M₁ and M₂ mAChRs activate PDK1 and regulate PKC βI and ε and the exocytotic apparatus at the NMJ

Area of Science:

• Neuroscience
• Molecular Biology
• Cellular Signaling

Background:

• Neuromuscular junctions (NMJ) control acetylcholine release via muscarinic acetylcholine autoreceptors (mAChR).
• The role of protein kinase C (PKC) in mAChR-mediated neurotransmission is not fully understood.
• Investigating the interaction between mAChRs and PKC isoforms is crucial for understanding cholinergic exocytosis.

Purpose of the Study:

• To determine if M1 and M2 mAChRs recruit and modulate PKCβI and PKCε isoforms.
• To elucidate the role of PDK1 in priming PKC isoforms at the presynaptic terminal.
• To understand how mAChRs influence PKC activity and translocation in neurotransmission.

Main Methods:

• Activation of M1 and M2 mAChRs.
• Analysis of PDK1 activation and PKC isoform priming.
• Assessment of PKC translocation and phosphorylation of neurosecretion targets (Munc18-1, SNAP-25, MARCKS).

Main Results:

• Both M1 and M2 mAChRs activate PDK1, priming presynaptic PKCβI and PKCε.
• M1 mAChR recruits primed PKCs, promoting phosphorylation of Munc18-1, SNAP-25, and MARCKS.
• M2 mAChR downregulates PKCε via PKA, inhibiting Munc18-1 synthesis and PKC phosphorylation.

Conclusions:

• A co-dependent balance between M1 and M2 mAChRs orchestrates presynaptic PKC activity.
• This balance regulates the SNARE-SM mechanism of acetylcholine release at the NMJ.
• The findings provide molecular insights into NMJ function and identify potential therapeutic targets.