Partial Rescue of Seizures, Weight Gain, and SUDEP in the scn1b-/- developmental and Epileptic Encephalopathy Mouse Model Using Aav-mediated Delivery of Sodium Channel β1 Subunits
Abstract number :
3.048
Submission category :
1. Basic Mechanisms / 1D. Mechanisms of Therapeutic Interventions
Year :
2022
Submission ID :
2204515
Source :
www.aesnet.org
Presentation date :
12/5/2022 12:00:00 PM
Published date :
Nov 22, 2022, 05:25 AM
Authors :
Heather O'Malley, PhD – University of Michigan; Chunling Chen, PhD – Pharmacology – University of Michigan; Yosuke Niibori, PhD – Pharmaceutical Sciences, Leslie Dan Faculty of Pharmacy – University of Toronto; Yan Chen, BS – Pharmacology – University of Michigan; David Hampson, PhD – Professor, Pharmaceutical Sciences, Leslie Dan Faculty of Pharmacy, University of Toronto; Lori Isom, PhD – Maurice Seevers H. Professor and Chair, Pharmacology, University of Michigan
Rationale: Developmental and epileptic encephalopathies (DEEs) are linked to variants in genes encoding voltage-gated sodium channels (VGSCs). Patients with biallelic loss-of-function variants in SCN1B, encoding the VGSC β1 and β1B subunits, present with DEE symptoms similar to, and sometimes more severe than, Dravet syndrome. SCN1B-linked DEE patients have severe pharmacoresistant seizures and a high rate of SUDEP, cognitive impairment and developmental delay, ataxia, gastrointestinal symptoms, and failure to thrive. VGSC β1 and β1B subunits are multifunctional. They modify channel gating and kinetics, participate in cell-cell and cell-matrix adhesive interactions that affect neuronal fasciculation and neuronal pathfinding, and modify gene expression following regulated intramembrane proteolysis. Scn1b-/- mice model SCN1B-linked DEE, with spontaneous seizures of multiple etiologies beginning at ~postnatal day (P)10, ataxia, failure to thrive, and SUDEP in 100% of mice by ~P21. We hypothesized that restoring β1 subunit expression using an AAV-mediated delivery mechanism would improve or rescue the Scn1b-/- phenotype.
Methods: Litters from Scn1b+/- breeding pairs (Scn1b +/+, +/-, and -/- pups) received bilateral intracerebroventricular injections of AAV9-pGad1-Navβ1-myc (AAV-β1) or AAV9-pCMV-empty vector (AAV-EV) at P2. The AAV-β1 vector contained β1 cDNA with an in-frame myc epitope tag. Pups were weighed weekly and monitored by infrared video for behavioral seizures and SUDEP. Scn1b+/- animals were euthanized at specified time points for collection of brain tissue. Brains were processed for immunofluorescence to monitor the expression patterns of myc-tagged β1 protein.
Results: Immunofluorescence data showed expression of myc-tagged β1 protein in subsets of excitatory and inhibitory neurons throughout the cortex and hippocampus, with some expression in midbrain and cerebellum. With the exception of one Scn1b-/- mouse that died prior to P21, AAV-β1-injected Scn1b-/- mice survived for 55-91 days, up to 3 times the lifespan of untreated Scn1b-/- mice. All AAV-EV-injected Scn1b-/- mice died prior to P21. AAV-EV and AAV-β1 injected Scn1b+/+ and Scn1b+/- mice gained weight throughout development. AAV-EV-injected Scn1b-/- mice reached no more than 5 g in size. In contrast, AAV-β1-injected Scn1b-/- mice reached weights up to 10.4 g (male) and 9.4 g (female). Infrared video monitoring of AAV-β1-injected mice showed that approximately half of the Scn1b-/- cohort had spontaneous behavioral seizures that were associated with SUDEP. The cohort of AAV-β1-injected Scn1b-/- mice that did not seize ultimately died of unknown causes.
Conclusions: Our data show that the Scn1b-/- DEE phenotype, including behavioral seizures, SUDEP onset, and reduced body weight, can be partially rescued by re-introduction of epitope-tagged β1 protein using a Gad1-targeted AAV construct. Thus, gene therapy may be a future therapeutic option for SCN1B-linked DEE patients.
Funding: R37 NS076752 (LLI) and the Canadian Rare Diseases: Models and Mechanism Network (DRH and LLI)
Basic Mechanisms