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Chronic hypoxia causes pulmonary hypertension with smooth muscle cell proliferation and matrix deposition in the wall of the pulmonary arterioles. We demonstrate here that hypoxia also induces a pronounced inflammation in the lung before the structural changes of the vessel wall. The proinflammatory action of hypoxia is mediated by the induction of distinct cytokines and chemokines and is independent of tumor necrosis factor-␣ signaling. We have previously proposed a crucial role for heme oxygenase-1 (HO-1) in protecting cardiomyocytes from hypoxic stress, and potent anti-inflammatory properties of HO-1 have been reported in models of tissue injury. We thus established transgenic mice that constitutively express HO-1 in the lung and exposed them to chronic hypoxia. HO-1 transgenic mice were protected from the development of both pulmonary inflammation as well as hypertension and vessel wall hypertrophy induced by hypoxia. Significantly, the hypoxic induction of proinflammatory cytokines and chemokines was suppressed in HO-1 transgenic mice. Our findings suggest an important protective function of enzymatic products of HO-1 activity as inhibitors of hypoxia-induced vasoconstrictive and proinflammatory pathways.A cute hypoxia in the lung causes arteriolar vasoconstriction whereas prolonged hypoxia promotes proliferation and migration of vascular smooth muscle cells (VSMC) and extracellular matrix deposition in the arterial wall, a process known as vascular remodeling (1). These abnormalities are characteristic of pulmonary hypertension (2). Several clinical conditions characterized by lung inflammation have been linked to the development of chronic pulmonary hypertension (3). Interestingly, perivascular inflammatory cell infiltration as well as increased serum levels of proinflammatory cytokines, such as IL-1␤ and IL-6, have been reported in clinical cases of primary pulmonary hypertension (4, 5). However, little attention has been given up to now to the role of pulmonary inflammation in the pathogenesis of pulmonary hypertension induced by hypoxia.Heme oxygenase (HO; EC 1.14.99.3) catalyzes the oxidation of heme to carbon monoxide (CO) and biliverdin, which is then converted to bilirubin by biliverdin reductase. Three isoforms of HO have been identified: the inducible HO-1 and the constitutively expressed HO-2 and HO-3 (6, 7). Our previous in vitro data suggest that CO released by HO-1 confers protection against vasoconstriction and vascular remodeling induced by hypoxia (8 -10). More recently, Soares et al. have suggested antiinflammatory properties of HO-1 in a cardiac transplantation model, although the molecular mechanisms have not been fully elucidated (11). Our recent in vivo data using an HO-1 null mouse model suggest that HO-1 plays a central role in protecting the right ventricle from hypoxic pulmonary pressure-induced injury (12).In the present study, we established transgenic mice that overexpress HO-1 in the lung and exposed them to hypoxia to investigate the effects of HO-1 activity on the developmen...

Regulation of fetal growth is multifactorial and complex. Diverse factors, including intrinsic fetal conditions as well as maternal and environmental factors, can lead to intrauterine growth restriction (IUGR). The interaction of these factors governs the partitioning of nutrients and rate of fetal cellular proliferation and maturation. Although IUGR is probably a physiologic adaptive response to various stimuli, it is associated with distinct short- and long-term morbidities. Immediate morbidities include those associated with prematurity and inadequate nutrient reserve, while childhood morbidities relate to impaired maturation and disrupted organ development. Potential long-term effects of IUGR are debated and explained by the fetal programming hypothesis. In formulating a comprehensive approach to the management and follow-up of the growth-restricted fetus and infant, physicians should take into consideration the etiology, timing, and severity of IUGR. In addition, they should be cognizant of the immediate perinatal response of the growth-restricted infant as well as the childhood and long-term associated morbidities. A multi disciplinary approach is imperative, including early recognition and obstetrical management of IUGR, assessment of the growth-restricted newborn in the delivery room, possible monitoring in the neonatal intensive care unit, and appropriate pediatric follow-up. Future research is necessary to establish effective preventive, diagnostic, and therapeutic strategies for IUGR, perhaps affecting the health of future generations.

