Submitted on April 2, 2007
Accepted on April 9, 2008
Prostacyclin analogues stimulate vascular endothelial growth factor (VEGF) production from human lung fibroblasts in culture
Koichiro Kamio1, Tadashi Sato2, Xiangde D. Liu2, Hisatoshi Sugiura3, Shinsaku Togo4, Tetsu Kobayashi5, Shin Kawasaki6, Xingqi Wang2, Lijun Mao7, Youngsoo Ahn2, Olaf Holz8, Helgo Magnussen8, and Stephen I. Rennard2*
1 Nippon Medical School, Division of Pulmonary Medicine, Medicine, Tokyo, Japan
2 University of Nebraska Medical Center, Omaha, Nebraska, United States
3 Third Department of Internal Medicine, Wakayama Medical University, Wakayama, Japan
4 Department of Respiratory Medicine, Juntendo University School of Medicine, Tokyo, Japan
5 The Third Department of Medicine, Mie Unviersity Graduate School of Medicine, Mie, Japan
6 Department of Respiratory Medicine, The University of Tokyo Hospital, Tokyo, Japan
7 Department of Rheumatology, The Third Hospital of Peking University, Beijing, China
8 Center for Pneumology and Toracic Surgery, Hospital Grosshansdorf, Grosshansdorf, Germany
* To whom correspondence should be addressed. E-mail: srennard{at}unmc.edu.
Prostacyclin is a short-lived metabolite of arachidonic acid that is produced by
several cells in the lung and prominently by endothelial cells. It increases
intracellular cAMP levels activating downstream signaling thus regulating vascular mesenchymal cell functions. The alveolar wall contains a rich capillary network as well as a population of mesenchymal cells, i.e. fibroblasts. The current study evaluated the hypothesis that prostacyclin may mediate signaling between endothelial and mesenchymal cells in the alveolar wall by assessing the ability of prostacyclin analogues to modulate fibroblast release of vascular endothelial growth factor (VEGF). To accomplish this study, human lung fibroblasts were cultured in routine culture on plastic support and in three-dimensional collagen gels with or without three prostacyclin analogues, carbaprostacyclin, iloprost and beraprost, and the production of VEGF was evaluated by enzyme-linked immunosorbent assay (ELISA) and quantitative real-time PCR. Iloprost and beraprost significantly stimulated VEGF mRNA levels and protein release in a concentration-dependent manner. These effects were blocked by the adenylate-cyclase inhibitor SQ22536 and by the protein kinase-A inhibitor KT-5720 and were reproduced by a direct PKA activator by not by an activator of Epac, indicating that cAMP activated PKA signaling mediated the effect. Since VEGF serves to maintain the pulmonary microvasculature, the current study suggests that prostacyclin is part of a bi-directional signaling network between the mesenchymal and vascular cells of the alveolar wall. Prostacyclin analogues, therefore, have the potential to modulate the maintenance of the pulmonary microcirculation by driving the production of VEGF from lung fibroblasts.
