Acidic and basic fibroblast growth factors involved in cardiac angiogenesis following infarction

Abstract

Acidic and basic fibroblast growth factors (FGF-1/FGF-2) promote angiogenesis in cancer. Angiogenesis is integral to cardiac repair following myocardial infarction (MI). The potential regulation of FGF-1/FGF-2 in cardiac angiogenesis postMI remains unexplored. Herein, we examined the temporal and spatial expression of FGF-1/FGF-2 and FGF receptors (FGFR) in the infarcted rat heart at days 1, 3, 7, and 14 postMI. FGF-1/-2 gene and protein expression, cells expressing FGF-1/-2 and FGFR expression were examined by quantitative in situ hybridization, RT-PCR; western blot, immunohistochemistry and quantitative in vitro autoradiography. Compared to the normal heart, we found that in the border zone and infarcted myocardium 1) FGF-1 gene expression was increased in the first week postMI and returned to control levels at week 2; FGF-1 protein levels were, however, largely reduced at day 1, then elevated at day 3 peaked at day 7 and declined at day 14; and cells expressing FGF-1 were primarily inflammatory cells; 2) FGF-2 gene expression was significantly elevated from day 1 to day 14; the increase in FGF-2 protein level was most evident at day 7 and cells expressing FGF-2 were primarily endothelial cells; 3) FGFR expression started to increase at day 3 and remained elevated thereafter; and 4) FGF-1/FGF-2 and FGFR expression remained unchanged in the noninfarcted myocardium. Thus, FGF-1/FGF-2 and FGFR expression are enhanced in the infarcted myocardium in the early stage after MI, which is spatially and temporally coincident with angiogenesis, suggesting that FGF-1/FGF-2 are involved in regulating cardiac angiogenesis and repair.

Figure 1

Temporal and spatial FGF-1 gene expression in the infarcted heart: FGF-1 mRNA was normally present in both left and right ventricles (LV, RV) (panel A). Following MI, increased FGF-1 mRNA levels were seen at the border zone at day 1 (panel B), followed by appearance in the infarcted myocardium at day 3 (panel C) and 7, and declined to control levels at day 14 (panel D). FGF-1 mRNA levels remained unchanged in the noninfarcted septum (S). Panels E and F show quantitative FGF-1 mRNA levels in the border zone (BZ) and infarcted myocardium at different time points postMI. *p<0.05 vs controls; †p<0.05 vs previous time point.

Figure 2

Temporal expression of cardiac FGF-1 postMI: Following MI, FGF-1 protein levels at the border zone (panel A) and infarcted myocardium (panel B) were significantly reduced at day 1, elevated at day 3, peaked at day 7, then declined, but still remained significantly higher than in controls at day 14.

Figure 3

Cells expressing FGF-1 in the normal and infarcted heart: Immunohistochemistry shows positive staining in the interstitial cells of the normal heart (panel A). Following MI, strong staining was seen in the border zone at day 7, where cells expressing FGF-1 were primarily inflammatory cells and fibroblast-like cells (panel B, brown). Panel C: negative control; Noninf: noninfarcted myocardium; X200

Figure 4

Quantitative FGF-2 gene expression in the border zone (panel A) and infarcted myocardium (panel B).

Figure 5

Temporal expression of cardiac FGF-2 postMI. Compared to controls, FGF-2 at the border zone (panel A) was slightly reduced at day 1, significantly increased at day 3, peaked at day 7 and declined to normal levels at day 14, while in the infarcted myocardium, it was decreased at days 1 and 3 and increased only at day 7 (panel B).

Figure 6

Cells expressing FGF-2 in the normal and infarcted heart: Positive FGF-2 staining was primarily distributed in myocytes of the normal heart (panel A). Following MI, strong staining was seen at the border zone at day 7, where cells expressing FGF-2 were primarily newly-formed microvessels (panel B, brown and arrows). Panel C: negative control. X400

Figure 7

Temporal and spatial expression of cardiac FGFR postMI: As detected by quantitative in vitro autoradiography, low levels of FGFR were present in the normal myocardium (panel A), while blood vessels contained higher levels of FGFR (arrows). Following MI, FGFR levels remained unchanged in the infarcted myocardium at day 1 (panel B), increased at day 3 (panel C), reached a peak at day 7 (panel D), and declined, but remained higher than controls at day 14 (panel E). FGFR level remained unchanged in the noninfarcted septum. Panel F shows quantitative FGFR levels in the infarcted myocardium at different time points postMI.