Abstract 480: The Neurotrophin p75 Receptor Impairs Angiogenesis and Endothelial Progenitor Cell function.
Neurotrophins (NTs), which are known to promote survival, differentiation, and regeneration of neural cells, were recently showed to exert cardiovascular actions. NTs act through two different classes of receptors, tropomyosin-related kinase receptors and a p75 receptor (NTR-p75), which belongs to the TNF receptor superfamily. We previously reported that NT-p75 expression by capillary ECs is insignificant under basal conditions, but it increases in the presence of diabetes and ischemia. Increased NTR-p75 expression by capillaries correlates with higher endothelial cell (EC) apoptosis and impaired angiogenesis. We hypothesized that NTR-p75 directly promotes apoptosis and depresses proliferation and migration of ECs and endothelial progenitor cells (EPCs). This would impair reparative neovascularization of ischemic muscles. To investigate our hypotheses, HUVECs and human blood-derived EPCs were infected with an adenovirus carrying NTR-p75 (Ad.NTR-p75) (100 to 500 moi) or with the control Ad.Null. Apoptosis was evaluated by the Caspase-Glo® assay and by counting the number of apoptotic microparticles released by the cells in the culture medium. Cell cycle was evaluated by flow cytometer. Cell migratory capacity versus SDF-1 (100 ng/mL) was assessed in 24-well transmigration chamber (membrane pore size of 5μm). Moreover, unilateral limb ischemia was induced in CD1 mice and Ad.NTR-p75 (109 pfu) was immediately delivered into the ischemic adductor muscles to study the effect on capillary EC proliferation and apoptosis (by PCNA staining and TUNEL assay at 3d post-ischemia, respectively), muscular neovascularization (capillary density counting at 14d post-ischemia), and blood flow recovery (Lisca colour Doppler at 0, 3, 7, and 14d post-ischemia). In vitro, NTR-p75 over-expression promoted apoptosis and the shedding of apoptotic microparticles, inhibited cell cycle progression, and impaired the migration versus SDF-1 of ECs and EPCs. In vivo, Ad.NTR-p75 inhibited proliferation and induced apoptosis of muscular ECs, thus impairing post-ischemic neovascularization and blood flow recovery. Our results identify for the first time the anti-angiogenic function of NTR-p75 and the underpinned cellular mechanisms.