Objective— The role of the nuclear receptor peroxisome-proliferator activated receptor (PPAR)-β/δ in endothelial cells remains unclear. Interestingly, the selective PPARβ/δ ligand GW501516 is in phase II clinical trials for dyslipidemia. Here, using GW501516, we have assessed the involvement of PPARβ/δ in endothelial cell proliferation and angiogenesis. Methods and Results— Western blot analysis indicated PPARβ/δ was expressed in primary human umbilical and aortic endothelial cells, and in the endothelial cell line, EAHy926. Treatment with GW501516 increased human endothelial cell proliferation and morphogenesis in cultures in vitro, endothelial cell outgrowth from murine aortic vessels in vitro, and angiogenesis in a murine matrigel plug assay in vivo. GW501516 induced vascular endothelial cell growth factor mRNA and peptide release, as well as adipose differentiation-related protein (ADRP), a PPARβ/δ target gene. GW501516-induced proliferation, morphogenesis, vascular endothelial growth factor (VEGF), and ADRP were absent in endothelial cells transfected with dominant-negative PPARβ/δ. Furthermore, treatment of cells with cyclo-VEGFI, a VEGF receptor1/2 antagonist, abolished GW501516-induced endothelial cell proliferation and tube formation. Conclusions— PPARβ/δ is a novel regulator of endothelial cell proliferation and angiogenesis through VEGF. The use of GW501516 to treat dyslipidemia may need to be carefully monitored in patients susceptible to angiogenic disorders.

Prostacyclin (PGI 2 ) plays important roles in hemostasis both as a vasodilator and an endogenous inhibitor of platelet aggregation. PGI 2 functions in these roles through a specific IP receptor, a G protein-coupled receptor linked to G s and increases in cAMP. Here, we report that intracellular prostacyclin formed by expressing prostacyclin synthase in human embryonic kidney 293 cells promotes apoptosis by activating endogenous peroxisome proliferator-activated receptor ␦ (PPAR␦). In contrast, treatment of cells with extracellular prostacyclin or dibutyryl cAMP actually reduced apoptosis. On the contrary, treatment of the cells with RpcAMP (adenosine 3,5-cyclic monophosphothioate, Rp-isomer), an antagonist of cAMP, enhanced prostacyclin-mediated apoptosis. The expression of an L431A/ G434A mutant of PPAR␦ completely blocked prostacyclin-mediated PPAR␦ activation and apoptosis. These observations indicate that prostacyclin can act through endogenous PPAR␦ as a second signaling pathway that controls cell fate.

Background-Prostacyclin (PGI 2 ) is a short-lived endogenous inhibitor of platelet aggregation and a potent vasodilator and regulator of the growth of vascular smooth muscle cells. To study the role of PGI 2 in the vascular system in vivo, PGI 2 -deficient (PGID) mice were established by genetic disruption of the PGI 2 synthase gene. Methods and Results-PGI 2 synthase-null mice were generated by replacing the exons of PGI 2 synthase gene that encodes for the catalytic site of the enzyme with a neomycin resistance gene. In these mice, PGI 2 levels in the plasma, kidneys, and lungs were reduced, whereas thromboxane and prostaglandin E 2 levels became elevated. Blood pressure and the amounts of urea nitrogen and creatinine in plasma of the PGID mice were significantly higher than those of wild-type mice (PϽ0.05). They developed progressive morphological abnormalities in the kidneys, accompanied by atrophy, surface irregularity, fibrosis, cyst, arterial sclerosis, and hypertrophy of vessel walls. Thickening of the thoracic aortic media and adventitia were observed in aged PGID mice. Importantly, these phenotypes have not been reported in PGI 2 receptor-deficient mice. Conclusions-PGI 2 deficiency resulted in the development of vascular disorders with the thickening of vascular walls and interstitial fibrosis, especially in mouse kidneys. The findings demonstrated in vivo that PGI 2 is important in the homeostasis of blood vessels. Our established PGID mice are useful for studies on the initiation and development of vascular diseases, such as ischemic renal disorders with arterial sclerosis and infarction, and also for studies on the novel signaling pathway of PGI 2 .

The renin-angiotensin system (RAS) is the most important regulator of electrolyte homeostasis and blood pressure. Our recently generated transgenic mice carrying either the human renin (hREN) or human angiotensinogen (hANG) genes did not develop hypertension but dual gene strains obtained by cross-mating separate lines of mice exhibited a chronically sustained increase in blood pressure, suggesting the presence of species-specific reactivity between renin and angiotensinogen. In order to examine this specificity, the present study was designed to perform a strictly comparative study on hydrolysis of hANG by hREN and mouse submandibular renin (mREN) in vitro by using pure proteins. The recombinant hANG (rhANG) and the synthetic human-type tridecapeptide (hTDP), Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu-Val-Ile-His, corresponding to the N-terminal sequences of hANG, were used to determine the species specificity of recombinant hREN (rhREN) and mREN. While hTDP was cleaved by both rhREN and mREN with similar Km and with the same order of kcat, rhANG was cleaved by mREN with 16.7-fold higher Km and with 28.2-fold lower kcat than by rhREN. These results showed that kcat/Km value of mREN for rhANG was 468-fold lower than that for rhREN acting on rhANG.