The NOTCH3 score: a pre-clinical CADASIL biomarker in a novel human genomic NOTCH3 transgenic mouse model with early progressive vascular NOTCH3 accumulation.

INTRODUCTION: CADASIL (Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy) is a hereditary small vessel disease caused by mutations in the NOTCH3 gene, leading to toxic NOTCH3 protein accumulation in the small- to medium sized arterioles. The accumulation is systemic but most pronounced in the brain vasculature where it leads to clinical symptoms of recurrent stroke and dementia. There is no therapy for CADASIL, and therapeutic development is hampered by a lack of feasible clinical outcome measures and biomarkers, both in mouse models and in CADASIL patients. To facilitate pre-clinical therapeutic interventions for CADASIL, we aimed to develop a novel, translational CADASIL mouse model. RESULTS: We generated transgenic mice in which we overexpressed the full length human NOTCH3 gene from a genomic construct with the archetypal c.544C > T, p.Arg182Cys mutation. The four mutant strains we generated have respective human NOTCH3 RNA expression levels of 100, 150, 200 and 350 % relative to endogenous mouse Notch3 RNA expression. Immunohistochemistry on brain sections shows characteristic vascular human NOTCH3 accumulation in all four mutant strains, with human NOTCH3 RNA expression levels correlating with age at onset and progression of NOTCH3 accumulation. This finding was the basis for developing the 'NOTCH3 score', a quantitative measure for the NOTCH3 accumulation load. This score proved to be a robust and sensitive method to assess the progression of NOTCH3 accumulation, and a feasible biomarker for pre-clinical therapeutic testing. CONCLUSIONS: This novel, translational CADASIL mouse model is a suitable model for pre-clinical testing of therapeutic strategies aimed at delaying or reversing NOTCH3 accumulation, using the NOTCH3 score as a biomarker.

Migraine pathophysiology: lessons from mouse models and human genetics.

Migraine is a common, disabling, and undertreated episodic brain disorder that is more common in women than in men. Unbiased genome-wide association studies have identified 13 migraine-associated variants pointing at genes that cluster in pathways for glutamatergic neurotransmission, synaptic function, pain sensing, metalloproteinases, and the vasculature. The individual pathogenetic contribution of each gene variant is difficult to assess because of small effect sizes and complex interactions. Six genes with large effect sizes were identified in patients with rare monogenic migraine syndromes, in which hemiplegic migraine and non-hemiplegic migraine with or without aura are part of a wider clinical spectrum. Transgenic mouse models with human monogenic-migraine-syndrome gene mutations showed migraine-like features, increased glutamatergic neurotransmission, cerebral hyperexcitability, and enhanced susceptibility to cortical spreading depression, which is the electrophysiological correlate of aura and a putative trigger for migraine. Enhanced susceptibility to cortical spreading depression increased sensitivity to focal cerebral ischaemia, and blocking of cortical spreading depression improved stroke outcome in these mice. Changes in female hormone levels in these mice modulated cortical spreading depression susceptibility in much the same way that hormonal fluctuations affect migraine activity in patients. These findings confirm the multifactorial basis of migraine and might allow new prophylactic options to be developed, not only for migraine but potentially also for migraine-comorbid disorders such as epilepsy, depression, and stroke.