Molecular Neurodegeneration

Tau pathology is a central driver of neurodegeneration, yet the molecular mechanisms linking tau accumulation to neuroinflammation, metabolic failure, and white matter degeneration remain incompletely understood. Galectin-3 (Gal3) is an inflammation-associated lectin expressed by activated microglia and has been implicated in neurodegenerative disease progression. Here, we investigated whether Gal3 modulates tau-driven pathology across cellular, molecular, and systems levels. Using the P301S tauopathy mouse model with genetic deletion of Gal3, we show that Gal3 loss robustly attenuates tau pathology across vulnerable brain regions, including cortex, hippocampus, and piriform-entorhinal cortex. Gal3 deletion reduced hyperphosphorylated and pathological tau species, normalized tau kinase signaling, and restored mitochondrial and vesicular trafficking pathways disrupted by tau accumulation. Proteomic and phosphoproteomic analyses revealed widespread normalization of tau-associated immune, metabolic, and trafficking pathways, with Tau-Gal3KO mice clustering closely with wild-type controls. In parallel, Gal3 deletion markedly reduced microglial activation and Gal3-positive inflammatory signatures, preserved white matter integrity, prevented axonal degeneration, and normalized oligodendrocyte and myelin abnormalities. Functionally, Gal3 deficiency enhanced microglial myelin phagocytosis and lysosomal degradation both in vitro and in vivo, suggesting improved clearance of myelin debris under inflammatory stress. Cell-type-specific analyses further revealed restoration of mitochondrial complex I subunit expression in both excitatory neurons and parvalbumin-positive interneurons. Importantly, translational studies in human iPSC-derived neurons demonstrated that extracellular Gal3 exacerbates tau hyperphosphorylation and aggregation following tau seeding, effects that were reversed by pharmacological Gal3 inhibition. Together, these findings identify Galectin-3 as a central upstream regulator linking tau pathology to neuroinflammation, proteomic dysregulation, mitochondrial dysfunction, and white matter degeneration. Targeting Gal3 represents a promising therapeutic strategy to mitigate tau-driven neurodegenerative processes.

Parkinsons disease (PD) is characterized by progressive degeneration of nigrostriatal dopamine neurons and synucleinopathy, which is the accumulation of aggregated -synuclein (-syn). Increasing evidence implicates -syn-associated neuroinflammation as a contributor to PD pathogenesis; however, immune mechanisms linking synucleinopathy to neurodegeneration remain incompletely defined. Activation of the complement cascade occurs in PD and other neurodegenerative disorders, but most studies report complement activation after overt neurodegeneration, making it difficult to conclude if complement is directly activated by pathological -syn or secondarily following neurodegeneration. We used the rat -syn preformed fibril (PFF) mode, in vitro complement assays and human postmortem PD tissue to test whether pathological -syn directly activates complement prior to overt neurodegeneration. The -syn PFF model exhibits a protracted pathological time course and distinct temporal separation between peak -syn aggregation and nigrostriatal degeneration; thus we quantified complement expression, activation, and regulation during the aggregation phase. Synucleinopathy induced complement activation prior to nigrostriatal degeneration, including upregulation of components of both the classical (C1qa, C1r, C4b) and alternative (Cfd, Cfb) pathways, the anaphylatoxin (C3aR, C5aR) and phagocytic (CR3) complement receptors, and activation of complement C3. During early synucleinopathy, microglia upregulated C3 which significantly correlated with synucleinopathy burden across several brain regions, including the substantia nigra pars compacta (SNc) and cortex. Concurrently, complement regulatory proteins, including CD55, CD59, neuronal pentraxin-1 (Nptx1), and the neuronal pentraxin receptor were downregulated in the synucleinopathy-affected SNc. Importantly, increased levels of C1q and iC3b along with downregulation of CD55 and NPTX1 were also observed in human postmortem PD SNc, supporting the translational relevance of our findings. Mechanistically, we demonstrate that aggregated, but not monomeric, -syn directly binds C1q and activates the complement cascade in a C1q-dpendent manner. These data provide the first in vivo evidence that synucleinopathy triggers complement activation and dysregulation prior to neurodegeneration.

