Neurobiology of Disease

L-DOPA remains the most effective therapy for Parkinsons disease (PD), yet its chronic use often induces involuntary movements known as L-DOPA-induced dyskinesia (LID). While abnormal cholinergic interneuron (ChI) activity is a hallmark of both PD and LID, emerging evidence suggests that the temporal organization of acetylcholine (ACh) signaling, rather than its overall magnitude, may determine its functional impact. Under physiological conditions, ChIs exhibit intrinsic delta-frequency activity reflected in coordinated, slow oscillations of extracellular ACh, which are thought to organize striatal network function and movement pattering. To determine how dopamine (DA) depletion and L-DOPA treatment reshape these ACh dynamics, we used in vivo GRAB-ACh fiber photometry in the unilateral 6-OHDA mouse model. DA depletion disrupted slow ACh rhythmicity, reducing delta-band regularity while increasing higher-frequency phasic activity. Acute L-DOPA broadly suppressed ACh activity across frequencies, partially normalizing this imbalance, but without restoring slow temporal structure. In addition, chronic L-DOPA treatment, associated with established dyskinesia, further impaired delta-band coordination in the DA-depleted striatum during the ON state, while OFF-state activity retained lesion-associated features. The anti-dyskinetic agent amantadine restored low-frequency temporal structure both before and after L-DOPA exposure. Together, these findings reveal a state-dependent reorganization of striatal ACh dynamics, characterized by a shift from coordinated slow oscillations to irregular phasic activity following DA loss, and a further breakdown of slow temporal organization during dyskinetic states. These results highlight the temporal structure of cholinergic signaling as a critical and underappreciated dimension of striatal function in PD and LID.

Hereditary spastic paraplegia type 7 (SPG7) is a neurodegenerative disorder characterized by progressive motor impairment and cerebellar dysfunction. Mutations in the SPG7 gene, encoding the mitochondrial metalloprotease paraplegin, disrupt mitochondrial homeostasis and lead to neuronal vulnerability and deficits in motor coordination. Recent studies have identified defective flickering of the mitochondrial permeability transition pore (mPTP) in SPG7 models, suggesting that altered pore dynamics may represent a functional biomarker of mitochondrial dysfunction. Here, we investigated whether pharmacological modulation of mPTP activity could improve mitochondrial function and motor performance in SPG7 models. Mitochondrial flickering was assessed in vitro, while motor behavior was evaluated in vivo following chronic treatment with berberine, a natural isoquinoline alkaloid known to modulate mitochondrial bioenergetics. Spg7-/- mice and age-matched Spg7+/ littermate controls received daily oral berberine administration for several weeks, and motor coordination was assessed using the accelerating rotarod test. Untreated Spg7-/- mice exhibited reduced rotarod performance compared with controls, indicating impaired motor coordination. Berberine treatment significantly improved motor performance in pre-symptomatic mutant mice. These findings indicate that pharmacological modulation of mitochondrial permeability transition pore dynamics can ameliorate motor dysfunction associated with SPG7 deficiency and highlight mPTP flickering as a functional readout of mitochondrial health.

