Flow Cytometric Measurement of Cell Organelle Autophagy

The term autophagy, (Type II Apoptosis) is derived from the Greek roots “auto” (self) and “phagy” (eat) and was first coined by De Duve in 1967 to epitomise this type of cell death. The mechanism of organelle autophagy in cells undergoing macro-autophagy (from here on termed autophagy) is poorly understood. Cytoplasm, misfolded protein aggregates, dysfunc‐ tional mitochondria and stressed endoplasmic reticulum (ER) are engulfed by the formation of a double membrane forming an autophagosome [1,2]. The formation of the autophagosome double membrane structure within the cytoplasm is thought to be formed from pre-existing membranes within the cell, although it is unknown whether the Golgi apparatus, endoplasmic reticulum (ER) or mitochondria are used preferentially to form the autophagosome structure [1,2]. During the formation of the autophagosome structure, organelles such as mitochondria, parts of the ER and Golgi apparatus are engulfed by the autophagosome with the final closure of the double membrane structure occurring next. This then fuses with nearby lysosomes, giving rise to an autolysosome, where the intracellular components are degraded by hydrolytic enzymes [1,3-5]. This process generates ATP, which may delay cell death if the cell is under nutrient depleted conditions leading to the survival of the cell. Thus it is unclear whether the process protects or causes diseases such as cancer and neurodegenerative disorders [6,7].