Soft substrate promotes pluripotent stem cell culture

December 15, 2010

CHAMPAIGN, Ill. -- University of Illinois researchers have found a key to keeping stem cells in their neutral state: It takes a soft touch.

In a paper published in the journal PLoS One, the researchers demonstrated that culturing mouse embryonic stem cells (mESCs) on a soft gel rather than on a hard plate or dish keeps them in their pluripotent state, a ground state with the ability to become any type of tissue. The soft substrate maintains homogeneous pluripotent colonies over long periods of time - without the need for expensive growth chemicals.

"This has huge applications in the future of regenerative medicine," said mechanical science and engineering professor Ning Wang, who co-led the group with animal sciences professor Tetsuya Tanaka. "It's an exciting area. There's still a lot of work to do, but our work is a step toward understanding the basic biology of stem cells."

The difficulty of maintaining mESC colonies that are homogeneously pluripotent has been one of the main obstacles in stem cell research. Pluripotent stem cells spontaneously differentiate, beginning to turn into specialized tissue types such as skin or muscle. Scientists use chemicals called growth factors to keep mESCs in their unchanged state, but even then it's not long before the culture is a mixture of cells in various stages of differentiation, with diverse gene expression and morphologies.

Such diversity in a sample makes it very difficult for researchers to induce a culture of stem cells to become a particular type of tissue - the ultimate goal of stem cell research.

"If we start from a homogenous population of undifferentiated cells, differentiation toward the tissue of our interest might become much more homogenous than we've been able to achieve," said Tanaka, who also is affiliated with the U. of I. Institute for Genomic Biology. "So then, in generating a specific cell type - the main application of pluripotent stem cells - I think that there is an advantage to having a homogeneous culture to start with."

After noticing that pluripotent mESCs tend to stick together in round colonies while cells on the colony edges in contact with the rigid growth plate tend to differentiate more quickly, the team decided to focus on mESC mechanics rather than chemistry. Since stem cells are 10 times softer than mature cells, the researchers wondered if the mechanical forces between the plate and the cells were spurring differentiation. Wang and Tanaka's earlier research found that even small mechanical forces could be used to direct cell differentiation; could mechanics also hamper differentiation?

The team did side-by-side comparisons of mESCs grown on a traditional medium with growth factor and mESCs grown on a soft gel with the same stiffness as the cells, both with and without growth factor. They found that cells grown on the soft gel had greater homogeneity and pluripotency, even without growth factor, and even more than three months and 20 passages later.

"It's two sides of the coin: Mechanical force can induce differentiation, and here we said if you can lower the forces between the substrate and the cells, they stay pluripotent. They are complementary processes," Wang said. "Our paper shows that mechanical environment plays at least as important a role as chemical growth factors, if not greater. In vivo, cells produce growth factors for a short time and then they stop. On the other hand, mechanical forces bear on every cell all the time."

Next, the researchers want to try their soft-substrate method with induced pluripotent stem cells (iPSCs), mature cells that have been genetically reprogrammed to a pluripotent state. These cells hold a lot of promise for medical applications, but are notoriously hard to culture and not as well understood as embryonic cells.

"We can try culturing mouse iPSCs on the same soft substrate and see if the same benefit applies to achieve homogenous stem cell cultures," Tanaka said. "If that's the case, the impact would be significant."
-end-
This work was supported by the National Institutes of Health, the United States Department of Agriculture, and the University of Illinois. Co-authors were graduate students Farhan Chowdhury, Yanzhen Li and Yeh-Chuin Poh, and visiting scholar Tamaki Yokohama-Tamaki.

Editor's note: To contact Tetsuya Tanaka, call 217-244-2522; e-mail ttanaka@illinois.edu. To reach Ning Wang, e-mail nwangrw@illinois.edu.

The paper, "Soft Substrates Promote Homogeneous Self-renewal of Embryonic Stem Cells via Downregulating Cell-matrix Tractions," is available online at http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0015655.

University of Illinois at Urbana-Champaign

Related Stem Cells Articles from Brightsurf:

SUTD researchers create heart cells from stem cells using 3D printing
SUTD researchers 3D printed a micro-scaled physical device to demonstrate a new level of control in the directed differentiation of stem cells, enhancing the production of cardiomyocytes.

More selective elimination of leukemia stem cells and blood stem cells
Hematopoietic stem cells from a healthy donor can help patients suffering from acute leukemia.

Computer simulations visualize how DNA is recognized to convert cells into stem cells
Researchers of the Hubrecht Institute (KNAW - The Netherlands) and the Max Planck Institute in Münster (Germany) have revealed how an essential protein helps to activate genomic DNA during the conversion of regular adult human cells into stem cells.

First events in stem cells becoming specialized cells needed for organ development
Cell biologists at the University of Toronto shed light on the very first step stem cells go through to turn into the specialized cells that make up organs.

Surprising research result: All immature cells can develop into stem cells
New sensational study conducted at the University of Copenhagen disproves traditional knowledge of stem cell development.

The development of brain stem cells into new nerve cells and why this can lead to cancer
Stem cells are true Jacks-of-all-trades of our bodies, as they can turn into the many different cell types of all organs.

Healthy blood stem cells have as many DNA mutations as leukemic cells
Researchers from the Princess Máxima Center for Pediatric Oncology have shown that the number of mutations in healthy and leukemic blood stem cells does not differ.

New method grows brain cells from stem cells quickly and efficiently
Researchers at Lund University in Sweden have developed a faster method to generate functional brain cells, called astrocytes, from embryonic stem cells.

NUS researchers confine mature cells to turn them into stem cells
Recent research led by Professor G.V. Shivashankar of the Mechanobiology Institute at the National University of Singapore and the FIRC Institute of Molecular Oncology in Italy, has revealed that mature cells can be reprogrammed into re-deployable stem cells without direct genetic modification -- by confining them to a defined geometric space for an extended period of time.

Researchers develop a new method for turning skin cells into pluripotent stem cells
Researchers at the University of Helsinki, Finland, and Karolinska Institutet, Sweden, have for the first time succeeded in converting human skin cells into pluripotent stem cells by activating the cell's own genes.

Read More: Stem Cells News and Stem Cells Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.