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You would think that once a human died, the body would have finished doing things; without blood circulation and air, the internal systems would be quickly exhausted. But due to an odd quirk of biology, there are things like the living dead – living cells, at least, in a made and dusted body.
Some human brain cells actually increase their activity after we die. These “zombie” cells speed up their gene expression and valiantly continue to try to perform their vital tasks, as if someone forgot to tell them that they are now redundant.
University of Illinois neurologist Jeffrey Loeb and colleagues observed that these cells stubbornly sprouted new tentacles and devoted themselves to household chores for hours after death.
“Most studies assume that everything in the brain shuts down when the heart stops beating, but it doesn’t,” Loeb said. “Our findings will be needed to interpret human brain tissue research. We simply haven’t quantified these changes so far.”
Most of the information we have about brain disorders like autism, Alzheimer’s disease and schizophrenia comes from experiments done on brain tissue after death; this approach is essential in finding treatments, as animal models for brain studies often fail to be translated to us.
Usually, this work is done on tissue from people who died more than 12 hours ago. By comparing gene expression in fresh brain tissue (taken as part of epilepsy surgery in 20 patients) to the aforementioned brain samples from deceased people, Loeb and his team found striking differences that did not exist. were not specific to age or disease.
They used data on gene expression, which they then corroborated by examining the histology of brain tissue, to understand changes in cell-specific activity over time since death, at room temperature.
While most gene activity remained stable for the 24 hours documented by the team, neural cells and their gene activity quickly depleted. Most notable however, the glial cells increased gene expression and processes.
Cells come to life after the human brain dies. (Dr Jeffrey Loeb / UIC)
While surprising at first, it actually makes a lot of sense, given that glial cells, such as waste-eating microglia and astrocytes, are called upon to act when things go wrong. And dying is about as “bad” as living things can go.
“The fact that glial cells enlarge after death is not too surprising given that they are inflammatory and their job is to clean things up after brain damage like oxygen deprivation or a stroke.” , Loeb said.
The team then demonstrated that the RNA expressed by genes does not change itself within 24 hours of death, so any change in its amount must indeed be due to continuing biological processes.
“Complete gene expression of freshly isolated human brain samples allows an unprecedented view of the genomic complexity of the human brain, due to the preservation of so many different transcripts that are no longer present in postmortem tissues,” wrote the researchers in their article.
This has huge implications for past and present studies using brain tissue to understand diseases that involve immune responses – such as those “ zombie ” glia cells that swell as they needlessly devour fragments of surrounding dying brains. .
However, after 24 hours, these cells also succumbed and were no longer distinguishable from the degrading tissue around them.
“Researchers need to take these genetic and cellular changes into account, and reduce the post-mortem interval as much as possible to reduce the magnitude of these changes,” Loeb explained.
“The good news from our findings is that we now know which genes and cell types are stable, which degrade and which increase over time, so the results of postmortem brain studies can be better understood. “
Even in death, we biological entities are never entirely static.
This research was published in Scientific reports.
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