Acta Neuropathologica Communications

Neuronal intranuclear inclusion disease (NIID) is a polyglycine disease that primarily affects the neuronal and neuromuscular systems. Here, we developed a novel transgenic mouse model that faithfully recapitulates the multisystemic impairments associated with polyG intranuclear inclusions. Our findings demonstrate that polyG expression induces neurodegeneration, behavioral deficits, and age-dependent accumulation of uN2CpolyG aggregates across multiple tissues.

BackgroundHuntingtons disease (HD) is a neurodegenerative disorder caused by an abnormal polyglutamine expansion in mutant huntingtin (mHTT) and is characterized by movement dysfunction and neuronal loss. Siglecs, a family of sialic acid-binding proteins, are expressed on brain microglia and implicated in Alzheimers disease. Sialic acids are abundant in mammalian brains and cap the termini of the glycocalyx of various brain cells. Alterations in sialoglycans or Siglecs may affect interactions between microglia and other brain cells. However, the roles of Siglecs in HD have not been investigated. MethodsWe profiled Siglecs in postmortem caudate nucleus samples from HD subjects and in a mouse model of HD (R6/2) using RT-qPCR and mass cytometry analyses. CD22 functions in microglia were evaluated using a microglial cell line (BV2) and primary microglia. Native ligands for microglial CD22 were assessed via glycomic profiling and flow cytometry. Regulation of CD22 ligands in astrocytes was investigated in an astrocytic cell line (C8-D1A) and primary astrocytes. The role of CD22 in HD was examined by genetic deletion in HD mice, followed by behavioral analyses and pathological evaluation with immunofluorescence staining and MRI. ResultsUpregulation of CD22 in microglia, observed in the brains of patients and mice with HD, impairs microglial phagocytosis via ITIM-ITAM signaling crosstalk. This CD22 upregulation was driven by chronic oxidative stress, as antioxidant treatment (N-acetylcysteine) markedly normalized CD22 levels. CD22 ligand, 2,6-sialylated-6-sulfo-LacNAc, primarily expressed by astrocytes, was significantly reduced in HD mice. mHTT, but not wild-type HTT, suppressed ligand synthesis in astrocytes under elevated oxidative stress, allowing more CD22 on the microglial surface to inhibit phagocytosis. Treatment with a neutralizing antibody or ligand-enriched extracellular vesicles depleted surface CD22 and restored the phagocytic function of microglia. Genetic deletion of CD22 in HD mice improved rotarod performance, reduced mHTT inclusion burden, increased Darpp32 expression, and alleviated brain atrophy, supporting the concept that CD22-mediated inhibition of microglial phagocytosis contributes to HD pathogenesis. ConclusionOur findings suggest that CD22 acts as a checkpoint-like regulator that restrains microglial phagocytosis and contributes to HD progression when astrocyte-microglia communication is impaired, thereby highlighting CD22 as a promising therapeutic target.

BackgroundALS is increasingly recognized as a biologically heterogeneous disease in which several molecular and pathological mechanisms converge on a similar clinical phenotype. One of these molecular markers is ferritin accumulation which is observed in a subset of ALS cases and has been shown to directly correlate with TDP-43 pathology in some brain regions. Additionally, TDP-43 proteinopathy is observed outside of ALS which may complicate the interpretation of case vs control approaches to target discovery. Here, we propose a pathology-stratified approach to empower targeted theranostics. We hypothesised that biologically distinct ALS subtypes may be defined by specific metabolic dysfunction linked to brain-accumulated ferritin and TDP-43 pathology. MethodsPost-mortem primary motor cortex tissue from 15 ALS cases and 20 age- and sex-matched controls was stratified, using immunohistochemistry, by single- or co-occurrence of ferritin accumulation, and pathological TDP-43. Untargeted metabolomics (>1,000 metabolites) was performed, and samples were stratified into dual positive (ferritin and TDP-43), single positive (either), or negative. Group-discriminating metabolites were identified using partial least squares discriminant analysis. ResultsDual ferritin and TDP-43 pathology reflected a distinct metabolomic profile, separable from single-pathology states. This dual positive metabolic signature was characterised by disruption of lysophospholipid, lysoplasmalogen, and fatty acid metabolism, consistent with impaired membrane and energy homeostasis. In contrast, pathological TDP-43 presence without ferritin, was characterised metabolically by significant depletion of secondary bile acids and increase in glycosylation markers, whilst ferritin accumulation alone reflected significant increase in oxidative stress and depletion of lipid peroxidation inhibition markers. The dual positive state suggests failure of compensatory metabolic responses present in single-pathology conditions. ConclusionsFerritin accumulation and TDP-43 pathology define biologically distinct subtypes associated with ALS with divergent metabolic vulnerabilities. The metabolic signature associated with dual pathology provides a mechanistic correlate to MRI-visible ferritin accumulated iron, supporting paired non-invasive biomarker and target discovery for pathology-dependent patient stratification. These findings argue for pathway-targeted, subtype-specific therapeutic strategies and highlight the necessity of precision medicine approaches in ALS. Short abstractAmyotrophic lateral sclerosis (ALS) exhibits profound molecular heterogeneity that is not captured by current clinical classifications. Additionally, TDP-43 proteinopathy is observed outside of ALS which may complicate the interpretation of case vs control approaches to target discovery. Here, we propose a pathology-stratified approach to therapeutic target discovery, identifying convergent iron dysregulation and TDP-43 pathology with specific metabolic consequences. Post-mortem primary motor cortex tissue from 15 ALS cases and 20 controls was investigated for ferritin, and pathological TDP-43 using RNA aptamer-based immunostaining. Untargeted metabolomics (>1,000 metabolites) was performed with stratification into dual positive, single positive, or negative groups, followed by partial least squares discriminant analysis. Dual ferritin and TDP-43 pathology produced a distinct metabolic state characterised by disruption of lysophospholipid, lysoplasmalogen, and fatty acid metabolism, indicating impaired membrane integrity and energy homeostasis. In contrast, single positive states engaged divergent compensatory pathways involving bile acid metabolism, glycosylation, or oxidative stress regulation. Ferritin-TDP-43 convergence defines a metabolically decompensated ALS subtype corresponding to MRI signatures, providing a mechanistic basis for imaging-guided, pathology-dependent patient stratification and targeted intervention. Key FindingsO_LIMetabolically distinct subtypes were defined by the presence or absence of ferritin-associated iron accumulation and TDP-43 pathology in the primary motor cortex. C_LIO_LIConcurrent ferritin and TDP-43 pathology produce a unique, metabolically decompensated state characterised by disrupted lipid, membrane, and energy metabolism, distinct from either pathology alone. C_LIO_LISingle positive states engage divergent compensatory metabolic pathways, which are lost when ferritin and TDP-43 co-occur. C_LIO_LIThe metabolic signature of dual positivity provides a mechanistic correlate to the MRI-visible motor band sign. C_LIO_LIThese findings support the use of pathology-based stratification of ALS patients and a foundation for pathway-targeted, precision therapeutic approaches. C_LI Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=115 SRC="FIGDIR/small/711539v1_ufig1.gif" ALT="Figure 1"> View larger version (32K): org.highwire.dtl.DTLVardef@69d482org.highwire.dtl.DTLVardef@1fee3a4org.highwire.dtl.DTLVardef@1135017org.highwire.dtl.DTLVardef@ef3f96_HPS_FORMAT_FIGEXP M_FIG C_FIG

