If you were starving on a desert island, you might choose to eat your left arm first to preserve your dominant hand, assuming that like most people you’re right handed. Similarly, starving cells can decide which organelles to degrade when they need to recycle nutrients. New research shows that mitochondria, which are like mini-powerhouses in the cell, can protect themselves from being cannibalised by their own cells. Cells regularly cannibalise their own organelles in a process known as autophagy. A European research team led by Professor Luca Scorrano published the research in Nature Cell Biology. They saw that mitochondria avoid being degraded during cellular autophagy by fusing together in an elongated shape. This helps cells survive periods of starvation because the elongated mitochondria can continue to produce energy.
Cellular autophagy is used by cells to break down their own organelles and recycle them into nutrients. The organelles are surrounded by a membrane and eventually broken down by enzymes in lysosomes. Lysosomes are the recycling plants of the cell which work to make new building blocks from used components of cells, and even the debris from micro-organisms killed by our immune systems. The cell’s own organelles are recycled as part of regular maintenance, but autophagy can also be activated when cells are deprived of nutrients.
Scorrano’s team found that mitochondria can avoid getting degraded by autophagy that has been triggered by starvation. These organelles are best known for their role in energy production, but they have other important jobs including regulating programmed cell death. During autophagy it’s apparently their energy production capability that the cells need to preserve. The elongated mitochondria that Scorrano’s team observed avoiding autophagy produced energy at an increased rate. When the researchers blocked mitochondria from elongating, the cells ran out of energy and died. This means that for cells to survive starvation their mitochondria have to be able to elongate and avoid autophagy so that the cells don’t run out of energy.
This research shows that mitochondria can change their shape to escape being eaten by their own cells, and keep on producing energy. It’s another chapter in the amazing lives of mitochondria, and explains how cells survive when they’re starving. Starvation is a scary prospect, but our cells are programmed to cannibalise themselves selectively – they’re survivors.
Gomes L.C., Di Benedetto G., Scorrano L. (2011). During autophagy mitochondria elongate, are spared from degradation and maintain cell viability. Nature Cell Biology Advanced Online Publication 10th April 2011.