Fetal Pulmonary Artery Smooth Muscle Cells Research Articles

Celastrol: A new potential therapeutic option in pulmonary hypertension associated to bronchopulmonary dysplasia

Bronchopulmonary dysplasia is a common pathology of premature newborns caused by oxidative stress and mechanical ventilation, resulting in hypoalveolization and impaired angiogenesis. It can be complicated by pulmonary hypertension (HTP-DBP) with excess mortality. Celastrol has anti-inflammatory and antioxidant properties. So, we addressed its potential therapeutic interest in HTP-DBP. Different concentrations of celastrol were used in a murine model of hyperoxic HTP-DBP (14 days with 90% O 2 ) and we evaluated hemodynamic parameters with echocardiography and lung remodeling with histological methods. Pulmonary arterial (PA) reactivity was addressed with myograph. Cytoplasmic calcium (Ca2 + i) response to endothelin-1 (ET-1) was evaluated in human fetal PA smooth muscle cells (fPASMC) with spectrophotometry in normoxic (21% O 2 ) and hyperoxic conditions (48 h with 60% O 2 ). Inflammation was addressed with IL6 ELISA assay in fPASMC. Celastrol reduces mortality at doses of 1 and 0.5 mg/kg/d compared to the hyperoxic control group. At 1 mg/kg/d, it normalizes PAAT (PA acceleration time) ( P < 0.001) and reduces vascular hyperreactivity to phenylephrine and ET-1 ( P < 0.001) with no effect on the alteration of the response to acetylcholine induced by hyperoxia. At doses of 0.1, 0.5 and 1 mg/kg/d, it decreases right heart hypertrophy and vascular remodeling (wall thickness) but has no effect on alveolization and vascular density (vWF staining). Finally, although celastrol (0.1 and 0.3 μM) decreases the increased Ca2 + i response to ET-1 in hyperoxia in fPASMC, expression of ET-1 receptors (Western blotting and qPCR for ET-A and ET-B) was unchanged. However, celastrol 0.5 μM decreases ET-1 concentration measured with an ELISA assay in human umbilical arterial endothelial cells. An increased concentration of IL6 was also observed in fPASMC in hyperoxia and was decreased by celastrol 0.5 μM. Celastrol has a preventive dose-dependent effect on some hallmarks of HTP induced by hyperoxia and could thus be considered as an interesting new potential therapeutic option for HTP-DBP.

Effect of celastrol on pulmonary hypertension associated to bronchopulmonary dysplasia

Bronchopulmonary dysplasia is a common pathology of premature newborns caused by oxidative stress and mechanical ventilation, resulting in hypoalveolization and impaired angiogenesis. It can be complicated by pulmonary hypertension (HTP-DBP) with excess mortality. Celastrol has anti-inflammatory and antioxidant properties and we addressed its potential therapeutic interest in HTP-DBP. Different concentrations of celastrol were used in a murine model of hyperoxic HTP-DBP (14 days with 90% O2) and we evaluated hemodynamic parameters with echocardiography and lung remodeling with histological methods. Pulmonary arterial (PA) reactivity was addressed with myograph. Cytoplasmic calcium (Ca2 + i) response to endothelin-1 (ET-1) was evaluated in human fetal PA smooth muscle cells (fPASMC) with spectrophotometry in normoxic (21% O2) and hyperoxic conditions (48 h with 60% O2). Inflammation was addressed with IL6 ELISA assay in fPASMC. Celastrol reduces mortality at doses of 1 and 0.5 mg/kg/d compared to the hyperoxic control group. At 1 mg/kg/d, it normalizes PAAT (PA acceleration time) ( P < 0.001) and reduces vascular hyperreactivity to phenylephrine ( P < 0.001) with no effect on the alteration of the response to acetylcholine induced by hyperoxia. At doses of 0.1, 0.5 and 1 mg/kg/d, it decreases right heart hypertrophy and vascular remodeling (wall thickness) but has no effect on alveolization and vascular density (vWF staining). Finally, although celastrol (0.1 and 0.3 μM) decreases the increased Ca2 + i response to ET-1 in hyperoxia in fPASMC, expression of ET-1 receptors (Western blotting and qPCR for ET-A and ET-B) was unchanged. However, celastrol 0.5 μM decreases ET-1 concentration measured with an ELISA assay in human umbilical arterial endothelial cells. An increased concentration of IL6 was also observed in fPASMC in hyperoxia and was decreased by celastrol 0.5 μM. Celastrol has a preventive dose-dependent effect on some hallmarks of HTP induced by hyperoxia and could thus be considered as an interesting new potential therapeutic option for HTP-DBP.

A comparison of mitochondrial respiratory function in adult and fetal sheep pulmonary arteries.