Alzheimers disease (AD) is characterized not only by tau and amyloid-{beta} aggregation but also by systemic disruptions in circadian rhythms, metabolism, and gut-brain communication that exacerbate neuroinflammation and neurodegeneration. While glial cells play central roles in inflammatory signaling and proteostasis, the contribution of the gut microbiome to glia-driven AD pathology remains poorly understood. Here, we used Drosophila models with glial-specific expressions of human tau and amyloid-associated transgenes to investigate how microbiome integrity influences disease progression. AD models exhibited significant shifts in gut microbial composition, particularly in Lactobacillus and Acetobacter species, suggesting an adaptive microbial response to pathological stress. Strikingly, microbiome depletion (axenic condition) markedly worsened behavioral and physiological outcomes, including disrupted sleep-circadian rhythms, impaired memory, and reduced locomotor function. These deficits were accompanied by amplified neuroinflammatory signaling (Upd-Dome-Hop-Stat92e axis), increased apoptotic gene expression, lipid dysregulation, and altered synaptic markers. Moreover, microbiome loss induced energy stress marked by elevated phospho-AMPK (p-AMPK), yet failed to restore proteostasis, as evidenced by accumulation of ubiquitinated proteins and the autophagy adaptor Ref2p, indicating impaired autophagic flux. This dysfunction correlated with increased tau, phospho-tau, and A{beta}42 accumulation. Together, our findings demonstrate that microbiome depletion exacerbates glial-mediated inflammation, disrupts circadian and metabolic homeostasis, impairs, and accelerates cognitive and motor decline. This work highlights a previously underappreciated role of the gut microbiome in restraining glial dysfunction and mitigating AD-like pathology, positioning microbial homeostasis as a critical modulator of neurodegenerative disease progression.

MicroRNAs (miRNA), are non-coding RNA that act as post-transcriptional regulators of gene expression in various organs including the brain where they play an important role in neurodegeneration. Circular RNAs are single-stranded, covalently closed loop RNA molecules recognized as upstream regulators of miRNA. Previous studies have shown that circRNAs are dysregulated in Alzheimers and other neurodegenerative diseases. However, a systematic, age-and region-specific circRNA atlas in primary tauopathy is lacking. To this end, we performed comprehensive circRNA sequencing of hippocampal and cortical tissues from a model of human tauopathy, h-Tau mice, at 3, 6, and 12 months of age. We identified circRNA-miRNA sponging networks that target and regulate key tau disease-associated pathways, including kinases, phosphatases, histone deacetylase, glutamatergic and GABAergic synapse, and microglial efferocytosis. Our study demonstrates an age- and region-specific circRNA landscape in the brain of a model of human tauopathy and identify candidate circRNA-miRNA-mRNA regulatory axes converging on core tau pathological processes. These findings support the novel hypothesis that specific circRNAs have the potential to be used as biomarkers and therapeutic targets against tau-driven neurodegeneration.

Tauopathies, including Alzheimers disease, involve progressive neurodegeneration and sustained neuroinflammation. We present a multi-compartment transcriptomic atlas of 9.6-month-old PS19 tauopathy mice compared with wild-type (WT) controls (n=8/group), profiling cortical mRNA, cortical non-coding RNA (ncRNA), and plasma small extracellular vesicle (pEV) ncRNA. In the PS19 cortex, mRNA sequencing identified 917 differentially expressed genes (DEGs), with microglial deconvolution revealing a robust transition toward disease-associated microglia (DAM) gene signature and downregulation of genes involved in oxidative phosphorylation and cholesterol biosynthesis relative to WT. Cortical ncRNA profiling identified 466 differentially expressed ncRNAs, primarily circular RNAs (circRNAs; n=331). In pEVs, 822 ncRNAs were differentially abundant, of which 657 circRNAs were identified in PS19 compared to WT mice. Cross-compartment integration demonstrated that pEV miRNA gene targets functionally mirrored genes involved in the brains inflammatory and metabolic failure. We identified a core shared signature of 33 ncRNAs, including miR-5114 (up in brain, down in pEV), circ_0008242 and circ_0002153 (up in brain and pEV), and circ_0007688 (down in brain and pEV) differentially enriched across both brain and periphery in PS19 compared to WT mice. These results demonstrate that the pEV non-coding landscape effectively tracks central tau-mediated changes in the brain transcriptional response. This study identifies circRNAs as the most numerically perturbed ncRNA class and provides a foundation for non-invasive biomarker development in tauopathy.

