Journal of Neurochemistry

Iatrogenic transmission of prions, the infectious agents of fatal Creutzfeldt-Jakob disease, through inefficiently decontaminated medical instruments remains a critical issue. Harsh chemical treatments are effective, but not suited for routine reprocessing of reusable surgical instruments in medical cleaning and disinfection processes due to material incompatibilities. The identification of mild detergents with activity against prions is therefore of high interest but laborious due to the low throughput of traditional assays measuring prion infectivity. Here, we report the development of TESSA (sTainlESs steel-bead Seed Amplification assay), a prion seed amplification assay that explores the propagation activity of prions with stainless steel beads. TESSA was applied for the screening of about 70 different commercially available and novel formulations and conditions for their prion inactivation efficacy. One hypochlorite-based formulation, two commercially available alkaline formulations and a manual alkaline pre-cleaner were found to be highly effective in inactivating prions under conditions simulating automated washer-disinfector cleaning processes. The efficacy of these formulations was confirmed in vivo in a murine prion infectivity bioassay, yielding a reduction of the prion titer for the bead surface adsorbed prions below detectability. Our data suggest that TESSA represents an effective method for a rapid screening of prion-inactivating detergents, and that alkaline and oxidative formulations are promising in reducing the risk of potential iatrogenic prion transmission through insufficiently decontaminated instrument surfaces.

Astrocytes associate with amyloid plaques in Alzheimers disease (AD). Astrocytes react to changes in the brain environment, including to increasing concentrations of amyloid-{beta} (A{beta}). However, the precise response of astrocytes to soluble small A{beta} oligomers at concentrations similar to those present in the human brain has not been addressed. In this study, we exposed astrocytes to neuronal media containing soluble human A{beta} oligomers and used proteomics to investigate changes in the astrocyte secretome. Our data shows dysregulated secretion of astrocytic proteins involved in the extracellular matrix and cytoskeletal organization and increase secretion of proteins involved in oxidative stress responses and those with chaperone activity. Several of these proteins have been identified in previous transcriptomic and proteomic studies using brain tissue from human AD and cerebrospinal fluid (CSF). Our work highlights the relevance of studying astrocyte secretion to understand the brain response to AD pathology and the potential use of these proteins as biomarkers for the disease.

Tau is an intracellular protein but also known to be released into the extracellular fluid. Tau release mechanisms have drawn intense attention as these are known to play a key role in Alzheimers disease (AD) pathology. However, tau can also be released under physiological conditions although its physiological function and release mechanisms have been poorly characterized, especially in human neuronal cells. We investigated endogenous tau release in ReNCell VM, a human neuroprogenitor cell line, under physiological conditions and found that tau is spontaneously released from cells. To study activity-dependent release of endogenous tau, human ReNCell VM culture was stimulated by 100M AMPA or 50mM KCl for one-hour, tau was actively released to the culture medium. The released tau was highly phosphorylated at nine phosphorylation sites (pSites) detected by phospho-specific tau antibodies including AT270 (T175/T181), AT8 (S202/T205), AT100 (T212/S214), AT180 (T231), and PHF-1 (S396/S404), showing that these pSites are important for activity-dependent tau release from human ReNCell VM. Intracellular tau showed various phosphorylation status across these sites, with AT270 and PHF-1 highly phosphorylated while AT8 and AT180 were minimally phosphorylated, suggesting that AT8 and AT180 pSites exhibit a propensity for secretion rather than being retained intracellularly. This activity-dependent tau release was significantly decreased by inhibition of GSK-3{beta}, demonstrating that GSK3{beta}-dependent phosphorylation of tau plays an important role in its release by neuronal activity. In this study, we showed that ReNCell VM serves as a valuable model for studying endogenous physiological tau release. Further, ReNCell model can be also used to study pathological release of human tau that will contribute to our understanding of the progression of AD and related dementias. HighlightsO_LIActivity-dependent release of endogenous human tau from human ReNCell VM cultures occurs under physiological conditions. C_LIO_LIReleased human tau is phosphorylated at nine sites (pSites) in the proline-rich domain and the C-terminal domain detected by AT270 (T175/T181), AT8 (S202/T205), AT100 (T212/S214), AT180 (T231), and PHF-1 (S396/S404) tau antibodies, strongly suggesting that these pSites are important for activity-dependent tau release from human ReNCell VM. C_LIO_LIIn contrast, intracellular human tau proteins have different phosphorylation status among these nine pSites: AT270 and PHF-1 pSites are highly phosphorylated, but AT8 and AT180 are weakly phosphorylated, suggesting AT8 and AT180 pSites are release-sensitive phosphorylation motifs. C_LIO_LIActivity-dependent release of endogenous human tau is decreased by a tau kinase GSK-3{beta} inhibitor SB 216763, indicating that GSK-3{beta}-dependent phosphorylation plays an important role in activity-dependent tau release. C_LIO_LIThe human ReNCell culture is an excellent model system to study mechanisms underlying physiological release of endogenous tau. C_LI

