Department of Pharmacology, Northwestern University Feinberg School of Medicine, Chicago, IL.
Center for Integrative Neuroscience, Kavli Institute for Fundamental Neuroscience, Department of Neurology, University of California, San Francisco, San Francisco, CA.
J Gen Physiol. 2020 Mar 2;152(3). doi: 10.1085/jgp.201912442.
Epileptic encephalopathies are severe forms of infantile-onset epilepsy often complicated by severe neurodevelopmental impairments. Some forms of early-onset epileptic encephalopathy (EOEE) have been associated with variants in SCN2A, which encodes the brain voltage-gated sodium channel NaV1.2. Many voltage-gated sodium channel genes, including SCN2A, undergo developmentally regulated mRNA splicing. The early onset of these disorders suggests that developmentally regulated alternative splicing of NaV1.2 may be an important consideration when elucidating the pathophysiological consequences of epilepsy-associated variants. We hypothesized that EOEE-associated NaV1.2 variants would exhibit greater dysfunction in a splice isoform that is prominently expressed during early development. We engineered five EOEE-associated NaV1.2 variants (T236S, E999K, S1336Y, T1623N, and R1882Q) into the adult and neonatal splice isoforms of NaV1.2 and performed whole-cell voltage clamp to elucidate their functional properties. All variants exhibited functional defects that could enhance neuronal excitability. Three of the five variants (T236S, E999K, and S1336Y) exhibited greater dysfunction in the neonatal isoform compared with those observed in the adult isoform. Computational modeling of a developing cortical pyramidal neuron indicated that T236S, E999K, S1336Y, and R1882Q showed hyperexcitability preferentially in immature neurons. These results suggest that both splice isoform and neuronal developmental stage influence how EOEE-associated NaV1.2 variants affect neuronal excitability.
癫痫性脑病是一种严重的婴儿期起病的癫痫，常伴有严重的神经发育障碍。一些早发性癫痫性脑病（EOEE）与 SCN2A 的变异有关，该基因编码大脑电压门控钠离子通道 NaV1.2。许多电压门控钠离子通道基因，包括 SCN2A，都经历了发育调控的 mRNA 剪接。这些疾病的早期发作表明，在阐明与癫痫相关的变异的病理生理后果时，NaV1.2 的发育调控选择性剪接可能是一个重要的考虑因素。我们假设 EOEE 相关的 NaV1.2 变体在发育早期表达的剪接异构体中表现出更大的功能障碍。我们将五种 EOEE 相关的 NaV1.2 变体（T236S、E999K、S1336Y、T1623N 和 R1882Q）构建到 NaV1.2 的成人和新生儿剪接异构体中，并进行全细胞电压钳来阐明它们的功能特性。所有变体都表现出可能增强神经元兴奋性的功能缺陷。五种变体中的三种（T236S、E999K 和 S1336Y）在新生儿异构体中的功能障碍比在成人异构体中观察到的更为严重。发育中皮质锥体神经元的计算模型表明，T236S、E999K、S1336Y 和 R1882Q 在不成熟神经元中表现出更强的兴奋性。这些结果表明，剪接异构体和神经元发育阶段都影响 EOEE 相关 NaV1.2 变体如何影响神经元兴奋性。
