ASN Neuro

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

Mutations in human LIS1 cause lissencephaly, a severe developmental brain malformation. Although most stud-ies focus on development, LIS1 is also expressed in adult mouse tissues. We previously induced LIS1 knockout (iKO) in adult mice using a Cre-Lox approach with an actin promoter driving CreERT2 expression. This proved to be rapidly lethal, with evidence pointing toward nervous system dysfunction. CreERT2 activity was observed in astrocytes, brainstem and spinal motor neurons, and axons and Schwann cells in the sciatic and phrenic nerves, suggesting dysfunctional cardiorespiratory and motor circuits. However, it is unclear how LIS1 knockout in these different cell types contributes to the lethal phenotype. We now report that LIS1 depletion from astro-cytes is not lethal to mice (male or female), although glial fibrillary protein (GFAP) expression is increased in all LIS1-depleted astrocytes. In contrast, LIS1 depletion from projection neurons causes motor deficits and rapid lethality in both males and females. This is accompanied by progressive, widespread axonal degeneration along the entire length of both motor and sensory axons. Interestingly, sensory neurons harvested from iKO mice ini-tially extend axons in culture but soon develop axonal swellings and fragmentation, indicating axonal degenera-tion. LIS1 is a prominent regulator of cytoplasmic dynein 1 (dynein, hereafter), a microtubule motor whose dis-ruption can cause both cortical malformations and later-onset neurodegenerative diseases, such as Charcot-Marie-Tooth disease. Our results raise the possibility that LIS1 depletion, through disruption of dynein function in mature axons, may lead to Wallerian-like axon degeneration without traumatic nerve injury.

Tau protein, the primary component in neurofibrillary tangles characteristic of Alzheimers Disease and related dementia disorders, normally regulates microtubule growth and stability. While tau dysfunction contributes to the progression of tauopathies, the role of microtubules in disease has remained unclear. Through forward genetic screening in Caenorhabditis elegans tauopathy models, we found multiple tubulin gene mutations that rescue tau-mediated neurodegeneration. Whole animal behavioral and in vitro biochemical assays were employed to characterize mutation-driven effects on neuron function, neurodegeneration, and effects on tubulin and tau proteins as well as microtubule function. Mutant tubulin genes were found to confer different levels of suppression correlating with the level of mutant gene expression. Mutant tubulins did not drastically alter total tau protein levels, tau phosphorylation or aggregation, however tau-induced neurodegeneration was rescued. The suppression of tau toxicity by tubulin gene mutations cannot be explained by changes in tau or tubulin expression, tau phosphorylation, or tau aggregation state. Rather the tubulin mutations appear to act by influencing global microtubule properties. In vitro experiments using C. elegans tubulin in semi-isolated and isolated contexts have indicated changes to microtubule properties without observable changes to tau-tubulin affinity. This work suggests that manipulation of microtubules can rescue tauopathy even when pathological tau species persist, supporting the importance of understanding microtubule contributions to disease progression and investigation into microtubule targeted gene therapy or small molecule approaches for tauopathy intervention.

IntroductionThe exploration of alternative strategies for neural tissue regeneration and repair is giving rise to a novel paradigm in neurosurgery: fusogenic therapy. This approach promises rapid restoration of peripheral nerve and spinal cord function by circumventing Wallerian degeneration and eliminating the delay associated with axonal regrowth. Its potential stems from the capacity of fusogens to induce axonal fusion and achieve immediate membrane sealing, complemented by their pronounced neuroprotective properties. However, experimental data on fusogens and their effects are inconsistent, often contentious, and derived using heterogeneous methodologies. MethodsWe present the first comprehensive systematic review covering nearly four decades of research on fusogens for axonal membrane repair and 26 years of their experimental and clinical application in mammalian and human models for peripheral and central nervous system restoration. The review includes a meta-analysis of fusogen efficacy following traumatic spinal cord and peripheral nerve injuries. ResultsConducted in accordance with the PRISMA 2020 flow protocol and PICO criteria, our analysis incorporates 86 sources, 20 of which were included in the meta-analysis. DiscussionIn summary, we have systematized the prevailing approaches and methods for fusogen application, delineated key contentious issues, and identified promising directions for the development of axonal fusion technology.

