Archetypal Arg169Cys mutation in NOTCH3 does not drive the pathogenesis in cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy via a loss-of-function mechanism.

BACKGROUND AND PURPOSE Cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy, the most common heritable small vessel disease of the brain, is caused by dominant mutations in the NOTCH3 receptor that stereotypically lead to age-dependent Notch3ECD deposition in the vessels. NOTCH3 loss of function has been demonstrated for few mutations. However, whether this finding applies to all mutations and whether a loss-of-function mechanism drives the manifestations of the disease remain yet unknown. This study investigated the in vivo functionality of the Arg169Cys archetypal mutation. METHODS We used mice with constitutive or conditional reduction of NOTCH3 activity, mice harboring the Arg169Cys mutation at the endogenous Notch3 locus (Notch3Arg170Cys), and mice overexpressing the Arg169Cys NOTCH3 mutant (TgPAC-Notch3R169C) on either a Notch3 wild-type or a null background. NOTCH3 activity was monitored in the brain arteries by measuring the expression of NOTCH3 target genes using real-time polymerase chain reaction. Notch3ECD deposits were assessed by immunohistochemistry. Brain parenchyma was analyzed for vacuolation and myelin debris in the white matter and infarcts. RESULTS We identified a subset of genes appropriate to detect NOTCH3 haploinsufficiency in the adult. Expression of these genes was unaltered in Notch3Arg170Cys mice, despite marked Notch3ECD deposits. Elimination of wild-type NOTCH3 did not influence the onset and burden of white matter lesions in 20-month-old TgPAC-Notch3R169C mice, and 20-month-old Notch3-null mice exhibited neither infarct nor white matter changes. CONCLUSIONS These data provide strong evidence that cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy can develop without impairment of NOTCH3 signaling and argue against a loss of NOTCH3 function as a general driving mechanism for white matter lesions in cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy.