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Use Embryonic Stem Cells To Awaken Latent Motor Nerve Repair (1)

Cod. A28062006

Source: Johns Hopkins Medical Institutions
 
Posted: June 26, 2006
 

Hopkins Scientists Use Embryonic Stem Cells, New Cues To Awaken Latent Motor Nerve Repair
In a dramatic display of stem cells’ potential for healing, a team of Johns Hopkins scientists reports that they’ve engineered new, completed, fully-working motor neuron circuits -- neurons stretching from spinal cord to target muscles -- in paralyzed adult animals.
 

The research, in which mouse embryonic stem (ES) cells were injected into rats whose virus-damaged spinal cords model nerve disease, shows that such cells can be made to re-trace complex pathways of nerve development long shut off in adult mammals, the researchers say.
 
“This is proof of the principle that we can recapture what happens in early stages of motor neuron development and use that to repair damaged nervous systems,” says Douglas Kerr, M.D., Ph.D., a neurologist who led the Hopkins team.
 
“It’s a remarkable advance that can help us understand how stem cells can begin to fulfill their great promise,” says Elias A. Zerhouni, director of the National Institutes of Health. “Demonstrating restoration of function is an important step forward, though we still have a great distance to go.”
 
The researchers created what amounts to a cookbook recipe to restore lost nerve function, Kerr explains. The approach could one day repair damage from such diseases as ALS (Lou Gehrig’s disease), multiple sclerosis or transverse myelitis or from traumatic spinal cord injury, the researchers say. “With small adjustments keyed to differences in nervous system targets,” Kerr says, “the approach may also apply to patients with Parkinson's or Huntington’s disease.”
 
In a report on the study, to be released online June 26 in the Annals of Neurology, the Hopkins team says 11 of the 15 treated rats gained significant, though partial, recovery from paralysis after losing motor neurons to an aggressive infection with Sindbis virus -- one that, in rodents, specifically targets motor neurons and kills them. The animals recovered enough muscle strength to bear weight and step with the previously paralyzed hind leg.
 
Kerr likens the approach to electrical repair. “Paralysis is like turning on a light switch and the light doesn’t go on. The connectivity is messed up but you don’t know where. We’ve asked stem cells to go where needed to fix the circuit.”
 
For a brief period after a nerve dies, it leaves behind what’s essentially an empty shell, with some scaffolding and non-nerve substances remaining. But with ES injections at the right time and place, and by adding the right cues, we’ve learned to restore the biological ‘memory’ for growing neurons, which is clearly still in place,” he added.
 
The motor circuit engineering combines recent discoveries on stem cell differentiation, a growing understanding of early development of the nervous system, and insights into behavior of the nervous system in traumatic injury, Kerr notes.
 
“As adults, our cells no longer respond to early developmental cues because those cues are usually gone,” says Kerr. “That’s why we don’t recover well from severe injuries. But that’s what we believe we have changed. We asked what was there when motor neurons were born, and specifically what let motor neurons extend outward. Then we tried to bring that environment back, in the presence of adaptable, receptive stem cells.”
 
In the study, Kerr’s team first pre-treated cultures of mouse embryonic stem cells with growth factors that both increase survival and prompt specialization into motor neurons. Adding retinoic acid and sonic hedgehog protein -- agents that direct cells in the first weeks of life to assume the proper places in the spinal cord -- readied the conditioned ES cells for the motor neuron circuit that starts in the spinal cord. Then, stem cells were fed into the paralyzed rats’ spinal cords.

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