Medium Spiny Neurons Research Articles

Somatic CAG repeat expansion in blood associates with biomarkers of neurodegeneration in Huntington's disease decades before clinical motor diagnosis.

Huntington's disease (HD) is an autosomal dominant neurodegenerative disease with the age at which characteristic symptoms manifest strongly influenced by inherited HTT CAG length. Somatic CAG expansion occurs throughout life and understanding the impact of somatic expansion on neurodegeneration is key to developing therapeutic targets. In 57 HD gene expanded (HDGE) individuals, ~23 years before their predicted clinical motor diagnosis, no significant decline in clinical, cognitive or neuropsychiatric function was observed over 4.5 years compared with 46 controls (false discovery rate (FDR) > 0.3). However, cerebrospinal fluid (CSF) markers showed very early signs of neurodegeneration in HDGE with elevated neurofilament light (NfL) protein, an indicator of neuroaxonal damage (FDR = 3.2 × 10-12), and reduced proenkephalin (PENK), a surrogate marker for the state of striatal medium spiny neurons (FDR = 2.6 × 10-3), accompanied by brain atrophy, predominantly in the caudate (FDR = 5.5 × 10-10) and putamen (FDR = 1.2 × 10-9). Longitudinal increase in somatic CAG repeat expansion ratio (SER) in blood was a significant predictor of subsequent caudate (FDR = 0.072) and putamen (FDR = 0.148) atrophy. Atypical loss of interruption HTT repeat structures, known to predict earlier age at clinical motor diagnosis, was associated with substantially faster caudate and putamen atrophy. We provide evidence in living humans that the influence of CAG length on HD neuropathology is mediated by somatic CAG repeat expansion. These critical mechanistic insights into the earliest neurodegenerative changes will inform the design of preventative clinical trials aimed at modulating somatic expansion. ClinicalTrials.gov registration: NCT06391619 .

Complementary cognitive roles for D2-MSNs and D1-MSNs during interval timing.

The role of striatal pathways in cognitive processing is unclear. We studied dorsomedial striatal cognitive processing during interval timing, an elementary cognitive task that requires mice to estimate intervals of several seconds and involves working memory for temporal rules as well as attention to the passage of time. We harnessed optogenetic tagging to record from striatal D2-dopamine receptor-expressing medium spiny neurons (D2-MSNs) in the indirect pathway and from D1-dopamine receptor-expressing MSNs (D1-MSNs) in the direct pathway. We found that D2-MSNs and D1-MSNs exhibited distinct dynamics over temporal intervals as quantified by principal component analyses and trial-by-trial generalized linear models. MSN recordings helped construct and constrain a four-parameter drift-diffusion computational model in which MSN ensemble activity represented the accumulation of temporal evidence. This model predicted that disrupting either D2-MSNs or D1-MSNs would increase interval timing response times and alter MSN firing. In line with this prediction, we found that optogenetic inhibition or pharmacological disruption of either D2-MSNs or D1-MSNs increased interval timing response times. Pharmacologically disrupting D2-MSNs or D1-MSNs also changed MSN dynamics and degraded trial-by-trial temporal decoding. Together, our findings demonstrate that D2-MSNs and D1-MSNs had opposing dynamics yet played complementary cognitive roles, implying that striatal direct and indirect pathways work together to shape temporal control of action. These data provide novel insight into basal ganglia cognitive operations beyond movement and have implications for human striatal diseases and therapies targeting striatal pathways.

