Investigation of Flt1 and VEGF signaling in connections during sprouting angiogenesis

Blood vessel formation is essential for vertebrate development and is primarily achieved by angiogenesis, the sprouting of endothelial cells from pre-existing vessels. Vessel networks expand when sprouts form new connections, a process whose regulation is poorly understood. Here we show that vessel anastomosis is spatially regulated by VEGFR1 (Flt1), a VEGF-A receptor that acts as a ligand decoy receptor. Expanding vessel networks in vivo favor interactions with flt-1 mutant endothelial cells. Live imaging in vitro revealed that stable connections are preceded by transient contacts from extending sprouts, suggesting sampling of potential target sites, and reduction of Flt1 reduced transient contacts. Endothelial cells at target sites with elevated protrusive activity and/or reduced Flt1 were more likely to form stable connections with incoming sprouts. Target cells with reduced membrane-localized Flt1 (mFlt1), but not soluble Flt1, recapitulated the bias towards stable connections, suggesting that relative mFlt1 expression spatially influences selection of stable connections. Thus multiple sprout anastomosis parameters are regulated by VEGF signaling, and stable connections are spatially regulated by endothelial cell-intrinsic modulation of mFlt1, suggesting new ways to manipulate how vessel networks formation.Doctor of Philosoph