Abstract Tunneling nanotubes (TNTs) play a crucial role in intercellular communication, enabling transfer of molecular cargoes over long distances between connected cells. Previous studies have demonstrated efficient, directional transfer of $$\alpha$$ α -Synuclein ( $$\alpha$$ α -Syn) aggregates from neurons to microglia, with endosomal trafficking and lysosomal processing identified as the primary events following $$\alpha$$ α -Syn internalization. Using human neuronal and microglial cell lines, we show that microglia exhibit higher lysosomal turnover, particularly through lysophagy, whereas neuronal lysosomes display compromised degradative capacity and impaired autophagic flux upon $$\alpha$$ α -Syn exposure, resulting in compromised aggregate clearance. Such a response to $$\alpha$$ α -Syn aggregates is also conserved in human iPSC-derived neurons and microglia. Moreover, perturbing aggregate clearance via autophagy inhibition enhances TNT-mediated transfer of $$\alpha$$ α -Syn from neuronal cells to microglia. Microglia co-cultured with $$\alpha$$ α -Syn-containing neurons upregulate autophagy flux, enabling efficient degradation of the transferred aggregates. These results highlight dysfunctional autophagy in neurons as a key driver outsourcing $$\alpha$$ α -Syn aggregates to microglia.

Background:Adverse childhood experiences (ACEs) may accelerate early menopause and influence neurodegenerative processes, contributing to sex-specific dementia risk. This study examined associations with cognitive decline and incident dementia in ACEs and early menopause. Methods:We studied 6093 women and 5784 men aged ≥50 years from the Health and Retirement Study, a US cohort spanning between 2010 and 2022. Incident dementia was based on self-report of physician-diagnosed dementia. Cognition was measured using a composite score of immediate and delayed recall, serial sevens subtraction, and counting backwards (range, 0-27). ACEs were assessed using seven items and classified into none, 1, 2, and ≥3 ACEs. Age at menopause was classified into <47, 47 to 52, and ≥53 years. We included men and defined the four categories of sex and age at menopause, assessing varying levels of female hormones with age at menopause serving as the proxy indicator of those differences. Covariates included lifestyle risk factors for dementia. We used a longitudinal panel design with each observation containing baseline covariates and 2-year follow-up outcomes. We applied a random-effects model to survival analysis for incident dementia and to linear regression analysis for cognition. Results:Here we show that experiencing 2 (hazard ratio: 1.32 [95% CI: 1.07-1.62]) or ≥3 ACEs (1.32 [1.03-1.68]) is associated with higher dementia risk compared with no ACEs. Dementia risk does not differ by sex and age at menopause in women. Women with early menopause (β = -0.22 [95%CI: -0.41 to -0.03]) and men (-0.92 [-1.06 to -0.78]) have worse cognition than women with late menopause. ACE level is not associated with cognition. No mediation by early menopause is observed between multiple ACEs, dementia, or cognition in women. Conclusions:Mechanisms linking ACEs and early menopause to dementia risk may differ. Risk reduction strategies should consider preventing and addressing ACEs and early menopause, respectively.

Most neurodegenerative diseases are believed to spread through the brain by prion-like mechanisms, where filamentous protein assemblies self-propagate by templated seeding 1 . Distinct conformations of amyloid filaments are thought to provide the physical basis for the strains that lead to different diseases 2 . However, a central pillar of the prion hypothesis, that strains retain their structural identity upon transmission, has not been demonstrated. Here we show that the injection of tau filaments from the brains of individuals with Alzheimer’s disease or corticobasal degeneration into the brains of wildtype mice leads to the seeded assembly of amyloid filaments made of mouse tau with the same structures as those of the seeds. Thereby, we establish that, like prion strains, tau filaments propagate through templated seeding, and that the mouse is a suitable model to study the molecular mechanisms by which distinct tau folds drive disease-specific pathology in the brain.