Neonatal pulmonary hypertension (PH) occurs in approximately 6/1000 term infants. It results from insufficient vasodilation of the pulmonary arteries at birth, although the underlying etiology is not well understood. This increase in pulmonary arterial pressure can lead to severe systemic hypoxia due to redirection of blood flow away from the lungs via ductus arteriosus, resulting in systemic hypoxia. PH is more common in human fetuses exposed to chronic hypoxia during gestation, a phenomenon that is also demonstrated in our high‐altitude fetal sheep model.There is growing evidence that the mitochondria of pulmonary artery smooth muscle cells (PASMCs) play a key role in establishing vascular tone. Mitochondria are exposed to profound changes in oxygen and substrate availability in the transition from fetus to newborn. To gain a better understanding of the developmental changes in mitochondrial function in PASMCs, we tested the hypothesis that mitochondria from fetal vs adult PASMCs would display different substrate‐dependent rates of oxygen consumption and energy production.Lungs were surgically removed from adult non‐pregnant ewes or near‐term fetuses following greater than 100 days of residing at an altitude of over 3801 meters using protocols approved by the Loma Linda University IACUC. 4th–6th generation intrapulmonary pulmonary arteries were isolated, and denuded of endothelium. The metabolic activity of the arterial segments was analyzed in a Seahorse XFe 24 Analyzer that measures the oxygen consumption rate (OCR) with values being normalized to the arterial segment dry weight. These experiments were conducted in the presence of selective antagonists to enable determination of proton leak, non‐mitochondrial oxygen consumption, basal respiration, ATP‐linked respiration, maximal respiration, and spare capacity.Four adults and six fetuses were studied. Compared to adults, fetal PASMCs demonstrated a greater maximal respiratory capacity [813.99 +/− 73.20 (pmol/min) vs. 601.64 +/− 58.09 (pmol/min)] and spare‐capacity [593.28+/− 48.56 (pmol/min) vs. 353.74 +/− 40.39 (pmol/min)] for oxygen consumption while using carbohydrates and amino acids as substrates (p≤ 0.003, ANOVA). Other parameters of OCR were not different between fetuses and adults.These experiments provide initial evidence that there are maturational changes in mitochondrial function. Ongoing studies are evaluating the contribution of long‐term high altitude exposure to these differences in mitochondrial respiration and their importance to phenotypic and functional aberrations in lung function.Support or Funding Information(Supported in part by NIH grant HD083132 (ABB), HD098477 (SMW))

Cyclic Nucleotides Reduce Ryanodine Receptor Mediated Ca2+ Spark Activation Independent of Long Term Hypoxia in Ovine Fetal Pulmonary Arterial Myocytes

Ryanodine receptors (RyR) release Ca2+ from smooth muscle sarcoplasmic reticulum in rapid events known as Ca2+ sparks. These Ca2+ sparks activate voltage and Ca2+ gated potassium channels (BK channels) that cause cell repolarization. Ca2+ spark‐BK channel mediated cell repolarization dilates many types of vessels and is essential to pulmonary arterial (PA) vasodilation during the fetal transition to breathing air. Infants who do not successfully negotiate this transition are at risk of developing pulmonary hypertension, which has significant morbidity and mortality. Previous work shows that long term hypoxia (LTH) decreases Ca2+ spark events in fetal pulmonary arterial smooth muscle cells (PASMCs) even though the Ca2+ stores have functional RyRs. Additional studies illustrate that cyclic nucleotides can increase RyR activity, which led us to test the hypothesis that cyclic nucleotides could rescue RyR activity in myocytes of LTH fetuses. This was examined by treating PAs isolated from low (700m; LA) and high altitude (3801m; HA) near‐term fetal sheep with exogenous cyclic AMP (cAMP) and cyclic GMP (cGMP) or the methylxanthine IBMX, a non‐specific cAMP and cGMP phosphodiesterase inhibitor. RyR activity was measured by confocal imaging of Ca2+ sparks in fluo‐4 labeled PASMCs. The spatial and temporal aspects to the Ca2+ sparks were evaluated using SparkLab, a custom software package. Contrary to our hypothesis, the prevalence of Ca2+ sparks decreased in the presence of cAMP, cGMP, and IBMX for PASMC from both LA and HA fetal sheep. These data suggest that cyclic nucleotides reduce instead of increase vasodilatory capacity via RyR‐BK channel coupling mechanisms. Furthermore, increased cyclic nucleotides had no effect on the spatial‐temporal aspects to the Ca2+ sparks. Even though the signaling pathway remains unclear, the reduction of Ca2+ sparks by cyclic nucleotides is potentially a novel mechanism of RyR modulation in sheep fetal PASMC. This data suggests that increasing cyclic nucleotides may be contra‐indicated in newborn infants who are at risk of developing pulmonary hypertension.Support or Funding InformationThis work is supported by The National Institutes of Health, Eunice Kennedy Shriver National Institute of Child Health and Human Development grant number HD083132, by the National Science Foundation under Grant No. MRI 0923559, and the Loma Linda University School of Medicine. SH was a Loma Linda University Summer Undergraduate Research Fellow.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Cyclic stretch stimulates mitochondrial reactive oxygen species and Nox4 signaling in pulmonary artery smooth muscle cells.