AO_SCPLOWBSTRACTC_SCPLOWO_ST_ABSBackgroundC_ST_ABSTransthyretin amyloidosis (ATTR) is a progressive, degenerative disease affecting the heart and other organ systems, as well as the peripheral, autonomic, and central nervous systems. Although pharmacological and genetic evidence establishes aggregation as a driver of ATTR pathology, the mechanism by which aggregation compromises post-mitotic tissue function is poorly understood. We utilized bottom-up proteomics on wild-type (WT) human cardiac (WT/WT genotype) and V122I human cardiac (V122I/WT genotype) tissue, combined with tissue clearing technology to create an optically transparent tissue architecture to visualize three-dimensional relationships, to better understand TTR cardiomyopathy (CM). MethodsFlash-frozen 0.5 mm cardiac tissue slices from human subjects with end-stage WT-TTR CM, end-stage V122I CM, and slices from an age-matched human control were used for these experiments. Fibril extraction from diseased tissue followed published protocols. Strong denaturant-mediated proteome tissue extraction on samples from each subject facilitated bottom-up proteomics by using liquid chromatography (LC)-mass spectrometry (MS)/MS. Tissue clearing was performed on 0.5 mm cardiac slices utilizing a lauryl sulfate-based lipid removal strategy. Slices were stained using indirect immunofluorescence with antibodies to protein targets identified by proteomics. We used an antibody to non-native TTR and AmyTracker 480 (an oligothiophene dye that binds to amyloid fibrils) to image TTR deposits. ATTR fibrils were characterized structurally using cryogenic electron microscopy (cryo-EM) followed by helical reconstruction. ResultsProteomic cardiac analysis afforded high spectral counts for transthyretin (TTR) and proteins typically associated with amyloid fibrils, e.g. serum amyloid P (APCS). Fibril and cardiac homogenate proteomics revealed high levels of angiogenic and hemostatic proteins, including those composing the complement and coagulation cascades. 3D imaging revealed loss of normal microvascular architecture in CM samples with regions of hyper- and hypovascularization. Microvascular obstruction by capillary thrombosis was also observed in CM. ATTR fibrils adopted the common spearhead fold and were decorated with collagen VI (COLVI), an extracellular matrix component. ConclusionsWe hypothesize that ATTR CM is a microangiopathy driven by capillary bed thrombo-inflammation and dysregulated angiogenic revascularization. Phenotypic convergence of WT ATTR CM and V122I ATTR CM was observed via proteomics, 3D imaging, and ex vivo fibril characterization by cryo-EM. We provide evidence of capillary thrombosis in ex vivo ATTR CM tissue. Vasodilation and increased capillary permeability expose components of the vascular basement membrane (VBM) to misfolded TTR. These components are known to promote TTR aggregation and stabilize amyloid fibrils in the extracellular space. Congestion of the VBM prevents appropriate revascularization, reducing cardiac exertional capacity over time, leading to heart failure. Our ATTR CM heart tissue proteomics data shows significant overlap with the proteomic profiles of human AD brain tissues, revealing key amyloid, coagulation, complement, and angiogenesis proteins being changed in amyloidoses.

