Angiogenesis is the process of new blood vessel formation, crucial for the development of an embryo as well as for organ growth and wound healing later in the adulthood. A key factor responsible for the stimulation of angiogenesis is VEGF165, the most potent splicing isoform of VEGF-A. Based on recent results obtained in the host laboratory, the driving hypothesis standing beyond this work was to investigate why endothelial cells in the skeletal muscle and in the neonatal heart respond to AAV-VEGF165 inducing angiogenesis, whereas in the adult heart they do not. For this purpose, we investigated the responsiveness of adult cardiac and neonatal endothelial cells (ECs), as well as of muscle ECs to the proangiogenic factor VEGF in vitro. Based on the observation that cardiac ECs lose their proliferative capacity at day 7 after birth, we performed a transcriptome analysis of the three EC populations and identified a few differentially expressed genes (DEGs). Particularly, we focused on Dhcr24, the most interesting gene among DEG between pre-natal and post-natal ECs. We developed a genome editing strategy to investigate its functional role in angiogenesis. In the first set of experiments, the proliferation of adult and neonatal cardiac ECs and muscle ECs was assessed after VEGF administration at different time points, followed by immunofluorescence staining and image acquisition. Interestingly and different from their in vivo behaviour, adult cardiac ECs proliferated in response to VEGF at both time points, suggesting that some inhibitory factor might block their response in the adult heart in vivo. In the second set of experiments, the CRISPR/Cas9 technology was used to silence Dhcr24 in SVEC and LG cell lines. Successful knockout was confirmed by the downregulation of Dhcr24 protein expression in Western blot. Development of an efficient genome editing strategy could offer an opportunity to genetically modify Dhcr24 in quiescent ECs and test its ability to restore the pro-angiogenic phenotype.