Journal of Neurochemistry

Blood-based proteomic profiling is now widely applied in neurodegenerative and neuroinflammatory disease, yet the choice between serum and plasma remains poorly characterised for high-multiplex platforms. Many legacy biobanks hold mainly serum, whereas most current NUcleic-acid-Linked Immuno-Sandwich Assay (NULISA) studies use plasma. We compared the 130-protein NULISAseq central nervous system (CNS) Disease Panel head-to-head in matched serum and plasma collected at the same draw from 62 participants (30 neurodegenerative, 19 demyelinating, 13 healthy controls). Agreement was measured with Spearman correlation (rho), Lin's concordance correlation coefficient (CCC), the intraclass correlation coefficient (ICC) and the mean paired serum-to-plasma difference (dNPQ). Concordance was moderate to high: 123 of 130 proteins reached significance and 18 reached rho >= 0.90, with a median rho of 0.72 (range 0.10-0.988). Proteins fell into three tiers. Cytoskeletal markers (NEFH rho=0.988; NEFL rho=0.947) and glial GFAP (rho=0.949, |dNPQ|<0.5) were interchangeable between matrices. Phosphorylated tau (pTau) species retained excellent rank concordance but carried a systematic plasma-greater-than-serum offset (pTau-181 rho=0.869, dNPQ=+0.67; pTau-217 rho=0.846, dNPQ=+0.64; pTau-231 rho=0.885, dNPQ=+0.89). Platelet-derived analytes (CD40LG rho=0.102, dNPQ=-4.74; BDNF rho=0.223, dNPQ=-2.69) and intracellular synaptic proteins (NRGN, SNAP25, ENO2) diverged markedly. For most clinically relevant neurodegeneration markers, especially cytoskeletal and glial proteins, serum is a valid substitute for plasma; absolute thresholds for phosphorylated tau and amyloid peptides require matrix-specific calibration, and platelet-sensitive analytes cannot be compared across matrices without strictly standardised pre-analytical conditions.

Endosomal sorting complexes required for transport (ESCRT) regulate membrane protein trafficking through coordinated cargo selection and endosomal processing, yet their contribution to neurotransmitter receptor sorting remains to be defined. Here, we examined how modulation of distinct complex components influences the surface expression of excitatory and inhibitory neurotransmitter receptors. Using surface biotinylation and imaging approaches in heterologous cells and primary neurons, we altered tumour susceptibility gene 101 (TSG101), a core complex I component, and vacuolar protein sorting-associated protein 4A (VPS4a), an ATPase required for complex III disassembly. Reduction of tumour susceptibility gene 101 increased receptor association with early endosomes and enhanced receptor surface localisation, whereas disruption of VPS4A promoted receptor accumulation within late endosomal compartments and impaired degradative progression. Inhibitory receptor subtypes displayed variable sensitivity. Together, these findings demonstrate that endosomal sorting complex components regulate receptor surface expression through stage-specific trafficking mechanisms associated with altered receptor recycling and degradative processing. Graphical abstractDistinct ESCRT components regulate neurotransmitter receptor trafficking through stage-specific control of the endosomal pathway. ESCRT-I disruption promotes early endosomal retention and recycling, whereas ESCRT-III impairment causes late endosomal accumulation and reduced degradation, together increasing receptor surface expression (created using Biorender). O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=150 SRC="FIGDIR/small/732891v1_ufig1.gif" ALT="Figure 1"> View larger version (49K): org.highwire.dtl.DTLVardef@1fe66b9org.highwire.dtl.DTLVardef@10a29d7org.highwire.dtl.DTLVardef@4109c4org.highwire.dtl.DTLVardef@1e84f19_HPS_FORMAT_FIGEXP M_FIG C_FIG