Temozolomide (TMZ) resistance remains a major obstacle in glioblastoma (GBM) therapy, yet the metabolic adaptations underlying this phenotype are incompletely understood. Here, we performed integrative lipidomic, ultrastructural, and pathway analyses to define lipid metabolic reprogramming associated with TMZ resistance and failure of statin-mediated sensitization. Targeted LC-MS lipidomics quantified 322 lipid species across 25 lipid classes in TMZ-sensitive and TMZ-resistant U251 cells under basal conditions and following TMZ, simvastatin, or combination treatment. Multivariate analyses (PCA, PLS-DA, and volcano plots) revealed a robust and treatment-resilient lipidomic signature in resistant cells characterized by enrichment of lysophospholipids, sphingolipids, and cholesteryl esters, alongside depletion of glycerolipid and phospholipid pools. Complementary univariate analysis confirmed these changes at the species level, demonstrating consistent elevation of lysophosphatidylcholine/ethanolamine, glycosphingolipid subclasses, and cholesteryl esters, together with reductions in phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, and diacylglycerol intermediates across multiple treatment conditions. In contrast, sensitive cells displayed dynamic lipid remodeling, including phosphatidylinositol and phosphatidylethanolamine enrichment associated with autophagic membrane expansion. KEGG pathway analysis linked the resistant phenotype to Rap1, PI3K-Akt, and phospholipase D signaling networks regulating vesicle trafficking and membrane homeostasis. Transmission electron microscopy confirmed a vesicle-rich intracellular architecture consistent with persistent autophagy flux blockade in resistant cells. Collectively, these findings define a stable lipid metabolic program characterized by lysophospholipid expansion and cholesteryl ester accumulation that supports membrane integrity and therapeutic resistance. Targeting lipid buffering and cholesterol storage pathways may represent a promising strategy to overcome chemoresistance in glioblastoma. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=134 HEIGHT=200 SRC="FIGDIR/small/712341v1_ufig1.gif" ALT="Figure 1"> View larger version (78K): org.highwire.dtl.DTLVardef@178acd7org.highwire.dtl.DTLVardef@19b6a79org.highwire.dtl.DTLVardef@6b3904org.highwire.dtl.DTLVardef@16c3d01_HPS_FORMAT_FIGEXP M_FIG C_FIG Lipidomic and autophagy differences between non-resistant (NR) and temozolomide-resistant (R) glioblastoma cells. NR cells show dynamic lipid remodeling and treatment-dependent autophagy responses, whereas R cells maintain blocked autophagy flux and persistent enrichment of LPC, SM, and cholesteryl esters across treatments.

BackgroundMitochondrial dysfunction is an early and central feature of Alzheimers disease (AD). In particular, intercellular mitochondrial transfer has emerged as a mechanism of neuronal support in brain injury and neurodegeneration. However, pathways governing astrocyte-to-neuron transfer and its role in AD pathogenesis remain unknown. MethodsUsing the AppNL-G-F knock-in AD model, we combined high-resolution 4D live-cell imaging with quantitative fluorescence-based reporters to assess synaptic function and mitochondrial network dynamics in neurons and astrocytes. Direct and extracellular vesicle (EV)-restricted neuron-astrocyte co-culture systems were used to investigate bidirectional mitochondrial transfer. We performed the first in-depth structural, proteomic, and functional characterization of astrocyte-derived mitochondrial extracellular vesicles (mitoEVs) using cryo-electron microscopy, quantitative mass spectrometry, and bioenergetic analyses to define their cargo composition and metabolic effects. ResultsWe identified cell-type-specific mitochondrial remodeling in early AD, with compartmentalized synaptic energy deficits in neurons and hyperdynamic, less interconnected, yet metabolically preserved networks in astrocytes, preceding global bioenergetic decline. Bidirectional mitochondrial transfer between astrocytes and neurons, also at axonal terminals, was mediated by specialized mitoEVs but significantly reduced in the AppNL-G-Fmodel. Comprehensive proteomic and functional profiling revealed that WT astrocyte-derived mitoEVs are enriched in inner membrane and matrix proteins, supporting oxidative phosphorylation, lipid and amino acid metabolism, and redox homeostasis. In contrast, AppNL-G-F mitoEVs are selectively depleted of respiratory and fatty acid oxidation components and exhibit impaired respiration with reduced Complex IV activity. Functionally, WT mitoEVs promote mobilization of abnormal accumulation of lipid droplets in AppNL-G-Fneurons, restore fatty acid oxidation, and increase neuronal bioenergetics, including at the synapses. In contrast, disease-derived mitoEVs fail to engage these pathways. ConclusionsTogether, these findings identify mitoEV-mediated mitochondrial transfer as a glia-to-neuron metabolic pathway compromised in early AD and reveal a coordinated role for oxidative phosphorylation and fatty acid oxidation in supporting synaptic energy homeostasis.