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

Motor Neurone Disease (MND) is characterised by progressive degeneration of upper and lower motor neurons, accompanied by cytoplasmic mislocalisation and hyperphosphorylation of TDP-43, hallmarks that implicate failure of endolysosomal proteostasis. The Endosomal Sorting Complexes Required for Transport (ESCRT) pathway governs multivesicular body (MVB) formation, lysosomal cargo delivery, and autophagosome closure, yet its expression profile in human MND tissue and mechanistic contribution to disease pathology have not been established. Here, we report subunit-specific dysregulation of ESCRT proteins in postmortem motor cortex and spinal cord from MND patients: CHMP2B (ESCRT-III) is significantly upregulated in both regions, whilst TSG101 (ESCRT-I) and VPS37A (ESCRT-I) are significantly downregulated in motor cortex, indicating a region-specific remodelling of the ESCRT network. In a tunicamycin-induced ER stress model using NSC-34 motor neuron-like cells and primary cortical neurons, TSG101 overexpression reduced total and phosphorylated TDP-43, suppressed mTOR signalling, and restored autophagic flux, whereas TSG101 knockdown exacerbated TDP-43 accumulation and cytoplasmic mislocalisation. CHMP2B modulation selectively regulated TDP-43 phosphorylation without altering total TDP-43 levels, consistent with a casein kinase 1-dependent mechanism operating independently of bulk autophagy. Both TSG101 and VPS4a were required to maintain neuronal CD9 tetraspanin localisation to early endosomes; their depletion redirected CD9 to late endosomal and lysosomal compartments under ER stress. Extracellular vesicle characterisation revealed a functional divergence: TSG101 is required for general exosome biogenesis, whereas VPS4a ATPase activity specifically mediates loading of pathological TDP-43 cargo into EVs. Dynamic light scattering confirmed that ER stress and ESCRT modulation produce distinct, condition-specific alterations in EV size and polydispersity. These findings establish ESCRT dysfunction as a multifaceted contributor to MND pathogenesis and identify TSG101, CHMP2B, and VPS4a as mechanistically distinct therapeutic targets warranting preclinical validation.

Super-refractory status epilepticus is a common neurological manifestation of mitochondrial disease caused by bi-allelic pathogenic variants in POLG. Epilepsy in POLG-related disease typically presents with an explosive onset of status epilepticus, often from an occipital focus, and is associated with extensive neurodegeneration. The neuropathological mechanisms underlying POLG-related mitochondrial epilepsy remain poorly understood, however, neuroinflammation and glial dysfunction are hypothesised to play a significant role. In this study, we performed a neuropathological and proteomic investigation of post-mortem brain tissues from 12 patients with POLG-related mitochondrial epilepsy (age range: 3 - 28 years) and matched control cases. Given that the primary visual cortex is prominently involved in this epileptic disorder, occipital cortical tissues (Brodmann area 17) were compared to frontal cortical tissues (Brodmann area 9). Liquid chromatography-mass spectrometry (LC-MS/MS) analysis identified a distinct immunometabolic signature in the occipital cortex, and to a lesser extent in the frontal cortex, in POLG-related epilepsy. This was characterised by decreased abundance of mitochondrial proteins coupled to an increased expression of innate immune and inflammatory proteins, consistent with neuroinflammation. To validate these observations, we confirmed an increased density of cells immunoreactive for acute phase proteins (C-reactive protein, osteopontin and serpin A3), immune co-receptors (CD14 and HLA-DR), the inflammatory glycoprotein YKL40, the cytokine TNF-alpha, and mitochondrial translocator protein (TSPO). We also demonstrate a decreased expression of mitochondrial oxidative phosphorylation (OXPHOS) subunits within POLG patient microglia, indicative of mitochondrial dysfunction. Finally, we show enrichment of mitochondrial OXPHOS and interneuron proteins in the control primary visual cortex compared with the frontal cortex, which may underlie the selective regional vulnerability observed in POLG-related mitochondrial disease. Overall, these findings provide strong neuropathological evidence implicating neuroinflammation and glial dysfunction in POLG-related epilepsy.

