UC San Francisco researchers have identified a molecular mechanism that may play an important role in activating platelets, the blood cells that coagulate to stop bleeding but also cause the clots leading to heart attack and stroke. The finding, published in the August 13 issue of Nature, requires further investigation, said the senior author of the study, Shaun R. Coughlin, MD, PhD, director of the Cardiovascular Research Institute (CRVI) and professor of medicine and cellular and molecular pharmacology at UCSF, but it could provide a new avenue for developing drugs for preventing heart attack and stroke.
The study, conducted in mice and on human platelets, explored the way in which the enzyme known as thrombin, one of several factors known to activate platelets, stimulates the blood cells into action. The initial observations in mice led the researchers to a potentially profound finding for humans.
In the mouse study, the researchers determined that thrombin is able to activate platelets by latching onto, and cleaving, a newly identified receptor in the membrane of the cells. When the enzyme (a protease) binds to the receptor, it instigates the transmembrane signaling that prompts platelet aggregation. The researchers named the receptor protease activated receptor (PAR) 4.
The investigators had previously identified a PAR in human platelets, which they named PAR1. They also had previously identified a PAR in mouse platelets, which they named PAR3.
In the current study, they created a mouse model with platelets lacking PAR3 and found that while the mice had a markedly delayed and diminished response to thrombin activation the response was not totally absent. The discovery of PAR4 explained the continued response. "We determined that PAR3 is necessary for normal thrombin responses in mouse platelets, but that PAR4 does contribute to thrombin signaling," said Coughlin.
The discovery that PAR3 and PAR4 appear to act as a dual-receptor syst
'"/>
Contact: Jennifer O'Brien
jobrien@itsa.ucsf.edu
(415) 476-2557
University of California - San Francisco
12-Aug-1998