BackgroundPATZ1 fusion-positive central nervous system (CNS) tumors frequently harbor MN1::PATZ1 fusions as driver mutations, provisionally classified as a rare DNA methylation class of low-grade neuroepithelial tumors. Radiographically, they resemble pilocytic astrocytomas with tumor and cystic components, but their supratentorial cortex location and higher recurrence rates are distinguishing features. An intermediate clinical course, despite focal high-grade histopathology, underscores the need for longitudinal molecular and immune analyses to refine classification and standard therapy. Case SummaryA female pediatric patient presented with neurological symptoms, including headache and right upper extremity weakness. MRI revealed a large cystic lesion in the left frontal lobe, leading to a differential diagnosis of low-grade glioma and ependymoma. Genomic analysis identified an MN1::PATZ1 fusion. The tumor recurred after gross total resection prompting a second resection. Transcriptomic and histopathologic assessments identified multiglial lineage, and high-grade features closely related to adult glioblastoma alongside pro-inflammatory activity in the primary tumor. The recurrent tumor showed reduced malignancy, and oligodendroglioma-like features. Increased MHC gene expression, immune checkpoint receptors (PDCD1, CTLA4, TIGIT,TIM3), T cell regulators (CXCR6), and elevated macrophage frequency, coupled with reduced PD-L1 in the recurrent tumor, suggest a complex anti-tumor immune response constrained by T cell dysregulation. This case, along with two other MN1::PATZ1 fusion-positive tumors, identifies a distinct transcriptomic subtype separate from circumscribed astrocytic glioma, highlighting upregulation of growth factor receptor pathways, like PI3K/AKT, and immune dysfunction linked to recurrence. ConclusionLongitudinal multi-omics analyses of recurrent MN1::PATZ1 fusion-positive CNS tumors revealed tumor maturation, immune dysfunction, and potential therapeutic targets. Introductory ParagraphPATZ1 fusion-positive central nervous system (CNS) tumors are rare, predominantly pediatric and frequently recurrent neoplasms provisionally classified as neuroepithelial tumors. Their pronounced histopathological and clinical heterogeneity, along with limited immunological characterization complicates their treatment standardization. We report a new case of an MN1::PATZ1 fusion-positive CNS tumor with recurrence, highlighting its radiographic similarities to low-to-intermediate grade pediatric glioma. Longitudinal multi-omics analyses of this case, along with additional MN1::PATZ1 fusion-positive CNS tumors, however, delineates a transcriptome subtype resembling adult high-grade glioma, with activated oncogenic and pro-inflammatory programs. The recurrent tumor exhibits features of decreased malignancy and enhanced glial differentiation, phenotypically shifting towards oligodendroglioma, suggesting tumor maturation. This was accompanied by increased antigen presentation programs, indicating immune engagement, while increased immune checkpoint expression and microglia/macrophage frequency indicate T cell exhaustion and immunomodulation, respectively. This longitudinal study highlights potential therapeutic strategies targeting both the tumor and its immune environment in MN1::PATZ1 fusion-positive CNS tumors.

Amyotrophic Lateral Sclerosis (ALS) is a devastating neurodegenerative disorder characterized by the cytoplasmic aggregation and nuclear depletion of the TDP-43 protein. The latter impairs TDP-43 function as an RNA-binding protein and compromises the repression of cryptic splicing events, affecting both glutamatergic upper motor neurons and cholinergic lower motor neurons. This study systematically investigated the molecular and functional consequences of TDP-43 knockdown in human induced pluripotent stem cell (hiPSC)-derived glutamatergic neurons (iGNs) and cholinergic motor neurons (iMNs) using antisense oligonucleotides. The results demonstrated that TDP-43 loss elicits widespread, cell-type-specific changes in gene expression and alternative splicing. Notably, a shared subset of ALS-associated targets, including STMN2 and UNC13A, were consistently downregulated and mis-spliced across both neuronal subtypes. Functionally, Microelectrode Array (MEA) electrophysiology recordings revealed that TDP-43 knockdown induces a hyperexcitable phenotype in both neuronal populations, though they exhibited distinct network patterns: iGNs displayed synchronized bursting and significant shifts in overall electrophysiological profiles, while iMNs showed asynchronous firing. Furthermore, the inclusion of astrocytes in co-culture models expanded the repertoire of detectable cryptic splicing, including an event in HDGFL2 previously identified in patient cerebrospinal fluid. Despite these profound molecular and functional deficits, TDP-43 depletion did not impact neuronal viability or increase susceptibility to glutamate-induced excitotoxicity. These findings validate hiPSC-derived iGNs and iMNs as relevant models for ALS and highlight the critical necessity of considering cell-type specificity when elucidating pathogenesis and developing targeted therapies.

Brain cancers hijack biological systems involved in neural development and synaptic plasticity. Medulloblastoma (MB), the most common malignant brain tumor in children, is thought to arise from disruptions in neurodevelopmental programs. Glutamatergic transmission mediated by -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors (AMPARs) has been implicated in synaptic communication between adult brain tumors and surrounding neurons; however, the possible role of AMPARs in MB remains largely unexplored. Here, we analyzed the expression of genes encoding AMPAR subunits, GRIA1-4, in datasets of MB tumors, revealing distinct expression patterns and subgroup-specific associations with overall survival (OS) across molecular subgroups and histological variants. Expression of GRIA1, GRIA3, and GRIA4 was significantly lower in MB in comparison with normal cerebellar tissue. Higher GRIA1, GRIA2, and GRIA4 transcription was associated with more favorable patient outcomes in specific MB subgroups. In contrast, high expression of GRIA3 in SHH, or of either GRIA3 or GRIA4 in Group 3 MB, was associated with worse prognosis. Particularly robust but opposing associations with patient survival were found for GRIA3 and GRIA4 in SHH MB. Analysis of GRIA mRNA levels in MB cell lines representing different molecular subgroups, using data from The Human Protein Atlas, showed partial concordance with expression patterns observed in tumors. Together, these findings suggest that GRIA genes and their corresponding AMPAR subunits may have subgroup-specific prognostic relevance in MB and merit further investigation.

