Phenotyping iPSC-derived neurons from Angelman patients and partial rescue via JNK pathway inactivation

Angelman Syndrome (AS, MIM #105,830) is a rare neurodevelopmental disorder caused by imprinting defects, and it is marked by motor impairment, intellectual disability, speech limitations, and seizures. The condition arises due to the loss of function in neurons of the maternally-inherited UBE3A gene, mapping in the imprinted chromosomal region 15q11.2-q13, through a variety of genetic and epigenetic mechanisms. UBE3A encodes a ubiquitin E3 ligase, which is essential for synaptic plasticity. Most studies of AS have been performed on animal models, while induced pluripotent stem cells (IPSCs), mainly generated from patients with deletion, remain limited in number. Here we report on the generation and characterization of human cortical neurons derived from IPSCs obtained from children representative of the main AS genotypes: 3 with 15q11–13 deletion, 3 with UBE3A mutations, 3 with uniparental disomy, and 2 with imprinting defects. During early neuronal differentiation, morphological analyses highlighted a reduced dendritic branching and an increased number of thin filopodia, while migration assays revealed reduced neurite mobility in AS human neurons with the most severe genetic defect, namely the 15q11-13 deletion. At a later differentiation time point, electrophysiological analyses revealed impaired neuronal activity in AS patient-derived neurons. To investigate pathways potentially involved in synaptic dysfunction, we examined the JNK (c-Jun N-terminal kinase) signalling pathway, which plays key roles in neuroinflammation and synaptic development. We found increased JNK activation and, importantly, treatment with a JNK-inhibitor, D-JNKI1, partially rescued the neuronal morphological defects, significantly reducing the number of immature protrusions, as well as defects in electrophysiological properties. Our patient-specific models contribute elucidate how loss of UBE3A leads to aberrant neuronal maturation and function in the precocious stages of neuronal development and how treatment with D-JNKI1 may pave the way for new therapeutic possibilities.