Blood-clotting receptor shown to have a role in normal stem cell differentiation

A receptor on the surface of adult cells that triggers inflammation and blood clotting also plays a role in guiding the development of embryonic stem cells, researchers at the University of Illinois at Chicago have found.

G-protein coupled receptors transmit a wide variety of external signals into cells and are a major target for drug development. But very little is known about how this group of receptors is involved in coordinating the differentiation of embryonic stem cells into fully-functioning, mature cells.

Asrar Malik

Asrar Malik, Schweppe Family Distinguished Professor and head of pharmacology, UIC College of Medicine

Asrar Malik, the Schweppe Family Distinguished Professor and head of pharmacology in the UIC College of Medicine, and his colleagues wanted to determine which G-protein coupled receptors become activated as embryonic stem cells are led to develop into mature endothelial cells — the thin, flattened cells that line the blood vessels.

When they screened for genes that are active during the differentiation of mouse embryonic stem cells into endothelial cells, they found high levels of the gene for PAR1, a G-protein coupled receptor involved in inflammation and blood clotting in adult cells that had never been studied in embryonic stem cells.

“During early development, when stem cells begin to differentiate, there is no inflammation or blood clotting,” said Malik, who is senior author on the study, published in the journal Stem Cell Reports. “But we saw that PAR1 levels substantially increased when the mouse embryonic stem cell differentiated into endothelial cells.”

When the researchers deleted the PAR1 gene, or activated PAR1 by providing its normal binding protein in mouse embryonic stem cells, the cells were unable to mature into endothelial cells.

“This made us think that maybe, in the stem cell setting, PAR1 isn’t acting as a receptor,” said Dr. Jalees Rehman, associate professor of pharmacology and cardiology and a co-author on the study. “We thought that it might be acting to bind and deactivate another receptor — a process known as scaffolding.”

When the researchers looked more closely at what PAR1 was doing as the cells underwent differentiation, they found that PAR1 blocked the activity of a growth factor called TGF beta that is known to prevent the formation of endothelial cells.

“This research shows how a receptor that does one thing in mature cells can have a completely different role during stem cell differentiation,” said Malik. “Identifying this novel scaffolding function of a G-protein coupled receptor in embryonic stem cells also raises the possibility that additional G-protein coupled receptors may have similar previously unrecognized scaffolding functions.”

Other co-authors are Haixia Gong, Shejuan An, Menglin Liu, Victoria Mastej, Manish Mittal, and Zhigang Hong of UIC; Antonia Sassmann and Stefan Offermanns of the Max-Planck Institute for Heart and Lung Research in Germany; and Wei Zhang of Northwestern University.

This research was funded by National Institutes of Health grants P01HL60678, R01HL45638, R01HL118068, R01HL90152, R01GM094220, T32HL007829 and American Heart Association grant 13SDG16910050.