A multi-omic approach utilizing a single biospecimen is important to avoid intra-sample heterogeneity associated with testing multiple omic single-samples, and for more efficient use of small volumes of precious biopsies (<30 mg). This is especially true for the microanatomy of post-mortem human brain samples. Using post-mortem human brain biospecimens from the NIH NeuroBioBank, a penta-omic sequential extraction method is described, Simultaneous Metabolomic, Proteomic, Lipidomic - DNA, RNA Extraction (SiMPL-DREx). Each sequential omic extract was compared to those obtained by the gold standard single omic method. Preserving RIN is critical for brain and tissue banks, as it is a primary measure of tissue quality. For all five omic extracts, the tissue integrity numbers and omic profiles did not significantly differ from those obtained by the respective omic gold standard method. Unlike past multi-omic studies, this study quantified the relative solvent percentages and upstream losses for both the organic and aqueous phases, confirming an omics loss of under 5%.

Amyotrophic lateral sclerosis (ALS) is a fatal, rapidly progressive neurodegenerative disease of motor neurons for which therapeutics are limited. Improved biomarkers are imperative to improve patient care and therapeutic development. Here, we employed 35-plex isobaric tandem mass tag labeling based on isobutyl-proline reporter group (TMTpro) to perform unbiased proteomic analysis of cerebrospinal fluid (CSF) and plasma from control (n= 28, n= 31) and sporadic ALS (sALS) (n= 39, n= 41), from the Target ALS Global Natural History Study (TALS GNHS). We identified 2,875 proteins in CSF and 1,118 proteins in plasma and identified known and novel differentially expressed proteins (DEPs) between controls and sALS, some of which were orthogonally validated using immunoassay. Comparison of TMTpro-MS and Olink proximity extension assay proteomics revealed common and non-overlapping differentially expressed proteins illustrating strengths unique to each platform. This initial cross-sectional proteomic study of biofluids from the TALS GNHS, with unrestricted availability of study results to the research community, highlights the potential of this resource as a potent platform for ALS biomarker discovery.

It is well established that activating the mGluR2 metabotropic glutamate receptor (mGluR2), which is the main presynaptic autoreceptor for glutamate in the brain, attenuates the behavioral and electrophysiological actions of LSD and other psychedelics. However, the mechanisms responsible for these actions are controversial. The two competing mechanistic hypotheses have been proposed to explain this phenomenon are: (1) direct actions mediated by mGluR2/5-HT2A heterodimers, and (2) inhibition of 5-HT2A-mediated excitation of pyramidal neurons via presynaptic inhibition of glutamate release by mGluR2 receptors. Consistent with prior reports, we show mGluR2 agonist pretreatment attenuates the head twitch response induced by the psychedelic drug 1-(2,5-Dimethoxy-4-iodophenyl)-2-aminopropane (DOI) in these mice. We next employed multiple orthogonal in vivo and in vitro approaches to explore the potential for direct physical interactions between mGluR2 and 5-HT2A receptors. We next engineered mice to express mGluR2-mCherry-CT and 5-HT2A-eGFP-CT tagged receptors and found no evidence for receptor colocalization or oligomerization under basal or 5-HT2A agonist-exposed conditions in vitro or in vivo. Radioligand binding and kinetic analyses revealed no evidence for mGluR2-mediated modulation of 5-HT2A ligand binding in vitro or in vivo. Collectively, our findings support models in which mGluR2 signaling modulates the activity of Gq-coupled 5-HT2A receptors in layer V pyramidal neurons, rather than models positing the requirement of mGluR2/5-HT2A multimers.

