How long the brain functions after death? What cells are responsible for that? Scientists have discovered that the human brain can function for more than 10 minutes after the body has died. But recently studies have shown that some genes in the brain can become active after the death of the human body. After death brain cells are still active and some cells even increase their activity and grow gigantically, according to new research from the University of Illinois Chicago.
In March 2021, news came out that a new study revealed the cell activity after death and the genes that may be responsible for such activity are termed to be ‘zombie genes’. Dr Jeffery Loeb, John S. Garvin professor and team proposed their findings and suggested that the brain do not stop functioning even the heart stops beating. They said that they have not quantified the research and the changes until now, but they explained certain aspects.
They explained that these zombie genes are inflammatory cells called glial cells. Glial cells consists of microglia and astrocytes. They are a part of nervous system but these cells do not transmit or receives signals, instead they help other brain cells binding neurons together and help them function. Glial cells enlarge after death. The glial cells are represented as clean up crew after the brain injury or brain disease like oxygen deprivation or stroke, so the scientists
Jeffrey Loeb (Photo: Jenny Fontaine/UIC)
expected the glial cells/genes to remain active.
For a majority of neuropsychiatric disorders such as Alzheimer’s disease, Autism, and Schizophrenia, only post mortem tissues are available. So they examined the fidelity of overall gene expression between fresh and post mortem human brain tissues for a number of brain disorders.
It was found that 1427 genes could be clustered. A cluster of 317 declining genes was predicted to be of neuronal cells and strongly overlapped with the activity dependent ( AD genes) . A second cluster of 474 genes was predicted to be glial cells, including astrocytes and microglia. Eventually, as the neuronal cell cluster swiftly fell, there was a reciprocal increase in the expression of the glial cell cluster. 80% genes were the neuronal while 20% consisted of the glial. Those neuronal were found stable over time, while the glial zombie genes peaked their increased activity approximately after 12 hours. The glial cells are responsible for taking care of damaged brain tissues .The cells for memory and other processes are degraded quickly and significantly.
The tissue used by Loeb and his team in this new study came from patients with epilepsy undergoing surgery to reduce seizures. This allowed the scientists to investigate the changes in the brain tissue gene expression from the moment of collection.
In 2016, a study had shown similar effects in animals showing more than 1000 genes to be active even after death, some of which arose 24 hours after death. This was at a university in Washington that they studied two lab animals mice and zebrafish to look for the genetic activity. They analysed the mRNA of both the animals and found the activity of 1063 genes. There was genetic activity from half hour upto 96 hours after death. The more mRNA will be the more active genes it will be. Some genes were also found to be active upto 4 days post mortem. Some genes did not only turn on, they ramped up including genes involving immunity, inflammation, stress and cancer.
Hence these studies have certain practical uses such as it can be help for forensic researchers tell the precise time of death. It is also better understood whether transplanted organs are susceptible to cancer due to activation of genes.
Loeb said that their findings are the route to know which genes and cell types are stable or exhibit degradative activity or which can increase over time by the post mortem brain studies. Further studies are still under progress.
Department of Biochemistry and Biotechnology
St. Xavier’s College