BackgroundAlzheimers disease (AD) is the most prevalent neurodegenerative disease, currently devoid of a cure. ADs clinical manifestations stem from a multitude of dysfunctional cellular processes, regulated by mitochondria-endoplasmic contact sites (MERCS), which undergo physical alterations and malfunction in AD brain. Despite ongoing research, the understanding of MERCS in AD remains in its nascent stages. We postulate that these subcellular interfaces are responsible for AD progression. Neuroinflammation contributes significantly to neurodegeneration and is primarily driven by microglia, the innate immune cells in the brain. In AD, activated microglia secrete pro-inflammatory cytokines that compromise neuronal vitality. The production of these cytokines is promoted by NLRP3 inflammasome. Although inflammasome activation has been observed at MERCS, the underlying MERCS-mediated mechanisms governing regulation of inflammasome activation remain to be elucidated. MethodsPrimary microglia were isolated from 3-4 months old wild-type (WT) and AppNL-G-F mice (AD). MERCS ultrastructure was analyzed by transmission electron microscopy. Mitochondrial Ca2+ level and metabolic function were assessed using Rhod-2 AM fluorescence and Seahorse extracellular flux analysis respectively. Inflammasome activation was induced by lipopolysaccharide and nigericin and evaluated by IL-1{beta} ELISA, caspase-1 activity assay, and ASC immunocytochemistry. MERCS were genetically modulated via siRNA-mediated knockdown of MERCS-associated proteins, and ER-to-mitochondria Ca{superscript 2} transfer was pharmacologically inhibited using Xestospongin C and MCU-i11. Microglial A{beta} phagocytosis was quantified using fluorescence-conjugated A{beta}1-42. ResultsAD microglia exhibited increased MERCS number and contact length, accompanied by a reduction in mitochondria-ER proximity. These structural changes were associated with elevated mitochondrial Ca2+ levels and enhanced respiratory activity, indicating metabolic reprogramming and functional change. Structural and functional decrease of microglial MERCS attenuated NLRP3 inflammasome activation and restored inflammasome-associated impairments in A{beta} phagocytosis. Pharmacological inhibition of Ca2+ channels at MERCS identified ER-to-mitochondria Ca2+transfer as a key regulatory mechanism for inflammasome activation. ConclusionsOur findings identify microglial MERCS remodeling as an early event in AD and establish ER-mitochondria coupling as an upstream regulator of energy metabolism, inflammation, and A{beta} clearance. Targeting MERCS may therefore represent a promising strategy to modulate neuroinflammation while preserving essential microglial functions in AD.

Therapeutic development in Alzheimers Disease (AD) has for the most part been focused on reducing {beta}-amyloid load. Nevertheless, neurofibrillary tangles (NFTs), produced by aggregation of hyper-phosphorylated Tau protein, correlate with neurodegeneration and cognitive impairment significantly better than amyloid accumulation in AD patients. Here we report that P301S mice, a model of AD tauopathy, carrying mutant variants of the p75 neurotrophin receptor (p75NTR) deficient in RhoA/ROCK signaling are protected from neurodegeneration and cognitive impairment. Both p75{Delta}DD, lacking the death domain, and triple mutant p75KKEA, unable to interact with RhoGDI, decreased NFT levels, reduced gliosis, neurodegeneration and synapse loss, and improved spatial learning and memory in P301S mice. Intriguingly, p75C259A, a variant unresponsive to neurotrophins but still competent for RhoA signaling induced by myelin-derived ligands, did not afford any neuroprotection. P301S neurons expressing p75{Delta}DD or p75KKEA, but not p75C259A, showed reduced phospho-Tau and ROCK and GSK3{beta} activity, the two main kinases responsible for Tau phosphorylation. In line with this, treatment with myelin-associated glycoprotein (MAG) enhanced Tau phosphorylation and ROCK activity in P301S neurons expressing wild type p75NTR or p75C259A, but not p75{Delta}DD or p75KKEA. Together, these results indicate that p75NTR contributes to AD tauopathy by enhancing the activity of the RhoA-ROCK pathway.

BackgroundGroup 3 (MYC-driven) medulloblastoma (MB) is a highly aggressive brain tumor with poor-prognosis and limited treatment options. We previously identified protein-arginine methyltransferase-5 (PRMT5) as a promising target in Group 3 MB with its control on MYC protein stability. In this follow up study, we further mechanistically investigated PRMT5 control on MYC transcription and targeted it pharmacologically for therapeutic proof-of-concept. MethodsUsing pharmacogenetic inhibition approaches against PRMT5 in MYC-amplified (Group 3) MB cell line and neurosphere models in vitro and in vivo, we investigated molecular mechanism(s) and anti-cancer efficacy of PRMT5 inhibition. ResultsOur experiments demonstrated that PRMT5 epigenetically regulates MYC transcription in MYC-amplified MB cells by binding to the proximal-promoter region of the MYC gene and contributing to the enriched symmetric-dimethylation of histone H4R3 in the same region. We further showed that PRMT5 is recruited to the MYC promoter by its interaction with BRD4, the major BET-protein responsible for MYC transcription. PRMT5 inhibition caused the suppression of MYC-induced transcriptional programs and target genes, with widespread disruption of splicing across the transcriptome, particularly affecting metabolism-related gene products. Pharmacologic inhibition of PRMT5 using a panel of selective small-molecule inhibitors demonstrates suppression of cell growth/survival in a MYC-dependent manner in MB cells. Moreover, our in vivo analyses of PRMT5 inhibition, in mice treated with one of the potent pharmacologic inhibitors, particularly a lipid-decorated form of it, demonstrated reduced cerebellar tumor growth with suppressed MYC expression and prolonged survival of mice with MYC-amplified MB xenografts. ConclusionsOur findings establish a functional link between PRMT5 and MYC-mediated transcriptional regulation, suggesting a promising therapeutic approach targeting the PRMT5-MYC axis for MYC-driven MB. Key PointsO_LIPRMT5 acts as an epigenetic regulator of MYC transcription, RNA splicing and associated energy metabolism in MYC-driven MB. C_LIO_LIPRMT5 inhibition selectively suppresses cell growth/survival in MYC-driven MB. C_LIO_LIPRMT5 inhibition reduces tumor burden and prolongs survival in a MYC-driven MB mouse model. C_LI Importance of the StudyGroup 3 medulloblastoma is a highly aggressive pediatric brain tumor marked by MYC amplification, malignant clinical behavior, and poor survival outcomes despite intensive multimodal therapy. Because MYC remains largely undruggable, there is an urgent need for effective and less toxic treatment options for affected children. This study identifies protein arginine methyltransferase 5 (PRMT5) as a key epigenetic regulator of MYC transcription and MYC-dependent oncogenic programs in Group 3 MB. We show that PRMT5 is recruited to the MYC promoter via BRD4, sustains MYC-driven transcription and RNA splicing networks associated with metabolism, and supports MB tumor growth. Importantly, pharmacologic inhibition of PRMT5 using a selective brain-penetrant inhibitor suppresses MYC expression, reduces cerebellar tumor burden, and prolongs survival in MYC-amplified MB models. These findings provide a strong translational rationale for PRMT5 inhibition as a targeted therapeutic strategy for high-risk MB, with the potential to improve outcomes while reducing treatment-related toxicity.

