A team of scientists has discovered that, in some brain cells, gene expression increases after death. The results, which are published in the journal Scientific Reports , detail the analysis of several samples of fresh brain tissue obtained from a tissue bank of patients with neurological disorders who have consented to the collection and storage of tissue for research after their use. death or during standard care surgery.
The ‘zombie genes’, those that increased their expression after the post-mortem interval, were specific to a very specific type of cell: glial cells, and the researchers observed that these grew and developed long appendages in the form of arms even many hours after death. ” This fact is not too surprising, since we are talking about inflammatory cells whose job is precisely to ‘clean the house’ after injuries such as a stroke or in situations of lack of oxygen”, explains Jeffrey Loeb, one of the authors of the work and Director of Neurology and Rehabilitation at the University of Illinois School of Medicine at Chicago.
For scientists, this discovery has very relevant implications, since most studies using postmortem human brain tissues to find potential treatments for disorders such as autism, schizophrenia and Alzheimer’s disease do not take into account possible cellular activity or gene expression that occurs after death.
“Most studies assume that everything in the brain stops when the heart stops beating, but it doesn’t,” says Loeb. “Our findings will be necessary to interpret research on human brain tissues. We just haven’t quantified these changes so far. “
A simulated death experiment
The researchers conducted a simulated death experiment observing the expression of all human genes at time intervals of 0 to 24 hours in brain tissue samples obtained thanks to the aforementioned brain tissue bank.
They found that about 80% of the genes analyzed remained relatively stable for 24 hours and their expression did not change much. These included so-called ‘housekeeping genes’, which provide basic cellular functions and are commonly used in research studies to show tissue quality. Another group of genes, which are known to be present in neurons and have been shown to be intricately involved in human brain activity, such as memory, thinking, and seizure activity, were rapidly degraded in the hours after death. These genes are important to researchers studying disorders such as schizophrenia and Alzheimer’s disease.
A third group of genes, the ‘zombie genes’, increased their activity at the same time that the neuronal genes decreased it. Furthermore, the pattern of post-mortem changes peaked around 12 o’clock.
” Our findings do not mean that we should scrap human tissue research programs, it just means that researchers should take into account these genetic and cellular changes, and reduce the post-mortem interval as much as possible to minimize the magnitude of these changes.” Loeb explains. “The good news from our findings is that we now know which genes and cell types are stable, which are degraded, and which increase over time, so the results of postmortem brain studies can be better understood.”
