Abstract 1303: PPAR-delta Agonist Enhances Vasculogenesis by Regulating Endothelial Progenitor Cells through Genomic and Non-genomic Activations of the PI3K/Akt Pathway.
Background : PPARs form a subfamily of the nuclear receptor superfamily and three isoforms, PPAR- α, -γ, -δ, have been identified. Among these, PPAR-δ is the least understood subtype. Especially, the impact of PPAR-δ activation in vascular biology is virtually unknown. Thus we investigated the effect of PPAR-δ activation on EPC, vasculogenesis and its signal pathway.
Methods and Results : Human EPCs were cultured under the variable concentration of GW501516, potent and selective PPAR-δ agonist. In trypan blue exclusion assay, PPAR-δ activation enhanced EPC proliferation, and inhibited hypoxia-induced apoptosis dose dependently. These were reconfirmed by cell cycle and apoptosis FACS. In Matrigel tube formation and transendothelial migration assay, treated EPC showed more tube formation and migration in proportion to GW501516 concentration. These actions of PPAR-δ activation in EPCs were mediated via the PI3K/Akt pathway. In Western blot assays, GW501516 phosphorylated Akt in EPC in PPAR-δ dependent manner, reversed by PPAR-δ antisense oligodeoxynucleotides transfection. PI3K blocker LY294002 abolished the several in vitro effects of PPAR-δ activation on EPC. The Akt phosphorylation occurred in a bimodal pattern at less than 1 hour and at 4 – 8hours. The late phosphorylation was dependent on transcription, which was suppressed by actinomycin D, whereas the early induction was not. Immunoprecipitation assay showed the early rapid/nontranscriptionally mediated phosphorylation occurred by binding between PPAR-δ and p85, the regulatory subunit of PI3K. To establish whether PPAR-δ activation really induces vasculogenesis, in vivo studies were performed. PPAR-δ treated human EPCs transplantation salvaged ischemic limbs by vessel formation in murine hindlimb ischemia model. Furthermore, systemic administration of GW501516 to C57BL/6 mice increased hematopoietic stem cells in bone marrow, EPCs in peripheral blood, and improved vasculo-genesis in cornea injury model.
Conclusions : Our study demonstrates that PPAR-δ activation upregulates EPC number, enhances EPC functions and promotes vasculogenesis in vitro and in vivo. Our data suggest that PPAR-δ agonist may be a novel therapeutic option in the treatment of ischemic vascular diseases.