. Fibrillar amyloid beta-protein mediates the pathologic accumulation of its secreted precursor in human cerebrovascular smooth muscle cells. J Biol Chem. 2000 Mar;275(13):9782-91.

Abstract:

Cerebrovascular deposition of the amyloid b-protein (Ab) is a key pathologic lesion seen in patients with Alzheimer's disease and certain related disorders, including hereditary cerebral hemorrhage with amyloidosis of the Dutch-type (HCHWA-D). The deposition of Ab has pronounced deleterious effects on smooth muscle cells within the cerebral vessel wall. We have previously shown that Ab(1-40) possessing the E22Q HCHWA-D mutation extensively assembles into fibrils on the surface of cultured human cerebrovascular smooth muscle (HCSM) cells. This cell-surface Ab fibril formation induces a series of pathologic responses in cultured HCSM cells, including a marked increase in the levels of cell-associated amyloid b-protein precursor (AbetaPP) and cell death. In the present study, we investigated the relationship between HCSM cell-surface Ab fibril formation and the striking increase in cell-associated AbPP. Time course studies showed that cell-surface HCHWA-D Ab(1-40) fibril formation occurred rapidly, whereas both the increase in cell-associated AbPP and loss of cell viability were delayed responses. Domain analysis using site-specific antibodies indicated that the vast majority of the increase in cell-associated AbPP was secreted AbPP (sAbPP). Localization studies showed that the sAbPP was present on the HCSM cell surface. This result raised the possibility that sAbPP may bind back to HCSM cell-surface fibrils formed by HCHWA-D Ab(1-40). Indeed, binding of biotinylated sAbPP to fibrillar HCHWA-D Ab(1-40) was demonstrated by transmission electron microscopy. Furthermore, solid-phase binding assays showed that biotinylated sAbPP exhibited dose-dependent, saturable binding to fibrillar (but not soluble) HCHWA-D Ab(1-40) with k(d) approximately 28 nM. Exon deletion experiments further defined a fragment of sAbPP (AbPP(18-119)), encoded by AbPP exons 2 and 3, to contain the fibrillar Ab-binding domain. In addition, AbPP(18-119) effectively blocked the cell-surface accumulation of sAbPP and subsequent cell death in HCSM cells treated with pathogenic Ab. Together, these findings could explain the accumulation of AbPP in cerebrovascular Ab deposits observed both in vitro and in vivo and may contribute to the pathologic responses evoked by pathogenic forms of Ab in HCSM cells.

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