Neurodevelopmental disorders (NDDs) are increasingly recognized as disorders of brain connectivity and circuit dysfunction. Growing evidence suggests that glial cell and myelin abnormalities may actively contribute to these alterations. Yet, they have been often considered secondary consequences of impaired neuronal development rather than primary drivers of circuit dysfunction. Primary autosomal recessive microcephaly type 17 (MCPH17) is a severe NDD caused by mutations in the CIT gene, encoding Citron kinase (CIT-K). The disease is associated with cognitive and motor deficits, epilepsy susceptibility, and marked hypomyelination in both patients and mouse models, suggesting a contribution of oligodendroglial dysfunction to disease pathophysiology. Here, we investigated the specific role of oligodendroglial Cit-k loss using Sox10Cre;Cit-kfl/fl mice, in which Cit-k is selectively deleted in oligodendrocyte-lineage cells. Mutant mice displayed impaired forebrain myelination at juvenile stages and persistent cortical hypomyelination in adulthood. Despite preserved gross motor function, adult mutants showed deficits in fine motor control, working and recognition memory, and auditory fear memory. These impairments were associated with altered cortico-cortical and cortico-hippocampal functional connectivity. Moreover, consistent with the clinical MCPH17 phenotype, mutant mice exhibited increased susceptibility to kainate-induced seizures. Together, our findings show that oligodendroglial Cit-k loss and the resulting hypomyelination are sufficient to produce long-lasting neurological and behavioral impairments independently of primary neuronal defects. These results identify oligodendrocytes as active contributors to MCPH17 and support a broader role for myelin abnormalities in NDDs. HighlightsO_LICit-k deletion in oligodendroglia disrupts forebrain myelination C_LIO_LICortical hypomyelination persists in adult mutant mice C_LIO_LIMutant mice show deficits in motor control and memory C_LIO_LICortico-cortical and cortico-hippocampal connectivity are altered C_LIO_LIligodendrocytes contribute to microcephaly-associated dysfunctions C_LI

Fragile X syndrome (FXS) is the leading inherited cause of intellectual disability, and is frequently accompanied by seizures. Early-life treatment with the hormone oxytocin (OXT) improves social behavior and cognitive function in rodent models of autism with intellectual disability, including FXS, but potential OXT treatment effects on seizure susceptibility have not been evaluated. Here we tested, in both sexes, if intranasal OXT (iOXT) or saline (iSAL) during the second postnatal week reduces audiogenic seizures (AGS) in the Fmr1-Knockout (KO) mouse model of FXS. OXT given daily from postnatal day (P) 7 to P13 significantly reduced the incidence and severity of AGS and the latency to seize in adult male Fmr1-KOs. Female KOs exhibited less severe seizures that were unaffected by treatment. Wild type mice did not exhibit AGS independent of treatment. To test if antiepileptic effects of iOXT are age-dependent, a separate cohort received iOXT daily from P30 to P36. Male KOs receiving later treatments exhibited robust seizures that were comparable between OXT- and SAL-treatment groups, suggesting that OXTs enduring antiepileptic effects are confined to early postnatal treatments. Tests of acute OXT effects in adulthood demonstrated an attenuation of male Fmr1-KO AGS at testing 30-60 min and 1 day post-treatment but these effects were not evident 15 days later. These findings reveal marked sex differences in the propensity for audiogenic seizures in Fmr1-KO mice and demonstrate that early-life OXT treatment mitigates seizure susceptibility in males FXS model mice.

Temporal lobe epilepsy (TLE) is associated with dysregulation of transforming growth factor {beta} (TGF{beta}) signaling, a key contributor to epileptogenesis. SARA (Smad Anchor for Receptor Activation), a central regulator of this pathway, is controlled by the E3 ubiquitin ligase Smurf2 through ubiquitination. However, the role of the SARA-Smurf2 axis in regulating TGF{beta} signaling during TLE has not previously been described, and whether this pathway can be therapeutically targeted remains unknown. Using a pilocarpine-induced status epilepticus (SE) model and astrocytes derived from patients with refractory TLE, we identified dysregulation of the SARA-Smurf2 pathway in both experimental systems. In SE rats, SARA and Glial Fibrillary Acidic Protein (GFAP) levels were significantly increased, whereas Smurf2 induction was insufficient to prevent SARA accumulation. In TLE-derived astrocytes, increased SARA and GFAP immunoreactivity was accompanied by reduced Smurf2 immunoreactivity and altered Smurf2 subcellular distribution. Losartan treatment restored SARA and Smurf2 immunoreactivity toward a control-like pattern in both models and reduced seizure frequency and duration in SE animals. These findings point towards a dysregulation of the SARA-Smurf2 axis as a molecular signature of TLE, support SARA as a potential therapeutic target, providing experimental evidence for the repositioning of Losartan as a potential treatment alternative for drug-resistant epilepsy, warranting further translational and clinical investigation. KEY POINTSO_LIDysregulation of the SARA-Smurf2 axis is a molecular signature of experimental and human temporal lobe epilepsy. C_LIO_LIImpaired Smurf2-dependent regulation of SARA may sustain TGF{beta} signaling, astrocyte reactivity, and epileptogenesis. C_LIO_LILosartan restores the SARA-Smurf2 axis and reduces seizures, supporting a novel therapeutic strategy for TLE. C_LI

