Pathophysiology of familial hemiplegic migraine: analysis of a newly generated transgenic SCN1A mouse model

家族性偏瘫型偏头痛是一种具有先兆的常染色体显性偏头痛亚型。本申请人通过定位克隆的方法，已经鉴定了SCN 1A作为第三种FHM基因（FHM 3; Dichgans*，Freilinger* 等Lancet 2005）。SCN 1A编码神经元电压门控钠通道（Nav1.1），其负责动作电位的产生和传播。先前在具有FHM相关突变的过表达Nav1.1通道的细胞中的研究指向FHM患者中突变通道的功能丧失（Kahlig，...，Freilinger等人Proc Natl Acad Sci U S A 2008）。为了阐明NaV1.1在偏头痛和偏头痛先兆的病理生理学中的重要性，申请人通过同源重组，已经为代表性的人SCN 1A突变（L1649 Q）产生了敲入小鼠模型。在对转基因动物进行生物化学和组织学方面的初步表征后，将在该新产生的动物模型中测试以下具体假设：1）scn 1a基因敲入动物表现出偶发性神经紊乱（例如偏瘫发作或癫痫发作）。Scn 1a基因敲入动物对皮层扩散去极化（CSD）诱导的敏感性增加，这可能与偏头痛相关。scn 1a基因敲入的动物具有神经生理学改变，这可以解释神经元的过度兴奋。Scn 1aL 1649 Q KI动物的多模式功能表征，特别关注偏头痛等同物和癫痫发作，2.）分析突变对体内实验诱导的CSD的影响，3.）通过对Scn 1aL 1649 Q KI动物的原代神经元细胞培养物中突变的电生理学表征，并辅以对急性脑切片和自发神经元网络活动的分析。通过这些研究，我们希望进一步了解FHM和偏头痛的病理生理学，这可能为开发新的治疗策略打开大门。值得注意的是，Scn 1a的突变也与癫痫有关。我们获得了一种转基因癫痫小鼠模型，该模型携带紧邻L1649的氨基酸突变（R1648 H）。这将允许这两种动物模型的直接头对头比较，旨在更好地理解偏头痛和癫痫的差异机制，即两种表型重叠的阵发性神经障碍。

Familial hemiplegic migraine (FHM) is a severe autosomal-dominant subtype of migraine with aura. The applicants, by means of positional cloning, have identified SCN1A as the third FHM gene (FHM3; Dichgans*, Freilinger* et al. Lancet 2005). SCN1A encodes a neuronal voltage-gated sodium channel (Nav1.1), which is responsible for the generation and propagation of action potentials.Previous studies in cells overexpressing Nav1.1 channels with FHM-associated mutations point towards a loss-of-function of mutant channels in FHM patients (Kahlig, ..., Freilinger et al. Proc Natl Acad Sci U S A 2008). However, the precise role of mutant NaV1.1 for migraine and migraine aura remains unclear to date.To unravel the significance of NaV1.1 in the pathophysiology of migraine and migraine aura, the applicants, by means of homologous recombination, have generated a knock-in mouse model for a representative human SCN1A mutation (L1649Q).After an initial characterization of transgenic animals with respect to biochemistry and histology, the following specific hypotheses will be tested in this newly generated animal model: 1.) Scn1a knock-in animals show episodic neurological disturbances (e.g. hemiplegic attacks or epileptic seizures).2.) Scn1a knock-in animals have an increased susceptibility to the induction of cortical spreading depolarisations (CSD), the likely correlate of migraine aura.3.) Scn1a knock-in animals have neurophysiological alterations, which can explain neuronal hyperexcitability.In detail, the following investigations are planned: 1.) multimodal functional characterization of Scn1aL1649Q KI animals, focussing specifically on migraine equivalents and epileptic seizures, 2.) analysis of the effects of the mutation on experimentally induced CSD in vivo, 3.) electrophysiological characterization of the mutation in primary neuronal cell cultures from Scn1aL1649Q KI animals complemented by an analysis of acute brain slices and spontaneous neuronal network activity.By means of these investigations, we hope to gain further insight into the pathophysiology of FHM and migraine in general, which may open the door for the development of novel therapeutic strategies.Of note, mutations in Scn1a are associated also with epilepsy. We have access to a transgenic epilepsy mouse model carrying a mutation of the amino acid immediately adjacent to L1649 (R1648H). This will allow a direct head-to-head comparison of these two animal models, aiming at a better understanding of the differential mechanisms of migraine and epilepsy, i.e. two phenotypically overlapping paroxysmal neurological disorders.