VASCULAR BIOLOGY Enhancement of vascular progenitor potential by protein kinase A through dual

Fine tuning of vascular endothelial growth factor (VEGF) signaling is critical in endo-thelial cell (EC) differentiation and vascu-lar development. Nevertheless, the sys-tem for regulating the sensitivity of VEGF signaling has remained unclear. Previ-ously, we established an embryonic stem cell culture reproducing early vascular development using Flk1 (VEGF receptor-2) cells as common progenitors, and demonstrated that cyclic adenosine monophosphate (cAMP) enhanced VEGF-induced EC differentiation. Here we show that protein kinase A (PKA) regulates sensitivity of Flk1 vascular progenitors to VEGF signaling for efficient EC differen-tiation. Blockade of PKA perturbed EC differentiation and vascular formation in vitro and ex vivo. Overexpression of con-stitutive active form of PKA (CA-PKA) potently induced EC differentiation and vascular formation. Expression of Flk1 and Neuropilin-1 (NRP1), which form a selective and sensitive receptor for VEGF165, was increased only in CA-PKA– expressing progenitors, enhancing the sensitivity of the progenitors to VEGF165 by more than 10 times. PKA activation induced the formation of a VEGF165, Flk1, and NRP1 protein complex in vascular progenitors. These data indicate that PKA regulates differentiation potential of vas-cular progenitors to be endothelial compe-tent via the dual induction of Flk1 and NRP1. This new-mode mechanism regu-lating “progenitor sensitivity ” would pro-vide a novel understanding in vascular development and regeneration. (Blood. 2009;114:3707-3716