Thousands of people face life-long losses in motor function and sensation due to spinal cord injury. This is because the components of a central nervous system do not regenerate. Along the spine runs the neurons with long wiry projections called axons protruding outward. The axons provide the sensation of touch and sight. This system is the communication network that connects all the parts of the body to the brain. If axons are severely damaged or severed, the connection is broken, which results in paralysis and blindness.
But now, Lewis Katz School of Medicine Temple University (LKSOM) researchers found a way to fix the axons. Their strategy involves upregulating (boosting expression of) a molecule (a protein) called Lin28, which regulates cell growth. In experiments with mice that had spinal cord injuries and damaged optical nerves, the protein helped them regain movement, feeling, and patched up the axons in the optical nerve.
Shuxin Li, MD, Ph.D., Professor of Anatomy and Cell Biology and senior investigator on the new study, explained:
Our findings show that Lin28 is a major regulator of axon regeneration and a promising therapeutic target for central nervous system injuries. We became interested in Lin28 as a target for neuron regeneration because it acts as a gatekeeper of stem cell activity. It controls the switch that maintains stem cells or allows them to differentiate and potentially contribute to activities such as axon regeneration.
The Lin28 gene is expressed in high amounts in embryonic stem cells early on but drops off as cells age. Ramping up levels has been found in past studies to help mice regrow bone, skin, cartilage, and other tissues – but not axons, until now.
Dr. Li said:
Our findings show that Lin28 is a major regulator of axon regeneration and a promising therapeutic target for central nervous system injuries. We observed a lot of axon regrowth, which could be very significant clinically since there currently are no regenerative treatments for spinal cord injury or optic nerve injury.
Injections of Lin28 helped axons regenerate along the entire optic nerve tract and as far as 3mm beyond the damaged area in the spinal cord in all the mice. The researchers speculate that other molecules involved with growth signaling could be bundled together with Lin28 for an even better result. Their next goal is to identify how to get Lin28 to injured tissues in humans safely and effectively.
There’s another separate study that has explicitly focused on fixing the axons in the eyes to cure blindness. Axons in the optic nerve (in the eye) shuffle signals through the neurons from the retina to the brain’s visual cortex to be interpreted and “seen” as images. A neuroscientist known as Thomas Reh, at the University of Washington in Seattle, has been trying to unlock the ability for retinal neurons to regenerate themselves by using stem cells. His team used an enzyme to coax the cells to renew in mice. However, they, too, now have to figure out a way for this to work in humans.
