Researchers calculate the speed of death

Researchers at the Stanford University School of Medicine have managed to calculate the speed of cell death. The team found that a continuous “trigger wave” signal travels across cells at 30 micrometres per minute. In the human body 50 billion cells die each day, so how does understanding this process benefit us?

Apoptosis is a genetically programmed form of cell death which is vital for a healthy organism. Cells in the body die by this process constantly in order to benefit the body as a whole. Programmed cell death is known to be a key driving force for the development of a foetus, and as an important way for the body to remove faulty cells or cells which are affected by disease.  When this process goes wrong, the effects on the body can be severe. Too much cell death can lead to neurodegenerative diseases like Alzheimer’s, whereas too little can result in the growth of cancerous tumours. Research which allows us to understand the triggers which cause cells to die, and the speed at which this happens allows the development of treatments which can increase or decrease apoptosis, helping to fight against many incurable diseases.

Programmed cell death is known to be a key driving force for the development of a foetus, and as an important way for the body to remove faulty cells or cells which are affected by disease

This new study, published in Science utilised fluorescent probes and microscopy to visually track the “trigger wave” of death across a cell. Frogs eggs were chosen because they are uniquely large cells, which makes tracking the wave through the cytoplasm much easier. The speed of this wave was found to be surprisingly slow, moving at just 30 micrometres a minute (2mm per hour). The average white blood cell is around 14.5 micrometres across, meaning it would take the wave approximately 29 seconds to travel from one end of the cell to the other. This has given us a brand-new understanding of how apoptosis spreads throughout a cell after it is triggered.

Dr James Ferrell, the lead author of the study, describes the trigger wave phenomenon as a “positive feedback loop”. He explains that one active “death signal molecule” known as a caspase can activate another, allowing the signal to travel without slowing. This explains why the speed of the wave is found to be faster than the rate at which one of these molecules could diffuse through the cell.  Dr Ferrell also remarks that this is just one way the body makes use of these “trigger waves”, despite most biologists being unfamiliar with the concept. He expresses hope that these finding will inform the development of interventions which treat disease.

The average white blood cell is around 14.5 micrometres across, meaning it would take the wave approximately 29 seconds to travel from one end of the cell to the other

With the number of people suffering from illnesses related to cell death still on the rise, research like this is a promising step towards much-needed interventions to stop these diseases in their tracks.