Structure‐Activity Analyses of β‐Amyloid Peptides: Contributions of the β25–35 Region to Aggregation and Neurotoxicity

Abstract

The neurodegeneration of Alzheimer's disease has been theorized to be mediated, at least in part, by insoluble aggregates of 8-amyloid protein that are widely distributed in the form of plaques throughout brain regions affected by the disease. Previous studies by our laboratory and others have demonstrated that the neurotoxicity of 8-amyloid in vitro is dependent upon its spontaneous adoption of an aggregated structure . In this study, we report extensive structure-activity analyses of a series of peptides derived from both the proposed active fragment of 8-amyloid, 825-35, and the full-length protein, 61-42. We examine the effects of amino acid residue deletions and substitutions on the ability of 8amyloid peptides to both form sedimentable aggregates and induce toxicity in cultured hippocampal neurons. We observe that significant levels of peptide aggregation are always associated with significant 6-amyloid-induced neurotoxicity. Further, both N-and C-terminal regions of 825-35 appear to contribute to these processes. In particular, significant disruption of peptide aggregation and toxicity result from alterations in the 833-35 region . In 81-42 peptides, aggregation disruption is evidenced by changes in both electrophoresis profiles and fibril morphology visualized at the light and electron microscope levels . Using circular dichroism analysis in a subset of peptides, we observed classic features of 8-sheet secondary structure in aggregating, toxic 8-amyloid peptides but not in nonaggregating, nontoxic 8-amyloid peptides . Together, these data further define the primary and secondary structures of 8-amyloid that are involved in its in vitro assembly into neurotoxic peptide aggregates and may underlie both its pathological deposition and subsequent degenerative effects in Alzheimer's disease.

Time-Course and Regional Analyses of the Physiopathological Changes Induced after Cerebral Injection of an Amyloid β Fragment in Rats

“…In vivo, the complete elimination of apoptotic cells prevents an inflammatory response, whereas necrosis often results in inflammatory reactions. 48 Moreover, in cell culture models, A␤ [25][26][27][28][29][30][31][32][33][34][35] was reported to induce apoptosis at lower concentrations (5 and 10 mol/L) 5 and necrosis at higher concentrations (20 and 40 mol/L). 49 Oxidative stress, apoptosis, and morphological damage induced by amyloid peptides suggest deficits in endogenous neuroprotective mechanisms.…”

“…4 Structure-activity studies revealed that peptides containing the highly hydrophobic 25-35 region formed stable aggregates and mediated neuronal death by necrosis or apoptosis. 5,6,7 The truncated A␤ 25-35 fragment includes extracellular and intramembrane residues that have been reported to represent an active region of A␤. 8…”

“…4 Structure-activity studies revealed that peptides containing the highly hydrophobic 25-35 region formed stable aggregates and mediated neuronal death by necrosis or apoptosis. 5,6,7 The truncated A␤ [25][26][27][28][29][30][31][32][33][34][35] fragment includes extracellular and intramembrane residues that have been reported to represent an active region of A␤. 8 In vivo, two nontransgenic rodent models of AD have been studied to analyze the molecular, morphological, and behavioral consequences of amyloid toxicity: the infusion of A␤ 1-40/42 protein and the injection of preaggregated A␤ [25][26][27][28][29][30][31][32][33][34][35] peptide.…”

Non-steroidal anti-inflammatory drugs have anti-amyloidogenic effects for Alzheimer's β-amyloid fibrils in vitro

“…The aggregation of Aß and ß-sheet formation are considered to be critical events that render these peptides neurotoxic (Pike et al, 1995). The presence of chronic neuroinflammation also contributes to the protracted degenerative course of AD (McGeer and McGeer, 1995), and it is also common to other neurodegenerative disorders, such as Parkinson's disease and Creutzfelt-Jacob disease (Eikelenboom et al, 2002;Gao et al, 2003).…”

Amyloid beta peptide directly inhibits PKC activation

“…Overproduction of Ah and its deposition into senile plaques are also frequently observed in sporadic AD cases (Ray et al, 1998;Saido, 1998). Moreover, Ah peptides exert neurotoxic effects in various systems (Loo et al, 1993;Mattson et al, 1993;Pike et al, 1995;Waite et al, 1992;Yankner et al, 1990). It is not entirely clear, however, how Ah contributes to the development of AD.…”