment. The objective of the paper is to provide a broad overview of the evolving landscape of current knowledge on rare diseases and specifically on the biology and genetics of the three spotlighted diseases, to outline challenges and evaluate growth opportunities, an aim to further efforts in solving the remaining challenges.

Identification of novel small molecule chaperone activators for neurodegenerative disease treatment

A pathological hallmark of neurodegenerative disease is the accumulation of aberrant protein aggregates which contribute to the cytotoxicity and are therefore a target for therapy development. One key mechanism to manage cellular protein homeostasis is heat shock proteins (HSPs), protein chaperones which are known to target aberrant protein accumulation. Activation of HSPs target aberrant TDP-43, tau and amyloid to rescue neurodegenerative disease. As an attempt to target HSP activation for neurodegeneration therapy, we here develop a drug screening assay to identify compounds that will activate the master regulator of HSPs, the transcription factor heat shock factor 1 (HSF1). As HSF1 is bound by HSP90 which prevents its activation, we developed a NanoBRET assay, which allows us to monitor and quantify the HSF1-HSP90 interaction in living cells to screen for compounds disrupting this interaction and thereby releasing HSF1 for activation. After the optimisation and validation of the assay, a two thousand compound library was screened which produced 10 hits including two known HSP90 inhibitors. Follow-up functional study showed that one of the hits oxyphenbutazone (OPB) significantly reduces the accumulation of insoluble TDP-43 in a cell model, eliciting no signs of stress or toxicity. Overall, this study demonstrates a viable strategy for new drug discovery in targeting aberrant proteins and identifies potential candidates for translation into neurodegenerative disease treatment.

Context-dependent Interactors Regulate TDP-43 Dysfunction in ALS/FTLD

TDP-43 mislocalization, aggregation, and loss of splicing function are neuropathological hallmarks in over 97% of Amyotrophic Lateral Sclerosis (ALS), 45% of Frontotemporal Lobar Degeneration (FTLD), and 60% of Alzheimer's Disease, which has been reclassified as LATE-NC. However, the mechanisms underlying TDP-43 dysfunction remain elusive. Here, we utilize APEX2-driven proximity labeling and mass spectrometry to characterize the context-dependent TDP-43 interactome in conditions of cytoplasmic mislocalization, impaired RNA-binding contributing to aggregation, and oxidative stress. We describe context-dependent interactors, including disrupted interactions with splicing-related proteins and altered biomolecular condensate (BMC) associations. By integrating ALS and FTLD snRNA-seq data, we uncover disease-relevant molecular alterations and validate our dataset through a functional screen that identifies key TDP- 43 regulators. We demonstrate that disrupting nuclear speckle integrity, particularly through the downregulation of the splicing factor SRRM2, promotes TDP-43 mislocalization and loss of function. Additionally, we identify NUFIP2 as an interactor associated with mislocalization that sequesters TDP-43 into cytoplasmic aggregates and co-localizes with TDP-43 pathology in patient tissue. We also highlight HNRNPC as a potent TDP-43 splicing regulator, where precise modulation of TDP-43 or HNRNPC can rescue cryptic exon splicing. These findings provide mechanistic insights and potential therapeutic targets for TDP-43 dysfunction.

Inducers and modulators of protein aggregation in Alzheimer's disease - Critical tools for understanding the foundations of aggregate structures

Amyloidogenic protein aggregation is a pathological hallmark of Alzheimer's Disease (AD). As such, this critical feature of the disease has been instrumental in guiding research on the mechanistic basis of disease, diagnostic biomarkers and preventative and therapeutic treatments. Here we review identified molecular triggers and modulators of aggregation for two of the proteins associated with AD: amyloid beta and tau. We aim to provide an overview of how specific molecular factors can impact aggregation kinetics and aggregate structure to promote disease. Looking toward the future, we highlight some research areas of focus that would accelerate efforts to effectively target protein aggregation in AD.

Current amyloid inhibitors: Therapeutic applications and nanomaterial-based innovations

Amyloid proteins have long been in the spotlight for being involved in many degenerative diseases including Alzheimer´s, Parkinson´s or type 2 diabetes, which currently cannot be prevented and for which there is no effective treatment or cure. Here we provide a comprehensive review of inhibitors that act directly on the amyloidogenic pathway (at the monomer, oligomer or fibril level) of key pathological amyloids, focusing on the most representative amyloid-related diseases. We discuss the latest advances in preclinical and clinical trials, focusing on cutting-edge developments, particularly on nanomaterials-based inhibitors, which offer unprecedented opportunities to address the complexity of protein misfolding disorders and are revolutionizing the landscape of anti-amyloid therapeutics. Notably, nanomaterials are impacting critical areas such as bioavailability, penetrability and functionality of compounds currently used in biomedicine, paving the way for more specific therapeutic solutions tailored to various amyloid-related diseases. Finally, we highlight the window of opportunity opened by comparative analysis with so-called functional amyloids for the development of innovative therapeutic approaches for these devastating diseases.

A stress-dependent TDP-43 SUMOylation program preserves neuronal function

Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Dementia (FTD) are overwhelmingly linked to TDP-43 dysfunction. Mutations in TDP-43 are rare, indicating that the progressive accumulation of exogenous factors - such as cellular stressors - converge on TDP-43 to play a key role in disease pathogenesis. Post translational modifications such as SUMOylation play essential roles in response to such exogenous stressors. We therefore set out to understand how SUMOylation may regulate TDP-43 in health and disease. We find that TDP-43 is regulated dynamically via SUMOylation in response to cellular stressors. When this process is blocked in vivo, we note age-dependent TDP-43 pathology and sex-specific behavioral deficits linking TDP-43 SUMOylation with aging and disease. We further find that SUMOylation is correlated with human aging and disease states. Collectively, this work presents TDP-43 SUMOylation as an early physiological response to cellular stress, disruption of which may confer a risk for TDP-43 proteinopathy.

Proteinopathies and the Neurodegenerative Aftermath of Stroke: Potential Biomarkers and Treatment Targets

Stroke remains a predominant cause of death and long-term disability among adults worldwide. Emerging evidence suggests that proteinopathies, characterized by the aggregation and accumulation of misfolded proteins, may play a significant role in the aftermath of stroke and the progression of neurodegenerative disorders. In this review, we explore preclinical and clinical research on key proteinopathies associated with stroke, including tau, Aβ (amyloid-β), TDP-43 (TAR DNA-binding protein 43), α-synuclein, and UCH-L1 (ubiquitin C-terminal hydrolase-L1). We focus on their potential as biomarkers for recovery management and as novel treatment targets that may enhance neuronal repair and mitigate secondary neurodegeneration. The involvement of these proteinopathies in various aspects of stroke, including neuroinflammation, oxidative stress, neuronal damage, and vascular dysfunction, underscores their potential. However, further investigations are essential to validate the clinical utility of these biomarkers, elucidate the mechanisms connecting proteinopathies to poststroke neurodegeneration, and develop targeted interventions. Identifying specific protein signatures associated with stroke outcomes could facilitate the advancement of precision medicine tailored to individual patient needs, significantly enhancing the quality of life for stroke survivors.

