To understand the effects of DS-linked SCN1A mutations on cardiac excitability using DS patient iPSC-derived CMs and DS mice. 1A. Our recent work describing DS patient-derived iPSC neurons (10) was the first iPSC model of a predominant epilepsy syndrome, and we have now generated the first iPSC model of CMs from epilepsy patients. We will determine if DS patient iPSC CMs have altered excitability using whole-cell voltage- and current-clamp techniques to compare INa density and
AP properties in iPSC CMs from DS subjects and controls. We will also explore whether K+ (IK) and Ca2+ (ICa)
currents are altered. 1B. Ventricular CMs from DS mutant SCN1A knock-in mice have increased transient
and persistent INa density, increased action potential (AP) duration, and cardiac arrhythmias. Importantly, the mice experience SUDEP as they are epileptic and 21% die suddenly by postnatal day (P) 150 (5). We will use optical mapping techniques to investigate arrhythmogenic mechanisms in isolated DS mouse hearts.
To determine how DS-linked SCN1A mutations influence the excitability of autonomic neurons, cardiac autonomic innervation, and autonomic control of cardiac function. Our preliminary data showing time and frequency domain analysis of heart rate variability (HRV) suggest significant changes in autonomic tone during the time leading up to SUDEP in DS mice compared to WT and compared to DS mice that do not die. Here we will: 2A. Investigate changes in heart rate variability and effects of
pharmacologic autonomic blockade in DS mice compared to controls. 2B. Investigate if INa density and neuronal excitability are altered in DS patient vs. control iPSC-derived autonomic neurons or in acutely isolated autonomic neurons from DS mice vs. controls. 2C. Compare the cardiac intrinsic neural plexus and vagus nerve in
WT and DS mice, including the molecular compositions of vagus nerve nodes of Ranvier.
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. We were the first to show that inheriting two lossof-function SCN1B alleles causes DS in humans (9). Scn1b null mice are thus a DS model (8, 11). They develop seizures at ~P10, ataxia and cardiac arrhythmia, and die by ~P21. Similar to DS mutant SCN1A knock-in mice, Scn1b null CMs have ~2-fold increased transient and persistent INa density and AP
Scn1b null central and dorsal root ganglion neurons are hyperexcitable (11, 12). We will investigate changes in excitability of SCN1B-DS patient-derived CMs and autonomic neurons, and of acutely isolated Scn1b null autonomic neurons, changes in the structure of the Scn1b null mouse cardiac intrinsic
neural plexus, and arrhythmogenesis in intact Scn1b null hearts using optical mapping. With the prior aims, this work will define whether two distinct genetic forms of DS show similar abnormalities that predispose to SUDEP.
To determine whether cardiac electrical and/or autonomic function is altered in DS patients atbaseline or peri-ictally. DS subjects have decreased basal heart rate variability and increased QT and P wave dispersion (13, 14), implicating cardiac autonomic dysfunction as a SUDEP mechanism.
Our preliminary data from DS patient iPSC CMs also suggest intrinsic cardiac abnormalities occur in DS.
However, how seizures acutely affect cardiac function in DS patients is unknown. To test the hypothesis that peri-ictal cardiac
autonomic and electrical disturbances occur in subsets of DS subjects with SCN1A mutations, we will
characterize ECG properties and measures of cardiac autonomic function during inpatient
video/EEG recordings of seizures. Importantly, the iPSC studies in Aims 1 and 2 will include samples from subjects, allowing us to correlate human cellular (CMs and autonomic neurons) and in vivo phenotypes. Together, with the prior aims, progress in this work should provide insight into
SUDEP mechanisms in DS, may yield biomarkers to identify at-risk patients, and offer a platform for
developing patient specific therapies to prevent SUDEP.