SummaryFrontotemporal dementia (FTD), a leading cause of young-onset dementia, is characterized by progressive behavioral and cognitive decline associated with frontotemporal cortical atrophy. Nearly 40% of cases exhibit tauopathy, yet the molecular drivers of tau aggregation leading to synaptic dysfunction remain poorly understood. Here, we investigated whether Phospholipase D1 (PLD1, a lipid signaling enzyme), implicated in Alzheimers disease (AD), and amyotrophic lateral sclerosis (ALS), contributes to tau pathology dependent synaptic deficits in FTD. Postmortem temporal (BA38) and frontal (BA9) cortices from clinically diagnosed FTD and age-matched control subjects were analyzed using fluorescence-assisted single synaptosome long-term potentiation (FASS-LTP), immunofluorescence, proximity ligation assays (PLA), and PLD1-interactome proteomics. FASS-LTP revealed markedly reduced glutamatergic potentiation in BA38 and BA9 crude synaptoneurosomes from FTD brains compared to controls. Western blotting demonstrated elevated PLD1 expression in both crude synaptoneurosomal and cytosolic fractions from FTD subjects in BA38, but not BA9. Bielschowsky staining confirmed increased Pick body burden in FTD temporal cortex. Immunofluorescence and PLA showed robust PLD1 co-localization with total tau (HT7), hyperphosphorylated tau (AT8), and acetylated tau oligomers (TOMA2), indicating a strong spatial association between PLD1 and pathological tau species. PLD1 also exhibited enhanced co-localization with astrocytic GFAP and synaptic markers (PSD95, Nrx1{beta}), suggesting compartmentalized involvement in glial and synaptic remodeling. Proteomic profiling of PLD1-associated complexes revealed compartment-specific alterations with cytosolic fractions enriched for metabolic enzymes, stress-response proteins, and GFAP, while crude synaptoneurosomal fractions showed depletion of presynaptic scaffolds, vesicle-trafficking regulators, and proteostasis components. Cross-compartment integration indicated that over one-third of proteins were redistributed from synapses to cytosol, consistent with trafficking and degradative impairments. Gene Ontology analysis highlighted lipid metabolism, astrocyte activation, and proteasome dysfunction as dominant pathways. Collectively, these findings identify PLD1 as a critical mediator of synaptic dysfunction and tau pathology in FTD, acting through astroglial activation and disrupting synaptic proteostasis. This study provides the human clinical relevance towards PLD1 attenuation as a therapeutic target for FTD and related tauopathies to mitigate tau-driven neurodegeneration and restore synaptic integrity.

Amyloid-related imaging abnormality (ARIA) is the most common adverse event associated with amyloid-beta (A{beta}) immunotherapy. The neuropathology underlying active ARIA lesions has been studied in only a few rare fatal cases. A faithful translational model of ARIA should allow a better understanding of pathogenic mechanisms and enable development of mitigation strategies. Since bapineuzumab induced the most frequent and severe forms of ARIA in humans, we assessed the ability of its murine precursor, 3D6, to induce ARIA-like lesions by applying clinically-validated MRI sequences in a mouse model with extensive amyloid deposition. Using this paradigm we documented ARIA-like changes based on their imaging features, location, and temporal evolution and established postmortem histopathologic correlates. We observed that ARIA-like lesions were ubiquitously induced with 3D6, including T2-hyperintense leptomeningeal effusions, T2-hyperintense parenchymal lesions and T2* hypointense parenchymal lesions. Histological assays demonstrated meningovascular inflammation as well as vascular mural permeation and microvascular lesions, including microhemorrhages and microinfarcts. Compared to 3D6-treated mice, animals treated with mouse analogues of aducanumab and gantenerumab showed less frequent radiologic and histopathologic ARIA-like lesions with delayed onset. Our results align well with the differential incidence of ARIA observed in humans treated with different anti-A{beta} antibodies. Collectively, our studies demonstrate that: i) anti-A{beta} antibodies chronically administered to 5xFAD mice can induce MRI lesions reminiscent of human ARIA; ii) this paradigm allows identification of transient lesions other than microhemorrhages, and (iii) the incidence and severity of ARIA-like lesions induced with three clinically tested antibodies faithfully recapitulates that seen in humans. One Sentence SummaryMRI and histological correlation in a preclinical ARIA mouse model treated with anti-A{beta} antibodies that recapitulates results seen in humans.

