Muscle Exosomes Regulate Local Synthesis at Neuromuscular Junctions

Molecular communication between the motor neuron and the muscle is vital for neuromuscular junction (NMJ) formation and maintenance. Disruption in the structure and function of NMJs is a hallmark of various neurodegenerative processes during both development and pathological events. Still due to the complexity of this process, it is very difficult to elucidate the cellular mechanisms underlying it, generating a keen interest for developing better tools for investigating it. Here we have developed a compartmental microfluidic platform with motor neuron cell bodies on one-side and muscle cells on the other that mimics the physiological environment of the motor unit. In this platform we use various methods to show the formation of functional NMJs and further reveal spatial aspects in the function of the Glial Derived Neurotrophic Factor (GDNF) in motor neurons. Further on, we demonstrate for the first time in-vitro neuromuscular phenotype for ALS and reveal a key role for muscles in neurodegeneration. Our newest data revels that exclusive inhibition of protein synthesis in axons leads a similar dysfunction in NMJs, suggesting motor neurons are strictly dependent on local protein synthesis. Finally, using proteomic analysis and high-resolution live-cell imaging, we characterized the release and retrograde delivery of exosomes from muscles to neurons. Intriguingly, these nano-sized vesicles contain RNA, RNA-processing machinery and translation-related factors suggesting a role for muscles in regulating local protein synthesis at NMJs. We now therefor wish to reveal the mechanism and nature of this process and to further understand its role in conserving the NMJ integrity.