Vascular endothelial growth factor (VEGF) plays an important role in angiogenesis and blood vessel remodeling. Its expression is up-regulated in vascular smooth muscle cells by a number of conditions, including hypoxia. Hypoxia increases the transcriptional rate of VEGF via a 28-base pair enhancer located in the 5-upstream region of the gene. The gas molecules nitric oxide (NO) and carbon monoxide (CO) are important vasodilating agents. We report here that these biological molecules can suppress the hypoxia-induced production of VEGF mRNA and protein in smooth muscle cells. In transient expression studies, both NO and CO inhibited the ability of the hypoxic enhancer we have previously identified to activate gene transcription. Furthermore, electrophoretic mobility shift assays indicated decreased binding of hypoxia-inducible factor 1 (HIF-1) to this enhancer by nuclear proteins isolated from COtreated cells, although HIF-1 protein levels were unaffected by CO. Given that both CO and NO activate guanylyl cyclase to produce cGMP and that a cGMP analog (8-Br-cGMP) showed a similar suppressive effect on the hypoxic induction of the VEGF enhancer, we speculate that the suppression of VEGF by these two gas molecules occurs via a cyclic GMP-mediated pathway.Low oxygen tension is a potent regulator of diverse biological processes, including erythropoiesis, angiogenesis, and vascular cell contractility. These effects are mediated by several proteins that are induced under hypoxic environments and modulate cell-cell interactions, cell proliferation, and differentiation. In the vasculature, hypoxia regulates the expression of genes encoding growth factors such as endothelin-1 (ET-1) 1 , platelet-derived growth factor-B (PDGF-B) and vascular endothelial growth factor (VEGF), as well as genes regulating the production of gas molecules such as nitric oxide (NO) and carbon monoxide (CO) (1)(2)(3)(4)(5). Whereas the expression of the endothelial nitric oxide synthase gene is suppressed by hypoxia, the expression of heme oxygenase-1 (HO-1), the enzyme catalyzing the production of CO, is up-regulated by hypoxia (5).Mechanisms by which hypoxia alters gene expression include transcriptional and post-transcriptional regulation (4, 6, 7). Several hypoxia-responsive cis-acting elements have been identified (8,9). We have reported the presence of a 28-bp enhancer located approximately 980 bp upstream of the VEGF transcription start site, which is necessary and sufficient to up-regulate transcription of the VEGF gene in response to hypoxia (10). This hypoxia response element contains a sequence homologous to (and now has been included into) the hypoxia-inducible factor 1 (HIF-1) consensus (11). HIF-1 is a basic helix-loop-helix transcription factor originally identified to mediate the transcriptional activation of the erythropoietin gene (8) leading to enhanced erythropoiesis under hypoxia. It was subsequently shown to regulate the expression of genes encoding glycolytic enzymes (12) and the gene for VEGF (10, 11) implicating it as an i...

