Scientists at UC Irvine’s Reeve-Irvine Research Center have discovered that injections of salmon fibrin injections into the injured spinal cord plus injections of a gene inhibitor into the brain restored voluntary motor function impaired by spinal cord injury.
Gail Lewandowski and Oswald Steward, director of the Reeve-Irvine Research Center at UCI, examined rodents that had received spinal cord injuries. They were able to heal the damage by developmentally turning back the clock in a molecular pathway that is critical to the formation of the corticospinal nerve tract, and by providing a scaffold for the growing neurons so that the axons of these growing neurons could grow and make the necessary connections with other cells. Their research was published in the July 23 issue of The Journal of Neuroscience.
The work of Steward and Lewandowski is an extension of previous research at UC Irvine from 2010. Steward and his colleagues discovered that the axon of neurons grow quite well once an enzyme called PTEN is removed from the cells. PTEN is short for “phosphatase and tensin homolog,” and it removes phosphate groups from specific proteins and lipids. In doing so, PTEN signals to cells to stop dividing and it can also direct cells to undergo programmed cell death (a kind of self-destruct program). PTEN also prevents damaged tissues from regenerating sometimes, because it is a protein that puts the brakes of cell division. Mutations in PTEN are common in certain cancers, but the down-regulation of PTEN is required for severed axons to re-form, extend, migrate to their original site, and form new connections with their target cells.
After two years, team from U.C. Irvine discovered that injections of salmon fibrin into the damaged spinal cord or rats filled cavities at the injury site and provided the axons with a scaffolding upon which they could grow, reconnect and facilitate recovery. Fibrin produced by the blood system when the blood vessels are breached and it is a fibrous, insoluble protein produced by the blood clotting process. Surgeons even use it as a kind of surgical glue.
“This is a major next step in our effort to identify treatments that restore functional losses suffered by those with spinal cord injury,” said Steward, professor of anatomy & neurobiology and director of the Reeve-Irvine Research Center. “Paralysis and loss of function from spinal cord injury has been considered irreversible, but our discovery points the way toward a potential therapy to induce regeneration of nerve connections.”
In their study, Steward and Lewandowski subjected rats to spinal cord injuries, and then assessed their defects. Because these were upper back injuries, the rats all showed impaired forelimb (hand) movement. Steward and Lewandowski then treated these animals with a combination of salmon fibrin at the site of injury and a modified virus that made a molecule that inhibited PTEN. These viruses were genetically engineered adenovirus-associated viruses encoded a small RNA that inhibited translation of the PTEN gene (AAVshPTEN). This greatly decreased the levels of PTEN protein in the neurons. Other rodents received control treatments of only AAVshPTEN and no salmon fibrin.
The results were remarkable. Those rats that received the PTEN inhibitor alone showed no improvement in their forelimb function, but those animals who were given AAVshPTEN plus the salmon fibrin recovered forelimb use (at least reaching and grasping).
“The data suggest that the combination of PTEN deletion and salmon fibrin injection into the lesion can significantly enhance motor skills by enabling regenerative growth of corticospinal tract axons,” Steward said.
Statistics compiled by the Christopher & Dana Reeve Foundation suggests that approximately 2 percent of Americans have some form of paralysis that is the result of a spinal cord injury. Spinal cord injuries break connections between nerves and muscles or nerves and other nerves. Even injuries the size of a grape can cause complete loss of function below the level of the injury. Injuries to the neck can cause paralysis of the arms and legs, an absence of sensation below the shoulders, bladder and bowel incontinence, sexual dysfunction, and secondary health risks such as susceptibility to urinary tract infections, pressure sores and blood clots due to an inability to move one’s legs.
Steward said the next objective is to learn how long after injury this combination treatment can be effectively administered. “It would be a huge step if it could be delivered in the chronic period weeks and months after an injury, but we need to determine this before we can engage in clinical trials,” he said.