Homozygous NOTCH 3 null mutation and impaired NOTCH 3 signaling in recessive early‐onset arteriopathy and cavitating leukoencephalopathy

Abstract

Notch signaling is essential for vascular physiology. Neomorphic heterozygous mutations in NOTCH3, one of the four human NOTCH receptors, cause cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). Hypomorphic heterozygous alleles have been occasionally described in association with a spectrum of cerebrovascular phenotypes overlapping CADASIL, but their pathogenic potential is unclear. We describe a patient with childhood-onset arteriopathy, cavitating leukoencephalopathy with cerebral white matter abnormalities presented as diffuse cavitations, multiple lacunar infarctions and disseminated microbleeds. We identified a novel homozygous c.C2898A (p.C966*) null mutation in NOTCH3 abolishing NOTCH3 expression and causing NOTCH3 signaling impairment. NOTCH3 targets acting in the regulation of arterial tone (KCNA5) or expressed in the vasculature (CDH6) were downregulated. Patient's vessels were characterized by smooth muscle degeneration as in CADASIL, but without deposition of granular osmiophilic material (GOM), the CADASIL hallmark. The heterozygous parents displayed similar but less dramatic trends in decrease in the expression of NOTCH3 and its targets, as well as in vessel degeneration. This study suggests a functional link between NOTCH3 deficiency and pathogenesis of vascular leukoencephalopathies.

The developmental biology of genetic Notch disorders

“…This mode of pathogenesis suggests that CADASIL-causing NOTCH3 mutations are not loss of function; rather they are likely neomorphic or toxic. This is further supported by the observation that patients harboring homozygous CADASIL mutations experience similar or only slightly more severe symptoms (Abou Al-Shaar et al, 2016;Liem et al, 2008;Pippucci et al, 2015;Ragno et al, 2013;Soong et al, 2013;Tuominen et al, 2001;Vinciguerra et al, 2014); if the mutations were loss of function, homozygous patients would be expected to suffer more severe consequences. Interestingly, previous reports have described a clustering of CADASIL-related NOTCH3 mutations in exon 4 ( Fig.…”

“…This patient was originally diagnosed with Sneddon syndrome at age 11 (Parmeggiani et al, 2000), but a worsening of neurological symptoms, with cavitating leukoencephalopathy, multiple lacunar infarctions and disseminated microbleeds, prompted re-examination of the diagnosis and revealed a homozygous nonsense mutation in EGF25 of NOTCH3 ( Fig. 7C; Pippucci et al, 2015). Both parents were asymptomatic, but had small vessel ischemic changes as revealed by brain MRI.…”

Notch Signaling in Vascular Smooth Muscle Cells

“…These results would seem to suggest that it is the gained aberrant function of GOM deposits that causes CADASIL phenotypes. However, a homozygous-null Notch3 mutation has been shown to produce a recessive early-onset arteriopathy and cavitating leukoencephalopathy very similar to CADASIL without the deposition of GOM (Pippucci et al, 2015), and a mouse model with combined deficiency of Notch1 and Notch3 causes pericyte dysfunction and models some phenotypes of CADASIL (Kofler et al, 2015). While it is still difficult at this point to definitively rule out any of the possible explanations, it seems likely that impaired Notch3 signaling plays at least some role in the CADASIL phenotypes, based on the known function of Notch3 in regulating cell survival in VSMCs and pericytes (Baeten & Lilly, 2015; Liu et al, 2010).…”

Oncogenic role of the Notch pathway in primary liver cancer

“…Young Notch3 KO mice are viable and fertile without any apparent phenotypic abnormalities, whereas adult Notch3 KO mice exhibit arterial defects due to abnormalities in differentiation (41). In the liver, Notch3 regulates the activation of hematopoietic stem cells and may exhibit an anti-fibrogenic effect (42).…”