Cognitive decline in Alzheimer's disease (AD) correlates more strongly with tau pathology than with amyloid plaques, switching the therapeutic focus towards targeting tau pathology. Tau silencing therapies present an increasing interest as potential therapeutical approaches to treat AD due to their efficiency in reducing pathological tau burden. However, the effects of tau silencing on tau pathology formation and spreading, as well as on cognitive deficits, have not been investigated in AD or AD preclinical models expressing WT tau. In this study, we investigated the effects of Tau siRNA on tau pathology propagation in a mouse model of AD expressing 6 human WT tau isoforms, in which tau pathology formation and spreading has been initiated by intracerebral injection of pathological tau from a human AD brain. Specifically, we examined whether tau silencing affects tau pathology progression when started either simultaneously with the induction of tau pathology or subsequent to the onset of tau lesions, thereby mimicking the clinical scenario in which AD patients are typically diagnosed. Three months after tau pathology was induced, spatial learning and tau pathology were assessed. Cognitive performance was rescued, and tau pathology development was reduced when tau silencing started simultaneously with the induction of tau lesions. Nevertheless, Tau siRNA was ineffective on both cognitive performance and tau pathology propagation when administered after some development of tau pathology. Our results indicate that tau silencing therapy should be administered in early stages of the disease to achieve therapeutic efficacy on the development of tau pathology in AD.
BACKGROUND AND AIMS:Rett syndrome (RTT) is a severe neurological disorder caused by pathogenic variants in the MECP2 gene associated with gastrointestinal (GI) motility disorders strongly impacting patients' quality of life. Intestinal motility relies on coordinated neuronal activity in the enteric nervous system (ENS) where MECP2 is highly expressed. Here, we sought to determine whether cholinergic-mediated excitatory neuromuscular transmission could be affected in the ENS of a RTT mouse model and the functional consequences on intestinal motility. METHODS:In this study, 55 days-old wild type (WT) and Mecp2-knock-out (KO) mice were used. After confirming the reduction in GI transit time in vivo, intestinal mechanical activity was assessed in vitro by evaluating contractile responses of small intestinal muscle to electrical field stimulation (EFS) of the enteric nervous system (ENS). The function of the cholinergic pathway was evaluated using gene expression, protein, and enzymatic activity quantifications of different factors of the acetylcholine (ACh) metabolism. RESULTS:Our in vivo results confirm that the mouse models replicate the slowed GI transit previously identified in RTT patients and in the mouse model. In vitro, successive EFS lead to a progressive and rapid decrease in the amplitude of cholinergic contractions in Mecp2-KO mice contrary to WT mice. Levels of ACh are decreased in the ENS of Mecp2-KO mice (-47%, P-value<0.01) due to decreased activity of the synthesizing enzyme choline-acetyltransferase (-39%, P-value = 0.04). In addition to the deficit of ACh, we found that both nicotinic and muscarinic cholinergic receptors are also significantly impacted. CONCLUSION:This is the first report of a major dysfunction of the enteric cholinergic pathway in a mouse model of RTT supporting its direct involvement in GI disorders in this disease. We propose that the rhythmic GI contractions occurring during fed conditions may cause a rapid depletion of the stock of enteric ACh that could largely depress the propulsive efficiency of, or even suppress, peristalsis during digestion.
Learning and memory are fundamental cognitive processes that rely on activity-dependent epigenetic mechanisms to shape synaptic and neuronal plasticity. Among these, DNA methylation and demethylation have emerged as pivotal regulators that convert transient neural activity into enduring transcriptional programs. In mammals, DNA methylation marks include 5-methylcytosine (5mC) as well as the less well-established N6-methyladenine (6mA) and the more enigmatic N4-methylcytosine (4mC). Compared with 5mC, the abundance, genomic distribution, and regulatory role of 6mA and 4mC remain incompletely defined, partly due to low abundance and technical challenges, yet these non-canonical marks may provide an additional regulatory layer in specific biological contexts. Accordingly, this review focuses on the best-characterized pathway in the nervous system, 5mC and its activity-regulated oxidative turnover. This system comprises a dynamic spectrum of cytosine modifications, including 5mC, 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC), and 5-carboxylcytosine (5caC), orchestrated by distinct enzyme families such as DNMTs, TETs, and TDG. We review current insights about how these regulators shape activity-induced gene expression programs underlying learning and memory, and we discuss how dysregulated DNA (de) methylation contributes to impaired transcriptional control and cognitive decline in neurodegenerative diseases, particularly Alzheimer’s disease. Finally, we highlight recent advances in high-resolution mapping technologies for DNA modifications, which are expanding our ability to resolve cell type- and locus-specific epigenetic dynamics in the brain. A deeper understanding of these pathways may inform targeted strategies to preserve or restore cognitive function in neurological disorders.