This study was designed to determine whether cyclic stretch induces a persistent pulmonary hypertension of the newborn (PPHN) phenotype of increased NADPH oxidase (Nox) 4 signaling in control pulmonary artery smooth muscle cells (PASMC), and to identify the signal transduction molecules involved. To achieve this, PPHN was induced in lambs by antenatal ligation of the ductus arteriosus at 128 days gestation. After 9 days, lungs and PASMC were isolated from control (twin) and PPHN lambs. Control PASMC were exposed to cyclic stretch at 1 Hz and 15% elongation for 24 h. Stretch-induced Nox4 expression was attenuated by inhibition of mitochondrial complex III and NF-κB, and stretch-induced protein thiol oxidation was attenuated by Nox4 small interfering RNA and complex III inhibition. NF-κB activity was increased by stretch in a complex III-dependent fashion, and stretch-induced cyclin D1 expression was attenuated by complex III inhibition and Nox4 small interfering RNA. This is the first study to show that cyclic stretch increases Nox4 expression via mitochondrial complex III-induced activation of NF-κB in fetal PASMC, resulting in ROS signaling and increased cyclin D1 expression. Targeting these signaling molecules may attenuate pulmonary vascular remodeling associated with PPHN.

Acute Hypoxia Differentially Modifies Ca 2+ Waves in Pulmonary Arterial Smooth Muscle Cells of Intact Arteries from Fetal and Adult Sheep

Ca2+ signaling is important to pulmonary arterial (PA) contraction during acute hypoxia. To better understand Ca2+ signals under acute hypoxia in fetal and adult sheep, we performed confocal imaging of Fluo-4 loaded intact ovine PA Smooth Muscle Cells (PASMCs). Recordings were made in a controlled atmospheric chamber at ~37°C under normoxic conditions at ~300 m or during acute hypoxia, induced by exposing arteries to ~4% O2 for 30 min. Automated analysis procedures were used to examine Ca2+ waves to determine the magnitude, duration, and the number of regions of interest that had events at similar times (“friends”). We tested the hypothesis that acute hypoxia differentially modifies Ca2+ signaling in PASMCs of fetuses versus adults. Adult normoxic PASMC Ca2+ waves had lower AUC and shorter duration compared to fetuses, comparable amplitudes, but greater number of friends. In fetal PASMCs, acute hypoxia decreased Ca2+ wave duration, amplitude, and the area under the curve (AUC) but did not alter the number of friends. In adult sheep, acute hypoxia reduced Ca2+ wave amplitude and the number of friends, but did not impact wave duration or AUC. These results indicate that acute hypoxia modifies fetal and adult PASMC Ca2+ waves in unique ways. These differences in the Ca2+ responses may help define the resultant vasoreactivity in response to acute hypoxia in fetal and adult PASMCs. (Support from NIH and NSF)

Cyclic nucleotides down regulate PAF receptor mediated effects in newborn ovine pulmonary arterial smooth muscle: significance in oxygen therapy of persistent pulmonary hypertension of the newborn (LB605)

Platelet activating factor (PAF) is implicated in the pathogenesis of persistent pulmonary hypertension of the newborn (PPHN). Baseline PAFr activity is higher in fetal ovine pulmonary artery smooth muscle cells (PASMC) and is augmented by hypoxia. In fetal PASMC we have shown evidence of crosstalk between PAFr‐mediated cell signaling and activity of cyclic nucleotides (Cnucs) via respective receptors PKG and PKA. Since these mechanisms are not well described in the newborn counterpart, we studied effects of Cnucs on PAFr protein expression in newborn PASMC. Because long term effects of oxygen therapy on newborn lung are not well understood, we included various oxygen tension study conditions. We hypothesize that PPHN results from failure of newborn lamb pulmonary system to down regulate PAFr activity or to up regulate vasodilatory Cnuc activity.PASMC harvested from ovine newborns 6‐12d old were incubated for 24h with culture media or media containing 10μM cGMP or cAMP analogs or 0.1μM of PAF in normoxia (pO2~100torr), hypoxia (pO2 &lt;40 torr) and hyperoxia (5% CO2, O2). Prostacyclin and TxA2 release were measured and compared to release by fetal PASMC. Proliferation studies were performed under the three conditions and PAFr, PKA and PKG expression were measured.Newborn PA baseline prostacyclin level was 9‐fold greater than in fetal PA, whereas baseline production of TxA2 by newborn PA was 7‐fold less. Overall, 24h hyperoxia attenuated cell proliferation across all treatments. Cnuc treatment attenuated PAF stimulation of proliferation and decreased PAFr expression.Elevated prostacyclin production over TxA2 suggests greater cyclooxygenase activity in newborn PA postnatally. Down regulation of PAFr effects by Cnucs indicates that normal newborn PA physiology favors vasodilatory pathways to minimize PAF‐induced hypertrophy or hyperplasia. Thus failure of newborn lung to anchor down regulation of vasoconstrictors with up regulation of vasodilators leads to pathogenesis of PPHN.

