Biology subjects

Shakkottai, V.

Publications and source records attributed to Shakkottai, V..

5 recordsLinked to original sources

bioRxiv2025

Resilience to Endoplasmic Reticulum Stress Mitigates Calcium-Dependent Membrane Hyperexcitability Underlying Late Disease Onset in SCA6

An enduring puzzle in many inherited neurological disorders is the late onset of symptoms despite expression of function-impairing mutant protein early in life. We examined the basis for onset of impairment in Spinocerebellar ataxia type 6 (SCA6), a canonical late-onset neurodegenerative ataxia which results from a polyglutamine expansion in the voltage gated calcium channel, Cav2.1. Cerebellar Purkinje cell spiking abnormalities are seen concurrent with motor impairment in SCA6 mice but the basis for these changes in spiking is unknown. We identify endoplasmic reticulum (ER) calcium depletion as the cause for Purkinje cell spiking abnormalities and that the impairments in Purkinje cell spiking are unrelated to Cav2.1 ion-flux function. Further, intact inhibitory neurotransmission in the cerebellar cortex is necessary for Purkinje neurons to exhibit spiking abnormalities in SCA6 mice. Based on serial cerebellar transcriptome analysis, we define a mechanism of disease that is related to ER stress. Further, our studies support a model whereby proteotoxicity from misfolded mutant Cav2.1 is mitigated by a HSP90-dependent unfolded protein response (UPR) and that age-related breakdown of this response causes motor dysfunction and aberrant Purkinje cell spiking. Redundant pathways of the UPR mediate this resilience to ER stress. These studies elucidate a mechanism of resilience connecting aberrant proteostasis and calcium-dependent intrinsic membrane hyperexcitability to explain delayed disease onset more widely in age-dependent neurodegenerative disease. Significance StatementAdvancing age is the single most important risk factor for neurodegenerative disease. Understanding how age intersects with genetic risk is therefore a critical challenge for neurodegenerative disease research. SCA6, a canonical late-onset degenerative cerebellar ataxia, results from a polyQ expansion in the voltage gated calcium channel, Cav2.1, encoded by CACNA1A. We define a mechanism of disease in SCA6 that is related to ER stress and unrelated to impaired calcium flux function of Cav2.1. Age-related decompensation of a HSP90-dependent unfolded protein response leads to disease onset. Mutant Cav2.1 misfolding as the basis for disease in SCA6 provides insight into a novel role for channelopathies to behave as proteinopathies and helps understand resilience to proteotoxicity more widely in adult-onset neurodegenerative disease.

neuroscience↗

bioRxiv2021

Longitudinal single-cell transcriptional dynamics throughout neurodegeneration in SCA1

Neurodegeneration is a protracted process involving progressive changes in myriad cell types that ultimately result in neuronal death. Changes in vulnerable neuronal populations are highly influenced by concomitant changes in surrounding cells, complicating experimental approaches to interrogate the simultaneous events that underlie neurodegeneration. To dissect how individual cell types within a heterogeneous tissue contribute to the pathogenesis and progression of a neurodegenerative disorder, we performed longitudinal single-nucleus RNA sequencing of the mouse and human spinocerebellar ataxia type 1 (SCA1) cerebellum, establishing continuous dynamic trajectories of each population. Furthermore, we defined the precise transcriptional changes that precede loss of Purkinje cells and identified early oligodendroglial impairments that can profoundly impact cerebellar function. Finally, we applied a deep learning method to accurately predict disease state and identify drivers of disease. Together, this work uncovers new roles for diverse cerebellar cell types in SCA1 and provides a generalizable analysis framework for studying neurodegeneration.

neuroscience↗

bioRxiv2020

THAP1 Modulates Oligodendrocyte Maturationby Regulating ECM Degradation in Lysosomes