Fabry disease (FD) is a genetic disorder caused by a deficiency of alpha-galactosidase A. Neuropathic pain is a hallmark of FD, beginning in early childhood and persisting throughout life. Current therapies for FD, such as enzyme replacement therapy and oral chaperone therapy, have limited impact on alleviating pain symptoms. Therefore, there is an urgent need to elucidate the precise molecular and metabolic mechanisms underlying FD-related pain to identify new therapeutic targets. In this study, we found that 8-week-old Fabry mice exhibited pronounced pain hypersensitivity, with no sex differences. Then, bilateral L4-L6 dorsal root ganglia (DRGs) were harvested from Fabry and wild-type (WT) mice of both sexes to dissect the molecular basis of pain. Transcriptomic profiling revealed distinct alterations in lipid metabolism-related genes within Fabry DRGs. Subsequent targeted lipidomic analysis identified robust accumulation of phosphatidylglycerol (PG), particularly elevated levels of PG (18:1/22:6) and PG (18:2/22:6) in Fabry DRGs. PG-associated synthase PGS1 was upregulated, while the PG hydrolytic activity of sPLA2s was inhibited. Following PGS1 knockdown or sPLA2s activity restoration, PG accumulation and pain hypersensitivity in Fabry mice were mitigated. Given the mitochondrial localization of PGS1, we observed profound mitochondrial disruption in Fabry DRGs, where aberrant PG metabolism contributes to this dysfunction. Thus, our study provides new insights into DRG pathogenesis in FD and uncovers dysregulated PG metabolism as a promising therapeutic target for alleviating Fabry pain.
Glucose transporter type 1 deficiency syndrome (Glut1DS) is a neurodevelopmental disorder caused by impaired cerebral glucose transport and clinically characterized by absence-type seizures, neurodevelopmental delays, movement disorders, and cognitive deficits. The consequences of chronic cerebral glucose deficiency for glial metabolism and myelin homeostasis remain poorly understood. In this study, we combined metabolic profiling, diffusion MRI, transcriptomic and lipidomic analyses to delineate the metabolic, molecular, and microstructural alterations induced by Glut1 haploinsufficiency in a Glut1+/- mouse model. Glut1+/- mice exhibited a global decrease in glucose, glycogen, and lactate levels across multiple brain regions, consistent with impaired glucose uptake and astrocytic energy metabolism. In addition to widespread metabolic deficits, diffusion MRI revealed selective microstructural abnormalities confined to the dorsolateral striatum, a critical hub for locomotor control. These changes were characterized by increased mean diffusivity and reduced mean kurtosis, indicative of reduced tissue microstructural complexity. Striatal transcriptomic profiling revealed a reactive astrocytic signature along with coordinated downregulation of genes involved in oligodendrocyte function, myelination, and galactolipid biosynthesis. Lipidomic analysis further identified selective reductions in myelin-enriched lipid classes, including hexosylceramides and ethanolamine plasmalogens, consistent with alterations in lipid pathways relevant to myelin organization and stability. Importantly, chronic L-lactate supplementation initiated during early postnatal development partially rescued motor deficits in young adult Glut1+/- mice. Collectively, these findings support a model in which chronic glucose transport deficiency is associated with alterations in glial metabolic homeostasis and myelin-related pathways, while highlighting lactate supplementation as a potential therapeutic strategy in Glut1DS.
Transposable elements (TEs) (mobile genetic elements comprising ∼45% of the human genome) have recently emerged as potential contributors to Parkinson's disease (PD); however their role and sex-specific impact remain poorly understood. Here, we present the first integrative meta-analysis of TE expression across 4 substantia nigra single-nucleus RNA-seq datasets, comprising a total of 66 donors, generating a cell-type-resolved atlas of TE dysregulation in PD. We identified widespread TE activation across major brain cell types (i.e. neurons, astrocytes, oligodendrocytes and microglia), with marked upregulation of L1s in neurons and HERVs in oligodendrocytes. Sex-stratified analyses revealed distinct male- and female-biased TE signatures, indicating regulatory programs uniquely affected in each sex, including MIR elements in microglia and Alu subfamilies in neurons. Correlation and genomic proximity analyses also uncovered TE-gene associations linked to important PD pathways such as neuroinflammation or myelination. Collectively, our study positions TEs as potential sex-modulated contributors to PD pathology and also provides a public web resource (PATOSS) to explore PD-associated TE transcriptional deregulation.