ObjectiveTo determine whether non-axon optic nerve morphometric features correlate with clinical visual function as strongly as the traditional axon count gold standard. DesignCross-sectional histological analysis with longitudinal clinical correlation. SubjectsEighteen mice from three strains: C57BL/6J (n=6), BXD51 (n=6), and DBA/2J (n=6). MethodsLeft eye (OS) optic nerves from mice euthanized at 12 months of age were resin-embedded and stained with p-phenylenediamine. Bright-field cross-sectional images were segmented using an AxonDeepSeg-based workflow to generate axon, myelin, whole nerve, and glial coverage masks for morphometric quantification. Seven morphometrics were extracted: axon count (nAx), axon density (AxDen), glial coverage area ratio (GliaR), mean solidity (Sol), mean axon diameter (AxDiam), mean myelin area (MyArea), and mean axon-myelin area (AxMyArea). Morphometrics were correlated with longitudinal clinical data collected at 1, 3, 6, 9, and 12 months, including visual acuity (VA), contrast threshold, intraocular pressure (IOP), and pattern electroretinography P50 and N95 amplitudes (PERG P50 and N95). Main Outcome MeasuresPearson correlation coefficients were used to assess associations between morphometric features and clinical measures, and Fisher z-transformed meta-analytic correlations were used to aggregate these associations across ages. ResultsVA and contrast threshold demonstrated strong correlations with GliaR that matched or exceeded nAx. Meta-analysis across ages revealed GliaR correlated with VA (r = -0.84, p = 4.49 x 10-21) and contrast threshold (r = 0.86, p=7.55 x 10-23), comparable to nAx correlations with VA (r = 0.80, p=8.13x10-17) and contrast threshold (r = -0.80, p= 1.74x10-16). Structure-function relationships shifted with age: at 6 months, GliaR had the strongest correlation with contrast threshold (r = 0.96), while at 12 months, AxDiam became the dominant correlate of both VA (r = 0.77) and contrast threshhold (r = -0.74). IOP, PERG P50, and PERG N95 exhibited weak correlations with all morphometrics (|r| < 0.27). ConclusionsNon-axon morphometrics, particularly glial coverage area ratio, correlate with visual function as strongly as traditional axon count. Automated optic nerve assessment should incorporate glial and other non-axon features. Further, stage-aware biomarker selection may better capture structure-function relationships in glaucoma.

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

Riluzole is the most commonly prescribed among the limited approved therapies for amyotrophic lateral sclerosis (ALS), a neurodegenerative disorder characterized by progressive motoneuron loss and paralysis. It is thought to act by suppressing motoneuron excitability and glutamate release, but its clinical benefits are modest and often diminish over time. We previously showed that homeostatic mechanisms in the SOD1G93A (mSOD1) mouse model of ALS are hyperactive and prone to overcompensation. Here, we tested whether such dysregulated homeostasis antagonizes the effects of riluzole. Wild-type (WT) and presymptomatic mSOD1 mice received therapeutic doses of riluzole in drinking water for 10 days, with untreated littermates of both genotypes serving as controls. Motoneuron excitability and synaptic inputs were then examined using intracellular recordings from the isolated sacral spinal cord. The data showed that chronic riluzole treatment increased motoneuron excitability and polysynaptic inputs in mSOD1 mice but produced no detectable changes in WT motoneurons. These results suggest that hyperactive homeostatic mechanisms in ALS counteract the suppressive effects of riluzole. Notably, mSOD1 motoneurons exhibited larger membrane capacitance than WT, consistent with their increased cell size at this disease stage. Riluzole treatment reduced motoneuron membrane capacitance in mSOD1 mice to the range observed in WT animals, indicating normalization of cell size and potentially reduction in metabolic demand. Together, these findings help explain the limited clinical efficacy of riluzole while revealing a previously unrecognized neuroprotective mechanism of the drug in ALS.

