Biology subjects

Halurkar, M. S.

Publications and source records attributed to Halurkar, M. S..

5 recordsLinked to original sources

bioRxiv2025

Single-nucleus transcriptomics reveal disrupted pathways in the prefrontal cortex of Scn2a-deficient mice

Truncating variants in SCN2A, which encodes the NaV1.2 sodium channel critical for action potential initiation and propagation, are associated with autism spectrum disorder (ASD) and epilepsy. To investigate SCN2A deficiency-related phenotypes, we developed a preclinical mouse model with under 50% NaV1.2 expression, exhibiting neuronal hyperexcitability and social deficits. However, the neuronal populations and molecular alterations underlying these phenotypes at single-cell resolution have not been investigated. In this study, we conducted single-nucleus RNA sequencing (snRNA-seq) of wild-type (WT), homozygous Scn2a-deficient (HOM) mice, and HOM mice with Scn2a restoration (HOM-FlpO) to examine the effects of Scn2a level on gene expression in the medial prefrontal cortex (mPFC), a critical brain region related to ASD development. Differential expression analysis in GABAergic and glutamatergic neurons between genotypes revealed gene expression enriched in neurotransmitter activity regulation and synapse organization. Lastly, snRNA-seq results in HOM-FlpO identified genes that were rescued after Scn2a restoration. These results reveal that reduced Scn2a expression disrupts RNA transcriptomes in multiple neuronal subtypes, providing insight into cell type-specific mechanisms underlying SCN2A-related disorders.

neuroscience↗

bioRxiv2025

Gene therapies alleviate absence epilepsy associated with Scn2a deficiency in DBA/2J mice

Mutations in the voltage-gated sodium channel gene SCN2A, which encodes the NaV1.2 channel, cause severe epileptic seizures. Patients with SCN2A loss-of-function (LoF) mutations, such as protein-truncating mutations, often experience later-onset and drug-resistant epilepsy, highlighting an urgent unmet clinical need for new therapies. We previously developed a gene-trap Scn2a (Scn2agt/gt) mouse model with a global NaV1.2 reduction in the widely used C57BL/6N (B6) strain. Although these mice display multiple behavioral abnormalities, EEG recordings indicated only mild epileptiform discharges, possibly attributable to the seizure-resistant characteristics associated with the B6 strain. To enhance the epileptic phenotype, we derived congenic Scn2agt/gt mice in the seizure-susceptible DBA/2J (D2J) strain. Notably, we found that these mice exhibit prominent spontaneous absence seizures, marked by both short and long spike-wave discharges (SWDs). Restoring NaV1.2 expression in adult mice substantially reduced their SWDs, suggesting the possibility of SCN2A gene replacement therapy during adulthood. RNA sequencing revealed significant alterations in gene expression in the Scn2agt/gt mice, in particular a broad downregulation of voltage-gated potassium channel (KV) genes, including KV1.1. The reduction of KV1.1 expression was further validated in human cerebral organoids with SCN2A deficiency, highlighting KV1.1 as a promising therapeutic target for refractory seizures associated with SCN2A dysfunction. Importantly, delivery of exogenous human KV1.1 expression via adeno-associated virus (AAV) in D2J Scn2agt/gt mice substantially reduced absence seizures. Together, these findings underscore the influence of mouse strain on seizure severity and highlight the potential of targeted gene therapies for treating SCN2A deficiency-related epilepsies. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=91 SRC="FIGDIR/small/657652v1_ufig1.gif" ALT="Figure 1"> View larger version (18K): org.highwire.dtl.DTLVardef@35374eorg.highwire.dtl.DTLVardef@1c22197org.highwire.dtl.DTLVardef@2b4582org.highwire.dtl.DTLVardef@e06e68_HPS_FORMAT_FIGEXP M_FIG C_FIG In briefScn2a deficiency leads to absence seizures in D2J mice and neuronal hyperexcitability with compensatory KV reduction; restoring NaV1.2 or introducing human KV1.1 reduces seizure burden. HighlightsO_LIScn2a deficiency induces robust absence seizures in the DBA/2J but not the C57BL/6N strain. C_LIO_LICortical neurons in adult DBA/2J mice with Scn2a deficiency exhibit intrinsic hyperexcitability. C_LIO_LISevere Scn2a deficiency leads to downregulation of multiple potassium channel genes. C_LIO_LIGenetic restoration of NaV1.2 expression alleviates spike-wave discharges (SWDs). C_LIO_LIAAV-mediated human KV1.1 delivery substantially reduced absence seizures, demonstrating the therapeutic potential of targeted gene therapy. C_LI

neuroscience↗

bioRxiv2025

Autism-associated SCN2A deficiency disrupts cortico-striatal circuitry in human brain assembloids

