Overlapping Protein Accumulation Profiles of CADASIL and CAA: Is There a Common Mechanism Driving Cerebral Small-Vessel Disease?

Abstract

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) and cerebral amyloid angiopathy (CAA) are two distinct vascular angiopathies that share several similarities in clinical presentation and vascular pathology. Given the clinical and pathologic overlap, the molecular overlap between CADASIL and CAA was explored. CADASIL and CAA protein profiles from recently published proteomics-based and immuno-based studies were compared to investigate the potential for shared disease mechanisms. A comparison of affected proteins in each disease highlighted 19 proteins that are regulated in both CADASIL and CAA. Functional analysis of the shared proteins predicts significant interaction between them and suggests that most enriched proteins play roles in extracellular matrix structure and remodeling. Proposed models to explain the observed enrichment of extracellular matrix proteins include both increased protein secretion and decreased protein turnover by sequestration of chaperones and proteases or formation of stable protein complexes. Single-cell RNA sequencing of vascular cells in mice suggested that the vast majority of the genes accounting for the overlapped proteins between CADASIL and CAA are expressed by fibroblasts. Thus, our current understanding of the molecular profiles of CADASIL and CAA appears to support potential for common mechanisms underlying the two disorders.

Figure 1

Differences and similarities between cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) and cerebral amyloid angiopathy (CAA) histopathology and protein profiles. A: The histopathologies of CADASIL and CAA vessels are compared. Both CADASIL and CAA feature abnormal protein accumulation. In CADASIL, the major protein involved is NOTCH3 ectodomain (brown deposits), whereas in CAA, the major protein involved is amyloid-β (Aβ; green deposits). CADASIL vessels also demonstrate dramatic intimal hyperplasia with accumulation of intimal proteins. Both CADASIL and CAA vessels involve significant smooth muscle cell degeneration in the medial layer and hyalinization of the vessel walls. B: Examination of published literature indicated 378 proteins differentially regulated in CADASIL and 58 proteins differentially regulated in vascular CAA. Of these, approximately 33% of the proteins differentially regulated in vascular CAA overlap with those differentially regulated in CADASIL. C: STRING version 11 analysis shows a high degree of interconnectedness among the shared proteins. Only norrin (NDP) does not have any known or predicted interactions with the other proteins. APCS, serum amyloid protein; APOE, apolipoprotein E; CLU, clusterin; COL1A2, collagen α-2(I) chain; COL6A2, collagen α-2(VI) chain; COL6A3, collagen α-3(VI) chain; C4A, complement C4-A; CST3, cystatin C; FN1, fibronectin; GFAP, glial fibrillary acidic protein; HSPG2, basement membrane–specific heparan sulfate proteoglycan core protein; HTRA1, serine protease HTRA1; LAMC1, laminin subunit γ 1; NFASC, neurofascin; PTGDS, prostaglandin H2 D isomerase; TIMP3, metalloproteinase inhibitor 3; TPM1, tropomyosin α 1 chain; VTN, vitronectin.

Figure 2

Identifying vascular cell types expressing genes encoding for overlapped proteins in cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) and cerebral amyloid angiopathy (CAA). To determine which vascular cells produce the overlapping proteins, vascular gene expression data were compared using an online database of single-cell RNA-sequencing data from adult murine brains (http://betsholtzlab.org/VascularSingleCells/database.html, last accessed August 23, 2020).^, Average counts from each cell type were used to generate the heat map using XLSTAT software version 2020.5 (Addinsoft Corp., Paris, France). Heat map colors were defined by SD. In normal murine brains, the primary cell types responsible for production of most of these proteins were fibroblasts. Only vitronectin (VTN), laminin subunit γ (LAMC1), and tropomyosin α 1 chain (TPM1) were primarily expressed by pericytes or venous, arterial, and arteriolar smooth muscle cells (vSMCs, aSMCs, and aaSMCs, respectively). AC, astrocyte; aEC, arterial EC; APOE, apolipoprotein E; capilEC, capillary EC; CLU, clusterin; COL1A2, collagen α-2(I) chain; COL6A2, collagen α-2(VI) chain; COL6A3, collagen α-3(VI) chain; C4A, complement C4-A; CST3, cystatin C; EC, endothelial cell; FB, vascular fibroblast-like cell; FN1, fibronectin; GFAP, glial fibrillary acidic protein; HSPG2, basement membrane–specific heparan sulfate proteoglycan core protein; HTRA1, serine protease HTRA1; MG, microglia; NDP, norrin; NFASC, neurofascin; OL, oligodendrocyte; PC, pericyte; PTGDS, prostaglandin H2 D isomerase; TIMP3, metalloproteinase inhibitor 3; vEC, venous EC; EC1,2,3 endothelial cell subtypes.^,