Orexin-A promotes neurite outgrowth and induces activity-regulated cytoskeleton associated protein (Arc) upregulation in SH-SY5Y cells

Current evidence suggests that orexin-A modulates events related to neuronal plasticity such as cell proliferation, neurogenesis, and synaptogenesis. Activity-regulated cytoskeleton associated protein (Arc), is an immediate early gene (IEG) whose transcription and translation are induced by neural activity. The aim of this investigation was to determine whether orexin-A induces neurite outgrowth in SH-SY5Y dopaminergic cells. Furthermore, we will investigate the ability of orexin-A to modify Arc protein content. Detection of orexin receptors and Arc levels was carried out with the western blot technique. To evaluate the number of cells and neurites, the cells were fixed and stained with DAPI to visualize the nuclei and with rhodamine phalloidin to visualize the F-actin filaments by confocal microscopy. Our results indicate that exposure to orexin-A (100 nM for 24 hours) increased the number of cells with longer neurites by 79.6% (215 cells with neurites of 21 to 80 µm) compared to control cells where the most cells (87.8%, 237 cells) had neurites with lengths from 0 to 40 µm. Orexin-A also improved the amount of Arc by 91.5%. This effect was abolished by blocking both receptors (OX1R and OX2R) with specific antagonists. We speculate that orexin A-induced effects on neurite length and Arc may be part of the mechanisms involved in modifying and strengthening synaptic strength in cellular events where orexins have been shown to play a key role, such as synaptogenesis and long-term empowerment.