Abstract
Fibroblast growth factor 2 (basic FGF or FGF2) has been shown to affect growth and differentiation in some tissues and to be required for cardiac hypertrophy in vivo. FGF2 has been shown in vitro to signal through the mitogen-activated protein kinase (MAPK) to affect cell survival and growth. To ascertain the role of FGF2 in cardiac hypertrophy, wildtype, Fgf2 knockout, non-transgenic, and FGF2 transgenic mice were treated with isoproterenol or saline via subcutaneous mini-osmotic pump implants to induce a hypertrophic response to β-adrenergic stimulation. Fgf2 knockout hearts are protected from isoproterenol-induced cardiac hypertrophy; whereas, FGF2 transgenic hearts show exacerbated cardiac hypertrophy as assessed by heart weight-to-body weight ratios and myocyte cross-sectional area. Echocardiography reveals significantly decreased fractional shortening in isoproterenol-treated FGF2 transgenic mice but not in Fgf2 knockout mice suggesting that FGF2 mediates the maladaptive cardiac dysfunction seen in cardiac hypertrophy induced by isoproterenol. Western blot analysis also reveals alterations in MAPK signaling in Fgf2 knockout and FGF2 transgenic hearts subjected to isoproterenol treatment, suggesting that this cascade mediates FGF2's pro-hypertrophic effect. Pharmacologic inhibition of extracellular signal-regulated kinase (ERK) signaling results in an attenuated hypertrophic response in isoproterenol-treated FGF2 transgenic mice, but this response is not seen with p38 mitogen-activated protein kinase (p38) pathway inhibition, suggesting that FGF2 activation of ERK but not p38 is necessary for FGF2's role in the mediation of cardiac hypertrophy.