Neural Stem Cells Sprout Long Axons
Stem cells derived from the skin of an 86-year-old man show a surprising capacity to survive and form long axons at the site of a spinal cord injury in rats. The results, [published August 7] in Neuron, suggest that even induced pluripotent stem cells (iPSCs) reprogrammed from aging human cells have an intrinsic ability to overcome inhibitory factors to form neurons and extend axons.
A rat neuronal stem cell (NSC) line had previously shown similar potential for regrowth: a 2012 study from the same research group demonstrated that rat NSCs could form axons that travelled great distances within rodent brains and spines, and restore movement to limbs after a spinal cord injury.
“Both studies are very provocative in terms of the amount of axon growth observed,” said neuroscientist Philip Horner of the University of Washington, who studies axonal regeneration but was not involved with the study. “The questions that the paper raises, however, are whether this is good and controllable [growth].”
Stem cell-based therapies hold tantalizing promise for treating spinal cord injuries. Previous studies have shown neural stem cells can extend axons far across lesions, remyelinate axons surrounding sites of partial injuries, and protect and restore conductivity across an injury. These properties raise intriguing prospects for experimental treatments. But suppressing a host’s immune system is crucial to the success of NSC grafts, and immunosuppression can pose high risks to patients already suffering spinal cord damage.
Mark Tuszynski and Paul Lu of the University of California, San Diego, sought to circumvent this need for immunosuppression by using iPSCs, which can be derived from a patient’s own skin and, eventually, autotransplanted. The researchers began by transducing dermal fibroblasts from a healthy subject with retroviral vectors to induce stem cell formation. NSCs derived from this process were implanted in a fibrin matrix infused with a cocktail of growth factors. These human iPSC-turned-NSCs were then grafted into rats two weeks after a spinal cord injury.