Structure-Activity Relationships and Evaluation of 2-(Heteroaryl-cycloalkyl)-1H-indoles as Tauopathy Positron Emission Tomography Radiotracers

Structure-activity relationship studies were performed on a library of synthesized compounds based on previously identified tau ligands. The top 13 new compounds had Ki values in the range of 5-14 nM in Alzheimer's disease (AD), progressive supranuclear palsy (PSP), and corticobasal degeneration (CBD) post-mortem brain tissues. One of the more promising new compounds ([3H]75) bound with high affinity in AD, PSP, and CBD tissues (KD's = 1-1.5 nM) and Pick's disease tissue (KD = 3.8 nM). Autoradiography studies with [3H]75 demonstrated specific binding in AD, PSP, and CBD post-mortem tissues. Nonhuman primate brain PET imaging with [18F]75 demonstrated a peak standardized uptake value (SUV) of ∼5 in the cerebellum, ∼4.5 in the cortex, and ∼4 in whole brain with SUV 2-to-90 min ratios of 3.9 in whole brain, 4.9 in cortex, and 4.5 in cerebellum. Compound [18F]75 is a promising candidate for translation to human brain PET imaging studies.

TDP-43 seeding induces cytoplasmic aggregation heterogeneity and nuclear loss of function of TDP-43

Cytoplasmic aggregation and nuclear depletion of TAR DNA-binding protein 43 (TDP-43) are hallmarks of several neurodegenerative disorders. Yet, recapitulating both features in cellular systems has been challenging. Here, we produced amyloid-like fibrils from recombinant TDP-43 low-complexity domain and demonstrate that sonicated fibrils trigger TDP-43 pathology in human cells, including induced pluripotent stem cell (iPSC)-derived neurons. Fibril-induced cytoplasmic TDP-43 inclusions acquire distinct biophysical properties, recapitulate pathological hallmarks such as phosphorylation, ubiquitin, and p62 accumulation, and recruit nuclear endogenous TDP-43, leading to its loss of function. A transcriptomic signature linked to both aggregation and nuclear loss of TDP-43, including disease-specific cryptic splicing, is identified. Cytoplasmic TDP-43 aggregates exhibit time-dependent heterogeneous morphologies as observed in patients-including compacted, filamentous, or fragmented-which involve upregulation/recruitment of protein clearance pathways. Ultimately, cell-specific progressive toxicity is provoked by seeded TDP-43 pathology in human neurons. These findings identify TDP-43-templated aggregation as a key mechanism driving both cytoplasmic gain of function and nuclear loss of function, offering a valuable approach to identify modifiers of sporadic TDP-43 proteinopathies.

ALS molecular subtypes are a combination of cellular and pathological features learned by deep multiomics classifiers

Amyotrophic lateral sclerosis (ALS) is a complex syndrome with multiple genetic causes and wide variation in disease presentation. Despite this heterogeneity, large-scale genomics studies revealed that ALS postmortem samples can be grouped into a small number of subtypes, defined by transcriptomic signatures of mitochondrial dysfunction and oxidative stress (ALS-Ox), microglial activation and neuroinflammation (ALS-Glia), or TDP-43 pathology and associated transposable elements (ALS-TE). In this study, we present a deep ALS neural net classifier (DANCer) for ALS molecular subtypes. Applying DANCer to an expanded cohort from the NYGC ALS Consortium highlights two subtypes that strongly correlate with disease duration: ALS-TE in cortex and ALS-Glia in spinal cord. Finally, single-nucleus transcriptomes demonstrate that ALS subtypes are recapitulated in neurons and glia, with both ALS-wide and subtype-specific alterations in all cell types. In summary, ALS molecular subtypes represent a combination of cellular and pathological features that correlate with clinical features of ALS.

Targeting necroptosis in Alzheimer's disease: can exercise modulate neuronal death?

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by cognitive decline and neuronal degeneration. Emerging evidence implicates necroptosis in AD pathogenesis, driven by the RIPK1-RIPK3-MLKL pathway, which promotes neuronal damage, inflammation, and disease progression. Exercise, as a non-pharmacological intervention, can modulate key inflammatory mediators such as TNF-α, HMGB1, and IL-1β, thereby inhibiting necroptotic signaling. Additionally, exercise enhances O-GlcNAc glycosylation, preventing Tau hyperphosphorylation and stabilizing neuronal integrity. This review explores how exercise mitigates necroptosis and neuroinflammation, offering novel therapeutic perspectives for AD prevention and management.

Inhibition of amyloid beta oligomer accumulation by NU-9: A unifying mechanism for the treatment of neurodegenerative diseases

Protein aggregation is a hallmark of neurodegenerative diseases, which connects these neuropathologies by a common phenotype. Various proteins and peptides form aggregates that are poorly degraded, and their ensuing pathological accumulation underlies these neurodegenerative diseases. Similarities may exist in the mechanisms responsible for the buildup of these aggregates. Therefore, therapeutics designed to treat one neurodegenerative disease may be beneficial to others. In ALS models, the compound NU-9 was previously shown to block neurodegeneration produced by aggregation-inducing mutations of SOD-1 and TDP-43 [B. Genç et al., Clin. Transl. Med. 11, e336 (2021)]. Here, we report that NU-9 also prevents the accumulation of amyloid beta oligomers (AβOs), small peptide aggregates that are instigators of Alzheimer's disease neurodegeneration [M. Tolar et al., Int. J. Mol. Sci. 22, 6355 (2021)]. AβO buildup was measured by immunofluorescence imaging of cultured hippocampal neurons exposed to exogenous monomeric Aβ. In this model, AβO buildup occurs via cathepsin L- and dynamin-dependent trafficking. This is prevented by NU-9 through a cellular mechanism that is cathepsin B- and lysosome-dependent, suggesting that NU-9 enhances the ability of endolysosomal trafficking to protect against AβO buildup. This possibility is strongly supported by a quantitative assay for autophagosomes that shows robust stimulation by NU-9. These results contribute additional understanding to the mechanisms of protein aggregation and suggest that multiple neurodegenerative diseases might be treatable by targeting common pathogenic mechanisms responsible for protein aggregation.

Regulatory Effects of RNA-Protein Interactions Revealed by Reporter Assays of Bacteria Grown on Solid Media

Reporter systems are widely used to study biomolecular interactions and processes in vivo, representing one of the basic tools used to characterize synthetic regulatory circuits. Here, we developed a method that enables the monitoring of RNA-protein interactions through a reporter system in bacteria with high temporal resolution. For this, we used a Real-Time Protein Expression Assay (RT-PEA) technology for real-time monitoring of a fluorescent reporter protein, while having bacteria growing on solid media. Experimental results were analyzed by fitting a three-variable Gompertz growth model. To validate the method, the interactions between a set of RNA sequences and the RNA-binding protein (RBP) Musashi-1 (MSI1) were evaluated, as well as the allosteric modulation of the interaction by a small molecule (oleic acid). This new approach proved to be suitable to quantitatively characterize RNA-RBP interactions, thereby expanding the toolbox to study molecular interactions in living bacteria, including allosteric modulation, with special relevance for systems that are not suitable to be studied in liquid media.