Oligodendrocyte precursor cells (OPCs) are unique glial cells that communicate bidirectionally with neurons. Neuronal inputs drive various OPC behaviors, including proliferation and differentiation, immunomodulation, blood brain barrier regulation, synapse engulfment and axonal remodeling. OPCs are implicated in numerous stress and pain conditions, where their involvement is likely driven by neuronal activity (ie. neurotransmitter and neuropeptide signaling). One neuropeptide causally involved in chronic pain and stress conditions is calcitonin gene-related peptide (CGRP). Here, we tested the hypothesis that OPCs receive direct inputs from CGRP-containing neurons in the adult brain. Using RNAscope, immunofluorescence and analysis of single-cell datasets, we find that OPCs express receptors for CGRP and we identify close spatial contacts between CGRP and OPCs, with nearly half of CGRP puncta occurring within 1 {micro}m of an OPC. Some of these contacts appear to be synaptic, with CGRP-OPC contacts colocalizing with the presynaptic protein Bassoon and the postsynaptic protein PSD-95. This work suggests the presence of both diffuse and more direct forms of CGRP signaling to OPCs, raising the importance of future experiments to identify both the mode of CGRP release onto OPCs and the functional effects of these different contact types.

Vestibular schwannomas (VS) cause vestibular function loss by mechanisms still poorly understood. We evaluated the vestibulo-ocular reflex by the video-assisted Head Impulse Test (vHIT) in patients with planned tumour resection by a trans-labyrinthine approach. The vestibular sensory epithelia were collected and processed by immunofluorescent labelling for confocal microscopy analysis of sensory hair cell subtypes (type I, HCI, and type II, HCII), calyx endings of the pure-calyx afferents, and the calyceal junction normally found between HCI and the calyx (n=23). Comparing Normofunction and Hypofunction patients, we concluded that worse vestibular function associates with decreased HCI and HCII counts in the sensory epithelia and with increased proportion of damaged calyces. A decrease in the number of HCI and calyx endings of the pure-calyx afferents was recorded to associate with age increase. Partial least squares regression (PLSR) models indicated that VS and age had independent, additive effects on vestibular function. Correlation analyses indicated that lower vHIT gains associate with lower numbers of HCI and increased percentages of damaged calyces. These data support the hypothesis that the deleterious effect of VS on vestibular function is mediated, at least in part, by its damaging impact on the vestibular sensory epithelium. They also provide further evidence for the dependency of the vestibulo-ocular reflex on HCI function and for the calyceal junction pathology as a common response of the sensory epithelium to HC stress.

BackgroundFlexibility and robustness of neuronal function are closely linked to degeneracy, the ability of distinct structural or parametric configurations to produce similar functional outcomes. At the cellular level, this often manifests as ion-channel degeneracy, in which multiple combinations of intrinsic conductances yield comparable electrophysiological phenotypes. MethodologyWe used a population-based, data-driven modelling framework to generate large ensembles of biophysically detailed CA1 pyramidal neuron models constrained by somatic electrophysiological features extracted from patch-clamp recordings in acute slices from early-birth rats. 10 reconstructed morphologies were incorporated, and model populations were analyzed using parameter correlation analysis, principal component analysis, and generalization tests to assess robustness, degeneracy, and morphology dependence of intrinsic properties. ConclusionsAcross the model population, similar somatic firing behaviours emerged from widely different combinations of intrinsic parameters, demonstrating robust two-level ion channel degeneracy both within and across morphologies. Each morphology occupied a distinct region of parameter space, indicating morphology-specific compensatory effects, while weak pairwise parameter correlations suggested distributed compensation rather than tight parameter dependencies. Even with a fixed morphology, multiple parameter subspaces supported comparable electrophysiological phenotypes. Generalization across morphologies was structure-dependent and non-reciprocal, with successful parameter similarity occurring preferentially between structurally similar neurons. Interestingly, to accurately simulate spike-frequency adaptation, it was important to retain some kinetic properties of the ion channel models as free parameters during optimization. Together, these findings show that dendrite morphology shapes the valid parameter space, and similar electrophysiology of CA1 pyramidal neurons arises from the interplay between structural variability and ion-channel diversity. This work highlights the importance of population-based modelling for capturing biological variability and provides insights into how neuronal robustness might be maintained despite substantial heterogeneity, and offers a scalable pipeline for generating biophysically realistic CA1 neuron populations for use in network simulations. Author summaryNeurons must reliably process information even though their internal components, such as ion channels and cellular shape, can vary widely from cell to cell. How stable behaviour emerges from such variability is a fundamental question in neuroscience. In this study, we explored this problem using detailed computer models of early-birth rat hippocampal CA1 pyramidal neurons, a cell type that plays a central role in learning and memory. Instead of building a single "average" neuron model, we created large populations of models that all reproduced key experimental recordings but differed in their internal parameters. We found that neurons with different shapes and different combinations of ion channels could nevertheless generate similar electrical activity. This phenomenon, known as ion channel degeneracy, allows neurons to remain functional despite biological variability or perturbations. Our results show that neuronal shape strongly influences which parameter combinations are viable, but that multiple solutions exist even for the same morphology. The population of models we provide offers a resource for future studies of early-birth CA1 pyramidal cell function and dysfunction.