In Parkinsons disease (PD), blood-based (BB) biomarkers ubiquitin c-terminal hydrolase L 1 (UCHL-1), glial fibrillary acidic protein (GFAP), and neurofilament light (NfL) correlate with motor or cognitive impairment. However, it is unclear if blood levels of these biomarkers represent changes in nigrostriatal neuron viability or dopamine (DA) signaling. In 6-OHDA and Pink1 knockout (KO) rat models that showed progressive loss of DA tissue and tyrosine hydroxylase (TH) protein, we quantified UCHL-1, GFAP, and NfL expression in striatum and substantia nigra (SN) at 7- and 28-days in the 6-OHDA model and 7- and 18-month old in Pink 1 KO. Substantial changes in all biomarkers occurred with TH loss in SN, but not striatum, in both models. UCHL-1 levels increased against remaining TH protein. Accordingly, serum UCHL-1 levels increased 25% at 28 days post-6-OHDA and 18-month old Pink1 KO. GFAP and NfL levels increased in SN 28 days post-6-OHDA and 18 month-old Pink1 KO. Serum GFAP levels increased 28 days post-6-OHDA and 18 month-old Pink1 KO. Serum levels of NfL increased 28 days post-6-OHDA, and in 18 month-old Pink1 KO and wild-type, without influence by genotype. Expression levels of each biomarker were greater in the SN vs striatum, suggesting the SN contributes greater quantities of biomarkers to the blood and reflect TH loss therein. Taken together, our preclinical results show alignment between serum levels of UCHL-1, GFAP, and NfL and loss of TH and DA in the SN. As such, these biomarkers may be relevant peripheral indicators of deficient nigrostriatal DA signaling, and reflect nigrostriatal function in PD.

Although prenatal alcohol exposure (PAE) has been proposed as an early-life risk factor for Alzheimers disease and related dementias (AD/ADRD), the mechanistic underpinnings are underexplored. Mutations in the Presenilin genes contribute to AD/ADRD, with Presenilin 1 acting as the catalytic subunit of the {gamma}-secretase complex responsible for cleaving Notch and amyloid precursor protein (APP). We hypothesized that PAE disrupts {gamma}-secretase activity during brain development, which persists and is associated with behavioral deficits later in life. Pregnant wild-type B6129 and 3xTg-AD mice were fed an ethanol-containing liquid diet during gestational days 13-15. From birth to adulthood, PAE increased APP C-terminal fragments and Notch intracellular domain (NICD) levels in cortical lysates. These changes were associated with impaired hippocampal-dependent learning and memory in wild-type mice at 3 and 6 months of age and exacerbated behavioral deficits in 4-month-old 3xTg-AD mice. Our findings provide the first mechanistic insight linking PAE to AD/ADRD vulnerability.

