The 3 stages of autophagy. Illustrated are distinct stages in the process of autophagy. i) Autophagy is initiated by pathways that inactivate mTOR. ii) Autophagosome synthesis involves the coupling of LC3-II to the autophagosome membrane and the formation of double membrane vesicles that sequester cytoplasmic material. iii) The final stage of autophagy, proteolysis, entails the fusion of mature autophagosomes with lysosomes and the release of breakdown products into the cytoplasm.