Alzheimers disease (AD) is a devastating neurodegenerative disorder characterized by memory loss and a decline in cognitive function. Hallmarks of AD include an age-dependent accumulation of toxic amyloid beta (A{beta}) 42 in the brain, energy dyshomeostasis caused by mitochondrial dysfunction, and iron overload. However, the role of iron overload and mitochondrial dysfunction in AD pathology is unknown and their precise relationship with A{beta} 42 toxicity in AD pathology is unclear. C. elegans provide a powerful model system to untangle and clarify these relationships. In this study, we quantify the temperature-dependence of iron toxicity (16, 20 and 25C) in neurons and muscle of C. elegans that overexpress A{beta} 42. We found that A{beta} 42, regardless of the cell-type expression, caused accelerated paralysis compared to age-matched WT worms with the greatest degree of paralysis observed at an elevated temperature (25C). Moreover, the combination of iron toxicity and A{beta} 42 results in an enhanced paralytic phenotype at 16C. Thus, iron exposure potentiates A{beta} toxicity observed at low temperatures. Iron toxicity stimulated both maximum (State 3) and leak (State 4) respiration in WT and A{beta} 42 worms. A{beta} 42 worms also exhibited increased leak respiration at baseline that was further exacerbated by iron toxicity. Iron burden and sensitivity increased A{beta} 42 peptide toxicity. A{beta} 42 worms exhibited reduced levels of Ca, Zn, Mn, and K. Overall, our results suggest that iron potentiates A{beta} toxicity at low temperature and enhances A{beta} peptide mediated mitochondrial bioenergetic dysfunction in C. elegans. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=140 SRC="FIGDIR/small/714217v1_ufig1.gif" ALT="Figure 1"> View larger version (29K): org.highwire.dtl.DTLVardef@9eaf46org.highwire.dtl.DTLVardef@542eforg.highwire.dtl.DTLVardef@16d9678org.highwire.dtl.DTLVardef@1b1b16d_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LITemperature stress modulates the synergetic interactions of iron toxicity and A{beta} 42 pathology C_LIO_LIIron sensitivity drives increased cell-type specific A{beta} 42 pathology C_LIO_LIEnergy dyshomeostasis via impaired mitochondrial function and increased proton leak contributes to iron- and A{beta}-induced pathology C_LI

BackgroundSpinal cord injury (SCI) triggers persistent neuroinflammation, gliosis, neuronal loss, and demyelination, leading to motor deficits and neuropathic pain. Botulinum neurotoxin type A (BoNT/A) has shown anti-inflammatory and neuroprotective effects in acute SCI, but its potential in the chronic phase remains unclear. This study investigates whether combining BoNT/A with electrical muscle stimulation (EMS) enhances recovery in chronic SCI. MethodsAdult mice with severe thoracic SCI (paraplegic) underwent EMS (30 min/day for 10 non-consecutive days starting 3 days post-injury) or no stimulation. Fifteen days after SCI, animals received a single intrathecal injection of BoNT/A (15 pg/5 L) or saline. Functional recovery was assessed up to 60 days as well as in moderate and mild SCI mice, neuropathic pain onset and maintenance were evaluated. Spinal cord tissue was analysed for astrocytic and microglial morphology, neuronal and oligodendroglia survival, myelin protein expression, and in vitro effects on oligodendrocyte precursor cells (OPCs). The phenotype of hindlimb muscles was evaluated through morphological and gene expression analyses. ResultsEMS was able to counteract muscle atrophy and fibrosis, and when combined with BoNT/A, also denervation. Moreover, the combination restored hindlimb motor function in chronic SCI, whereas BoNT/A or EMS alone were ineffective. Neuropathic pain, a common comorbidity associated with SCI, was mitigated by BoNT/A treatment even when administered in the chronic phase. BoNT/A reduced astrocytic hypertrophy and excitatory synapse association and was associated with a morphology-based redistribution of microglial profiles toward a resting-like classification, decreased apoptosis, and increased neuronal and oligodendroglia survival. Myelin basic protein expression was significantly elevated in vivo. In vitro, BoNT/A promoted OPC differentiation into myelinating oligodendrocytes, increased process complexity, and upregulated Myelin basic protein, galactocerebroside C, proteolipid protein, and myelin oligodendrocyte glycoprotein under both proliferative and differentiating conditions. Cleaved SNAP25 colocalization with OPC confirmed direct BoNT/A internalization and activity. ConclusionsBoNT/A exerts multi-cellular neuroprotective actions in chronic SCI, supporting neuronal and oligodendroglia survival, reducing neuroinflammation, enhancing remyelination and the combination with EMS promotes substantial recovery of muscle homeostasis within a permissive microenvironment shaped by early stimulation. Its efficacy depends on a permissive microenvironment achieved through EMS. These results provide strong rationale for the clinical evaluation of BoNT/A as a therapeutic strategy for chronic SCI.