The immediate-early gene Arc is a master regulator of synaptic plasticity and plays a critical role in memory consolidation. However, there has not been a comprehensive analysis of the itinerary of Arc protein, linking its function at different subcellular locations with corresponding time points after neuronal network activation. When cultured hippocampal neurons are treated with a combination of pharmacological agents to induce long term potentiation, they express high levels of Arc, allowing to study its spatiotemporal distribution. Our experiments show that neuronal activity-induced Arc expression was not restricted to neurons, but that its spatiotemporal dynamics involved a shift to astrocytes at a later timepoint. Specifically, astrocytic Arc is not due to endogenous transcription, but is dependent on the production of neuronal Arc and accumulates potentially via the recently reported intercellular transfer mechanism through Arc capsids. In conclusion, we found that Arc accumulates within astrocytes in a neuronal activity-dependent manner, which is independent of endogenous astrocytic Arc transcription, therefore highlighting the need to study the purpose of this pool of Arc, especially in learning and memory.

Excitotoxicity, a neuronal death process in neurological disorders, is initiated by over-stimulation of neuronal ionotropic glutamate receptors. The over-stimulated receptors dysregulate proteases, protein kinases and phosphatases, which in turn modify target neuronal proteins to induce cell death. To decipher this cell death mechanism, we used quantitative proteomics, phosphoproteomics and N-terminomics to identify modified proteins in excitotoxic neurons. Data, available in ProteomeXchange (identifiers: PXD019527 and PXD019211), enabled us to identify over one thousand such proteins with calpains, cathepsins and over twenty protein kinases as their major modifiers. These protein modification events can potentially perturb signalling pathways governing cell survival, synaptogenesis, axonal guidance and mRNA processing. Importantly, blocking the modification of Src protein kinase, a signalling hub in excitotoxic neurons, protected against neuronal loss in vivo in a rat model of neurotoxicity. Besides offering new insights into excitotoxic neuronal death mechanism, our findings suggest potential neuroprotective therapeutic targets for treating neurological disorders. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=162 SRC="FIGDIR/small/151456v1_ufig1.gif" ALT="Figure 1"> View larger version (38K): org.highwire.dtl.DTLVardef@1f0191forg.highwire.dtl.DTLVardef@17ba2org.highwire.dtl.DTLVardef@15c0848org.highwire.dtl.DTLVardef@123d28b_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIMulti-dimensional proteomic analysis identified proteins modified by proteolysis and altered phosphorylation in neurons undergoing excitotoxic cell death. C_LIO_LICalpains, cathepsins and over twenty protein kinases are major modifiers of these proteins. C_LIO_LIThese protein modification events are predicted to impact cell survival, axonal guidance, synaptogenesis and mRNA processing. C_LIO_LIBlocking modification of an identified protein Src, which acts as a major signalling hub in neurons, was protective against excitotoxic injury in vivo. C_LI In BriefUsing multidimensional proteomic approaches, Ameen, et al. mapped the changes of proteome, phosphoproteome and N-terminome of cultured primary neurons during excitotoxicity, a crucial neuronal death process in neurological disorders. These proteomic changes document new excitotoxicity-associated molecular events, and offer insights into how these events are organized to induce neuronal death. Potential therapeutic relevance of these molecular events is illustrated by the demonstration that in vivo blockade of one of these events could protect against excitotoxic neuronal loss.

