HIF1A and obstructive sleep apnea syndrome: One of the main signaling pathways involved in both OSA patients and animal models in response to hypoxemia is an increase in oxidative stress, which in turn enhances the activity of the hypoxia-inducible factor 1 (HIF-1) transcription factor [22,27,28], as well as the expression of its target genes, including vascular endothelial growth factor (VEGF) [18,29,30] and endothelin-1 (ET-1) [28,31].