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Use Embryonic Stem Cells To Awaken Latent Motor Nerve Repair (2)

Extending new motor neurons in an adult nervous system, however, meant overcoming hurdles. One involved myelin, the fatty material that insulates mature motor neurons. Like the coating on electrical wire, myelin prevents weakening of the traveling electrical impulse and lets it continue long distances. In humans, the myelinated sciatic nerve, for example, exits the spinal cord and extends to the leg muscles it activates, carrying impulses several feet.
 
Once laid down, however, myelin inhibits further nerve growth -- nature’s way to discourage excessive wiring in the nervous system. “We had to overcome inhibition from myelin lingering in the dead nerve pathways,” Kerr explains. Two recently-developed agents, rolipram and dbcAMP enabled that.
 
The assorted treatments let the new motor neurons survive, grow through the spinal cord and extend slightly into the outlying nervous system. A second hurdle remained in getting the neurons to skeletal muscle targets.
 
As suggested by earlier work by team member Ahmet Hoke on repair in the outlying, peripheral nervous system, the researchers applied GDNF, a powerful stimulator of neuron growth, to the remains of the newly-dead sciatic nerve at a point near its former leg muscle contacts. GDNF attracted the extending motor neurons, “luring” them to the muscles. To ensure a continuous supply of GDNF, the researchers relied on injected fetal mouse neural stem cells, a known source of the molecule.
 
Of some 4,100 new motor neurons created in the spinal cord, roughly 200 exited the cord and 120 reached skeletal muscle, forming typical nerve-muscle junctions, with appropriate, typical chemical markers. Microscopically, the neurons and their muscle associations appear identical to natural ones in healthy animals.
 
Fifty of the new neurons were found to carry electrical impulses. (Because such testing is time and labor intensive, only a small area of leg muscle was assayed. The improved ability of treated rats, however, suggests more functional neurons are likely.) The rats gained weight, were more mobile in their cages and measures of muscle strength increased.
 
Animals treated without even one component of the “cocktail” experienced no such recovery. Novel ways of tracing the neurons back to their source assured the scientists that they indeed had come from the injected stem cells, not from lingering host neurons.
 
Research begins this summer to see how well the technique applies to human nerve recovery, using federally-approved human ES cells in larger mammals like pigs, Kerr says. Each of six academic institutions in a new collaboration will tackle a different major question of safety and effectiveness. Questions of tumor-formation, often a concern with ES cells, of the safety of surgery and of the ES cells’ ability to form healthy motor circuits are major questions to answer. Several years of testing and thorough data evaluation would occur before applying to the FDA to approve human clinical trials. The study was supported by Families of SMA, Andrew’s Buddies/Fight SMA, the ALS Association and The Robert Packard Center for ALS Research at Johns Hopkins, the Muscular Dystrophy Association, Wings Over Wall Street, and a grant from the NIH.
 
Kerr is a grantee of The Packard Center for ALS Research at Johns Hopkins. He also directs Project RESTORE, a Hopkins-based undertaking to advance therapies for transverse myelitis and multiple sclerosis.
 
source: www.sciencedaily.com