“Myelin disorders have a lot of appeal versus other diseases like Parkinson, where you are trying to replace dead and/or dying neurons,” stated Ian Duncan, Ph.D., professor of neurology, school of veterinary medicine at the University of Wisconsin, Madison. “It’s rather straightforward with myelin disease—we know myelin sheaths are replaceable if you have the right cells.”
The biggest challenge is isolating sufficient cells capable of replacing myelin in focal lesions in significant numbers of patients. Dr. Duncan said it’s an issue of cell cultivation. “Although things are improving technically, we’d like to be able to make oligodendrocytes in large numbers in culture before taking the cells into an intermediate stage. We’d like to have confidence in vitro that there’s significant differentiation toward those cells prior to trying it in vivo.”
He added that the derivatives of embryonic stem cells have not been as successful as those of human neural crest stem cells. But they are not ruling out using induced pluripotent stem cells or oligodendrocyte progenitors as potential cell sources.
Another goal is to repair focal areas of damage that are strategically significant. Dr. Duncan’s group would like to deliver cells in a “disseminated way throughout the entire CNS, but that’s a big challenge. It’s unlikely that you could put cells into the spinal cord and have them migrate to the brain.”
Dr. Duncan said that he has demonstrated re-myelination of a damaged segment of spinal cord in a mouse model. He added that although they have a better idea of how to make a lot of oligodendrocyte progenitors from human embryonic stem cells, they still haven’t obtained the quantity and good differentiation potential they would like.
Epidermal Neural Crest Cells
Epidermal neural crest cells (EPI-NCSC) are remnants of the embryonic neural crest and give rise to hair, skin, sweat glands, peripheral nerves, facial bones and cartilage, pigment, and some endocrine glands. Maya Sieber-Blum, Ph.D., professor of stem cell science at Newcastle University, said that some of these cells survive in hair follicles, where her group discovered them by accident. “When we saw these neural crest cells in the bulge of hair follicles, we first had to prove they were stem cells.”
The cells were molecularly characterized by long serial analysis of gene expression (longSAGE). Data showed that 19 genes are characteristic for both embryonic neural crest stem cells and EPI-NCSC, but are not expressed by epidermal stem cells. These 19 genes were validated at the protein level by immunocytochemistry. “We used that molecular signature to compare it to other published data to find out if our cells are unique—and they are unique among skin resident stem cells.”
One of the challenges in working with human EPI-NCSC is expansion in cell culture. Dr. Blum said her lab has developed a technique to efficiently accomplish this, but was unable to provide details due to IP restrictions.
In another study, Dr. Blum wanted to see if her cells expressed the same four genes that are used for induced pluripotent stem cells. Data shows that Myc, Sox2, Klf4, and Lin28 are expressed at levels similar to mouse embryonic stem cells. However, the pluripotency genes Nanog and Oct4 are expressed at 700- to 800-fold lower compared to embryonic stem cells. “This likely explains the fact that EPI-NCSC did not form tumors in the spinal cord of mice.”
In collaboration with the Brain Research Institute, the cells were tested in mice with spinal cord injuries. Data showed integration into the spinal cord, cell survival in high numbers, vascularization of the scar, bridging of the lesion, and no tumor formation. Potential therapeutic applications include spinal cord injury, repair of neural degeneration, as well as bone transplants.