BackgroundPhospholipase C gamma-2 (PLC{gamma}2) catalyzes the hydrolysis of the membrane phosphatidylinositol-4,5-bisphosphate (PIP2) to form diacylglycerol (DAG) and inositol trisphosphate (IP3), feeding into diverse downstream signaling pathways. PLCG2 polymorphisms have been associated with reduced and/or increased risk of Alzheimers disease (AD) and related dementias, longevity, autoinflammation, and immune disorders. In the brain, PLC{gamma}2 is expressed in microglia, and other neuroimmune and vascular interface populations, yet its role in brain homeostasis remains incompletely defined. MethodsWe analyzed the brains of three-month-old Plcg2 wild-type (WT), heterozygous (Het KO) and homozygous knockout (Homo KO) littermate mice modeling human PLCG2 loss-of-function risk alleles linked to AD risk using a multiomic approach that included lipidomics, metabolomics, proteomics, and transcriptomics, together with immunofluorescence, as well as flow-cytometric profiling of peripheral and brain-draining immune compartments. ResultsPlcg2 deficiency substantially impaired early survival and produced splenomegaly without increasing total spleen cellularity, instead shifting spleen composition toward myeloid/innate-enriched cells and away from B cells, with expansion of age-associated B-cell (ABC-like) subsets and parallel reductions in CD4 and CD8 regulatory T cells in spleen and cervical lymph nodes. Brain lipidomics revealed selective depletion of PIP2, despite very low bulk PLC{gamma}2 protein abundance relative to other PLC family members. PLC{gamma}2 loss led to significant reductions in myelin-enriched lipid classes and myelin/paranode-associated proteins, accompanied by compensatory upregulation of oligodendrocyte/myelin genes, and modest shifts in microglial, lysosomal, complement, and oxidative metabolism pathways by NanoString and DIA-MS. Targeted acylcarnitine profiling demonstrated reprogramming of brain oxidative metabolism, with increased short-, medium-, and long-chain acylcarnitines and enrichment of mitochondrial matrix fatty-acid and amino-acid catabolic enzymes in Homo KO brains. ConclusionsLoss of PLC{gamma}2 installs a coordinated program that compromises systemic immune tolerance and subtly erodes central myelin and phosphoinositide homeostasis while enhancing brain oxidative metabolism, effects that extend beyond microglial phagocytic signaling and may underlie increased vulnerability to AD pathology and aging, providing a mechanistic framework for how PLCG2 variation may link systemic immune regulation, white-matter integrity, and neurodegenerative risk. LimitationsBecause constitutive Plcg2 Homo KO mice display high early mortality and intestinal vascular abnormalities, observed phenotypes may reflect developmental compensation and may not fully recapitulate protective human PLCG2 variants.

Parkinson's disease (PD) exhibits pronounced sex differences, yet the underlying genetic and molecular mechanisms remain poorly understood. We performed the largest-to-date meta-analysis of sex-stratified genome-wide association studies of PD followed by brain proteogenomics-based causal inference analyses. We nominated 10 candidate proteins that appear important to sex-biased PD risk, of which 2 female-biased, GALC and PSMG1, and 3 male-biased, ACTR1B, WDR41, and CD151, were most robustly prioritized. Together, our findings provide evidence for genetic sex differences in PD, prioritizing sex-biased proteins implicated in lysosomal regulation, neuroinflammation, lipid biology, and other PD-relevant mechanisms, and highlighting potential sex-informed therapeutic opportunities.

