STRADA Deficiency Impairs Cortical Interneuron Development in Humans and Mice

Polyhydramnios, Megalencephaly, and Symptomatic Epilepsy syndrome (PMSE/STRADA-related disorder) is a rare neurodevelopmental disorder characterized by megalencephaly (ME), early-onset drug-resistant epilepsy, neurocognitive impairment, and high early mortality, often due to status epilepticus. PMSE is caused by a multi-exon deletion in STRADA, encoding STRADA, which regulates the mechanistic target of rapamycin (mTOR) pathway. GABAergic inhibitory interneurons (INs) critically modulate the excitatory:inhibitory balance in cortical and hippocampal networks, and IN deficits contribute to epileptogenesis in several epileptic encephalopathies. However, no studies have investigated INs in PMSE. We used a multimodal approach to study INs in a Strada-/- mouse model engineered with the same causative 5-exon deletion identified in human PMSE. We demonstrate that Strada/STRADA loss causes a reduction of INs in the somatosensory cortex and a corresponding increase in the striatum, representative of remnant ganglionic eminence progenitor origin, in Strada-/- mice and a single PMSE brain tissue specimen. RNA sequencing comparing wildtype to Strada-/- cortex and striatum corroborated these findings, revealing increased IN-related gene expression (e.g., Dlx2) in the striatum and decreased IN-related gene expression (e.g., Pvalb) in the developing cortex. Cytoskeletal (e.g., Tpp3, Kank4, Map1a) and mTOR-associated genes (e.g., Rictor, Cryab) are differentially expressed in the developing cortex, mature striatum, and mature cortex of Strada-/- mice. Functional validation confirmed enlarged INs in mouse and human Strada/STRADA-deficient brain and enhanced S6 phosphorylation in Strada-/- striatum. Together, these findings suggest STRADA/Strada loss contributes to failed IN migration -- the first such report in a developmental, mTOR-associated megalencephaly syndrome -- highlighting INs as a therapeutic target for seizure prevention in PMSE. Key PointsO_LI- Reduced numbers of cortical inhibitory interneurons were observed in the cerebral cortex of Strada-/- mice, with striatal interneuron aggregation C_LIO_LI- Reduced numbers of cortical inhibitory interneurons, with an aggregation in striatum, were observed in human PMSE brain, supporting the observations in Strada-/- mouse C_LIO_LI- Transcriptomic analysis in Strada-/- mice reveals evidence of early developmental interneuron and cytoskeletal dysfunction C_LIO_LI- We introduce a loss of cortical interneurons as a salient feature of PMSE developmental pathogenesis, potentially contributing to a loss of inhibitory modulation C_LIO_LI- This is the first study proposing interneuron migration impairment in the developmental pathogenesis of an mTOR-associated megalencephaly syndrome C_LI