Background: Norepinephrine (NE) released from locus coeruleus (LC) projections regulates astrocyte structure and function through adrenergic receptor signaling. We previously showed that increasing noradrenergic tone with the NE reuptake inhibitor desipramine increases astrocyte ramification in the molecular layer of the dentate gyrus. However, whether tonic LC-derived noradrenergic tone is required to maintain astrocyte morphological complexity in vivo, and whether {beta}-adrenergic receptor activation is the effector pathway, remained unclear. Methods: Adult male C57BL/6J mice received DSP-4 (50 mg/kg X 3 days i.p.), a selective LC neurotoxin, with or without concurrent isoproterenol that continued for 21 additional days post cessation of DSP-4 treatment (ISO; 2 mg/kg/day X 24 days), or saline (n = 4 mice per group). Animals were sacrificed 22 days after the final DSP-4 injection. Noradrenergic denervation was confirmed by dopamine {beta}-hydroxylase (DBH) immunostaining. GFAP-immunostained astrocytes in the molecular layer of the dentate gyrus were morphologically characterized using Sholl analysis. Astrocyte density was quantified by SOX9 immunostaining. Results: DSP-4 produced >83% reduction in DBH fiber coverage in the molecular layer. Sholl analysis revealed significant reductions in astrocyte branching complexity in both treatment groups, with the reductions concentrated at distances of 5-15 m from the soma. The maximum number of intersections was also significantly reduced in both groups. Unexpectedly, ISO did not rescue morphological complexity. While DSP-4 alone did not alter astrocyte density, as measured by the number of SOX9-expressing astrocytes, DSP-4+ISO increased SOX9-positive cell density, dissociating the effects of adrenergic signaling on morphology from those on cell numbers. Conclusions: LC-derived noradrenergic tone is required for the maintenance of astrocyte arbour complexity in the dentate gyrus molecular layer. {beta}-adrenergic receptor activation alone is insufficient to restore structural integrity following noradrenergic denervation, yet promotes astrocyte density independently of structural remodeling. These findings have implications for understanding how LC neurodegeneration in Alzheimer's disease and depression may compromise hippocampal astrocyte structure and function.

Tauopathy is characterized by progressive synaptic failure and neuroinflammation, yet the laminar-specific nature of these disruptions remains poorly understood. We investigated hippocampal functional integrity and glial reactivity in 8-10-month-old PS19 (P301S) mice. Electrophysiological recordings in the CA1 stratum radiatum revealed an unexpected increase in basal synaptic transmission despite profound deficits in both maintenance and early induction of the LTP phase. Conversely, the dentate gyrus exhibited reduced basal transmission and impaired LTP maintenance, alongside significant paired-pulse plasticity changes not observed in CA1. Furthermore, we demonstrate that transregional metaplasticity, as driven by prior activity in the stratum oriens (SO) in a way that inhibits subsequent LTP in wild-type mice, is occluded in PS19 mice. These data suggest that the tauopathic hippocampus exists in a "metaplastic" state, which inhibits future LTP. Immunofluorescence studies revealed that while astrogliosis and microglial activation were pan-hippocampal, specific neuroinflammatory markers exhibited striking laminar specificity. Mean fluorescence intensity for the neuroinflammatory astrocyte marker C3 was significantly upregulated only in the SO, and the lysosomal marker CD68 showed heightened occupancy specifically in the SO and stratum lacunosum-moleculare. Our findings indicate that tau pathology does not affect the hippocampus uniformly. Instead, it induces region-specific shifts in synaptic efficacy and a breakdown of metaplastic control that coincides with anatomically localized neuroinflammatory signaling.