Perivascular phosphorylated TDP-43 inclusions are associated with Alzheimer's disease pathology and loss of CD146 and Aquaporin-4

The majority of patients with Alzheimer's disease (AD) exhibit aggregates of Trans-active response DNA binding protein 43 (TDP-43) in their hippocampus, which is associated with a more aggressive disease progression. The TDP-43 inclusions are commonly found in neurons, but also in astrocytes. The impact of the inclusions in astrocytes is less known. In the current study, we investigate the presence of phosphorylated TDP-43 (pTDP-43) inclusions in astrocytic endfeet and their potential association with blood-brain barrier (BBB) damage, glymphatic system dysfunction, and AD pathology. By staining postmortem hippocampal sections from AD patients and non-demented controls against TDP-43 and pTDP-43 together with the astrocytic markers glial fibrillary acidic protein (GFAP), astrocytic endfeet marker Aquaporin-4 (AQP4), and markers for BBB alterations (CD146) and leakiness (Immunoglobulin A), we demonstrate a close association between perivascular pTDP-43 or TDP-43 inclusions and GFAP or AQP4. These perivascular inclusions were more prominent in AD and correlated with the disease severity and loss of CD146 and AQP4. The findings indicate a relationship between pTDP-43 accumulation in astrocytic endfeet and BBB and glymphatic system dysfunction, which may contribute to the downstream pathological events seen in AD patients and the aggressive disease progression.

TDP43 is a newly identified substrate for PS1, enhancing the expression of APP following cleavage

Alzheimer's disease (AD) has been comprehensively studied; however, most research has focused on Aβ plaque deposition and Tau protein phosphorylation. Emerging evidence suggests that TDP43 may be significantly involved AD and potentially worsening its pathology. To investigate the role of TDP43 in the pathological development of AD, we employed the STRING protein network interaction tool to identify potential relationships between TDP43 and other proteins, including PS1 and APP. Subsequent co-immunoprecipitation experiments were conducted, and the results indicated that TDP43 could interact with PS1. Further studies have shown that the interaction between the two would also lead to the loss of nuclear localization of TDP43. We also found that overexpression or knockdown of PS1 in both primary cells, HeLa and NSC34 cells indicated that TDP43 is likely to be a substrate of PS1. Subsequent use of the L685,458 and z-VAD, the PS1 mutant plasmids D257A and D385A, and bioinformatics approaches demonstrated that PS1 is dependent on γ-secretase and caspase activity to cleave TDP43, and that the cleavage site is at amino acid 315 of TDP43. Besides, our study demonstrated that the interaction of TDP43 with PS1 in primary cells, HeLa and NSC34 cells can promote APP expression, resulting in elevated Aβ levels. Finally, we investigated whether the interaction between TDP43 and PS1 affects the expression of other PS1 substrates, Notch and E-cadherin. Our results demonstrated that TDP43 cleaved by PS1 only promoted APP expression and had no effect on other PS1 substrates. In conclusion, these results suggest that TDP43 is a new substrate of PS1 and that TDP43 cleaved by PS1 promotes APP expression, which leads to increased Aβ content, which may explain why TDP43 promotes AD development. These insights enhance our understanding of TDP43's role in AD development.

Multiple Neuropathologies Underly Hippocampal Subfield Atrophy in a Case With a Slowly Progressive Amnestic Syndrome: Challenging the Notion of Pure LATE-NC

Alzheimer's disease (AD) is the leading cause of dementia in the elderly, marked by abnormal protein buildup (beta-amyloid and tau) resulting in neuronal loss, especially in the medial temporal lobe and other limbic regions. The presence of transactive response DNA binding protein 43 (TDP-43) immunoreactive inclusions in medial temporal lobe regions has also been associated with neuroimaging changes in limbic regions. It has been proposed that hypometabolism in limbic regions on [18F] fluorodeoxyglucose positron emission tomography (FDG-PET) in a patient with a slowly evolving amnestic syndrome may be a signature of the presence of TDP-43. In this context, we observed an 86-year-old Caucasian female with dementia characterized by a slowly evolving amnestic syndrome, along with focal medial temporal atrophy evident on MRI and hypometabolism in limbic regions on FDG-PET. The patient subsequently died and underwent an autopsy. We performed detailed neuroimaging and digital neuropathological analyses of the hippocampal subfields to better understand the relationship between clinico-imaging findings and histopathology. In addition to TDP-43, we identified three other pathological processes in the medial temporal lobe: sequestosome-1/p62, argyrophilic grain disease (AGD), and primary age-related tauopathy (PART). Hippocampal subfield volumes and rates of atrophy were no different from those of matched healthy controls, except for the atrophy rate in cornu ammonis 1 (CA1). Digital histopathology revealed the relative highest burden of pathology for p62, followed by TDP-43, AGD, and PART in CA1. Multiple pathological processes appear to have contributed to the hippocampal atrophy and hypometabolism in our patient with a slowly progressive amnestic syndrome.

CSF IL-6, GDF-15, GFAP and NfL levels in early Alzheimer disease: a pilot study

Background

Despite their potential usefulness as biomarkers, no study has investigated the interactions between cerebrospinal fluid (CSF) changes of neurofilament light chain (NfL), glial fibrillary acidic protein (GFAP), growth differentiation factor 15 (GDF-15), transactive response DNA binding protein (TDP-43) and interleukin-6 (IL-6) and the core AD CSF biomarkers in the same cohort of AD patients.

Objectives

The aim of this pilot study is to evaluate the CSF levels of these analytes in patients with AD and assess their clinical relevance in this neurological condition.

Design

Cross-sectional study.

Methods

We assessed the levels of NfL, GFAP, GDF-15, TDP-43 and IL-6 in the CSF samples of 52 early AD patients and evaluated their partial reciprocal correlations and those with Abeta42, p-Tau, t-Tau and Mini-Mental State Examination (MMSE), always adding age, sex and educational level as covariates.

Results

MMSE score showed a positive correlation with the Aβ 1-42 concentrations (r = 0.485; p < 0.001), and a negative correlation with GDF-15 concentrations (r = -0.418; p = 0.002). IL-6 concentrations showed a positive correlation with NfL concentrations (r = 0.312; p = 0.026) and a negative correlation with TDP-43 concentrations (r = -0.322; p = 0.021). TDP-43 concentrations showed a positive correlation with GFAP (r = 0.33, p = 0.018). The mediation analysis suggests that the association between GDF-15 and MMSE is primarily mediated by Aβ 1-42. CSF GDF-15 concentrations were higher in AD patients with low Aβ 1-42 concentrations than those with high Aβ 1-42 concentrations (p < 0.001).

Conclusion

Our findings highlight that CSF IL-6 levels correlate positively with markers of neuronal damage. CSF TDP-43 levels significantly correlated with GFAP, suggesting a potential link with reactive gliosis and astrocyte activation. In addition, while CSF GDF-15 levels negatively correlate with MMSE scores, mediation analysis revealed that this association is primarily indirect and mediated through Aβ 1-42 levels.

