Human AHC Neuron Response to Flunarizine

Mutations in ATP1A3 encoding the catalytic subunit of neuronal Na,K-ATPase explain the majority of alternating hemiplegia of childhood (AHC) cases.1,2 Flunarizine, a lipophilic diphenylpiperazine derivative and ion channel blocker, has been widely used to treat AHC but the response is highly variable and the neurophysiological mechanism responsible for its efficacy is unknown.3,4 We propose to investigate the cellular effects of flunarizine on human neurons derived from AHC patient-specific induced pluripotent stem cells (iPSCs) and to compare effects on neurons from patients who responded or did not respond to the drug. Objective 1 - To determine effects of flunarizine on the electrophysiological properties of cultured human AHC neurons. Our laboratory has pioneered the investigation of the electrophysiological defects in human AHC neurons by exploiting a panel of patient-derived induced pluripotent stems cells (iPSCs). We propose to investigate the effects of flunarizine on AHC neurons to identify cellular mechanisms responsible for the drug’s efficacy. In previous studies, we have demonstrated that cortical neurons carrying the ATP1A3 mutation p.G947R exhibit a depolarized resting membrane potential, lower ‘pump current’ and impaired excitability. We now plan to investigate the electrophysiological properties of these neurons in the presence and absence of flunarizine. The objective of these experiments is to determine if flunarizine can reverse the abnormal membrane potential and restore normal cellular excitability consistent with the observed clinical efficacy of the drug in AHC patients. We will also interrogate plasma membrane calcium and sodium currents, known targets of flunarizine, in the absence and presence of drug. Objective 2 - To compare effects of flunarizine on cultured human neurons derived from AHC subjects who responded or did not respond to the drug. We propose to compare the effects of flunarizine on human iPSC-derived neurons from AHC subjects who had positive responses to the drug with those who did not respond. We have previously developed iPSC lines from a young female with AHC who carries the ATP1A3 mutation p.G947R and who was observed to benefit from flunarizine therapy. We plan to develop iPSC lines from a second young female AHC patient from France carrying the same mutation but who did not response to flunarizine. This French patient was recently described by Prof. Emmanuel Roze and colleagues from Salpêtrière Hospital in Paris.5 In addition, Dr. Roze will identify additional French AHC subjects with clear responses to flunarizine including responders and non-responders and provide our laboratory with cryopreserved blood cells that we will reprogram to iPSC lines. Up to 10 new iPSC lines will be created. All lines will be made available to other AHC researchers. We will next differentiate cortical excitatory neurons from pairs of iPSC lines representing flunarizine responders vs non-responders. We will then compare the electrophysiological properties of neurons from these two subjects and determine the effects of flunarizine on resting membrane potential, ‘pump’ current, neuronal excitability and plasma membrane calcium and sodium current. These comparisons will provide us insight into which cellular effects correlate best with clinical responsiveness to flunarzine and will provide us new functional markers of drug efficacy in AHC that can be exploited to test other approved drugs and new therapies.