Tau is a microtubule-associated protein with diverse roles in the healthy brain but contributes to neurodegenerative disorders when dysregulated. Although tau ablation has shown protective effects in several disease models, how its absence confers this protection remain unclear. Here, we performed and analyzed single-nucleus RNA sequencing on cortices of aged tau knockout (Mapt-/-) mice in a wild type background as well as in a vascular amyloid model to evaluate the effect on disease context. Comparisons in a wild type setting revealed that tau ablation induced compensatory remodeling across multiple cell types. Excitatory neurons expanded into a distinct subtype with unique glutamatergic signaling, astrocytes adopted synaptoprotective states, oligodendrocytes upregulated genes supporting connectivity and plasticity, and microglia engaged structural remodeling programs. In contrast, in disease, tau removal not only restored functions disrupted by vascular amyloid pathology, but also generated new phenotypes. Excitatory neurons rewired receptor and postsynaptic signaling, astrocytes and oligodendrocytes recovered wild-type-like gene programs related to neurotransmitter cycling, synaptic support, and myelin integrity, and microglia reprogrammed toward sensing and mounting responses. Together, these findings demonstrate that tau ablation reshapes brain cellular programs in a context-dependent manner, exerting adaptive responses in the otherwise healthy brain while restoring homeostatic functions under vascular amyloid pathology. These results position tau as a key regulator of neuronal-glial network balance and highlight the importance of understanding how tau influences distinct cellular programs within specific disease environments.

Frontotemporal lobar degeneration (FTLD) and Alzheimers disease (AD) differ in their clinical features and genetic etiologies but share progressive cognitive decline. Emerging evidence implicates lipid dysregulation in neurodegeneration, but its extent across FTLD subtypes and how it compares to AD are unclear. Here, we performed integrated lipidomic and proteomic analyses of matched frontal (disease-vulnerable) and occipital (relatively spared) post-mortem cortices from individuals with genetic and sporadic FTLD-TDP, FTLD-tau (Picks disease, PiD), AD, and controls. FTLD and AD exhibited convergent lipid alterations, including reduced levels of cardiolipins and phosphatidylethanolamines, alongside increased gangliosides, diacylglycerols, cholesterol esters, acylcarnitines, and coenzyme Q, with generally greater changes in FTLD frontal cortex. FTLD displayed additional alterations, including reductions in bis(monoacylglycerol)phosphate, ceramides, phosphatidylserines, phosphatidylinositols, and sulfatides. These lipid changes were accompanied by proteomic alterations involving lysosomal proteins, phospholipases, phospholipid remodeling enzymes, and fatty acid oxidation pathways. Although lipidomic and proteomic signatures were broadly shared across FTLD subtypes, GRN associated FTLD-TDP and PiD showed the most extensive alterations. Triglycerides were selectively reduced in PiD in association with decreased DGAT1 expression, whereas cholesterol esters were elevated across all subtypes except C9orf72 associated FTLD-TDP. These findings identify shared disruptions in lipid homeostasis and lysosomal lipid metabolism across FTLD and AD, highlighting convergent metabolic pathways underlying neurodegeneration.

The neuropathology of Parkinson's disease is characterized by -synuclein (-syn) aggregation and dopaminergic (DAergic) neurodegeneration. While neuronal loss in C. elegans -syn-induced neurodegeneration models is temporally age-dependent, prior research indicates it is uncoupled from the organismal aging process. Here we examined transgenic C. elegans expressing human A53T -syn in DAergic neurons to determine the impact of localized DA metabolism on both neurodegeneration and organismal lifespan. Increasing endogenous DA levels through overexpression of tyrosine hydroxylase (CAT-2) exacerbated A53T-induced DAergic degeneration, whereas DA depletion via{Delta} cat-2 mutation rescued neuronal survival. By mutating a DA interaction motif within -syn, neurodegeneration was rendered insensitive to DA manipulation, thus confirming a structural basis for in vivo toxicity. We identified a DA--syn interaction that acts as a common upstream bridge whereby localized stress induces physiological responses in C. elegans. Genetically, this biochemical interaction acts as a pleiotropic trigger driving two compartmentalized responses: localized DAergic neurodegeneration via oxidative stress, and organism-wide, TFEB/hlh-30-dependent proteostatic remodeling that extends lifespan. Modulating autophagy, without exacerbating DA-mediated oxidative stress, represents a promising strategy to preserve adaptive systemic remodeling while limiting targeted neuronal damage.