Neural stem cell (NSC) transplantation is a promising strategy for repairing the injured spinal cord, but transplanted cells typically require immunosuppressive therapy to prevent rejection, even for induced pluripotent stem cell (iPSC)-derived autologous grafts. However, the effects of immunosuppressive drugs on neurite outgrowth and axonal regeneration, processes critical for neural circuit reconstruction, have not been fully characterized. In this study, we tested nine clinically relevant immunosuppressants on human iPSC-derived neurons and primary human spinal cord NSCs in vitro at concentrations approximating clinical exposure levels. The drug panel included FK-506 (tacrolimus), cyclosporine A (CsA), rapamycin, belatacept (Nulojix), etanercept (Enbrel), mycophenolate mofetil (CellCept), cyclophosphamide (Cytoxan), prednisone, and azathioprine (Imuran). Neurite outgrowth was quantified via automated high-content imaging. Multiple agents, including CsA, Imuran, Nulojix, and CellCept, induced significant reductions in neurite outgrowth in a cell type- and dose-dependent manner, with CsA producing the most robust and consistent inhibition across both cell lines. In contrast, FK-506 showed no significant effect on neurite extension at clinically relevant concentrations. Consistent with the in vitro results, human neural progenitor cell grafts in a rodent spinal cord injury model exhibited significantly reduced graft-derived axon extension in the host spinal cord when hosts were treated with CsA rather than FK-506. These findings demonstrate that immunosuppressant choice can profoundly influence neural graft integration and axonal regeneration. Our study underscores the importance of preclinical evaluation of immunosuppressive regimens and suggests that selecting agents such as FK-506 over CsA may improve outcomes in future stem cell-based therapeutic trials for spinal cord injury and related disorders of the central nervous system.

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.

Heat stroke is characterized by profound central nervous system dysfunction and vascular abnormalities. Previous studies have demonstrated the marked vulnerability of the CNS to thermal stress, resulting in neuronal injury and glial activation. However, the metabolic mechanisms linking acute injury to chronic neurological long-term effects remain understood. The neuropathological changes are closely associated with neuroinflammatory and metabolic disturbances, including dysregulation of the kynurenine pathway, whose metabolites modulate neurotoxicity, neuroprotection, and immune responses. Here, we present the first comprehensive characterization of kynurenine pathway metabolomic profile across both plasma and brain tissue in a mouse model of heat stroke. Using a validated and sensitive LC-MS/MS method, we simultaneously measured and quantified 13 analytes (kynurenine, kynurenic acid, quinolinic acid, nicotinic acid, picolinic acid, xanthurenic acid, anthranilic acid, 3-hydroxykynurenine, 3-hydroxyanthranilic acid, indole-3-acetic acid, indole-3-lactic acid, 5-hydroxyindoleacetic acid and neopterin). The findings reveal a biphasic metabolic response, characterized by an acute serotonergic disruption and reduced neuroprotective capacity, followed by chronic activation of the kynurenine pathway, depletion of central serotonin metabolites, and metabolic signatures consistent with gut microbiota dysbiosis. The acute phase is marked by a transient imbalance favoring neurotoxic kynurenine pathway metabolites, whereas the chronic phase reflects sustained pathway activation. Notably, the plasma-brain dissociation of 5-hydroxyindoleacetic acid emerged as the most prominent cross-compartment finding, suggesting a potential biomarker of central serotonergic depletion and a mechanistic link between peripheral and central metabolic changes, with implications for therapeutic targeting during the subacute recovery phase.

Decreases in brain pH are associated with numerous neurological and neuropsychiatric conditions yet the molecular mechanisms linking decreased brain pH with these disorders are incomplete. The ionotropic glutamate receptors (iGluRs) mediate the majority of excitatory neurotransmission in the brain and are inhibited by extracellular protons; however, the proton sensitivity of the delta-glutamate receptor subclass of iGluRs is unknown. Using whole-cell patch-clamp recordings of serotonin neurons in mouse brain slices and activating alpha 1-adrenergic receptors to induce delta 1 glutamate receptor (GluD1R) current, we demonstrated that GluD1R current is inhibited by physiological drops in extracellular pH. Unlike other iGluRs, protons inhibited GluD1R current via a voltage-independent decrease in unitary current. Moreover, mice lacking GluD1R showed impaired behavioral responses to inhalation of CO2. Taken together, this study continues to expand on the growing body of evidence positing GluD1R as functional ion channels and suggests that GluD1R facilitate pH sensing in vivo.

