Human organoids reveal how to reverse “irreversible” nerve damage

Researchers at the University of Cambridge have developed miniature human brain and spinal cord systems in the laboratory that replicate how movement signals are transmitted through the nervous system. These lab-grown organoids demonstrated that nerve damage, previously thought to be permanent, may be reversible under certain conditions. The team found that human neurons gradually lose their ability to regrow damaged axons during development, but this regenerative capacity can potentially be reactivated. They identified a gene network controlling this process and showed that an existing hormone drug significantly enhanced nerve fiber regrowth. The study builds on earlier work where scientists created "brain organoids" from patient stem cells to model neurological diseases such as motor neurone disease. In the new research, the team physically separated brain and spinal cord organoids but observed axons growing across the gap to form functional neural circuits capable of triggering muscle cell contractions. By maintaining these systems for over a year, they discovered that axon regrowth was robust until about day 150 of development—roughly mid-pregnancy—after which the neurons’ regenerative ability sharply declined. This decline in nerve regrowth capacity explains why injuries to the brain or spinal cord often result in permanent disabilities such as paralysis or loss of movement. It also has implications for neurodegenerative diseases like multiple sclerosis and motor neurone disease, where nerve damage accumulates over time. The identification of a gene network regulating this developmental switch, along with the discovery that a hormone drug can boost regrowth, opens new avenues for therapeutic strategies aimed at reversing nerve damage previously considered irreversible. These findings represent a significant advance in neuroscience, offering hope for treatments that could restore function after spinal cord injuries or neurodegenerative conditions. The use of human organoids provides a powerful platform for studying nervous system development and repair, potentially accelerating the development of drugs that promote nerve regeneration in patients.