Authors :
Presenting Author: Chanapa Mann, BS – University of Colorado, Anschutz Medical Campus
Rebecca Han, BS – University of Colorado, Anschutz Medical Campus
Ruth Fulton, MS – University of Colorado Anschutz Medical Campus
Manisha Patel, PhD – University of Colorado Anschutz Medical Campus
Rationale:
Dravet syndrome (DS) is a severe developmental and epileptic encephalopathy predominately caused by de novo mutations in the SCN1A gene. Conventional DS models utilizing global Scn1a haploinsufficient mice attribute interneuron dysfunction as the primary driver in the disease. However, the potential roles of principal neurons in DS pathology are poorly understood. To investigate the contributions of principal neurons in DS, our lab has developed a novel principal neuron-specific Scn1a (nScn1a) mutant mouse model with intact interneurons. Our goal is to characterize our nScn1a model which will further our understanding of principal neuron-specific contributions underlying the DS pathology.
Methods:
The nScn1a model was created by introducing a knock-in A1783V missense mutation restricted to the central nervous system in forebrain principal neurons to generate nScn1a heterozygous (HET), homozygous (KI), and wild-type (WT) mice. 1–4-month-old nScn1a mice were evaluated for spontaneous seizures using simultaneous video and electroencephalographic (EEG) recordings for a 1-week period, hyperthermic seizures, behavioral tests (open field and rotarod), and observed for premature mortality. To examine if interneurons were intact in the nScn1a mice, immunohistochemical (IHC) analysis of forebrain sections stained for parvalbumin (PV) and somatostatin (SOM) was performed.
Results:
Video/EEG recordings revealed that nScn1a KI mice develop spontaneous tonic-clonic seizures (n=4), while nScn1a HET mice exhibited hyperexcitability and abnormal behavior (n=4). Epileptiform activity did not occur in the WT mice (n=3). Hyperthermia-induced seizures occurred in nScn1a KI mice at 39.2°C (n=3), but not in the nScn1a HET or WT mice at 40.4°C (n=3). Spontaneous locomotion was not different in the HET (p=0.9257) or KI (p=0.1437) mice relative to the WT mice (n=7). Significant motor impairments were observed in the nScn1a KI mice (p< 0.0001), while there were no differences in the HET (p=0.1626) mice relative to WT mice (n=7). Premature death of nScn1a KI mice was observed at 92.6 days, but did not occur in the HET and WT mice. IHC analysis of forebrain GABAergic interneuron populations yielded no significant differences in the nScn1a KI mice in the cortex (PV p=0.2248, SOM p=0.1588) and hippocampus (PV p=0.2039, SOM p=0.2101) compared to the WT mice (n=5).
Conclusions:
Forebrain principal neuron-specific nScn1a KI mice recapitulate key features of the DS epileptic and behavioral phenotypes independent of interneuron loss. While this study utilizes nScn1a mice compared to DS models using non-cell-specific Scn1a haploinsufficient mice, the prolonged survival of the nScn1a mice highlights the importance of considering cell-type-specific contributions in the disease. Together, the prolonged survival of nScn1a mice could enable long-term investigations into DS disease mechanisms, including assessments of factors modulating disease vulnerabilities and severity.
Funding:
NIH Grant R37NS03597 (M.P.)