M1 muscarinic receptor modulation drives sex-specific alterations of Alzheimer's pathophysiology in APPswe/PSEN1ΔE9 mice.

Alzheimer's disease (AD) is a neurodegenerative disorder marked by cognitive decline, where females account for 60% of diagnosed cases. AD is featured by β-amyloid deposition, which influences the activity of M1 muscarinic acetylcholine receptors (M1 mAChRs) that are essential for memory and learning. We previously demonstrated that VU0486846, a M1 mAChR positive allosteric modulator, improves cognitive function in AD mice by ameliorating β-amyloid pathology. However, it remains unclear how changes in M1 mAChR signaling and subcellular localization in AD brain influences its mechanism and how this differs between sexes. Nine-month-old male and female APPswe/PSEN1ΔE9 (APP/PS1) and wild-type mice were treated with VU0486846 (10 mg/kg/day) or vehicle via drinking water for 8 weeks. Elevated extracellular signal-regulated kinase 1/2 signaling, a plausible driver for β-amyloid pathology, was observed in female but not male APP/PS1 mice cortices, whereas VU0486846 mitigated this change. Additionally, VU0486846 enhanced the phosphorylation of the neuronal transcription factor cAMP response element-binding protein and increased the level of c-Fos, which regulate neuronal survival, in female wild-type and APP/PS1 mice only. In contrast, only male APP/PS1 mice exhibited increased levels of p62/SQSTM1 and decreased glycogen synthase kinase-3β activity, indicative of impaired autophagic flux, a change that was ameliorated by VU0486846 treatment. In subcellular fractions obtained from mice cortices, VU0486846 only increased cytosolic M1 mAChR level in female wild-type and APP/PS1 mice but not in males. Our findings indicate that M1 mAChR signaling is disrupted in APP/PS1 mice in a sex-dependent manner. VU0486846 enhances prosurvival signaling in females, potentially by increasing the cytosolic pool of M1 mAChRs, while modulating autophagy pathways in males, highlighting a sex-specific mechanism of action and underscoring its therapeutic potential. SIGNIFICANCE STATEMENT: The study highlights the sex-specific role of M1 muscarinic acetylcholine receptor (M1 mAChR) in Alzheimer's disease (AD) pathophysiology, providing evidence that the ability of M1 mAChR positive allosteric modulation to alleviate β-amyloid pathology occurs through distinct mechanisms. It rescues neuronal activity in females, which could be linked to enhanced cytosolic receptor pooling, while restoring autophagic flux in males. The study also reinforces the therapeutic potential of M1 mAChR positive allosteric modulators and supports the development of sex-tailored interventions for AD.