Toxicity of Dutch (E22Q) and Flemish (A21G) Mutant Amyloid β Proteins to Human Cerebral Microvessel and Aortic Smooth Muscle Cells

Abstract

Background and Purpose-Cerebral amyloid angiopathy (CAA) is characterized by the deposition of amyloid ␤ protein (A␤) in cortical and leptomeningeal vessels of patients with Alzheimer's disease and hereditary cerebral hemorrhage with amyloidosis, Dutch type. Smooth muscle cells (SMC) from cerebral microvessels (MV) are of particular interest as a site of A␤-related injury because CAA is much more pronounced in the tunica media of cortical arterioles than meningeal arteries. Patients carrying point mutations at residues 22 (E22Q) and 21 (A21G) of A␤ show severe CAA with various degrees of brain parenchymal A␤ deposition. The purpose of this study was to investigate the effects of 2 mutant E22Q-and A21G-A␤ peptides on MV and aortic SMC. Methods-SMC were isolated from human cerebral MV and aorta. Cell morphology, viability, and proliferation as parameters of A␤ toxicity were investigated after 3 days of peptide treatment by trypan blue exclusion and [ 3 H]thymidine incorporation. Results-E22Q-A␤ induced significant decreased cellular proliferation and viability, as well as obvious degeneration of both MV and aortic SMC. A21G-A␤ and wild-type A␤ did not cause significant toxicity, as judged by cell morphology, viability, or cell proliferation, on either type of SMC. Conclusions-E22Q-A␤ induced greater toxicity in all parameters than A21G-A␤ and wild-type A␤ with respect to both MV and aortic SMC. A21G-A␤ did not show a significant toxic effect on MV and aortic SMC. This differential effect may be linked to cell type-specific processing and metabolism of mutant forms of A␤. Mutations in amyloid precursor protein may lead to CAA by different pathogenetic mechanisms or share an unknown property that distinguishes them from wild-type A␤. (Stroke. 2000;31:534-538.)Key Words: amyloid Ⅲ cerebral circulation Ⅲ microcirculation Ⅲ muscle, smooth Ⅲ mutation C erebral amyloid angiopathy (CAA) is characterized by the deposition of fibrillar amyloid in the media and adventitia of cerebral cortical and meningeal blood vessels. 1,2 Amyloid ␤ protein (A␤) is the main constituent of vascular amyloid in sporadic/Alzheimer disease-associated CAA, Down syndrome, and hereditary cerebral hemorrhage with amyloidosis, Dutch type (HCHWA-D). [3][4][5] The presence of amyloid in the cerebrovascular tunica media is closely associated with degeneration of smooth muscle cells (SMC) in this locus. 1,6 -8 HCHWA-D is an autosomal dominant disease caused by a point mutation at codon 693 of the ␤ amyloid precursor protein (APP). This mutation results in a glutamic acid to glutamine substitution at residue 22 (E22Q) of A␤. HCHWA-D patients consistently develop severe CAA and cerebral hemorrhage but only rarely have significant numbers of senile plaques or neurofibrillary tangles within the See Editorial Comment, page 538 brain. 4,9,10 This makes the clinicopathological phenotype of HCHWA-D unique by comparison with clinicopathological phenotypes associated with other APP mutations. [11][12][13][14][15] This issue is of particular interest when HCHWA-D ...

Structural and Functional Disruption of Vascular Smooth Muscle Cells in a Transgenic Mouse Model of Amyloid Angiopathy

“…12 Amyloid is toxic to endothelial cells in culture, 13 and a mutant form of the A␤ peptide is toxic to SMCs in culture, although the 1-40 form that predominates in the Tg2576 mouse did not demonstrate direct toxicity to SMCs. 14,15 The clear in vivo loss of SMC function, then, may reflect a preliminary stage in a cascade of events that leads to cell loss. The SMC loss seen in the Tg2576 mouse model of amyloid deposition parallels that previously described at the ultrastructural level in postmortem human AD cases.…”

Cerebral Amyloid Angiopathy and Vessel Dysfunction

“…Another early feature of this illness is cognitive deterioration, often associated with white matter abnormalities on MRI scan and small ischemic infarctions and hemorrhages on pathologic examination [21, 22]. The Dutch mutation produces an Aβ peptide with substitution of glutamine for glutamic acid at position 22, resulting in altered fibrillogenesis [23, 24, 25] and toxicity to vascular cells [25, 26, 27, 28, 29, 30] in various experimental systems.…”

Abnormality of G-Protein-Coupled Receptor Kinases at Prodromal and Early Stages of Alzheimer's Disease: An Association with Early β-Amyloid Accumulation

“…For example, with a minimum effective concentration (EC min ) of ϳ4 M, A␤ dose dependently increased vascular cytotoxicity in hours or days Wang et al, 2000;Mok et al, 2002). On the other hand, although nanomolar (subthreshold) A␤ had no direct effects, it sensitized vascular cells in a dose-dependent manner (with an EC range of 20 -1000 nM) so that vasoconstrictions induced by phenylephrine or endothelin-1 (ET-1) were strongly potentiated (Thomas et al, 1996;Crawford et al, 1997Crawford et al, , 1998aParis et al, 2000).…”