Perinatal hypoxia triggers alterations in K+ channels of adult pulmonary artery smooth muscle cells

IK channel activation increases tumor growth and induces differential behavioral responses in two breast epithelial cell lines

Many potassium channel families are over-expressed in cancer, but their mechanistic role in disease progression is poorly understood. Potassium channels modulate membrane potential (Vmem) and thereby influence calcium ion dynamics and other voltage-sensitive signaling mechanisms, potentially acting as transcriptional regulators. This study investigated the differential response to over-expression and activation of a cancer-associated potassium channel, the intermediate conductance calcium-activated potassium channel (IK), on aggressive behaviors in mammary epithelial and breast cancer cell lines. IK was over-expressed in the highly metastatic breast cancer cell line MDA-MB-231 and the spontaneously immortalized breast epithelial cell line MCF-10A, and the effect on cancer-associated behaviors was assessed. IK over-expression increased primary tumor growth and metastasis of MDA-MB-231 in orthotopic xenografts, demonstrating for the first time in any cancer type that increased IK is sufficient to promote cancer aggression. The primary tumors had similar vascularization as determined by CD31 staining and similar histological characteristics. Interestingly, despite the increased in vivo growth and metastasis, neither IK over-expression nor activation with agonist had a significant effect on MDA-MB-231 proliferation, invasion, or migration in vitro. In contrast, IK decreased MCF-10A proliferation and invasion through Matrigel but had no effect on migration in a scratch-wound assay. We conclude that IK activity is sufficient to promote cell aggression in vivo. Our data provide novel evidence supporting IK and downstream signaling networks as potential targets for cancer therapies.

Impact of early- and late-onset preeclampsia on features of placental and newborn vascular health

INTRODUCTION

Offspring exposed to preeclampsia (PE) show an increased risk of cardiovascular disease in adulthood. We hypothesize that this is mediated by a disturbed vascular development of the placenta, umbilical cord and fetus. Therefore, we investigated associations between early-onset PE (EOPE), late-onset PE (LOPE) and features of placental and newborn vascular health.

METHODS

We performed a nested case-control study in The Rotterdam Periconceptional Cohort, including 30 PE pregnancies (15 EOPE, 15 LOPE) and 218 control pregnancies (164 uncomplicated controls, 54 complicated controls including 28 fetal growth restriction, 26 preterm birth) and assessed macroscopic and histomorphometric outcomes of the placenta and umbilical cord.

RESULTS

A significant association was observed between PE and a smaller umbilical vein area and wall thickness, independent of gestational age and birth weight. In EOPE we observed significant associations with a lower weight, length and width of the placenta, length of the umbilical cord, and thickness and wall area of the umbilical vein and artery. These associations attenuated after gestational age and birth weight adjustment. In LOPE a significant association with a larger placental width and smaller umbilical vein wall thickness was shown, independent of gestational age and birth weight.

DISCUSSION

Our study suggests that PE is associated with a smaller umbilical cord vein area and wall thickness, independent of gestational age and birth weight, which may serve as a proxy of disturbed cardiovascular development in the newborn. Follow-up studies are needed to ultimately predict and lower the risk of cardiovascular disease in offspring exposed to PE.

Perinatal nitric oxide therapy prevents adverse effects of perinatal hypoxia on the adult pulmonary circulation

Adverse events in utero are associated with the occurrence of chronic diseases in adulthood. We previously demonstrated in mice that perinatal hypoxia resulted in altered pulmonary circulation in adulthood, with a decreased endothelium-dependent relaxation of pulmonary arteries, associated with long-term alterations in the nitric oxide (NO)/cyclic GMP pathway. The present study investigated whether inhaled NO (iNO) administered simultaneously to perinatal hypoxia could have potential beneficial effects on the adult pulmonary circulation. Indeed, iNO is the therapy of choice in humans presenting neonatal pulmonary hypertension. Long-term effects of neonatal iNO therapy on adult pulmonary circulation have not yet been investigated. Pregnant mice were placed in hypoxia (13% O₂) with simultaneous administration of iNO 5 days before delivery until 5 days after birth. Pups were then raised in normoxia until adulthood. Perinatal iNO administration completely restored acetylcholine-induced relaxation, as well as endothelial nitric oxide synthase protein content, in isolated pulmonary arteries of adult mice born in hypoxia. Right ventricular hypertrophy observed in old mice born in hypoxia compared to controls was also prevented by perinatal iNO treatment. Therefore, simultaneous administration of iNO during perinatal hypoxic exposure seems able to prevent adverse effects of perinatal hypoxia on the adult pulmonary circulation.