NMDAR and LGI1 encephalitis are the two most common forms of autoimmune encephalitis and are associated with persistent cognitive sequelae, particularly episodic memory impairment. Patients also report lasting difficulties with spatial orientation and navigation, yet these symptoms remain poorly characterized. Both disorders affect neural systems supporting spatial navigation, including prominent hippocampal pathology alongside cingulate, temporo-parietal, thalamic and cerebellar alterations identified in advanced neuroimaging studies. Here, we therefore investigated the frequency and clinical relevance of spatial navigation impairment in post-acute NMDAR and LGI1 encephalitis, its relationship with episodic memory dysfunction, and its structural correlates. We included 80 post-acute patients from the autoimmune encephalitis outpatient clinic at Charite - Universitatsmedizin Berlin: 50 with NMDAR encephalitis (mean age 35.0 years, range 19-71; 90% female; median 6.9 years from onset) and 30 with LGI1 encephalitis (mean age 63.6 years, range 33-84; 67% male; median 2.7 years from onset). Spatial navigation was assessed using a passive map-assisted task (VIENNA Young) and an active wayfinding task (Sea Hero Quest), and its relationship with verbal episodic memory was examined using the Rey Auditory Verbal Learning Test. Structural MRI analyses assessed cortical thickness, subcortical volumes and diffusion measures in preselected navigation- and memory-related regions. Patients with NMDAR and LGI1 encephalitis performed worse than matched controls on map-assisted navigation, and navigation performance showed strong convergence across the two navigation paradigms. Norm-referenced navigation impairment affected 57% of patients with NMDAR encephalitis and 70% with LGI1 encephalitis. In NMDAR encephalitis, selective navigation impairment was more common than selective memory impairment (41% versus 14%; {chi}2 = 6.26, p = .012), supporting partial dissociation. In LGI1 encephalitis, navigation and memory impairments were similarly frequent and strongly overlapping, with 53% of patients impaired in both domains. Older age was a shared risk factor for navigation impairment. Structurally, NMDAR encephalitis showed partly distinct navigation- and memory-related alteration patterns, with navigation-specific parietal-paracentral and cerebellar abnormalities and memory-specific temporal-hippocampal-thalamic involvement. LGI1 encephalitis showed more widespread, predominantly memory-related alterations without a robust navigation-specific structural signature. Our findings identify spatial navigation as a frequently affected but under-assessed cognitive domain in post-acute NMDAR and LGI1 encephalitis. They provide clinical evidence that navigation and episodic memory are partially dissociable yet overlapping functions whose degree of separability varies with the extent and distribution of network pathology. Incorporating norm-referenced navigation assessment into longitudinal follow-up could improve the characterization of cognitive profiles and related support needs, while reducing the risk that impairments relevant to everyday functioning and long-term quality of life remain undetected.

Traumatic brain injuries (TBIs) are associated with increased risk of neurodegenerative disease, including Alzheimers disease (AD); however, the mechanisms by which TBI promotes AD pathogenesis remain poorly understood. It also remains unclear whether post-TBI sequelae, including sleep disturbances and seizures, play a role in driving disease progression. To investigate these relationships, we employed a translational approach using the Closed-Head Injury Model of Engineered Rotational Acceleration (CHIMERA) of repeated mild TBI (rmTBI) and an AD knock-in mouse model to assess sleep, power spectral density, epileptiform activity, and A{beta} pathology one month post-injury. RmTBI caused elevated neurofilament-light and glial fibrillary acidic protein, markers of neuronal damage. Sex differences were observed in acute injury outcomes, sleep measures, and A{beta} plaque size. Specifically, females exhibited longer recovery post-injury, higher mortality, decreased non-rapid eye movement sleep duration, and larger average plaque size than males at equivalent impact energy. These findings highlight the importance of including both sexes when establishing injury severity thresholds. Future studies should incorporate validated TBI biomarkers of neural injury to define equivalent injury parameters across sexes and examine the chronic effects of rmTBI on sleep, epileptiform activity and AD pathology.

Fetal Alcohol Spectrum Disorders (FASDs) are associated with alterations in learning and memory that persist throughout the lifespan. Thus, determining the neural mechanisms driving these alterations has the potential to identify novel therapeutic targets for improving memory in those with FASD. Given the newly realized role of the Retrosplenial cortex (RSC) for learning and memory, as well as the profound neural apoptosis that exposure to alcohol during development causes to this brain region, we recorded electrophysiological activity from mice exposed to alcohol during the third trimester-equivalent developmental time period. We observed a large number of Epileptiform Discharges (EDs) in alcohol-exposed subjects compared to controls, which were found to drive with High-frequency Oscillations (HFOs). Furthermore, many features of HFOs (amplitude/duration/etc.) were found to be directly proportional to the temporal distance from ED onset. These findings identify EDs for the first time as a critical feature in a preclinical model of FASD, and suggest their relationship to RSC HFOs may be a key mechanism driving memory alterations.