Microglia aggregates define distinct immune and neurodegenerative niches in Alzheimer's disease hippocampus

In Alzheimer's disease (AD), microglia form distinct cellular aggregates that play critical roles in disease progression, including Aβ plaque-associated microglia (PaM) and the newly identified coffin-like microglia (CoM). PaM are closely associated with amyloid-β (Aβ) plaques, while CoM are enriched in the pyramidal layer of the CA2/CA1 hippocampal subfields, where they frequently engulf neurons and associate with tau-positive tangles and phosphorylated α-synuclein. To elucidate the role of these microglial subtypes, we employed high-content neuropathology, integrating Deep Spatial Profiling (DSP), multiplex chromogenic immunohistochemistry and confocal microscopy, to comprehensively map and characterise their morphological and molecular signatures, as well as their neuropathological and astrocytic microenvironments, in AD and control post-mortem samples. PaM and PaM-associated astrocytes exhibited signatures related to complement system pathways, ErbB signalling, and metabolic and neurodegenerative processes. In contrast, CoM displayed markers associated with protein degradation and immune signalling pathways, including STING, TGF-β, and NF-κB. While no direct association between CD8 + T cells and either microglial type was observed, CD163 + perivascular macrophages were frequently incorporated into PaM. These findings provide novel insights into the heterogeneity of microglial responses, in particular their distinct interactions with astrocytes and infiltrating immune cells, and shed light on specific neurodegenerative hotspots and their implications for hippocampal deterioration in AD.

TDP-43 as a potential retinal biomarker for neurodegenerative diseases

TDP-43 proteinopathies are a spectrum of neurodegenerative diseases (NDDs) characterized by the pathological cytoplasmic aggregation of the TDP-43 protein. These include amyotrophic lateral sclerosis (ALS), frontotemporal lobar degeneration (FTLD), Alzheimer's disease (AD), chronic traumatic encephalopathy (CTE), and others. TDP-43 in the eye shows promise as a biomarker for these NDDs. Several studies have identified cytoplasmic TDP-43 inclusions in retinal layers of donors with ALS, FTLD, AD, CTE, and other conditions using immunohistochemistry. Our findings suggest that pathological aggregates of TDP-43 in the human retina are most prevalent in FTLD-TDP, ALS, and CTE, suggesting these diseases may provide the most reliable context for studying the potential of TDP-43 as a retinal biomarker. Animal model studies have been pivotal in exploring TDP-43's roles in the retina, including its nuclear and cytoplasmic localization, RNA binding properties, and interactions with other proteins. Despite these advances, more research is needed to develop therapeutic strategies. A major limitation of human autopsy studies is the lack of corresponding brain pathology assessments to confirm TDP-43 proteinopathy diagnosis and staging. Other limitations include small sample sizes, lack of antemortem eye pathology and clinical histories, and limited comparisons across multiple NDDs. Future directions for the TDP-43 as a retinal biomarker for NDDs include retinal tracers, hyperspectral imaging, oculomics, and machine learning development.

TDP-43 Aggregate Seeding Impairs Autoregulation and Causes TDP-43 Dysfunction

The aggregation, cellular mislocalization and dysfunction of TDP-43 are hallmarks of multiple neurodegenerative disorders. We find that inducing TDP-43 aggregation through prion-like seeding gradually diminishes normal TDP-43 nuclear localization and function. Aggregate-affected cells show signature features of TDP-43 loss of function, such as DNA damage and dysregulated TDP-43-target expression. We also observe strong activation of TDP-43-controlled cryptic exons in cells, including human neurons treated with proteopathic seeds. Furthermore, aggregate seeding impairs TDP-43 autoregulation, an essential mechanism controlling TDP-43 homeostasis. Interestingly, proteins that normally interact with TDP-43 are not recruited to aggregates, while other factors linked to TDP-43 pathology, including Ataxin 2, specifically colocalize to inclusions and modify seeding-induced aggregation. Our findings indicate that TDP-43 aggregation, mislocalization and loss of function are strongly linked and suggest that disruption of TDP-43 autoregulation establishes a toxic feed-forward mechanism that amplifies aggregation and may be central in mediating this pathological connection.

Multi-omic quantitative trait loci link tandem repeat size variation to gene regulation in human brain

Tandem repeat (TR) size variation is implicated in ~50 neurological disorders, yet its impact on gene regulation in the human brain remains largely unknown. In the present study, we quantified the impact of TR size variation on brain gene regulation across distinct molecular phenotypes, based on 4,412 multi-omics samples from 1,597 donors, including 1,586 newly sequenced ones. We identified ~2.2 million TR molecular quantitative trait loci (TR-xQTLs), linking ~139,000 unique TRs to nearby molecular phenotypes, including many known disease-risk TRs, such as the G2C4 expansion in C9orf72 associated with amyotrophic lateral sclerosis. Fine-mapping revealed ~18,700 TRs as potential causal variants. Our in vitro experiments further confirmed the causal and independent regulatory effects of three TRs. Additional colocalization analysis indicated the potential causal role of TR variation in brain-related phenotypes, highlighted by a 3'-UTR TR in NUDT14 linked to cortical surface area and a TG repeat in PLEKHA1, associated with Alzheimer's disease.

Aberrant splicing in Huntington's disease accompanies disrupted TDP-43 activity and altered m6A RNA modification

Huntington's disease (HD) is caused by a CAG repeat expansion in the HTT gene, leading to altered gene expression. However, the mechanisms leading to disrupted RNA processing in HD remain unclear. Here we identify TDP-43 and the N6-methyladenosine (m6A) writer protein METTL3 to be upstream regulators of exon skipping in multiple HD systems. Disrupted nuclear localization of TDP-43 and cytoplasmic accumulation of phosphorylated TDP-43 occurs in HD mouse and human brains, with TDP-43 also co-localizing with HTT nuclear aggregate-like bodies distinct from mutant HTT inclusions. The binding of TDP-43 onto RNAs encoding HD-associated differentially expressed and aberrantly spliced genes is decreased. Finally, m6A RNA modification is reduced on RNAs abnormally expressed in the striatum of HD R6/2 mouse brain, including at clustered sites adjacent to TDP-43 binding sites. Our evidence supports TDP-43 loss of function coupled with altered m6A modification as a mechanism underlying alternative splicing in HD.

RNA dysregulation in neurodegenerative diseases

Dysregulation of RNA processing has in recent years emerged as a significant contributor to neurodegeneration. The diverse mechanisms and molecular functions underlying RNA processing underscore the essential role of RNA regulation in maintaining neuronal health and function. RNA molecules are bound by RNA-binding proteins (RBPs), and interactions between RNAs and RBPs are commonly affected in neurodegeneration. In this review, we highlight recent progress in understanding dysregulated RNA-processing pathways and the causes of RBP dysfunction across various neurodegenerative diseases. We discuss both established and emerging mechanisms of RNA-mediated neuropathogenesis in this rapidly evolving field. Furthermore, we explore the development of potential RNA-targeting therapeutic approaches for the treatment of neurodegenerative diseases.

Synapse vulnerability and resilience underlying Alzheimer's disease

Synapse preservation is key for healthy cognitive ageing, and synapse loss represents a critical anatomical basis of cognitive dysfunction in Alzheimer's disease (AD), predicting dementia onset, severity, and progression. Synapse loss is viewed as a primary pathologic event, preceding neuronal loss and brain atrophy in AD. Synapses may, therefore, represent one of the earliest and clinically most meaningful targets of the neuropathologic processes driving AD dementia. The synapse loss in AD is highly selective and targets particularly vulnerable synapses while leaving others, termed resilient, largely unaffected. Yet, the anatomic and molecular hallmarks of the vulnerable and resilient synapse populations and their association with AD neuropathologic changes (e.g. amyloid-β plaques and tau tangles) and memory dysfunction remain poorly understood. Characterising the selectively vulnerable and resilient synapses in AD may be key to understanding the mechanisms of cognitive preservation versus loss and enable the development of robust biomarkers and disease-modifying therapies for dementia.