Complementary cognitive roles for D2-MSNs and D1-MSNs during interval timing

The role of striatal pathways in cognitive processing is unclear. We studied dorsomedial striatal cognitive processing during interval timing, an elementary cognitive task that requires mice to estimate intervals of several seconds and involves working memory for temporal rules as well as attention to the passage of time. We harnessed optogenetic tagging to record from striatal D2-dopamine receptor-expressing medium spiny neurons (D2-MSNs) in the indirect pathway and from D1-dopamine receptor-expressing MSNs (D1-MSNs) in the direct pathway. We found that D2-MSNs and D1-MSNs exhibited distinct dynamics over temporal intervals as quantified by principal component analyses and trial-by-trial generalized linear models. MSN recordings helped construct and constrain a four-parameter drift-diffusion computational model in which MSN ensemble activity represented the accumulation of temporal evidence. This model predicted that disrupting either D2-MSNs or D1-MSNs would increase interval timing response times and alter MSN firing. In line with this prediction, we found that optogenetic inhibition or pharmacological disruption of either D2-MSNs or D1-MSNs increased interval timing response times. Pharmacologically disrupting D2-MSNs or D1-MSNs also changed MSN dynamics and degraded trial-by-trial temporal decoding. Together, our findings demonstrate that D2-MSNs and D1-MSNs had opposing dynamics yet played complementary cognitive roles, implying that striatal direct and indirect pathways work together to shape temporal control of action. These data provide novel insight into basal ganglia cognitive operations beyond movement and have implications for human striatal diseases and therapies targeting striatal pathways.

Astrocytes Mediate Psychostimulant-Induced Alterations ofSpike-Timing Dependent Synaptic Plasticity.

At cellular and circuit levels, drug addiction is considered a dysregulation of synaptic plasticity. In addition, dysfunction of the glutamate transporter 1 (GLT-1) in the nucleus accumbens (NAc) has also been proposed as a mechanism underlying drug addiction. However, the cellular and synaptic impact of GLT-1 alterations in the NAc remain unclear. Here we show in the NAc that 10 days withdraw after 5 days treatment with cocaine or amphetamine decreases GLT-1 expression in astrocytes, which results in the prolongation of the excitatory postsynaptic potential (EPSP) decay kinetics in D1 receptor-containing medium spiny neurons (D1R-MSNs). Using the spike timing dependent plasticity (STDP) paradigm, we found that enlargement of EPSP duration results in switching the LTP elicited in control animals to LTD in psychostimulant-treated mice. In contrast to D1-MSNs, D2-MSNs did not display changes in EPSP kinetics and synaptic plasticity. Notably, the psychostimulant-induced synaptic transmission and synaptic plasticity effects were absent in IP3R2-/- mice, which lack astrocyte calcium signal, but were mimicked by the selective astrocytes stimulation with DREADDs. Finally, ceftriaxone, which upregulates GLT-1, restored normal GLT-1 function, EPSP kinetics, and synaptic plasticity in psychostimulant-treated mice. Therefore, we propose that cocaine and amphetamine increase dopaminergic levels in the NAc, which stimulates astrocytes and downregulates the GLT-1. The decreased GLT-1 function prolonged the EPSP kinetics, leading to the modulation of the STDP, transforming the LTP observed in control animals into LTD in psychostimulant-treated mice. Present work reveals a novel mechanism underlying the synaptic plasticity changes induced by these drugs of abuse.

Enhanced motivated behavior mediated by pharmacological targeting of the FGF14/Nav1.6 complex in nucleus accumbens neurons

Protein/protein interactions (PPI) play crucial roles in neuronal functions. Yet, their potential as drug targets for brain disorders remains underexplored. The fibroblast growth factor 14 (FGF14)/voltage-gated Na+ channel 1.6 (Nav1.6) complex regulates excitability of medium spiny neurons (MSN) of the nucleus accumbens (NAc), a central hub of reward circuitry that controls motivated behaviors. Here, we identified compound 1028 (IUPAC: ethyl 3-(2-(3-(hydroxymethyl)-1H-indol-1-yl)acetamido)benzoate), a brain-permeable small molecule that targets FGF14R117, a critical residue located within a druggable pocket at the FGF14/Nav1.6 PPI interface. We found that 1028 modulates FGF14/Nav1.6 complex assembly and depolarizes the voltage-dependence of Nav1.6 channel inactivation with nanomolar potency by modulating the intramolecular interaction between the III-IV linker and C-terminal domain of the Nav1.6 channel. Consistent with the compound’s effects on Nav1.6 channel inactivation, 1028 enhances MSN excitability ex vivo and accumbal neuron firing rate in vivo in murine models. Systemic administration of 1028 maintains behavioral motivation preferentially during motivationally deficient conditions in murine models. These behavioral effects were abrogated by in vivo gene silencing of Fgf14 in the NAc and were accompanied by a selective reduction in accumbal dopamine levels during reward consumption in murine models. These findings underscore the potential to selectively regulate complex behaviors associated with neuropsychiatric disorders through targeting of PPIs in neurons.