Hydrocortisone normalizes phosphodiesterase-5 activity in pulmonary artery smooth muscle cells from lambs with persistent pulmonary hypertension of the newborn.

Phosphodiesterase-5 (PDE5) is the primary phosphodiesterase in the pulmonary vasculature. It degrades cyclic guanosine monophosphate (cGMP) and inhibits cGMP-mediated vasorelaxation. We previously reported that hydrocortisone treatment decreased hyperoxia-induced PDE5 activity and markers of oxidative stress in lambs with persistent pulmonary hypertension of the newborn (PPHN) ventilated with 100% O2. The objective of our study was to determine the molecular mechanism by which hydrocortisone downregulates PDE5 and oxidative stress in fetal pulmonary artery smooth muscle cells (FPASMCs) from PPHN lambs. PPHN FPASMC were incubated for 24 hours in either 21% or 95% O2. Some cells were treated with 100 nM hydrocortisone and/or ±1 μM helenalin, an inhibitor of nuclear factor κ B (NFκB), a redox-sensitive transcription factor. Exposure to hyperoxia led to increased PDE5 activity, oxidative stress, and NFκB activity. Pretreatment of PPHN FPASMC with hydrocortisone normalized PDE5 activity, decreased cytosolic oxidative stress, increased expression of extracellular superoxide dismutase and NFκB inhibitory protein, and decreased NFκB activity. Similarly, treatment with NFκB inhibitor, helenalin, decreased PDE5 activity. These data suggest that hyperoxia activates NFκB, which in turn induces PDE5 activity in PPHN FPASMC, whereas treatment with hydrocortisone attenuates these changes by blocking reactive oxygen species-induced NFκB activity.

Brief Hyperoxia Increases Mitochondrial Oxidation and Increases Phosphodiesterase 5 Activity in Fetal Pulmonary Artery Smooth Muscle Cells

Oxygen is a pulmonary vasodilator, but data suggest high O(2) concentrations impede that response. We previously reported 24 h of 100% O(2) increased phosphodiesterase 5 (PDE5) activity in fetal pulmonary artery smooth muscle cells (FPASMC) and in ventilated neonatal lambs. PDE5 degrades cyclic GMP (cGMP) and inhibits nitric oxide (NO)-mediated cGMP-dependent vasorelaxation. We sought to determine the mechanism by which hyperoxia initiates reactive oxygen species (ROS) production and regulates PDE5. Thirty minutes of hyperoxia increased mitochondrial ROS versus normoxia (30.3±1.7% vs. 21.1±2.8%), but had no effect on cytosolic ROS, measured by roGFP, a ratiometric protein thiol redox sensor. Hyperoxia increased PDE5 activity (220±39%) and decreased cGMP responsiveness to NO (37±17%). Mitochondrial catalase overexpression attenuated hyperoxia-induced mitochondrial roGFP oxidation, compared to FPASMC infected with empty adenoviral vector (50±3% of control) or mitochondrial superoxide dismutase. MitoTEMPO, mitochondrial catalase, and DT-3, a cGMP-dependent protein kinase I alpha inhibitor, decreased PDE5 activity (32±13%, 26±21%, and 63±10% of control, respectively), and restored cGMP responsiveness to NO (147±16%,172±29%, and 189±43% of control, respectively). C57Bl6 mice exposed to 90%-100% O(2) for 45 min±mechanical ventilation had increased PA PDE5 activity (206±39% and 235±75%, respectively). This is the first description that hyperoxia induces ROS in the mitochondrial matrix prior to the cytosol. Our results indicate that short hyperoxia exposures can produce significant changes in critical cellular signaling pathways. These results indicate that mitochondrial matrix oxidant signals generated during hyperoxia, specifically H(2)O(2), activate PDE5 in a cGMP-dependent protein kinase-dependent manner in pulmonary vascular smooth muscle cells.

Cinaciguat, a soluble guanylate cyclase activator, augments cGMP after oxidative stress and causes pulmonary vasodilation in neonatal pulmonary hypertension.

