Abstract 5570: β-2 Adrenergic Receptors Overexpression Promotes Angiogenesis in the Failing Myocardium through Activation of Vascular Endothelial Growth Factor/Akt Transduction Pathway
β-2 adrenergic receptor (β-2AR) plays a pivotal role in endothelial cell proliferation and promotes angiogenesis in response to hindlimb ischemia. Desensitization/uncoupling of cardiac β-2AR represents a well established phenomenon in heart failure (HF). In this study we aimed to investigate the role of β-2AR in the impairment of angiogenic processes occurring in the failing myocardium. To this purpose, we explored the angiogenic effects of β-2AR in a rat model of post-myocardial infarction (MI) HF. Cardiac adenoviral-mediated β-2AR overexpres-sion has been obtained via direct intramyocardial injection (4 x 1011 PFU) 4 weeks after MI. We also extended our observation to β-2AR knockout (β2KO) mice developing HF after large anterior MI (infarct size 45 ± 6%). Cardiac β-2AR overexpression in HF rats markedly increased capillary and arteriolar length density, and induced larger left ventricular (LV) hypertrophic responses than that observed in untreated HF animals. Such LV adaptive remodelling was associated to reduced LV diameters and improved cardiac LV fractional shortening (FS) and +dP/dt. At molecular level, cardiac β-2AR gene transfer induced sustained activation of p-Akt and S6 kinase (S6K) phosphorylation and increased p-eNOS and VEGF levels that were instead reduced in untreated HF rats. In β2KO mice, we found a ~25% reduction of cardiac capillary and arteriolar density compared to WT mice. In β2KO mice, MI was associated with a dramatically higher 21-day mortality compared to WT (70% vs 30%, respectively). Survivors β2KO mice showed increased LV end diastolic and systolic diameters, and worse global cardiac contractility compared to controls. Cardiac Akt activation, S6K phosphorylation, p-eNOS, and VEGF-A production were significantly blunted in HF β2KO mice.
Conclusions. β-2ARs play an important role in regulating angiogenic responses in post-MI HF hearts. The activation of Akt signal transduction pathway seems to be strongly involved in these mechanisms.