Toxic Amyloid-β42 Conformer May Accelerate the Onset of Alzheimer's Disease in the Preclinical Stage

APP Knock-In Mice Produce E22P-Aβ Exhibiting an Alzheimer's Disease-like Phenotype with Dysregulation of Hypoxia-Inducible Factor Expression

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that requires further pathological elucidation to establish effective treatment strategies. We previously showed that amyloid β (Aβ) toxic conformer with a turn at positions 22-23 is essential for forming highly toxic oligomers. In the present study, we evaluated phenotypic changes with aging in AD model AppNL-P-F/NL-P-F (NL-P-F) mice with Swedish mutation (NL), Iberian mutation (F), and mutation (P) overproducing E22P-Aβ, a mimic of toxic conformer utilizing the knock-in technique. Furthermore, the role of the toxic conformer in AD pathology was investigated. NL-P-F mice produced soluble toxic conformers from an early age. They showed impaired synaptic plasticity, glial cell activation, and cognitive decline, followed by the accumulation of Aβ plaques and tau hyperphosphorylation. In addition, the protein expression of hypoxia-inducible factor (HIF)-1α was increased, and gene expression of HIF-3α was decreased in NL-P-F mice. HIF dysregulation due to the production of soluble toxic conformers may be involved in AD pathology in NL-P-F mice. This study could reveal the role of a highly toxic Aβ on AD pathogenesis, thereby contributing to the development of a novel therapeutic strategy targeting the toxic conformer.

Structural basis of the 24B3 antibody against the toxic conformer of amyloid β with a turn at positions 22 and 23

Amyloid β-protein (Aβ) oligomers are involved in the early stages of Alzheimer's disease (AD) and antibodies against these toxic oligomers could be useful for accurate diagnosis of AD. We identified the toxic conformer of Aβ42 with a turn at positions 22/23, which has a propensity to form toxic oligomers. The antibody 24B3, developed by immunization of a toxic conformer surrogate E22P-Aβ9-35 in mice, was found to be useful for AD diagnosis using human cerebrospinal fluid (CSF). However, it is not known how 24B3 recognizes the toxic conformation of wild-type Aβ in CSF. Here, we report the crystal structure of 24B3 Fab complexed with E22P-Aβ11-34, whose residues 16-26 were observed in electron densities, suggesting that the residues comprising the toxic turn at positions 22/23 were recognized by 24B3. Since 24B3 bound only to Aβ42 aggregates, several conformationally restricted analogs of Aβ42 with an intramolecular disulfide bond to mimic the conformation of toxic Aβ42 aggregates were screened by enzyme immunoassay. As a result, only F19C,A30homoC-SS-Aβ42 (1) bound significantly to 24B3. These data provide a structural basis for its low affinity to the Aβ42 monomer and selectivity for its aggregate form.