Although inhaled NO (iNO) therapy is often effective in treating infants with persistent pulmonary hypertension of the newborn (PPHN), up to 40% of patients fail to respond, which may be partly due to abnormal expression and function of soluble guanylate cyclase (sGC). To determine whether altered sGC expression or activity due to oxidized sGC contributes to high pulmonary vascular resistance (PVR) and poor NO responsiveness, we studied the effects of cinaciguat (BAY 58-2667), an sGC activator, on pulmonary artery smooth muscle cells (PASMC) from normal fetal sheep and sheep exposed to chronic intrauterine pulmonary hypertension (i.e., PPHN). We found increased sGC α(1)- and β(1)-subunit protein expression but lower basal cGMP levels in PPHN PASMC compared with normal PASMC. To determine the effects of cinaciguat and NO after sGC oxidation in vitro, we measured cGMP production by normal and PPHN PASMC treated with cinaciguat and the NO donor, sodium nitroprusside (SNP), before and after exposure to 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, an sGC oxidizer), hyperoxia (fraction of inspired oxygen 0.50), or hydrogen peroxide (H(2)O(2)). After treatment with ODQ, SNP-induced cGMP generation was markedly reduced but the effects of cinaciguat were increased by 14- and 64-fold in PPHN fetal PASMC, respectively (P < 0.01 vs. controls). Hyperoxia or H(2)O(2) enhanced cGMP production by cinaciguat but not SNP in PASMC. To determine the hemodynamic effects of cinaciguat in vivo, we compared serial responses to cinaciguat and ACh in fetal lambs after ductus arteriosus ligation. In contrast with the impaired vasodilator response to ACh, cinaciguat-induced pulmonary vasodilation was significantly increased. After birth, cinaciguat caused a significantly greater fall in PVR than either 100% oxygen, iNO, or ACh. We conclude that cinaciguat causes more potent pulmonary vasodilation than iNO in experimental PPHN. We speculate that increased NO-insensitive sGC may contribute to the pathogenesis of PPHN, and cinaciguat may provide a novel treatment of severe pulmonary hypertension.

Impaired NO-cGMP signaling in the pathogenesis of neonatal pulmonary hypertension and therapeutic implications

Background Postnatal survival is dependent upon successful transition of the pulmonary circulation at birth. Persistent pulmonary hypertension of the newborn (PPHN) is a clinical syndrome that is characterized by the failure to achieve or sustain a marked reduction of pulmonary vascular resistance (PVR) after delivery. High PVR causes extra-pulmonary right-to-left shunt, leading to profound hypoxemia, asphyxia and significant morbidity and mortality. Past studies have shown that NO-cGMP signaling contributes significantly to the normal fall in PVR at birth, and that decreased NO production or activity contributes to PPHN. Multicenter studies have shown that inhaled NO is effective in the treatment of clinical PPHN, but nearly 40% of newborns with PPHN fail to respond to iNO therapy. These findings suggest that additional therapies are essential for enhancing NO-cGMP signaling and improving outcomes of neonates with severe PPHN. Since recent studies demonstrated increased oxidative stress in experimental PPHN, we hypothesized that impaired NO responsiveness in PPHN may be due to decreased soluble guanylate cyclase (sGC) activity due to oxidation. Cinaciguat (BAY 58-2667) is a novel sGC activator that causes vasodilation even in the presence of oxidized heme, but its hemodynamic effects in the perinatal lung are unknown. Therefore, we performed a series of physiologic studies in chronically-prepared, late gestation fetal lambs. Additional in vitro studies were performed with isolated pulmonary artery smooth muscle cells (SMC) from normal and PPHN lambs. Results We found that in the normal fetus, cinaciguat (0.1 to 100 mcg over 10 min) caused dose-related increases in pulmonary blood flow greater than 4-fold above baseline values and reduced PVR by 80%. Treatment with ODQ, an sGC oxidizing inhibitor, enhanced cinaciguat-induced pulmonary vasodilation by over 150%. The pulmonary vasodilator effect of cinaciguat was prolonged, decreasing PVR for more than 1.5 hours after brief intrapulmonary infusion. In vitro stimulation of fetal pulmonary artery SMC with cinaciguat after ODQ treatment demonstrated a 14-fold increase in cGMP in comparison without ODQ. We further studied the pulmonary vascular effects of cinaciguat in fetal sheep with chronic pulmonary hypertension after partial ligation of the ductus arteriosus (PPHN). We found that in contrast with the loss of acetylcholineinduced pulmonary vasodilation 5 days after surgery, the cinaciguat response persisted and was enhanced in PPHN lambs. After cesarean-section delivery and mechanical ventilation, neonatal lambs with PPHN demonstrated markedly impaired vasodiliation to inhaled NO (20 and 40 ppm). In contrast, brief infusion of cinaciguat caused marked and prolonged pulmonary vasodilation.

Maturation of intracellular calcium homeostasis in sheep pulmonary arterial smooth muscle cells

