Probes for NOTCH3

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is an inherited form of cerebral small vessel disease caused by mutations in conserved residues of NOTCH3. Affected arteries of CADASIL feature fibrosis and accumulation of NOTCH3. A variety of collagen subtypes (types I, III, IV, and VI) have been identified in fibrotic CADASIL vessels. Biglycan (BGN) and decorin (DCN) are class I members of the small leucine-rich proteoglycan (SLRP) family that regulate collagen fibril size. Because DCN has been shown to deposit in arteries in cerebral small vessel disease, we tested whether BGN accumulates in arteries of CADASIL brains. BGN was strongly expressed in both small penetrating and leptomeningeal arteries of CADASIL brain. BGN protein was localized to all three layers of arteries (intima, media, and adventitia). Substantially, more immunoreactivity was observed in CADASIL brains compared to controls. Immunoblotting of brain lysates showed a fourfold increase in CADASIL brains (compared to controls). Messenger RNA encoding BGN was also increased in CADASIL and was localized by in situ hybridization to all three vascular layers in CADASIL. Human cerebrovascular smooth muscle cells exposed to purified NOTCH3 ectodomain upregulated BGN, DCN, and COL4A1 through mechanisms that are sensitive to rapamycin, a potent mTOR inhibitor. In addition, BGN protein interacted directly with NOTCH3 protein in cell culture and in direct protein interaction assays. In conclusion, BGN is a CADASIL-enriched protein that potentially accumulates in vessels by mTOR-mediated transcriptional activation and/or post-translational accumulation via protein interactions with NOTCH3 and collagen.

The most common inherited cause of vascular dementia and stroke, cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), is caused by mutations in NOTCH3. Post-translationally altered NOTCH3 accumulates in the vascular media of CADASIL arteries in areas of the vessels that exhibit profound cellular degeneration. The identification of molecules that concentrate in the same location as pathological NOTCH3 may shed light on processes that drive cytopathology in CADASIL. We performed a two phase immunohistochemical screen of markers identified in the Human Protein Atlas to identify new proteins that accumulate in the vascular media in a pattern similar to pathological NOTCH3. In phase one, none of 16 smooth muscle cell (SMC) localized antigens exhibited NOTCH3-like patterns of expression; however, several exhibited disease-dependent patterns of expression, with antibodies directed against FAM124A, GZMM, MTFR1, and ST6GAL demonstrating higher expression in controls than CADASIL. In contrast, in phase two of the study that included 56 non-SMC markers, two proteins, CD63 and CTSH, localized to the same regions as pathological NOTCH3, which was verified by VesSeg, a customized algorithm that assigns relative location of antigens within the layers of the vessel. Proximity ligation assays support complex formation between NOTCH3 fragments and CD63 in degenerating CADASIL media. Interestingly, in normal mouse brain, the two novel CADASIL markers, CD63 and CTSH, are expressed in non-SMC vascular cells. The identification of new proteins that concentrate in CADASIL vascular media demonstrates the utility of querying publicly available protein databases in specific neurological diseases and uncovers unexpected, non-SMC origins of pathological antigens in small vessel disease.

CADASIL is a small vessel disease caused by mutations in NOTCH3 that lead to an odd number of cysteines in the EGF-like repeat domain, causing protein misfolding and aggregation. The main symptoms are migraine, psychiatric disturbances, recurrent strokes and dementia, being executive function characteristically impaired. The molecular pathways altered by this receptor aggregation need to be studied further. A genome-wide transcriptome study (four cases paired with three healthy siblings) was carried out, in addition to a qRT-PCR for validation purposes (ten new cases and eight new controls). To study the expression profile by cell type of the significant mRNAs found, we performed an in situ hybridization (ISH) (nine cases and eight controls) and a research in the Single-nuclei Brain RNA-seq expression browser (SNBREB). Pathway analysis enrichment was carried out with Gene Ontology and Reactome. Neuropsychological tests were performed in five of the qRT-PCR cases. The two most significant differentially expressed mRNAs (BANP, p-value = 7.23 × 10-4 and PDCD6IP, p-value = 8.36 × 10-4) were selected for the validation study by qRT-PCR. Additionally, we selected two more mRNAs (CAMK2G, p-value = 4.52 × 10-3 and E2F4, p-value = 4.77 × 10-3) due to their association with ischemic neuronal death. E2F4 showed differential expression in the genome-wide transcriptome study and in the qRT-PCR (p = 1.23 × 10-3), and it was upregulated in CADASIL cases. Furthermore, higher E2F4 expression was associated with worse executive function (p = 2.04 × 10-2) and attention and information processing speed (IPS) (p = 8.73 × 10-2). In situ hibridization showed E2F4 expression in endothelial and vascular smooth vessel cells. In silico studies indicated that E2F4 is also expressed in brain endothelial cells. Among the most significant pathways analyzed, there was an enrichment of vascular development, cell adhesion and vesicular machinery terms and autophagy process. E2F4 is more highly expressed in the skin biopsy of CADASIL patients compared to controls, and its expression is present in endothelial cells and VSMCs. Further studies are needed to understand whether E2F4 could be useful as a biomarker, to monitor the disease or be used as a therapeutic target.