Placenta Endothelial Protein 1 Is a Novel Neural Guidance Molecule on Angiogenesis.

Angiogenic Processes are tightly regulated by guidance molecules for directed blood vessel growth during development and under diseased conditions. Here we report a novel protein, Placenta Endothelial Protein-1 (PEP1), which may participate in the neurovascular interaction and vessel guidance. Identified by SAGE database mining, PEP1 is highly expressed in human placenta vasculatures and is well-conserved among all vertebrates. In silico analysis predicted the potential roles of PEP1 may involve in the cell migration and cell-to-ECM interaction. To investigate the function of PEP1, we altered endogenous PEP1 expression in human umbilical vein endothelial cells (HUVECs) for subsequent angiogenesis assays. Our data indicated overexpression of PEP1 in HUVEC significantly decreased cell motility and tubular formation capability, whereas knockdown of PEP1 in HUVECs resulted in the opposing effects. To characterize PEP1 in vivo, we next examined the physiological roles of zPEP1 (PEP1 ortholog in zebrafish) during zebrafish embryonic development. Real-time quantitative PCR analysis first indicated zPEP1 to express after 16 hours post-fertilization (hpf), which coincides with the start of vascular development. To our surprise, whole mount in situ hybridization showed that zPEP1 was expressed prominently in the neural stem cells of developing nervous system, suggesting PEP1 may function as a neural guidance molecule. By injecting morpholino antisense oligos to knockdown zPEP1 expression in developing embryos, we observed stalled growth of intersegmental vessels, reaffirming the role of PEP1 in regulating angiogenesis. Besides, confocal immunocytochemistry analysis shown a co-localization of PEP1 and paxillin in HUVEC, implying the regulatory effect of PEP1 may enact via the paxillin-dependent signal pathway. Taken together, our study revealed the significant roles of PEP1 in neurovascular interaction and vascular patterning. Future analysis on this novel vessel patterning protein shall shed light on the complex communication network between nervous and vascular systems.