There is really life after death! But not as you might imagine. Like a machine whose components would take longer to shut down than others, the cells inside a dead body maintain biochemical activity for several hours after death. This is shown by an international team in a study published in the journal Nature Communication in mid-February 2018. “We observed active processes of certain genes after death, that is, an activity at the Genetic transcription mechanisms persist in some cells several hours after death,” says lead author Roderic Guigó, professor of computational biology at the Institute of Science and Technology in Barcelona, Spain.
The observation of these post mortem cellular reactions was made from 36 different cell types taken from 540 deceased donors. The researchers studied the expression of certain genes in each tissue (brain, liver, kidneys, lungs, blood, etc.). Specifically, the genetic transcription mechanisms by which DNA directs the cell to synthesize particular proteins; biochemical orders that pass through the messenger RNA, a molecule very close to the DNA which is the copy of a portion of the genome intended to transmit the genetic message. It is this mRNA that continues to be transcribed into certain tissues after death. In short, the death of an individual does not coincide exactly with the death of the whole organism.
“Some parts of the body are still alive when death is pronounced,” says Roderic Guigó.
What does it mean? What is the difference between the death of an individual and the death of the parts that make up the individual? Am I my liver, my stomach, my kidney? All these organs continue to function after death.They are alive, but I am dead. In truth, life can be defined as the coordinated action of all its parts, and death as the end of this coordination.
— Roderic Guigó
More surprisingly, if the activity of certain genes decreases – those associated with the immune response or metabolism — it can be stimulated in others. The expression of genes associated with stress, for example, was stronger after death during the study. The researchers suggest that it could be a compensatory effect of the body that, in a way, did not completely give up on the idea of living.
Thanks to computer modeling and machine learning techniques, this work enabled the team to develop an algorithm that accurately assesses the time of death. Thanks to the measurement of 399 body expression variations, the software was able to determine the time of death of 129 people. Indeed, for each cell type, it was possible to establish a timed report of post mortem genetic activity. The greatest variations of activity have been observed between 7 and 14 hours after death : some genes “go out” when others to the contrary “activate”.
For Roderic Guigó, a more in-depth observation of these phenomena could even make it possible to establish the cause of death from models of variation in gene expression. “One can imagine a future where laboratories will be equipped with artificial intelligence using gene expression and other contextual information to determine the time and cause of death,” says Ilias Tagkopoulos, Computer Science researcher at the University of California Davis, who did not participate in the study. The program developed by Prof. Guigó’s team, however, remains an experimental tool to date. But in the 24 hours following death, the analysis of gene expressions would prove in any case more precise than that of bacteria whose activity varies little over this period of time. This work could also provide a better understanding of the reactions following an organ transplant, according to the researchers. This residual gene expression may have implications for post-transplant cancer occurrence.
In 2017, another team had already shown in mouse and zebra that genetic activity persisted or even woke up to 4 days after death; a story of “zombie genes”.