Trans-ancestry genome-wide study of depression identifies 697 associations implicating cell types and pharmacotherapies.

In a genome-wide association study (GWAS) meta-analysis of 688,808 individuals with major depression (MD) and 4,364,225 controls from 29 countries across diverse and admixed ancestries, we identify 697 associations at 635 loci, 293 of which are novel. Using fine-mapping and functional tools, we find 308 high-confidence gene associations and enrichment of postsynaptic density and receptor clustering. A neural cell-type enrichment analysis utilizing single-cell data implicates excitatory, inhibitory, and medium spiny neurons and the involvement of amygdala neurons in both mouse and human single-cell analyses. The associations are enriched for antidepressant targets and provide potential repurposing opportunities. Polygenic scores trained using European or multi-ancestry data predicted MD status across all ancestries, explaining up to 5.8% of MD liability variance in Europeans. These findings advance our global understanding of MD and reveal biological targets that may be used to target and develop pharmacotherapies addressing the unmet need for effective treatment.

An ultra low frequency spike timing dependent plasticity based approach for reducing alcohol drinking

Alcohol use disorder (AUD) is a chronic relapsing brain disorder characterized by an impaired ability to stop or control alcohol consumption despite adverse social, occupational, or health consequences. AUD affects nearly one-third of adults at some point during their lives, with an associated cost of approximately $249 billion annually in the U.S. alone. The effects of alcohol consumption are expected to increase significantly during the COVID-19 pandemic, with alcohol sales increasing by approximately 54%, potentially exacerbating health concerns and risk-taking behaviors. Unfortunately, existing pharmacological and behavioral therapies for AUD are associated with poor success rates, with approximately 40% of individuals relapsing within three years of treatment.Pre-clinical studies have shown that chronic alcohol consumption leads to significant changes in synaptic function within the dorsal medial striatum (DMS), one of the brain regions associated with AUD and responsible for mediating goal-directed behavior. Specifically, chronic alcohol consumption has been associated with hyperactivity of dopamine receptor 1 (D1) medium spiny neurons (MSN) and hypoactivity of dopamine receptor 2 (D1) MSNs within the DMS. Optogenetic, chemogenetic, and transgenic approaches have demonstrated that reducing the D1/D2 MSN signaling imbalance decreases alcohol self-administration in rodent models of AUD.Here, we present an electrical stimulation approach that uses ultra-low (≤ 1 Hz) frequency (ULF) spike-timing-dependent plasticity (STDP) in mouse models of AUD to reduce DMS D1/D2 MSN signaling imbalances by stimulating D1-MSN afferents into the GPi and ACC glutamatergic projections to the DMS in a time-locked stimulation sequence. Our data suggest that GPi/ACC ULF-STDP selectively decreases DMS D1-MSN hyperactivity leading to reduced alcohol consumption without evoking undesired affective behaviors using electrical stimulation rather than approaches requiring genetic modification. This work represents a step towards fulfilling the unmet need for a reliable method of treating severe AUD through cell-type-specific control with clinically available neuromodulation tools.

Long-term, cell type-specific effects of prenatal stress on dorsal striatum and relevant behaviors in mice.

