Optimal neuromuscular performance requires motor neuron phosphagen kinases

Area of Science:

• Neuroscience
• Cellular bioenergetics
• Muscle physiology

Background:

• Phosphagen systems are vital for muscle ATP regeneration during high-intensity activity.
• Their role in motor neurons (MNs) is less understood, despite links to neurological impairments.
• Arginine kinase 1 (ArgK1) is the primary phosphagen kinase.

Purpose of the Study:

• Investigate the role of phosphagen systems in MN energy metabolism and neurotransmission.
• Assess the impact of ArgK1 knockdown on presynaptic energy dynamics and neuronal function.
• Determine the contribution of phosphagens to MN performance under varying activity demands.

Main Methods:

• Knocked down ArgK1 expression in Drosophila larval MNs.
• Utilized fluorescent metabolic probes to analyze presynaptic energy metabolism.
• Conducted performance assays measuring endurance and neurotransmission.
• Employed computational modeling to simulate presynaptic bioenergetics.

Main Results:

• ArgK1 knockdown led to deficits in presynaptic energy metabolism with some glycolytic compensation.
• Neurotransmission deficits, specifically impaired exocytosis, occurred at high firing frequencies (>2x fictive locomotion).
• Endurance tests (Ca2+ pumping, body-wall contractions) showed no deficits.
• Computational models predicted ATP/ADP ratio decline only at high firing frequencies.

Conclusions:

• MNs rely on phosphagen systems for intense energetic demands, similar to muscle fibers.
• The phosphagen system's primary role in MNs appears to be ADP removal near ATP hydrolysis sites.
• Deficits manifest as impaired neurotransmitter release at high activity levels, not reduced endurance.