In vivo evaluation of the cardioprotective activity of VEGF-B

Members of the vascular endothelial growth factor (VEGF) family and their receptors are important regulators of vasculogenesis, angiogenesis, and vessel maintenance in both embryos and adults. In particular, the 165‐aa isoform of VEGF‐A exerts its highly potent angiogenic and arteriogenic activity mainly through binding to VEGFR‐2 in spite of its high affinity binding to VEGFR‐1. However, the biological significance of VEGF interaction with VEGFR‐1 remains elusive. One of our previous studies in dogs unveiled an unexpected cardioprotective activity of VEGF‐A, which was already evident at 48 hours after the induction of a myocardial infarction and was even more marked at 4 weeks. Multiple recent evidences suggested that VEGF‐B, a VEGFR‐1 exclusive ligand, could be selectively active in the myocardium. However the available data did not define clearly the cardiac benefits of VEGF‐B. Therefore, in the present study we wanted to investigate and compare the cardioprotective role of both VEGF‐A (and in particular its 165 aminoacid isoform) and VEGF‐B (167 aminoacid isoform) in a rat model of myocardial infarction through intracardiac injection of the respective genes. For the efficient and prolonged expression of these factors, we exploited viral vectors based on the Adeno‐ Associated Virus (AAV), as an efficient tool for in vivo gene transfer. By analyzing cardiac function by echocardiography, we observed that the prolonged expression of both VEGF factors induced a marked improvement in cardiac contractility, preserving viable cardiac tissue, and preventing left ventricular remodeling over time. In addition, we performed histopatho‐ logical studies on a subset of representative samples. Consistent with the functional outcome, we observed a more potent cardioprotection using the VEGFR‐1 selective ligand, VEGF‐B, despite its inability to induce angiogenesis. We then tried to dissect the molecular mechanisms by which VEGF‐B might act on cardiomyocytes both in vitro and in vivo. We found that the action of VEGF‐B was mainly mediated by the upregulation of VEGFR‐1 and that stimulation of this receptor exerted positive inotropic and anti‐apoptotic effects on cardiomyocytes. In addition, VEGF‐B elicited a gene expression pattern reminiscent to the one observed in compensatory heart hypertrophy, both in cultured cardiomyocytes and in infarcted hearts. We further expanded our investigation on the cardio protection conferred by VEGF‐B167 in a pacinginduced hear failure model in canines. Interestingly, the findings obtained in this model were similar and totally in keeping with the observations done in the myocardial ischemic model in rats, again showing that VEGF‐B167 exerted cardio protective effects in the absence of angiogenesis or pathological hypertrophy. Instead, it delayed the progression towards heart failure and prevented cardiomyocytes from apoptosis by controlling pro‐apoptotic intracellular mediators, such as Akt and its downstream targets GSK‐3β and FoxO3a.