Application 6 of this SUDEP Research Alliance Centers Without Walls (CWOW) grant proposal, "iPSC and Mouse Neurocardiac Models," explores cardiac arrhythmia and autonomic dysfunction as potential causes of SUDEP. Although SUDEP is the most devastating consequence of epilepsy and the leading cause of epilepsy mortality, astonishingly little is understood about its causes and no biomarkers exist to identify at risk epilepsy patients. To advance our understanding of these critical issues, we will focus on Dravet Syndrome (DS), a severe childhood epileptic encephalopathy associated with a high SUDEP incidence. DS is most frequently caused by mutations in the voltage-gated Na+ channel (VGSC) gene SCN1A, encoding NaV1.1. As NaV1.1 is expressed in brain, heart, and peripheral nerves, a compelling idea is that altered Na+ currents (INa) in DS cardiac myocytes (CMs) or autonomic neurons, in addition to central neurons, lead to arrhythmias and SUDEP. We used the induced pluripotent stem cell (iPSC) method to derive central and peripheral neurons and CMs from fibroblasts of DS subjects. Preliminary data from DS patient CMs suggest that a subset of DS subjects shows abnormal CM INa and excitability. In studies of a DS human mutant SCN1A knock-in mouse model, we observed spontaneous seizures and SUDEP, increased ventricular CM INa density, and ventricular arrhythmias at the time of SUDEP. Similarly, we found increased ventricular CM INa density, spontaneous seizures and SUDEP in a Scn1b null DS mouse model. Our work, studies of Scn1a heterozygous null DS mice, and clinical ECG studies in DS also show altered cardiac autonomic function. Thus, we hypothesize that SUDEP in DS is caused by VGSC mutations that produce cardiac electrical and/or autonomic dysfunction, in addition to brain dysfunction. Furthermore, that combined insights from studies of DS patient-derived cells, mouse models and patient peri-ictal ECG data will yield biomarkers of SUDEP risk in DS.
Four specific aims will test these hypotheses: 1) To understand the effects of DS-linked SCN1A mutations on cardiac excitability using DS patient iPSC-derived CMs and DS mice;2) To determine how DS-linked SCN1A mutations influence the excitability of autonomic neurons, cardiac autonomic innervation, and autonomic control of cardiac function using DS patient iPSC-derived autonomic neurons and DS mice;3) To investigate changes in autonomic excitability in a second mouse model of DS, Scn1b null mice, and in SCN1B-DS patient iPSC CMs and neurons;and 4) To determine whether cardiac electrical and/or autonomic function is altered in DS patients at baseline or peri-ictally. Our wor will synergize with the entire CWOW proposal to not only uncover SUDEP mechanisms in DS, but also to provide advances in understanding SUDEP causes and biomarkers that will be applicable to other refractory epilepsies due to ion channelopathies and perhaps other etiologies. This work will also show proof-of-principle for the use of multiple platforms (cellular and clinical data from the same patients, and multiple mouse models) to individualize SUDEP risk and develop patient-specific preventative treatments.
Application 6 of this SUDEP Research Alliance Centers Without Walls (CWOW) grant proposal, entitled iPSC and Mouse Neurocardiac Models, aims to determine whether heart rhythm disturbances are a cause of Sudden Unexplained Death in Epilepsy (SUDEP) in Dravet Syndrome, a severe childhood epilepsy with a high risk of SUDEP. The proposed studies involve a unique combination of experiments using patient-derived heart cells and neurons, mouse models, and patient electrocardiogram data obtained before, during and after seizures. Progress in these Aims will complement and synergize with the other projects in this CWOW proposal to not only uncover SUDEP mechanisms in Dravet Syndrome that will likely be applicable to other severe epilepsies, but also to provide advances in identifying biomarkers to define at-risk patients.