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

Abstract

Progressive deposition of amyloid 3-protein In brain, whether A,B has any physiological role is unknown. Studies aimed at elucidating the biological effects of A/3 on the nervous system have yielded equivocal results. Addition of synthetic peptides corresponding to the first 28 or 42 amino acids of the Al3 sequence to culture medium resulted in a dose-dependent effect on survival and neurite outgrowth of rat hippocampal neurons (3, 4). With a similar paradigm, AP-(1-40) peptide was found to be both trophic and toxic to hippocampal neurons, depending on the peptide dose and maturity ofthe neurons in vitro (5). In such systems, increased evidence favors a role of excitatory amino acids in A,B-induced neurotoxicity (6), possibly because A,B destabilizes calcium homeostasis (7). A recent study further suggested that peptide aggregation may enhance A,B toxicity in cultured hippocampal neurons (8). Finally, two reports suggested that transfection of either full-length APP or its C-terminal 100 residues, both ofwhich contain the AP region, into neural cells may result in cell degeneration upon neuronal differentiation (9, 10).Central to many of these studies is the addition of soluble AP3 in relatively high concentrations to culture medium. In one study, acetonitrile and trifluoroacetic acid were used to solubilize A,B before addition to culture medium (5 show that immobilized A,B has no detrimental effect on neurite outgrowth. On the contrary, in the presence of low amounts of extracellular matrix (ECM) components, A,B promotes neurite outgrowth in a dose-dependent manner. MATERIALS AND METHODSPeptides. Six synthetic peptides were used: AP-(1-40),A,B-(1-28), and A,B-(21-37) (all from the human APP sequence) and, as controls, a 40-residue peptide having all A,B amino acids but randomly scrambled (NH2-VIEVLVGE-LDAFDGHVAGFSHDQKGNHVKGGARYMVSIFE), the 37-residue islet amyloid polypeptide (amylin; Peninsula Laboratories), and a 10-residue substance P peptide (Peninsula Laboratories). All peptides were HPLC purified, and the first four peptides were additionally analyzed by mass spectroscopy. All peptides were dissolved in deionized water at a concentration of 1 mg/ml. A sample of AP3 peptide was aggregated before use by dissolving in phosphate-buffered saline at 10 mg/ml, incubating at 37°C for 48 hr, and storing at 4°C for 1 week. The peptide was resuspended in water at 1 mg/ml just before use. On SDS/PAGE, the sample consisted primarily of mono-and dimeric forms, with smaller amounts of tetrameric aggregates. Substrate Preparation. Tissue culture substrates were prepared under sterile conditions by coating 35-mm Petri dishes with a premixed solution consisting of peptide, ECM, or both. All dishes were coated with peptide concentrations ranging from 0.5 to 5.0 pug/cm2. The ECM component con- §To whom reprint requests should be addressed. 4748The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C...

Substrate‐Bound β‐Amyloid Peptides Inhibit Cell Adhesion and Neurite Outgrowth in Primary Neuronal Cultures

“…A similar idea was proposed by Koo et al (1993), who found that low levels of A␤ in combination with ECM proteins such as fibronectin and laminin were able to stimulate neurite outgrowth. For this reason, further studies on the effects of A␤ on ECM are needed.…”

“…Low amounts of A␤1-40 and A␤1-42 (0.1-1.0 ng/well) stimulate neurite outgrowth, whereas higher amounts (Ն3 g/well) inhibit neurite outgrowth. The dose dependence of the A␤ effects may explain why Koo et al (1993) found that neurite outgrowth from rat dorsal root ganglion neurons was stimulated by low amounts of substrate-bound A␤1-40 (0.5-5.0 g/cm 2 ), whereas Fraser et al (1994) reported that larger amounts of substrate-bound A␤ (ϳ1 mg/mm 2 ) inhibited neurite outgrowth from mouse neuroblastoma cells. The view that A␤ can inhibit neurite outgrowth is also supported by the studies of Tolar et al (1998), which showed that when sympathetic neurons were grown on slices of AD amygdala, neurite outgrowth was less in plaque-rich regions of the tissue.…”

“…To date, there have been few studies that have examined the effects of substrate-bound A␤ on neuronal function. Koo et al (1993) reported that A␤ stimulated neurite outgrowth from rat dorsal root ganglion neurons when in substrate-bound form. However, Fraser et al (1994) found that substrate-bound A␤ strongly inhibited neurite outgrowth from mouse neuroblastoma cells.…”

Amyloid-β peptide–Receptor for Advanced Glycation Endproduct interaction elicits neuronal expression of macrophage-colony stimulating factor: A proinflammatory pathway in Alzheimer disease

“…The extracellular deposits of beta-amyloid (A␤), which accumulate in the brain in Alzheimer disease (AD) as a component of the neuritic plaque, bring about neuronal damage and dysfunction (1)(2)(3)(4)(5)(6)(7)(8)(9), and microglial activation through specific interactions with these cells (10)(11)(12)(13)(14). A␤ perturbs cellular properties by multiple mechanisms, including induction of oxidant stress, challenging cellular antioxidant defenses and redirecting protein synthesis.…”

Catalytic antibodies to amyloid β peptide in defense against Alzheimer disease

“…The neurotrophic effects of very low Aβ concentrations in tissue culture have been reported. 36 However, there appears to be no physiological purpose for accumulation of Aβ in the brains of AD patients. Therefore, it is assumed that removal of excess Aβ will be without negative effects.…”