We report the clinicopathological and biochemical findings of ALS associated with a UBQLN2 P494L mutation. Autopsy revealed widespread TDP-43 pathology and UBQLN2-positive inclusions. Immunoblot analysis demonstrated a marked reduction of soluble UBQLN2, supporting functional UBQLN2 insufficiency as a pathogenic mechanism underlying TDP-43 aggregation.

TDP-43 proteinopathies, such as frontotemporal degeneration (FTLD) and amyotrophic lateral sclerosis (ALS), are classified into five neuropathological subtypes, Types A to E, according to the morphology of TDP-43 inclusions. Recent cryo-electron microscopy analysis of FTLD-TDP cases demonstrated that TDP-43 filaments composing the inclusions are structurally different depending on the subtype, and remarkably, co-assembled heteromeric filaments of TDP-43 and annexin A11 (ANXA11) were identified in Type C. Therefore, the involvement of ANXA11 in TDP-43 proteinopathy should be further examined. Here, we pathologically and biochemically analyzed four cases of primary lateral sclerosis-phenotype FTLD/motor neuron disease (MND) with TDP-43 pathology (PLS-TDP), and found that ANXA11 co-localizes with FTLD-TDP Type A pathology in PLS-TDP. Immunoblot analysis of the PLS-TDP cases revealed that the banding patterns of C-terminal and chymotrypsin-resistant fragments of TDP-43 are distinct from those of FTLD-TDP Types A, B and C. In addition, the N-terminal fragments of ANXA11 appear to be different from those of FTLD-TDP Type C. Filaments extracted from PLS-TDP cases were TDP-43- and ANXA11-immunopositive, suggesting the presence of TDP-ANXA11 heteromeric filaments. These results suggest that co-aggregation of ANXA11 and TDP-43 may serve as a neuropathological and biochemical indicator distinguishing PLS from ALS in FTLD/MND.

We report an autopsy case of frontotemporal lobar degeneration (FTLD)-TDP type C with severe striatal involvement and annexin A11- and phosphorylated TDP-43-positive glial cytoplasmic inclusions. The patient developed progressive asymmetric rigidity accompanied by marked striatal atrophy and showed both upper and lower motor neuron involvement. These findings expand the clinicopathological spectrum of FTLD-TDP type C and may support the concept of an annexin A11-associated pathogenic continuum linking FTLD and amyotrophic lateral sclerosis.

Neuronal central chromatolysis (CC) is the histopathological hallmark of pellagra encephalopathy, a neurological deficit resulting from vitamin deficiencies. Pellagrous CC neurons are morphologically similar to ballooned achromatic neurons in other conditions but the distinct pathomechanisms remain unclear. We performed a clinico-neuropathological analysis of 10 autopsy cases of pellagra encephalopathy. The pellagra encephalopathy cases were immunohistochemically compared with disease controls, including cases of axonal injury and neurodegenerative diseases. Electron microscopic evaluation and immunohistochemical examinations targeting mitochondrial fragmentation were performed for a representative case. Four of 10 pellagra encephalopathy patients exhibited prolonged impairment of consciousness distinguishable from alcohol withdrawal delirium. Pellagrous CC neurons were negative for cytoskeletal markers whereas ballooned achromatic neurons in the disease control cases were positive. Immunohistochemical analysis of mitochondrial markers revealed that CC neurons exhibited more intense immunoreactivity for COX-IV and mitochondrial fissure factor compared to the disease controls. Transmission electron microscopy of these CC neurons revealed a marked increase in the mitochondria with amorphous densities. These findings indicate that the pathomechanism of pellagrous CC is distinct from that of the ballooned achromatic neurons of other etiologies. Mitochondrial alterations in pellagrous CC neurons suggest that neuronal energy deficits resulting from nicotinamide adenine dinucleotide deficiency induce mitochondrial fragmentation.