Maternal stress during pregnancy, or prenatal stress, is a risk factor for neurodevelopmental disorders in offspring, including autism spectrum disorder (ASD). In ASD, dorsal striatum displays abnormalities correlating with symptom severity, but there is a gap in knowledge about dorsal striatal cellular and molecular mechanisms that may contribute. Using a mouse model, we investigated how prenatal stress impacted striatal-dependent behavior in adult offspring. We observed enhanced motor learning and earlier response times on an interval timing task, with accompanying changes in time-related medium spiny neuron (MSN) activity. We performed adult dorsal striatal single-cell RNA sequencing following prenatal stress which revealed differentially expressed genes (DEGs) in multiple cell types; downregulated DEGs were enriched for ribosome and translational pathways consistently in MSN subtypes, microglia, and somatostatin neurons. DEGs in MSN subtypes over-represented ASD risk genes and were enriched for synapse-related processes. These results provide insights into striatal alterations relevant to neurodevelopmental disorders.

Epac2-mediated synaptic insertion of Ca2+-permeable AMPARs in the nucleus accumbens contributes to incubation of cocaine craving.

The accumulation of GluA2-lacking Ca2+-permeable AMPARs (CP-AMPARs) in the medium spiny neurons (MSNs) of the nucleus accumbens (NAc) is required for the expression of incubation of cocaine craving. The exchange protein directly activated by cAMP (Epac) is an intracellular effector of cAMP and a guanine nucleotide exchange factor for the small GTPase Rap1. Epac2 has been implicated in the trafficking of AMPA receptors at central synapses. We tested the hypothesis that Epac2 activation contributes to the accumulation of CP-AMPARs in NAc MSNs and incubation of cocaine craving. Here we demonstrate that the selective Epac2 agonist S-220 facilitated the synaptic insertion of GluA2-lacking CP-AMPARs at excitatory synapses onto NAc MSNs. In addition, prolonged abstinence from cocaine self-administration in rats resulted in elevated Rap1-GTP levels in the NAc, implying that Epac2 is activated during incubation. Importantly, we show that AAV-mediated shRNA knockdown of Epac2 in the NAc core attenuated the accumulation of CP-AMPARs and cue-induced drug-seeking behavior after prolonged abstinence from cocaine self-administration. In contrast, acute pharmacological inhibition of Epac2 with the selective Epac2 inhibitor ESI-05 did not alter CP-AMPARs that had already accumulated during incubation, and intra-NAc application of ESI-05 did not significantly affect cue-induced drug seeking following prolonged abstinence. Taken together, these results suggest that Epac2 activation during the period of incubation, but not during cue-induced drug seeking, leads to the accumulation of CP-AMPARs in NAc MSNs, which in turn contributes to incubation of cocaine craving.

Exploring PDE5A upregulation in bipolar disorder: insights from single-nucleus RNA sequencing of human basal ganglia

