Functions as a negative feedback regulator of TOR function. Highly expressed in muscle-enriched tissues (at protein level). Up-regulated by reactive oxygen species/ROS generated, for instance, upon chronic TOR signaling activation. Sesn-null flies do not exhibit developmental abnormalities. However, fat bodies from third-instar larvae contain more lipids and adults also contain more triglycerides. Flies heart function is compromised with arrhythmia and decreased heart rate. Skeletal muscle undergo accelerated age-related degeneration. Belongs to the sestrin family.