(174n) Neuronal Innervation Regulates the Secretion of Neurotrophic Myokines and Exosomes from Skeletal Muscle

Skeletal muscles are well known for enabling voluntary movement, yet they also crucially stabilize internal homeostasis and the functions of organs throughout the body. Skeletal muscles secrete a variety of peptides and cytokines, named myokines, which affect cells through autocrine, paracrine, and endocrine actions. Moreover, muscles produce extracellular vesicles such as exosomes, which hold promise in alleviating neurodegenerative conditions, Alzheimer's Disease included.

There is increasing evidence suggesting that individuals with muscular dystrophy and other neuromuscular disorders often suffer from issues that affect multiple organs, the immune system, and cognitive processes. These health concerns may stem from the altered secretion patterns of myokines and exosomes when neuromuscular junctions are damaged. Nonetheless, the precise processes at play remain elusive. Particularly in diseases featuring nerve damage, one pivotal question emerges: What role do motor neuron connections and activity play in the regulation of muscle secreting behavior?

Our research proposes that the connections and activity of neurons are crucial in determining the release and functional impact of myokines and exosomes secreted by muscles. We engineered a two-dimensional muscle construct on both flat and micro-grooved polymer substrates to manipulate the extent of neural connections and muscular efficacy. Neural stem cells were then differentiated into motor neurons directly atop the muscle layer, prompting the formation of neuromuscular junctions. We evaluated how such neural interaction influences muscle contractions, the expression of genes linked to myokines, the secretion of myokines, and the release of exosomes. Furthermore, we cataloged the miRNAs within exosomes sourced from both neuron-absent and neuron-innervated muscle tissue, exploring their impact on neural growth. Additionally, we explored how these muscle-derived factors promote the development, intercellular vesicle transport, and firing activity of cultured primary hippocampal neurons. Summarily, our investigation highlights the vital role of neuronal innervation in the modulation of skeletal muscle secretions, generating neuro-supportive myokines and exosomes with significant ramifications for in vitro nervous system cultures.