The serpin-enzyme complex receptor recognizes soluble, nontoxic amyloid-beta peptide but not aggregated, cytotoxic amyloid-beta peptide.
There is now extensive evidence that amyloid-beta peptide is toxic to neurons and that its cytotoxic effects can be attributed to a domain corresponding to amyloid-beta 25-35, GSNKGAIIGLM. We have shown recently that the serine proteinase inhibitor (serpin)-enzyme complex receptor (SEC-R), a receptor initially identified for binding of alpha1-antitrypsin (alpha1-AT) and other serine protease inhibitors, also recognizes the amyloid-beta 25-35 domain. In fact, by recognizing the amyloid-beta 25-35 domain, SEC-R mediates cell surface binding, internalization, and degradation of soluble amyloid-beta peptide. In this study, we examined the possibility that SEC-R mediates the neurotoxic effect of amyloid-beta peptide. A series of peptides based on the sequences of amyloid-beta peptide and alpha1-AT was prepared soluble in dimethyl sulfoxide or insoluble in water and examined in assays for SEC-R binding, for cytotoxicity in neuronal PC12 cells and murine cortical neurons in primary culture, and for aggregation in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis. The results show that amyloid-beta peptide 25-35 and amyloid-beta peptide 1-40 prepared soluble in dimethyl sulfoxide compete for binding to SEC-R, are nontoxic, and migrate as monomers in SDS-PAGE analysis. In contrast, the same peptides aged in water did not compete for binding to SEC-R but were toxic and migrated as aggregates in SDS-PAGE. An all-D-amyloid-beta 25-35 peptide was not recognized at all by SEC-R but retained full toxic/aggregating properties. Using a series of deleted, substituted, and chimeric ambeta/alpha1-AT peptides, toxicity correlated well with aggregation but poorly with SEC-R recognition. In a subclone of PC12 cells which developed resistance to the toxic effect of aggregated amyloid-beta 25-35 there was a 2.5-3-fold increase in the number of SEC-R molecules/cell compared with the parent PC12 cell line. These data show that SEC-R does not mediate the cytotoxic effect of aggregated amyloid-beta peptide. Rather, SEC-R could play a protective role by mediating clearance and catabolism of soluble, monomeric amyloid-beta peptide, if soluble amyloid-beta peptide proves to be an in vivo precursor of the insoluble, toxic peptide.
Boland
K
K
Department of Pediatrics, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Behrens
M
M
Choi
D
D
Manias
K
K
Perlmutter
D H
DH
D000595:Amino Acid Sequence; D016229:Amyloid beta-Peptides / Q000378:metabolism* / Q000633:toxicity; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003603:Cytotoxins / Q000378:metabolism* / Q000633:toxicity; D004305:Dose-Response Relationship, Drug; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009474:Neurons / Q000187:drug effects; D009498:Neurotoxins / Q000378:metabolism* / Q000633:toxicity; D016716:PC12 Cells; D010446:Peptide Fragments / Q000378:metabolism* / Q000633:toxicity; D011485:Protein Binding; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism*; D012995:Solubility
D016229:Amyloid beta-Peptides; D003603:Cytotoxins; D009498:Neurotoxins; D010446:Peptide Fragments; D011956:Receptors, Cell Surface; C074636:amyloid beta-protein (25-35); C064184:serpin-enzyme complex receptor