Hypoxia Enhances Cellular Proliferation and Inositol 1,4,5-Triphosphate Generation in Fibroblasts from Bovine Pulmonary Artery But Not from Mesenteric Artery

Abstract

When pulmonary hypertension occurs in the face of hypoxia there is remodeling of all three layers of the pulmonary vessels, but in particular, there is an increase in number of adventitial fibroblasts. Hypoxia causes vasoconstriction in the pulmonary circulation and vasodilation in the systemic circulation. We hypothesized that there are fundamental differences in oxygen sensing and cell signaling between systemic and pulmonary artery cells in response to hypoxia. Here, we determined the effect of hypoxia either alone or in combination with known growth factors such as serum, endothelin-1 (ET-1), and platelet-derived growth factor (PDGF) on the proliferative responses of bovine pulmonary artery and mesenteric artery fibroblasts. Fibroblasts were obtained from primary cultures. Growth was assessed by [3H]thymidine incorporation. Inositol 1,4,5-triphosphate (IP3) generation was measured using a competitive binding assay. Hypoxia alone increased proliferation of pulmonary artery fibroblasts (611 +/- 24%), but not in those from the mesentery. Furthermore, hypoxia had the effect of increasing the replicative response of pulmonary fibroblasts to serum and PDGF, but no change was observed in the mesenteric cells. ET-1 had no effect on growth of either cell type. PDGF gave rise to a significant elevation in IP3 production under hypoxic conditions in the pulmonary artery cells (234%), but not in the mesenteric cells. ET-1 caused no change in IP3 production in any cell type. These data suggest that hypoxia sensitizes pulmonary artery fibroblasts to the proliferative effect of mitogens through a pathway that is not present, or is present but repressed, in the mesenteric cells.

Hypoxia-induced Proliferative Response of Vascular Adventitial Fibroblasts Is Dependent on G Protein-mediated Activation of Mitogen-activated Protein Kinases

“…However, a few reports have suggested positive roles for this kinase in promoting cell hypertrophy (39), ischemic preconditioning (40), and hemopoietic (41) and T cell proliferation or differentiation (42,43). Our results with the widely used pyr- idinyl imidazole inhibitor of p38, SB202190, demonstrating attenuation of hypoxia-induced proliferative responses of neonatal PA fibroblasts are consistent with previous reports of the role of p38 MAP kinase in the hypoxia-induced proliferative response of adult PA fibroblasts and mesangial cells (14,29). The fact that the same dose of SB202190 that attenuated hypoxia-induced proliferation augmented serum-induced proliferation also suggests potentially unique roles for p38 isozymes in hypoxic cell responses.…”

“…However, the physiological end point of hypoxia-induced activation of MAP kinases in these cells was not examined. It has been reported that hypoxia activates JNK and p38 MAP kinase and stimulates proliferation in adult bovine PA adventitial fibroblasts (12,29). Interestingly, in these cells hypoxia has little effect on ERK.…”

Selective expansion of fibroblast subpopulations from pulmonary artery adventitia in response to hypoxia

“…We and others have documented that aggregate populations of fibroblasts from the PA demonstrate increased DNA synthesis under hypoxic conditions (7,8,44,50). Similar findings have been reported in aggregate populations of fibroblasts from skin and gingiva (1,5,32,44,47).…”

Genomic assessment of a multikinase inhibitor, sorafenib, in a rodent model of pulmonary hypertension

“…The suggestion that VEGFR-2-independent pathways cause severe PH (54) led us to explore other activities contributing to the attenuated PH phenotype. Previous reports have demonstrated increased SMC proliferation to hypoxia both in vivo and in vitro via the protein kinase C (PKC)/MAPK pathway (24,31,60,61). In this study, compared with the hypoxia-alone group the combined hypoxia/ SU-5416 group had higher levels of phosphorylated MEK1/2 and ERK.…”