Chronic traumatic encephalopathy (CTE) is a progressive neurodegenerative disease characterized by the presence of abnormally phosphorylated tau aggregates. Tau is a microtubule-associated protein expressed mainly in axons of neurons with a role in the regulation of microtubule dynamics and axonal transport. It is totally unknown when and how tau is abnormally hyperphosphorylated in CTE brains. Unlike other tauopathies such as Alzheimer’s disease, in which diseases start several decades before clinical symptoms and the time point of onset is not clear, in the case of CTE it is evident when and what impacts are given to cause the diseases. Repetitive mild traumatic brain injury (rmTBI) is a known causative factor for CTE, particularly in athletes engaged in contact sports, individuals involved in traffic accidents, and military personnel exposed to blast injuries. We hypothesized rmTBI to be a useful experimental paradigm for investigating the initial processes of tau hyperphosphorylation in CTE. Among the various experimental models for TBI reported to date, we focus on the Closed-Head Impact Model of Engineered Rotational Acceleration (CHIMERA), because it appears to replicate human TBI more faithfully than other models particularly regarding on the impact mechanism and pathology. After verifying that CHIMERA rmTBI induced brain injuries analogous to human CTE, we investigated tau pathology in wild-type (WT) and P301S human tau transgenic (Tg) mice subjected to CHIMERA rmTBI. While no hyperphosphorylated tau signal was observed in any region of the WT mouse brain, an increased number of AT8-positive cells were detected in the motor and sensory cortices of P301S Tg mouse brains, accompanied by dendritic abnormalities, after rmTBI. Further, we found that CHIMERA rmTBI enhanced the spreading of tau pathology in brains of WT mice when tau fibrils were inoculated. These results suggest a possibility that rmTBI constitutes a risk factor stimulating the progression and propagation of tau pathology, rather than causing the initial events, if tau aggregates are present in the brain and that CHIMERA rmTBI may serve as a valuable experimental model for investigating its molecular mechanisms.

Intraneuronal α-synuclein (αS) accumulation is a central event in the pathogenesis of Parkinson’s disease and dementia with Lewy bodies. The spread of αS pathology throughout the central nervous system contributes to disease progression via seed-dependent propagation, yet disease-modifying therapies remain unavailable. We previously reported that porphyrin compounds inhibit αS aggregation in vitro; however, because of their high molecular weight, porphyrins poorly penetrate the blood–brain barrier (BBB). Heme, a porphyrin derivative, is synthesized from 5-aminolevulinic acid (5-ALA) via the heme biosynthetic pathway. In this study, we investigated whether 5-ALA modulates αS accumulation and propagation. Although porphyrin compounds inhibited αS seeding in vitro, 5-ALA itself did not. However, treatment of mouse primary neurons with 5-ALA enhanced heme synthesis and suppressed seed-dependent αS aggregation, suggesting a potential role for intracellular heme in modulating αS propagation. We further evaluated the effects of 5-ALA in an in vivo αS propagation model. Preformed αS fibrils were unilaterally injected into the striatum of wild-type mice, followed by oral administration of 5-ALA at three doses (0, 1.7, and 20 mg/kg/day) for 4 weeks. Biochemical analyses demonstrated that 5-ALA significantly reduced the propagation of sarkosyl-insoluble αS to the contralateral hemisphere. Immunohistochemical analyses revealed a marked reduction in phosphorylated αS pathology in the amygdala and substantia nigra in the 5-ALA-treated groups. Collectively, these findings indicate that oral administration of 5-ALA suppresses αS propagation in vivo, potentially through enhancement of intracellular heme synthesis. Modulation of the heme biosynthetic pathway may represent a novel therapeutic strategy for synucleinopathies.

Tunneling nanotubes (TNTs) enable direct intercellular transfer of macromolecules, organelles, and pathogenic protein aggregates. While α-synuclein (α-Syn) aggregates are known to promote TNT formation, the underlying mechanisms remain poorly defined. Here, using human neuronal and microglial cell lines, as well as iPSC-derived dopaminergic neurons and microglia, we show that α-Syn aggregates induce severe mitochondrial damage, leading to cytosolic release of mitochondrial DNA (mtDNA) and activation of the cGAS-STING-NF-κB-IRF3 pathway. This innate immune response drives actin cytoskeleton remodeling and the formation of TNT-like structures, promoting intercellular transfer of α-Syn from neurons to microglia. Additionally, neuronal cells transfer damaged mitochondria to microglia, where they undergo lysosome-mediated degradation. Neuron-to-microglia communication under α-Syn-induced stress also triggers a bystander inflammatory response in microglia, suggesting a neuroimmune activation. Our findings identify mitochondrial damage and STING-mediated inflammation as key drivers of TNT formation and α-Syn propagation, highlighting potential targets to modulate disease progression in Synucleinopathies.

