ABSTRACT Neurodegenerative disease is a major cause of death and permanent disability in Veterans; vascular disease of the brain plays an outsized role in the progression of neurodegenerative diseases including Alzheimer’s Disease and Related Dementias (ADRD). On its own, vascular disease of the brain can cause one form of ADRD, vascular cognitive impairment and dementia (VCID). In collaboration with disorders such as Alzheimer’s disease, brain vascular disease significantly augments the pace and severity of dementing disorders. Unfortunately, effective treatments that target vascular disease of the brain are currently not available. As such, there is an unmet need to uncover the molecular mechanisms of brain vascular disease. The most common inherited cause of brain vascular disease is cerebral autosomal dominant arteriopathy with subcortical infarcts and dementia (CADASIL). CADASIL is an outstanding model for understanding pathology of brain blood vessels and is caused by mutations in NOTCH3 that are predicted to alter cysteine number. We have discovered a sequence of changes in the configuration of NOTCH3 in association with CADASIL mutations. First, NOTCH3 in CADASIL is more likely to harbor multiple reduced cysteines (a form called mrc-N3). Second, NOTCH3 that is multiply reduced undergoes cleavage at the N-terminus that releases a 41-amino acid peptide, the NOTCH3 N-terminal fragment (NTF). Based on the molecular process driving NTF generation, in new experiments, we describe the identification of a second cleavage event that is predicted to result in a second 41-amino acid peptide NTF2. Antibodies generated to NTF2 demonstrate that CADASIL vessels are enriched in this cleavage product. Moreover, a novel monoclonal antibody has been identified that recognizes a conformation of NTF2 that is only expressed in a subset of vessels (NTF2*). In this proposal, we will test the hypothesis that NTF2* is associated with advanced pathology of CADASIL blood vessels. We will also test if NTF2* is deposited in a gradient from the surface to the deep white matter, which would point to the possibility that NTF2* is a predictable marker for vascular disease progression.