Anti-N-methyl D-aspartic acid receptor (anti-NMDAR) encephalitis is caused by anti-NMDAR antibodies (Abs) that induce neurologic and psychiatric symptoms, explained mainly by NMDAR hypofunction. In the long-term, these Abs decrease surface NMDAR and NMDAR-mediated intracellular Ca2+ ([Ca2+]i) influx. However, there are contradictory findings regarding short-term mechanisms. We investigated NMDAR function in cultured neurons after 60 min treatment with three commercial, rabbit, anti-NMDAR Abs (anti-GluN1 extracellular (EC) domain; anti-GluN2B EC domain; and anti-GluN1 intracellular (IC) domain). The anti-GluN2B and anti-GluN1 IC Abs were previously reported to mimic patient[s] Ab effects in a rodent in vivo model and decreased NMDAR-mediated [Ca2+]i entry after 24 h treatment in our cells. After 60 min incubation with anti-GluN2B or anti-GluN1 IC decreased the NMDAR-mediated [Ca2+]i rise, whereas anti-GluN1 EC slightly increased it. Interestingly, all Abs induced p38 phosphorylation (p-p38). However, surprisingly, it was also elicited by a rabbit Ab directed against a non-NMDAR intracellular epitope, which also reduced NMDAR-mediated [Ca2+]i entry. We further investigated the cellular mechanisms regulated by the anti-GluN2B Ab after 60 min. This Ab did not reduce surface NMDAR and p38 inhibition partially prevented its effect on NMDAR function. This Ab did not elicit per se an [Ca2+]i rise, whereas NMDAR inhibitors 7DCK and MK-801 did not prevent p-p38. Nonetheless, 7DCK prevented NMDAR-mediated [Ca2+]i reduction by the Ab, suggesting a role of GluN1 flux-independent signaling. These data indicate that anti-NMDAR and non-anti-NMDAR Ab modulate NMDAR function distinctly and p38 signaling in the short-term, and a role of a third-party mediator. Finally, our results suggest the involvement of NMDAR flux-independent signaling.

ObjectiveSubgroups of mental illness patients have been seen to display disturbed proteostasis, with specific proteins aggregating in their brain, which is generally determined by assaying protein insolubility in the post mortem samples. Such studies typically only look at one region of the brain, and therefore we aimed to determine the distribution of protein across a single brain, using this insolubility-based approach. MethodsWe looked at 20 post mortem tissue samples from across the brain of a single patient, with schizophrenia and Alzheimers disease, determined which protein(s) aggregated in his brain relative to controls, based on purification of insoluble protein fractions. The individual samples were then similarly analysed. ResultsDisrupted in Schizophrenia 1 (DISC1) protein was seen to be insoluble in the patients brain, however in a very heterogenous picture, with differences in insoluble DISC1 even between samples of the same region, but opposite hemispheres. ConclusionsWhile caution must be taken in extrapolating from a single individual, this raises the possibility that aggregates of DISC1 may spread throughout the brain, as is the case for proteins in neurodegenerative disorders, and suggests that current studies looking at single brain regions may be underestimating the prevalence of protein aggregates in schizophrenia.

Glucose is a predominant fuel for the brain supporting its high energy demand associated with neuronal signaling and synaptic activity. Long-term potentiation (LTP) is required for learning and memory formation by generating long lasting increase in synaptic strength and signal transmission between two neurons. While the electrophysiological bases of LTP are well established, much less is known about the metabolic demands of neurons involved in LTP. Common protocols used to examine synaptic activity rely on high glucose concentrations which are far from physiological glucose levels found in the brain. Here we used primary hippocampal neurons cultured under physiological (2.5 mM) and high (25 mM) glucose to investigate the metabolic effects of chemically induced LTP. Physiological glucose was associated with neuronal survival while high glucose promoted "PAS granule" accumulation. Changes in glucose altered extracellular lactate and pyruvate concentrations and affected key intracellular metabolic intermediates and neurotransmitter levels in neuronal cells without depleting the TCA cycle. LTP induction was comparable, but mitochondrial and neurotransmitter response to LTP was differentially affected physiological and high glucose conditions. Glycogen phosphorylase inhibition had minimal effects in physiological glucose but impaired synaptic responses and altered metabolite dynamics in high glucose. Our findings demonstrate that neuronal mitochondrial metabolism is closely linked to synaptic plasticity and highlight the importance of studying neurophysiological activity physiologically relevant glucose conditions.

Protein AMPylation is a pervasive posttranslational modification with an emerging role in neurodevelopment. In metazoans the two highly conserved protein AMP-transferases together with a diverse group of AMPylated proteins have been identified using chemical proteomics and biochemical techniques. However, the function of this modification remains largely unknown. Particularly problematic is the localization of thus far identified AMPylated proteins and putative AMP-transferases. Here, we uncover protein AMPylation as a novel posttranslational modification of luminal lysosomal proteins characteristic in differentiating neurons. Through a combination of chemical proteomics, advanced gel-based separation of modified and unmodified proteins and activity assay, we show that an AMPylated, lysosomal soluble form of exonuclease PLD3 increases dramatically during neuronal maturation and that AMPylation inhibits its catalytic activity. Together, our findings unveil so far unknown lysosomal posttranslational modification, its connection to neuronal differentiation and putatively provide a novel molecular rationale to design of therapeutics for lysosomal storage diseases.

In a healthy brain, astrocytes maintain neuronal homeostasis by removing proteins like tau from the extracellular space, preventing their uptake by neurons. In Alzheimers disease (AD), this function is impaired, contributing to tau accumulation. Many AD risk genes are linked to endocytosis pathways, suggesting their role in AD pathogenesis. Astrocytes can internalize, degrade, and release tau, but the mechanisms remain unclear. BAG3, a multifunctional protein, regulates vacuolar processes and interacts with clathrin-mediated endocytosis (CME) components. However, its role in astrocytic CME and tau processing is not fully understood. We show BAG3 depletion in astrocytes reduces clathrin-AP-2 interaction, inhibits CME-dependent epidermal growth factor receptor internalization, and decreases tau uptake. Live-cell imaging reveals BAG3 depletion impairs CME dynamics, increasing clathrin particle lifetimes. BAG3 depletion also alters endolysosomal compartments, increasing Lamp1+ puncta and tau co-localization. These findings highlight BAG3s role in CME, tau trafficking, and vacuolar processes, suggesting its dysfunction may contribute to AD pathogenesis.

Post-acute sequelae of SARS-CoV-2 infection (PASC), commonly referred to as Long COVID, comprise a constellation of persistent, recurrent, or newly emerging symptoms that may endure for months or years following acute infection. Beyond respiratory impairment, PASC is characterized by a wide spectrum of extrapulmonary manifestations, among which neurological and neuropsychiatric symptoms are highly prevalent. Reported features include olfactory dysfunction with loss of smell and taste, fatigue, neuroinflammation, cognitive and memory impairment, depression, and anxiety, with some symptoms persisting up to one year post-infection. Despite increasing recognition of these complications, the molecular mechanisms underlying post-COVID neurological sequelae remain poorly defined. In this study, we employed a label-free quantitative (LFQ) proteomics approach to investigate protein alterations in olfactory neuroepithelium-derived stem cells (ONEs), a unique population of neural progenitors located in the olfactory mucosa at the interface between the respiratory system and both the peripheral and central nervous systems. Due to their anatomical exposure and susceptibility to SARS-CoV-2, ONEs represent a highly relevant translational model for exploring virus-associated neurobiological processes. ONEs derived from healthy donors were incubated with serum from either asymptomatic PCR-positive individuals (AS; n=4) or critically ill hospitalized patients (CR; n=6). Proteomic profiling revealed a distinct differential protein expression pattern in ONEs exposed to CR serum compared with AS serum. Altered pathways were associated with viral infection responses, respiratory and cardiovascular dysfunction, and notably, cerebrovascular and nervous system disorders. These findings highlight the vulnerability of ONEs to systemic factors associated with severe COVID-19 and provide molecular insight into mechanisms potentially contributing to persistent neurological sequelae in PASC. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=110 SRC="FIGDIR/small/710460v1_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@12cfda5org.highwire.dtl.DTLVardef@c0636borg.highwire.dtl.DTLVardef@bf303eorg.highwire.dtl.DTLVardef@1f861e9_HPS_FORMAT_FIGEXP M_FIG C_FIG