Argyrophilic grain disease is an age-related disorder characterized by the presence of argyrophilic grains. Argyrophilic grain disease has a sequential distribution pattern that begins in the ambient gyrus (Saito Stage I), spreads to the medial temporal lobe (Saito Stage II) and reaches the basal forebrain and cingulate gyrus (Saito Stage III). A strong association with cognitive decline, especially in cases of Saito Stage III argyrophilic grain disease, has also been reported. The main clinical feature includes cognitive decline characterized by memory disturbance, although conflicting results have been reported. Recent studies suggest an association with parkinsonism. To clarify the association between argyrophilic grain disease, cognitive decline and parkinsonism, we performed a clinicopathological study using the Brain Bank for Aging Research autopsy cohort in Japan. Approximately half (227) of the 452 consecutive autopsy cases had argyrophilic grain disease, and the frequency and stage of argyrophilic grain disease increased with age. Among the argyrophilic grain disease cases, 20 were demented without any comorbid pathology responsible for it, a condition referred to as dementia with grains. Furthermore, 6 of the 20 dementia with grains cases presented with parkinsonism, particularly postural instability, in addition to memory disturbance. Dementia with grains cases with parkinsonism had significantly more argyrophilic grains in the substantia nigra than those without parkinsonism and showed significantly decreased anti-dopamine transporter immunoreactivity in the putamen compared to control cases. Given these findings, argyrophilic grain disease is strongly associated with cognitive decline, especially in Saito Stage III cases, and parkinsonism is a new common clinical presentation. The extension of argyrophilic grain disease pathology to the nigrostriatal system may contribute to the development of parkinsonism.

Background:Pick's disease (PiD) is a subtype of frontotemporal lobar degeneration. However, the pathogenesis and symptomatic lesions remain unclear. We report a case of PiD with a short disease duration and compare it to a case series to reveal the association between degenerative patterns and clinical manifestations. Case Presentation:The patient showed a marked decline in motivation at the age of 54 years. He was admitted with a clinical diagnosis of depressive disorder at the age of 56 years. He exhibited only apathy and lacked typical behavioral symptoms. Specialist observation revealed behavioral symptoms such as disinhibition, a lack of empathy, and hyperorality that had previously unnoticed by the patient's family members. The patient died of acute heart failure 4 days after hospitalization. Postmortem examination revealed a brain weight of 1090 g, with focal atrophy of the bilateral frontal and temporal lobes. Neuropathological findings mainly presented as numerous Pick bodies (PBs), mainly in the frontal lobe and hippocampus. PBs were immunopositive for phosphorylated tau and 3-repeat tau but negative for 4-repeat tau. The pathological findings in this case corresponded to phase II of PiD staging as defined in a previous study. Conclusion:The clinical symptoms in this case, primarily characterized by apathy with minimal behavioral symptoms, were consistent with the predominant pathological involvement of the dorsolateral frontal lobe. The present case was interpreted as early-phase PiD. A comparison of the case series suggested that early-phase PiD cases may help clarify the association between early clinical manifestations and focal degenerative lesions in the frontal lobe.

