Biology subjects

Somarowthu, A.

Publications and source records attributed to Somarowthu, A..

6 recordsLinked to original sources

bioRxiv2025

Novel mouse model reveals neurodevelopmental origin of PMM2-CDG brain pathology

Congenital disorders of glycosylation (CDG) are a group of neurogenetic conditions resulting from disruptions in the cellular glycosylation machinery. The majority of CDG patients have compound heterozygous pathogenic variants in the phosphomannomutase 2 (PMM2) gene. Individuals with PMM2-CDG exhibit multi-systemic symptoms, prominently featuring neurological deficits with nearly all patients exhibiting cerebellar hypoplasia and ataxia. To overcome embryonic lethality caused by whole body knock-out of Pmm2 and mimic patient-related compound heterozygous pathogenic variants, we paired a Pmm2 flox allele (Pmm2fl) with a catalytically inactive knock-in allele (Pmm2R137H), commonly present in PMM2-CDG patients. Mice with post-mitotic loss of PMM2 from neurons or astrocytes are indistinguishable from unaffected littermates, including in a broad battery of neurological assessments. In contrast, removal of PMM2 from embryonic neural precursor cells leads to cerebellar hypoplasia, ataxia, seizures, and early lethality. Comprehensive multi-omics profiling, including metabolomics, glycomics, single-cell transcriptomics, proteomics, and glycoproteomics, reveal widespread molecular disturbances throughout the brain, with the cerebellum showing the most pronounced disruption. These findings highlight the heightened dependency of the developing cerebellum on intact N-glycosylation, aligning with clinical observations in PMM2-CDG patients. Importantly, glycoproteomic alterations identified in our mouse model are corroborated in PMM2-CDG patient post-mortem cerebellar tissue, underscoring the translational relevance of our findings and implicating impaired synaptic transmission as a key pathogenic mechanism.

neuroscience↗

bioRxiv2024

Electroconvulsive therapy generates a hidden wave after seizure

Electroconvulsive therapy (ECT) is a fast-acting, highly effective, and safe treatment for medication-resistant depression. Historically, the clinical benefits of ECT have been attributed to generating a controlled seizure; however, the underlying neurobiology is understudied and unresolved. Using optical neuroimaging of neural activity and hemodynamics in a mouse model of ECT, we demonstrated that a second brain event follows seizure: cortical spreading depolarization (CSD). We found that ECT pulse parameters and electrode configuration directly shaped the wave dynamics of seizure and subsequent CSD. To translate these findings to human patients, we used non-invasive diffuse optical monitoring of cerebral blood flow and oxygenation during routine ECT treatments. We observed that human brains reliably generate hyperemic waves after ECT seizure which are highly consistent with CSD. These results challenge a long-held assumption that seizure is the primary outcome of ECT and point to new opportunities for optimizing ECT stimulation parameters and treatment outcomes.

neuroscience↗

bioRxiv2024

Impaired excitability of fast-spiking neurons in a novel mouse model of KCNC1 epileptic encephalopathy

The recurrent pathogenic variant KCNC1-p.Ala421Val (A421V) is a cause of developmental and epileptic encephalopathy characterized by moderate-to-severe developmental delay/intellectual disability, and infantile-onset treatment-resistant epilepsy with multiple seizure types including myoclonic seizures. Yet, the mechanistic basis of this disease, and of the KCNC1 disease spectrum, is unclear. KCNC1 encodes Kv3.1, a voltage-gated potassium channel subunit that is highly and selectively expressed in neurons capable of generating action potentials at high frequency, including parvalbumin-positive fast-spiking GABAergic inhibitory interneurons in cerebral cortex (PV-INs) known to be important for cognitive function and plasticity as well as control of network excitation to prevent seizures. In this study, we generate a novel transgenic mouse model with conditional expression of the Ala421Val pathogenic missense variant (Kcnc1-A421V/+ mice) to explore the specific physiological mechanisms of KCNC1 developmental and epileptic encephalopathy. Our results indicate that global heterozygous expression of the A421V variant leads to cognitive impairment, epilepsy, and premature lethality. We observe decreased PV-IN cell surface expression of Kv3.1 via immunohistochemistry, decreased voltage-gated potassium current density in PV-INs using outside-out nucleated macropatch recordings in brain slice, and profound impairments in the intrinsic excitability of cerebral cortex PV-INs (but not excitatory neurons) in current-clamp electrophysiology. In vivo two-photon calcium imaging revealed altered basal activity in Kcnc1-A421V/+ PV-INs and excitatory cells, as well as hypersynchronous discharges correlated with brief paroxysmal movements that were subsequently shown to be myoclonic seizures on electroencephalography. We found alterations in PV-IN-mediated inhibitory neurotransmission in young adult but not juvenile Kcnc1-A421V/+ mice relative to wild-type controls. Together, these results establish the specific impact of the recurrent Kv3.1-A421V variant on neuronal excitability and synaptic physiology across development to drive network dysfunction underlying KCNC1 epileptic encephalopathy.

neuroscience↗

bioRxiv2022

The SCN1A Philadelphia variant - a gain-of-function mutation causing an early-onset epileptic encephalopathy

