Apolipoprotein A-I directly interacts with amyloid precursor protein and inhibits A beta aggregation and toxicity.
Amyloid precursor protein (APP) is the source of the neurotoxic amyloid beta (Abeta) peptide associated with Alzheimer's disease. Apolipoprotein A-I (apoA-I), a constituent of high-density lipoprotein complexes, was identified by a yeast two-hybrid system as a strong and specific binding partner of full-length APP (APPfl). This association between apoA-I and APPfl was localized to the extracellular domain of APP (APPextra). Furthermore, the interaction between apoA-I and APPfl was confirmed by coprecipitation using recombinant epitope-tagged APPextra and purified apoA-I. Several functional domains have been identified in APPextra, and we focused on a possible interaction between apoA-1 and the pathologically important Abeta peptide, because APPextra contains the nontransmembrane domain of Abeta. The binding between apoA-I and Abeta was saturable (K(d) = 6 nM), specific, and reversible. APPextra also competed with apoA-I for binding to Abeta. Direct evidence for this interaction was obtained by the formation of an SDS-resistant Abeta-apoA-I complex in polyacrylamide gels. Competitive experiments with apolipoprotein E (isoforms E2 and E4) showed that apoA-I had a higher binding affinity for Abeta. We also found that apoA-I inhibited the beta-sheet formation of Abeta with a mean inhibitory concentration close to that of alpha2-macroglobulin. Finally, we demonstrated that apoA-I attenuated Abeta-induced cytotoxicity. These results suggest apoA-I binds to at least one extracellular domain of APP and has a functional role in controlling Abeta aggregation and toxicity.
Koldamova
R P
RP
Department of Pharmacology, University of Pittsburgh, School of Medicine, Pittsburgh, Pennsylvania 15261, USA.
Lefterov
I M
IM
Lefterova
M I
MI
Lazo
J S
JS
D016229:Amyloid beta-Peptides / Q000037:antagonists & inhibitors* / Q000378:metabolism / Q000633:toxicity*; D016564:Amyloid beta-Protein Precursor / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D016632:Apolipoprotein A-I / Q000378:metabolism* / Q000494:pharmacology*; D004797:Enzyme-Linked Immunosorbent Assay; D005110:Extracellular Space / Q000378:metabolism; D006801:Humans; D016297:Mutagenesis, Site-Directed; D010084:Oxidation-Reduction; D016716:PC12 Cells / Q000187:drug effects / Q000378:metabolism; D017434:Protein Structure, Tertiary / Q000235:genetics; D051381:Rats; D012967:Sodium Dodecyl Sulfate; D013778:Tetrazolium Salts / Q000378:metabolism; D013844:Thiazoles / Q000378:metabolism; D020798:Two-Hybrid System Techniques
D016229:Amyloid beta-Peptides; D016564:Amyloid beta-Protein Precursor; D016632:Apolipoprotein A-I; D013778:Tetrazolium Salts; D013844:Thiazoles; D012967:Sodium Dodecyl Sulfate; C022616:thiazolyl blue