Abstract 18201: PPAR-δ Augments the Interaction Between Platelets and Late EPCs via EDG-2 Signaling Pathway, Leading to Vascular Regeneration
BACKGROUND EDG (endothelial differentiation gene)-2 is a membrane receptor for LPA (lysophosphatidic acid) which is the major lysophospholipid growth factor generated by platelet activation. We focused on the role of EDG-2 in late EPCs and its regulation by PPAR (peroxisome proliferator activated receptor)-δ.
METHODS & RESULTS We confirmed the expression of EDG-2 in human late EPCs. Interestingly, EDG-2 expression was upregulated by GW501516, a highly selective PPAR-δ agonist treatment. ChIP and promoter assays showed it occurred via direct transcriptional activation. GW501516 or the supernatant of activated platelets which should contain LPA increased the proliferation (BrdU) of late EPCs, and enhanced their provasculogenic functions such as chemotaxis (Transwell), planar migration (scratch wound healing), and tube formation (in vitro Matrigel). Co-treatment of GW501516 and the supernatant resulted in synergism. The above effects were reversed by GSK0660 (PPAR-δ antagonist) or Ki16425 (EDG-2 blocker) treatment, but not so much by PDGF neutralizing antibody. In vivo Matrigel plug assay, neither late EPCs (10^6/plug) nor activated platelets induced capillary formation. But the combination of them robustly formed capillaries filled with RBCs. GW501516 potentiated their interaction, leading to more capillaries. In a mouse carotid injury model, late EPCs (DiI tagging) showed more homing to injury site 30 minutes after operation by GW501516 treatment. IF staining confirmed their interaction with platelets (CD61). After 14 days, GW501516-treated late EPC group showed more re-endothelization (IHC for CD31) and less neointimal formation. PPAR-δ or EDG-2 siRNA transfection blocked all 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 candidate for ischemic vascular disease.
- Regenerative medicine stem cells
- Progenitor cell
- Signal transduction
- Receptor-mediated signaling
- © 2011 by American Heart Association, Inc.