Traces of HERV infection in ancient humans, still active while producing proteins
Viruses such as COVID-19 virus, flu virus, and cold virus feel very annoying and uncomfortable. However, a large part of our body is already made up of viruses. 8% of the human genome (the total amount of genes) is a virus. These are ‘human endogenous retroviruses (HERVs)’ left behind by our ancestors millions of years ago from experiencing infectious diseases.
According to a new study recently published by a research team from the Department of Genetics at Tufts University in the United States, traces of the pandemic that occurred in the ancestors are still active in the body of healthy people.
Viruses have become part of the human genome in a unique way of replication. Like today’s HIV virus, ancient retroviruses inserted their genetic material into the host’s genome to replicate themselves. These viral genetic materials are usually not passed on to the next generation, but some ancient retroviruses have acquired the ability to infect reproductive cells, such as eggs and sperm.
Transmission of retroviral DNA to human descendants through infected germ cells. With their cleverness in targeting germ cells, retroviruses have been entwined with the human genome for millions of years, and are still engraved in the human body to this day.
Viruses insert their genomes into the host’s body in the form of ‘proviruses’ (cells that stay in the host cell and do no harm). There are regarding 30 types of retroviruses and more than 60,000 proviruses that have entered the human body. This shows the history of infectious diseases that mankind has suffered in the course of evolution.
It is a proven fact that retroviral genes are active in diseased tissues such as tumors. In addition, the Tufts University team confirmed whether the virus was active in healthy tissues. The research team focused on HML-2, which is the most active among retroviruses. HML-2, a virus that went extinct 5 million years ago, now remains partially within the human genome, retaining its ability to make viral proteins.
The team examined the genetic material of 14,000 whole-body tissue samples and found 37 activated HML-2 proviruses. Not only are traces of ancient viruses still left in the human genome, but they are also producing proteins in the body of normal healthy people.
Whether the genetic remnants of these viruses directly cause disease in humans is still under investigation. The research team discovered HML-2 particles in cancer cells and is also confirming the association with ALS, multiple sclerosis, and schizophrenia. However, since it is also present in healthy tissues, the association with disease may not be significant.
This means that retroviral genes or proteins cannot be good targets for drugs. In the meantime, retroviruses have been studied as targets for various potential drugs. Conversely, the research team is also studying aspects of retroviruses that are beneficial to humans.
