Monet-Leprêtre Marie, Bardot Boris, Lemaire Barbara, Domenga Valérie, Godin Ophélia, Dichgans Martin, Tournier-Lasserve Elisabeth, Cohen-Tannoudji Michel, Chabriat Hugues, Joutel Anne
INSERM U740, Faculté de Médecine Paris 7, Site Villemin, 10 avenue de Verdun, Paris, France.
Brain. 2009 Jun;132(Pt 6):1601-12. doi: 10.1093/brain/awp049. Epub 2009 Mar 17.
Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is an autosomal dominant small-vessel disease of the brain caused by mutations in the NOTCH3 receptor. The highly stereotyped nature of the mutations, which alter the number of cysteine residues within the epidermal growth factor-like repeats (EGFR), predicts that all mutations share common mechanisms. Prior in vitro assays and genetic studies in the mouse support the hypothesis that common mutations do not compromise canonical Notch3 function but instead convey a non-physiological and deleterious activity to the receptor through the unpaired cysteine residue. Intriguingly, in vitro studies predict that mutations located in the Delta/Serrate/LAG-2 ligand binding domain-(EGFR10-11) may result in a loss of Notch3 receptor function. However, the in vivo relevance and functional significance of this with respect to the pathogenic mechanisms and clinical expression of the disease remain largely unexplored. To ascertain, in vivo, the functional significance of EGFR10-11 mutations, we generated transgenic mice with one representative mutation (C428S) in EGFR10 of Notch3. These mice, like those with a common R90C mutation, developed characteristic arterial accumulation of Notch3 protein and granular osmiophilic material upon aging. By introducing the mutant C428S transgene into a Notch3 null background, we found that, unlike the R90C mutant protein, the C428S mutant protein has lost wild-type Notch3 activity and exhibited mild dominant-negative activity in three different biological settings. From a large prospectively recruited cohort of 176 CADASIL patients, we identified 10 patients, from five distinct pedigrees carrying a mutation in EGFR10 or 11. These mutations were associated with significantly higher Mini-Mental State Examination and Mattis Dementia Rating Scale scores (P < 0.05), when compared with common mutations. Additionally, we found a strong effect of this genotype on the burden of white matter hyperintensities (P < 0.01). Collectively, these results highlight distinctive functional and phenotypic features of EGFR10-11 mutations relative to the common CADASIL mutations. Our findings are compatible with the hypothesis that EGFR10-11 mutations cause the disease through the same gain of novel function as the common mutations, and lead us to propose that reduced Notch3 signalling acts as a modifier of the CADASIL phenotype.
伴有皮质下梗死和白质脑病的常染色体显性遗传性脑动脉病（CADASIL）是一种由NOTCH3受体突变引起的常染色体显性遗传性脑小血管疾病。这些突变具有高度刻板的性质，改变了表皮生长因子样重复序列（EGFR）中的半胱氨酸残基数量，这表明所有突变都有共同的机制。先前的体外试验和小鼠遗传研究支持这样一种假说，即常见突变不会损害Notch3的正常功能，而是通过未配对的半胱氨酸残基赋予受体一种非生理性的有害活性。有趣的是，体外研究预测位于Delta/Serrate/LAG-2配体结合域（EGFR10-11）的突变可能导致Notch3受体功能丧失。然而，这在体内对于该疾病的致病机制和临床表型的相关性及功能意义在很大程度上仍未得到探索。为了在体内确定EGFR10-11突变的功能意义，我们构建了在Notch3的EGFR10中带有一个代表性突变（C428S）的转基因小鼠。这些小鼠与具有常见R90C突变的小鼠一样，随着年龄增长出现了Notch3蛋白和嗜锇颗粒物质在动脉中的特征性积聚。通过将突变的C428S转基因导入Notch3基因敲除背景中，我们发现，与R90C突变蛋白不同，C428S突变蛋白丧失了野生型Notch3活性，并在三种不同的生物学环境中表现出轻度的显性负性活性。在一个前瞻性招募的由176名CADASIL患者组成的大型队列中，我们从五个不同的家系中鉴定出10名携带EGFR10或11突变的患者。与常见突变相比，这些突变与显著更高的简易精神状态检查表和马蒂斯痴呆评定量表得分相关（P<0.05）。此外，我们发现这种基因型对白质高信号负担有强烈影响（P<0.01）。总体而言，这些结果突出了EGFR10-11突变相对于常见CADASIL突变所具有的独特功能和表型特征。我们的发现与这样一种假说相符，即EGFR10-11突变通过与常见突变相同的新功能获得来导致疾病，并使我们提出Notch3信号传导减少作为CADASIL表型的一种修饰因素。