Role of histone deacetylases in regulation of phenotype of ovine newborn pulmonary arterial smooth muscle cells

OBJECTIVE

Pulmonary arterial hypertension, characterized by pulmonary vascular remodelling and vasoconstriction, is associated with excessive proliferative changes in pulmonary vascular walls. However, the role of HDACs in the phenotypic alteration of pulmonary arterial smooth muscle cells (PASMC) is largely unknown.

MATERIAL AND METHODS

Pulmonary arterial smooth muscle cells were isolated from newborn sheep. Cell cycle analysis was performed by flow cytometry. mRNA and protein expression were measured by real-time PCR and Western blot analysis. Wound-healing scratch assay was used to measure cell migration. Contractility of newborn PASMCs was determined by gel contraction assay. Chromatin immunoprecipitation was used to examine histone modifications along the p21 promoter region. Global DNA methylation was measured by liquid chromatography-mass spectroscopy.

RESULTS

Inhibition of class I and class II HDACs by apicidin and HDACi VIII suppressed proliferation of newborn PASMC and induced cell cycle arrest in G1 phase. Acetyl H3 levels were higher in newborn PASMC treated with apicidin and HDACi VIII. This was accompanied by increased expression of p21 and reduced expression of CCND1 but not p53. HDAC inhibition altered histone codes around the p21 promoter region in NPASMC. Apicidin inhibited serum-induced cell migration, and modulated profiling of expression of genes encoding pro-oxidant and antioxidant enzymes. Contractility and global DNA methylation levels of newborn PASMCs were also markedly modulated by apicidin.

CONCLUSION

Our results demonstrate that class I HDACs are clearly involved in phenotypic alteration of newborn PASMC.

Endothelial and smooth muscle cell ion channels in pulmonary vasoconstriction and vascular remodeling

The pulmonary circulation is a low resistance and low pressure system. Sustained pulmonary vasoconstriction and excessive vascular remodeling often occur under pathophysiological conditions such as in patients with pulmonary hypertension. Pulmonary vasoconstriction is a consequence of smooth muscle contraction. Many factors released from the endothelium contribute to regulating pulmonary vascular tone, while the extracellular matrix in the adventitia is the major determinant of vascular wall compliance. Pulmonary vascular remodeling is characterized by adventitial and medial hypertrophy due to fibroblast and smooth muscle cell proliferation, neointimal proliferation, intimal, and plexiform lesions that obliterate the lumen, muscularization of precapillary arterioles, and in situ thrombosis. A rise in cytosolic free Ca(2+) concentration ([Ca(2+)]cyt) in pulmonary artery smooth muscle cells (PASMC) is a major trigger for pulmonary vasoconstriction, while increased release of mitogenic factors, upregulation (or downregulation) of ion channels and transporters, and abnormalities in intracellular signaling cascades are key to the remodeling of the pulmonary vasculature. Changes in the expression, function, and regulation of ion channels in PASMC and pulmonary arterial endothelial cells play an important role in the regulation of vascular tone and development of vascular remodeling. This article will focus on describing the ion channels and transporters that are involved in the regulation of pulmonary vascular function and structure and illustrating the potential pathogenic role of ion channels and transporters in the development of pulmonary vascular disease.