BACKGROUND:Baseline neurofilament light chain (NFL) predicts amyotrophic lateral sclerosis (ALS) outcomes, but it does not summarize early repeated biomarker information. We evaluated whether cumulative NFL exposure (cuNFL), calculated over an early monitoring window, and longitudinal NFL trajectory groups were associated with subsequent adverse events in a prospective cohort. METHODS:This prospective study enrolled patients with ALS from 32 provinces in China between January 2024 and January 2025. Plasma NFL was measured at baseline, month 1, and month 2. We used K-means clustering to describe longitudinal NFL patterns and multivariable survival models to evaluate prognostic associations. Inverse-probability weighting and causal-forest analyses were used as exploratory, confounding-adjusted analyses of high versus low cuNFL. RESULTS:K-means clustering identified three longitudinal NFL groups: Low-Stable (n = 183), Moderate (n = 225), and High-Progressive (n = 100). The High-Progressive group had the shortest event-free survival (P < 0.001). Each 1-SD increment in cuNFL was associated with higher odds of adverse events (adjusted OR 1.99; 95% CI 1.52-2.60; P < 0.001). Using the manuscript-defined 127-event outcome, apparent discrimination was AUC 0.730 for cuNFL and 0.717 for baseline NFL. The paired DeLong comparison was not statistically significant (P = 0.084). Exploratory machine-learning analyses suggested heterogeneity in the association of high cuNFL with outcome by age and respiratory function. CONCLUSION:Early repeated NFL measurements summarized as cuNFL and longitudinal trajectory groups were associated with short-term adverse events in this cohort. These findings support further external validation of longitudinal NFL-based risk stratification. They do not establish a causal biological effect or a basis for routine repeated measurement.
Several lines of evidence suggest that the cellular isoform of prion protein (PrPC) plays one or more roles in Alzheimer's Disease (AD). We previously found, in mouse neuroblastoma N2a cells that express human APP carrying the Swedish mutation (N2a-APPswe), that PrPC expression correlated with the secretion of Aβ42 peptide, the product of proteolytic processing of the amyloid precursor protein (APP) that is central to AD. To determine whether PrPC modulates APP processing to affect Aβ42 release and if any effect of PrPC is selective for APPswe, we applied the MesoScale Discovery (MSD) platform to assess APP processing and Aβ secretion before and after siRNA-induced knockdown of PrPC in APPswe and wild-type APP (APPwt) N2a cells. We found that PrPC knockdown reduced the major isoforms of secreted Aβ peptides in both cell lines (with the exception of Aβ42 in N2a-APPwt cells) in the absence of a reduction in either APP expression or enhanced Aβ degradation. Additionally, the soluble ectodomain of β-secretase cleavage (sAPPβ) was reduced in both cell lines whereas the ectodomain of α-secretase cleavage (sAPPα) was increased only in N2a-APPwt cells. PrPC overexpression led to an increase in Aβ42 in HEK cells and sAPPβ in both N2a cells and HEK cells expressing APPswe, confirming that PrPC promotes the amyloidogenic processing pathway independent of cell type. Biotinylation and immunofluorescence studies in the N2a cell lines revealed an increase in APP labeling at the plasma membrane, an increase in APP endocytosis, and an accumulation of APP C-terminal fragments (CTFs) after PrPC knockdown. We propose that PrPC limits delivery of APP to the plasma membrane, which acts to promote the amyloidogenic pathway by increasing its exposure to BACE1 within early secretory compartments.
Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder characterized by the progressive loss of motor neurons, with most cases lacking a clear genetic basis. Emerging evidence highlights the involvement of non-coding RNAs, particularly circular RNAs (circRNAs), in disease onset and progression. Here, we investigated circRNAs implicated in ALS and related motor neuron diseases (MNDs). Here, we provide a general overview of circular RNA metabolism and cellular functions. We then present our systematic literature review that identified ALS-associated circRNAs, followed by in silico analyses of 15 circular RNA candidates that were selected based on the most compelling data regarding ALS. Our results revealed that several circular RNAs regulate ALS-related genes, such as unfolded protein response, oxidative stress, cell cycle regulation, and apoptosis. Protein-RNA interaction analysis further showed that ALS-related circRNAs can sponge 20 RNA-binding proteins. Additionally, molecular docking analysis demonstrated that ALS-associated FUS variants significantly alter its binding affinity to circular RNAs. RNA-seq data from ALS patients confirmed significant alterations in the expression of host genes of ALS-related circRNAs and hub proteins in ALS-affected CNS tissues. Collectively, our findings identify circRNAs as potential key contributors to ALS pathogenesis.
Multiple System Atrophy (MSA) and Parkinson's Disease (PD) are neurodegenerative diseases characterized by abundant α-synuclein (αSyn) aggregation in the brain. Compared to PD patients, MSA patients have more widespread neurodegeneration and a more aggressive disease course. PD-related αSyn pathology is primarily neuronal, whereas MSA brains characteristically display oligodendroglial inclusions. The strain hypothesis poses that polymorphisms of the αSyn aggregates, so-called strains, may explain disease heterogeneity. The present study investigates the differential properties of αSyn fibrils derived from MSA and PD patients' brains using the protein misfolding cyclic amplification (PMCA) method in cultured neurons and in vivo. MSA- and PD-derived αSyn species were administered to primary murine neuronal cell cultures or injected intrastriatally into wildtype mice, along with de novo generated αSyn fibrils of the ribbon and fibril types. The potency to induce phosphorylated αSyn (pSyn) pathology, microglial reactivity, and the extent of oligodendroglial pSyn pathology were compared among the different seeding materials using immunohistochemical and immunofluorescent approaches. In summary, the various seeding materials induced pSyn pathology of distinguishable potency and morphology. PMCA-derived material from MSA brains and the fibril polymorph induced more pSyn pathology in both neuronal cultures and in mice compared to PMCA-derived material from PD brains and the ribbon polymorph. Interestingly, amplified material from MSA brains induced significantly more oligodendroglial pSyn aggregates than amplified material from PD brains. Additionally, mice injected with the fibril polymorph, showed mild changes in microglial reactivity. Our findings suggest specific properties of the MSA- and PD-derived fibrils, and overall support the strain hypothesis.
First-line stimulant therapies for attention deficit hyperactivity disorder (ADHD) implicate the forebrain monoaminergic neurotransmitter systems of dopamine, noradrenaline and serotonin. However, there is no curative treatment. Investigation of neurochemical monoaminergic changes, followed by curative treatments, requires sub-type specific animal models. In a novel rat model of the hyperactive-impulsive and attentive subtype of ADHD, specific changes in forebrain monoamines, and correlations with ADHD-like hyperactivity/impulsivity after delayed reward, are unknown. To address this, we investigated the monoaminergic systems using high performance liquid chromatography at ~2 and 7 months-of-age. We correlated the latter findings with ADHD-like hyperactivity and impulsivity that was measured after delayed reward. We observed long-term effects on the serotonergic, dopaminergic and noradrenergic systems in the forebrain of ADHD-like, hyperactive-impulsive male rats exposed to repeated hypoxia during postnatal day 1-3, the equivalent of extreme prematurity. These long-term effects were strikingly correlated with ADHD-like impulsive, and mostly with ADHD-like hyperactive, behaviour after delayed reward. The correlation was stronger for the dopaminergic and noradrenergic systems and weaker for the serotonergic system. The findings strongly implicate the dopaminergic system in the right prefrontal cortex, the noradrenergic system in the left prefrontal cortex and the serotonergic system in the right posterior caudate-putamen in ADHD-like hyperactivity and ADHD-like impulsivity. Earlier reports of forebrain lateralisation and lifespan changes of monoamines and their metabolites, and of marked differences between the anterior versus posterior caudate-putamen bilaterally, were confirmed and extended. New treatments to collectively cure the neurochemical changes can now be investigated in this unique, ADHD-like subtype-specific animal model.
