Modeling Alternating Hemiplegia of Childhood with iPSC-Derived Neurons
Snow, John Patrick
Alternating hemiplegia of childhood (AHC) is a rare and devastating neurodevelopmental disorder caused by de novo heterozygous missense mutations in ATP1A3, a crucial gene encoding the 3 subunit of the Na,K-ATPase (NKA) ion transporter. Patients with AHC present early in life with symptoms including ocular abnormalities, seizures, dystonia, and alternating hemiplegic events that are often initiated by external triggers. Neurologic deficits including developmental delay and intellectual disabilities persist over time. AHC is part of an expanding spectrum of conditions associated with ATP1A3 mutations that share symptom profiles but maintain strong genotype-to-phenotype relationships. Unfortunately, only symptomatic, anecdotal, and ineffective treatment options exist for patients diagnosed with AHC. Common AHC-causing mutations in the NKA-3 subunit include D801N, E815K, and G947R. While it is known that these variants cause impaired ion transporting ability without impacting protein trafficking to the plasma membrane, data from human-based neuronal model systems remain sparse. To better understand the impacts of AHC-causing mutations on human neurons, we generated a patient-specific induced pluripotent stem cell (iPSC)-derived neuronal model of disease. This system focused on the phenotypically severe heterozygous E815K mutation in ATP1A3, and leveraged CRISPR/Cas9 genome editing methods to create isogenic wildtype controls. iPSC-derived cortical neurons generated from patient and control iPSCs were then used to study AHC pathophysiology, phenotypes, and potential treatment approaches in vitro. Using this model system, we discovered elevated levels of ATP1A3 mRNA transcripts in AHC lines compared to both isogenic and unrelated controls, without significant changes to protein expression. AHC patient-derived cortical neurons displayed hyperactivity following exposure to heat stress on microelectrode array analysis, mimicking triggered symptoms seen in patients and animal models of disease. Further investigations described the basis of endocannabinoid signaling in AHC iPSC-derived neurons, possible metabolic abnormalities in this model system, and the adoption of new differentiation techniques to generate more rapid and reproducible data. These findings provide novel information regarding an in vitro human model system and will serve as the foundation for future mechanistic study and therapeutic testing in AHC.