Autophagy

The cell's process for breaking down and recycling its own damaged proteins and internal components.

• A membrane engulfs worn-out parts and fuses with the lysosome, an acid-filled compartment full of digestive enzymes.
• It rises during fasting and exercise, when growth signals such as mTOR drop, and declines with age; its mechanism won the 2016 Nobel Prize.
• When it fails, misfolded proteins build up, a feature of Alzheimer's, Parkinson's and Huntington's disease.
• Boosting it is a drug target, but it is hard to measure in living people, and tumours can use it to survive stress.