Part 2 of 2 Parts (Please read Part 1 first)
The researchers also checked the level of tau proteins in the blood samples. It can accumulate in tangles in neurodegenerative diseases such as Alzheimer. The team also measured neurofilaments light chain (NfL) which is a protein that can increase when parts of the neurons in the brain called axons are injured. A fourth protein that was studied was glial fibrillary acidic protein (GFAP) which is involved in the development of astrocytes. Astrocytes are star-shaped cells in the brain that clear waste out of the cerebrospinal fluid and protect the brain from harmful substances. When GFAP increases, this usually means that the cell is working harder to clear out waste.
The researchers discovered that NfL, GFAP and one of the types of amyloid protein were also significantly higher after the Russian cosmonauts returned from the ISS than they were before they had been launched into orbit. The levels of these selected proteins increased one day and one week after the end of their orbital mission, but the levels started to decrease by three weeks after their return to Earth. They did not return preflight levels.
On the other hand, the study revealed that the total level of tau protein first increased slightly and then decreased below the initial level before the space mission. Zetterberg concluded that this might be because tau protein is typically cleared more rapidly from cells than the other biomarkers. Or it could be related to the test that is currently used to measure levels of tau. He said that the current test is not as good as it is for the other biomarkers.
This research did not determine exactly what caused the increase in these proteins, but the researchers believe that it could be related to the effect of microgravity on the waste elimination system in the brains of the cosmonauts.
Zetterberg said, “It looks like this system might have been dysfunctional. When you get back on Earth, then it starts to work again, and then all these proteins come out in the bloodstream and are degraded.”
This could involve the abnormal impacts that microgravity has on the fluid of the brain. Previous research mentioned above examined the brains and eyes of astronauts and cosmonauts and found such effects. The researchers also think that some of their research results could reflect a brain injury that was caused by microgravity.
The study examined cosmonauts who had been in orbit for a long period of time. Zetterberg said that it is probable that a shorter duration space mission would also have negative impacts on the brain. This research will be of particular importance as humans begin to spend more time in space. A landing on Mars would require people to spend as much as two years in space. NASA intends to launch a manned space mission to Mars in the early 2030s. Zetterberg said in an email, “That's a very long time.” Most of us, he wrote, “need to make sure we can stay on Earth.”