Basal ganglia is proposed to mediate symptoms underlying bipolar disorder (BD). To understand the cell type-specific gene expression and network changes of BD basal ganglia, we performed single-nucleus RNA sequencing of 30,752 nuclei from caudate, putamen, globus pallidus, and substantia nigra of control human postmortem brain and 24,672 nuclei from BD brain. Differential expression analysis revealed major difference lying in caudate, with BD medium spiny neurons (MSNs) expressing significantly higher PDE5A, a cGMP-specific phosphodiesterase. Gene co-expression analysis (WGCNA) showed a strong correlation of caudate MSNs and gene module green, with a PDE5A-containing hub gene network. Gene regulatory network analysis (SCENIC) indicated key regulons among different cell types and basal ganglia regions, with downstream targets of key transcriptional factors showing overlapping genes such as PDEs. Upregulation of PDE5A was further validated in 7 pairs of control and BD caudate sections. Overexpression of PDE5A in primary cultured lateral ganglion eminence-derived striatal neurons led to decreased dendrite complexity, increased apoptosis, and enhanced neuronal excitability and membrane resistance. This effect could be rescued by PDE5 specific inhibitor, tadalafil. Overexpression of PDE5A in mouse striatum by stereotaxic injection caused a decreased cGMP level, an increased gene expression profile of neuroinflammation, and BD-like behaviors. Collectively, our findings provided cell type-specific gene expression profile, and indicated a causative role of PDE5A upregulation in BD basal ganglia.This study provides a single-nucleus transcriptomic profile of human control and bipolar disorder (BD) basal ganglia. Differential expression, gene co-expression, and gene regulatory network analyses collectively indicated upregulation of PDE5A in BD caudate medium spiny neurons (MSNs), which was further validated in another cohort of BD brains. The causative role of PDE5A upregulation in BD etiology is supported by the effects of PDE5A overexpression in cultured mouse MSNs in vitro and in adult mouse striatum in vivo. The former led to reduced dendrite complexity, increased apoptosis, and neuronal hyper-excitability, which could be rescued by PDE5 specific inhibitor tadalafil. The latter caused lower cGMP levels, upregulated genes associated with neuroinflammation, and BD-like behaviors.

ABHD6 loss-of-function in mesoaccumbens postsynaptic but not presynaptic neurons prevents diet-induced obesity in male mice.

α/β-hydrolase domain 6 (ABHD6) is a lipase linked to physiological functions affecting energy metabolism. Brain ABHD6 degrades 2-arachidonoylglycerol and thereby modifies cannabinoid receptor signalling. However, its functional role within mesoaccumbens circuitry critical for motivated behaviour and considerably modulated by endocannabinoids was unknown. Using three viral approaches, we show that control of the nucleus accumbens by neuronal ABHD6 is a key determinant of body weight and reward-directed behaviour in male mice. Contrary to expected outcomes associated with increasing endocannabinoid tone, loss of ABHD6 in nucleus accumbens, but not ventral tegmental area, neurons completely prevents diet-induced obesity, reduces food- and drug-seeking and enhances physical activity without affecting anxiodepressive behaviour. These effects are explained by attenuated inhibitory synaptic transmission onto medium spiny neurons. ABHD6 deletion in nucleus accumbens neurons and dopamine ventral tegmental area neurons produces contrasting effects on effortful responding for food. Intraventricular infusions of an ABHD6 inhibitor also restrain appetite and promoteweight loss. Together, these results reveal functional specificity of pre- and post-synaptic mesoaccumbens neuronal ABHD6 to differentially control energy balance and propose ABHD6 inhibition as a potential anti-obesity tool.

Neuroligin 1 Regulates Autistic-Like Repetitive Behavior through Modulating the Activity of Striatal D2 Receptor-Expressing Medium Spiny Neurons.

Restricted and repetitive behavior (RRB) is a primary symptom of autism spectrum disorder (ASD), which poses a significant risk to individuals' health and is becoming increasingly prevalent. However, the specific cellular and neural circuit mechanisms underlying the generation of RRB remain unclear. In this study, it is reported that the absence of the ASD-related protein Neuroligin 1 (NLGN1) in dopamine receptor D2-expressing medium spiny neurons (D2-MSNs) in the dorsal striatum is associated with the duration and frequency of self-grooming and digging behaviors. The Nlgn1-deficient D2-MSNs are hyperactivated, which correlates with excessive self-grooming and digging behaviors. Inhibiting the activity of D2-MSNs reduces the duration and frequency of these RRBs. Furthermore, it is demonstrated that the generation of self-grooming and digging behaviors depends on distinct patterns of D2-MSN activity. Finally, through single-nucleus RNA sequencing (sn-RNAseq) and protein detection verification, it is revealed that the overactivation of protein kinase C (PKC) in Nlgn1-deficient mice contributes to excessive repetitive behaviors and increased neuronal excitability. In this study, potential mechanisms are proposed for the generation of self-grooming and digging behaviors, as well as suggest possible treatments and interventions ASD.

