Controlled Differentiation: Chemicals and Electric Fields

In theory, stem cells can fix many problems, but only as long as we know how to control them. Dr.Ye, an assistant professor at Loyola University, conducts research on the mechanisms underlying stem cell differentiation into neurons and stem cell migration. Both differentiation and migration are key to successful repair of damage in vivo. Unfortunately, current transplantation methods are quite invasive and the injured microenvironment does not help in proper differentiation. Instead of differentiating into neurons (which would reestablish neural networks), the cells are more likely to become glial cells forming scar tissue. Dr. Ye’s research suggests that DC electric field (EF) exposure increases the percentage of cells differentiating into neurons. The neural precursor cells (NPCs) move in a cathodal direction when subject to an electric field, yet the differentiated cells do not. While the mechanism underlying this difference is still currently being explored, one thing is certain; once we understand how to control these cells, we can start designing better methods to support neuroregeneration.

Figure 1. Neural Stem Cell Differentiation Diagram. Neural stem cells have limited potency into neurons, glia, astrocytes, and oligodendrocytes.

The retina contains many specialized neurons that are necessary for vision. Retinal Ganglion Cells (RGCs), the first neurons that respond with action potentials in the visual system, are particularly vulnerable to damage in glaucoma and multiple sclerosis. Researchers at John Hopkins recently published an article in Scientific Reports, Differentiation of human ESCs to retinal ganglion cells using a CRISPR engineered reporter cell line, presenting a new method to collect a purified population of RGCs (Sluch et al.). They used a CRISPR-engineered RGC fluorescent reporter that allowed for fluorescence upon co-expression with BRN3B, a gene expressed in mature RGCs. Coupling this method with FACS, fluorescence-activated cell sorting, the researchers were able to sort individual cells and separate a purified population. The researchers were also able to demonstrate that forskolin, a naturally occurring chemical in plants, was able to promote stem cells differentiation into RGCs. Without forskolin, in accordance to the protocol established, only 3-5% of the population of stem cells differentiate into RGCs. Upon growth in a 25 um forskolin medium for 30 days, the percentage of RGCs doubled to approximately 7-11%.  

Figure 2. Cellular Arrangement of Cells in the Eye.  Visual information is transduced from the rods and cones, to the bipolar cells and lastly, ganglion cells. 

Neuroregeneration is limited by what the body can provide. In areas of damage, such as the retina or spinal cord, specialized cells are necessary for proper functioning. In the case of Dr. Ye’s work, electric fields are shown to promote neuronal differentiation. Sluch et al. suggests exposure to forskolin increases RGC differentiation. Future studies should include the development of a non invasive technique to deliver the RGCs to areas of damage in the retina. Despite the great advancements of the present day, there is much to learn before we can start designing clinical techniques for such procedures.

Sources:

Valentin M. Sluch, Chung-ha O. Davis, Vinod Ranganathan, Justin M. Kerr, Kellin Krick, 

Russ Martin, Cynthia A. Berlinicke, Nicholas Marsh-Armstrong, Jeffrey S. Diamond, 

Hai-Quan Mao, Donald J. Zack. Differentiation of human ESCs to retinal ganglion

cells using a CRISPR engineered reporter cell line. Scientific Reports, 2015;

http://www.sciencedaily.com/releases/2015/11/151130163432.htm

Figure 1:https://www.sigmaaldrich.com/life-science/cell-biology/cell-biology-products.html?TablePage=20848687
Figure 2:http://www.salk.edu/news-release/from-eye-to-brain-salk-researchers-map-functional-connections-between-retinal-neurons-at-single-cell-resolution/