TMEM106B is a lysosomal membrane protein and major genetic modifier of multiple neurodegenerative diseases, including frontotemporal lobar degeneration, Alzheimers disease, and amyotrophic lateral sclerosis. Proteolytically generated C-terminal fragments of TMEM106B assemble into amyloid fibrils that accumulate in the brains of individuals with neurodegenerative disease and in cognitively normal aged adults, yet how these fibrils produce neuronal dysfunction has remained unclear. Here, we show that cytosolic and lysosome-directed TMEM106B C-terminal fragments (CTF and gCTF) form detergent-insoluble amyloid aggregates, drive redistribution of endogenous TDP-43 from the nucleus to the cytoplasm, and accelerate neuronal death. Unbiased proximity proteomics identified the inner nuclear membrane LAP1-TorsinA axis as a fragment-specific interactome, and co-immunoprecipitation confirmed a direct physical interaction between gCTF and LAP1 that was not observed with full-length TMEM106B. Fragment expression disrupted Lamin B1 organization, mislocalized the nuclear import machinery KPNB1 and RanGAP1, and impaired importin-dependent nuclear transport in primary cortical neurons. Critically, neurons harboring endogenous TMEM106B fibrillar pathology in aged human frontal cortex exhibited the same phenotypes, namely disrupted Lamin B1 and LAP1 localization and cytoplasmic redistribution of TDP-43, whereas fibril-negative neurons from the same cases and younger control tissue retained intact nuclear envelope organization. These findings define TMEM106B proteinopathy as an upstream driver of nuclear envelope disruption and nucleocytoplasmic transport failure, linking a widespread feature of brain aging to a central mechanism of neurodegeneration.

Microglial activation has been closely associated with accelerated ALS disease progression. However, specific microglial pathways that regulate microglial activation and ALS disease progression remain limitedly understood. Here, we determined the role of Clec7a (or Dectin-1), a core signature gene of disease-associated microglia (DAM) in ALS, in regulating microglial activation and ALS disease progression. Our spinal cord scRNA-Seq results found that Clec7a deficiency specifically attenuated microglial neuroimmune gene expression in SOD1G93A mice and human ALS. In addition, in vivo two-photon imaging of human (h) TDP43 phagocytosis by microglia in the cortex showed that Clec7a deficiency promotes microglial phagocytosis of pathological hTDP43 by enhancing microglial process dynamics. Subsequent survival analysis further showed that selective deletion of Clec7a in microglia mitigates motor neuron degeneration and delays disease progression in SOD1G93A ALS mice. Together, our results establish that Clec7a is a key regulator in shaping disease microglial functions and promotes disease progression in ALS.

Parkinsons disease (PD) is the fastest-growing neurologic disease and a leading cause of disability worldwide. PD affects the body and mind, is progressive, and there is no prevention or cure. Gut microbiome, a recently recognized contributing factor in PD, offers new leads for understanding the underlying pathobiology and devising new treatments. Here, we present the most comprehensive study of the PD gut microbiome to date, comprising three large datasets with a sample size of 1,006 PD and 544 neurologically healthy controls, generated with uniform methodology from subject recruitment to data analysis, and characterized using deep shotgun metagenome sequencing, genome-wide genotypes, and metadata. We begin by describing the gut dysbiosis at the species, gene, pathway, and functional level. Next, we find that PD-associated genetic variants at the SNCA gene region are associated with increased abundance of opportunistic pathogens and depletion of fiber degraders in the PD gut. We show that the presence of opportunistic pathogens at high levels in the gut increases the penetrance of SNCA variants for PD risk, raising the GWAS-derived odds ratio from less than 1.5 to over 8. The genetic variants identified here control splicing of the SNCA transcripts into alpha-synuclein isoforms with varying affinity for pathological aggregation. These data suggest pathogens are triggers for disease in the setting of genetic susceptibility, and the link to the genome implicates the microbes in the causation of PD. Finally, shifting focus to translation, we show that not all PD patients have the same dysbiotic features, and propose a conceptual framework to identify microbiome-based biomarkers to select appropriate patients for targeted microbiome-based clinical trials and personalized treatment.

