In the hours after death, certain cells in the human brain are still active. Some even they increase their activity and grow to gigantic proportions, according to new research from the University of Illinois at Chicago.
In this study, the researchers analyzed gene expression in fresh brain tissue, which was collected during routine brain surgery, several times after extraction to simulate postmortem interval and death. Thus, they discovered that gene expression in some cells increased after death.
These “zombie genes”, those that increased expression after the post-mortem interval, were specific to one cell type: inflammatory cells called glial cells. The researchers observed that these cells grow and sprout in the form of arms for many hours after death.
“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 injuries, such as a lack of oxygen or a stroke,” explains Dr. Jeffrey Loeb, one of the study authors.
What caught the attention of the researchers were the implications of that discovery: most research studies use postmortem human brain tissues to find potential treatments and cures for disorders such as autism, schizophrenia or Alzheimer’s, and do not take into account post-mortem gene expression or cellular activity.
Loeb and his team noted that the global pattern of gene expression in fresh human brain tissue did not match any of the published reports on postmortem brain gene expression from people without neurological disorders or from people with a wide variety of neurological disorders, ranging from autism to Alzheimer’s.
In this sense, they decided conduct a mock death experiment, observing the expression of all human genes, in time points from 0 to 24 hours, and from a large block of brain tissue, which were left to rest at room temperature to replicate the autopsy.
Thus, they discovered that, about 80% of the genes analyzed remained relatively stable for 24 hours and his expression didn’t change much. These included genes, often referred to as housekeeping genes that 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 which have been shown to be involved in the activity of the human brain, such as memory or thinking, degraded rapidly in the hours after death. These genes are important to researchers studying disorders such as schizophrenia or Alzheimer’s.
On the other hand, a third group of genes, the “zombie genes”, increased their activity at the same time that neural genes decreased. The pattern of post-mortem changes reached its peak around 12 o’clock.
“Our findings do not mean that we should scrap human tissue research programs, but rather that researchers should take these genetic and cellular changes into account and thus reduce the post-mortem interval as much as possible to reduce the magnitude of those changes. “Says Loeb, who also adds:” The good news is that we now know which genes and cell types are stable, which degrade, and which increase over time, so the results of post-mortem brain studies can be understood best”.