Emergent role of SARAF and store-operated Ca²⁺ entry in angiogenesis: Calcium Signaling and Excitation–Contraction in Cardiac, Skeletal and Smooth Muscle

Angiogenesis is a multistep process that controls endothelial cell (EC) functioning to form new blood vessels from preexisting vascular beds. This process is tightly regulated by pro-angiogenic factors, such as vascular endothelial growth factor (VEGF), which promotes signaling pathways involving the increase in the intracellular Ca²⁺ concentration ([Ca²⁺]_i). Recent evidence suggests that store-operated Ca²⁺ entry (SOCE) might play a role in angiogenesis. However, little is known regarding the role of SARAF, SOCE-associated regulatory factor in this process. The aim of this study is to examine the role of SARAF in angiogenesis. In vitro angiogenesis was studied using human umbilical endothelial cells (HUVECs) for tube formation assay and vessel sprouting using rat aortic ring by Matrigel assay supplemented with endothelial cell basal medium enriched with different growth factors (VEGF, FGF, b-EGF, and IGF). HUVECs migration was evaluated by wound healing assay, and HUVECs proliferation using Ki67⁺ marker. Ex vivo angiogenesis was examined by whole mount mice retina on P6 in neonatal mice injected with increasing concentrations of a SOCE inhibitor, GSK-7975A, on P3, P4, and P5. We observed that SOCE inhibition with GSK-7975A blocks aorta sprouting, as well as HUVEC tube formation and migration. The intraperitoneal injection of GSK-7975A also delays the development of retinal vasculature assessed at postnatal day 6 in mice since it reduces vessel length and the number of junctions while it increases lacunarity. Moreover, we found that knockdown of SARAF using siRNA impairs VEGF-mediated [Ca²⁺]_i increase and HUVEC tube formation, proliferation, and migration. Our data show for the first that SOCE inhibition prevents angiogenesis using different approaches and we provide evidence indicating that SARAF plays a critical role in angiogenesis.