Abstract 19674: Late Endothelial Progenitor Cells (EPCs) and Platelets Interact through Endothelial Differentiation Gene (Edg)-2-Lysophosphatidic Acid (LPA) Axis under the Regulation of Peroxisome Proliferator-Activated Receptor (PPAR)-δ, Leading to Vasculogenesis

Abstract

Background PPAR-δ has been implicated in various cellular metabolism, but the roles in vascular biology are largely unexplored. Here, we investigated the effects of PPAR-δ activation on late EPC-platelet network. Methods & Results GW501516 (500nM), a highly selective PPAR-δ agonist treatment enhanced BrdU incorporation to human late EPCs, and augmented their pro-vasculogenic effects such as Matrigel tube formation and scratch-wound healing dose-dependently. To reveal the mechanism, the expression level of Edg family members was screened in late EPCs after PPAR-δ activation. We found that only Edg-2 mRNA and protein expression, which is a major receptor for LPA, were specifically upregulated by GW501516. ChIP and promoter assays demonstrated the direct transcriptional regulation of Edg-2. Edg-2 is a membrane receptor for LPA which is the major lysophospholipid growth factor generated on platelet activation. GW501516 (500nM), the supernatant of activated platelets, or LPA (100nM) induced the proliferation (BrdU incorporation) of late EPCs, and enhanced their provasculogenic functions such as chemotaxis (Transwell), planar migration (scratch wound healing), and capillary tube formation (in vitro Matrigel). Co-treatment of GW501516 and the supernatant synergistically enhanced the above results, suggesting the interaction between late EPCs and platelets augmented by PPAR-δ activation. But GSK0660 (1μM, PPAR-δ antagonist) or Ki16425 (3μM, EDG-2 blocker) treatment reversed the results. In vivo Matrigel plug assay (n=4, each group), the combination of late EPCs (106/plug) and platelets robustly induced capillary formation, compared with late EPCs or platelets alone. GW501516 potentiated the interaction, leading to more capillaries. In vivo mouse skin wound model (n=4, each group), late EPCs in platelet gel enhanced the wound healing with new vessel formation, which was augmented by GW501516 , confirming the interaction in vivo. PPAR-δ or EDG-2 siRNA transfection blocked all the in vivo effects of GW501516. Conclusions Platelets and late EPCs play a key role in vascular regeneration via Edg-2 - LPA axis. PPAR-δ augments the interaction through Edg-2 upregulation, suggesting its agonist as a good therapeutic tool for vascular regeneration.