Scientists at the Hebrew University of Jerusalem report the development of a new cocktail that effectively coaxes adult cells to become quality stem cells. The resulting induced pluripotent stem cells (iPSCs) could be used to replace those lost to damage or disease. However, the process of reprogramming adult cells can introduce genetic abnormalities that limit the cells' usefulness in research and medicine. The researchers published their study (“The Developmental Potential of iPSCs Is Greatly Influenced by Reprogramming Factor Selection”) in Cell Stem Cell.
To make iPSCs, researchers expose adult cells to a mixture of genes that are active in embryonic stem cells. iPSCs can then be made to differentiate into other cell types such as nerve or muscle. However, the standard combination of factors used to reprogram cells leads to a high percentage of serious genomic aberrations in the resulting cells. The reprogramming factors are Oct4, Sox2, Klf4, and Myc—known collectively as OSKM.
However, a team led by Yosef Buganim, Ph.D., at the Institute for Medical Research Israel-Canada in the Hebrew University's Faculty of Medicine, collaborating with researchers at the lab of Whitehead Institute founding member Rudolf Jaenisch, Ph.D., reasoned that changing the reprogramming factors could reprogram the adult cells in a more controlled way and yield high-quality iPSCs. Working with mouse cells, Dr. Buganim and his group used bioinformatic analysis to design a new suite of reprogramming factors (Sall4, Nanog, Esrrb, and Lin28, known collectively as SNEL).
Their results showed that the interaction between reprogramming factors plays a crucial role in determining the quantity and quality of resulting iPSCs, and that a different combination of reprogramming factors can in fact produce a much higher quality product.
The new SNEL cocktail created fewer colonies of iPSCs, but approximately 80% of those produced passed the most stringent pluripotency test. This is highly preferable to the traditional OSKM cocktail, which produces a large number of colonies but the majority of which fail the pluripotency test.
“We found that ectopic expression of Sall4, Nanog, Esrrb, and Lin28 (SNEL) in mouse embryonic fibroblasts (MEFs) generated high-quality iPSCs more efficiently than other combinations of factors, including OSKM,” wrote the investigators. “Although differentially methylated regions, transcript number of master regulators, establishment of specific superenhancers, and global aneuploidy were comparable between high- and low-quality lines, aberrant gene expression, trisomy of chromosome 8, and abnormal H2A.X deposition were distinguishing features that could potentially also be applicable to human.”
Dr. Buganim hypothesizes that SNEL may reprogram cells better than OSKM because it does not rely on the master regulators Oct4 and Sox2, which might activate part of the adult cell genome. He adds that the research demonstrates the effectiveness of bioinformatics tools in producing high-quality iPSCs.
This study takes the regenerative medicine field one step closer to the clinic, where it may be able to help patients in need of cellular transplantation therapy, according to Dr. Buganim. The researchers will now seek to define the optimal combinations for reprogramming human iPSCs, which are harder to reprogram than mouse cells and which could not be reprogrammed using the SNEL cocktail.