PurposeRetinal ganglion cells (RGCs) are essential for visual signal transmission, yet they are vulnerable to injury and degeneration. Gene modulation in RGCs using adeno-associated virus (AAV) offers a promising avenue for neuroprotection and regeneration, but promoters lack sufficient RGC specificity, limiting precision needed for preclinical studies. This study aims to identify novel promoter-enhancer combinations (PECs) to achieve gene expression preferentially in RGCs. MethodsWe evaluated existing transcriptomic data to identify Neuritin 1(Nrn1) as a gene with highly restricted RGC expression in the retina. Synthetic PECs derived from human and mouse Nrn1 loci were incorporated into AAV2 vectors driving expression of a nuclear-targeted reporter GreenLantern. AAVs were delivered via intravitreal injection into C57BL6/J mice, and transduction efficiency and RGC specificity were evaluated in both young and aged retinas and those subjected to intraorbital optic nerve crush (ONC), using immunohistochemistry and quantitative analysis of RBPMS+ cells. ResultsWe found that AAV2 with a human Nrn1 PEC drives gene expression in RGCs. Quantitative analysis revealed that over 83% of transduced cells were RBPMS-positive, indicating robust RGC selectivity and significantly outperforming ubiquitous promoters. Notably, the Nrn1 PEC retained strong and selective transgene expression in RGCs in aged mice and following ONC, demonstrating its resilience under aged and injury conditions. ConclusionThe Nrn1 PEC enables efficient and injury-resilient gene expression in RGCs, addressing a key limitation in cell-specific targeting. This AAV-incorporated PEC offers a robust platform for evaluating neuroprotective interventions and accelerates translational development of gene therapies for glaucoma and other optic neuropathies.

Open-angle glaucoma (OAG) affects approximately 57.5 million individuals worldwide and is characterized by the progressive loss of retinal ganglion cells (RGC) and irreversible optic nerve damage resulting from chronic ocular hypertension. Intraocular pressure (IOP) is the only major modifiable risk factor in OAG and clinical treatments necessarily aim to lower IOP in order to preserve RGCs and prevent vison loss. Pharmacological therapies, such as prostaglandin analog containing eye drops, are known to be effective at reducing IOP, but are critically undermined by poor patient compliance and are unable to control for potentially damaging diurnal fluctuations in IOP, leading to vision loss even in patients diagnosed early. Herein we evaluate the effectiveness of a long-acting, single use, prostaglandin-based recombinant adeno-associated virus (rAAV)-mediated IOP-lowering gene therapy treatment in glaucomatous DBA/2J mice and demonstrate that sustained IOP reduction leads to preservation of both optic nerve anatomy and function in end-stage glaucomatous disease. One Sentence SummaryIOP-lowering gene therapy provides partial anatomical and functional rescue in glaucomatous mouse model following single dose treatment