Structural insights into the high basal activity and inverse agonism of the orphan receptor GPR6 implicated in Parkinson's disease.

GPR6 is an orphan G protein-coupled receptor with high constitutive activity found in D2-type dopamine receptor-expressing medium spiny neurons of the striatopallidal pathway, which is aberrantly hyperactivated in Parkinson's disease. Here, we solved crystal structures of GPR6 without the addition of a ligand (a pseudo-apo state) and in complex with two inverse agonists, including CVN424, which improved motor symptoms in patients with Parkinson's disease in clinical trials. In addition, we obtained a cryo-electron microscopy structure of the signaling complex between GPR6 and its cognate Gs heterotrimer. The pseudo-apo structure revealed a strong density in the orthosteric pocket of GPR6 corresponding to a lipid-like endogenous ligand. A combination of site-directed mutagenesis, native mass spectrometry, and computer modeling suggested potential mechanisms for high constitutive activity and inverse agonism in GPR6 and identified a series of lipids and ions bound to the receptor. The structures and results obtained in this study could guide the rational design of drugs that modulate GPR6 signaling.

Developmental and Adult Striatal Patterning of Nociceptin Ligand Marks Striosomal Population With Direct Dopamine Projections.

Circuit influences on the midbrain dopamine system are crucial to adaptive behavior and cognition. Recent developments in the study of neuropeptide systems have enabled high-resolution investigations of the intersection of neuromodulatory signals with basal ganglia circuitry, identifying the nociceptin/orphanin FQ (N/OFQ) endogenous opioid peptide system as a prospective regulator of striatal dopamine signaling. Using a prepronociceptin-Cre reporter mouse line, we characterized highly selective striosomal patterning of Pnoc mRNA expression in mouse dorsal striatum, reflecting the early developmental expression of Pnoc. In the ventral striatum, Pnoc expression in the nucleus accumbens core was grouped in clusters akin to the distribution found in striosomes. We found that PnoctdTomato reporter cells largely comprise a population of dopamine receptor D1 (Drd1) expressing medium spiny projection neurons localized in dorsal striosomes, known to be unique among striatal projection neurons for their direct innervation of midbrain dopamine neurons. These findings provide a new understanding of the intersection of the N/OFQ system among basal ganglia circuits with particular implications for developmental regulation or wiring of striato-nigral circuits.

Oligodendrocytes in Huntington's Disease: A Review of Oligodendrocyte Pathology and Current Cell Reprogramming Approaches for Oligodendrocyte Modelling of Huntington's Disease.

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder traditionally characterized by the selective loss of medium spiny neurons in the basal ganglia. However, it has become apparent that white matter injury and oligodendrocyte dysfunction precede the degeneration of medium spiny neurons, garnering interest as a key pathogenic mechanism of HD. Oligodendrocytes are glial cells found within the central nervous system involved in the production of myelin and the myelination of axons. Myelin is a lipid-rich sheath that wraps around axons, facilitating signal conduction and neuronal viability. The degeneration of myelin hinders effective communication and leaves neurons vulnerable to external damage and subsequent degeneration. Abnormalities in oligodendrocyte maturation have been established in the HD human brain, however, investigations into the underlying dysfunction of human oligodendrocytes in HD are limited. This review will detail the involvement of oligodendrocytes and white matter damage in HD. Recent developments in modeling human-specific oligodendrocyte pathology in HD will be discussed, with a particular focus on emerging somatic cell reprogramming approaches.