The genetics of TDP43-Type-C neurodegeneration: a whole genome sequencing study

Frontotemporal lobar degeneration-TDP Type C (TDP-C) is a unique neurodegenerative disease that starts by attacking the anterior temporal lobe leading to language and/or behavioral syndromes. Current literature on the genetic associations of TDP-C, which we have reviewed here, is uneven and lacks a discernible corpus of robust findings. In our study, we completed genome wide hypothesis-free analyses utilizing artificial Intelligence (AI) to identify rare and common variants associated with TDP-C. We then investigated ANXA11 and TARDBP in a hypothesis-driven analysis, since it was recently shown that TDP-43 and Annexin A11 co-aggregate in all TDP-C cases. 1) Whole genome sequencing was completed to identify pathogenic rare variants prioritized with Illumina's AI-based Emedgene software on 37 confirmed or probable TDP-C cases from the Northwestern-University Cohort. 2) A genome wide association study was then completed to identify common variants associated with TDP-C cases vs 290 controls. 3) Next, common and rare variants in TARDBP, and ANXA11 were investigated in TDP-C vs controls. These analyses identified novel genetic associations between FIG4 , UBQLN2 , INPP5A , and ANXA11 with TDP-C. Of these FIG4, UBQLN2 and ANXA11 have been associated previously with Amyotrophic lateral sclerosis (ALS). To further assess the observed potential genetic overlap between ALS and TDP-C, we leveraged Mendelian randomization (MR) to assess if the ALS genetic load is associated with TDP-C risk, and found evidence supporting this association. The genetic association of ANXA11 with TDP-C is particularly interesting in view of the recently discovered role of Annexin A11 in forming heterodimers with TDP-43 in all abnormal precipitates, a feature not found in TDP-A or TDP-B, which have no similar predilection for the anterior temporal lobe. In addition to the observed overlap between ALS genetics/ genetic load and TDP-C, it is worth mentioning that FIG4, INPP5A and ANXA11 have been implicated in the inositol metabolism pathway, a feature that remains to be elucidated mechanistically. Our TDP-C genetic literature review identified a surprising paucity of neuropathologically confirmed cases in published investigations. Nonetheless, the literature offers support for some of our findings and reemphasizes the absence of dominant or major pathogenic genes for TDP-C, another feature that sets this neuropathologic entity apart from TDP-A and TDP-B.

Behavioral and Psychological Symptoms (BPSD) in Alzheimer's Disease (AD): Development and Treatment

Behavioral and psychological symptoms of dementia (BPSD), such as agitation, apathy, and psychosis, are highly prevalent and have a significant impact on patients and their care partners. The neurobiology of BPSD involves a complex interplay of structural brain changes and alterations in the neurotransmitter system. Various genetic and plasma biomarkers have also been studied. Research in BPSD has been limited by heterogeneity in the diagnostic criteria and assessment tools. As such, there have been ongoing efforts to develop a gold-standard assessment tool and diagnostic criteria. Current practice guidelines recommend nonpharmacological therapies as first-line treatments. Pharmacological options are often used when there is an insufficient response to nonpharmacological strategies, but there can be serious adverse effects with existing pharmacological agents. This has resulted in growing efforts to develop novel therapeutics with more favorable tolerability profiles, with some showing promising results. Other biological therapies, such as neurostimulation, have also demonstrated positive results. As our understanding of BPSD evolves, ongoing research efforts in treatment of BPSD are warranted in order to enhance the quality of life for patients and their care partners.

Decoding TDP-43: the molecular chameleon of neurodegenerative diseases

TAR DNA-binding protein 43 (TDP-43) has emerged as a critical player in neurodegenerative disorders, with its dysfunction implicated in a wide spectrum of diseases including amyotrophic lateral sclerosis (ALS), frontotemporal lobar degeneration (FTLD), and Alzheimer's disease (AD). This comprehensive review explores the multifaceted roles of TDP-43 in both physiological and pathological contexts. We delve into TDP-43's crucial functions in RNA metabolism, including splicing regulation, mRNA stability, and miRNA biogenesis. Particular emphasis is placed on recent discoveries regarding TDP-43's involvement in DNA interactions and chromatin dynamics, highlighting its broader impact on gene expression and genome stability. The review also examines the complex pathogenesis of TDP-43-related disorders, discussing the protein's propensity for aggregation, its effects on mitochondrial function, and its non-cell autonomous impacts on glial cells. We provide an in-depth analysis of TDP-43 pathology across various neurodegenerative conditions, from well-established associations in ALS and FTLD to emerging roles in diseases such as Huntington's disease and Niemann-Pick C disease. The potential of TDP-43 as a therapeutic target is explored, with a focus on recent developments in targeting cryptic exon inclusion and other TDP-43-mediated processes. This review synthesizes current knowledge on TDP-43 biology and pathology, offering insights into the protein's central role in neurodegeneration and highlighting promising avenues for future research and therapeutic interventions.

Differential risk of Alzheimer's disease in MCI subjects with elevated Abeta

BACKGROUNDS

People with elevated beta amyloid have different risk and progress speed to Alzheimer's disease.

PURPOSE

The research is to validate the risk classification of AD developed in the Shanghai mild cognitive impairment (MCI) cohort study using ADNI data.

METHODS

The risk classification of AD in MCI was based on several optimal cut-off points of a novel parameter Cog_Vol.

RESULTS

In total, 843 subjects with MCI were included, of whom 220 had elevated PET beta amyloid. 273 (32.3 %) and 70 (31.8 %) progressed to AD in all subjects and in those with elevated PET beta amyloid, respectively. The risk of AD in subjects whose Cog_Vol >340 was very low, while the risk for those with Cog_Vol less than 101 indicated a super high within 4 years of follow-up.

DISCUSSION

Risk classification using Cog_Vol at an optimal value was able to detect subjects among those with PET-amyloid-elevated MCI were at greater risk of developing AD and were unlikely to develop AD within 4 years of follow-up.

The mechanisms, hallmarks, and therapies for brain aging and age-related dementia

Age-related cognitive decline and dementia are significant manifestations of brain aging. As the elderly population grows rapidly, the health and socio-economic impacts of cognitive dysfunction have become increasingly significant. Although clinical treatment of dementia has faced considerable challenges over the past few decades, with limited breakthroughs in slowing its progression, there has been substantial progress in understanding the molecular mechanisms and hallmarks of age-related dementia (ARD). This progress brings new hope for the intervention and treatment of this disease. In this review, we categorize the latest findings in ARD biomarkers into four stages based on disease progression: Healthy brain, pre-clinical, mild cognitive impairment, and dementia. We then systematically summarize the most promising therapeutic approaches to prevent or slow ARD at four levels: Genome and epigenome, organelle, cell, and organ and organism. We emphasize the importance of early prevention and detection, along with the implementation of combined treatments as multimodal intervention strategies, to address brain aging and ARD in the future.

