Cambridge researchers have built miniature human brain and spinal cord systems in the laboratory and discovered something that challenges decades of neurology doctrine: nerve damage long considered irreversible may actually be fixable.
The finding emerged from work with organoids, tiny structures grown from stem cells that replicate how the brain and spinal cord communicate. Scientists at the University of Cambridge maintained these systems for over a year, tracking how neurons develop and lose their capacity to regenerate after injury.
The central nervous system normally loses the ability to regrow damaged nerve fibers, or axons, as it matures. That's why spinal cord injuries typically result in permanent paralysis and why diseases like motor neurone disease cause irreversible decline. Understanding when and why this regenerative window closes has eluded researchers for years.
Dr. András Lakatos and his team created the organoid systems by keeping brain and spinal cord tissue separate but allowing axons to grow across the gap and form functional connections. This setup let them observe exactly when neurons lose their regenerative power. Around day 150 of development, roughly the midpoint of pregnancy, a sharp decline occurred.
George Gibbons, first author of the study published in Cell Reports, explained the stark difference: "Neurons taken from less mature organoids regrew long fibers after injury, but those from more mature organoids showed a sharp drop in their ability to regrow." The immature neurons essentially retained a biological flexibility that mature neurons had lost.
The researchers pinpointed a network of genes acting as a biological brake on axon growth. When they blocked key regulators in this network, neurons regained the ability to extend new fibers. This discovery opened a path to potential treatments.
Testing a database of existing drugs, the team identified lynestrenol, a hormone medication used for menstrual disorders and contraception, as a compound that significantly improved axon regrowth in damaged neurons. The drug targets the same genetic network that normally restricts regeneration in mature neurons.
Lakatos cautioned that lynestrenol itself may not solve spinal cord injuries, but the principle matters enormously. "It shows us that, in principle, it should be possible to directly target human neurons and regenerate their axons," he said. "Although we still need to show that this strategy will also help to re-establish appropriate connections between the brain and spinal cord cells, this gives us hope that one day we may be able to treat conditions previously thought untreatable."
The work highlights why human organoid technology is becoming essential to neuroscience. Animal models like mice have been the foundation of regeneration research, but rodent neurons behave significantly differently from human neurons. Human stem cell-derived organoids bridge that critical gap, moving findings closer to actual patient applications while reducing reliance on animal testing.
Cambridge researchers are already applying organoid technology to repair damaged livers, investigate childhood Crohn's disease, and study early pregnancy biology. The spinal cord regeneration work, funded by UK Research and Innovation and Spinal Research, represents one of the most clinically promising applications yet.
Author Jessica Williams: "This work demolishes the myth that nerve damage is locked in stone, and the fact that an existing drug works in these human systems is a genuine opening that warrants serious clinical pursuit."
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