The Use of Microfluidic Chambers and Microtechnology to Study hESC-derived Neural Cells

Funding Type: 
SEED Grant
Grant Number: 
ICOC Funds Committed: 
Disease Focus: 
Stem Cell Use: 
Embryonic Stem Cell
Public Abstract: 
Human embryonic stem cells (hESCs) have the potential to revolutionize medical therapeutics by providing transplantable cells for future treatments of a variety of disorders, including diabetes, heart disease, and degenerative and traumatic nerve diseases, such as Multiple Sclerosis, Parkinson’s Disease, and spinal cord injury. It is imperative to determine which hESC lines are superior candidates for use in these treatments, prior to use in humans, since it is well accepted that there are subtle differences between the currently available cell lines. It is likely that these rather subjectively observed differences between commonly used cell lines will translate into variably successful cell-based therapies unless these differences are taken into account early in the course of stem cell research. The goal of this research is to utilize microtechnology to objectively compare the function and health of differentiated cells derived from various hESC lines so that optimal choices of stem cells can be determined for cell-based therapies of neurologic diseases. It is our hypothesis that neurons derived from different stem cell lines will demonstrate subtle differences in their physiology when compared side by side with the use of microtechnology tools such as microfluidic chips. These chips use tiny grooves to isolate the neuron’s cell body from their axons that will grow across the grooves into a separate chamber for study. These chips will be attached to arrays of microelectrodes and then used to isolate axons for electrical measurements. Once the axons grow across the grooved barrier and the multielectrode array into the isolation chamber, specific parameters will be recorded to determine the healthiest and most functional cell lines. In addition, the axon shape and appearance will be analyzed by optical and fluorescent microscopy. We anticipate that the results will show that stem cell lines are not interchangeable for different purposes and that they can be objectively evaluated using this microfludic platform. This type of quality control is essential. The effects of variable agents that these transplanted cells might encounter in the body can also be evaluated, such as immune system factors and pharmacologic compounds. Additionally, the design of the microfluidic chip can be altered in the future to best accommodate and test different cell types from other organ systems.
Statement of Benefit to California: 
California led the nation in acknowledging the potential benefit of using human embryonic stem cells (hESCs) for medical research. More significantly, they committed the resources to explore these benefits by establishing CIRM. The research proposed in this application will use microtechnology tools to evaluate the quality of different hESC lines as a source for transplantable human neural cells. This type of quality assurance is essential prior to use of hESC cell-based therapies in human subjects. We are hopeful that this research will show that technology can provide the tools to adequately evaluate hESC lines, while minimizing the sacrifice of experimental animals for this purpose. This chip can also be used to evaluate the effects of variable agents that these transplanted cells might encounter in vivo, such as cytokines and other inflammatory factors, and pharmacologic compounds. In addition, based on the small scale of these test chambers, massively parallel, automated, pre-programmed studies can be carried out allowing systematic trial of thousands of combinations of conditions at minimal financial expense for high throughput screening of the hESC progeny. This could lead to industrial development of this microtechnology for the study of hESCs. Finally, the design of the microfluidic chip can be altered to best accommodate different cell types (islet cells, cardiac muscle, etc.) for optimal testing of progeny for diseases of other organ systems. We feel that applying this “cutting edge” microfluidic and MEA technology to the “cutting edge” biology of hESCs is very innovative. Although it might be considered risky by some, the results could help to change how cell-based therapies are developed and tested, and optimize the chances of success for this application of hESCs. We therefore believe that this research is well aligned with the goals of the CIRM Seed Grant Research Program, and proving the utility of this tool will be of great benefit to the State of California and its citizens.
Progress Report: 
  • Human embryonic stem cells contain roughly 3 million “jumping genes” or mobile genetic retroelements that comprise up to 45% of human genome. While many of these retroelements have been silenced during evolution by crippling mutations, many remain active and capable of jumping to new chromosomal locations potentially producing disease-causing mutations or cancer. In tissues, mobility of these elements is suppressed by DNA methylation, which inactivates expression of the retroelement RNAs. In sharp contrast, embryonic stem cells exhibit very dynamic changes in DNA methylation, where the methylation patterns are gained and lost at high rates. During periods of low DNA methylation, retroelement RNA expression likely increases. Accordingly, hESCs must deploy other defensive strategies in order to maintain genomic integrity. Recent studies have identified the APOBEC3 family of genes (A3A-A3H) as powerful antiviral factors. These A3s interrupt the conversion of viral RNA into DNA (reverse transcription), a key step also employed by retroelements for their successful retrotransposition. We hypothesized that one or more of the APOBECs function as guardians of genome integrity in hESCs. In the last two years we have found that six out of the seven human A3 genes located in a tandem array on chromosome 22 are expressed in hESCs. A3A, which in prior studies was suggested to exert the greatest anti-retroelement effects, surprisingly is not expressed in hESCs. Further, we find that the A3 proteins decrease when pluripotent cells differentiate into somatic cells suggesting an important function of these A3 proteins in pluripotent hESCs. We established a LINE1 retrotransposition assay in hESCs that allows us to visualize genetic jumping of this class of “marked” retroelements via flow cytometry. Using this assay we have found that LINE1 elements effectively jump in hESCs. To test our central hypothesis, namely that A3 proteins guard the genome in hESCs, we have established experimental conditions for RNAi knock-down of all expressed A3 genes. By combining the knock-down and the retrotransposition assay we demonstrated that the knock-down of one member of the A3 protein family leads to a 3.5-fold increase in LINE1 retrotranspositon. This finding highlights a protective role for the A3 family of cytidine deaminases that helps safeguard the genome integrity of hESCs.

© 2013 California Institute for Regenerative Medicine