Eneida Torres

Inhibition of the SDF-1/CXCR4 Axis Attenuates Neonatal Hypoxia-Induced Pulmonary Hypertension

Exposure of the neonatal lung to chronic hypoxia produces significant pulmonary vascular remodeling, right ventricular hypertrophy, and decreased lung alveolarization. Given recent data suggesting that stem cells could contribute to pulmonary vascular remodeling and right ventricular hypertrophy, we tested the hypothesis that blockade of SDF-1 (stromal cell–derived factor 1), a key stem cell mobilizer or its receptor, CXCR4 (CXC chemokine receptor 4), would attenuate and reverse hypoxia-induced cardiopulmonary remodeling in newborn mice. Neonatal mice exposed to normoxia or hypoxia were randomly assigned to receive daily intraperitoneal injections of normal saline, AMD3100, or anti–SDF-1 antibody from postnatal day 1 to 7 (preventive strategy) or postnatal day 7 to 14 (therapeutic strategy). As compared to normal saline, inhibition of the SDF-1/CXCR4 axis significantly improved lung alveolarization and decreased pulmonary hypertension, right ventricular hypertrophy, vascular remodeling, vascular cell proliferation, and lung or right ventricular stem cell expressions to near baseline values. We therefore conclude that the SDF-1/CXCR4 axis both prevents and reverses hypoxia-induced cardiopulmonary remodeling in neonatal mice, by decreasing progenitor cell recruitment to the pulmonary vasculature, as well as by decreasing pulmonary vascular cell proliferation. These data offer novel insights into the role of the SDF-1/CXCR4 axis in the pathogenesis of neonatal hypoxia-induced cardiopulmonary remodeling and have important therapeutic implications.

Long-term reparative effects of mesenchymal stem cell therapy following neonatal hyperoxia-induced lung injury.

Background:Mesenchymal stem cell (MSC) therapy may prevent neonatal hyperoxia-induced lung injury (HILI). There are, however, no clear data on the therapeutic efficacy of MSC therapy in established HILI, the duration of the reparative effects, and the exact mechanisms of repair. The main objective of this study was to evaluate whether the long-term reparative effects of a single intratracheal (IT) dose of MSCs or MSC-conditioned medium (CM) are comparable in established HILI.Methods:Newborn rats exposed to normoxia or hyperoxia from postnatal day (P)2)–P16 were randomized to receive IT MSCs, IT CM, or IT placebo (PL) on P9. Alveolarization and angiogenesis were evaluated at P16, P30, and P100.Results:At all time periods, there were marked improvements in alveolar and vascular development in hyperoxic pups treated with MSCs or CM as compared with PL. This was associated with decreased expression of inflammatory mediators and an upregulation of angiogenic factors. Of note, at P100, the improvements were more substantial with MSCs as compared with CM.Conclusion:These data suggest that acute effects of MSC therapy in HILI are mainly paracrine mediated; however, optimum long-term improvement following HILI requires treatment with the MSCs themselves or potentially repetitive administration of CM.

CXCR4 Blockade Attenuates Hyperoxia-Induced Lung Injury in Neonatal Rats

Background: Lung inflammation is a key factor in the pathogenesis of bronchopulmonary dysplasia (BPD). Stromal-derived factor-1 (SDF-1) and its receptor chemokine receptor 4 (CXCR4) modulate the inflammatory response. It is not known if antagonism of CXCR4 alleviates lung inflammation in neonatal hyperoxia-induced lung injury. Objective: We aimed to determine whether CXCR4 antagonism would attenuate lung injury in rodents with experimental BPD by decreasing pulmonary inflammation. Methods: Newborn rats exposed to normoxia (room air, RA) or hyperoxia (FiO2 = 0.9) from postnatal day 2 (P2) to P16 were randomized to receive the CXCR4 antagonist, AMD3100 or placebo (PL) from P5 to P15. Lung alveolarization, angiogenesis and inflammation were evaluated at P16. Results: Compared to the RA pups, hyperoxic PL pups had a decrease in alveolarization, reduced lung vascular density and increased lung inflammation. In contrast, AMD3100-treated hyperoxic pups had improved alveolarization and increased angiogenesis. This improvement in lung structure was accompanied by a decrease in the macrophage and neutrophil counts in the bronchoalveolar lavage fluid and reduced lung myeloperoxidase activity. Conclusion: CXCR4 antagonism decreases lung inflammation and improves alveolar and vascular structure in neonatal rats with experimental BPD. These findings suggest a novel therapeutic strategy to alleviate lung injury in preterm infants with BPD.

Stem cell factor improves lung recovery in rats following neonatal hyperoxia-induced lung injury

Background:Stem cell factor (SCF) and its receptor, c-kit, are modulators of angiogenesis. Neonatal hyperoxia-induced lung injury (HILI) is characterized by disordered angiogenesis. The objective of this study was to determine whether exogenous SCF improves recovery from neonatal HILI by improving angiogenesis.Methods:Newborn rats assigned to normoxia (RA: 20.9% O2) or hyperoxia (90% O2) from postnatal day (P) 2 to 15, received daily injections of SCF 100 μg/kg or placebo (PL) from P15 to P21. Lung morphometry was performed at P28. Capillary tube formation in SCF-treated hyperoxia-exposed pulmonary microvascular endothelial cells (HPMECs) was determined by Matrigel assay.Results:As compared with RA, hyperoxic-PL pups had decrease in alveolarization and in lung vascular density, and this was associated with increased right ventricular systolic pressure (RVSP), right ventricular hypertrophy, and vascular remodeling. In contrast, SCF-treated hyperoxic pups had increased angiogenesis, improved alveolarization, and attenuation of pulmonary hypertension as evidenced by decreased RVSP, right ventricular hypertrophy, and vascular remodeling. Moreover, in an in vitro model, SCF increased capillary tube formation in hyperoxia-exposed HPMECs.Conclusion:Exogenous SCF restores alveolar and vascular structure in neonatal rats with HILI by promoting neoangiogenesis. These findings suggest a new strategy to treat lung diseases characterized by dysangiogenesis.

