When a stroke hits the brain, some tissue dies right away, and around it a zone remains where cells are still alive but already suffering from a lack of blood. Doctors call it the penumbra. Act fast and those cells can be saved. But in elderly people recovery goes worse, and for a long time scientists couldn't figure out why.
Researchers took the brains of young and old mice after a stroke and looked at which genes were switched on at every point of the penumbra. It turned out that old mice have just as many cells in this zone, but their "internal factories" run poorly. The genes responsible for energy and for connections between neurons are almost silent, while inflammation genes are, by contrast, too active.
Now scientists know that what needs treating isn't cell death itself, but the cells' ability to fix themselves. The gene map built in this study will help find drugs that restore energy and repair signals to the aging brain.
In old mice, the transcriptomic penumbra turned out to be larger at day 14 after stroke, even though MRI showed no difference in infarct size compared with young mice. This means that tissue that looks dead on a scan may still retain molecular signs of salvageability.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.