Dentate Gyrus Granule Cells Are a Locus of Pathology in scn8a Developmental Encephalopathy
Abstract number :
3.015
Submission category :
1. Basic Mechanisms / 1B. Epileptogenesis of genetic epilepsies
Year :
2024
Submission ID :
395
Source :
www.aesnet.org
Presentation date :
12/9/2024 12:00:00 AM
Published date :
Authors :
Presenting Author: Wenxi Yu, PhD – University of Michigan
Sophie Hill, PhD – Children's Hospital of Philadelphia
Limei Zhu, PhD – University of Michigan
Yiannos Demetriou, BS – University of Michigan
Faith Reger, MS – University of Michigan
Joanna Mattis, MD,PhD – University of Michigan
Miriam Meisler, PhD – University of Michigan
Rationale: DEEs (Developmental and Epileptic Encephalopathies) are rare genetic disorders characterized by refractory seizures, developmental delay, and impaired movement. De novo mutations of SCN8A encoding the voltage-gated sodium channel Nav1.6 have been identified in >800 cases of DEE. Most mutant alleles exhibit gain-of-function changes such as premature channel opening and impaired channel inactivation. Elevated activity of neurons in the corticohippocampal circuit has been reported in mouse models of DEE. However, the impact of chronic seizure on gene expression in hippocampus is not well characterized.
Methods: We used single-nucleus RNA-sequencing (snRNA-seq) to examine the effect of chronic seizures on gene expression in the hippocampus expressing the patient mutation SCN8A-N1768D. Hippocampus was obtained from Scn8aN1768D/+ mice at 10 weeks after seizure onset, and from wildtype controls. Hippocampal RNA was prepared and analyzed by 10X Genomics 3’ snRNA-seq. Dentate gyrus granule cells exhibited the most differently expressed genes (DEGs). We also assessed the impact of the Scn8aN1768D mutation on the intrinsic excitability of granule cells. We evaluated the therapeutic effect of targeted downregulation of Scn8aN1768D in hippocampus by an AAV-shRNA construct.
Results: One hundred and eighty four DEGs were identified in dentate gyrus granule cells, many more than in other cell types. Electrophysiological recording demonstrated ~40% higher maximum steady-state firing frequency in Scn8aN1768D/+ neurons than wildtype controls. AP peaks were also higher in mutant granule cells. These data indicated neuronal hyperexcitability in mutant granule neurons. Targeted reduction of Scn8a expression in the dentate gyrus by viral delivery of an shRNA resulted in doubling of median survival time from 4 months to 8 months. Hippocampal CA1and CA3 pyramidal neurons also exhibited elevated activity. But delivery of shRNA to the CA1 and CA3 regions did not result in lengthened survival.
Conclusions: Gene expression in dentate gyrus granule cells is altered by chronic seizures, with many more DEGs than other hippocampal cells. The firing frequency of dentate gyrus granule cells is elevated in Scn8aN1768D/+ mice. Targeted reduction of Scn8a expression in the dentate gyrus prolonged survival of mutant mice, while targeting of CA1 and CA3 regions did not. Granule cells of the dentate gyrus appear to represent a locus of pathology in SCN8A-DEE.
Funding: Supported by NINDS grants R01-NS34509 to MHM and K08-NS121464 to JM.
Basic Mechanisms