Opposite changes in APP processing and human Aβ levels in rats carrying either a protective or a pathogenic APP...

Area of Science:

• Neuroscience
• Genetics
• Molecular Biology

Background:

• Amyloid precursor protein (APP) cleavage by BACE1 initiates the amyloidogenic pathway, producing Amyloid-beta (Aβ), a hallmark of Alzheimer's disease (AD).
• Conversely, α-secretase initiates the non-amyloidogenic pathway, preventing Aβ production.
• Specific APP mutations are linked to familial AD, while others, like the Icelandic mutation near the BACE1 site, confer protection against sporadic dementia, highlighting APP's central role in neurodegenerative diseases.

Purpose of the Study:

• To investigate the protective and pathogenic mechanisms of APP processing in dementia.
• To elucidate the impact of specific APP mutations on APP metabolic pathways and cognitive function.

Main Methods:

• Generation of knock-in rat models carrying either the protective Icelandic (App) or the pathogenic Swedish (App) mutation.
• Analysis of APP cleavage by BACE1 (β-secretase) and α-secretase in the generated rat models.
• Quantification of amyloidogenic and non-amyloidogenic APP metabolites.

Main Results:

• In App rats, α-cleavage of APP is favored over β-processing, leading to increased non-amyloidogenic and decreased amyloidogenic metabolites.
• The pathogenic Swedish mutation (App) induced the reverse shift in APP processing.
• These opposing alterations in APP β/α-processing suggest that dementia protection and pathogenesis depend on the balance of APP metabolism, rather than solely on Aβ levels.

Conclusions:

• The study demonstrates that the modulation of APP β/α-processing by specific mutations significantly influences dementia risk and pathogenesis.
• Protection from dementia and cognitive aging may be mediated by distinct but related alterations in APP metabolism.
• These findings underscore the complex role of APP processing in neurodegeneration and cognitive decline.