Abstract
Vesicle-mediated transport is necessary for maintaining cellular homeostasis and proper signaling. The synaptosome-associated protein 23 (SNAP23) is a member of the SNARE protein family and mediates the vesicle docking and membrane fusion steps of secretion during exocytosis. Skeletal muscle has been established as a secretory organ; however, the role of SNAP23 in the context of skeletal muscle development is still unknown. Here, we show that depletion of SNAP23 in C2C12 mouse myoblasts reduces their ability to differentiate into myotubes as a result of premature cell cycle exit and early activation of the myogenic transcriptional program. This effect is rescued when cells are seeded at a high density or when cultured in conditioned medium from wild type cells. Proteomic analysis of collected medium indicates that SNAP23 depletion leads to a misregulation of exocytosis, including decreased secretion of the insulin-like growth factor 1 (IGF1), a critical protein for muscle growth, development, and function. We further demonstrate that treatment of SNAP23-depleted cells with exogenous IGF1 rescues their myogenic capacity. We propose that SNAP23 mediates the secretion of specific proteins, such as IGF1, that are important for achieving proper differentiation of skeletal muscle cells during myogenesis. This work highlights the underappreciated role of skeletal muscle as a secretory organ and contributes to the understanding of factors necessary for myogenesis.