Traumatic brain injury (TBI) has long-term consequences that include chronic traumatic encephalopathy (CTE) and an elevated risk for Alzheimer Disease (AD). These dementias ultimately manifest as tauopathies but may begin with acute neuronal dysfunction including post-traumatic seizures. Provocative evidence suggests that these prodromal seizures are a viable target to mitigate the later onset of dementias, and anti-epileptic drugs (AED) that increase the threshold of action potentials have indeed been shown to mitigate later tauopathies[1, 2]. Here, we test whether AEDs and other compounds that modulate synaptic transmission, applied immediately after TBI, can also act as prophylactics that block subsequent CTE-like tau aggregation and neurodegeneration in a larval zebrafish model. Levetiracetam (LEV) is an AED that modulates synaptic vesicle release. Application of LEV immediately following TBI abrogated TBI-induced tau tau aggregation (IC50 = 3.168 x10-3 mM) and cell death in the larval zebrafish TBI model. We next considered a polypharmacy approach involving mGluR2, because mGluR2 positively allosteric modulators (PAMs) such as JNJ-42153605 have previously been able to improve LEVs action in reducing some recalcitrant forms of seizure in a mouse model. We found that JNJ-42153605 was itself effective at blocking TBI-induced tau aggregation (IC50 = 8.691 x10-5 mM). Moreover, a subeffective dose of JNJ-42153605 (10-5 mM) was able to substantially improve the efficacy of LEV (~16-fold) in its prophylactic actions. Thus, LEV and JNJ-42153605 applied briefly after TBI offer a potent polypharmacy approach, at least in our preclinical animal model, to tackle the later tau aggregation and neurodegeneration that follows from TBI neurotrauma. These results warrant further investigation, including testing into mammalian TBI models (with longer disease course).

Neurodegeneration is a major determinant of disability progression in multiple sclerosis (MS), yet the pathophysiological mechanisms associating inflammation to neuronal insult remain poorly understood. We recently identified Dendritic Syntaphilin Intrusion (DSI), a novel excitoxicity pathway in which the axonal mitochondrial anchor syntaphilin (SNPH) aberrantly translocates into dendrites, causing neurodegeneration in a non-inflammatory model of MS. However, whether this protein intrudes abruptly into dendrites in inflammatory MS pathology is still not clear. Here, we investigated the role of synaptic and extrasynaptic NMDA receptors (NMDAR) in regulating the intrusion of Syntaphilin into dendrites. Using primary hippocampal neuronal cultures, we examined how the balance between synaptic GluN2A-containing and extrasynaptic GluN2B-containing NMDARs influences DSI under inflammatory conditions. Pharmacological and viral-mediated approaches were employed to manipulate NMDAR subtype activity and evaluate their impact on DSI. Inflammatory cytokines discernibly sensitized neurons to DSI. Our results revealed that blockade of synaptic NMDARs significantly increased DSI, whereas inhibition of extrasynaptic NMDARs reduced DSI. These findings demonstrate opposing roles of NMDAR subtypes, with GluN2A-containing synaptic receptors inhibiting DSI and fostering neuronal survival, while GluN2B-containing extrasynaptic receptors enhancing DSI and neurodegenerative signaling. Manipulation of the GluN2A/GluN2B balance showed opposite effect on DSI, suggesting a relationship between NMDAR subtype signaling and SNPH mislocalization. Overall, our findings extend the relevance of DSI from non-inflammatory MS to inflammatory MS and identify DSI as a downstream convergence point linking inflammatory cytokines and excitotoxic NMDAR signaling to neuronal insult. These results reveal DSI as a potential mechanistic link between inflammatory signaling and excitotoxic neuronal injury and indicate that modulation of GluN2B-dependent pathways warrants further investigation in inflammatory neurodegenerative disorders.

