Rescuable folding defective NaV1.1 (SCN1A) mutants in epilepsy: Properties, occurrence, and novel rescuing strategy with peptides targeted to the endoplasmic reticulum

Here, we have evaluated functional properties and cell surface expression of six NaV1.1 epileptogenic missense mutations in different rescuing conditions, including a novel one that we have developed expressing a selective sodium channel toxin (CsEI) targeted to the endoplasmic reticulum (ER). All the mutants showed loss of function and reduced cell surface expression, consistently with possibility of rescue. Four of them were rescuable by incubation at low temperature and interactions with different co-expressed proteins or a pharmacological chaperone (phenytoin). Notably, CsEI was able to rescue four mutants. Thus, NaV1.1 folding defective mutants can be relatively common and mutations inducing rescuable folding defects are spread in all NaV1.1 domains. Importantly, epileptogenic mutants showed overall loss of function even upon rescue, differently than FHM-III ones. The effectiveness of CsEI demonstrates that interactions in the ER are sufficient for inducing rescue, and provides a proof of concept for developing possible therapeutic approaches that may overcome some limitations of pharmacological chaperones.