Traumatic brain injury, alone or with striatal hemorrhage-like extension, transiently decreases GABA and glutamate levels along motor deficits in the rat striatum: an in vivo study

The cerebral cortex is connected to the striatum via the axons of the pyramidal glutamatergic neurons, and this pathway is intimately involved in motor function. In the striatum, glutamatergic afferents initiate the activity of GABAergic medium spiny neurons. This study addressed whether traumatic brain injury (TBI) affects GABA and glutamate extracellular levels in the dorsal striatum as an indicator of effects on the cortico-striatal pathway, in rats with motor deficits and recovered animals. Animals were assigned to a sham group, a TBI-alone group, and a TBI + striatal injury group (local injection of a FeCl2 solution to mimic hemorrhagic lesion). In the TBI-alone and TBI + striatal injury groups, motor deficits were accompanied by decreased extracellular GABA and glutamate levels in the striatum at 3 days post-injury. The TBI + striatal injury group showed higher motor deficits, which lasted 7 days longer, and GABA levels were significantly different compared to the TBI alone group. At 18 days post-injury, in recovered rats from the TBI-alone group GABA and glutamate levels returned to control levels. Alterations in extracellular GABA and glutamate levels indicate damage to the cortico-striatal pathway, underscoring the importance of studying this pathway for treatment and recovery after TBI.

Striatum-enriched protein, arginase 2 localizes to medium spiny neurons and controls striatal metabolic profile

Arginase 2 (Arg2) is the predominant arginase isoenzyme in the brain, however its distribution appears to be limited to selected, region-specific subpopulations of cells. Although striatum is highly enriched with Arg2, precise localization and function of striatal Arg2 have never been studied. Here, we confirm that Arg2 is the only arginase isoenzyme in the striatum, and, using genetic model of total Arg2 loss, we show that Arg2 in this region is fully responsible for arginase catalytic activity, and its loss doesn't induce compensatory activation of Arg1. We exhibit that Arg2 is present in medium spiny neurons (MSNs), striatum-specific projecting neurons, where it localizes in soma and neuronal processes, and is absent in astrocytes or microglia. Finally, analysis of NMR spectroscopy-measured metabolic profiles of striata of Arg2-null mice enabled to recognize two metabolites (NADH and malonic acid) to be significantly altered compared to control animals. Multivariate comparison of the data using orthogonal projections to latent structures discriminant analysis, allowed for discrimination between control and Arg2-null mice and identified metabolites that contributed the most to this between-group dissimilarity. Our study reveals for the first time the localization of Arg2 in MSNs and demonstrates significant role of this enzyme in regulating striatal metabolism. These findings may be especially interesting in the context of Huntington's disease (HD), a disorder that specifically affects MSNs and in which, with the use of mouse models, the onset of pathological phenotypes was recently shown to be preceded by progressive impairment of striatal Arg2, a phenomenon of an unknown significance for disease pathogenesis.

Single-cell transcriptomics unveils molecular signatures of neuronal vulnerability in a mouse model of prion disease that overlap with Alzheimer’s disease

Understanding why certain neurons are more sensitive to dysfunction and death caused by misfolded proteins could provide therapeutically relevant insights into neurodegenerative disorders. Here, we harnessed single-cell transcriptomics to examine live neurons isolated from prion-infected female mice, aiming to identify and characterize prion-vulnerable neuronal subsets. Our analysis revealed distinct transcriptional responses across neuronal subsets, with a consistent pathway-level depletion of synaptic gene expression in damage-vulnerable neurons. By scoring neuronal damage based on the magnitude of depleted synaptic gene expression, we identified a diverse spectrum of prion-vulnerable glutamatergic, GABAergic, and medium spiny neurons. Comparison between prion-vulnerable and resistant neurons highlighted baseline gene expression differences that could influence neuronal vulnerability. For instance, the neuroprotective cold-shock protein Rbm3 exhibited higher baseline gene expression in prion-resistant neurons and was robustly upregulated across diverse neuronal classes upon prion infection. We also identified vulnerability-correlated transcripts that overlapped between prion and Alzheimer’s disease. Our findings not only demonstrate the potential of single-cell transcriptomics to identify damage-vulnerable neurons, but also provide molecular insights into neuronal vulnerability and highlight commonalties across neurodegenerative disorders.