Stem cell therapy represents a promising strategy for the replacement and functional restoration of damaged neural tissue in neurodegenerative conditions. Human dental pulp stem cells (hDPSCs) have emerged as potential candidates for neuroregeneration due to their ease of isolation, neural crest origin, neurotrophic and anti-inflammatory capacity, and demonstrated ability to differentiate in vitro into neuronal-like cells exhibiting electrophysiological activity. Although the immunomodulatory and neuroprotective properties of hDPSCs have been reported in multiple models of brain disease, their capacity to functionally integrate into host neuronal circuits remain poorly understood. In this study, we have grafted green fluorescent protein (GFP)-transduced, neural preconditioned hDPSCs into the CA1 region of the hippocampus of C57BL/6J mice. One month after transplantation, GFP+-hDPSCs survived in the brains of non-immunosuppressed mice and remained localized within the grafted area. Notably, the transplanted cells underwent in situ differentiation and exhibited a neuroblast-like phenotype, characterized by positive doublecortin expression and immature neuronal-like electrophysiological properties, like high membrane input resistance, low capacitance, and the ability to generate single action potentials after stimulation. Together, these findings provide the first evidence that hDPSCs can survive and integrate into the hippocampal network of the mouse brain at one-month post graft, supporting their potential use for future therapeutic applications in acute brain lesions and neurodegenerative disorders.

Traumatic brain injury (TBI) induces rapid neuroinflammatory responses not only in the brain but also in anatomically and immunologically connected central nervous system (CNS) compartments, including the retina. In our study, we investigated retinal microglial activation, retinal ganglion cell (RGC) calcium dynamics, and caspase-3 activation in adult mice subjected to severe traumatic brain injury using the Marmarou impact-acceleration model at 24 and 48 h post-injury. Carrying out Ca{superscript 2}-imaging, immunohistochemistry, and ex vivo time-lapse microscopy, we found robust microglial activation in both the superficial and deep retinal layers following TBI, accompanied by increased microglial motility. RGCs exhibited a transient surge in degeneration-induced spontaneous activity at 24 h, followed by a marked reduction below control levels at 48 h, consistent with early degenerative changes. Activated caspase-3 levels were significantly elevated in both microglia and other retinal cell types at both time points, indicating ongoing apoptotic effects. Together, these findings demonstrate that TBI rapidly triggers inflammatory and apoptotic mechanisms in the retina, which are detectable within the first 48 hours. Our results highlight the retina as a sensitive indicator of early CNS pathology after traumatic injury and underscore the potential of retinal analysis for monitoring TBI-induced neurodegeneration for future clinical implementation. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=78 SRC="FIGDIR/small/734783v1_ufig1.gif" ALT="Figure 1"> View larger version (14K): org.highwire.dtl.DTLVardef@5bc694org.highwire.dtl.DTLVardef@14a4ce4org.highwire.dtl.DTLVardef@fe2d32org.highwire.dtl.DTLVardef@149419d_HPS_FORMAT_FIGEXP M_FIG C_FIG

Background: Stress-induced childhood-onset neurodegeneration with variable ataxia and seizures (CONDSIAS) is a rare autosomal recessive disorder caused by biallelic variants in ADPRHL2, which encodes ADP-ribosylhydrolase 3 (ARH3), a key enzyme involved in poly (ADP-ribose) (PAR) metabolism. Although Minocycline has been reported to attenuate PAR-mediated neurotoxicity primarily through modulation of PARP-dependent pathways, whether it may also interact with ARH3 or influence the structural behavior of pathogenic ARH3 variants remains unknown. This study was designed to explore this possibility by integrating clinical observation with computational structural analyses. Methods: Comprehensive clinical evaluation, targeted Sanger sequencing, and in silico pathogenicity analyses were performed. Protein modeling, molecular docking, and 100-ns molecular dynamics simulations were conducted to evaluate the predicted structural consequences of the p.Thr79Pro variant and to explore potential interactions between ARH3 and Minocycline. Results: A homozygous ADPRHL2 variant (NM_017825.3:c.235A>C; p.Thr79Pro) was identified in a child with CONDSIAS. Computational analyses predicted reduced structural stability and increased conformational flexibility of the mutant ARH3 protein relative to the wild-type structure. MM-GBSA calculations estimated differences in binding free energies between the wild-type (-34.51 kcal/mol) and mutant (-39.76 kcal/mol) ARH3-Minocycline complexes, suggesting subtle differences in their predicted energetic profiles. Clinically, neurological progression appeared stable, with improved motor function observed during approximately one year of follow-up and no notable treatment-related adverse effects. Conclusions: By integrating clinical observations with computational structural analyses, this study provides preliminary computational support for the hypothesis that Minocycline may influence ARH3 conformational behavior in addition to its proposed effects on PARP-dependent pathways. Although these findings do not demonstrate direct molecular binding or therapeutic efficacy, they provide a biologically plausible framework for future biochemical, cellular, and functional investigations. Keywords: CONDSIAS; ADPRHL2; ARH3; Minocycline; molecular docking; molecular dynamics simulation; structural bioinformatics; translational medicine