Targeted protein degradation: expanding the technology to facilitate the clearance of neurotoxic proteins in neurodegenerative diseases

In neurodegenerative diseases (NDDs), disruptions in protein homeostasis hinder the clearance of misfolded proteins, causing the formation of misfolded protein oligomers and multimers. The accumulation of these abnormal proteins results in the onset and progression of NDDs. Removal of non-native protein is essential for cell to maintain proteostasis. In recent years, targeted protein degradation (TPD) technologies have become a novel means of treating NDDs by removing misfolded proteins through the intracellular protein quality control system. The TPD strategy includes the participation of two primary pathways, namely the ubiquitin-proteasome pathway (for instance, PROTAC, molecular glue and hydrophobic tag), and the autophagy-lysosome pathway (such as LYTAC, AUTAC and ATTEC). In this review, we systematically present the mechanisms of various TPD strategies employed for neurotoxic protein degradation in NDDs. The article provides an overview of the design, in vitro and in vivo anti-NDD activities and pharmacokinetic properties of these small-molecular degraders. Finally, the advantages, challenges and perspectives of these TPD technologies in NDDs therapy are discussed, providing ideas for further development of small molecule degraders in the realm of NDDs.

Co-Aggregation of TDP-43 with Other Pathogenic Proteins and Their Co-Pathologies in Neurodegenerative Diseases

Pathological aggregation of a specific protein into insoluble aggregates is a common hallmark of various neurodegenerative diseases (NDDs). In the earlier literature, each NDD is characterized by the aggregation of one or two pathogenic proteins, which can serve as disease-specific biomarkers. The aggregation of these specific proteins is thought to be a major cause of or deleterious result in most NDDs. However, accumulating evidence shows that a pathogenic protein can interact and co-aggregate with other pathogenic proteins in different NDDs, thereby contributing to disease onset and progression synergistically. During the past years, more than one type of NDD has been found to co-exist in some individuals, which may increase the complexity and pathogenicity of these diseases. This article reviews and discusses the biochemical characteristics and molecular mechanisms underlying the co-aggregation and co-pathologies associated with TDP-43 pathology. The TDP-43 aggregates, as a hallmark of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD), can often be detected in other NDDs, such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD) and spinocerebellar ataxia type 2 (SCA2). In many cases, TDP-43 is shown to interact and co-aggregate with multiple pathogenic proteins in vitro and in vivo. Furthermore, the co-occurrence and co-aggregation of TDP-43 with other pathogenic proteins have important consequences that may aggravate the diseases. Thus, the current viewpoint that the co-aggregation of TDP-43 with other pathogenic proteins in NDDs and their relevance to disease progression may gain insights into the patho-mechanisms and therapeutic potential of various NDDs.

Pure LATE-NC: Frequency, clinical impact, and the importance of considering APOE genotype when assessing this and other subtypes of non-Alzheimer's pathologies

Pure limbic-predominant age-related TDP-43 encephalopathy neuropathologic changes (pure LATE-NC) is a term used to describe brains with LATE-NC but lacking intermediate or severe levels of Alzheimer's disease neuropathologic changes (ADNC). Focusing on pure LATE-NC, we analyzed data from the National Alzheimer's Coordinating Center (NACC) Neuropathology Data Set, comprising clinical and pathological information aggregated from 32 NIH-funded Alzheimer's Disease Research Centers (ADRCs). After excluding subjects dying with unusual conditions, n = 1,926 autopsied subjects were included in the analyses. For > 90% of these participants, apolipoprotein E (APOE) allele status was known; 46.5% had at least one APOE 4 allele. In most human populations, only 15-25% of people are APOE ε4 carriers. ADRCs with higher documented AD risk allele (APOE or BIN1) rates had fewer participants lacking ADNC, and correspondingly low rates of pure LATE-NC. Among APOE ε4 non-carries, 5.3% had pure LATE-NC, 37.0% had pure ADNC, and 3.6% had pure neocortical Lewy body pathology. In terms of clinical impact, participants with pure LATE-NC tended to die after having received a diagnosis of dementia: 56% died with dementia among APOE ε4 non-carrier participants, comparable to 61% with pure ADNC. LATE-NC was associated with increased Clinical Dementia Rating Sum of Boxes (CDR-SOB) scores, i.e. worsened global cognitive impairments, in participants with no/low ADNC and no neocortical Lewy body pathology (p = 0.0023). Among pure LATE-NC cases, there was a trend for higher LATE-NC stages to be associated with worse CDR-SOB scores (p = 0.026 for linear trend of LATE-NC stages). Pure LATE-NC was not associated with clinical features of disinhibition or primary progressive aphasia. In summary, LATE-NC with no or low levels of ADNC was less frequent than pure ADNC but was not rare, particularly among individuals who lacked the APOE 4 allele, and in study cohorts with APOE 4 frequencies similar to those in most human populations.

Prion-like Spreading of Disease in TDP-43 Proteinopathies

TDP-43 is a ubiquitous nuclear protein that plays a central role in neurodegenerative disorders collectively known as TDP-43 proteinopathies. Under physiological conditions, TDP-43 is primarily localized to the nucleus, but in its pathological form it aggregates in the cytoplasm, contributing to neuronal death. Given its association with numerous diseases, particularly ALS and FTLD, the mechanisms underlying TDP-43 aggregation and its impact on neuronal function have been extensively investigated. However, little is still known about the spreading of this pathology from cell to cell. Recent research has unveiled the possibility that TDP-43 may possess prion-like properties. Specifically, misfolded TDP-43 aggregates can act as templates inducing conformational changes in native TDP-43 molecules and propagating the misfolded state across neural networks. This review summarizes the mounting and most recent evidence from in vitro and in vivo studies supporting the prion-like hypothesis and its underlying mechanisms. The prion-like behavior of TDP-43 has significant implications for diagnostics and therapeutics. Importantly, emerging strategies such as small molecule inhibitors, immunotherapies, and gene therapies targeting TDP-43 propagation offer promising avenues for developing effective treatments. By elucidating the mechanisms of TDP-43 spreading, we therefore aim to pave the way for novel therapies for TDP-43-related neurodegenerative diseases.

Alzheimer's Disease: Exploring the Landscape of Cognitive Decline

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by cognitive decline, memory loss, and impaired daily functioning. The pathology of AD is marked by the accumulation of amyloid beta plaques and tau protein tangles in the brain, along with neuroinflammation and synaptic dysfunction. Genetic factors, such as mutations in APP, PSEN1, and PSEN2 genes, as well as the APOE ε4 allele, contribute to increased risk of acquiring AD. Currently available treatments provide symptomatic relief but do not halt disease progression. Research efforts are focused on developing disease-modifying therapies that target the underlying pathological mechanisms of AD. Advances in identification and validation of reliable biomarkers for AD hold great promise for enhancing early diagnosis, monitoring disease progression, and assessing treatment response in clinical practice in effort to alleviate the burden of this devastating disease. In this paper, we analyze data from the CAS Content Collection to summarize the research progress in Alzheimer's disease. We examine the publication landscape in effort to provide insights into current knowledge advances and developments. We also review the most discussed and emerging concepts and assess the strategies to combat the disease. We explore the genetic risk factors, pharmacological targets, and comorbid diseases. Finally, we inspect clinical applications of products against AD with their development pipelines and efforts for drug repurposing. The objective of this review is to provide a broad overview of the evolving landscape of current knowledge regarding AD, to outline challenges, and to evaluate growth opportunities to further efforts in combating the disease.

Pilot implementation of the revised criteria for staging of Alzheimer's disease by the Alzheimer's Association Workgroup in a tertiary memory clinic

INTRODUCTION

We aimed to evaluate the feasibility of the 2024 Alzheimer's Association Workgroup's integrated clinical-biological staging scheme in outpatient settings within a tertiary memory clinic.

