Browsing by Author "Peletier, Pim"

Cardiovascular diseases are reported to be the main cause of death. Inducing the growth of blood vessels, called angiogenesis, holds promising potential for improved vessel reperfusion after myocardial infarction. The vascular endothelial growth factors (VEGFs) and receptors (VEGFRs) are important regulators of blood vessel development, growth, and maintenance. VEGF-A is the protagonist of the family, but as a therapeutical measure, severe side effects impede its use. On the contrary, VEGF-B, which is mainly expressed in the heart and skeletal muscle, lacks a general pro-angiogenic effect. However, overexpression seems to carry angiogenic promise by increasing VEGF-A availability for VEGFR-2 through competition for VEGFR-1 binding. VEGF-B transcripts undergo alternative splicing, resulting in two isoforms, namely VEGF-B167 and VEGF-B186. The different isoform properties affect the VEGF-B bioavailability; thus, they should hold different translational potentials. In vivo, adeno-associated viral vector-mediated transduction of the VEGF-B isoforms resulted in cardiac hypertrophy and increased proliferation of endothelial cells. Both were more potently induced by VEGF-B186 than VEGF-B167, and the proliferation was mostly detected in the sub-endocardial region of the heart. Although the transcript levels were comparable between the isoform groups, the protein level of VEGF-B186 was much greater than VEGF-B167, implying a difference in VEGF-B isoform degradation and receptor binding dynamics. In vitro, endothelial cell regulation of the VEGF-B isoforms suggested a faster degradation of the VEGF-B167 protein. Blocking of neuropilin-1, a VEGFR-1 co-receptor, decreased the amount of VEGF-B167 protein, bound to cultured endothelial cells, whereas blocking of VEGFR-1 increased it, indicating internalization and subsequent degradation through VEGFR-1. Intracellularly, the VEGF-B167 protein increased upon blocking of ubiquitin-mediated degradation using MG132, suggesting that the protein is targeted by the ubiquitin-proteasome system. Thus, overexpression of VEGF-B stimulated a pro-angiogenic response, but of the two isoforms, VEGF-B186 had a more potent effect in the heart, presumably because VEGF-B167 was degraded more rapidly by the endothelial cells. Besides further validation of the in vitro degradation dynamics, live imaging of VEGF-B and its binding targets fused with fluorescent proteins could visualize the binding dynamics. Understanding the different properties and degradation patterns of the VEGF-B isoforms should aid in the clinical translation of their angiogenic potential, but further work is needed to elucidate the function, binding targets, and turnover of VEGF-B.