MicroRNAs track radiation doses

Humans and other animals may make natural radiation detectors in their blood.  

Some microRNAs, tiny pieces of genetic material that help regulate protein production, change levels in the blood of mice after exposure to radiation, researchers report in the May 13 Science Translational Medicine. Different radiation doses changed levels of different sets of microRNAs, allowing researchers to distinguish which rodents were likely to survive.

“Humanized” mice carrying human blood-producing stem cells had changes in the same radiation-responsive microRNAs as normal mice did. That finding raises hope that the molecules could help predict whether people can recover from high radiation doses, such as those suffered during nuclear accidents.

It’s not easy to tell how much radiation a person has gotten or how much damage a dose has done to the body, says study leader Dipanjan Chowdhury, a molecular geneticist at Harvard Medical School. Half of people getting 4 grays of radiation will die, but it isn’t immediately obvious who the victims will be. Blood-forming stem cells don’t start to die until a few weeks to two months after getting a potentially lethal dose of 2 to 6 grays. A gray is a measure of absorbed radiation roughly equivalent to getting 100,000 chest X-rays.

Researchers had previously shown in mice that levels of some microRNAs increase in the blood after radiation exposure. Chowdhury and colleagues wanted to know which microRNAs indicate damage. “It’s not about the radiation dose really, it’s about the impact,” he says.

The group found 68 microRNAs that change levels in mice 24 hours after radiation exposure. The altered levels persisted for at least a week. Humans have the same microRNAs, although no one knows if people will respond the same way mice do. A group of five microRNAs, including one called miR-150-5p, were altered when mice got up to 2 grays of radiation. A different set of microRNAs changed between 2 and 6.5 grays, and a third set was characteristic of 6.5 to 8 grays of exposure. Because the researchers could distinguish between a lethal dose at 8 grays and a harmful but not quite lethal 6.5-gray exposure, Chowdhury says the microRNAs may tell doctors who should get treatment and who is beyond help. The molecules may also be useful for measuring the efficacy of drugs designed to counteract the effect of radiation.

In a previous study, radiation biologist Naduparambil Jacob of Ohio State University Wexner Medical Center in Columbus also found that miR-150 could indicate radiation dose. He was not involved in the new study, but says he is pleased that Chowdhury’s work confirms his finding. “This supports previous studies showing the possibility of using microRNAs as biomarkers of radiation exposure,” he says.