Vascular endothelial growth factor (VEGF)-A: role on cardiac angiogenesis following myocardial infarction

Abstract

The current study is to determine the regulatory role of VEGF-A in cardiac angiogenesis following myocardial infarction (MI). Cardiac angiogenic response and temporal/spatial expression of VEGF-A/VEGF receptors (VEGFR) were examined at 1, 2, 6, 12 h and 1, 2, 3, 4, 7, 14, and 28 days postMI. We found that following MI, newly formed vessels first appeared at the border zone between noninfarcted and infarcted myocardium as early as day 3 and subsequently in the infarcted myocardium. Vascular density in the infarcted myocardium peaked at day 7 and then gradually declined. VEGF-A mRNA started to increase at the border zone at 2 h postMI, reached peak at 12 h, declined at day 1, and returned to normal levels at day 2 and thereafter. VEGF-A protein levels at the border zone were only increased during day 1 postMI. VEGF-A within the infarcted myocardium levels, however, was persistently suppressed postMI. VEGFR expression was significantly increased only at the border zone at day 1, but not in the later stages. The expression of VEGF-A/VEGFR remained unchanged in the noninfarcted myocardium. Thus, the early rise of VEGF-A/VEGFR at the border zone suggests that VEGF-A initiates the cardiac angiogenic response postMI, but short-lived VEGF-A/VEGFR activation at the border zone and consistently suppressed VEGF-A within the infarcted myocardium suggests that VEGF-A may not be crucial to the later stages of angiogenesis.

Figure 1

Angiogenesis in the infarcted heart: As detected by immunohistochemical CD31 labeling, normal myocardium (CTL) was rich in capillaries (brown). Following MI, pre-existing vessels were totally lost in the infarcted myocardium at day 1, newly formed microvessels appeared at the border zone at day 3. Abundant new microvessels were seen in the infarcted myocardium at day 7. Vascular density was then declined at day 14 and 28. x200

Figure 2

Temporal changes of microvascular density in the infarcted myocardium. *p<0.05 vs CTL; †p<0.05 vs previous time point.

Figure 3

Temporal and spatial gene expression of VEGF-A in the infarcted heart: As detected by in situ hybridization, VEGF-A mRNA was normally present in both left and right ventricles (RV, LV). Following MI, VEGF-A mRNA levels remained unchanged in the infarcted myocardium at 1 hour. VEGF-A mRNA levels were increased at the border zone (arrows) and endocardium (arrowheads) at 2 hours, became more evident at 6 hours, reached peak at 12 hours, declined, but was still higher than controls at day 1 and returned to normal level at day 2. VEGF-A mRNA was increased constantly reduced in the infarcted myocardium for over the course of 4 weeks. VEGF-A mRNA levels remained unchanged in the noninfarcted septum (S).

Figure 4

Quantitative VEGF-A mRNA levels in the border zone and infarcted myocardium at different time points postMI.

Figure 5

Temporal changes of VEGF-A protein levels in the border zone postMI: As detected by western blot, VEGF₁₈₈ and VEGF₁₆₄ were normally expressed in the rat heart. Following MI, both VEGF₁₈₈ and VEGF₁₆₄ were significantly increased at 2, 6, 12 and 24 hours. VEGF₁₈₈ declined to the normal level at day 2 and thereafter, while VEGF₁₆₄ levels were significantly lower than controls at day 2 and beyond.

Figure 6

Temporal changes of VEGF-A protein levels in the infarcted myocardium: Compared to controls, VEGF₁₈₈ and VEGF₁₆₆ gradually declined in the infarcted myocardium for over the course of 4 weeks postMI.

Figure 7

Cardiac VEGFR expression: As detected by in vitro autoradiography, VEGFR binding was normally expressed in both LV and RV. Following MI, VEGFR binding was greatly increased at border zone (arrows) at day 1, but not in the later stages. VEGFR was largely decreased in the infarcted myocardium at day 1 postMI and returned to the control level at day 7. VEGFR binding density remained unchanged in the noninfarcted septum and right ventricle compared to controls.

Figure 8

Quantitative specific VEGFR binding density in the border zone and infarcted myocardium.