What really happens to us after death? Once a person stops breathing, and their heart ceases to pump blood, they're what doctors consider "clinically dead." On a biological level, the eventual decomposition of cells, organs, and brain tissue signal its final and irreversible stages.
But what if that's not actually the end? Two new studies claim that hundreds of genes actually kept expressing—and, in some cases, become more active—after death occurred. This came as a surprise to the researchers, because forensic pathologists have long suspected that gene activity degrades postmortem, which is why their rate of change is sometimes used to calculate time of death.
According to the lead author of both papers, microbiologist Peter Noble of the University of Washington, the discovery of "undead" genes could help to improve the preservation of organs destined for transplantation. The two studies are currently available on the pre-print server bioRxiv, and it's important to note that neither have undergone peer review yet.
Noble says his most recent research was inspired by a three-year-old study published in Forensic Science International that discovered a host of genes that remained active in human cadavers for up to 12 hours after death.
In order to investigate the unwinding of the genetic clock, in these latest studies, the team extracted and measured messenger RNA (mRNA) levels in the tissue of recently deceased mice and zebrafish. Since mRNA plays an important role in gene expression, higher levels of this molecule should indicate more genetic activity.
In one of the studies, Noble and his colleagues were able to describe more than 1,000 genes that stayed "alive" postmortem. A total of 515 mice genes continued to operate for up to two days, while 548 zebrafish genes remained functional for an entire four days after death.
"It's an experiment of curiosity to see what happens when you die," Noble told Science Magazine.
One of the most surprising findings, however, was that hundreds of genes actually fired up—boosting their activity—within the first 24 hours after the animals had died. Noble suspects that many of them might have been suppressed or shut off by a network of other genes when their host was alive, and only after death were they free to "reawaken."
The team also found that many of the genes that persisted postmortem are typically active during embryonic development, which led them to theorize that, on a cellular level, newly developing lifeforms might share a lot in common with degenerating corpses.
Other genes they identified were associated with promoting the growth of cancerous cells. These researchers believe the activation of cancer-related genes postmortem could partly explain why many transplant recipients are at higher risk of developing cancer after receiving a new organ, although this has long been attributed to the immunosuppressive drugs they're typically prescribed. A lot more research still needs to be done.
"Since our results show that the system has not reached equilibrium yet," one of the studies broadly speculates, "it would be interesting to address the following question: what would happen if we arrested the process of dying by providing nutrients and oxygen to tissues? It might be possible for cells to revert back to life or take some interesting path to differentiating into something new or lose differentiation altogether, such as in cancer."
In addition to offering potentially valuable new insights into the expiration of vital transplant organs, the researchers hope their findings can also be used by forensic scientists to more accurately pinpoint time of death, which is apparently harder than it sounds.
"The headline of this study is that we can probably get a lot of information about life by studying death," said Noble.