Abstract 18396: Peroxisome Proliferator-Activated Receptor Gamma- Deficiency in Endothelial Cells Leads to Impaired Angiogenesis
Rationale: TIE2 promoter mediated loss-of peroxisome proliferator-activated receptor gamma (PPARγ) in mice (TIE2CrePPARγflox/flox) (KO) leads to endothelial cell (EC) dysfunction, pulmonary arterial hypertension and osteopetrosis through loss-of osteoclasts. Although some of the functions and mechanisms of PPARγ-mediated regulation of vascular homeostasis have been revealed, the exact role of PPARγ in angiogenesis is obscure.
Methods: The role of PPARγ in angiogenesis was evaluated in vivo in KO and wild type (WT) mice by matrigel plug assays. As the level of endothelial progenitor cells (EPC) (CD34+/VEGFR2+/CD45-) especially in circulation can reflect angiogenic capacity, their levels were assessed in peripheral blood, spleen and bone marrow (BM) in both mouse models by flow cytometry. BM transplantations were used to switch EPC phenotypes. Magnetic beads were used to isolate mouse pulmonary ECs (PEC) for functional studies. In human ECs (HMVEC) PPARγ-deficiency was studied using siRNA strategy.
Results: In vivo angiogenesis assay showed a significant attenuation of angiogenic capacity in KO mice when compared to WT. In contrast to WT, KO mice implanted with matrigel plugs showed no significant angiogenic response to BMP2. Interestingly, KO mice had significantly (>50%) reduced EPC levels in spleen and circulation when compared to WT but their levels in bone marrow (BM) were 3-fold in KO mice suggesting a mobilization defect from the BM. WT BM transplantation rescued the mobilization defect in KO mice and normalized the EPC levels but did not rescue the angiogenesis defect. In vitro studies with mature PECs isolated from KO mice showed a 40% decrease in tube-formation and migration after VEGF and BMP2 stimulation when compared to WT cells. In line with this, PPARy-deficient HMVECs showed a similar angiogenic defect in vitro (P<0.001, N=9).
Conclusion: PPARγ plays an important role in sustaining angiogenic potential in mature ECs both in mice and humans. Osteoclasts are essential for mobilization of EPCs from the BM.
- © 2013 by American Heart Association, Inc.