Pathogenesis Of Cerebral Amyloid Angiopathy Research Articles

Apolipoprotein E Transgenic Mouse Model of Cerebral Amyloid Angiopathy

76 Background: Cerebral amyloid angiopathy (CAA) is the second most common etiology for non-traumatic intracerebral hemorrhage (ICH). There is a significantly increased frequency of the apolipoprotein E (apoE) ε4 and ε2 alleles in patients with CAA and CAA-related ICH. This suggests a role for apoE in the pathogenesis of CAA and ICH. We have developed a unique transgenic mouse model using the human apoE gene to study the molecular mechanisms underlying CAA. Methods: The transgenic mouse model was created by gene targeting, which results in the expression of each human apoE isoform at physiologic levels in a correct spatial and temporal pattern. These mice do not contain any mutations in the amyloid precursor protein or cystatin C gene. Mice of all apoE genotypes were bred, and were matched for age and sex. Brains from aged mice were analyzed for gross ICH. Brain sections were stained with anti-mouse A-beta antibody (4G8) to detect vascular amyloid. Sections were also stained for blood using hematoxylin and eosin (H&E), and a Prussian Blue stain was used to detect iron and hemosiderin deposition. A thioflavin-S stain was used to determine if the vascular amyloid was fibrillar. Results: Brains from sacrificed aged (mean age=80 weeks) apoE transgenic mice showed positive staining for CAA in predominantly neocortical vessels. The apoE ε2/ε2 mice had the highest occurrence of CAA (70%, 7 of 10), followed by the ε4/ε4 mice (40%, 4 of 10). Only 10% (1 of 10) of the ε3/ε3 mice had CAA. Two aged mice homozygous for apoE ε4 had gross ICH at post-mortem inspection. Brain sections from these mice demonstrated red blood cell infiltration and iron/hemosiderin deposition in the brain parenchyma when examined by light microscopy. Conclusions: This human apoE transgenic mouse model provides a genetically well defined and environmentally controlled animal model for the study of CAA that closely resembles the condition found in humans. This model may be useful for the study of therapies for the prevention and treatment of CAA.

Apolipoprotein E Transgenic Mouse Model of Cerebral Amyloid Angiopathy

76 Background: Cerebral amyloid angiopathy (CAA) is the second most common etiology for non-traumatic intracerebral hemorrhage (ICH). There is a significantly increased frequency of the apolipoprotein E (apoE) e4 and e2 alleles in patients with CAA and CAA-related ICH. This suggests a role for apoE in the pathogenesis of CAA and ICH. We have developed a unique transgenic mouse model using the human apoE gene to study the molecular mechanisms underlying CAA. Methods: The transgenic mouse model was created by gene targeting, which results in the expression of each human apoE isoform at physiologic levels in a correct spatial and temporal pattern. These mice do not contain any mutations in the amyloid precursor protein or cystatin C gene. Mice of all apoE genotypes were bred, and were matched for age and sex. Brains from aged mice were analyzed for gross ICH. Brain sections were stained with anti-mouse A-beta antibody (4G8) to detect vascular amyloid. Sections were also stained for blood using hematoxylin and eosin (H&E), and a Prussian Blue stain was used to detect iron and hemosiderin deposition. A thioflavin-S stain was used to determine if the vascular amyloid was fibrillar. Results: Brains from sacrificed aged (mean age=80 weeks) apoE transgenic mice showed positive staining for CAA in predominantly neocortical vessels. The apoE e2/e2 mice had the highest occurrence of CAA (70%, 7 of 10), followed by the e4/e4 mice (40%, 4 of 10). Only 10% (1 of 10) of the e3/e3 mice had CAA. Two aged mice homozygous for apoE e4 had gross ICH at post-mortem inspection. Brain sections from these mice demonstrated red blood cell infiltration and iron/hemosiderin deposition in the brain parenchyma when examined by light microscopy. Conclusions: This human apoE transgenic mouse model provides a genetically well defined and environmentally controlled animal model for the study of CAA that closely resembles the condition found in humans. This model may be useful for the study of therapies for the prevention and treatment of CAA.

