Toll-like receptor
Once thought as merely the by-products of cellular metabolism, mitochondrial ROS are increasingly viewed as important signaling molecules, whose levels of generation at 11 currently-identified sites vary depending on cellular energy supply and demand. At low levels, mitochondrial ROS are considered to be important for metabolic adaptation as seen in hypoxia. Mitochondrial ROS, stimulated by danger signals such as lysophosphatidylcholine and Toll-like receptor 4 and Toll-like receptor 2 bacterial ligands lipopolysaccharide (LPS) and lipopeptides, are involved in regulating inflammatory response. Finally, high levels of mitochondrial ROS activate apoptosis/autophagy pathways capable of inducing cell death.