ObjectiveLoss-of-function variants in SCN1A cause Dravet Syndrome, the most common genetic developmental and epileptic encephalopathy (DEE). However, emerging evidence suggests separate entities of SCN1A-related disorders due to gain-of-function variants. Here, we aim to refine the clinical, genetic, and functional electrophysiological features of a recurrent p.R1636Q gain-of-function variant, identified in four individuals at a single center. MethodsIndividuals carrying the recurrent SCN1A p.R1636Q variant were identified through diagnostic testing. Whole-cell voltage-clamp electrophysiological recording in HEK-293T cells was performed to compare the properties of sodium channels containing wild-type Nav1.1 or Nav1.1-R1636Q along with both Nav{beta}1 and Nav{beta}2 subunits, including response to oxcarbazepine. To delineate differences to other SCN1A-related epilepsies, we analyzed electronic medical records. ResultsAll four individuals had an early-onset DEE characterized by focal tonic seizures and additional seizure types starting in the first few weeks of life. Electrophysiological analysis showed a mixed gain-of-function effect with normal current density, a leftward (hyperpolarized) shift of steady-state inactivation, and slower inactivation kinetics leading to a prominent late sodium current (INa). The observed functional changes closely paralleled effects of pathogenic variants in SCN3A and SCN8A at corresponding positions. Both wildtype and variant exhibited sensitivity to block by oxcarbazepine, partially correcting electrophysiological abnormalities of the SCN1A p.R1636Q variant. Clinically, a single individual responded to treatment with oxcarbazepine. Across 51 individuals with SCN1A-related epilepsies, those with the recurrent p.R1636Q variants had the earliest ages of onset. InterpretationThe recurrent SCN1A p.R1636Q variant causes a clinical entity with a wider clinical spectrum than previously reported, characterized by ultra early-onset epilepsy and absence of prominent movement disorder. Functional consequences of this variant lead to mixed loss- and gain-of-function that is partially corrected by oxcarbazepine. The recurrent p.R1636Q variant represents one of the most common causes of early-onset SCN1A-related epilepsies with separate treatment and prognosis implications. Key PointsO_LILoss-of-function variants in SCN1A cause Dravet syndrome, but gain-of-function variants have an emerging clinical spectrum. C_LIO_LIThe SCN1A p.R1636Q variant shows similar overall gain-of-function effects to identical missense variants in other voltage-gated sodium channels. C_LIO_LIFeatures of four unreported individuals with SCN1A p.R1636Q from a single center expand the SCN1A gain-of-function phenotype. C_LIO_LIIndividuals with this variant are recognizable by their ultra early-onset seizures in contrast to Dravet syndrome. C_LI

genetics↗

bioRxiv2021

Developmentally-regulated impairment of parvalbumin interneuron synaptic transmission in an experimental model of Dravet syndrome

Dravet syndrome (DS) is a neurodevelopmental disorder defined by epilepsy, intellectual disability, and sudden death, due to heterozygous variants in SCN1A with loss of function of the sodium channel subunit Nav1.1. Nav1.1-expressing parvalbumin GABAergic interneurons (PV-INs) from pre-weanling Scn1a+/- mice show impaired action potential generation. A novel approach assessing PV-IN function in the same mice at two developmental time points showed that, at post-natal day (P) 16-21, spike generation was impaired all mice, deceased prior or surviving to P35. However, synaptic transmission was selectively dysfunctional in pre-weanling mice that did not survive. Spike generation in surviving mice normalized by P35, yet we again identified abnormalities in synaptic transmission. We conclude that combined dysfunction of PV-IN spike generation and synaptic transmission drives disease severity, while ongoing dysfunction of synaptic transmission contributes to chronic pathology. Modeling revealed that PV-IN axonal propagation is more sensitive to decreases in sodium conductance than spike generation.

neuroscience↗

bioRxiv2021

Corticohippocampal circuit dysfunction in a mouse model of Dravet syndrome

Dravet syndrome (DS) is a neurodevelopmental disorder defined by treatment-resistant epilepsy, autism spectrum disorder, and sudden death, due to pathogenic variants in SCN1A encoding the Nav1.1 sodium channel subunit. Convergent data suggest hippocampal dentate gyrus (DG) pathology. We found that optogenetic stimulation of entorhinal cortex was ictogenic in DS (Scn1a+/-) but not wild-type mice in vivo. Two-photon calcium imaging in brain slice demonstrated profound impairment in filtering of perforant path input by DG in young adult Scn1a+/- mice due to enhanced excitatory input to granule cells. Excitability of parvalbumin interneurons (PV-INs) was near-normal and selective activation of PV-INs rescued circuit impairments. This demonstrates developmental reorganization of hippocampal circuitry that can be modulated by recruitment of functional PV-INs, suggesting potential therapeutic approaches towards seizure modulation. The identified circuit abnormality mirrors that seen in models of chronic temporal lobe epilepsy, suggesting convergent mechanisms linking genetic and acquired causes of temporal lobe-onset seizures.

neuroscience↗