Introduction: Neuropsychiatric symptoms in dementia (NPS) are common and among the most troubling aspects of living with dementia, yet their underlying mechanisms remain unclear. Here, we aimed to identify cerebrospinal fluid (CSF) proteins associated with NPS. Methods: Proteomes were profiled from CSF collected at baseline from participants of the Alzheimer's Disease Neuroimaging Initiative (ADNI) using mass spectrometry. Here, we included participants having positive AD CSF biomarkers (i.e., pTtau181 / Abeta42 ratio >0.025) and mild cognitive impairment or AD dementia (n=419). Eight NPS domains were assessed longitudinally with the Neuropsychiatric Symptom Inventory Questionnaire. Severity of cognitive impairment was evaluated using the CDR-SB. Proteome-wide differential expression analysis for each NPS domain at baseline was performed. Significant protein-NPS associations underwent mediation analysis to test whether they were mediated by cognitive impairment severity. Cox proportional hazard was modeled for baseline CSF proteins and incident NPS. Additionally, we tested whether candidate NPS causal proteins previously identified in brain are associated with NPS in CSF. Results: We identified 8 CSF proteins associated with apathy at baseline (FDR q<0.05) after adjusting for sex, age, and education - NTNG2, S100A1, FZD1, FSTL5, CDH7, CHODL, FBXO2, and CACNA2D2. Mediation analysis revealed these associations were independent of cognitive impairment severity in four proteins and only partially mediated by cognitive impairment severity in the remaining four proteins. Among the 10 NPS candidate causal proteins previously identified in brain and detected in CSF, the abundance of two proteins (CPD, GRN) in CSF was associated with baseline disinhibition and of two other proteins (PIK3IP1, PCMT1) with both baseline apathy and incident apathy after adjusting for sex, age, and education. Discussion: These findings suggest that proteomic alterations in apathy in MCI/AD encompass synaptic connectivity, calcium regulation, Wnt-signaling, and neuronal proteostasis, highlighting potential CSF biological processes and biomarker candidates for apathy.

Many nonhuman primate species recapitulate the neuropathological features of sporadic Alzheimer's disease (AD) to varying degrees. As with humans, the assessment of AD-related pathology in nonhuman primates has historically relied on the use of postmortem brain tissues. In vivo alternatives, such as PET imaging tracers and fluid biomarkers, have been developed for use in humans but require further validation in nonhuman primates before replacing postmortem analyses. Here we employed the Nucleic Acid-Linked Immuno-Sandwich Assay (NULISATM) CNS Disease panel to compare age-related changes in plasma biomarkers in two nonhuman primate species (rhesus monkeys and baboons). In addition, we examined whether amyloid and tau biomarkers were associated with brain atrophy, as measured by gray matter volume. We found significant associations between age and multiple biomarkers of neurodegeneration for both species, as well as significant differences in the patterns of these associations between the two species. For the phosphorylated tau measures, though rhesus monkeys had higher values, baboons showed significant and stronger associations with age. By contrast, rhesus monkeys exhibited an earlier age-related decline in A{beta}42/A{beta}40 ratio than baboons. Finally, in both species, lower A{beta}42/A{beta}40 ratios were associated with lower gray matter volumes. This is the first systematic comparative study of age-related changes in neurodegeneration biomarkers in two closely related nonhuman primates using comparable age ranges and sample sizes, and the same multiplex assay. Future studies should examine longitudinal changes in these biomarkers as well as validate the plasma findings using cerebral spinal fluid.