Arsenic trioxide (ATO), an industrial and environmental chemical with potential for accidental or intentional exposure, exerts profound neurotoxic effects. Its single acute exposure has been linked to delayed neurological and neurodegenerative outcomes. However, the molecular and cellular pathways driving these long-term manifestations remain poorly defined. In this study, combining human iPSC-derived neuronal and in vivo mouse model, we uncovered that the acute ATO exposure activates cellular stress pathway, which drives long-term neurotoxic and associated functional outcomes. We found that ATO induces integrated stress response (ISR) signaling in human iPSC-derived neurons. To model the impact of accidental ATO exposure in vivo, we administered a single high dose of ATO to C57BL/6J wild type mice. Four weeks post-treatment, ATO-exposed mice displayed neuropsychological symptoms and cognitive deficits. Brain analyses of ATO-challenged mice revealed elevated ISR activity marked by the increased phosphorylation of PERK and eIF2 and upregulation of the transcription factors, CHOP and ATF4. Transcriptomic profiling using bulk RNAseq revealed activation of pathways associated with stress and neuroinflammatory responses. Consistently, increased DNA damage and dysregulation of the STING-mediated innate immune response were also found in the brain of ATO-challenged mice. Pharmacological inhibition of the ISR with a small-molecule inhibitor, ISRIB mitigated ISR activation and preserved synaptic integrity in mouse hippocampal cells. In conclusion, our data identify ISR activation and DNA damage-driven immune dysregulation as key pathogenic drivers of ATO-induced delayed neurotoxicity and cognitive deficits and highlight ISR inhibitors as promising therapeutics to mitigate these effects.

Human neural organoids (NOs) provide a powerful platform for investigating synaptic development and dysfunction during early neurodevelopment. However, methodologies for isolating functional synaptic structures from these models remain limited. Here, we present a differential centrifugation protocol enabling the enrichment of growth cone particles (GCPs) and immature synaptosomes from air-liquid interface cerebral organoids (ALI-COs) at distinct developmental stages (day 90 and 150). Notably, the method avoids density gradients, requires minimal starting material while maintaining reproducibility across human and murine tissues. Quantitative proteomic profiling revealed significant enrichment of growth cone markers (e.g. GAP43) and classical synaptosomal proteins (e.g. PCLO, BSN, SYN1). Transmission electron microscopy (TEM) confirmed the presence of membrane-enclosed GCPs with fibrous content and mitochondria in day 90 isolates, and immature synaptosomes containing synaptic vesicles on day 150. Functional viability of both types of synaptic structures was demonstrated through KCl-induced depolarization, which triggered phosphorylation changes in growth cone proteins (GAP43, MARCKS, MARCKSL1), cytoskeletal regulators (DCLK1, SHTN1, MARK4, MAP1B) and protein kinases (CAMK2G, PRKCE) in day 90 GCPs, as well as classical synaptic vesicle cycle proteins (SYN1, DNM1, RPH3A) at day 150. Overall, this study establishes a centrifugation-based protocol for isolating growth cones and immature synapses from human organoids, capturing key stages of synaptic development and enabling scalable, patient-compatible models to study synaptic function and dysfunction in neurodevelopmental and neurodegenerative disorders.

