Placenta growth factor augments endothelin-1 and endothelin-B receptor expression via hypoxia-inducible factor-1α

Abstract

Pulmonary hypertension (PHT) develops in sickle cell disease (SCD) and is associated with high mortality. We previously showed that erythroid cells produce placenta growth factor (PlGF), which activates monocytes to induce proinflammatory cytochemokines, contributing to the baseline inflammation and severity in SCD. In this study, we observed that PlGF increased expression of endothelin-1 (ET-1) and endothelin-B receptor (ET-BR) from human pulmonary microvascular endothelial cells (HPMVECs) and monocytes, respectively. PlGF-mediated ET-1 and ET-BR expression occurred via activation of PI-3 kinase, reactive oxygen species and hypoxia inducible factor-1␣ (HIF-1␣). PlGF increased binding of HIF-1␣ to the ET-1 and ET-BR promoters; this effect was abrogated with mutation of hypoxia response elements in the promoter regions and HIF-1␣ siRNA and confirmed by chromatin immunoprecipitation analysis. Furthermore, PlGF-mediated ET-1 release from HPMVECs and ET-BR expression in monocytes creates a PlGF-ET-1-ET-BR loop, leading to increased expression of MCP-1 and IL-8. Our studies show that PlGF-induced expression of the potent vasoconstrictor ET-1 and its cognate ET-BR receptor occur via activation of HIF-1␣, independent of hypoxia. PlGF levels are intrinsically elevated from the increased red cell turnover in SCD and in other chronic anemia (eg, thalassemia) and may contribute to inflammation and PHT seen in these diseases. (Blood. 2008;112:856-865) IntroductionThe clinical manifestations of sickle cell disease (SCD) include chronic hemolytic anemia, frequent infections, and intermittent episodes of vascular occlusion. [1][2][3][4][5][6] Pulmonary disease, both acute and chronic, is the second most common cause of hospitalization and a leading cause of both morbidity and mortality in adults with SCD. 1,[7][8][9] The most frequent form of acute pulmonary disease is the acute chest syndrome (ACS), which occurs in 15% to 40% of patients with SCD. 10 Pulmonary hypertension (PHT) occurs in both adults and children with SCD: it develops with increasing age and portends an extremely poor prognosis. PHT is a significant risk factor for early mortality in SCD. 9,[11][12][13] Studies have shown that there is a clinical syndrome of hemolysis-associated PHT in SCD 9 that results from global impairment in nitric oxide (NO) bioavailability from its quenching by free heme. 14 It is known that vascular tone is also modulated by vasoconstrictors such as endothelin-1 (ET-1). Studies have shown increased plasma levels of ET-1 in patients with SCD and ACS. 15,16 Tissue hypoxemia due to microvascular occlusion and chronic mild-moderate desaturations in SCD may contribute to increased levels of ET-1, which is released from endothelial cells in response to hypoxia. 17 Increased levels of ET-1, if sustained as a result of the underlying SCD pathophysiology, can contribute to the development of PHT.SCD is also characterized by presence of a chronic inflammatory state manifested by leukocytosis and monocytosis and increased circulating levels of p...

PlGF: A Multitasking Cytokine with Disease-Restricted Activity

“…PlGF levels are further increased in SCD patients with pulmonary hypertension (Brittain et al 2010). Consistent herewith, overexpression of PlGF in erythroid cells of healthy mice induces pulmonary hypertension via elevated endothelial production of the vasoconstrictor endothelin-1, which is elevated in SCD patients as well (Patel et al 2008;Sundaram et al 2010). The protease inhibitor PAI-1 is similarly elevated in SCD patients and mice.…”

“…PlGF is released by erythroid cells and plasma PlGF is elevated in patients with sickle cell disease (SCD), correlating with hemolysis (Patel et al 2008;Brittain et al 2010). PlGF levels are further increased in SCD patients with pulmonary hypertension (Brittain et al 2010).…”

Placenta Growth Factor (PlGF), a Novel Inducer of Plasminogen Activator Inhibitor-1 (PAI-1) in Sickle Cell Disease (SCD)

“…PlGF is an angiogenic growth factor that, in the fetus, is made by placental syncytiotrophoblasts and, postnatally, by erythroblasts. We showed that PlGF activates downstream target genes in endothelial cells via HIF-1␣ in a hypoxia-independent manner (27). Because PAI-1 expression is induced by HIF-1␣ (in a hypoxia-dependent fashion) and PlGF activates HIF-1␣ (in a hypoxia-independent fashion), we hypothesized that the PAI-1 elevation in SCD is mediated via PlGF acting through HIF-1␣.…”

“…Cells and Reagents-Primary human pulmonary microvascular endothelial cells (HPMVEC) were obtained from Lonza Group Ltd. (Basel, Switzerland) and grown as described previously (27). Cultured HPMVEC were confirmed to express CD31 and von Willebrand factor (data not shown).…”

“…EMSA-Nuclear extracts from untreated and PlGF-treated HPMVEC were subjected to EMSA analysis using WT and mutant oligonucleotide probes (Table 1), as described previously (27).…”