CEREBRAL AMYLOID ANGIOPATHY

BACKGROUND Cerebral amyloid angiopathy (CAA) is increasingly recognized as an important cause of lobar intracerebral hemorrhage in the elderly and is the only major form of stroke without effective treatment. It is characterized by deposition of congophilic material in small- to medium-sized blood vessels of the brain and leptomeninges. In the most severe stages of the disease, amyloid deposits cause breakdown of the blood vessel wall with consequent hemorrhage. Presently, definitive diagnosis of CAA-related hemorrhage requires examination of the brain at autopsy. REVIEW SUMMARY This article reviews the pathology and pathogenesis of CAA. To aid in identifying patients at risk for CAA, the range of clinical presentations is discussed. Particular attention is devoted to lobar intracerebral hemorrhage, the most common and devastating manifestation of CAA. We review recent developments in the epidemiology of CAA, particularly the lessons learned from studies of the apolipoprotein E genotype. We conclude with a discussion of antemortem diagnosis, the differential diagnosis and management of CAA, and future directions for the development of treatments. CONCLUSIONS CAA will become increasingly common as the population ages. Its presence should be considered in any elderly patient with lobar hemorrhage or dementia. Recognition of CAA is particularly important in the setting of anticoagulant therapy, which places patients with CAA at high risk for intracerebral hemorrhage. Finally, patients with CAA-related hemorrhage are at high risk for recurrent hemorrhage. (THE NEUROLOGIST 6:315-325, 2000)

Apolipoprotein E, smooth muscle cells and the pathogenesis of cerebral amyloid angiopathy: the potential role of impaired cerebrovascular A beta clearance.

Cerebral amyloid angiopathy (CAA) is caused by the deposition of beta-amyloid (A beta) in Alzheimer disease brains. It also occurs isolated, representing a major cause for cerebral hemorrhage in the elderly. The E4 genotype of apolipoprotein E (ApoE) is a risk factor for CAA; however, the molecular mechanism underlying this genetic association is unknown. Various findings suggest that cerebrovascular A beta is derived from the soluble A beta contained in the cortical extracellular space or the cerebrospinal fluid (CSF) that communicates and surrounds small cortical or leptomeningeal vessels. CAA deposits are always intimately associated with smooth muscle cells (SMCs) or SMC-derived pericytes. As we have previously reported, SMCs internalize A beta in vitro via a lipoprotein pathway involving ApoE and the low-density lipoprotein receptor family. Internalized A beta is subsequently located to lysosomes, suggesting its intracellular degradation. We show that A beta is internalized via multiple pathways, because class A and class B scavenger receptors are also colocalized to A beta-containing endosomes in SMCs, and A beta uptake is inhibited by various scavenger receptor antagonists. It has been recently shown for different cell types that the cellular uptake of ApoE is more efficient for the ApoE3 isoform when compared to ApoE4 and that this isoform-specific difference depends on the presence of heparan sulfate proteoglycan (HSPG). HSPG is produced by SMCs and promotes A beta fibrillogenesis. We propose a pathogenetic model of CAA, in which the ApoE- and HSPG-mediated clearance of CSF-derived A beta peptides by SMCs protects the vascular extracellular matrix against critical A beta concentrations. Impairment of this pathway or its reduced efficiency in carriers of the ApoE4 genotype may increase the risk of developing CAA.

Cerebral amyloid angiopathy: An overview

Cerebral amyloid angiopathy (CAA) is characterized by amyloid deposition in cortical and leptomeningeal vessels. Several cerebrovascular amyloid proteins (amyloid beta-protein (Abeta), cystatin C (ACys), prion protein (AScr), transthyretin (ATTR), gelsolin (AGel), and ABri (or A-WD)) have been identified, leading to the classification of several types of CAA. Sporadic CAA of Abeta type is commonly found in elderly individuals and patients with Alzheimer's disease. Cerebral amyloid angiopathy is an important cause of cerebrovascular disorders including lobar cerebral hemorrhage, leukoencephalopathy, and small cortical hemorrhage and infarction. We review the clinicopathological and molecular aspects of CAA and discuss the pathogenesis of CAA with future perspectives.

