In the hours after death, certain cells of the human brain are still active. Some cells even they increase their activity and grow to gigantic proportions, according to new research from the University of Illinois in Chicago (USA), recently published in the journal ‘Scientific Reports’.
The UIC researchers analyzed gene expression in fresh brain tissue, which was collected during routine brain surgery, on several occasions after extraction to simulate post-mortem interval and death. They found out that gene expression in some cells actually increased after death.
These ‘zombie genes’, those that increased expression after the postmortem interval, were specific to one type of cell: inflammatory cells called glial cells. The researchers observed that glial cells grow and sprout long appendages in the form of arms for many hours after death.
“That glial cells enlarge after death is not too surprising since they are inflammatory and their job is to clean things up after brain injuries like lack of oxygen or a stroke, “says the doctor. Jeffrey loeb, John S. Garvin Professor and Director of Neurology and Rehabilitation at the UIC School of Medicine and corresponding author of the article.
According to the researcher, what is significant are the implications of this discovery– Most research studies using post-mortem human brain tissues to find potential treatments and cures for disorders such as autism, schizophrenia, and Alzheimer’s disease, do not take into account post-mortem gene expression or its cellular activity.
“Most studies assume that everything in the brain stops when the heart stops beating, but it doesn’t. Our findings will be needed to interpret research on human brain tissues. We just haven’t quantified these changes so far, “he explains.
Loeb and his team noted that the overall pattern of gene expression in human (fresh) brain tissue did not match any of the published reports of postmortem brain gene expression from people without neurological disorders or people with a wide variety of neurological disorders, ranging from autism to Alzheimer’s disease.
“We decided to a mock death experiment observing the expression of all human genes, at time points from 0 to 24 hours, from a large block of brain tissues recently collected, which were left to rest at room temperature to replicate the autopsy, “explains Loeb.
Loeb and his colleagues have a particular advantage when it comes to studying brain tissue. Loeb is director of the UI NeuroRepository, a human brain tissue bank of patients with neurological disorders who have consented to the collection and storage of tissue for research after their death or during standard care surgery to treat disorders such as epilepsy.
For instance, during certain surgeries to treat epilepsy, epileptic brain tissue is removed to help eliminate seizures. Not all tissue is necessary for pathological diagnosis, so some can be used for research. This is the tissue that Loeb and his colleagues analyzed in their research.
They found that about 80 percent of the genes analyzed remained relatively stable for 24 hours; his expression didn’t change much. These included genes often called housekeeping genes They 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 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. The pattern of post-mortem changes peaked around 12 o’clock.
“Our findings don’t mean we should scrap human tissue research programs, it just means that Researchers must take into account these genetic and cellular changes, and reduce the postmortem interval as much as possible to reduce the magnitude of these changes. The good news from our findings is that we now know which genes and cell types are stable, which ones degrade, and which ones increase over timeso that the results of postmortem brain studies can be better understood “, concludes the researcher.