N-methyl-D-Aspartate receptors (NMDARs) are calcium-permeable ion channels that are ubiquitously expressed within the glutamatergic postsynaptic density. Phosphorylation of NMDAR subunits defines receptor activity and surface localization. Modulation of NMDAR phosphorylation by kinases and phosphatases regulates calcium entering the cell and subsequent activation of calcium-dependent processes. Spinophilin is the major synaptic protein phosphatase 1 (PP1) targeting protein that controls phosphorylation of myriad substrates via targeting or inhibition of PP1. Spinophilin limits NMDAR function in a PP1-dependent manner and we have previously shown that spinophilin sequesters PP1 away from the GluN2B subunit of the NMDAR, which results in increased phosphorylation of Ser-1284. However, how spinophilin modifies NMDAR function is unclear. Herein, we detail that while Ser-1284 phosphorylation increases calcium influx via GluN2B-containing NMDARs, overexpression of spinophilin decreases GluN2B-containing NMDAR activity by decreasing its surface expression. In hippocampal neurons isolated from spinophilin knockout animals there is an increase in cleaved caspase-3 levels compared to wildtype mice; however, this effect is not exclusively due to NMDAR activation; suggesting multiple putative mechanisms by which spinophilin may modulate caspase cleavage. Behaviorally, our data suggest that spinophilin knockout mice have deficits in spatial cognitive flexibility, a behavior associated GluN2B function within the hippocampus. Taken together, our data demonstrate a unique mechanism by which spinophilin modulates GluN2B containing NMDAR phosphorylation, channel function, and trafficking and that loss of spinophilin promotes pathological sequelae associated with GluN2B dysfunction. HIGHLIGHTSO_LISpinophilin bidirectionally regulates GluN2B-containing NMDAR function. C_LIO_LILoss of spinophilin in primary hippocampal neurons increases a pro-apoptotic marker. C_LIO_LILoss of spinophilin in vivo decreases measures of spatial cognitive flexibility. C_LI Graphical AbstractSpinophilin increases the phosphorylation of Ser-1284 on GluN2B, thereby enhancing calcium influx through the GluN2B containing NMDARs. In contrast, spinophilin limits GluN2B-containing surface expression putatively due to modulation of GluN2B interactions with endocytotic proteins. Since the second effect of spinophilin occurs independent of the first, we observe an overall decrease in calcium influx through GluN2B containing NMDARs when spinophilin is present. This low, basal calcium influx is less likely to be promote calcium-dependent activation of caspase and downstream apoptotic pathways and permits flexible search strategies and behaviors. In the absence of spinophilin, the spinophilin-driven internalization of the receptors is decreased, more receptors are expressed on the surface and calcium influx into the cell is increased. This high levels of intracellular calcium triggers apoptotic pathways leading to cell death. This impact may be more dramatic in cells with high expression of GluN2B-containing NMDA receptors. This loss of spinophilin reduces cognitive flexibility in hippocampal dependent tasks. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=116 SRC="FIGDIR/small/424812v1_ufig1.gif" ALT="Figure 1"> View larger version (37K): org.highwire.dtl.DTLVardef@1548b5org.highwire.dtl.DTLVardef@158a0aaorg.highwire.dtl.DTLVardef@19c185dorg.highwire.dtl.DTLVardef@103848b_HPS_FORMAT_FIGEXP M_FIG C_FIG

Extensive research has focused on extracellular-signal regulated kinase (ERK) 1/2 phosphorylation across various memory and plasticity models. However, the precise mechanisms linking ERK activity to memory stabilization and restabilization are still poorly understood, and the role of ERK1/2 dimerization remains unexplored. ERK dimerization is essential for the binding and activation of cytoplasmic targets, many of which are involved in memory and plasticity. In this study, we investigated the role of ERK2 dimerization in long-term memory and synaptic plasticity. We found that reactivation of a weak inhibitory avoidance (wIA) memory led to a significant reduction in hippocampal ERK2 dimerization. Furthermore, intrahippocampal infusion of DEL-22379 (DEL), an ERK dimerization inhibitor, following memory reactivation had a bidirectional effect: it blocked the reconsolidation of a strong inhibitory avoidance (sIA) memory but enhanced the reconsolidation of a wIA memory. Moreover, DEL administration blocked hippocampal ERK2 dimerization in vivo and impaired high-frequency stimulation-induced long-term potentiation (LTP) in hippocampal slices. These findings demonstrate that ERK2 dimerization occurs in the intact mouse nervous system and plays a pivotal role in plasticity and memory. While further research is needed, this study highlights the relevance of ERK dimerization in these processes.