Retrospective studies in patients with non-muscle invasive bladder cancer (NMIBC) have reported a significant reduction in Alzheimers disease (AD) incidence (12-78%) among Bacillus Calmette-Guerin (BCG) recipients versus controls. To investigate the underlying mechanisms, we evaluated BCG in the PS19 mouse model of tauopathy. We found that BCG administration reduced hippocampal phospho-tau and microgliosis while preserving neuronal markers. In vivo volumetric T2-MRI demonstrated attenuation of brain atrophy accompanied by increased glutamate-weighted CEST-MRI signals. Functionally, BCG-treated mice showed improved performance in the novel object recognition test (NORT), as well as improved body-weight maintenance and survival. Transcriptomic profiling of the hippocampus revealed near complete normalization of the PS19 disease-associated gene expression signature towards that of healthy controls. Flow cytometric profiling of brain myeloid populations demonstrated a reduction in activated resident microglia, but total microglia cells remain elevated. Moreover, an increase of the co-stimulatory marker CD80 on the recruited peripheral myeloid cells ensues following BCG treatment. Consistent with this shift in myeloid state, primary brain myeloid cells from BCG-treated mice also exhibited enhanced phagocytosis of FITC-labeled tau fibrils and increased lactate production. Together, these findings indicate that BCG induces systemic and CNS myeloid cell reprogramming that limits neuroinflammation, enhances tau clearance, and rescues cognitive and neurodegenerative phenotypes in a tauopathy model. BCG is a safe, readily available therapy that merits consideration as a preventive agent against dementia. One sentence summaryBCG therapy prevents tauopathy in PS19 mouse model.

Long non-coding RNAs (lncRNAs) are increasingly implicated in neurodegenerative disease, yet their roles in tauopathy remain poorly understood. Here, we defined the lncRNA landscape across iPSC-derived neurons, astrocytes, and microglia harboring the frontotemporal dementia-associated MAPT IVS10+16 mutation and investigated how lncRNA dysregulation interfaces with tau pathology. Transcriptomic analyses revealed extensive cell-type specific lncRNA expression changes, with neurons exhibiting the greatest degree of mutation-associated remodeling. Comparative analyses with MAPT IVS10+16 patient brain tissue identified NORAD and MIR22HG as lncRNAs significantly dysregulated across all three cell types and human brains. NORAD was also altered in Alzheimer disease and Parkinson disease brains, suggesting a broader role in neurodegenerative disease. Mechanistically, NORAD-associated protein networks converged on pathways related to RNA regulation, cytoskeletal organization, proteostasis, and tau interaction networks. Given the established role of NORAD in regulating PUM1 and PUM2 RNA-binding (pumilio) proteins, we examined the NORAD-pumilio axis and identified enrichment of pumilio-associated pathways linked to autophagy, endocytosis, proteostasis, and cytoskeletal regulation. NORAD depletion reduced tau seeding and uptake, whereas functional depletion of PUM1 or PUM2 increased both processes, supporting an antagonistic relationship between NORAD and pumilio signaling in modulation of tau aggregation. Together, these findings identify widespread lncRNA dysregulation across neural cell types in the setting of a MAPT mutation and nominate the NORAD-pumilio axis as a regulatory pathway linking RNA homeostasis and tau propagation biology.

