Neurodegeneration induced by beta-amyloid peptides in vitro: the role of peptide assembly state

Abstract

The progressive neurodegeneration of Alzheimer's disease has been hypothesized to be mediated, at least in part, by beta-amyloid protein. A relationship between the aggregation state of beta-amyloid protein and its ability to promote degeneration in vitro has been previously suggested. To evaluate this hypothesis and to define a structure-activity relationship for beta-amyloid, aggregation properties of an overlapping series of synthetic beta-amyloid peptides (beta APs) were investigated and compared with beta AP neurotoxic properties in vitro. Using light microscopy, electrophoresis, and ultracentrifugation assays, we found that few beta APs assembled into aggregates immediately after solubilization, but that over time peptides containing the highly hydrophobic beta 29-35 region formed stable aggregations. In short-term neuronal cultures, toxicity was associated specifically with those beta APs that also exhibited significant aggregation. Further, upon the partial reversal of beta 1-42 aggregation, a concomitant loss of toxicity was observed. A synthetic peptide derived from a different amyloidogenic protein, islet amyloid polypeptide, exhibited aggregation but not toxicity, suggesting that beta AP-induced neurotoxicity in vitro is not a nonspecific reaction to aggregated protein. The correlation between beta AP aggregation and neurotoxicity was also observed in long-term neuronal cultures but not in astrocyte cultures. These data are consistent with the hypothesis that beta-amyloid protein contributes to neurodegeneration in Alzheimer's disease.

Minocycline provides protection against β-amyloid(25-35)-induced alterations of the somatostatin signaling pathway in the rat temporal cortex

“…The experimental conditions were selected according to previous studies demonstrating that they mimic some of the pathological processes in AD brain, including the cognitive deficits (Nitta et al, 1994). This fragment is proposed to be the functional domain of A␤ responsible for its neurotoxic properties (Pike et al, 1993). In the past, the presence of A␤(25-35) in vivo was controversial.…”

Preparation and characterization of toxic Aβ aggregates for structural and functional studies in Alzheimer's disease research

“…A critical challenge in understanding the mechanism of Aβ toxicity, and in the subsequent design of intervention strategies, has been the correlation of a particular aggregate structure or size with biological effects, especially toxicity. Initially, fibrils were reported to be toxic, and inhibition of fibril formation or disruption of fibrils was considered to be a viable strategy for inhibiting Aβ toxicity [62][63][64] . Subsequent studies, using SEC-purified protofibrils and monomers, showed that protofibrils exhibit stronger toxicity than monomeric and fibrillar Aβ 14,20,21 .…”

Interleukin-1β impairs brain derived neurotrophic factor-induced signal transduction

“…Primary cultures of dissociated cerebral cortical neurons were prepared from the brains of embryonic day 18 (E 18) rats as described previously [54]. Cell plated at 2.5 × 10 5 cells/cm 2 were cultured in poly-L-lysine coated six well plates (for western blot analysis) or on 24 well plates (for immunocytochemistry and assays for cell viability) and maintained in serum-free optimal Dulbecco's modified Eagles medium (DMEM) supplemented with B-27 components (Invitrogen, Carlsbad, CA).…”

“…Cultures were maintained for 5-7 days before treatments. Neuronal survival was determined by trypan blue exclusion [54] or using the MTT 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay [30]. The purity of the preparations was checked occasionally using double staining with MAP-2 (for neurons) and GFAP (for astrocytes).…”