Pathogenic Mechanism of Epilepsy in Sebaceous Nevus Syndrome by Dysregulation of RAS/MAPK Pathway

Abstract

RAS/MAPK pathway involves not only biological processes such as differentiation, proliferation, and migration but also many diseases such as cancer. RASopathies, which are a group of developmental disorders caused by mutation of the RAS/MAPK pathway component, suggest the crucial role of this pathway in normal development. Sebaceous nevus syndrome (SNS), one of the RASopathies, is caused by somatic gain-of-function mutation of HRAS or KRAS. The symptoms of SNS include central-nervous system-related defects such as cerebral defects, intellectual disability, and epilepsy. To examine the pathogenesis of neurological symptoms in SNS, we generated the disease mouse model by overexpression of KRAS p.G12V in developing cortex using in utero electroporation. This model successfully recapitulated histological manifestations observed in the patient, such as heterotopic neurons, gliosis, and hypomyelination. It also showed abnormal neuronal differentiation and migration and neuronal dysmorphogenesis. To investigate neuronal excitability at a cellular level, we analyzed electrophysiological properties using patch-clamp. Both neurons with and without KRAS p.G12V overexpression showed hyperexcitability. Interneurons also showed abnormal action potential properties. To elucidate the molecular mechanism underlying observed pathological phenotypes in SNS, we generated drug-inducible KRAS pathogenic mutation expressing human NPC line using destabilization domain. In this cell line, several pathological phenotypes were rescued by ceasing the expression of the pathogenic mutation at the neuron stage. Stage-specific modulation of the KRAS variant will allow us to characterize molecular and cellular phenotypes that can be reversed. Taken together, these results indicate how KRAS p.G12V interrupts normal brain development and leads to neuropathology including epilepsy in SNS and suggest the possibility of relieving neurological symptoms in SNS patients by recently developed KRAS inhibitors.2