Presenilin 2 (PS2) mutations cause familial Alzheimers disease, yet their effects beyond amyloid processing remain poorly understood. Here, we investigated how PS2 deletion and the N141I mutation affect neuronal lipid homeostasis and mitochondrial dynamics in mouse primary neurons. Both PS2 deletion and N141I mutation reduced neuronal lipid content. However, exogenous lipid supplementation rescued this deficit only in N141I-expressing neurons, indicating a partial loss-of-function effect. N141I neurons also displayed reduced OPA1, a mitochondrial fusion regulator, restored by lipid supplementation. RNA-sequencing identified Gbf1, a Golgi-specific guanine nucleotide exchange factor, as selectively downregulated in N141I but not knockout tissue, which was confirmed at the protein level in mouse brain and primary neurons. Gbf1 knockdown in mouse embryonic fibroblasts (MEFs) recapitulated the N141I lipid profile. Together, these findings reveal a PS2-GBF1-lipid-mitochondria axis disrupted specifically by the N141I mutation, suggesting an amyloid-independent pathway contributing to neurodegeneration and identifying potential therapeutic targets for familial Alzheimers disease.

While Apolipoprotein E4 (APOE4) is the greatest known genetic risk factor for late-onset Alzheimers disease, its mechanistic role in the brain-resident macrophage, microglia, remains elusive. Microglia are important in the clearance of pathology in disease, heavily relying on lysosome functionality; therefore, we sought to understand the impact of APOE4 on microglial function. APOE44 microglia have been shown to have lipid accumulation, yet the mechanisms leading to this accumulation are unknown. Using induced pluripotent stem cell-derived microglia, we found that the APOE4 haplotype resulted in transcriptional state shifts in microglia, suppressing activated-response microglia (ARMs) and promoting a G2 senescent-like state. We found that APOE44 microglia accumulate cholesterol esters and provide less lipid support to fibroblast-induced neurons, decreasing their synaptic connections. APOE44 microglia secrete significantly less lipoproteins, leading to the accumulation of lipoproteins within the cells including the lysosomes. APOE44 microglia exhibit impaired lysosomal acidification and degradation capacity. Further, our results elucidated that APOE44 microglia are proinflammatory and shift away from fatty acid oxidation towards glycolysis, due to dysfunctional mitochondria. Taken together, our findings indicate that a loss-of-function in lipoprotein secretion drives intracellular lipid accumulation, including within lysosomes, ultimately disrupting the lysosome-endoplasmic reticulum-mitochondrial axis. This drives a proinflammatory and metabolically compromised microglial phenotype with impaired neuro-supportive functions. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=138 SRC="FIGDIR/small/724612v1_ufig1.gif" ALT="Figure 1"> View larger version (44K): org.highwire.dtl.DTLVardef@18d6a2org.highwire.dtl.DTLVardef@b3644dorg.highwire.dtl.DTLVardef@17e3716org.highwire.dtl.DTLVardef@1529caf_HPS_FORMAT_FIGEXP M_FIG C_FIG

Background: Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by death of upper and lower motor neurons, usually presented with clinical heterogeneity. Fluid biomarker development remains dominated by neurofilament light chain (NEFL), a marker of neuroaxonal injury. NEFL is however unspecific to ALS and its phenotypes and there is currently a lack of biomarkers that capture ALS heterogeneity such as onset site and ALS-frontotemporal spectrum disorder (ALS-FTSD). Therefore, we investigated whether plasma proteomics could reveal pathway-level signatures that stratify and explain ALS heterogeneity. Methods: We profiled ~5,400 plasma proteins (Olink Explore HT) in 299 patients with ALS and 50 age- and sex comparable healthy controls. We used two complementary analytic frameworks: (i) differential protein abundance analysis to identify altered proteins in ALS and across clinical subgroups, and (ii) weighted gene correlation network analysis (WGCNA) to identify coordinated protein modules and relate them to ALS diagnosis and to ALS-specific clinical traits (site of onset, ALS-FTSD, ALS functional rating scale-revised (ALSFRS-R) score, and plasma NEFL). Results: Differential abundance analysis identified 56 proteins altered in ALS versus controls, of which 40 were increased. WGCNA identified 11 co-expression modules, with ALS samples having the strongest correlation to a protein module (n=51) highly enriched for muscle-related proteins. Out of the 40 proteins that had increased expression levels, 29 overlapped with the muscle-enriched protein module, indicating that muscle related proteins are the dominant circulating proteomic signature in ALS. This signal extended to clinical stratification: spinal-onset patients showed a strong positive association with the muscle-module. Further, differential abundance analysis of spinal- versus bulbar-onset ALS identified changes that mapped predominantly to the same module, supporting a molecular signature of onset phenotype. In contrast, cognitive status (ALS-FTSD) mapped to distinct modules enriched for extracellular matrix/cell-adhesion pathways, consistent with a separable biological axis of disease heterogeneity. Although multiple modules correlated with NEFL, trait-specific signatures were not fully explained by neuroaxonal injury. Notably, the muscle-enriched module increased with higher NEFL and lower ALSFRS-R, supporting its interpretation as a severity-linked, muscle-involvement proxy. Conclusions: Large-scale plasma proteomics reveals that heterogeneity in ALS reflects underlying biological structures. We identified a dominant muscle-associated protein network that distinguished ALS patients from controls and correlated with disease onset phenotype and severity, alongside distinct protein networks linked to ALS-FTSD. By integrating differential protein abundance with network-based analysis, we defined pathway-level biomarker signatures that extend beyond NEFL, enabling biologically informed patient stratification and improved therapeutic monitoring.

