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August 11, 2018

Here’s how Stanford scientists measured the speed of death

by John_A

How fast does death move? No, it’s not a riddle, but an actual honest-to-goodness question examined by researchers at Stanford University. For the first time ever, scientists have been able to observe the speed at which death spreads across a cell once the self-destruct so-called “trigger wave” has been initiated. Their conclusion? Death moves at around 30 micrometers per minute.

“Trigger waves are just now being appreciated as a recurring theme in cell regulation,” James Ferrell, a professor of Chemical and Systems Biology and of Biochemistry at Stanford University, told Digital Trends.

For their study, the researchers used cytoplasm, the fluid inside a cell, taken from frog eggs. This was then placed in Teflon tubes several millimeters in length, after which the molecular “death signal” apoptosis process of cell death was initiated. Using a fluorescent technique associated with the activation of apoptosis, the researchers were able to watch the way that the cell’s self-destruction, marked by fluorescence, moved the length of the tube.

“Ideally you’d like to carry out the experiments in real cells,” Ferrell continued. “However there is a problem with that: Most cells are too small to make the distinction [obvious] between a trigger wave, where the wavefront moves with a constant speed, and random walk diffusion, where the farther you go, the slower you go.”

The researchers further backed up their observations by using fluorescence microscopy to study intact frog eggs. Due to the eggs’ opacity, this proved more difficult, but they nonetheless noted a similar ripple of pigmentation change at the egg’s surface as the trigger wave moved through it.

So what did the scientists learn from their research? Namely, that death inside a cell takes place a bit like a group of fans doing the wave in a stadium; as a series of rolling surges in which the self-destruction of one bit of the cell triggers the self-destruction of the next. Similar trigger waves are found in nerve impulses and, on a much larger scale, in the spread of wildfires.

“Trigger waves allow electrical signals to be propagated down axons, and allow waves of calcium to spread through cells, waves of mitosis, and — we now know — of apoptosis,” Ferrell said.

While this might sound of only theoretical interest, it could turn out to be vital information in future medical research, in which we either want dying cells to live (in neurodegenerative diseases) or living cells to die (in cancer). In terms of future work, the researchers hope to look at other “biological contexts” in which these trigger waves occur.

A paper describing the work was recently published in the journal Science.

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