33 | Identification of mTORC1-dependent muscle-specific factors involved in neuromuscular junction maintenance

Paula Aranda-Martínez¹, M. Baraldo², S. Zorzato¹, H. Nolte³, B. Blaauw¹ | ¹Department of Biomedical Sciences, Padua Univ., Italy; ²Biozentrum, Basel Univ., Basel; ³Max Planck Institute for Biology of Ageing, Cologne.

Neuromuscular junction (NMJ) dysfunction contributes to muscle wasting in numerous neuromuscular diseases such as ALS and age-related sarcopenia. Interestingly, in the last few years it has become clear that skeletal muscle fibers play a critical role to maintain a proper connection between nerve and muscle, and inhibition of muscle-specific protein synthesis leads to rapid presynaptic degeneration. mTORC1 is a key regulator of muscle protein homeostasis, and we previously showed that its activity in muscle fibers is essential to maintain NMJ structure and function. To understand the underlying mechanisms, we generated two novel tissue-specific mouse models; musclespecific RiboTag mice that allow us to observe the expression of the ribosomal protein RPL22 exclusively in skeletal muscle, and muscle-specific MetRS mice which permit the labelling and tracking of de novo synthesized muscle proteins. RiboTag mice labelling revealed increased-ribosomal protein RPL22 expression arou nd the NMJ, suggestive of increased ribosome content and, consequently, elevated translational activity. RNA sequencing of RiboTag-derived mRNA identified a strong enrichment of mTORC1 pathway components at the NMJ, suggesting a role for localized mTORC1 signaling. Furthermore, the MetRS model revealed muscle-derived proteins within the sciatic nerve and spinal cord, supporting muscle-to-nerve communication. Using musclespecific RiboTag Raptor knockout and AKT overexpression models, we observed altered translation of NMJ-related genes, reinforcing the regulatory role of mTORC1 in the NMJ translatome. Finally, we are implementing a sciatic nerve crush model to study the dynamics of muscle reinnervation and functional recovery, aiming to elucidate the contribution of mTOR signaling to this regenerative process. Together, our findings highlight the importance of mTORC1-dependent translational control in NMJ maintenance and muscle-nerve interaction.