Reprogrammed human lateral ganglionic eminence precursors generate striatal neurons and restore motor function in a rat model of Huntington’s disease

BackgroundHuntington’s disease (HD) is a genetic neurological disorder predominantly characterised by the progressive loss of GABAergic medium spiny neurons in the striatum resulting in motor dysfunction. One potential strategy for the treatment of HD is the development of cell replacement therapies to restore neuronal circuitry and function by the replacement of lost neurons. We propose the generation of lineage-specific human lateral ganglionic eminence precursors (hiLGEP) using direct reprogramming technology provides a novel and clinically viable cell source for cell replacement therapy for HD.MethodshiLGEPs were derived by direct reprogramming of adult human dermal fibroblasts (aHDFs) using chemically modified mRNA (cmRNA) and a defined reprogramming medium. hiLGEPs were differentiated in vitro using an optimised striatal differentiation medium. Acquisition of a striatal precursor and neural cell fate was assessed through gene expression and immunocytochemical analysis of key markers. hiLGEP-derived striatal neuron functionality in vitro was demonstrated by calcium imaging using Cal-520. To investigate the ability for hiLGEP to survive, differentiate and functionally integrate in vivo, we transplanted hiLGEPs into the striatum of quinolinic acid (QA)-lesioned rats and performed behavioural assessment using the cylinder test over the course of 14 weeks. Survival and differentiation of hiLGEPs was assessed at 8 and 14-weeks post-transplant by immunohistochemical analysis.ResultsWe demonstrate the capability to generate hiLGEPs from aHDFs using cmRNA encoding the pro-neural genes SOX2 and PAX6, combined with a reprogramming medium containing Gö6983, Y-27,632, N-2 and Activin A. hiLGEPs generated functional DARPP32 + neurons following 14 days of culture in BrainPhys™ media supplemented with dorsomorphin and Activin A. We investigated the ability for hiLGEPs to survive transplantation, differentiate to medium spiny-like striatal neurons and improve motor function in the QA lesion rat model of HD. Fourteen weeks after transplantation, we observed STEM121 + neurons co-expressing MAP2, DARPP32, GAD65/67, or GABA. Rats transplanted with hiLGEPs also demonstrated reduction in motor function impairment as determined by spontaneous exploratory forelimb use when compared to saline transplanted animals.ConclusionThis study provides proof-of-concept and demonstrates for the first time that aHDFs can be directly reprogrammed to hiLGEPs which survive transplantation, undergo neuronal differentiation to generate medium spiny-like striatal neurons, and reduce functional impairment in the QA lesion rat model of HD.

Reduced striatal M4-cholinergic signaling following dopamine loss contributes to parkinsonian and l-DOPA-induced dyskinetic behaviors.

A dynamic equilibrium between dopamine and acetylcholine (ACh) is essential for striatal circuitry and motor function, as imbalances are associated with Parkinson's disease (PD) and levodopa-induced dyskinesia (LID). Conventional theories posit that cholinergic signaling is pathologically elevated in PD as a result of increased ACh release, which contributes to motor deficits. However, using approaches to measure receptor-mediated signaling, we found that, rather than the predicted enhancement, the strength of cholinergic transmission at muscarinic M4 receptor synapses on direct pathway medium spiny neurons was decreased in dopamine-depleted mice. This adaptation was due to a reduced postsynaptic M4 receptor function, resulting from down-regulated receptors and downstream signaling. Restoring M4 transmission unexpectedly led to a partial alleviation of motor deficits and LID dyskinetic behavior, revealing an unexpected prokinetic effect in addition to the canonical antikinetic role of M4 receptors. These findings indicate that decreased M4 function differentially contributes to parkinsonian and LID pathophysiology, representing a promising target for therapeutic intervention.