Non-Fibrillar β-Amyloid Protein is Associated with Smooth Muscle Cells of Vessel Walls in Alzheimer Disease

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Abstract
Meningeal blood vessels were studied in Alzheimer disease (AD) and control brain specimens obtained from autopsies within 16 hours after death. Serial sections were stained with thioflavine S and Congo red and immunostained for the presence of β-amyloid precursor protein (βPP) and β-protein and for smooth muscle-specific proteins myosin, α-actin, and desmin. Isolated blood vessels were studied by immunoblotting for the presence of βPP, fragments of βPP, and β-protein. The arteries that were strongly immunopositive for β-protein in all layers of the walls were also positive for amyloid fibrils on thioflavine S and Congo red stainings. The focal immunostaining for β-protein in less affected vessels was located in the tunica media in the cytoplasm of smooth muscle cells or formed granules between myocytes. The cytoplasmic β-protein and some of the small deposits present between cells were negative for amyloid fibrils. The vessels isolated from specimens containing β-protein-immunoreactive material contained 3 kD, 4.2-4.5 kD, 8.5-9 kD, and 17.5 kD β-protein-immunoreactive bands. These bands were not found in the samples assessed as β-protein-negative by immunocytochemistry. These data indicate that during formation of amyloid in AD vessel walls, nonfibrillar, monomeric, and oligomeric β-protein accumulate.

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