Young animals heal in ways adults cannot, and nerves in particular lose most of their ability to regrow as we mature. A team led by Zhigang He of Harvard Medical School now argues that the switch flips at a very specific moment: the first breath of life.
The researchers watched mTOR, a signalling pathway that serves as a gauge of how ready cells are to grow. In mouse pups delivered by caesarean section, it stayed active while they remained inside the amniotic sac. Once they started breathing air, it dropped within minutes, even with the umbilical cord still feeding them. Keeping the pups warm or reducing oxygen made no difference.
The culprit turned out to be carbon dioxide leaving the body. As newborns exhale and CO2 levels fall, the inside of their cells turns more alkaline. This chemical shift wakes up SNRK, an enzyme that then dials mTOR down. Raising the CO2 in the surrounding air to 10 percent stopped the decline.
The striking part is that the brake can apparently be released. When adult mice breathed air enriched with 10 percent CO2, the pathway revived in muscle, heart and brain tissue, and damaged optic nerve fibres grew back after injury. He said his group was “very surprised and excited” by the result.
Nahum Sonenberg of McGill University called the findings “very tantalising” but added a careful “if correct”. The work has been posted as a preprint on bioRxiv and has not yet been peer-reviewed.
He himself cautions that other changes around birth could also shape regeneration. His hope is that one day a gentle gas-based therapy might help people with damaged spines or brains. Any route from mice to patients, though, will take years of testing.
