Abstract 2892: Soluble Vascular Endothelial Growth Factor Receptor (sVEGFR-1) Prevents Capillary Growth in Pressure-Overload Hypertrophy
Inadequate capillary growth in pressure-overload hypertrophy impairs myocardial perfusion and substrate delivery, contributing to progression to failure. New capillary development is tightly regulated by pro-angiogenic growth factors such as Vascular Endothelial Growth Factor (VEGF) and endogenous angiogenesis inhibitors such as the splice variant of VEGFReceptor-1 (sVEGFR-1). Binding VEGF to sVEGFR-1 restricts the amount of VEGF available for VEGFR-2 activation to induce angiogenesis. We hypothesized that in pressure-overload hypertrophy, inadequate VEGF isoform expression and differential expression of VEGF receptors determine capillary growth in LV hypertrophy at the onset of failure. Banding of the thoracic aorta was performed in 10-day-old rabbits. Tissue was harvested for RNA and protein isolation at 6wks of age (early decompensation) in hypertrophied and control animals (6–12/group). mRNA expression of total VEGF, VEGF isoforms (121,165,183,189), VEGFR-1, sVEGFR-1 and VEGFR-2 was performed by SYBR® green qRT-PCR and normalized to GAPDH and 18S. Protein levels were determined by immunoblotting and expressed as arbitrary densitometry units. Immuno-precipitation was performed to demonstrate binding of VEGF to sVEGFR-1. Data are expressed as mean±SEM with P<0.05 considered significant by t-test. mRNA and protein levels of VEGFR-1 and sVEGFR-1 were significantly up-regulated in hypertrophied hearts (mRNA expression ratio - 7 fold up-regulated; protein levels - VEGFR-1: Hypertrophy: 44±8 vs. Control: 23±1; p=0.031 and sVEGFR-1: Hypertrophy: 71±13 vs. Control: 31±3; p=0.016.) There was no difference in total VEGF (Control: 184±4 vs. Hypertrophy: 173±4; p=0.063) or any of the isoform mRNA or protein levels nor with VEGFR-2 (Control: 18±2 versus Hypertrophy: 20±4; p=0.662). Co-immuoprecipitation with sVEGFR-1 confirmed binding to VEGF in vivo. These results indicate that lack of angiogenic response in pressure-overload, which leads to heart failure, is likely due to up-regulation of VEGFR-1 and its splice variant, the soluble VEGFR-1. Strategies aimed at up-regulating VEGF or binding the soluble VEGFR-1 may be useful in maintaining capillary density and preventing heart failure.