Synaptojanin 1 is a brain enriched phosphoinositide phosphatase implicated in endocytosis at the synapse. A mutation (R258Q) that selectively impairs its Sac1 phosphatase domain causes early onset familial Parkinsonism. Neurons of mice with this mutation display synaptic vesicle traffic defects across the brain, but selective dystrophic changes in a subset of dopaminergic axons in the dorsolateral striatum. Using correlative light microscopy-FIB-SEM of mutant mouse striata to visualize in 3D these abnormal structures we show that they represent clusters of focal axonal dilations harboring massive, onion-like DAT enriched plasma membrane infoldings, generally localized next to cell bodies of neighboring cells, often engulfing evaginations of such cells. This dysmorphia was associated with a deficit in dopamine release in the same striatal region. Given the involvement of Synj1 in endocytic mechanisms, these structures may reflect an imbalance between exocytosis and endocytosis. Their occurrence only in a subset of axons suggest a vulnerability threshold of these axons beyond which the expansion of the plasma membrane is not counteracted by compensatory mechanisms.

Parkinsons disease (PD) is strongly age-associated, yet how aging reshapes PD-related transcriptional changes remains unclear. We performed an age-stratified meta-analysis of 16 bulk RNA-seq datasets (646 samples: 314 PD, 332 controls) to distinguish early-onset (<60 years) from late-onset ([&ge;]60 years) signatures. In the full dataset, 131 significantly (padj<0.05, |log2FC|>1) differentially expressed genes (DEGs) were observed, spanning neuronal activity-dependent genes (NPAS4, PVALB, ARC, FOSB) and immune/stress-related transcripts (IL3RA, SLC25A6, HSPA1A/B). Age-specific analyses revealed 31 DEGs in <60, dominated by large-effect changes in uncharacterized lncRNA LINC02188, pseudogene loci (MUC20P1, RPS28P7), calcium-modulating gene CALML6, lipid{square}associated gene TLCD3B, and cytoskeletal regulators (TIAM2, KCTD8). In contrast, the [&ge;]60 group showed 181 DEGs enriched for neuronal markers (NPAS4, PVALB) and immune-metabolic genes (FGA, NPC1L1, UPK1A, HSPA1A/B). GO/KEGG analyses indicated that the <60 signature centers on actin remodeling, filopodia, axonogenesis, and Rap1-mediated adhesion/signaling, consistent with early neurite and structural reorganization. The [&ge;]60 signature was enriched for blood microparticles, chemokine activity, infection-related pathways, ER protein processing, and arachidonic/ether lipid and cytokine signaling, pointing to broad immune-metabolic and proteostasis dysregulation. Cross-age comparison showed that classical PD neuronal immediate-early gene changes are largely [&ge;]60-driven, whereas early-onset PD involves novel lncRNA-calcium-lipid and cytoskeletal modules. These findings highlight LINC02188, TLCD3B and related cytoskeletal/lncRNA genes as novel early-onset PD-associated candidates, and NPC1L1, IL3RA and PVALB as age-amplified markers within the broader PD transcriptomic signature.