METHODS

The 2018 syndromal cognitive staging system, coupled with a binary biomarker classification, was implemented for 236 outpatients with cognitive concerns. The 2024 numeric clinical staging framework, incorporating biomarker staging, was specifically applied to 154 individuals within the Alzheimer's disease (AD) continuum.

RESULTS

The 2024 staging scheme accurately classified 95.5% AD. Among these, 56.5% exhibited concordant clinical and biological stages (canonical), 34.7% demonstrated more advanced clinical stages than biologically expected (susceptible), and 8.8% displayed the inverse pattern (resilient). The susceptible group was characterized by a higher burden of neurodegeneration and inflammation than anticipated from tau, whereas the resilient group showed the opposite.

DISCUSSION

The 2024 staging scheme is generally feasible. A discrepancy between clinical and biological stages is relatively frequent among symptomatic patients with AD.

HIGHLIGHTS

The 2024 AA staging scheme is generally feasible in a tertiary memory clinic. A discrepancy between clinical and biological stages is relatively frequent in AD. The mismatch may be influenced by a non-specific pathological process involved in AD. Individual profiles like aging and lifestyles may contribute to such a mismatch. Matched and mismatched cases converge toward similar clinical outcomes.

The Basis of Cognitive and Behavioral Dysfunction in Amyotrophic Lateral Sclerosis

OBJECTIVE

To summarize and evaluate evidence pertaining to the clinical, genetic, histopathological, and neuroimaging correlates of cognitive and behavioral dysfunction in amyotrophic lateral sclerosis (ALS).

METHODOLOGY

We comprehensively reviewed the literature on cognitive and behavioral manifestations of ALS, narrating findings from both cross-sectional and longitudinal studies. We discussed knowledge gaps in the evidence base and key limitations affecting studies to date, before formulating a framework for future research paradigms aimed at investigating clinicopathological correlates of neuropsychological dysfunction in ALS.

RESULTS

Studies have demonstrated clinical associations with cognitive dysfunction in ALS e.g., bulbar-onset of symptoms, pathological associations (extramotor TDP-43 deposition), and imaging associations (frontotemporal involvement). The most common behavioral deficit, apathy, is highly associated with verbal fluency, but longitudinal studies assessing behavioral dysfunction in ALS are comparatively lacking.

CONCLUSION

Longitudinal studies have been helpful in identifying several potential correlates of cognitive and behavioral dysfunction but have frequently been confounded by selection bias and inappropriate testing platforms. This review provides a framework for more robust assessment of clinicopathological associations of neuropsychological abnormalities in ALS in the future, advocating for greater utilization of pre-symptomatic C9orf72 repeat expansion-carrying cohorts.

TDP43 aggregation at ER-exit sites impairs ER-to-Golgi transport

Protein aggregation plays key roles in age-related degenerative diseases, but how different proteins coalesce to form inclusions that vary in composition, morphology, molecular dynamics and confer physiological consequences is poorly understood. Here we employ a general reporter based on mutant Hsp104 to identify proteins forming aggregates in human cells under common proteotoxic stress. We identify over 300 proteins that form different inclusions containing subsets of aggregating proteins. In particular, TDP43, implicated in Amyotrophic Lateral Sclerosis (ALS), partitions dynamically between two distinct types of aggregates: stress granule and a previously unknown non-dynamic (solid-like) inclusion at the ER exit sites (ERES). TDP43-ERES co-aggregation is induced by diverse proteotoxic stresses and observed in the motor neurons of ALS patients. Such aggregation causes retention of secretory cargos at ERES and therefore delays ER-to-Golgi transport, providing a link between TDP43 aggregation and compromised cellular function in ALS patients.

Blood-Based Biomarkers in Alzheimer's Disease: Advancing Non-Invasive Diagnostics and Prognostics

Alzheimer's disease (AD), the most prevalent form of dementia, is expected to rise dramatically in incidence due to the global population aging. Traditional diagnostic approaches, such as cerebrospinal fluid analysis and positron emission tomography, are expensive and invasive, limiting their routine clinical use. Recent advances in blood-based biomarkers, including amyloid-beta, phosphorylated tau, and neurofilament light, offer promising non-invasive alternatives for early AD detection and disease monitoring. This review synthesizes current research on these blood-based biomarkers, highlighting their potential to track AD pathology and enhance diagnostic accuracy. Furthermore, this review uniquely integrates recent findings on protein-protein interaction networks and microRNA pathways, exploring novel combinations of proteomic, genomic, and epigenomic biomarkers that provide new insights into AD's molecular mechanisms. Additionally, we discuss the integration of these biomarkers with advanced neuroimaging techniques, emphasizing their potential to revolutionize AD diagnostics. Although large-scale validation is still needed, these biomarkers represent a critical advancement toward more accessible, cost-effective, and early diagnostic tools for AD.

Potential Mechanisms of Tunneling Nanotube Formation and Their Role in Pathology Spread in Alzheimer's Disease and Other Proteinopathies

Alzheimer's disease (AD) is the most common type of dementia worldwide. The etiopathogenesis of this disease remains unknown. Currently, several hypotheses attempt to explain its cause, with the most well-studied being the cholinergic, beta-amyloid (Aβ), and Tau hypotheses. Lately, there has been increasing interest in the role of immunological factors and other proteins such as alpha-synuclein (α-syn) and transactive response DNA-binding protein of 43 kDa (TDP-43). Recent studies emphasize the role of tunneling nanotubes (TNTs) in the spread of pathological proteins within the brains of AD patients. TNTs are small membrane protrusions composed of F-actin that connect non-adjacent cells. Conditions such as pathogen infections, oxidative stress, inflammation, and misfolded protein accumulation lead to the formation of TNTs. These structures have been shown to transport pathological proteins such as Aβ, Tau, α-syn, and TDP-43 between central nervous system (CNS) cells, as confirmed by in vitro studies. Besides their role in spreading pathology, TNTs may also have protective functions. Neurons burdened with α-syn can transfer protein aggregates to glial cells and receive healthy mitochondria, thereby reducing cellular stress associated with α-syn accumulation. Current AD treatments focus on alleviating symptoms, and clinical trials with Aβ-lowering drugs have proven ineffective. Therefore, intensifying research on TNTs could bring scientists closer to a better understanding of AD and the development of effective therapies.

MAD-microbial (origin of) Alzheimer's disease hypothesis: from infection and the antimicrobial response to disruption of key copper-based systems

Microbes have been suspected to cause Alzheimer's disease since at least 1908, but this has generally remained unpopular in comparison to the amyloid hypothesis and the dominance of Aβ and Tau. However, evidence has been accumulating to suggest that these earlier theories are but a manifestation of a common cause that can trigger and interact with all the major molecular players recognized in AD. Aβ, Tau and ApoE, in particular appear to be molecules with normal homeostatic functions but also with alternative antimicrobial functions. Their alternative functions confer the non-immune specialized neuron with some innate intracellular defenses that appear to be re-appropriated from their normal functions in times of need. Indeed, signs of infection of the neurons by biofilm-forming microbial colonies, in synergy with herpes viruses, are evident from the clinical and preclinical studies we discuss. Furthermore, we attempt to provide a mechanistic understanding of the AD landscape by discussing the antimicrobial effect of Aβ, Tau and ApoE and Lactoferrin in AD, and a possible mechanistic link with deficiency of vital copper-based systems. In particular, we focus on mitochondrial oxidative respiration via complex 4 and ceruloplasmin for iron homeostasis, and how this is similar and possibly central to neurodegenerative diseases in general. In the case of AD, we provide evidence for the microbial Alzheimer's disease (MAD) theory, namely that AD could in fact be caused by a long-term microbial exposure or even long-term infection of the neurons themselves that results in a costly prolonged antimicrobial response that disrupts copper-based systems that govern neurotransmission, iron homeostasis and respiration. Finally, we discuss potential treatment modalities based on this holistic understanding of AD that incorporates the many separate and seemingly conflicting theories. If the MAD theory is correct, then the reduction of microbial exposure through use of broad antimicrobial and anti-inflammatory treatments could potentially alleviate AD although this requires further clinical investigation.