Profound autism spectrum disorder (ASD) is frequently attributable to single-gene mutations, with SCN2A (voltage-gated sodium channel NaV1.2) protein-truncating variants (PTVs) being one of the most penetrant. Although cortico-striatal circuitry is implicated as a key node in ASD, the impact of SCN2A deficiency on human neural circuits is unknown. Using the human cortico-striatal assembloid model, we show that the autism-causing PTV SCN2A-C959X impairs long-range cortical axonal projections, reduces striatal spine density, and attenuates excitatory cortical-striatal synaptic transmission. Surprisingly, these assembloids carrying the heterozygous SCN2A nonsense mutation exhibited pronounced network hyperexcitability, a human cell-specific phenotype not observed in Scn2a+/- mice, highlighting a human-specific circuit vulnerability. Collectively, our study unveils human circuit-specific dysfunctions of SCN2A deficiency and SCN2A-mediated ASD. HighlightsO_LIAxonal projections facilitate synapse formation and functional connectivity in human brain assembloids. C_LIO_LINaV1.2 is expressed along neuronal axons, extending to soma and dendrites in human brain assembloids. C_LIO_LISCN2A-C959X disrupts axonal projection patterns, impairs excitatory synaptic transmission, reduces spine density, and results in elevated neuronal excitability. C_LI Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=90 SRC="FIGDIR/small/657036v1_ufig1.gif" ALT="Figure 1"> View larger version (27K): org.highwire.dtl.DTLVardef@6d5b1forg.highwire.dtl.DTLVardef@1795ecdorg.highwire.dtl.DTLVardef@13f0d7eorg.highwire.dtl.DTLVardef@8ee059_HPS_FORMAT_FIGEXP M_FIG C_FIG In briefO_ST_ABSSCN2A haploinsufficiency impairs cortico-striatal circuitry.C_ST_ABSSCN2A haploinsufficiency disrupts axon initial segment (AIS) integrity, leading to hyperexcitability (red arrow), reduced axon projections, and impaired synaptic transmission (decreased sEPSCs and altered network firing). These deficits result in dysfunction within the cortico-striatal circuitry.

neuroscience↗

bioRxiv2025

Restoration of excitation/inhibition balance enhances neuronal signal-to-noise ratio and rescues social deficits in autism-associated Scn2a-deficiency

Social behavior is critical for survival and adaptation, which is profoundly disrupted in autism spectrum disorders (ASD). Social withdrawal due to information overload was often described in ASD, and it was suspected that increased basal noise, i.e., excessive background neuronal activities in the brain could be a disease mechanism. However, experimental test of this hypothesis is limited. Loss-of-function mutations (deficiency) in SCN2A, which encodes the voltage-gated sodium channel NaV1.2, have been revealed as a leading monogenic cause of profound ASD. Here, we revealed that Scn2a deficiency results in robust and multifaceted social impairments in mice. Scn2a-deficient neurons displayed an increased excitation-inhibition (E/I) ratio, contributing to elevated basal neuronal noise and diminished signal-to-noise ratio (SNR) during social interactions. Notably, the restoration of Scn2a expression in adulthood is able to rescue both SNR and social deficits. By balancing the E/I ratio and reducing basal neuronal firing, an FDA-approved GABAA receptor-positive allosteric modulator improves sociability in Scn2a-deficient mice and normalizes neuronal activities in translationally relevant human brain organoids carrying autism-associated SCN2A nonsense mutation. Collectively, our findings revealed a critical role of the NaV1.2 channel in the regulation of social behaviors, and identified molecular, cellular, and circuitry mechanisms underlying SCN2A-associated disorders. HIGHLIGHTSO_LINaV1.2 deficiency leads to pronounced social deficits in mice. C_LIO_LINaV1.2 deficiency results in an overall enhanced E/I ratio, elevated basal neuronal activity, and impaired signal-to-noise ratio. C_LIO_LIBoth the enhanced E/I ratio and impaired sociability are reversible through the restoration of NaV1.2 expression in adulthood. C_LIO_LITargeted restoration of NaV1.2 in striatum-projecting neurons rescues social impairments. C_LIO_LIGABA transmission is reduced in both mouse and human organoid models of SCN2A deficiency, and acute systemic administration of GABAA receptor-positive allosteric modulators restores sociability. C_LI Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=193 HEIGHT=200 SRC="FIGDIR/small/641498v1_ufig1.gif" ALT="Figure 1"> View larger version (42K): org.highwire.dtl.DTLVardef@154a323org.highwire.dtl.DTLVardef@1a27fbaorg.highwire.dtl.DTLVardef@16fa3beorg.highwire.dtl.DTLVardef@6712c2_HPS_FORMAT_FIGEXP M_FIG C_FIG Graphical abstract: Severe Scn2a deficiency leads to a predominate decrease in GABA transmission with an overall enhanced E/I ratio, elevated basal neuronal activity, impaired SNR, and social deficits in adult NaV1.2-deficient mice.

neuroscience↗

bioRxiv2023

The widely used Ucp1-CreEvdr transgene elicits complex developmental and metabolic phenotypes.

Bacterial artificial chromosome transgenic models, including most Cre-recombinases, enable potent interrogation of gene function in vivo but require rigorous validation as limitations emerge. Due to its high relevance to metabolic studies, we performed comprehensive analysis of the Ucp1-CreEvdr line which is widely used for brown fat research. Hemizygotes exhibited major brown and white fat transcriptomic dysregulation, indicating potential altered tissue function. Ucp1-CreEvdrhomozygotes also show high mortality, growth defects, and craniofacial abnormalities. Mapping the transgene insertion site revealed insertion in chromosome 1 accompanied by large genomic alterations disrupting several genes expressed in a range of tissues. Notably, Ucp1-CreEvdr transgene retains an extra Ucp1 gene copy that may be highly expressed under high thermogenic burden. Our multi-faceted analysis highlights a complex phenotype arising from the presence of the Ucp1-CreEvdr transgene independently of the intended genetic manipulations. Overall, comprehensive validation of transgenic mice is imperative to maximize discovery while mitigating unexpected, off-target effects. HighlightsO_LIHemizygous Ucp1-CreEvdr mice exhibit substantial brown and white fat tissue dysregulation. C_LIO_LIHomozygous Ucp1-CreEvdr mice display high mortality, growth defects, and craniofacial abnormalities. C_LIO_LIThe Ucp1-CreEvdr transgene integration resulted in major genomic disruptions affecting multiple genes. C_LIO_LIThe Ucp1-CreEvdr transgene retains a possibly functional extra Ucp1 copy. C_LI

molecular biology↗