Hypoxic pulmonary hypertension of the newborn

Hypoxic pulmonary hypertension of the newborn is characterized by elevated pulmonary vascular resistance and pressure due to vascular remodeling and increased vessel tension secondary to chronic hypoxia during the fetal and newborn period. In comparison to the adult, the pulmonary vasculature of the fetus and the newborn undergoes tremendous developmental changes that increase susceptibility to a hypoxic insult. Substantial evidence indicates that chronic hypoxia alters the production and responsiveness of various vasoactive agents such as endothelium-derived nitric oxide, endothelin-1, prostanoids, platelet-activating factor, and reactive oxygen species, resulting in sustained vasoconstriction and vascular remodeling. These changes occur in most cell types within the vascular wall, particularly endothelial and smooth muscle cells. At the cellular level, suppressed nitric oxide-cGMP signaling and augmented RhoA-Rho kinase signaling appear to be critical to the development of hypoxic pulmonary hypertension of the newborn.

Perinatal hypoxia enhances cyclic adenosine monophosphate-mediated BKCa channel activation in adult murine pulmonary artery

Exposure to perinatal hypoxia results in alteration of the adult pulmonary circulation, which is linked among others to alterations in K(+) channels in pulmonary artery (PA) smooth muscle cells. In particular, large conductance Ca(2+)-activated K(+) (BK(Ca)) channels protein expression and activity were increased in adult PA from mice born in hypoxia compared with controls. We evaluated long-term effects of perinatal hypoxia on the cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) pathway-mediated activation of BK(Ca) channels, using isoproterenol, forskolin, and dibutyryl-cAMP. Whole-cell outward current was higher in pulmonary artery smooth muscle cells from mice born in hypoxia compared with controls. Spontaneous transient outward currents, representative of BK(Ca) activity, were present in a greater proportion in pulmonary artery smooth muscle cells of mice born in hypoxia than in controls. Agonists induced a greater relaxation in PA of mice born in hypoxia compared with controls, and BK(Ca) channels contributed more to the cAMP/PKA-mediated relaxation in case of perinatal hypoxia. In summary, perinatal hypoxia enhanced cAMP-mediated BK(Ca) channels activation in adult murine PA, suggesting that this pathway could be a potential target for modulating adult pulmonary vascular tone after perinatal hypoxia.

Regulation of the Pulmonary Circulation in the Fetus and Newborn

During the development of the pulmonary vasculature in the fetus, many structural and functional changes occur to prepare the lung for the transition to air breathing. The development of the pulmonary circulation is genetically controlled by an array of mitogenic factors in a temporo-spatial order. With advancing gestation, pulmonary vessels acquire increased vasoreactivity. The fetal pulmonary vasculature is exposed to a low oxygen tension environment that promotes high intrinsic myogenic tone and high vasocontractility. At birth, a dramatic reduction in pulmonary arterial pressure and resistance occurs with an increase in oxygen tension and blood flow. The striking hemodynamic differences in the pulmonary circulation of the fetus and newborn are regulated by various factors and vasoactive agents. Among them, nitric oxide, endothelin-1, and prostaglandin I2 are mainly derived from endothelial cells and exert their effects via cGMP, cAMP, and Rho kinase signaling pathways. Alterations in these signaling pathways may lead to vascular remodeling, high vasocontractility, and persistent pulmonary hypertension of the newborn.

Morphological and functional alterations of the ductus arteriosus in a chicken model of hypoxia-induced fetal growth retardation

The hypoxic conditions in which children with intrauterine growth retardation (IUGR) develop are hypothesized to alter the development of the ductus arteriosus (DA). We aimed to evaluate the effects of in ovo hypoxia on chicken DA morphometry and reactivity. Hypoxia (15% O2 from day 6 to 19 of the 21-d incubation period) produced a reduction in the body mass of the 19-d fetuses and a shortening of right and left DAs. However, ductal lumen and media cross-sectional areas were not affected by hypoxia. The ductal contractions induced by oxygen, KCl, H2O2, 4-aminopyridine, and endothelin-1 were similar in control and hypoxic fetuses. In contrast, the DAs from the hypoxic fetuses showed increased contractile responses to norepinephrine and phenylephrine and impaired relaxations to acetylcholine, sodium nitroprusside, and isoproterenol. The relaxations induced by 8-Br-cGMP, forskolin, Y-27632, and hydroxyfasudil were not altered by chronic hypoxia. In conclusion, chronic in ovo hypoxia-induced growth retardation in fetal chickens and altered the response of the DA to adrenergic agonists and to endothelium-dependent and -independent relaxing agents. Our observations support the concept that prolonged patency of the DA in infants with IUGR may be partially related with hypoxia-induced changes in local vascular mechanisms.

