The majority of researchers working with human embryonic stem cells (hESCs), cells which produce any type of specialized adult cells in the human body, use animal-based materials for culturing the cells. But because these materials are animal-based, they could transmit viruses and other pathogens to the hESCs, making the cells unsuitable for medical use.
Now, a stem-cell scientist at University of California, Riverside (UCR), has devised a method of growing hESCs in the lab that uses no animal-derived materials, an important advance in the use of hESCs for future medical purposes.
Because of their tremendous potential, hESCs are considered promising sources for future cell therapy to treat diseases such as Parkinson’s disease and diabetes mellitus.
Noboru Sato, an assistant professor of biochemistry, developed the new method. The method is not only cleaner and easier to use than conventional methods of culturing hESCs, but also results in hESCs whose pluripotency is uncompromised. Pluripotency is the potential to differentiate into any of the specialized cells of the body such as neurons, cardiac muscles, and insulin-producing cells.
Currently in labs worldwide, many researchers grow hESCs on Matrigel-coated culture plates. Matrigel is the trade name for a gelatinous extract, taken from mouse tumor cells, that contains extracellular matrices (ECMs), made up of special proteins. The Matrigel coating provides the scaffolding to which the hESCs first attach and then grow in undifferentiated colonies before differentiating into specialized cells.
The development of animal-free coating methods for hESCs still remains a major challenge due to the complexity of ECMs and insufficient knowledge about how hESCs control cell-cell and cell-ECM interactions, explained Sato, who led the research project.
His lab identified a specific signaling pathway, called Rho-Rock, which the hESCs use during colony formation and which plays an important role in physical interactions between hESCs. When the researchers blocked the pathway, they found, as expected, that the normal colony formation of hESCs was considerably impaired. They also found that the hESCs maintained their pluripotency.
Until now, it was generally assumed that the hESC colony formation was pivotal for maintaining pluripotency, Sato said. But we show that pluripotency can be retained independent of close cell-cell contact.
Prue Talbot, the director of UCR’s Stem Cell Center of which Sato is a member, noted that Sato’s discovery could affect the way embryonic stem cells are grown in the future.
His work is certainly an important step forward in both understanding signal transduction pathways in stem cells and in the development of an improved methodology for culturing stem cells, she said.
In the study, Sato’s group extensively screened various types of scaffold materials in combination with Y27632, a chemical compound that blocks the Rho-Rock pathway, and found that the Matrigel coating could be replaced with poly-D-lysine, a chemically synthesized ECM. The major advantages of poly-D-lysine over Matrigel are that poly-D-lysine is completely animal-free, easy to handle, and its quality is consistent.
We found that the growth of the hESCs under this novel culture condition was almost identical to the growth of hESCs on Matrigel-coated culture plates, with no compromise in pluripotency, Sato said.
Illustration: hESCs grown on Matrigel in defined culture media. The mesh-like structure in the background is Matrigel. –University of California, Riverside.
University of California, Riverside News Release (08/19/08)
Science Daily (08/20/08)
Abstract (Public Library of Science ONE; 3(8) (08/20/08))