Amyloid beta-protein as a substrate interacts with extracellular matrix to promote neurite outgrowth

Progressive deposition of amyloid beta-protein (A beta) in brain parenchyma and blood vessels is a characteristic feature of Alzheimer disease. Recent evidence suggests that addition of solubilized synthetic A beta to medium may produce toxic or trophic effects on cultured hippocampal neurons. Because soluble A beta may not accumulate in significant quantities in brain, we asked whether immobilized A beta peptide as a substrate alters neurite outgrowth from cultured rat peripheral sensory neurons. This paradigm may closely mimic the conditions in Alzheimer disease brain tissue, in which neurites contact insoluble, extracellular aggregates of beta-amyloid. We detected no detrimental effects of A beta substrate on neurite outgrowth. Rather, A beta in combination with low doses of laminin or fibronectin enhanced neurite out-growth from these neuronal explants. Our results suggest that insoluble A beta in the cerebral neuropil may serve as a neurite-promoting matrix, perhaps explaining the apparent regenerative response of neurites observed around amyloid plaques in Alzheimer disease. Moreover, in concert with the recent discovery of A beta production by cultured neurons, our data suggest that A beta plays a normal physiological role in brain by complexing with the extracellular matrix.