1.Cholesterol in the central nervous system (CNS) is largely unesterified (>99%) and is predominantly present in the myelin sheath ([~]70% of total CNS cholesterol). Damage to the myelin sheath can result in the conversion of cholesterol to cholesterol esters, which occurs in many neurological diseases, including multiple sclerosis. In this study, we measured longitudinal CNS free cholesterol and cholesterol ester levels in a genetic mouse model during postnatal myelination, demyelination, and remyelination using gas chromatography-mass spectrometry with single ion monitoring technique (GC-MS-SIM) and liquid chromatography mass spectrometry (LC-MS). Cholesterol levels in healthy mouse brains increased up to 38 weeks. In contrast, cholesterol in the healthy spinal cord increased during postnatal timepoints, but then remained steady out to 38 weeks. Interestingly, cholesterol esters in the spinal cord were highest at P1 and drastically reduced by P42, while the brain had similar levels during all postnatal time points. During demyelination, both brain and spinal cord cholesterol levels were significantly reduced as compared to healthy mice and failed to return to normal cholesterol levels even during remyelination. Absolute quantification of cholesterol esters during peak demyelination revealed that cholesterol esters comprise 19% of the total cholesterol pool in the brain and 65% in the spinal cord. The lack of recovery in CNS cholesterol levels after demyelination suggests that healthy de novo cholesterol synthesis pathways are disrupted in this model. Absolute quantification of CNS cholesterol is critical for revealing mechanisms of cholesterol regulation during disease and identifying targets for restoring cholesterol to promote myelin repair.

Amyloid-{beta} (A{beta}) oligomers are believed to be important in the pathogenesis of Alzheimers disease (AD). A{beta}*56 is an A{beta} oligomer that has been reported in several lines of transgenic mice modeling AD, including Tg2576, hAPP-J20, 3xTgAD, 5xFAD, and APPTTA. In Tg2576 mice, A{beta}*56 appears several months before neuritic plaques and impairs memory when injected into the brains of healthy rodents. A{beta}*56 has several distinctive biochemical features: 1) it is soluble in aqueous buffers, 2) it is stable in the ionic detergent sodium dodecyl sulfate (SDS), 3) it has an apparent mass of 56 kDa whether measured by denaturing SDS polyacrylamide gel electrophoresis or non-denaturing size-exclusion chromatography, 4) it binds to A11 conformational antibodies that recognize non-fibrillar oligomeric assemblies, and 5) it contains canonical A{beta}(1-40) and/or A{beta}(1-42). Here, we show its presence in Tg2576 brain extracts enriched for extracellular proteins and conclude that A{beta}*56 is present in the extracellular space.

IntroductionThe etiology and progression of sporadic Alzheimers Disease (AD) have been studied for decades. One proposed mechanism is that amyloid-beta (A{beta}) proteins induce neuroinflammation, synapse loss, and neuronal cell death. Microglia play an especially important role in A{beta} clearance, and alterations in microglial function due to aging or disease may result in A{beta} accumulation and deleterious effects on neuronal function. However, studying these complex factors in vivo, where numerous confounding processes exist, is challenging, and until recently, in vitro models have not allowed sustained culture of microglia, astrocytes and neurons in the same culture. Here, we employ a tri-culture model of rat primary neurons, astrocytes, and microglia and compare it to co-culture (neurons and astrocytes) and mono-culture enriched for microglia to study microglial function (i.e., motility and A{beta} clearance) and proteomic response to exogenous A{beta}. MethodsWe established cortical co-culture (neurons and astrocytes), tri-culture (neurons, astrocytes, and microglia), and mono-culture (microglia) from perinatal rat pups. On days in vitro (DIV) 7 - 14, the cultures were exposed to fluorescently-labeled A{beta} (FITC-A{beta}) particles for varying durations. Images were analyzed to determine the number of FITC-A{beta} particles after specific lengths of exposure. A group of cells were stained for {beta}III-tubulin, GFAP, and Iba1 for morphological analysis via quantitative fluorescence microscopy. Cytokine profiles from conditioned media were obtained. Live-cell imaging with images acquired every 5 minutes for 4 hours was employed to extract microglia motility parameters (e.g., Euclidean distance, migration speed, directionality ratio). Results and discussionFITC-A{beta} particles were more effectively cleared in the tri-culture compared to the co-culture. This was attributed to microglia engulfing FITC-A{beta} particles, as confirmed via epifluorescence and confocal microscopy. Adding FITC-A{beta} significantly increased the size of microglia, but had no significant effect on neuronal surface coverage or astrocyte size. Analysis of the cytokine profile upon FITC-A{beta} addition revealed a significant increase in proinflammatory cytokines (TNF-, IL-1, IL-1{beta}, IL-6) in tri-culture, but not co-culture. In addition, A{beta} addition altered microglia motility marked by swarming-like motion with decreased Euclidean distance yet unaltered speed. These results highlight the importance of cell-cell communication in microglia function (e.g., motility and A{beta} clearance) and the utility of the tri-culture model to further investigate microglia dysfunction in AD.

