Abstracts

Rationale: Dravet syndrome is characterized by a seizure onset commonly provoked by fever, either due to infection or vaccination, and subsequently evolves into pleomorphic seizures that are refractory to existing anticonvulsants. About 30 drugs are approved for treatment of epilepsy, but 1/3 of patients do not respond to these medications, which only control symptoms without addressing the underlying mechanisms. It is known that de novo SCN1A mutation is a hallmark of Dravet syndrome, however its detailed pathophysiology remains unclear. We have pioneered a mechanistic study trying to unravel the immunological contribution to Dravet pathogenesis using an Scn1a+/- heterozygous null mouse model developed in Dr. Jennifer Kearney’s lab that closely recapitulates features of Dravet syndrome. This model has been validated as a platform for drug screening using human response data from Dr. Linda Laux’s group. We have preliminarily demonstrated marked infiltration of a heterogeneous population of blood-borne immune cells in the brain parenchyma of the Scn1a+/- mice 1 week before the onset of clinical seizures. The goal of this project is to understand potential immunological mechanisms underlying the pathogenesis of Dravet syndrome and more importantly to design novel therapies using immune-modulating approaches independent of broad-acting steroids and nonsteroidal immunosuppressive agents which are associated with severe side effects. Methods: SCN1Atm1Kea global knockout is maintained on pure 129 strain background (129.SCN1A+/-) and are crossed to C57Bl/6 to generate F1 mice. Both female and male F1 heterozygous knockout (KO) mice and the wildtype (WT) littermate controls were intravenously injected at post-natal day 18 (P18) with extra carboxylated nanoparticles made with FDA-approved biodegradable polymers poly(lactide-co-glycolide) (PLG) for 4 consecutive days. Hyperthermia-induced seizure was measured by video monitoring at P22 and spontaneous seizure was continuously measured for another week. Results: We have previously reported detection of brain-infiltrating blood-borne immune cells in the KO mice compared with gender-matched littermate controls prior to the seizure onset. A short course of PLG nanoparticles at the onset of the disease significantly ameliorates the severity of the hyperthermia-induced seizure one day after the treatment. Importantly, the early intervention of an active immune response has the potential of delay the spontaneous seizure during the follow-up video monitoring. Use of biodegradable PLG nanoparticle achieves the goal of immunemodulation in the absence of systemic immunosuppression and common side effectos of steroid, while providing a remarking seizure control outcome. Conclusions: Our preliminary data demonstrated for the first time that Scn1a+/- mice treated with immune-modulating biodegradable PLG nanoparticles at onset improved outcomes at the acute phase and delayed spontaneous seizure. Modulation of seizure is most likely exerted through dampening overt immune responses in the brain, while promoting recovery of neuronal damage cause by inflammatory mediators. These findings suggest that the immune system may play a critical role in pathogenesis of Dravet even before clinical onset and that immune-modifying approaches can effectively reduce seizure burden. Funding: This work is supported by grant NIH/NINDS R01NS073768 and R21NS094999 to S.K. and S.D.M., and a post-doctoral fellowship 262243 from the Epilepsy Foundation of America to D.X.