Microglia are the resident immune cells of the central nervous system and play key roles in the healthy brain during development and adulthood, as well as during neurodegenerative diseases - including Parkinsons disease (PD). Yet the role of microglia in PD pathogenesis has not been fully elucidated. Limitations of 2D cell culture and animal models in simulating human microglia in the brain parenchyma have contributed to this knowledge gap. Human midbrain organoids (hMOs) provide a promising model that can recapitulate elements of PD pathology but lack microglial cells. Here we adapt protocols for the differentiation of hMOs and human iPSC-derived microglia (iMG) to generate iMG-hMO assembloids. Within assembloids, integrated iMG (intMG) express canonical microglia markers and induce the release of cytokines and chemokines. Transcriptomic profiling by single cell RNA sequencing reveals that intMG adopt a more mature and inflammation-responsive state compared to 2D iMG. The integration of microglia results in increased signaling through inflammatory and trophic pathways that drive altered transcriptional signatures of dopaminergic neurons and astrocytes within assembloids. Overall, iMG-hMO assembloids have the potential to more faithfully model the role of microglia and neuroinflammation in PD pathogenesis.

Duchenne Muscular Dystrophy (DMD) is a debilitating degenerative condition with complex musculoskeletal and cognitive symptoms. The protein responsible, dystrophin, is expressed in both muscle tissue and within the central nervous system (CNS) where it localizes to inhibitory synapses. Recent work has shown that dystrophin loss in skeletal muscle leads to abnormalities in endocannabinoid signaling, particularly related to Cannabinoid Receptor Type 1 (CB1R) signaling pathways. CB1Rs are highly expressed throughout the CNS, and have been implicated in short- and long-term plasticity mechanisms. Despite this curious overlap, no work examines how dystrophin loss impacts CB1R signaling in the CNS, a mechanism that may contribute to the diverse neurological pathologies seen in DMD patients. To address this, we used a combination of immunofluorescent labeling and ex vivo electrophysiology to examine CB1R signaling at three classes of synapses within the cerebellum. Utilizing DMDmdx mice, a mouse model of DMD, we find that loss of dystrophin significantly impairs CB1R signaling specifically at parallel fiber-Purkinje Cell synapses, a key location for cerebellar learning. We also find that endocannabinoid-mediated long-term depression at these synapses is absent. Loss of endocannabinoid signaling and synaptic plasticity may contribute to cerebellar dysfunction and motor control symptoms in DMD. These data suggest that dystrophin loss may have previously undescribed consequences for CNS function, and that modulation of endocannabinoid signaling may be a therapeutic strategy for symptom management. Significance StatementDuchenne Muscular Dystrophy (DMD) is a degenerative condition with severe CNS deficits in addition to the well-known muscle weakening. However, no effective treatments currently exist for CNS-related aspects of this disease. Given that endocannabinoid signaling is altered in dystrophic muscle and the importance of endocannabinoid signaling in CNS function, we examined endocannabinoid signaling in the cerebellum of DMDmdx mice, a model of DMD. Utilizing immunolabeling and ex vivo electrophysiology, we find a significant decrease in CB1R expression and functionality specifically at parallel fiber synapses, resulting in reduced or abolished short- and long-term synaptic plasticity. These findings demonstrate that changes in endocannabinoid function contribute to CNS deficits in DMD and open the door to new potential therapeutic targets for treatment.

Hypoxic-ischemic injury is a major cause of olfactory dysfunction, yet the cellular and morphological mechanisms underlying this sensory loss remain poorly understood. Here, we investigated the structural, cellular, and functional effects of acute hypoxic exposure on the olfactory system of adult zebrafish (Danio rerio) of both sexes, a model organism with remarkable neuroregenerative capacity. Fish were subjected to 15 minutes of acute severe hypoxia (0.8 mg/L dissolved oxygen) and assessed at 1 and 5 days post-hypoxia (dph). We evaluated olfactory function by means of cadaverine-evoked aversive behavioral assays. Structural and morphological integrity and inflammation of the olfactory epithelium (OE) and olfactory bulb (OB) were characterized using immunohistochemistry, histological stainings, and a 2,3,5-triphenyltetrazolium chloride (TTC) colorimetric assay. Acute hypoxic exposure impaired olfactory-mediated behaviors without affecting locomotion or exploratory behavior. In the peripheral OE, hypoxia caused neurodegeneration, disruption of the nasal mucus layer, and robust leukocytic infiltration. We observed reduced mitochondrial dehydrogenase activity in the olfactory bulb (OB) along with reactive astrogliosis. Olfactory function recovered by 5 days, coinciding with full restoration of OE morphology, and supported by a strong proliferative response. These findings reveal a coordinated degenerative and regenerative response to hypoxia across the olfactory axis, with implications for understanding hypoxia-induced sensory loss and neural repair. SIGNIFICANCEThis work addresses an important gap in knowledge regarding the mechanisms linking hypoxic insult and olfactory dysfunction. By using adult zebrafish, an extraordinarily regenerative vertebrate, it also provides insight into neuronal repair and regenerative processes supporting olfactory recovery. The novelty of our study resides in that, to our knowledge, there are no studies that provide a comprehensive characterization of the effects of hypoxia in the olfactory system across molecular, histological, and functional levels. These findings advance our understanding of hypoxia-induced sensory neurodegeneration and regeneration, and highlight the zebrafish olfactory system as a powerful model for investigating neural repair mechanisms relevant to hypoxic-ischemic brain injury.