The ability to incorporate changing information from the environment into our actions is essential for flexible behavior. The orbitofrontal cortex (OFC) is involved in integrating new information into on-going and future actions. As elsewhere in the brain, neuronal activity in the OFC is subject to fine-tuning by neurotransmitters like serotonin, dopamine, and norepinephrine. The purpose of this review is to highlight other neuromodulatory factors that have received less attention but are also potent regulators of OFC-dependent decision making. Specifically, we summarize the impacts of endocannabinoids, the neurotrophin Brain-derived Neurotrophic Factor, and cell adhesion systems in both medial and lateral compartments of the OFC. Generally speaking, perturbations to these systems disrupt flexible decision making, resulting in behaviors resembling poor learning, perseveration, and deferral to habitual actions. Understanding the molecular mechanisms supporting OFC function may drive the discovery of novel therapeutic approaches to alleviating these symptoms in various neuropsychiatric disorders.
Cognitive impairment is a common non-motor sym.ptom of neurodegenerative Parkinson's disease (PD). However, the onset and severity of cognitive impairment is heterogenous and currently cannot be predicted. This makes it challenging for informing patients in advance, and for the application of early therapeutic interventions. Moreover, the biological pathways that underlie cognitive impairment in PD remain to be fully determined. To better predict and understand the biological pathways involved in cognitive impairment, we have integrated multimodal datasets including clinical, demographic, biomarker and high throughout proteomic data from the longitudinal Parkinson's progression markers initiative (PPMI). The integrated dataset was used to develop three machine learning models that could predict the development of cognitive impairment nine years in the future, compared to patients that remained cognitively normal over the same duration. The best model could predict future cognitive impairment with 88% area under the curve. Permutation feature importance revealed that cytokine, interleukin-2 (IL-2) and insulin like growth factor (IGF) signalling were significant biological pathways contributing to the prediction of future cognitive impairment.
OBJECTIVE:Research on freezing of gait (FOG) in Parkinson's disease (PD) has identified relevant electrophysiological markers. However, their brief temporal windows limit their utility for individualized deep brain stimulation (DBS). This study explored gait performance and neural features in freezing-susceptible walking to develop novel FOG-predictive biomarkers. METHODS:Gait kinematics and local field potentials (LFP) from the cortex and subthalamic nucleus (STN) were simultaneously acquired in FOG patients during walking. Using the gait cycle as the analytic unit, we compared freezing trials (FOGT) and non-freezing trials (nFOGT) under the no-intervention condition (OFF) to identify gait parameters and neural features associated with FOG risk. Subsequently, we assessed the modulatory effects of high-frequency (HFS) and low-frequency (LFS) STN-DBS on abnormal gait and cortical power. Finally, we analyzed changes in abnormal gait and cortico-STN coherence after levodopa administration. RESULTS:FOGT showed aberrant gait parameters compared to nFOGT, along with disrupted lowbeta oscillations in primary somatosensory cortex (S1) and superior parietal lobule (SPL). Both HFS and LFS mitigated gait impairment and freezing severity, with LFS exerting broader effects: HFS reversed pathological lowbeta power reduction in SPL during the double support phase, while LFS restored phase-dependent oscillations between the stance phase and swing phase in S1. Additionally, abnormal theta coherence between S1 and STN could be modulated by levodopa, accompanied by gait recovery. CONCLUSION:This study identifies gait-cycle-locked cortico-STN signatures for FOG, which have extended temporal windows and are modulable by DBS, suggesting the gait cycle as a promising intervention target.
