Differential molecular and behavioural alterations in mouse models of GABRG2 haploinsufficiency versus dominant negative mutations associated with human epilepsy
Differential molecular and behavioural alterations in mouse models of GABRG2 haploinsufficiency versus dominant negative mutations associated with human epilepsy
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DOI：
10.1093/hmg/ddw168
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发表时间：
2016-08-01
影响因子：
3.5
通讯作者：
Kang, Jing-Qiong
中科院分区：
文献类型：
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作者：
Warner, Timothy A.;Shen, Wangzhen;Kang, Jing-Qiong
遗传性癫痫是一种常见的表型变异疾病，但变异的基础尚不清楚。比较同一癫痫基因突变的分子病理生理学可能为表型异质性提供机制见解。 GABRG2 是一种已确定的癫痫基因，其突变会产生不同严重程度的癫痫综合征。在某些情况下，疾病表型可能是由简单的亚基功能丧失（功能性单倍体不足）引起的，而其他情况可能是由功能丧失加上显性失活抑制和其他细胞毒性引起的。然而，详细的分子缺陷和相应的癫痫发作以及由单倍体不足和显性失活突变引起的相关合并症尚未进行比较。在这里，我们比较了与不同严重程度的癫痫相关的GABRG2功能丧失突变的两种小鼠模型：Gabrg2(+/Q390X)敲入(KI)和Gabrg2(+/-)敲除(KO)小鼠。杂合子 Gabrg2(+/Q390X) KI 小鼠由于突变的显性负效应而与严重癫痫性脑病相关，而杂合子 Gabrg2(+/-) KO 小鼠由于简单单倍体不足而与轻度失神性癫痫相关。在转录水平上没有变化，患有严重癫痫的KI小鼠的神经元中突变的γ2亚基积累，树突和突触中剩余的功能性野生型亚基减少，而患有轻度癫痫的KO小鼠没有突变亚基的细胞内积累，并且剩余的野生型亚基的生物合成不受影响。因此，与 KO 小鼠相比，具有显性失活突变的 KI 小鼠的野生型受体表达要少得多，癫痫发作和行为合并症更严重。这项工作提供了对癫痫综合征异质性的病理生理学和设计基于机制的疗法的见解。
Genetic epilepsy is a common disorder with phenotypic variation, but the basis for the variation is unknown. Comparing the molecular pathophysiology of mutations in the same epilepsy gene may provide mechanistic insights into the phenotypic heterogeneity. GABRG2 is an established epilepsy gene, and mutations in it produce epilepsy syndromes with varying severities. The disease phenotype in some cases may be caused by simple loss of subunit function (functional haploinsufficiency), while others may be caused by loss-of-function plus dominant negative suppression and other cellular toxicity. Detailed molecular defects and the corresponding seizures and related comorbidities resulting from haploinsufficiency and dominant negative mutations, however, have not been compared. Here we compared two mouse models of GABRG2 loss-of-function mutations associated with epilepsy with different severities, Gabrg2(+/Q390X) knockin (KI) and Gabrg2(+/-) knockout (KO) mice. Heterozygous Gabrg2(+/Q390X) KI mice are associated with a severe epileptic encephalopathy due to a dominant negative effect of the mutation, while heterozygous Gabrg2(+/-) KO mice are associated with mild absence epilepsy due to simple haploinsufficiency. Unchanged at the transcriptional level, KI mice with severe epilepsy had neuronal accumulation of mutant gamma 2 subunits, reduced remaining functional wild-type subunits in dendrites and synapses, while KO mice with mild epilepsy had no intracellular accumulation of the mutant subunits and unaffected biogenesis of the remaining wild-type subunits. Consequently, KI mice with dominant negative mutations had much less wild-type receptor expression, more severe seizures and behavioural comorbidities than KO mice. This work provides insights into the pathophysiology of epilepsy syndrome heterogeneity and designing mechanism-based therapies.