Astrocytes are key regulators of lipid metabolism, and dysregulated astrocytic lipid processing is implicated in Parkinsons disease (PD) pathogenesis. Our prior genome-wide screens identified ACSBG1, an astrocyte-enriched acyl-CoA synthetase, as a candidate regulator of -synuclein (-Syn) levels. However, how ACSBG1 links lipid reprogramming to inflammatory astrocyte activation and -Syn pathology remains unknown. We compared the transcriptomic, cytokine, and lipid secretomes of TNF- and IL-1 stimulated primary astrocytes from wild-type (WT) and Acsbg1 knockout (KO) mice. In vivo, we crossed Acsbg1 KO mice with a Thy1--Syn PD model to assess behavior, neuroinflammation, synaptic integrity, and -Syn levels. Following cytokine exposure, Acsbg1 KO astrocytes mounted an attenuated inflammatory transcriptional response, secreting significantly fewer inflammatory mediators (e.g., IL-6, RANTES, MIP-3) and less long-chain Sphingosine 20:1 than WT astrocytes. Importantly, exogenous Sphingosine 20:1 or cytokines from WT reactive astrocytes induced neuronal -Syn phosphorylation (pS129). In vivo, Acsbg1 deletion in Thy1--Syn mice reduced astrogliosis, rescued synaptic and behavioral deficits, and decreased total and pS129--Syn. These findings establish ACSBG1 as a key regulator of inflammatory astrocyte signaling that contributes to -Syn phosphorylation via specific cytokine and lipid mediators, identifying ACSBG1 as a novel therapeutic target for modulating astrocyte-neuron communication in PD.

Progressive and chronic neuroinflammation is associated with numerous neurodegenerative diseases, including primary tauopathies such as frontotemporal dementia and progressive supranuclear palsy. Unlike Alzheimer's disease, there is no clear genetic association implicating microglial dysfunction as a primary driver of tauopathy. As such, the contributions of microglia to tauopathy pathogenesis have been less well defined. Here, we explore the cell autonomous effects of the pathogenic MAPT-S305N variant on microglial function, across two distinct iPSC-microglia protocols, followed by examination of the non-cell autonomous effects of microglial MAPT genotype on neuronal health and function. We find that different protocols produce cells of equivalent microglial identity, but result in microglia in different functional states, thereby influencing reactivity and detectable phenotypes. Regardless, across both protocols we find that MAPT-S305N induces microglial hypoactivity, evidenced by impaired phagocytosis, reduced cytokine release and diminished regulation of synaptic function. We conclude that microglial hypoactivity may be an early event in disease pathogenesis, where MAPT mutation microglia fail to adequately respond to pathogenic stimuli, thereby contributing to subsequent neuronal vulnerability and susceptibility. Further studies are required to understand how and when this initial hypoactive state may switch to a toxic pro-inflammatory state, and whether early detection and correction may be of therapeutic value.