Synthetic oxytocin (Pitocin) is the most commonly used pharmacologic agent for induction and augmentation of labor. Beyond its uterotonic effects, oxytocin plays a critical role in neurodevelopment and social behavior. Dysregulated oxytocin signaling has been implicated in autism spectrum disorder (ASD), raising concern that perinatal exposure to exogenous oxytocin may have lasting neurodevelopmental consequences. This study aimed to determine whether offspring harboring a genetic predisposition for ASD are differentially impacted by perinatal oxytocin exposures, with a focus on long-term oxytocin signaling and autism-like behavior. Pregnant mice carrying offspring with heterozygous mutations in phosphatase and tensin homolog deleted on chromosome ten (Pten), a well-established monogenic risk factor for ASD, received continuous oxytocin versus phosphate-buffered saline (PBS) control via micro-osmotic pumps during late gestation. Wild-type (WT) offspring exposed to each treatment served as a secondary control. Adult offspring were assessed for oxytocin receptor (Oxtr) methylation in the frontal cortex and hippocampus, oxytocin expression in the hypothalamus, serum oxytocin levels, and were subject to a battery of social and anxiety-related behavior tests. Perinatal oxytocin exposure produced genotype-dependent effects in offspring. Epigenetic analyses revealed bidirectional remodeling of Oxtr methylation in the frontal cortex and hippocampus, with increased exon 1 methylation in WT mice and decreased methylation in Pten-mutant mice, resulting in significant genotype-treatment interactions. Hypothalamic oxytocin expression increased following treatment regardless of genotype, though baseline levels were higher in Pten-mutant mice. Neither oxytocin treatment nor genotype impacted long-term serum oxytocin levels. Behavioral outcomes were modest but context-specific: repetitive behaviors and cognition performance were unchanged, but oxytocin-treated Pten-mutant mice exhibited increased anxiety-like behavior alongside improved social memory. In contrast, oxytocin-treated WT mice showed reduced social novelty preference. Exploratory analyses suggested potential sex-dependent trends. Our findings support a model in which genetic susceptibility shapes the epigenetic encoding of early-life hormonal signals, thereby recalibrating oxytocin system function and downstream behavioral outcomes. Together, these data highlight the context-dependent effects of perinatal oxytocin exposure and argue against uniformly beneficial or detrimental effects, emphasizing the importance of gene-environment interactions in neurodevelopmental trajectories.
PRPH2 mutations cause inherited retinal dystrophies (IRDs), but how photoreceptor outer segment (OS) disruption reshapes the surrounding retina remains unclear. Using a heterozygous Prph2C213Y/+ mouse model generated by CRISPR/Cas9, we characterized age-related retinal pathology and responses of retinal pigment epithelium (RPE) and Müller glia. Independent age- and sex-matched cohorts were examined at 1, 3, and 6 months by electroretinography, optical coherence tomography, and fundus autofluorescence. Mutant mice showed rod dysfunction from 1 month, RPE dysfunction from 3 months, and cone dysfunction by 6 months, accompanied by progressive outer retinal thinning and hyperautofluorescent deposits. Histological and ultrastructural analyses revealed OS disorganization, shortened RPE microvilli, RPE monolayer remodeling, increased RPE autofluorescence, and reactive Müller gliosis. Single-cell spatial transcriptomics of wild-type and mutant retinas at 6 months resolved nine cell populations and identified RPE cells and Müller glia as prominently perturbed non-photoreceptor populations. RPE cells showed an epithelial-mesenchymal transition-related remodeling state linked to a candidate Nfib-Fstl1 module, whereas Müller glia showed activation of activator protein 1 (AP-1) regulons, including Fos, Fosl2, and Junb, with predicted targets Osmr, A2m, and Stat3. Cell-cell communication analyses indicated coordinated changes in neuroprotective, inflammatory, and matrix-related signaling from RPE cells and Müller glia toward photoreceptors. These findings indicate that PRPH2-associated retinal dystrophy is a multicellular process in which OS disruption drives coordinated RPE and Müller glial remodeling with potentially protective or pro-degenerative effects, and nominate the RPE Nfib-Fstl1 program, Müller glial AP-1 responses with predicted STAT3 involvement, and support-cell-derived growth factor signaling as candidate mutation-independent therapeutic targets.
The main motor symptoms of Parkinson's disease (PD) emerge following dopamine depletion in the dorsal striatum and are associated with structural and functional adaptations of striatal medium spiny neurons (MSN). Although the indirect pathway MSN (iMSN) selectively expresses dopamine D2 receptors (D2R), the contribution of D2R signaling to these adaptations remains incompletely understood. Here, we examined neuronal morphology, dendritic spine density, corticostriatal transmission, and intrinsic excitability in direct pathway MSN (dMSN) and iMSN from constitutive D2R knockout mice, with or without chronic nigrostriatal lesions induced by 6-hydroxydopamine. D2R ablation reduced dendritic length and complexity in both MSN subtypes, although the effects were markedly greater in iMSN. In iMSN, D2R ablation also reduced spine density and increased intrinsic excitability, reproducing well known effects of nigrostriatal lesions and largely occluding additional effects of dopamine denervation. In contrast, D2R ablation produced only modest changes in dMSN spine density and excitability and did not prevent the additional spine loss and hyperexcitability induced by 6-OHDA lesions. Basal corticostriatal transmission remained largely preserved after D2R ablation in either MSN subtype, except for a slower excitatory postsynaptic current decay in iMSN, which was not enhanced further by the dopamine depleting lesion. Remarkably, nigrostriatal lesions continued to depress corticostriatal excitatory postsynaptic currents in D2R-deficient mice, indicating that this synaptic adaptation does not require D2R signaling. Together, these findings identify D2R signaling as a major determinant of iMSN structural and intrinsic physiological integrity and demonstrate that global loss of D2R function reproduces many of the adaptations induced by dopamine depletion. More broadly, they indicate that dopamine depletion drives distinct forms of plasticity through separable D2R dependent and independent mechanisms, with depression of corticostriatal synaptic currents in iMSN arising independently of D2R signaling.
