First Observation of Rigor Mortis in Worms Could Help Us Understand Death by Old Age

By Ryan F. Mandelbaum on at

Living creatures do amazing things. They grow toward the sun, build cities, lay eggs, and some even bone. But living things must die, and when they do, they tend to get smelly and mushy pretty quickly. But the moments after death, before decomposition, can be amazing in their own right. Scientists have just learned a bit more about this mysterious time by studying common worms.

Take the ubiquitous C. elegans worm. Scientists observed rigor mortis in these worms for the first time, alongside its telltale “death fluorescence” visible under ultraviolet light. Humans don’t fluoresce, but studying these worms’ death could shed some light on our own demise.

The authors explain that there are three major mysteries on how death by old age occurs. Those are: how old age creates diseases; how those diseases cause death; and how the dying actually happens. “This study yields insights into the two latter issues,” the authors write in the paper published today in Cell Reports.

These researchers have previously spotted some true oddities in the way C. elegans worms die, including the ripple of fluorescent light through their bodies that can last for six hours, reports Scientific American. But there’s more, according to the new paper.

The researchers killed worms of different ages with both heat and a poison. At death, the worms released a wave of calcium, contracted their muscles, and had a wave of decreasing ATP—the molecule, adenosine triphosphate, that the body uses for energy. Past research has suggested that ATP levels decrease as the worms age, but that’s not something demonstrated by this study.

The contraction process looked a whole lot like rigor mortis in humans, the process that happens a few hours after death in which our limbs stiffen. Except in worms, the contraction sets in at the moment of death, and lasts for a few minutes, after which the worm slowly returns to its previous length.

A sped-up view of a worm going through rigor mortis and death fluorescence. Image: Galimov et al (Cell Reports 2018)

And even stranger, modifying one of the worm genes previously linked to longevity (which you can read all about here) allowed them to stave off rigor mortis, though they did die eventually. Researchers are still wondering how one set of proteins, the insulin/IGF-1 pathway, affects the worm’s longevity.

So, what’s going on? Perhaps the calcium release and ATP decrease triggers death, and the actual dying occurs in waves of rigor mortis and fluorescence throughout the worm, killing cells along the way.

As for the difference between worms and mammals, the authors suggest that, while rigor mortis happens a few hours after the brain and heart stop working in mammals, these worms don’t have vascular systems. That means there’s no need to wait.

One researcher not involved with the study thought the paper could offer important insights into death. “This study... found that under normal aging, ATP levels actually do not decline,” Marina Ezcurra, Lecturer in Neuroscience at Queen Mary University of London, told Gizmodo. “Only in animals very close to death were decreases in ATP found, suggesting that decreased ATP levels are the result of aging and pathology, rather than the other way around.”

These are worms, not humans, so it’s not clear yet how one is generalisable to the other. But it seems that dying is a complex process—one that may occur in waves, with similarities spanning all sorts of species. [Cell Reports]

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