Spinal muscular atrophy (SMA) is characterized by motor neuron degeneration caused by deficiency of the survival motor neuron (SMN) protein. However, evidence increasingly supports broader systemic involvement. This study aimed to examine cardiac pathology in SMA patients and to investigate how reduced SMN levels impact cardiomyocyte homeostasis. We analyzed postmortem data from 14 SMA type I patients from the pre-treatment era, integrating gross anatomical, histopathological, and clinical findings. To investigate cardiomyocyte-intrinsic effects of SMN deficiency, healthy human cardiomyocytes were subjected to SMN knockdown and assessed using metabolic assays and transcriptomic profiling. Key findings were further investigated in vivo using the Smn2B/- mouse model of SMA. We found heterogeneous cardiac involvement in SMA patients, including cardiomegaly, variable fat deposition and interstitial fibrosis. SMN knockdown in human cardiomyocytes induced a metabolic shift and widespread transcriptional dysregulation, with pathway analyses identifying selective upregulation of PTEN signaling. Elevated PTEN protein levels were observed in a subset of human SMA hearts and in early postnatal hearts of Smn2B/- mice. Our results demonstrate that the heart remains a biologically relevant target of SMN deficiency and highlights cardiomyocyte-specific metabolic and PTEN signaling alterations as potential contributors to cardiac involvement in SMA.

Frontotemporal lobar degeneration with tau inclusions (FTLD-tau) comprise a class of fatal heterogeneous neurodegenerative diseases. Approximately 10% arise from pathogenic MAPT mutations and often cause severe, early-onset disease with pathology that is distinct yet partially overlapping with sporadic cases. Here, we evaluated post-mortem tissue from a patient with FTLD-tau due to MAPT S305I showing neuropathology most consistent with argyrophilic grain disease (AGD), a prevalent limbic tauopathy of aging. Structures determined by cryo-electron microscopy reveal tau filament folds that differ from those found in sporadic AGD or other tauopathies and feature a 4-layer architecture stabilized by the Ile substitution within its core. Comparative structural analysis reveals conserved motifs are shared among AGD, corticobasal degeneration, and MAPT P301T. A well-defined density stacks along a cationic cleft, indicative of a bound RNA-like polyanion or small-molecule. In vitro analysis shows the S305I mutation promotes fibrilization relative to normal tau. These results demonstrate that MAPT S305I stabilizes a distinct aggregation-prone tau fold that likely contributes to disease pathology and heterogeneity beyond its known splicing defects, and underscore potential limitations of using the most pathologically similar genetic form as a model for sporadic FTLD-tau.

A prominent radiological manifestation of cerebral amyloid angiopathy (CAA) is enlargement of perivascular spaces (EPVS), which is suggested to result from fluid stagnation due to impaired perivascular clearance. Here, we report a novel observation of hypointense rims in cerebral white matter surrounding EPVS near haemorrhages on in vivo 7T Gradient Echo MRI. We hypothesised that the observed black rim pattern denotes iron accumulation that may be caused by incomplete clearance following bleeding. We investigated the occurrence and localisation of this marker on in vivo and ex vivo MRI and examined its histopathological correlates. From MRI data of the prospective longitudinal natural history study of hereditary Dutch-type CAA (D-CAA) at Leiden University Medical Centre, we selected the first 20 consecutive patients who underwent 7T imaging and assessed the presence of black rims on MRI. Post-mortem material was available from one donor with black rims on in vivo scans. Formalin-fixed coronal brain slabs were scanned at 7T MRI, including a high-resolution T2*-weighted sequence. Guided by ex vivo MRI, tissue blocks from representative areas with black rims were sampled for histopathological analysis. Serial sections were stained for iron, calcium, myelin, and general tissue morphology. On in vivo 7T MRI, 9 out of 20 participants exhibited one or several black rims, all located close to a haemorrhage. In the D-CAA donor, ex vivo MRI signal loss matched the in vivo contrast changes. Thirty-six vessels with ex vivo-observed black rims were retrieved and histopathologically examined, showing iron accumulation surrounding perivascular spaces, but the pattern and severity of iron deposition varied. Across groups, vessels displayed microvascular degeneration, including hyaline vessel wall thickening, adventitial fibrosis, and perivascular inflammation. We identified black rims on in vivo 7T MRI and confirmed their correspondence on ex vivo imaging. Iron deposition was determined as the underlying correlate of black rims, but the histopathology appears heterogeneous. The preferential deposition of iron around EPVS may indicate incomplete clearance of iron-positive blood-breakdown products after bleeding. The varied pattern of iron accumulation and microvascular alterations may reflect different pathophysiological mechanisms related to the formation and maintenance of black rims in D-CAA.

Alzheimers disease (AD) is a neurodegenerative disorder characterised by progressive dementia, brain atrophy, and ultimately death. Using cerebral organoids derived from human induced pluripotent stem cells (hiPSCs) carrying the familial PSEN1 A246E variant, we investigated the temporal relationship between amyloid-{beta} (A{beta}) dysregulation and spontaneous neuronal activity. Multielectrode array recordings from the differentiation day 60 (DD60) to at least DD130 revealed that AD organoids exhibited transient hyperexcitability and hypersynchrony compared with wild-type (WT) controls, followed by a gradual decline in activity. During the enhanced excitability stage, both elevated A{beta}42/40 and A{beta} aggregate size showed positive correlations with the percentage of active electrodes and the global synchrony index (GSI) in AD organoids. These findings indicate that A{beta} dysregulation might contribute to transient network hyperexcitability in early AD. The results also suggest that patient-derived cerebral organoids may serve as a translational model to examine early network dysfunction and inform future investigations of potential A{beta}-induced changes in excitability during the preclinical stages of AD.

