Abstract
OBJECTIVE: Pressure-overload hypertrophy is associated with decreased capillary density in myocardium resulting in impaired substrate delivery. Treatment of hypertrophied hearts with vascular endothelial growth factor (VEGF) induces angiogenesis. Since angiogenesis is associated with extracellular matrix degradation, we sought to determine whether VEGF induced angiogenesis in hypertrophy required matrix metalloproteinases (MMP) activation. METHODS: Newborn rabbits underwent aortic banding. Progression of hypertrophy (mass-to-volume (M/V) ratio) and mid-wall contractility index was monitored by echocardiography. At 4 and 6 weeks, VEGF (2 microg/kg), vehicle or VEGF combined with GM6001 (5 mg/kg), a MMP inhibitor, was administered intrapericardially. CD-31 (indicator of angiogenesis), MMP-2, MT1-MMP and TIMPs (endogenous MMP inhibitors) expression were measured by immunoblotting. MMP-2 activity was determined by gelatin zymography. RESULTS: Untreated hypertrophied hearts progressed to ventricular dilatation at 7 wks (M/V ratio: 0.75 +/- 0.07), but compensatory hypertrophy was maintained with VEGF (0.91 +/- 0.07; p < 0.05). LV contractility declined in untreated hearts from -0.41 +/- 0.9 (5 wks) to -0.73 +/- 0.5 (7 wks; p < 0.05) but remained normal with VEGF (+1.61 +/- 0.6 vs. +0.47 +/- 0.2). MMP-2 expression and activity were significantly elevated in VEGF treated hypertrophied hearts (p < 0.05) and were blocked by concomitant administration of GM6001. VEGF induced neovascularization was inhibited by addition of GM6001. MT1-MMP showed a trend to higher levels in VEGF treated hearts. TIMPs were unchanged in all three groups. CONCLUSIONS: Exogenous VEGF and resultant MMP-2 activation leads to increased capillary formation in severe hypertrophy, preventing progression to ventricular dilation and dysfunction. VEGF and the associated MMP-2 activation play an important and potentially therapeutic role in vascular remodeling of hypertrophied hearts.