Deciding whether and how to act depends on a trade-off between the effort required to execute a given action and the potential reward for completing it. Impairments in this effort-reward trade-off have been proposed to underlie reduced movement vigor, or bradykinesia, in Parkinsons disease (PD). However, several mechanisms could alter the effort-reward trade-off in PD, each with unique implications for understanding and treating bradykinesia. Therefore, we individually examined whether people with PD (both on and off dopamine medication) demonstrated reduced sensitivity to reward value, increased perception of effort, or a biased mapping between effort and reward, compared to age- and sex-matched neurotypical controls. We found that people with PD exhibited increased effort perception and, surprisingly, no reduced sensitivity to reward value or a biased mapping between effort and reward. These findings suggest that effort perception could be an important factor driving bradykinesia in PD.

Glutamatergic neuronal synapses in the mouse neocortex mature during the first two months after birth. A key event during synaptic maturation is a change in short-term synaptic plasticity (STP), i.e. a switch from strong synaptic depression to a weaker depression or even facilitation. Glutamatergic pyramidal neurons located in the cortical layers II/III, layer V, and layer VI project axons through the corpus callosum where they release glutamate along their shafts and form glutamatergic synapses with oligodendrocyte precursor cells (OPCs). Here, we used single-cell electrophysiological recordings in brain slices to investigate synaptic plasticity at neuron-OPC synapses along axonal shafts in the white matter, and applied computation approaches to pinpoint the mechanisms of this plasticity. We found that during postnatal development of mice, there is a switch from short-term synaptic depression to short-term synaptic facilitation at glutamatergic neuron-OPC synapses in the corpus callosum. Synaptic delay of phasic neuron-OPC excitatory postsynaptic current shortens, and the amount of asynchronous release at neuron-OPC synapses decrease as animals mature, indicating that glutamate release becomes more synchronized. Our computational modelling suggests that both pre- and postsynaptic changes may contribute to the functional development and changes of plasticity at neuron-OPC synapses in the white matter. Taking together, our findings indicate that synaptic release machineries located at different sites along the same axon (i.e. axonal shaft in the white matter vs synaptic boutons in the grey matter) mature in a very similar fashion, STP occurs at both synaptic sites, and STP dynamics represent an important event during brain maturation.

Relay neurons of the dorsal lateral geniculate nucleus (dLGN) receive convergent inputs from retinal ganglion cells (RGCs). Retinogeniculate synapses exhibit a highly skewed distribution of synaptic strength, with a few strong inputs and many weak ones. Strong synapses are thought to dominate relay neuron activity. However, the contribution of individual inputs might not just depend on strength but also on short-term plasticity Using minimal stimulation recordings in acute mouse brain slices, we analyzed the electrophysiological properties of individual retinogeniculate synapses. We observed a robust inverse correlation between synaptic strength and short-term plasticity: weak synapses showed facilitation, whereas strong synapses exhibited pronounced depression. This was consistent with increasing vesicle release probability and enhanced AMPA receptor desensitization at stronger synapses. Analysis of synaptic current kinetics further suggested that variability in synaptic strength reflects not only differences in synapse size and AMPA receptor content but also differences in the electrotonic distance of synapses from the soma. Together, these results reveal systematic heterogeneity in both presynaptic and postsynaptic properties of retinogeniculate synapses. Therefore, the relative contribution of weak and strong inputs to relay neuron firing is likely activity-dependent, with strong synapses dominating when RGCs fire few action potentials and weaker inputs contributing more during sustained or high-frequency firing with several action potentials.