Parkinsons disease is characterized by the progressive and preferential degeneration of dopaminergic neurons in the substantia nigra pars compacta, and intraneuronal alpha-synuclein (Syn) accumulation. Dopaminergic neurons (DANs) are anatomically and molecularly heterogeneous, but the impact of Syn pathology on distinct subpopulations is not well defined. One midbrain DAN sub-population expresses Aldehyde Dehydrogenase 1A1 (ALDH1A1), an enzyme that detoxifies aldehyde by-products of dopamine metabolism, and has been associated with differential vulnerability. Here, we applied GeoMx spatial transcriptomics to profile ALDH1A1-positive (ALDH1A1+) and ALDH1A1-negative (ALDH1A1-) DAN subpopulations in the mouse midbrain in situ at 3- and 8-weeks following adeno-associated virus (AAV)-mediated Syn overexpression. Analyzing 10,532 genes, we identified robust transcriptional differences between ALDH1A1+ and ALDH1A1- DANs under control conditions, supporting their characterization as distinct molecular subpopulations. In AAV-Syn-injected mice, we observed increased Snca expression and a reduction in ALDH1A1- DANs in the ipsilateral substantia nigra. Syn overexpression induced subpopulation-specific and time-dependent transcriptional responses, with dysregulation in ALDH1A1- DANs characterized by early down-regulation of pathways related to synaptic function, neurotransmitter handling, and bioenergetics, including glycolysis. In contrast, ALDH1A1+ DANs displayed later up-regulation of genes enriched for Acetyl-CoA and cholesterol metabolism pathways, reflecting subpopulation-specific adaptations to Syn overexpression. Analysis of human single nucleus RNA-sequencing data revealed partial conservation of the metabolic dysregulation signature. Together, our findings show that murine midbrain ALDH1A1+ and ALDH1A1- DANs represent molecularly distinct subpopulations with divergent temporal responses to Syn overexpression, emphasizing the importance of cell-type and disease-stage context in studies of Parkinsons disease mechanisms.

Huntingtons disease (HD) is an autosomal dominant neurodegenerative disorder caused by a CAG-repeat expansion in the HTT gene. Progressive loss of striatal projection neurons leads to cognitive, psychiatric, and motor impairments that typically manifest in midlife, despite the presence of the expansion from conception. Increasing evidence supports a neurodevelopmental component to HD; however, authentic human developing HD striatal tissue has not previously been characterised. We analysed an HD positive human fetal striatal sample alongside an age- and sex-matched control. CAG-repeat length was determined, and single-cell RNA sequencing was used to investigate gene expression. We compared the fetal HD transcriptional signature with publicly available datasets from postmortem adult HD brain tissue. We identified 2,032 differentially expressed genes and defined nine cellular clusters, each exhibiting distinct transcriptional profiles. Gene enrichment analysis revealed disruption of key biological processes across the developing HD striatum, with pathway-level dysregulation varying between clusters. There was overlap in gene expression changes between fetal and adult HD striatal tissues. Together, these findings demonstrate that molecular features of HD pathology are present during early human striatal development, supporting the concept that disease mechanisms are established decades prior to clinical onset.

The human ABCA7 gene, which encodes ATP-binding cassette transporter A7 (ABCA7), is one of the strongest genetic risk factors for late-onset Alzheimers disease (AD), yet the molecular mechanisms linking ABCA7 deficiency to AD remain incompletely understood. Because impaired insulin signaling and neuroinflammation are increasingly recognized as key contributors to AD pathogenesis, and ABCA7 has been implicated in both metabolic and immune processes, we investigated whether ABCA7 deficiency is associated with alterations in these pathways using comparative brain proteomics. Whole-brain proteomes from wild-type, Abca7 knockout, AD model (APP), and APP- Abca7 knockout mice were analyzed at 50, 100, 150, and 200 days of age using label-free quantitative proteomics, followed by differential abundance analysis, gene ontology enrichment, subcellular localization analysis, protein-protein interaction network analysis, and comparison with human AD brain proteomic datasets. Comparative analyses identified age-dependent proteomic alterations associated with Abca7 deficiency, amyloid-beta pathology, and their interaction. Across all genotype comparisons, recurrently altered proteins and functional interaction networks consistently converged on insulin receptor and PI3K/AKT signaling, MAPK signaling, immune and complement pathways, vesicle trafficking and acidification, and the ubiquitin-proteasome system. Subcellular enrichment analysis further indicated preferential involvement of membrane-associated proteins, consistent with the established role of ABCA7 in membrane lipid transport and trafficking. Comparison with human AD proteomic data demonstrated substantial overlap while also identifying potentially novel proteins associated with Abca7deficiency in our mouse models. Together, these findings provide a systems-level characterization of the brain proteomic consequences of Abca7 deficiency and suggest that dysregulation of interconnected metabolic, immune, and vesicle-associated pathways may contribute to AD-related brain pathology.

