You would think that once a human died, the body would become things; without the circulation of blood and air, the internal systems would run out quickly. But because of a strange biological peculiarity, there are things like the living dead: living cells, at least, inside a finished, dusty body.
Some cells in the human brain increase in activity after death. These ‘zombie’ cells increase their gene expression and continue to bravely try to do their vital tasks, as if someone forgot to tell them that they are now redundant.
Neurologist Jeffrey Loeb of the University of Illinois and colleagues watched as these cells stubbornly sprouted new tentacles and engaged in work for hours after death.
“Most studies assume that the whole brain stops when the heart stops beating, but that’s not the case,” Loeb said. “Our findings will be needed to interpret research on human brain tissue. We just haven’t quantified these changes so far.”
Much of the information we have about brain disorders such as autism, Alzheimer’s, and schizophrenia comes from experiments performed on brain tissue after death; this approach is central to the search for treatments, as animal models for brain studies often do not translate to us.
Typically, this work is done on tissues from people who died more than 12 hours ago. By comparing gene expression in fresh brain tissue (removed as part of the epilepsy surgery of 20 patients) with aforementioned brain samples from dead people, Loeb and the team found striking differences that were not specific to the brain. age or disease.
They used data on gene expression, which they later corroborated by examining the histology of brain tissue, to understand the specific changes in cell activity over time since death, at room temperature.
Although most gene activity remained stable for the 24 hours documented by the team, the neuronal cells and their gene activity rapidly depleted. Most notable is that glial cells increased gene expression and processes.
Cells come to life after the death of the human brain. (Dr. Jeffrey Loeb / UIC)
While surprising at first, this makes a lot of sense, as glial cells, such as waste-consuming microglia and astrocytes, are put into action when things go wrong. And dying is as “wrong” as living things can come out.
“Getting glial cells to grow after death is not too surprising, as they are inflammatory and their job is to clean things up after brain injuries like oxygen deprivation or stroke,” Loeb said.
The team showed that RNA expressed by genes does not change in itself within 24 hours after death, so any change in their amount must be due to the continuation of biological processes.
“The complete gene expression of newly 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,” they wrote the researchers in their article.
This has huge implications for both past and current studies that use brain tissue to understand diseases that involve immune responses, such as these “zombie” glial cells that swell while uselessly devouring pieces of dying brains.
After 24 hours, however, these cells also succumbed and were no longer distinguishable from the degrading tissue surrounding them.
“Researchers need to consider these genetic and cellular changes 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 that the results of post-mortem brain studies can be better understood. “.
Even in death, biological entities are never completely static.
This research was published in Scientific reports.