During early pregnancy, placentation occurs in a relatively hypoxic environment that is essential for appropriate embryonic development. Intervillous blood flow increases around 10 to 12 weeks of gestation and results in exposure of trophoblast cells to increased oxygen tension. Before this time, low oxygen appears to prevent trophoblast differentiation toward an invasive phenotype. Using human villous explants of 5-8 weeks' gestation, we found that low oxygen tension triggered trophoblast proliferation, fibronectin synthesis, α 5 integrin expression, and gelatinase A activity. These biochemical markers were barely detectable under oxic conditions. We therefore examined the placental expression of hypoxia-inducible factor-1 (HIF-1), a master regulator of oxygen homeostasis, and determined that expression of HIF-1α subunit during the first trimester of gestation parallels that of TGFβ 3 , an inhibitor of extravillous trophoblast differentiation. Expression of both molecules is high in early pregnancy and falls around 9 weeks of gestation, when placental pO 2 levels are believed to increase. Increasing oxygen tension induced a similar decrease in expression in cultured explants. Moreover, antisense inhibition of HIF-1α expression in hypoxic explants inhibited expression of TGFβ 3 , arrested cell proliferation, decreased α 5 expression and gelatinase A activity, and triggered biochemical markers of an invasive trophoblast phenotype such as α 1 integrin and gelatinase B expression. These data suggest that the oxygen-regulated early events of trophoblast differentiation are in part mediated by TGFβ 3 through HIF-1 transcription factors.

Background-Myocardial ischemia provides a potent stimulus to angiogenesis, and the mobilization and differentiation of endothelial progenitor cells (EPCs) has been shown to be important in this process. An elevated level of C-reactive protein (CRP) has emerged as one of the most powerful predictors of cardiovascular disease. However, the impact of CRP on EPC biology is unknown. Methods and Results-EPCs were isolated from the peripheral venous blood of healthy male volunteers. Cells were cultured in endothelial cell basal medium-2 in the absence and presence of CRP (5 to 20 g/mL), rosiglitazone (1 mol/L), and/or vascular endothelial growth factor. EPC differentiation, survival, and function were assayed. CRP at concentrations Ն15 g/mL significantly reduced EPC cell number, inhibited the expression of the endothelial cell-specific markers Tie-2, EC-lectin, and VE-cadherin, significantly increased EPC apoptosis, and impaired EPC-induced angiogenesis. EPC-induced angiogenesis was dependent on the presence of nitric oxide, and CRP treatment caused a decrease in endothelial nitric oxide synthase mRNA expression by EPCs. However, all of these detrimental CRP-mediated effects on EPCs were attenuated by pretreatment with rosiglitazone, a peroxisome proliferator-activated receptor-␥ (PPAR␥) agonist. Conclusions-Human recombinant CRP, at concentrations known to predict adverse vascular outcomes, directly inhibits EPC differentiation, survival, and function, key components of angiogenesis and the response to chronic ischemia. This occurs in part via an effect of CRP to reduce EPC eNOS expression. The PPAR␥ agonist rosiglitazone inhibits the negative effects of CRP on EPC biology. The ability of CRP to inhibit EPC differentiation and survival may represent an important mechanism that further links inflammation to cardiovascular disease.

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Abstract-The (pro)renin receptor ([P]RR) is a transmembrane protein that binds both renin and prorenin with high affinity, increasing the catalytic cleavage of angiotensinogen and signaling intracellularly through mitogen-activated protein kinase activation. Although initially reported as having no homology with any known membrane protein, other studies have suggested that the (P)RR is an accessory protein, named ATP6ap2, that associates with the vacuolar H ϩ -ATPase, a key mediator of final urinary acidification. Using in situ hybridization, immunohistochemistry, and electron microscopy, together with serial sections stained with nephron segment-specific markers, we found that (P)RR mRNA and protein were predominantly expressed in collecting ducts and in the distal nephron. Within collecting ducts, the (P)RR was most abundant in microvilli at the apical surface of A-type intercalated cells. Dual-staining immunofluorescence demonstrated colocalization of the (P)RR with the B1/2 subunit of the vacuolar H ϩ -ATPase, the ion exchanger that secretes H ϩ ions into the urinary space and that associates with an accessory subunit homologous to the (P)RR. In collecting duct/distal tubule lineage Madin-Darby canine kidney cells, extracellular signal-regulated kinase 1/2 phosphorylation, induced by either renin or prorenin, was attenuated by the selective vacuolar H ϩ -ATPase inhibitor bafilomycin. The predominant expression of the (P)RR at the apex of acid-secreting cells in the collecting duct, along with its colocalization and homology with an accessory protein of the vacuolar H ϩ -ATPase, suggests that the (P)RR may function primarily in distal nephron H ϩ transport, recently noted to be, at least in part, an angiotensin II-dependent phenomenon. Key Words: (pro)renin receptor Ⅲ intercalated cell Ⅲ vacuolar H ϩ -ATPase Ⅲ ATP6ap2 Ⅲ prorenin Ⅲ renin-angiotensin system Ⅲ bafilomycin A little more than a decade ago, the binding characteristics and activity of a specific renin receptor in cultured mesangial cells were reported. 1 This was followed in 2002 by the identification of an apparently novel, 350 amino acid, single-transmembrane protein that binds both renin and prorenin with high affinity. 2 Ligand binding to this (pro)renin receptor ([P]RR) induced a 4-fold increase in the catalytic cleavage of angiotensinogen, as well as stimulating intracellular signaling, with activation of mitogen-activated protein kinases extracellular signal-regulated kinase (ERK) 1/2 2 and induction of transforming growth factor-␤ expression. 3 The existence of a (P)RR not only expanded our understanding of the physiology of the renin-angiotensin system (RAS) but also provided insight into the potential pathogenetic role of prorenin, the enzymatically inactive zymogen that is elevated in disease states, eg, diabetes mellitus, where it predicts the subsequent development of nephropathy and retinopathy. 4 Given its localization to the mesangium, its actions in augmenting local angiotensin II production, and its ability to increase mesangial tr...