ABSTRACT
Utilizing in utero aortopulmonary vascular graft placement, we developed a lamb model of congenital heart disease and increased pulmonary blood flow. We showed previously that these lambs have increased pulmonary vessel number at 4 wk of age. To determine whether this was associated with alterations in VEGF signaling, we investigated vascular changes in expression of VEGF and its receptors, Flt-1 and KDR/Flk-1, in the lungs of shunted and age-matched control lambs during the first 8 wk of life. Western blot analysis demonstrated that VEGF, Flt-1, and KDR/Flk-1 expression was higher in shunted lambs. VEGF and Flt-1 expression was increased at 4 and 8 wk of age (P <0.05). However, KDR/Flk-1 expression was higher in shunted lambs only at 1 and 4 wk of age (P <0.05). Immunohistochemical analysis demonstrated that, in control and shunted lambs, VEGF localized to the smooth muscle layer of vessels and airways and to the pulmonary epithelium while increased VEGF expression was localized to the smooth muscle layer of thickened media in remodeled vessels in shunted lambs. VEGF receptors were localized exclusively in the endothelium of pulmonary vessels. Flt-1 was increased in the endothelium of small pulmonary arteries in shunted animals at 4 and 8 wk of age, whereas KDR/Flk-1 was increased in small pulmonary arteries at 1 and 4 wk of age. Our data suggest that increased pulmonary blood flow upregulates expression of VEGF and its receptors, and this may be important in development of the vascular remodeling in shunted lambs.
Subject(s)
Endothelial Growth Factors/metabolism , Hypertension, Pulmonary/metabolism , Intercellular Signaling Peptides and Proteins/metabolism , Lymphokines/metabolism , Pulmonary Circulation/physiology , Vascular Endothelial Growth Factor Receptor-1/metabolism , Vascular Endothelial Growth Factor Receptor-2/metabolism , Age Factors , Amino Acid Sequence , Animals , Antibody Specificity , Endothelial Growth Factors/chemistry , Endothelial Growth Factors/immunology , Female , Hypertension, Pulmonary/physiopathology , Immunoblotting , Immunohistochemistry , Intercellular Signaling Peptides and Proteins/chemistry , Intercellular Signaling Peptides and Proteins/immunology , Lung/blood supply , Lung/metabolism , Lymphokines/chemistry , Lymphokines/immunology , Molecular Sequence Data , Pregnancy , Rabbits , Sheep , Vascular Endothelial Growth Factor A , Vascular Endothelial Growth FactorsABSTRACT
Vascular endothelial growth factor (VEGF) and basic (b) fibroblast growth factor (FGF-2/bFGF) are involved in vascular development and angiogenesis. Pulmonary artery smooth muscle cells express VEGF and FGF-2 and are subjected to mechanical forces during pulsatile blood flow. The effect of stretch on growth factor expression in these cells is not well characterized. We investigated the effect of cyclic stretch on the expression of VEGF and FGF-2 in ovine pulmonary artery smooth muscle cells. Primary confluent cells from 6-wk-old lambs were cultured on flexible silicon membranes and subjected to cyclic biaxial stretch (1 Hz; 5-25% stretch; 4-48 h). Nonstretched cells served as controls. Expression of VEGF and FGF-2 was determined by Northern blot analysis. Cyclic stretch induced expression of both VEGF and FGF-2 mRNA in a time- and amplitude-dependent manner. Maximum expression was found at 24 h and 15% stretch (VEGF: 1.8-fold; FGF-2: 1.9-fold). These results demonstrate that mechanical stretch regulates VEGF and FGF-2 gene expression, which could play a role in pulmonary vascular development or in postnatal pulmonary artery function or disease.