Cytosolic Ca(2+) signaling dynamics are important to pulmonary arterial reactivity, and alterations are implicated in pulmonary vascular disorders. Yet, adaptations in cellular Ca(2+) homeostasis and receptor-mediated Ca(2+) signaling with maturation from fetal to adult life in pulmonary arterial smooth muscle cells (PASMCs) are not known. The present study tested the hypothesis that cytosolic Ca(2+) homeostasis and receptor-generated Ca(2+) signaling adapt with maturation in sheep PASMCs. Digitalized fluorescence microscopy was performed using isolated PASMCs from fetal and adult sheep that were loaded with the Ca(2+) indicator fura 2. The results show that basal cytosolic and sarcoplasmic reticulum Ca(2+) levels are attained before birth. Similarly, Ca(2+) efflux pathways from the cytosol and basal as well as capacitative Ca(2+) entry (CCE) are also developed before birth. However, receptor-mediated Ca(2+) signaling adapts with maturation. Prominently, serotonin stimulation elicited Ca(2+) elevations in very few fetal compared with adult PASMCs; in contrast, phenylephrine elevated Ca(2+) in a similar percentage of fetal and adult PASMCs. Serotonin and phenylephrine elicited Ca(2+) increases of a similar magnitude in reactive cells of fetus and adult, supporting the assertion that inositol trisphosphate signaling is intact. Caffeine and ATP elevated Ca(2+) in equivalent numbers of fetal and adult PASMCs. However, the caffeine-induced cytosolic Ca(2+) increase was significantly greater in fetal PASMCs, whereas the ATP-elicited increase was greater in adult cells. Overall, the results of this study demonstrate selective adaptations in receptor-mediated Ca(2+) signaling, but not in cellular Ca(2+) homeostasis.

Hyperoxia Increases Phosphodiesterase 5 Expression and Activity in Ovine Fetal Pulmonary Artery Smooth Muscle Cells

In the pulmonary vasculature, cGMP concentrations are regulated in part by a cGMP-dependent phosphodiesterase (PDE), PDE5. Infants with persistent pulmonary hypertension of the newborn (PPHN) are often mechanically ventilated with high oxygen concentrations. The effects of hyperoxia on the developing pulmonary vasculature and PDE5 are largely unknown. Here, we demonstrate that exposure of fetal pulmonary artery smooth muscle cells (FPASMCs) to high levels of oxygen for 24 hours leads to decreased responsiveness to exogenous NO, as determined by a decreased intracellular cGMP response, increased PDE5 mRNA and protein expression, as well as increased PDE5 cGMP hydrolytic activity. We demonstrate that inhibition of PDE5 activity with sildenafil partially rescues cGMP responsiveness to exogenous NO. In FPASMCs, hyperoxia leads to increased oxidative stress without increasing cell death. Treatment of normoxic FPASMCs with H2O2 is sufficient to induce PDE5 expression and activity, suggesting that reactive oxygen species mediate the effects of hyperoxia in FPASMCs. In support of this mechanism, a chemical antioxidant, N-acetyl-cysteine, is sufficient to block the hyperoxia-mediated increase in PDE5 expression and activity and rescue cGMP responsiveness to exogenous NO. Finally, ventilation of healthy neonatal sheep with 100% O2 for 24 hours leads to increased PDE5 protein expression in the resistance pulmonary arteries and increased PDE5 activity in whole lung extracts. These data suggest that PDE5 expression and activity play a critical role in modulating neonatal pulmonary vascular tone in response to common clinical treatments for PPHN, such as oxygen and inhaled NO.

Increased hydrogen peroxide downregulates soluble guanylate cyclase in the lungs of lambs with persistent pulmonary hypertension of the newborn

Similar to infants born with persistent pulmonary hypertension of the newborn (PPHN), there is an increase in circulating endothelin-1 (ET-1) and decreased cGMP-mediated vasodilation in an ovine model of PPHN. These abnormalities lead to vasoconstriction and vascular remodeling. Our previous studies have demonstrated that reactive oxygen species (ROS) levels are increased in pulmonary arterial smooth muscle cells (PASMC) exposed to ET-1. Thus the initial objective of this study was to determine whether the development of pulmonary hypertension in utero is associated with elevated production of the ROS hydrogen peroxide (H(2)O(2)) and if this is associated with alterations in antioxidant capacity. Second we wished to determine whether chronic exposure of PASMC isolated from fetal lambs to H(2)O(2) would mimic the decrease in soluble guanylate cyclase expression observed in the ovine model of PPHN. Our results indicate that H(2)O(2) levels are significantly elevated in pulmonary arteries isolated from 136-day-old fetal PPHN lambs (P 0.05). In addition, we determined that catalase and glutathione peroxidase expression and activities remain unchanged. Also, we found that the overnight exposure of fetal PASMC to a H(2)O(2)-generating system resulted in significant decreases in soluble guanylate cyclase expression and nitric oxide (NO)-dependent cGMP generation (P 0.05). Finally, we demonstrated that the addition of the ROS scavenger catalase to isolated pulmonary arteries normalized the vasodilator responses to exogenous NO. As these scavengers had no effect on the vasodilator responses in pulmonary arteries isolated from age-matched control lambs this enhancement appears to be unique to PPHN. Overall our data suggest a role for H(2)O(2) in the abnormal vasodilation associated with the pulmonary arteries of PPHN lambs.