Aggregation of α-synuclein is a central pathological feature of Parkinson’s disease (PD), yet reliable and broadly applicable fluid biomarkers reflecting disease-relevant α-synuclein biology remain limited. We aimed to establish acetylated α-synuclein (Ac-αSyn), the predominant proteoform in vivo , as a novel biomarker for PD and to evaluate its diagnostic utility based on a sensitive immunoassay. Using a single molecule array technique capable of quantitatively detecting N-terminally acetylated α-synuclein, plasma Ac-αSyn levels were measured in 110 samples obtained from 52 patients with PD, 24 patients with multiple system atrophy (MSA), and 34 healthy controls (HCs). In a subset of PD patients, plasma Ac-αSyn measurements and 123 I-metaiodobenzylguanidine (MIBG) cardiac scintigraphy were performed in the same individuals, enabling direct comparison between these two testing modalities. Ac-αSyn levels were also quantified in 91 cerebrospinal fluid (CSF) samples obtained from 51 patients with PD, 25 patients with MSA, and 15 non-parkinsonian disease controls (DCs). Plasma Ac-αSyn levels robustly differentiated PD from both MSA and HCs ( p < 0.0001). Receiver operating characteristic analysis demonstrated high diagnostic performance (area under the curve [AUC] = 0.89 for PD vs MSA; AUC = 0.94 for PD vs HCs), comparable to established imaging biomarkers. In the same individuals, plasma Ac-αSyn levels correlated with the heart-to-mediastinum ratio derived from MIBG cardiac scintigraphy. CSF Ac-αSyn levels also clearly differentiated PD from both MSA and DCs ( p < 0.0001), with high diagnostic performance (AUC = 0.85 for PD vs MSA; AUC = 0.93 for PD vs DCs), supporting the biological relevance of plasma Ac-αSyn as a biomarker. This study identifies Ac-αSyn in plasma as a novel biomarker for PD, enabled by quantitative immunoassay-based detection. Plasma Ac-αSyn represents a practical and minimally invasive biomarker that supports biology-based diagnosis of PD and discrimination from MSA.

Tau protein, a central player in Alzheimer's disease (AD), exhibits cytotoxicity upon fibril formation. Understanding the early stages of tau fibrillization is therefore critical for the development of effective therapeutics. Previous work [Rasmussen. et. al, J. Mol. Biol., 2023] reported the rapid formation of Thioflavin T (ThT)-inactive clusters upon mixing tau with anionic polymers, yet the functional role of these clusters remained unclear. Here, we demonstrate that these transient clusters act as obligatory precursors in the fibrillization pathway. Using small-angle X-ray scattering (SAXS) and ThT fluorescence, we show that disrupting the clusters via NaCl addition hinders fibril formation, highlighting their reversible and targetable nature. This behavior is analogous to polymer crystallization, in which disordered chains undergo structural ordering through intermediate precursor states. We propose that similar physical principles underlie the aggregation of other intrinsically disordered proteins such as α-synuclein.

Multiplication of the α-synuclein gene (SNCA) can cause familial Parkinson's disease (PD). In the present study, we investigated the neuropathological and biochemical profiles in the central and peripheral nervous systems of an autopsy case with SNCA duplication. The patient began to show gait disturbance and resting tremors at the age of 34. The motor symptoms of the patient responded well to levodopa therapy. However, the condition progressed to Hoehn and Yahr stage V at age 44, and the patient died of toxic shock syndrome at age 46. Post-mortem neuropathological examination revealed some common features of SNCA duplication, such as prominent neuronal loss in the substantia nigra and locus coeruleus, and widespread Lewy pathology from the brainstem to the neocortex. Marked Lewy neurites were also observed in the cornu Ammonis 2/3 region of the hippocampus; however, without apparent neuronal loss. Large Lewy bodies were frequently observed in the tuberomammillary nucleus of the hypothalamus. Additionally, Lewy pathology was frequently visible in the peripheral nervous system, including the sympathetic and dorsal root ganglia. Western blotting revealed bands, and immunoelectron microscopy analyses showed filaments typical of Lewy body disease in the central and peripheral nervous systems. These results show that duplication of the SNCA gene facilitates the formation of Lewy bodies in the central and peripheral nervous systems. These Lewy bodies show the same biochemical profiles as sporadic Lewy body disease.