Multiple system atrophy (MSA) is a sporadic progressive neurodegenerative disorder characterised by central nervous system alpha-synuclein inclusions. MSA pathologically most commonly shows a spectrum of two patterns, olivopontocerebellar atrophy and striatonigral degeneration, with significant overlap. Although germline variants are unlikely to play a major role, an association with the KCTD7 gene was recently reported. Somatic mutations are abundant in the brain, and may play a role in neurodegeneration. In MSA, somatic SNCA (alpha-synuclein) copy number gains occur, but single nucleotide mutations have not been investigated. In Alzheimers disease, somatic mutations in tumour suppressor genes were reported in microglia. We hypothesised that brain somatic mutations in SNCA, KCTD7, or the tumour suppressor genes mutated in Alzheimers, may contribute to MSA. To test this, we developed a targeted duplex sequencing pipeline using unique molecular identifiers, encompassing SNCA, KCTD7, and 10 tumour suppressor genes. Seven of these are involved in clonal haematopoiesis, an age-related process which predisposes to haematological malignancy, and can be subdivided into myeloid and lymphoid, based on the cell type affected, with the former much more frequent. We analysed DNA from the cerebellum, cingulate cortex, and putamen of 20 MSA cases (10 olivopontocerebellar atrophy, 10 striatonigral degeneration) and 9 controls. We observed an enrichment of clonal haematopoiesis gene mutations in MSA brains (median 1 vs 0, p=0.054). These included mutations in DNMT3A and TET2, the most frequently affected myeloid clonal haematopoiesis genes, and a recurrent mutation in three cases in KMT2D, a lymphoid clonal haematopoiesis gene. Clonal haematopoiesis mutations were often found in multiple brain regions, and multiregional mutations occurred in 12/20 MSA cases versus 1/9 controls (p=0.020), with 11 cases harbouring clonal haematopoiesis mutations in all three brain regions, compared to 0/9 controls (p=0.005). In striatonigral degeneration, clonal haematopoiesis mutations showed elevated variant allele fractions in the most pathologically affected region, the putamen, versus the cerebellum (p=0.013). MSA clonal haematopoiesis mutations included eight unique non-synonymous variants, which had higher allelic fractions than synonymous changes (p=0.076), and five of these were predicted to confer a proliferative advantage and were found in multiple brain regions. We detected no coding SNCA mutations, and the small number of KCTD7 variants, including one coding deletion, precludes any conclusions. These findings reveal enrichment of clonal haematopoiesis mutations in MSA brain, potentially due to infiltration from the periphery, suggesting a disease-associated proliferative process extending beyond peripheral haematopoiesis.

BackgroundPeri-synaptic astrocyte processes (PAPs) play a fundamental role in synapse formation and function. Central afferent synapse loss and astrocyte dysfunction greatly impede sensory-motor circuitry in spinal muscular atrophy (SMA) disease progression, however mechanisms underpinning tripartite synapse dysfunction remains to be fully elucidated. The aims of this study were to further define PAP and motor neuron synaptic defects in human SMA disease pathology and implement a therapeutic intervention strategy to improve motor neuron function. MethodsWe derived astrocyte monocultures and motor neuron astrocyte co-cultures from healthy and SMA patient induced pluripotent stem cell (iPSC) lines to assess intrinsic astrocyte filopodia defects and phenotypes occurring at the synapse-PAP interface, respectively, using cell surface capture mass spectrometry proteomics, confocal and super resolution microscopy, synaptogliosome isolation, and electrophysiology. ResultsSMA astrocytes demonstrated intrinsic filopodia actin defects featuring low abundance of actin-associated cell surface N-glycoproteins, and decreased filopodia density and CDC42-GTP levels after actin remodeling stimulation. This phenotype is likely driven by the significant reduction of CD44 and phosphorylated ezrin, radixin and moesin ERM proteins (pERM) within SMA astrocyte filopodia. The dual combination of SMN1 gene therapy and forskolin treatment, an adenylyl cyclase activator leading to increased cyclic adenosine monophosphate (cAMP) levels and actin signaling pathway stimulation, led to extensive branching and increased filopodia density of SMA astrocytes during actin remodeling. SMA patient-derived motor neuron and astrocyte co-cultures, particularly samples derived from male patient iPSC lines, demonstrated a significant decrease in synapse number, actin-associated pre-synaptic neurotransmitter release protein, synapsin I (SYN1), and PAP-associated expression of pERM and glutamate transporter, EAAT1. Our astrocyte-targeted SMN1 augmentation and forskolin treatment paradigm restored SYN1 protein levels within the SMA synaptogliosome, resulting in significant increases in motor neuron synapse formation and function, but did not fully restore PAP-associated proteins levels at the synapse. ConclusionsSMA astrocytes demonstrate intrinsic actin-associated defects within filopodia, which correlates with decreased pERM levels at tripartite motor neuron synapses. We also define a SMN- and cAMP-targeted treatment paradigm that significantly increases pre-synaptic neurotransmitter release protein levels to improved SMA motor neuron synapse formation and function. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=117 SRC="FIGDIR/small/714618v1_ufig1.gif" ALT="Figure 1"> View larger version (44K): org.highwire.dtl.DTLVardef@1257ab8org.highwire.dtl.DTLVardef@19c0010org.highwire.dtl.DTLVardef@c84552org.highwire.dtl.DTLVardef@3f1e62_HPS_FORMAT_FIGEXP M_FIG C_FIG