Endothelin-1 decreases endothelial NOS expression and activity through ETA receptor-mediated generation of hydrogen peroxide

Similar to infants born with persistent pulmonary hypertension of the newborn (PPHN), there is an increase in circulating endothelin-1 (ET-1) and decreased endothelial nitric oxide synthase (eNOS) gene expression in an ovine model of PPHN. These abnormalities lead to vasoconstriction and vascular remodeling. Our previous studies have demonstrated that reactive oxygen species (ROS) levels are elevated in the pulmonary arteries from PPHN lambs and that ET-1 increases ROS production in pulmonary arterial smooth muscle cells (PASMC) in culture. Thus the objective of this study was to determine whether there was a feedback mechanism between the ET-1-mediated increase in ROS in fetal PASMC (FPASMC) and a decrease in eNOS gene expression in fetal pulmonary arterial endothelial cells (FPAEC). Our results indicate that ET-1 increased H2O2 levels in FPASMC in an endothelin A receptor-dependent fashion. This was observed in both FPASMC monoculture and in cocultures of FPASMC and FPAEC. Conversely, ET-1 decreased H2O2 levels in FPAEC monoculture in an endothelin B receptor-dependent fashion. Furthermore, ET-1 decreased eNOS promoter activity by 40% in FPAEC in coculture with FPASMC. Promoter activity was restored in the presence of catalase. In FPAEC in monoculture treated with 0-100 microM H2O2, 12 microM had no effect on eNOS promoter activity, but it increased eNOS protein levels by 50%. However, at 100 microM, H2O2 decreased eNOS promoter activity and protein levels in FPAEC by 79 and 40%, respectively. These data suggest a role for smooth muscle cell-derived H2O2 in ET-1-mediated downregulation of eNOS expression in children born with PPHN.

Combined superoxide dismutase/catalase mimetics alter fetal pulmonary arterial smooth muscle cell growth.

Reactive oxygen species (ROS) are known to play an important role in the proliferation and viability of vascular smooth muscle cells. We have shown previously that treatment of fetal pulmonary arterial smooth muscle cells (FPASMC) with concentrations of 25 microM and higher of EUK-134, a superoxide dismutase/catalase mimetic, decreased cell viability via the induction of apoptosis. Here we demonstrate a dose-dependent decrease in serum-induced FPASMC growth at lower doses of EUK-134. This was due to the attenuation of FPASMC proliferation rather than the induction of apoptosis. Moreover, we found that the inhibition of FPASMC proliferation was observed using EUK-134 at concentrations as low as 5 microM. This inhibition of proliferation correlated with a 31% decrease in superoxide levels, as estimated using the oxidation of dihydroethidium. Flow cytometry revealed an increase in FPASMC in G2 after 24 h of exposure to 10 microM EUK-134. This was associated with a twofold increase in levels of the cell-cycle regulatory protein p21. This, together with our previous data, suggests that ROS levels determine the rate of FPASMC proliferation and, when below a threshold level, trigger apoptosis. Titration of ROS with antioxidants may help to prevent, or reverse, the vascular remodeling manifest in many cardiovascular disease states.

Fetal pulmonary hypertension prolongs the endothelin-1 induced increase in pulmonary artery smooth muscle cell cytosolic calcium concentration

Introduction: At birth, pulmonary artery (PA) blood flow increases 8–10 fold and PA pressure falls by 50% within 24 hours. The mechanisms responsible for postnatal adaptation of the pulmonary circulation remain incompletely understood. High serum endothelin-1 (ET-1) levels are found in infants with persistent pulmonary hypertension of the newborn. We hypothesized that chronic intrauterine pulmonary hypertension (PHT) potentiates agonist induced increase of cytosolic calcium concentration ([Ca2+]i) in fetal PA smooth muscle cells(SMC). Methods: Chronic intrauterine pulmonary hypertension was induced by intrauterine ligation of the ductus arteriosus (DA) in late-gestation fetal lambs. 7–10 days following DA ligation, animals were euthanized. Distal PAs (>4th generation) were removed from the lung and PA SMC were isolated and maintained in normoxic (95%O2) primary culture. Age-matched non-PHT controls were sacrificed at ∼132 days gestation and cells were cultured in the same manner. Fluorescence microscopy using fura-2 was used to determine the effect of ET-1 (10−6 -10−8 M) on PA SMC [Ca2+]i from PHT and control animals. To determine the effect of PHT on endothelin A and B (ETA and ETB) receptor mRNA expression, quantitative, internally controlled RT-PCR was performed on distal PAs and SMC in culture. Results: ET-1 (10−8 M) caused a monophasic increase in [Ca2+]i (206 +/- 47%, p < 0.01 vs baseline) above baseline in controls (n = 25), while PHT SMC [Ca2+]i did not increase significantly. When PHT SMC were treated with 10−6M ET-1, in those cells that responded, [Ca2+]i increased 174 +/- 81% above baseline(p < 0.01 vs baseline). Only 3/33 (9%) of PHT SMC responded to ET-1 compared to 90% of controls. Additionally, the duration of the increase in [Ca2+]i was longer in the PHT SMC: PHT SMC [Ca2+]i fell to baseline after 328 +/- 16 sec, where control [Ca2+]i fell to baseline after 117 sec. ETA and ETB receptor mRNA expression are both increased in PHT. Conclusions: PHT decreases PA SMC sensitivity to ET-1 by ∼100 fold, however, PHT increases the duration of the ET-1 induced increase in [Ca2+]i. We conclude that PHT prolongs the response of PA SMC to ET-1. This prolongation may lead to significant increases in PA SMC [Ca2+]i that results in attenuated postnatal adaptation of the pulmonary circulation.