Bone marrow-derived c-kit+ cells attenuate neonatal hyperoxia-induced lung injury.

Recent studies suggest that bone marrow (BM)-derived stem cells have therapeutic efficacy in neonatal hyperoxia-induced lung injury (HILI). c-kit, a tyrosine kinase receptor that regulates angiogenesis, is expressed on several populations of BM-derived cells. Preterm infants exposed to hyperoxia have decreased lung angiogenesis. Here we tested the hypothesis that administration of BM-derived c-kit+ cells would improve angiogenesis in neonatal rats with HILI. To determine whether intratracheal (IT) administration of BM-derived c-kit+ cells attenuates neonatal HILI, rat pups exposed to either normobaric normoxia (21% O2) or hyperoxia (90% O2) from postnatal day (P) 2 to P15 were randomly assigned to receive either IT BM-derived green fluorescent protein (GFP)+ c-kit–cells (PL) or BM-derived GFP+ c-kit+ cells on P8. The effect of cell therapy on lung angiogenesis, alveolarization, pulmonary hypertension, vascular remodeling, cell proliferation, and apoptosis was determined at P15. Cell engraftment was determined by GFP immunostaining. Compared to PL, the IT administration of BM-derived c-kit+ cells to neonatal rodents with HILI improved alveolarization as evidenced by increased lung septation and decreased mean linear intercept. This was accompanied by an increase in lung vascular density, a decrease in lung apoptosis, and an increase in the secretion of proangiogenic factors. There was no difference in pulmonary vascular remodeling or the degree of pulmonary hypertension. Confocal microscopy demonstrated that 1% of total lung cells were GFP+ cells. IT administration of BM-derived c-kit+ cells improves lung alveolarization and angiogenesis in neonatal HILI, and this may be secondary to an improvement in the lung angiogenic milieu.

Intra-Amniotic Soluble Endoglin Impairs Lung Development in Neonatal Rats

Abstract Soluble endoglin (sENG) is increased in the amniotic fluid of women with preeclampsia and chorioamnionitis. Preterm infants born to women with these disorders have an increased risk of aberrant lung development. Whether this increased risk is secondary to elevated sENG levels is unclear. The objective of this study was to determine whether intrauterine exposure to an adenovirus overexpressing sENG impairs neonatal lung angiogenesis by modulating lung endothelial nitric oxide synthase (eNOS) signaling. Pregnant Sprague‐Dawley rats were randomly assigned to receive ultrasound‐guided intra‐amniotic injections of adenovirus overexpressing sENG (Ad‐sENG) or control adenovirus (Ad‐control) on embryonic day 17. After this exposure, rat pups were maintained in normoxia and evaluated on postnatal day 14. Intra‐amniotic Ad‐sENG decreased lung vascular endothelial growth factor receptor 2 and eNOS expression in rat pups. This was accompanied by a marked decrease in lung angiogenesis and alveolarization. Ad‐sENG‐exposed pups also had an increase in right ventricular systolic pressure, weight ratio of right ventricle to left ventricle plus septum, and pulmonary vascular remodeling. In addition, exposure of human pulmonary artery endothelial cells to recombinant sENG reduced endothelial tube formation and protein levels of eNOS, phosphorylated eNOS, and phosphorylated Smad1/5. Together, our findings demonstrate that intrauterine exposure to an adenovirus overexpressing sENG disrupts lung development by impairing Smad1/5‐eNOS signaling. We speculate that sENG‐mediated dysregulation of Smad1/5‐eNOS signaling contributes to impaired lung development and potentially primes the developing lung for further postnatal insults. Further studies exploring the relationship between amniotic fluid sENG levels and preterm respiratory outcomes will be necessary.

Antagonism of Stem Cell Factor/c-kit Signaling Attenuates Neonatal Chronic Hypoxia-Induced Pulmonary Vascular Remodeling

Background:Accumulating evidence suggests that c-kit-positive cells are present in the remodeled pulmonary vasculature bed of patients with pulmonary hypertension (PH). Whether stem cell factor (SCF)/c-kit-regulated pathways potentiate pulmonary vascular remodeling is unknown. Here, we tested the hypothesis that attenuated c-kit signaling would decrease chronic hypoxia-induced pulmonary vascular remodeling by decreasing pulmonary vascular cell mitogenesis.Methods:Neonatal FVB/NJ mice treated with nonimmune IgG (placebo), or c-kit neutralizing antibody (ACK2) as well as c-kit mutant mice (WBB6F1-KitW-v/+) and their congenic controls, were exposed to normoxia (FiO2 = 0.21) or hypoxia (FiO2 = 0.12) for 2 wk. Following this exposure, right ventricular systolic pressure (RVSP), right ventricular hypertrophy (RVH), pulmonary vascular cell proliferation, and remodeling were evaluated.Results:As compared to chronically hypoxic controls, c-kit mutant mice had decreased RVSP, RVH, pulmonary vascular remodeling, and proliferation. Consistent with these findings, administration of ACK2 to neonatal mice with chronic hypoxia-induced PH decreased RVSP, RVH, pulmonary vascular cell proliferation, and remodeling. This attenuation in PH was accompanied by decreased extracellular signal-regulated protein kinase (ERK) 1/2 activation.Conclusion:SCF/c-kit signaling may potentiate chronic hypoxia-induced vascular remodeling by modulating ERK activation. Inhibition of c-kit activity may be a potential strategy to alleviate PH.