Long-term effects of prenatal hypoxia on endothelium-dependent relaxation responses in pulmonary arteries of adult sheep

Chronic hypoxia during the course of pregnancy is a common insult to the fetus. However, its long-term effect on the pulmonary vasculature in adulthood has not been described. In this study, the vasorelaxation responses of conduit pulmonary arteries in adult female sheep that were chronically hypoxic as fetuses and raised postnatally at sea level were investigated. Vessel tension studies revealed that endothelium-dependent relaxation responses were attenuated in pulmonary arteries from adult sheep that experienced prenatal hypoxia. Endothelial nitric oxide synthase (eNOS) protein expression was unchanged, but eNOS activity was significantly decreased in pulmonary arteries from prenatally hypoxic sheep. Protein expression of eNOS partners, caveolin-1, calmodulin, and heat shock protein 90 (Hsp90) did not change following prenatal hypoxia. However, the association between eNOS and caveolin-1, its inhibitory binding partner, was significantly increased, whereas association between eNOS and its stimulatory partners calmodulin and Hsp90 was greatly decreased. Furthermore, phosphorylation of Ser(1177) in eNOS decreased, whereas phosphorylation of Thr(495) increased, in the prenatally hypoxic pulmonary arteries, events that are related to eNOS activity. These data demonstrate that prenatal hypoxia results in persistent abnormalities in endothelium-dependent relaxation responses of pulmonary arteries in adult sheep due to decreased eNOS activity resulting from altered posttranslational regulation.

Blunted hypoxic pulmonary vasoconstriction in experimental neonatal chronic lung disease

RATIONALE

Neonatal chronic lung disease (CLD), caused by prolonged mechanical ventilation (MV) with O(2)-rich gas, is the most common cause of long-term hospitalization and recurrent respiratory illness in extremely premature infants. Recurrent episodes of hypoxemia and associated ventilator adjustments often lead to worsening CLD. The mechanism that causes these hypoxemic episodes is unknown. Hypoxic pulmonary vasoconstriction (HPV), which is partially controlled by O(2)-sensitive voltage-gated potassium (K(v)) channels, is an important adaptive response to local hypoxia that helps to match perfusion and ventilation in the lung.

OBJECTIVES

To test the hypothesis that chronic lung injury (CLI) impairs HPV.

METHODS

We studied preterm lambs that had MV with O(2)-rich gas for 3 weeks and newborn rats that breathed 95%-O(2) for 2 weeks, both of which resulted in airspace enlargement and pulmonary vascular changes consistent with CLD.

MEASUREMENTS AND MAIN RESULTS

HPV was attenuated in preterm lambs with CLI after 2 weeks of MV and in newborn rats with CLI after 2 weeks of hyperoxia. HPV and constriction to the K(v)1.x-specific inhibitor, correolide, were preferentially blunted in excised distal pulmonary arteries (dPAs) from hyperoxic rats, whose dPAs exhibited decreased K(v)1.5 and K(v)2.1 mRNA and K(+) current. Intrapulmonary gene transfer of K(v)1.5, encoding the ion channel that is thought to trigger HPV, increased O(2)-sensitive K(+) current in cultured smooth muscle cells from rat dPAs, and restored HPV in hyperoxic rats.

CONCLUSIONS

Reduced expression/activity of O(2)-sensitive K(v) channels in dPAs contributes to blunted HPV observed in neonatal CLD.