Alzheimer's β-amyloid peptides induce inflammatory cascade in human vascular cells: the roles of cytokines and CD40

Accumulating evidence suggests that β-amyloid (Aβ)-induced inflammatory reactions may partially drive the pathogenesis of Alzheimer's disease (AD). Recent data also implicate similar inflammatory processes in cerebral amyloid angiopathy (CAA). To evaluate the roles of Aβ in the inflammatory processes in vascular tissues, we have tested the ability of Aβ to trigger inflammatory responses in cultured human vascular cells. We found that stimulation with Aβ dose-dependently increased the expression of CD40, and secretion of interferon-γ (IFN-γ) and interleukin-1β (IL-1β) in endothelial cells. Aβ also induced expression of IFN-γ receptor (IFN-γR) both in endothelial and smooth muscle cells. Characterization of the Aβ-induced inflammatory responses in the vascular cells showed that the ligation of CD40 further increased cytokine production and/or the expression of IFN-γR. Moreover, IL-1β and IFN-γ synergistically increased the Aβ-induced expression of CD40 and IFN-γR. We have recently found that Aβ induces expression of adhesion molecules, and that cytokine production and interaction of CD40–CD40 ligand (CD40L) further increase the Aβ-induced expression of adhesion molecules in these same cells. These results suggest that Aβ can function as an inflammatory stimulator to activate vascular cells and induces an auto-amplified inflammatory molecular cascade, through interactions among adhesion molecules, CD40–CD40L and cytokines. Additionally, Aβ 1–42, the more pathologic form of Aβ, induces much stronger effects in endothelial cells than in smooth muscle cells, while the reverse is true for Aβ 1–40. Collectively, these findings support the hypothesis that the Aβ-induced inflammatory responses in vascular cells may play a significant role in the pathogenesis of CAA and AD.

Characteristics of thein VitroVasoactivity of β-Amyloid Peptides

The β-amyloid (Aβ1–40) peptide has previously been shown to enhance phenylephrine contraction of aortic ringsin vitro.We have employed a novel observation, that Aβ peptides enhance endothelin-1 (ET-1) contraction, to examine the relationship between vasoactivity and potential amyloidogenicity of Aβ peptides, the role played by free radicals and calcium in the vasoactive mechanism, and the requirement of an intact endothelial layer for enhancement of vasoactivity. Rings of rat aortae were constricted with ET-1 before and after addition of amyloid peptide and/or other compounds, and a comparison was made between post- and pretreatment contractions. In this system, vessel constriction is consistently dramatically enhanced by Aβ1–40, is enhanced less so by Aβ1–42, and is not enhanced by Aβ25–35. The endothelium isnotrequired for Aβ vasoactivity, and calcium channel blockers have a greater effect than antioxidants in blocking enhancement of vasoconstriction by Aβ peptides. In contrast to Aβ-induced cytotoxicity, Aβ-induced vasoactivity is immediate, occurs in response to low doses of freshly solubilized peptide, and appears to be inversely related to the amyloidogenic potential of the Aβ peptides. We conclude that the mechanism of Aβ vasoactivity is distinct from that of Aβ cytotoxicity. Although free radicals appear to modulate the vasoactive effects, the lack of requirement for endothelium suggests that loss of the free radical balance (between NO and O−2) may be a secondary influence on Aβ enhancement of vasoconstriction. These effects of Aβ on isolated vessels, and reported effects of Aβ in cells of the vasculature, suggest that Aβ-induced disruption of vascular tone may be a factor in the pathogenesis of cerebral amyloid angiopathy and Alzheimer's disease. Although the mechanism of enhanced vasoconstriction is unknown, it is reasonable to propose thatin vivocontact of Aβ peptides with small cerebral vessels may increase their tendency to constrict and oppose their tendency to relax. The subclinical ischemia resulting from this would be expected to up-regulate βAPP production in and around the vasculature with further increase in Aβ formation and deposition. The disruptive and degenerative effects of such a cycle would lead to the complete destruction of cerebral vessels and consequently neuronal degeneration in the affected areas.

Association of vascular amyloid beta and cells of the mononuclear phagocyte system in hereditary cerebral hemorrhage with amyloidosis (Dutch) and Alzheimer disease.