Pathological C-terminal phosphomimetic substitutions alter the mechanism of liquid-liquid phase separation of TDP-43 low complexity domain

C-terminally phosphorylated TAR DNA-binding protein of 43 kDa (TDP-43) marks the proteinaceous inclusions that characterize a number of age-related neurodegenerative diseases, including amyotrophic lateral sclerosis, frontotemporal lobar degeneration and Alzheimer's disease. TDP-43 phosphorylation at S403/S404 and (especially) at S409/S410 is, in fact, accepted as a biomarker of proteinopathy. These residues are located within the low complexity domain (LCD), which also drives the protein's liquid-liquid phase separation (LLPS). The impact of phosphorylation at these LCD sites on phase separation of the protein is a topic of great interest, as these post-translational modifications and LLPS are both implicated in proteinopathies. Here, we employed a combination of experimental and simulation-based approaches to explore this question on a phosphomimetic model of the TDP-43 LCD. Our turbidity and fluorescence microscopy data show that phosphomimetic Ser-to-Asp substitutions at residues S403, S404, S409 and S410 alter the LLPS behavior of TDP-43 LCD. In particular, unlike the LLPS of unmodified protein, LLPS of the phosphomimetic variants displays a biphasic dependence on salt concentration. Through coarse-grained modeling, we find that this biphasic salt dependence is derived from an altered mechanism of phase separation, in which LLPS-driving short-range intermolecular hydrophobic interactions are modulated by long-range attractive electrostatic interactions. Overall, this in vitro and in silico study provides a physiochemical foundation for understanding the impact of pathologically relevant C-terminal phosphorylation on the LLPS of TDP-43 in a more complex cellular environment.

Molecular Mechanisms of Phase Separation and Amyloidosis of ALS/FTD-linked FUS and TDP-43

FUS and TDP-43, two RNA-binding proteins from the heterogeneous nuclear ribonucleoprotein family, have gained significant attention in the field of neurodegenerative diseases due to their association with amyotrophic lateral sclerosis (ALS) and frontotemporal degeneration (FTD). They possess folded domains for binding ATP and various nucleic acids including DNA and RNA, as well as substantial intrinsically disordered regions (IDRs) including prion-like domains (PLDs) and RG-/RGG-rich regions. They play vital roles in various cellular processes, including transcription, splicing, microRNA maturation, RNA stability and transport and DNA repair. In particular, they are key components for forming ribonucleoprotein granules and stress granules (SGs) through homotypic or heterotypic liquid-liquid phase separation (LLPS). Strikingly, liquid-like droplets formed by FUS and TDP-43 may undergo aging to transform into less dynamic assemblies such as hydrogels, inclusions, and amyloid fibrils, which are the pathological hallmarks of ALS and FTD. This review aims to synthesize and consolidate the biophysical knowledge of the sequences, structures, stability, dynamics, and inter-domain interactions of FUS and TDP-43 domains, so as to shed light on the molecular mechanisms underlying their liquid-liquid phase separation (LLPS) and amyloidosis. The review further delves into the mechanisms through which ALS-causing mutants of the well-folded hPFN1 disrupt the dynamics of LLPS of FUS prion-like domain, providing key insights into a potential mechanism for misfolding/aggregation-prone proteins to cause neurodegenerative diseases and aging by gain of functions. With better understanding of different biophysical aspects of FUS and TDP-43, the ultimate goal is to develop drugs targeting LLPS and amyloidosis, which could mediate protein homeostasis within cells and lead to new treatments for currently intractable diseases, particularly neurodegenerative diseases such as ALS, FTD and aging. However, the study of membrane-less organelles and condensates is still in its infancy and therefore the review also highlights key questions that require future investigation.

TDP-43 ameliorates aging-related cartilage degradation through preventing chondrocyte senescence

Senescent chondrocytes or signaling mechanisms leading to senescence are promising new therapeutic approaches for ameliorating cartilage degradation. Herein, we show that the transactive response DNA/RNA-binding protein (TDP-43) regulates chondrocyte senescence and ameliorates cartilage degradation. First, a significant decrease in TDP-43 was observed in 16-month-old mice compared with younger mice. Immunohistochemistry (IHC) analysis of mouse articular cartilage showed that p21, p16, p53, and matrix metalloprotein-13 (MMP13) were increased, but laminB1 and Collagen type II alpha1 1 chain (Col2a1) were decreased in 16-month-old mice. Furthermore, TDP-43 levels were decreased in vivo following D-galactose (D-gal) induction. Therefore, we investigated the role of TDP-43 in the senescent chondrocytes. ATDC5 cells were induced to overexpress TDP-43. Western blot analysis showed increased expression of laminB1, Ki67, and PCNA but decreased expression of p21, p16, p53, and MMP13. Senescence-associated-β-galactosidase (SA-β-Gal) assay, γH2AX staining, and EdU were performed to assess changes in chondrocytes, showing weaker SA-β-Gal and γH2AX staining but stronger EdU and Alican Blue staining. However, TDP-43 deficiency had opposing effects, and similar to D-gal stimulation results. Taken together, our data verified that TDP-43 negatively correlated with senescence markers, positively correlated with cell proliferation markers, and could alleviate cartilage degradation induced by D-gal. This may be an essential mechanism of cellular senescence and cartilage degradation.

HIV-1 Vpu induces neurotoxicity by promoting Caspase 3-dependent cleavage of TDP-43

Despite the efficacy of highly active antiretroviral therapy in controlling the incidence and mortality of AIDS, effective interventions for HIV-1-induced neurological damage and cognitive impairment remain elusive. In this study, we found that HIV-1 infection can induce proteolytic cleavage and aberrant aggregation of TAR DNA-binding protein 43 (TDP-43), a pathological protein associated with various severe neurological disorders. The HIV-1 accessory protein Vpu was found to be responsible for the cleavage of TDP-43, as ectopic expression of Vpu alone was sufficient to induce TDP-43 cleavage, whereas HIV-1 lacking Vpu failed to cleave TDP-43. Mechanistically, the cleavage of TDP-43 at Asp89 by HIV-1 relies on Vpu-mediated activation of Caspase 3, and pharmacological inhibition of Caspase 3 activity effectively suppressed the HIV-1-induced aggregation and neurotoxicity of TDP-43. Overall, these results suggest that TDP-43 is a conserved host target of HIV-1 Vpu and provide evidence for the involvement of TDP-43 dysregulation in the neural pathogenesis of HIV-1.