Spinocerebellar ataxia type 7 (SCA7) is a rare neurodegenerative disorder characterized by progressive cerebellar ataxia and visual impairment. We investigated longitudinal changes in resting-state functional connectivity and their clinical associations. Resting-state functional MRI was acquired from 16 individuals with SCA7 and 16 age- and sex-matched healthy controls across three visits over 24 months. Network-to-network functional connectivity was quantified, and machine-learning models were trained using functional connectivity features. SCA7 showed lower MoCA (p = 0.045) and MMSE (p = 0.025) scores and progressive worsening of ataxia (SARA, p < 0.001). Significant Group x Visit interactions were observed for Visual-Default Mode (p = 0.012) and Somatomotor-Cerebellar Dorsal Attention connectivity (p = 0.038). Functional connectivity abnormalities involved cortical, cortico-cerebellar, and cerebellar networks that became more widespread at the final follow-up assessment, with the visual network emerging as the most consistently affected system across analyses. Functional connectivity abnormalities were associated with cognitive performance (MMSE: r = -0.62, p = 0.01) and disease severity (SARA: r = 0.589, p = 0.016). Functional connectivity features accurately classified SCA7 and healthy controls (accuracy = 96.4%, F1 = 0.969). These findings support resting-state functional connectivity as a candidate biomarker warranting further validation in larger, independent cohorts.

Tau pathology is central to Alzheimers disease and related tauopathies, yet mechanisms driving neuronal dysfunction and degeneration downstream of pathological changes in tau remain poorly understood. Drosophila melanogaster models provide a genetically tractable system with an intact nervous system and short lifespan that allows investigation of mechanisms of many diseases. However, in Drosophila, developmental expression of human tau frequently causes lethality and developmental phenotypes, limiting the study of neurodegenerative disease processes. Further, sex is rarely considered in Drosophila studies of tau pathology despite clear sex differences being observed in many aspects of human tauopathies. Here, we used an inducible, pan-neuronal GeneSwitch system to express human tau isoforms exclusively in adulthood, enabling the dissection of tau toxicity independent of development. We combined longitudinal behavioural monitoring with lifespan and neurodegeneration analyses, and performed a targeted genetic screen to identify modifiers of tau-induced dysfunction. Adult-onset tau expression produced striking, sexually dimorphic effects on survival and behaviour. Neuronal expression of the human tau isoform with 4 microtubule binding repeats and neither alternatively spliced N-terminal exon (0N4R tau) caused pronounced neurodegeneration and reduced lifespan, which was exacerbated in flies expressing the phospho-mimetic 0N4R-TauE14 variant. Tau expression produced sexually dimorphic effects on survival and behaviour, with females exhibiting a greater reduction in lifespan, while the induction-dependent increase in vacuolar neurodegeneration was broadly comparable between sexes. Behaviourally, tau expression induced elevated daytime inactivity in females, whereas males exhibited hyperactivity, revealing opposing functional outcomes between sexes. A targeted genetic screen further identified modifiers of tau-dependent behavioural impairment. APOE2 expression in glia, syndecan overexpression in neurons, and increased global expression of the chaperone heat shock protein 90 all reduced 0N4R-TauE14-induced behavioural changes. Seventeen candidate perturbations enhanced the TauE14-induced behavioural phenotype, including manipulations of APOE3, CLU, INPP5D/INPP5K, BIN1/Amph, synaptogyrin, LRP1, NPC1, and Hsp90 pathways. Together, these findings establish an adult-onset Drosophila model of tauopathy that uncouples neurotoxicity from development, reveals sex as a major determinant of tau-induced behavioural outcomes in flies, and uncovers genetic modulators of tau-induced dysfunction. This work highlights the importance of incorporating sex as a biological variable and provides a platform for mechanistic and translational studies of tauopathy.