Mechanisms controlling myelination during CNS maturation play a pivotal role in the development and refinement of CNS circuits. The transcription factor THAP1 is essential for timing the inception of myelination during CNS maturation through a cell-autonomous role in the oligodendrocyte lineage. Here, we demonstrate that THAP1 modulates ECM composition by regulating glycosaminoglycan (GAG) catabolism within oligodendrocyte progenitor cells (OPCs). Thap1-/- OPCs accumulate and secrete excess GAGs, inhibiting their maturation through an auto-inhibitory mechanism. THAP1 controls GAG metabolism by binding to and regulating the GusB gene encoding {beta}-glucuronidase, a GAG-catabolic lysosomal enzyme. Applying GAG-degrading enzymes or overexpressing {beta}-glucuronidase rescues Thap1-/- OL maturation deficits in vitro and in vivo. Our studies establish lysosomal GAG catabolism within OPCs as a critical mechanism regulating oligodendrocyte development.

neuroscience↗

bioRxiv2020

A chlorzoxazone-baclofen combination improves cerebellar impairment in spinocerebellar ataxia type 1

BackgroundA combination of central muscle relaxants, chlorzoxazone and baclofen (chlorzoxazone-baclofen), has been proposed for treatment of cerebellar symptoms in human spinocerebellar ataxia (SCA). However, central muscle relaxants can worsen balance. The optimal dose for target engagement without toxicity remains unknown. ObjectivesUsing the genetically precise Atxn1154Q/2Q model of SCA1, we determine the role of cerebellar dysfunction in motor impairment. We also aim to identify appropriate concentrations of chlorzoxazone-baclofen needed for target engagement without toxicity to plan for human clinical trials. MethodsWe use patch clamp electrophysiology in acute cerebellar slices and immunostaining to identify the specific ion channels targeted by chlorzoxazone-baclofen. Behavioral assays for coordination and grip strength are used to determine specificity of chlorzoxazone-baclofen for improving cerebellar dysfunction without off-target effects in Atxn1154Q/2Q mice. ResultsWe identify irregular Purkinje neuron firing in association with reduced expression of the ion channels Kcnma1 and Cacna1g in Atxn1154Q/2Q mice. Using in vitro electrophysiology in brain slices, we identify concentrations of chlorzoxazone-baclofen that improve Purkinje neuron spike regularity without reducing firing frequency. At a disease stage in Atxn1154Q/2Q mice when motor impairment is due to cerebellar dysfunction, orally administered chlorzoxazone-baclofen improves motor performance without affecting muscle strength. ConclusionWe identify a tight relationship between baclofen-chlorzoxazone concentrations needed to engage target, and levels above which cerebellar function will be compromised. We propose to use this information for a novel clinical trial design, using sequential dose escalation within each subject, to identify dose levels that are likely to improve ataxia symptoms while minimizing toxicity.

neuroscience↗

bioRxiv2020

Altered Capicua expression drives regional Purkinje neuron vulnerability through ion channel gene dysregulation in Spinocerebellar ataxia type 1

Selective neuronal vulnerability in neurodegenerative disease is poorly understood. Using the ATXN1[82Q] model of spinocerebellar ataxia type 1 (SCA1), we explored the hypothesis that regional differences in Purkinje neuron degeneration could provide novel insights into selective vulnerability. ATXN1[82Q] Purkinje neurons from the anterior cerebellum were found to degenerate earlier than those from the nodular zone, and this early degeneration was associated with selective dysregulation of ion channel transcripts and altered Purkinje neuron spiking. Efforts to understand the basis for selective dysregulation of channel transcripts revealed modestly increased expression of the ATXN1 corepressor Capicua (Cic) in anterior cerebellar Purkinje neurons. Importantly, lentiviral overexpression of Cic in the nodular zone accelerated both aberrant Purkinje neuron spiking and neurodegeneration. These findings reinforce the central role for Cic in SCA1 cerebellar pathophysiology and suggest that only modest reductions in Cic are needed to have profound therapeutic impact in SCA1.

neuroscience↗