Amyotrophic lateral sclerosis/parkinsonism-dementia complex (ALS/PDC) is a fatal neurodegenerative disorder that was once hyperendemic in the island of Guam (Mariana Islands, US) and a few other Pacific locales. Despite extensive investigations into its origins, the etiology of ALS/PDC remains unclear. ALS/PDC is, at the neuropathology level, characterized by tau-dominant multiple proteinopathy in brain and spinal cord. It was recently reported that Guam ALS/PDC brain extracts exhibit tau seeding activity in fluorescence resonance energy transfer (FRET)-based biosensor cells. To build upon those findings and explore the nature of tau seeds in ALS/PDC in more detail, we used an alanine mutational scanning (Ala scan) approach to determine the seeding profile of tau in nervous tissues of Guam ALS/PDC cases. First, we confirmed the detection of tau seeding activity in ALS/PDC brain samples in tau biosensor cells. Notably, we could also detect potent tau seeding activity in spinal cord. Subsequent Ala scan assays demonstrated that ALS/PDC tau displays an aggregate incorporation pattern that resembles that of chronic traumatic encephalopathy (CTE)-type tau. This result is consistent with recent electron cryo-microscopy studies of tau, which revealed that ALS/PDC tau filaments are predominantly of the CTE-type. The structural characteristics and seeding behavior of ALS/PDC tau, as well as the regional distribution of tau pathology at post-mortem, suggest that ALS/PDC is a CTE-like tauopathy. Significance StatementNeurodegenerative tauopathies are characterized by proteinaceous deposits containing microtubule-associated tau in nervous tissue. Emerging evidence suggests that disease-associated tau proteins adopt abnormal, self-propagating conformations characteristic of prions. Here, we employed alanine mutational scanning (Ala scan) to determine the nature of prion-like tau seeds in ALS/PDC, a mysterious disorder that occurred formerly in high incidence in certain regions in the western Pacific. We show that the Ala scan incorporation profile of ALS/PDC tau is similar to that of abnormal tau proteins in chronic traumatic encephalopathy (CTE). The findings lend support to the idea that ALS/PDC can be classified structurally as a CTE-like tauopathy. This work may have important implications for our understanding of ALS/PDC as well as common neurological disorders beyond the Pacific.

Alzheimer's disease is clinically and biologically heterogeneous. We asked whether plasma proteomics separates patients into discrete molecular subtypes or instead reflects continuous biological variation. We studied 5,895 Global Neurodegeneration Proteomics Consortium (GNPC) participants with Alzheimer's disease or mild cognitive impairment using protein coexpression networks, clustering, and continuous molecular-axis analysis. External analyses used Stanford Alzheimer's Disease Research Center (ADRC) biomarker/imaging data and UK Biobank proteomics.Four continuous axes captured 81.5% of module-level proteomic variation. Although a two-cluster solution was reproducible, separation was weak and added little clinical information beyond the continuous axes. Stanford ADRC analyses showed selected fluid biomarker associations, but imaging and PET results did not provide consistent support. In UK Biobank, projected axes were more strongly related to APOE genotype and systemic hematologic, renal, lipid, inflammatory, and hepatic traits than to clear dementia-risk replication. Plasma proteomics did not support robust Alzheimer's disease subtypes. Continuous molecular coordinates better describe plasma proteomic heterogeneity and may guide future biological stratification.