title: Homocysteic acid induces intraneuronal accumulation of neurotoxic Abeta42: implications for the pathogenesis of Alzheimer's disease.
abstract: The causes of neuronal dysfunction and degeneration in Alzheimer's disease (AD) are not fully understood, but increased production of neurotoxic forms of amyloid beta-peptide-42 (Abeta42) seems of major importance. Large extracellular deposits of aggregated Abeta42 (plaques) is a diagnostic feature of AD, but Abeta42 may be particularly cytotoxic when it accumulates inside neurons. The factors that may promote the intracellular accumulation of Abeta42 in AD are unknown, but recent findings suggest that individuals with elevated homocysteine levels are at increased risk for AD. We show that homocysteic acid (HA), an oxidized metabolite of homocysteine, induces intraneuronal accumulation of a Abeta42 that is associated with cytotoxicity. The neurotoxicity of HA can be attenuated by an inhibitor of gamma-secretase, the enzyme activity that generates Abeta42, suggesting a key role for intracellular Abeta42 accumulation in the neurotoxic action of HA. Concentrations of HA in cerebrospinal fluid (CSF) were similar in AD and control subjects. CSF homocysteine levels were elevated significantly in AD patients, however, and homocysteine exacerbated HA-induced neurotoxicity, suggesting a role for HA in the pathogenic action of elevated homocysteine levels in AD. These findings suggest that the intracellular accumulation of Abeta42 plays a role in the neurotoxic action of HA, and suggest a potential therapeutic benefit of agents that modify the production and neurotoxic actions of HA and homocysteine.
authors.affiliation: Saga Women's Junior College, Honjyou Town, Japan. hasegawa@saga-wjc.ac.jp
authors.forename: Tohru
authors.initials: T
authors.lastname: Hasegawa
authors.forename: Wataru
authors.initials: W
authors.lastname: Ukai
authors.forename: Dong-Gyu
authors.initials: DG
authors.lastname: Jo
authors.forename: Xiangru
authors.initials: X
authors.lastname: Xu
authors.forename: Mark P
authors.initials: MP
authors.lastname: Mattson
authors.forename: Masaya
authors.initials: M
authors.lastname: Nakagawa
authors.forename: Wataru
authors.initials: W
authors.lastname: Araki
authors.forename: Toshikazu
authors.initials: T
authors.lastname: Saito
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Yamada
mesh_terms: D000544:Alzheimer Disease / Q000097:blood / Q000134:cerebrospinal fluid; D053829:Amyloid Precursor Protein Secretases; D016229:Amyloid beta-Peptides / Q000378:metabolism*; D000818:Animals; D016282:Aspartic Acid Endopeptidases / Q000187:drug effects / Q000378:metabolism; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D010450:Endopeptidases; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006710:Homocysteine / Q000031:analogs & derivatives* / Q000097:blood / Q000134:cerebrospinal fluid / Q000378:metabolism*; D006801:Humans; D002479:Inclusion Bodies / Q000378:metabolism* / Q000473:pathology; D009474:Neurons / Q000378:metabolism* / Q000473:pathology; D010446:Peptide Fragments / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar
chemical_list: D016229:Amyloid beta-Peptides; D004791:Enzyme Inhibitors; D010446:Peptide Fragments; C075222:amyloid beta-protein (1-42); D006710:Homocysteine; C007956:homocysteic acid; D053829:Amyloid Precursor Protein Secretases; D010450:Endopeptidases; D016282:Aspartic Acid Endopeptidases; C509280:BACE1 protein, human