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Abstract: Cerebral amyloid angiopathy (CAA) is a common pathological finding in Alzheimer''s disease and hereditary cerebral hemorrhage with amyloidosis of the Dutch type; in this latter condition it is caused by deposition of mutated amyloid β protein (Aβ Glu22Gln; D-Aβ1–40). Previously, we found a dependence of the Aβ-mediated toxicity and apolipoprotein E (apoE) production by cultured pericytes on apoE genotype. Given their close association with the cerebrovascular wall both astrocytes and pericytes may be involved in CAA development, a process that includes Aβ deposition and clearance and that may be affected by interaction with locally produced apolipoprotein E (apoE). Although astrocytes are regarded as the major source of apolipoprotein E (apoE) in the brain, also pericytes produce apoE. In this study we compared the apoE production capacity, the effects of apoE on D-Aβ1–40 internalization, D-Aβ1–40 cell surface accumulation and the vulnerability for D-Aβ1–40-induced toxicity of either cell type in order to quantify the relative contributions of astrocytes and pericytes in the various processes that contribute to CAA formation. Strikingly, cultured astrocytes produced only 3–10% of the apoE amounts produced by pericytes. Furthermore, pericytes with the apoE ɛ4 allele produced three times less apoE and were more vulnerable to D-Aβ1–40 treatment than pericytes without an ɛ4 allele. Such relations were not observed with astrocytes in vitro. Both pericytes and astrocytes, however, were protected from Aβ-induced cytotoxicity by high levels of pericyte-derived apoE, but not recombinant apoE. In addition, pericyte-derived apoE dose-dependently decreased both internalization of Aβ and Aβ accumulation at the cell surface in either cell type. The present data suggest that apoE produced by pericytes, rather than astrocyte-produced apoE, modulates Aβ cytotoxicity and Aβ removal near the vasculature in the brain. Furthermore, since apoE production in pericytes is genotype dependent, this may contribute to the apoE genotype-dependent development of CAA in vivo. [Copyright &y& Elsevier]

The major component of senile plaques and vascular amyloid in Alzheimer's disease (AD) brains is the amyloid beta protein (Abeta). Besides Abeta, several other proteins have been identified in these lesions, in particular heparan sulfate proteoglycans (HSPG). However, it is still unclear, what causes the excessive accumulation of HSPG in AD brains. Therefore, we investigated if Abeta may influence production and expression of two major Abeta-associated HSPG species, agrin and glypican-1. When human brain pericytes (HBP) were cultured in the presence of Abeta, protein and mRNA expression of both agrin and glypican-1 were increased and more radioactive sulfate was incorporated in the glycosaminoglycan fraction of Abeta-treated HBP. Furthermore, after Abeta treatment, these HSPG were found in association with the amyloid fibrils attached to the cell membrane, in contrast to the intracellular agrin and glypican-1 staining observed in untreated cells. We conclude that Abeta can modulate the cellular expression of agrin and glypican-1, which may contribute to the accumulation of these HSPG in AD lesions.

Small heat shock proteins Hsp20 and HspB2/B3 co-localize with Abeta deposition in senile plaques and cerebral amyloid angiopathy in Alzheimer's disease brains, respectively. It was the aim of our study to investigate if these and other sHsps bind to wild-type Abeta1-42 or the more toxic Abeta1-40 carrying the 'Dutch' mutation (22Glu-->Gln) (D-Abeta1-40), affect Abeta aggregation and thereby influence Abeta cytotoxicity. Binding affinity between sHsps and Abeta was investigated by surface plasmon resonance. Abeta aggregation was studied by using circular dichroism spectroscopy and electron microscopy. Furthermore, we used cultured cerebrovascular cells to investigate the effects of sHsps on Abeta-mediated cytotoxicity. Hsp20, Hsp27 and alphaB-crystallin, but not HspB2/B3, bound to Abeta (both D-Abeta1-40 and Abeta1-42) and reduced or completely inhibited aggregation of D-Abeta1-40 into mature fibrils but did not affect Abeta1-42 aggregation. Furthermore, these sHsps were effective inhibitors of the cerebrovascular toxicity of Abeta (both D-Abeta1-40 and Abeta1-42) in vitro. Binding affinity of the sHsps to D-Abeta1-40 correlated to the degree of inhibition of Abeta-mediated cytotoxicity and the potential to reduce Abeta beta-sheet and fibril formation. With Abeta1-42, a similar correlation between binding affinity and cytotoxicity was observed, but not with its aggregation state. In conclusion, sHsps may regulate Abeta aggregation and serve as antagonists of the biological action of Abeta, but the extent of their interaction depends on the type of sHsp and Abeta peptide.

Amyloid-beta protein (A beta) deposition in the cerebral vascular walls is one of the key features of Alzheimer's disease and hereditary cerebral hemorrhage with amyloidosis-Dutch type (HCHWA-D). A beta(1-40) carrying the 'Dutch' mutation (HCHWA-D A beta(1-40)) induces pronounced degeneration of cultured human brain pericytes. In this study, we aimed to identify inhibitors of A beta-induced toxicity in human brain pericytes. The toxic effect of HCHWA-D A beta(1-40) on human brain pericytes was inhibited by co-incubation with catalase, but not with superoxide dismutase, glutathione or vitamin E analogue Trolox. Catalase interacts with A beta, both in cell cultures and in cell-free assays, and has a prominent effect on the amount and conformational state of A beta binding to the cell surface of human brain pericytes. This activity of catalase is likely based on its ability to bind and slowly degrade A beta and not by its usual capacity to convert hydrogen peroxide. Our data confirm that assembly of A beta at the cell surface of human brain pericytes is a crucial step in A beta-induced cellular degeneration of human brain pericytes. Inhibition of fibril formation at the cell surface could be an important factor in therapy aimed at reducing cerebral amyloid angiopathy.