High levels of placenta growth factor in sickle cell disease promote pulmonary hypertension

Abstract

Pulmonary hypertension is associated with reduced nitric oxide bioavailability and early mortality in sickle cell disease (SCD). We previously demonstrated that placenta growth factor (PlGF), an angiogenic factor produced by erythroid cells, induces hypoxiaindependent expression of the pulmonary vasoconstrictor endothelin-1 in pulmonary endothelial cells. Using a lentivirus vector, we simulated erythroid expression of PlGF in normal mice up to the levels seen in sickle mice. Consequently, endothelin-1 production increased, right ventricle pressures increased, and right ventricle hypertrophy and pulmonary changes occurred in the mice within 8 weeks. These findings were corroborated in 123 patients with SCD, in whom plasma PlGF levels were significantly associated with anemia, endothelin-1, and tricuspid regurgitant velocity; the latter is reflective of peak pulmonary artery pressure. These results illuminate a novel mechanistic pathway linking hemolysis and erythroid hyperplasia to increased PlGF, endothelin-1, and pulmonary hypertension in SCD, and suggest that strategies that block PlGF signaling may be therapeutically beneficial. IntroductionPulmonary hypertension (PH) occurs in 10% to 30% of patients with sickle cell disease (SCD) [1][2][3] and is associated with a 17% 2-year mortality in adults. 1 Factors implicated in SCD PH include endothelial dysfunction, pulmonary vasoconstriction, and remodeling, all mechanistically associated with chronic hemolysis, hypoxia, hemostatic activation, and inflammation. [4][5][6] Nitric oxide (NO) and endothelin-1 are opposing pulmonary vasoactive factors that regulate pulmonary vascular tone. 7,8 Hemolysis in SCD results in quenching of NO by extracellular hemoglobin and reduces availability of NO-synthase substrate. 6,8 Endothelin-1, a potent pulmonary vasoconstrictor, is normally induced from endothelial cells by hypoxia-mediated up-regulation of hypoxia inducible factor-1␣ (HIF-1␣), and its levels are elevated in PH. 9 Indeed, endothelin-1 receptor antagonists are used for the treatment of primary PH. Endothelin-1 levels are also significantly elevated in patients with SCD, 10,11 and endothelin-1 receptor antagonists have been recently found to be beneficial in sickleAntilles-hemoglobin-D mice. 12 We recently showed the mechanism of endothelin-1 induction via a novel hypoxia-independent up-regulation of HIF-1␣ in cultured human pulmonary microvascular endothelial cells by placenta growth factor (PlGF). 13 Bone marrow erythroid cells produce PlGF, and PlGF levels are significantly increased in patients with chronic hemolytic anemias, SCD, and ␤-thalassemia, as part of the compensatory erythroid hyperplasia response. 14,15 This study was designed to test the hypothesis that chronically elevated PlGF in SCD contributes to PH. Methods Vector constructsThe mouse PGF cDNA was cloned downstream of the ␤-globin promoter to replace green fluorescent protein (GFP) in the lentiviral vector s␤-GFP, 16 to generate s␤-PlGF (Figure 1). We have shown this transcription cassette to exp...

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.…”

Peroxisome Proliferator-activated Receptor-α-mediated Transcription of miR-199a2 Attenuates Endothelin-1 Expression via Hypoxia-inducible Factor-1α

“…Placenta growth factor is elaborated from bone marrow erythroid cells, and its levels are significantly increased in patients with chronic hemolytic anemia, including SCD, because of a compensatory erythroid hyperplastic response (20). Moreover, our studies show elevated PlGF levels in Berke-ley sickle (BK-SS) mice and SCD patients are associated with increased levels of ET-1 and clinical markers of pulmonary hypertension (16). These studies clearly indicate the importance of PlGF in regulation of ET-1 and its role in PH in SCD.…”

“…Next, we examined the effect of PPAR␣ agonists on ET-1, a downstream gene regulated by HIF-1␣ and a key mediator of PHT in SCA (16). As expected, ET-1 mRNA levels were reduced by ϳ80 and ϳ60%, by fenofibrate and clofibrate, respectively, in HMEC-1 cells (Fig.…”

“…A number of factors, such as chronic hemolysis, hypoxia, hemostatic activation, and inflammation have been implicated in endothelial dysfunction, pulmonary vasoconstriction, and remodeling in PH in SCD (3,(5)(6)(7)(8)(9)(10). Reduced bioavailability of nitric oxide caused by quenching of NO by extracellular hemoglobin (11)(12)(13)(14) and increased levels of endothelin-1 (ET-1) have been implicated in PH in SCD (15,16).…”

Pulmonary Vascular and Ventricular Dysfunction in the Susceptible Patient (2015 Grover Conference Series)

“…In addition to the anemic state, increases in placental growth factor, a mediator that activates HIF-1α in normoxia, have been associated with elevated systolic PA pressures in SCD. 141 On the basis of these observations, we hypothesized that the upregulated hypoxic response in SCD might contribute to altered gene expression and the development of PH. To test this hypothesis, we compared clinical data and PBMC genomic profiles of subjects with SCD to those of subjects with Chuvash polycythemia, a monogenic hematologic disorder characterized by an upregulated hypoxic response and elevated systolic PA pressures.…”