Glial cells are essential to understand Alzheimers disease (AD) progression, given their role in neuroinflammation and neurodegeneration. There is a need for reliable and easy to manipulate models that allow studying the mechanisms behind neuron and glia communication. Currently available models such as cocultures require complex methodologies and/or might not be affordable for all laboratories. With this in mind, we aimed to establish a straightforward in vitro setting with neurons and glial cells to study AD. We generated a triple co-culture with neurons, microglia and astrocytes. Immunofluorescence, western blot and ELISA techniques were used to characterize the effects of oligomeric A{beta} (oA{beta}) in this model. We found that, in the triple co-culture, microglia increased the expression of anti-inflammatory markers Arginase I and TGF-{beta}1, and reduced pro-inflammatory iNOS and IL-1{beta}, compared with microglia alone. Astrocytes reduced expression of pro-inflammatory A1 markers AMIGO2 and C3, and displayed a ramified morphology resembling physiological conditions. Lastly, neurons increased post-synaptic markers, and developed more and longer branches than in individual primary cultures. Addition of oA{beta} in the triple coculture reduced synaptic markers and increased microglial activation, which are hallmarks of AD. Consequently, we developed a reliable model, where cells better resemble physiological conditions: microglia are less inflammatory, astrocytes are less reactive and neurons display a more mature morphology than in individual primary cultures. Moreover, we were able to recapitulate A{beta}-induced synaptic loss and inflammation. This model emerges as a powerful tool to study neurodegeneration and inflammation in the context of AD and other neurodegenerative diseases. Table of content image O_FIG_DISPLAY_L [Figure 1] M_FIG_DISPLAY C_FIG_DISPLAY Main pointsO_LIIn our model, microglia and astrocytes are less reactive, and neurons have a more mature morphology than in primary cultures. C_LIO_LIoA{beta} reduced synaptic markers and increased microglial activation. C_LIO_LIThis triple co-culture is a reliable tool to study neurodegeneration and gliosis in vitro. C_LI

Cuprizone is a copper chelator that induces mitochondrial dysfunction in myelin-producing oligodendrocytes and hepatic cells. Inhibition of oxidative phosphorylation has been proposed as a potential mechanism, but the exact relationship between shape changes and metabolic alterations is not well-understood. Here we explore how mitochondrial shape influences oxidative phosphorylation rates by performing simultaneous imaging and respiration measurements within intact cells. We observed that MO3.13 cells exposed to cuprizone undergo an initial increase in respiration followed by mitochondrial dysfunction and genetic dysregulation within 8 hours. Oxygen consumption was measured within 30 minutes of treatment and found to be elevated. This increase was followed by swelling of mitochondria over the first 8 hours, but preceded cell death by 24 hours. A transcriptomic analysis of early changes in cellular gene expression identified alterations within the electron transport chain, stress response pathways, and mitochondrial dynamics compared to control cells. These results suggest that pathological mitochondrial swelling is associated with increased oxygen consumption rates leading to transcriptional changes in respiratory complexes and ultimately mitochondrial failure.