Tumor necrosis factor (TNF) is rapidly induced after ischemic stroke, but its proposed cell-specific and sex-dependent functions during post-stroke inflammation remain insufficiently understood. Here, we investigated the role of microglia-derived TNF in the acute and subacute response to permanent middle cerebral artery occlusion (pMCAO). Tnf expression was transiently upregulated after stroke, becoming significant at 4 h, peaking at 12-24 h, and returning to baseline by 5 days. In situ hybridization confirmed strong Tnf expression in the infarct and peri-infarct regions. Whole-brain transcriptomic profiling showed that global TNF deficiency reshaped the early post-ischemic response, shifting it from microglia-associated phagocytic and wound-healing pathways toward an interferon-related inflammatory signature. To define the specific contribution of microglial TNF, we used inducible Cx3cr1CreER:Tnffl/fl mice. Microglial TNF deletion had no effect on infarct volume in males at 24 h or 5 days after pMCAO, but significantly increased infarct size in females at both time points. In both sexes, brain TNF levels peaked at 24 h and were significantly reduced in Cx3cr1CreER:Tnffl/fl mice, confirming microglia as a major source of early post-ischemic TNF. However, downstream consequences diverged by sex. At 5 days, male Cx3cr1CreER:Tnffl/fl mice showed reduced microglial reactivity and 18 kDa translocator protein (TSPO) signal, with no change in T-cell infiltration, and exhibited increased density of mature oligodendrocytes. In contrast, female Cx3cr1CreER:Tnffl/fl mice displayed enhanced microglial reactivity, increased TSPO binding, higher peri-infarct T-cell infiltration, and reduced oligodendrocyte density and myelin integrity. Together, these findings identify microglial TNF as a sex-dependent regulator of post-stroke inflammation and myelin injury.
Degenerative cervical myelopathy (DCM) encompasses several conditions that cause compression of the cervical spinal cord. While the pathobiology underlying compression-induced neural degeneration remains incompletely understood, microglial synaptic pruning, driven by CX3CR1, is thought to be a main contributor. The current study builds on previous work demonstrating that Cx3cr1−/− mice exhibit improved gait following DCM and seeks to determine if CX3CR1-mediated synaptic pruning underlies this improvement. We compared C57BL/6 (WT, wild-type) and Cx3cr1−/− mice across 12-weeks of DCM. Locomotor and pain function were assessed using CatWalk and Von Frey outcome measures, respectively. Synaptic and electrophysiological changes were characterized at baseline and after 4-weeks of DCM using pre- and post-synaptic markers, motor evoked potentials (MEPs), and whole-cell patch-clamp recordings. Cx3cr1−/− and WT mice showed differences in locomotion at baseline. Normalization of all groups revealed that Cx3cr1−/− mice exhibited improved locomotion across 12-weeks and greater mechanical sensitivity on Von Frey. 4-weeks post-DCM induction, the microglia of Cx3cr1−/− mice displayed reduced engulfment of excitatory and inhibitory synapses in the dorsal and ventral horns. This was accompanied by a disruption to the dorsal horn excitation-to-inhibition (E/I) balance, driven primarily by a loss of inhibitory transmission as confirmed by whole-cell patch clamp recording, and altered corticospinal-neuromuscular excitability, as confirmed by motor evoked potentials. Together, our findings reveal CX3CR1-mediated microglial synaptic pruning as a potential novel contributor to early DCM pathobiology. Specifically, our results suggest that an absence of pruning shifts the synaptic E/I balance in the dorsal horn, which may underlie the gait benefits observed in Cx3cr1−/− mice.
