Combinatorial Therapy Elicits Spinal Cord Regeneration

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Combinatorial therapy elicits spinal cord regeneration more than a year after injury

New research finds that adult neurons can still regenerate as long as 15 months after a spinal cord injury. The study, published by Cell Press in the October 29th issue of the journal Neuron, highlights the success of a strategy that targets multiple environmental and intrinsic obstacles known to limit nervous system plasticity and regeneration.

"Despite advances in promoting axonal regeneration after acute spinal cord injury, elicitation of regeneration of key neuronal processes, called axons, after chronic spinal cord injury remains a formidable challenge," explains senior study author Dr. Mark H. Tuszynski from the University of California, San Diego. "In fact, few studies have examined axonal regeneration when therapies are administered at delays greater than 8 weeks after injury."

Dr. Tuszynski and colleagues examined the capacity of axons to regenerate when experimental therapies were provided after exceptionally prolonged delays in adult rats with injuries to the upper part of the spinal cord. The researchers focused on the dorsal column sensory tract because it has a projection that is anatomically well-defined and normally fails to regenerate after injury.

Both the intrinsic growth state of the neurons projecting to the lesion site and the surrounding inhibitory environment were modified. Specifically, neuron-intrinsic regeneration-associated gene expression was up-regulated, bone marrow stromal cells were grafted to the lesion site, and a key neurotrophic factor was expressed in the dorsal column at time points ranging from 6 weeks to 15 months after injury.

The combination of delayed therapies induced activation of transcription factors and regeneration-associated genes that are normally seen with acute injury. This suggests recruitment of critical intrinsic molecular mechanisms that promote axon regeneration. Further, the researchers confirmed regeneration of axons beyond the lesion site. Importantly, examination of control animals revealed that modification of intrinsic growth state alone, or the environment alone, was insufficient to support axonal regrowth beyond the site of injury.

"Our results demonstrate that axonal regeneration in the adult central nervous system could be induced at unprecedented post-injury time points when experimental treatments modified the intrinsic growth state of the neurons and the non-permissive injury environment," says Dr. Tuszynski. "The ultimate goal is to provide rational, safe therapies that may improve the quality of life of humans with devastating spinal cord injuries." The first author of the study was Dr. Ken Kadoya, also of the University of California, San Diego. The work was supported by the National Institutes of Health and the Veteran's Administration.

The researchers include Ken Kadoya, University of California, San Diego, La Jolla, CA; Shingo Tsukada, University of California, San Diego, La Jolla, CA; Paul Lu, University of California, San Diego, La Jolla, CA, Veterans Affairs Medical Center, San Diego, CA; Giovanni Coppola, University of California, Los Angeles, Los Angeles, CA; Dan Geschwind, University of California, Los Angeles, Los Angeles, CA; Marie T. Filbin, Hunter College, New York, NY; Armin Blesch, University of California, San Diego, La Jolla, CA; and Mark H. Tuszynski, University of California, San Diego, La Jolla, CA, Veterans Affairs Medical Center, San Diego, CA.

Regeneration can be achieved after chronic spinal cord injury

Scientists at the University of California, San Diego School of Medicine report that regeneration of central nervous system axons can be achieved in rats even when treatment delayed is more than a year after the original spinal cord injury.

"The good news is that when axons have been cut due to spinal cord injury, they can be coaxed to regenerate if a combination of treatments is applied," said lead author Mark Tuszynski, MD, PhD, professor of neurosciences and director of the Center for Neural Repair at UC San Diego, and neurologist at the Veterans Affairs San Diego Health System. "The chronically injured axon is not dead."

While there are more than 10,000 new spinal cord injuries annually in the United States, nearly 250,000 patients are living in the chronic stages of injury. Yet nearly all previous spinal cord injury studies have attempted to stimulate regeneration when treatment is begun almost immediately after injury - because, in part, scientists considered it very difficult to achieve regeneration at such long time points after injury. None had shown successful regeneration in the late, chronic stages.

Reporting in the October 29 issue of the Cell Press journal Neuron, the UC San Diego team demonstrated successful regeneration of adult spinal cord axons into, and then beyond, an injury site in the cervical spinal cord, the middle region of the neck. Treatment was begun at time periods ranging from six weeks to as long as 15 months after the original injury in rats.

A number of mechanisms create formidable barriers to regeneration of injured axons in chronic spinal cord injury. These include scar formation at the injury site, a partial deficiency in the intrinsic growth capacity of adult neurons, the presence of inhibitors to growth, and, sometimes, extensive inflammation. Chronically injured neurons show a loss of expression of regeneration-promoting genes, and there is progressive degeneration of spinal cord white matter beyond lesion sites - all contributing to a poor environment for axonal re-growth.

Even under ideal laboratory circumstances, axonal re-growth is complex, requiring a combination of three things: a cellular bridge in the lesion site; a nervous system growth factor to guide axons to the correct target; and a stimulus to the injured neuron that turns on regeneration genes. Using this combinatorial treatment, the research team achieved axonal bridging beyond the original lesion site in rats when treatment was delayed for up to 15 months after the original spinal cord injury. Animals lacking the full combination treatment did not exhibit axonal regrowth.

The scientists also conducted genetic studies to measure how broad sets of genes in cells can be activated when treatment is delayed after injury. They discovered that, despite considerable delays, most genes could still be turned on to support regeneration, indicating that a chronically injured cell can still be "primed" to grow.

The studies were done in sensory systems that relay the sense of touch from the body to the brain. In ongoing studies, the scientists are testing these approaches for regenerating axons that control movement in chronically injured rats.

"Our findings indicate that there is potential for promoting repair of the injured spinal cord even in chronic stages of injury," said Tuszynski. "While the regenerating axons grow for relatively short distances, even this degree of growth could be useful. For example, restoration of nerve function even one level below an injury in the neck might improve movement of a wrist or hand, providing greater quality of life or independence."

Contributors to the study include first authors Ken Kadoya and Shingo Tsukada, UCSD Department of Neurosciences; Paul Lu, UCSD Neurosciences and Veterans Affairs Medical Center, San Diego; Giovanni Coppola and Dan Geschwind, UCLA Department of Neurology; Marie Filbin, Hunter College, NY; and Armin Blesch, UCSD Department of Neurosciences. The study was funded by the National Institutes of Health, the Veterans Administration, the Dr. Miriam and Sheldon G. Adelson Medical Research Foundation, and the Bernard and Anne Spitzer Charitable Trust.