Arterial and arteriolar amyloid-beta (A beta) deposition in hereditary cerebral hemorrhage with amyloidosis (Dutch) (HCHWA-D) and Alzheimer disease (AD) cerebral amyloid angiopathy (CAA) were studied as to morphology, extent, and association with mononuclear phagocyte system (MPS) cells using A beta, a-smooth muscle actin, and monocyte/macrophage marker (HLA-DR, CD68, CD11c, CD45) immunohistochemistry. The HCHWA-D/AD arterial/arteriolar media showed compact A beta deposits, first appearing at the media/adventitia junction, and concomitant smooth muscle loss. Only HCHWA-D CAA featured (a) severe involvement of larger arteries and (b) arterioles showing a single or double ring of radial A beta surrounding compact A beta. Radial A beta appeared to develop at the media/adventitia junction. Monocyte/macrophage marker-positive foci/cells co-localized with HCHWA-D arterial A beta. Focal HLA-DR/CD11c positivity was observed at the media/adventitia junction of AD/HCHWA-D arteries in the absence of local A beta, but not in controls. Monocyte/macrophage marker positivity co-localizing with radial A beta appeared continuous with perivascular cells and microglia clustering perivascularly. These results suggest that (a) MPS cells are topographically associated with HCHWA-D arterial A beta and radial arteriolar A beta, and (b) HLA-DR/CD11c immunoreactivity may appear at the media/adventitia junction prior to A beta. The latter finding and the assumed formation of radial A beta at the media/adventitia junction may relate to involvement of the abluminal basement membrane in CAA pathogenesis. The role of MPS cells in this process remains to be established.

Experimental deposition of Alzheimer amyloid beta-protein in canine leptomeningeal vessels.

To study the pathogenesis of cerebral amyloid angiopathy (CAA), organ cultures of canine leptomeninges were incubated with fluorescein-conjugated amyloid beta-protein (FA beta, residues 1-40; 10 nM to 200 microM). Fluorescence microscopy showed focal and dose-dependent FA beta binding to blood vessels affected by CAA at FA beta-concentrations as low as 10 nM. The new A beta deposits appeared to be extracellular and were localized to the middle and outer layers of leptomeningeal arterioles. FA beta partially co-localized with apolipoprotein E (ApoE) as revealed by confocal microscopy, suggesting that A beta in situ binds to ApoE. Young dogs or old dogs without CAA showed no deposition of FA beta. Our results indicate that after initiation of CAA pathology, physiological concentrations of soluble A beta are sufficient to sustain its further deposition and therefore the progression of CAA.

Immunohistochemical study of cerebral amyloid angiopathy. III. Widespread alzheimer A4 peptide in cerebral microvessel walls colocalizes with gamma trace in patients with leukoencephalopathy

Brain tissue from 11 patients with cerebral amyloid angiopathy, changes of Alzheimer's disease, and variable degrees of subcortical leukoencephalopathy was examined by immunohistochemical methods, using primary antibodies to peptide segments representing portions of the Alzheimer A4 (beta-) peptide or gamma-trace peptide (seen most commonly in Icelandic patients with cerebral hemorrhage (hereditary cerebral hemorrhage with amyloidosis [HCHWA-I]). Variable A4 immunostaining was seen within cortical (and rarely white matter) parenchyma in the form of senile plaques (with or without central cores), and within capillary and arteriolar walls. Within individual patients, A4 deposits were often primarily parenchymal or vascular, and when they were vascular they tended to be more prominent in arteriolar than in capillary wall segments. Perivascular A4 deposits were often detected around strongly immunoreactive microvessels. Gamma-trace immunoreactivity was noted in many A4-positive microvessel walls, but staining was always less intense than with the anti-A4 antibody. We conclude that patients with severe cerebral amyloid angiopathy may show wide variation in the severity and topography of A4 deposits within brain parenchyma. A4 may colocalize with gamma-trace peptide, suggesting that A4 and gamma-trace forms of cerebral amyloid angiopathy may not be as biochemically distinctive as has been suggested. Other proteases or protease inhibitors may contribute to the pathogenesis of cerebral amyloid angiopathy or cerebral amyloid angiopathy-related stroke syndromes.