Submitted on August 4, 2008
Revised on March 16, 2009
Accepted on March 31, 2009
Chronic Exposure to Fibrin and Fibrinogen Differentially Regulates Intracellular Ca2+ in Human Pulmonary Arterial Smooth Muscle and Endothelial Cells
Amy L. Firth1, Jocelyn Yau1, Amanda White1, Peter G. Chiles2, James J. Marsh1, Timothy A. Morris1, and Jason X.-J. Yuan3*
1 University of California, San Diego
2 University of Califonria, San Diego
3 University of Califormia, San Diego
* To whom correspondence should be addressed. E-mail: xiyuan{at}ucsd.edu.
Acute pulmonary embolism occurs in more than half a million people a year in the United States. Chronic thromboembolic pulmonary hypertension (CTEPH) develops in ~4% of these patients due to unresolved thromboemboli. CTEPH is thus a relatively common, progressive and potentially fatal disease. One currently proposed theory for the poor resolution advocates that modification of fibrinogen in CTEPH patients causes resistance of emboli to fibrinolysis. The current study investigated the regulation of cytosolic Ca2+ ([Ca2+]cyt), central to the control of cell migration, proliferation and contraction, by chronic exposure of pulmonary artery smooth muscle (PASMC) and endothelial (PAEC) cells to fibrinogen and fibrin. Basal [Ca2+]cyt was substantially elevated in PAEC after culture on fibrinogen, fibrin and thrombin and in PASMC on fibrinogen and fibrin. In PAEC, fibrinogen significantly decreased the peak [Ca2+]cyt transient (P<0.001), without a change in the transient peak width (at 50% of the peak height). This response was independent of effects on the proteinase-activated receptor 1 (PAR-1). Furthermore, chronic exposure to thrombin, an activator of proteinase-activated receptors, significantly reduced the peak agonist-induced Ca2+ release in PAEC, but increased it in PASMC. The recovery rate of the agonist-induced [Ca2+]cyt transients decelerated in PASMC chronically exposed to fibrin; a small increase of the peak Ca2+ was also observed. Substantial augmentation of PASMC (but not PAEC) proliferation was observed in response to chronic fibrin exposure. In conclusion, chronic exposure to fibrinogen, fibrin and thrombin caused differential changes in [Ca2+]cyt in PAEC and PASMC. Such changes in [Ca2+]cyt may contribute to vascular changes in patients who have CTEPH where the pulmonary vasculature is persistently exposed to thromboemboli.