Contribution of the K(Ca) channel to membrane potential and O2 sensitivity is decreased in an ovine PPHN model.

Ca2+-sensitive K+ (K(Ca)) channels play an important role in mediating perinatal pulmonary vasodilation. We hypothesized that lung K(Ca) channel function may be decreased in persistent pulmonary hypertension of the newborn (PPHN). To test this hypothesis, pulmonary artery smooth muscle cells (PASMC) were isolated from fetal lambs with severe pulmonary hypertension induced by ligation of the ductus arteriosus in fetal lambs at 125-128 days gestation. Fetal lambs were killed after pulmonary hypertension had been maintained for at least 7 days. Age-matched, sham-operated animals were used as controls. PASMC K+ currents and membrane potentials were recorded using amphotericin B-perforated patch-clamp techniques. The increase in whole cell current normally seen in response to normoxia was decreased (333.9 +/- 63.6% in control vs. 133.1 +/- 16.0% in hypertensive fetuses). The contribution of the K(Ca) channel to the whole cell current was diminished in hypertensive, compared with control, fetal PASMC. In PASMC from hypertensive fetuses, a change from hypoxia to normoxia caused no change in membrane potential compared with a -14.6 +/- 2.8 mV decrease in membrane potential in PASMC from control animals. In PASMC from animals with pulmonary hypertension, 4-aminopyridine (4-AP) caused a larger depolarization than iberiotoxin, whereas in PASMC from control animals, iberiotoxin caused a larger depolarization than 4-AP. These data confirm the hypothesis that the contribution of the K(Ca) channel to membrane potential and O2 sensitivity is decreased in an ovine model of PPHN, and this may contribute to the abnormal perinatal pulmonary vasoreactivity associated with PPHN.

ET-1 stimulates pulmonary arterial smooth muscle cell proliferation via induction of reactive oxygen species.

Recent studies implicate reactive oxygen species (ROS) such as superoxide anions and H(2)O(2) in the proliferation of systemic vascular smooth muscle cells (SMCs). However, the role of ROS in SMC proliferation within the pulmonary circulation remains unclear. We investigated the effects of endothelin-1 (ET-1), a potential SMC mitogen, on ROS production and proliferation of fetal pulmonary artery SMCs (FPASMCs). Exposure to ET-1 resulted in increases in superoxide production and viable FPASMCs after 72 h. These increases were prevented by pretreatment with PD-156707. Treatment with pertussis toxin blocked the effects of ET-1, whereas cholera toxin stimulated superoxide production and increased viable cell numbers even in the absence of ET-1. Wortmannin, LY-294002, diphenyleneiodonium (DPI), 4-(2-aminoethyl)benzenesulfonyl fluoride, and apocynin also prevented the ET-1-mediated increases in superoxide production and viable cell numbers. Exposure to H(2)O(2) or diethyldithiocarbamate increased viable cell number by 37% and 50%, respectively. Conversely, ascorbic acid and DPI decreased viable cell number, which appeared to be due to an increase in programmed cell death. Our data suggest that ET-1 exerts a mitogenic effect on FPASMCs via an increase in ROS production and that antioxidants can block this effect via induction of apoptosis. Antioxidant treatment may therefore represent a potential therapy for pulmonary vascular diseases.

Pulmonary vascular response to normoxia and K(Ca) channel activity is developmentally regulated.

To address developmental regulation of pulmonary vascular O(2) sensing, we tested the hypotheses that 1) fetal but not adult pulmonary artery smooth muscle cells (PASMCs) can directly sense an acute increase in O(2), 2) Ca2+-sensitive K(+) (K(Ca)) channel activity decreases with maturation, and 3) PASMC K(Ca) channel expression decreases with maturation. We used fluorescence microscopy to confirm that fetal but not adult PASMCs are able to sense an acute increase in O(2) tension. Acute normoxia induced a 22 +/- 2% decrease in cytosolic Ca2+ concentration ([Ca2+](i)) in fetal PASMCs and no change in ([Ca2+](i)) in adult PASMCs (P < 0.01). The effects of K(+) channel antagonists were studied on fetal and adult PASMC ([Ca2+](i)). Iberiotoxin (10(-9) M) caused PASMC ([Ca2+](i)) to increase by 694 +/- 22% in the fetus and caused no change in adult PASMCs. K(Ca) channel expression and mRNA levels in distal pulmonary arteries from fetal and adult sheep were examined. Both K(Ca) channel protein and mRNA expression in the distal pulmonary vasculature decreased with maturation. We conclude that maturation-dependent changes in PASMC O(2) sensing render the fetal PASMCs uniquely sensitive to an acute increase in O(2) tension at a biologically critical time point.