Uncoupling of M1 muscarinic receptor/G-protein interaction by amyloid β(1-42)

Area of Science:

• Neuroscience
• Biochemistry
• Molecular Biology

Background:

• Alzheimer's disease (AD) is characterized by β-amyloid (Aβ) overproduction, leading to amyloid deposits and cognitive impairment.
• Previous studies noted muscarinic receptor dysfunction preceding amyloid plaques and cognitive deficits in AD models.
• The precise molecular mechanisms underlying early Aβ-induced receptor dysfunction remain unclear.

Purpose of the Study:

• To investigate the in vitro effects of non-aggregated Aβ(1-42) on muscarinic receptor subtypes.
• To elucidate the mechanisms of Aβ(1-42) interaction with M1 muscarinic receptors and G-protein coupling.
• To correlate findings with early molecular changes in AD transgenic mouse models.

Main Methods:

• Utilized Chinese hamster ovary (CHO) cells expressing M1 muscarinic receptors.
• Assessed binding characteristics of muscarinic ligands (N-methylscopolamine, carbachol) after Aβ(1-42) treatment.
• Measured M1 receptor-stimulated phosphatidylinositol breakdown and G-protein/receptor expression levels.
• Analyzed gene and protein expression of G-proteins in young APPswe/PS1dE9 mice.

Main Results:

• Prolonged (4-day) treatment with 100 nM Aβ(1-42) altered carbachol binding to M1 receptors in CHO cells.
• Aβ(1-42) treatment reduced M1 receptor-stimulated phosphatidylinositol breakdown without causing overt toxicity or affecting receptor/G-protein expression.
• Young APPswe/PS1dE9 mice showed impaired muscarinic receptor-mediated G-protein activation despite normal receptor and G-protein gene/protein expression.

Conclusions:

• Early Aβ(1-42) exposure impairs M1 muscarinic receptor function.
• The primary mechanism involves compromised coupling between the M1 receptor and the G(q/11) G-protein.
• This molecular deficit precedes amyloid deposition and cognitive decline, offering a potential therapeutic target for early AD intervention.