Abstract 1481: Inactivation of Conditional Jagged-1, but not DII-1, by mx-Cre Leads to Defects of Functional EPC Kinetics and Post-Natal Vascularization
Accumulating evidence highlights the beneficial effects of endothelial progenitor cells on vascular repair in ischemic disease. However, the molecular mechanism toward the origin and commitment in marrow structure or ischemic sites is still not clear. To investigate the therapeutic potential and functional importance of Notch signals on EPC mediated-neovascularization, we analyzed conditional knockout mice of jagged-1 or DII-1, a ligand of Notch signals. Inactivation of conditional jagged-1, not DII-1 by mx-Cre leads to defects of post-natal neovascularization with immature restoration of vascular structure in sites of ischemia, demonstrated by hind limb ischemia model (p<0.01, n=8). Among the functional EPC kinetics, EPC commitment in bone marrow was preferentially impaired in Jagged-1 null mice, not DII-1, demonstrated by flow cytometry, EPC colony assay and Ac-LDL uptake using marrow progenitor cells or circulating cells. Cycling EPC enriched cells (BrdU+ Sca-1+ cells) significantly reduced in Jagged-1 mutant mice in circulation, while mobilization capacity was intact. Importantly, CXCR4 (+) or Flk-1 (VEGFR2) (+) cells in Sca-1 (+) cells in peripheral blood were significantly decreased by inactivation of jagged-1, but not DII-1. These EPC enriched cells were resulted from impaired progenitor maturation in bone marrow, eventually resulting in significantly reduced in vitro invasive capacity and in vivo incorporation into sites of ischemia. In the study of gain of function using stromal cells expressing Notch ligands, jagged-1, DII-1 and DII-4, we also found that Jagged-1 or DII-4 derived signals evidently promoted EPC differentiation, resulting in postnatal vascularization with restored vascular structure. Finally, vascular dysfunction occurred in Jagged-1 mutant mice were profoundly rescued by Jagged-1 experienced EPC, not DII-1groups. In conclusion, these findings indicate that Notch signals subsequently contribute to EPC commitment and postnatal neovascularization. To our knowledge, this is first evidence that Notch signals are required for postnatal neovascularization via EPC maturation, providing us critical clue of elucidating the mechanism of cell fate determination of EPC and its functional therapeutic cascade.