NFE2L2 and obstructive sleep apnea syndrome: Presently, the cause of a significant, CPAP-reversible increase in extracellular/plasma CySS, glutamate, as well as of intracellular GSH with OSA remains unclear, but may involve a common adaptive mechanism, given the correlation between CySS and glutamate as GSH precursors: As a major regulator of antioxidative defense and survival pathways, the transcription factors nuclear factor erythroid 2-related factor 2 (NFE2L2, NRF2) is effectively activated (stabilized and translocated) through hypoxia and/or oxidative or nitrosative stress, even in large tissues like skeletal muscle [57,58,59].