Alzheimer's disease (AD) is characterized by extracellular amyloid plaques composed of amyloid-β and intracellular neurofibrillary tangles composed of aggregated tau protein. In sporadic AD, the distribution of pathological tau progresses in a stereotypical manner and correlates with clinical staging, whereas the distribution of amyloid-β plaques does not. This suggests that the spread of tau pathology is a critical process that plays a key role in neurodegeneration and disease progression. Accurate models of tau propagation are therefore necessary to develop disease-modifying drugs for AD. The prion-like propagation hypothesis is a potential mechanism for the progressive distribution of tau pathology in the brain. In 2009, it was experimentally demonstrated that the intracerebral injection of brain extracts from transgenic mice that overexpress a mutated form of human tau protein into other tau transgenic mice induced the spread of pathological tau in vivo. Since then, this approach has been widely used to model tau propagation. More recently, newer models that more closely replicate the pathology of AD have been developed. This review summarizes the latest developments in animal models of tau propagation in sporadic AD.

Nuclear factor erythroid 2-like 1 (NFE2L1/Nrf1), an endoplasmic reticulum (ER)-associated transcription factor, is responsible for the coordinated expression of proteasome subunit genes upon proteasomal dysfunction. N -glycosylated proteins undergo protein sequence editing by peptide: N -glycanase (NGLY1)-mediated conversion of N -glycosylated asparagine residues to aspartic acid. Nrf proteins are the only transcription factors that undergo sequence editing for transcriptional activation. However, the mechanism via which sequence editing regulates the transcriptional activity of Nrf1 has remained unclear. Here, we demonstrated that sequence editing of the ninth N -glycosylation site (Asn574) in human Nrf1 is required for proteasome gene expression in HeLa cells. Editing of Asn574 is essential for interaction with host cell factor C1 and O -GlcNAc transferase, which is required for Nrf1 chromatin binding and sufficient proteasome expression. Furthermore, sequence editing of N -glycosylation sites other than Asn574 is required for the interaction with the coactivator CREBBP/EP300, thereby enhancing Nrf1’s transcriptional activity. Unexpectedly, the expression of Nrf1 mutants that mimic proteolytic processing by DNA-damage-inducible 1 homolog 2 and sequence editing by NGLY1 markedly diminished the growth rate in HeLa cells, suggesting that the constitutive activation of Nrf1 exhibits cytotoxicity. Collectively, our study explains the strategy of on-demand Nrf1 activation for survival benefits. Nrf1 is synthesized as a proteasome-targeting protein and is highly glycosylated in the ER. Nrf1 is activated via sequence editing-dependent coactivator complex formation only when the proteasome needs to be compensated for.

BackgroundArgyrophilic grain disease (AGD) is a four-repeat tauopathy characterized by the accumulation of argyrophilic grains. Its primary clinical manifestation is late-onset amnestic dementia. While the extension of argyrophilic grains to the substantia nigra may be related to its potential association with parkinsonism, biochemical analyses are lacking.ObjectivesTo elucidate the extent of AGD to the midbrain, including the substantia nigra, using histopathological examination and biochemical analysis in a pathologically proven case of AGD presenting with parkinsonism and cognitive impairment.MethodsWe describe the case of a patient suggestive of progressive supranuclear palsy. Neuropathological and biochemical investigations were performed.ResultsNeurological examination of an 80-year-old man with a 6-year history of gait disturbance revealed parkinsonism, including gait freezing, postural instability, bradykinesia, and cognitive impairment. The patient was diagnosed with progressive supranuclear palsy with progressive gait freezing. Five years later, the patient reported falling backward repeatedly, became wheelchair-bound, and died of pneumonia. Macroscopic observations revealed marked amygdala atrophy. Microscopic findings revealed argyrophilic grains in the limbic system, compatible with Saito stage III, as well as in the substantia nigra and midbrain tegmentum. Western blotting showed an AGD-specific band pattern, and immunoelectron microscopy analyses showed an AGD-specific tau filament of abnormally phosphorylated tau in both the nucleus accumbens and midbrain.ConclusionsThis report further confirmed that AGD presents with parkinsonism, commensurate with AGD pathology and biochemical findings extending to the midbrain. Therefore, AGD should be considered in the differential diagnosis of cases presenting with parkinsonism and cognitive impairment in the older population.