Schematic overview of autophagy in mammalian cells. (1) Initiation of macroautophagy (herein, autophagy): An isolation membrane develops at the ER or other endomembrane and encloses cytosolic materials, including damaged organelles. (2) Maturation and completion of an autophagosome: The cytosolic compartments are sequestered in the double-membraned autophagosome. (3) Fusion of the autophagosome with the lysosomes: The outer membrane of the autophagosome fuses with the lysosomal membrane to form an autolysosome. (4) Degradation of intravesicular components within autolysosomes: Internal materials are degraded by various acidic hydrolases, and the degraded monomeric units, such as amino acids and fatty acids, are exported to the cytosol through channels (brown circles) for reuse. (5) Formation of a recycled lysosome: An autophagic lysosome is reformed from an autolysosome.