Abstract-We investigated the role of heme oxygenase (HO)-1 in the development of hypoxia-induced pulmonary hypertension. HO catalyzes the breakdown of heme to the antioxidant bilirubin and the vasodilator carbon monoxide. Hypoxia is a potent but transient inducer of HO-1 in vascular smooth muscle cells in vitro and in the lung in vivo. By using agonists of HO-1, we sustained a high expression of HO-1 in the lungs of rats for 1 week. We report that this in vivo enhancement of HO-1 in the lung prevented the development of hypoxic pulmonary hypertension and inhibited the structural remodeling of the pulmonary vessels. The mechanism(s) underlying this effect may involve a direct vasodilating and antiproliferative action of endogenous carbon monoxide, as well as an indirect effect of carbon monoxide on the production of vasoconstrictors. These results provide evidence that enhancement of endogenous adaptive responses may be used to prevent hypoxia-induced pulmonary hypertension. (Circ Res. 2000;86:1224-1229.)Key Words: vascular remodeling Ⅲ gene expression Ⅲ hypoxia H eme oxygenase (HO) is the rate-limiting enzyme in the degradation of heme to biliverdin and subsequently to bilirubin. The reaction catalyzed by HO is the major source of carbon monoxide (CO) in the body, which is increasingly recognized as a physiologically important molecule rather than a toxic waste product. 1 There are 3 known isoforms of HO. HO-1 is inducible, 2 whereas HO-2 and HO-3 are constitutively expressed. 3,4 HO-3 is highly homologous to HO-2 but has not been characterized fully. HO-2 is the predominant form expressed in the central nervous system, where CO is thought to act as a neurotransmitter via the soluble guanylate cyclase/cGMP pathway. 5 HO-1, the inducible form of the enzyme, is highly expressed in erythropoietic tissues, where its function is heme degradation, but it is also expressed in vascular smooth muscle cells (SMCs), 6 where its role may include regulation of vascular tone. Several lines of investigation provide evidence that CO may be a physiological regulator of cellular interactions in the vasculature, acting as a direct and indirect vasodilator; directly, CO acts via activation of soluble guanylate cyclase and elevation of cGMP, as in rat aortic and coronary vascular SMC preparations 6,7 as well as in dog femoral, carotid, and coronary arteries. 8 Indirectly, SMC-derived CO may cause SMC relaxation by inhibiting the hypoxic induction of the vasoconstrictors endothelin-1 (ET-1) and platelet-derived growth factor-B (PDGF-B) in adjacent endothelial cells. 9 In addition to its vasodilatory actions, CO was shown to inhibit SMC proliferation by regulating the cell cycle-specific transcription factor E2F-1, 10 as well as the expression of the mitogens ET-1 and PDGF-BB in culture. 9 A variety of cellular stressors, such as heat shock, oxidative stress, heavy metals, and hemoproteins, induce HO-1. 11-13 Therefore, a protective/antioxidant role has been proposed for HO-1, as well as its enzymatic product, bilirubin. 14 We found t...

Vascular endothelial growth factor (VEGF) is a potent mitogenic and permeability factor targeting predominantly endothelial cells. At least two tyrosine kinase receptors, Flk-1 and Flt-1, mediate its action and are mostly expressed by endothelial cells. VEGF and VEGF receptor expression are upregulated by hypoxia in vivo and the role of VEGF in hypoxia-induced angiogenesis has been extensively studied in a variety of disease entities. Although VEGF and its receptors are abundantly expressed in the lung, their role in hypoxic pulmonary hypertension and the accompanying vascular remodeling are incompletely understood. We report in this in vivo study that hypoxia increases mRNA levels for both VEGF and Flk-1 in the rat lung. The kinetics of the hypoxic response differ between receptor and ligand: Flk-1 mRNA showed a biphasic response to hypoxia with a significant, but transient, rise in mRNA levels observed after 9-15 h of hypoxic exposure and the highest levels noted after 3 wk. In contrast, VEGF mRNA levels did not show a significant increase with acute hypoxia, but increased progressively after 1-3 wk of hypoxia. By in situ hybridization, VEGF mRNA was localized predominantly in alveolar epithelial cells with increased signal in the lungs of hypoxic animals compared with controls. Immunohistochemical staining with anti-VEGF antibodies localized VEGF peptide throughout the lung parenchyma and was increased in hypoxic compared with normoxic animals. Furthermore, hypoxic animals had significantly higher circulating VEGF concentrations compared with normoxic controls. Lung vascular permeability as measured by extravasation of Evans Blue dye was not significantly different between normoxic and hypoxic animals, although a tendency for increased permeability was seen in the hypoxic animals. These findings suggest a possible role for VEGF in the pulmonary response to hypoxia.

Background Risk factors for maternal vitamin D deficiency and preterm birth overlap but the distribution of 25-hydroxyvitamin D (25(OH)D) levels among preterm infants is not known. We aimed to determine associations between 25(OH)D levels and gestational age. Methods We measured umbilical cord plasma levels of 25(OH)D from 471 infants born at Brigham and Women’s Hospital in Boston. We used generalized estimating equations to determine whether preterm (<37 weeks’ gestation) or very preterm (<32 weeks’ gestation) infants had greater odds of 25(OH)D levels < 20 ng/ml than more mature infants. We adjusted for potential confounding by season of birth, maternal age, race, marital status and singleton or multiple gestation. Results Mean cord plasma 25(OH)D level was 34.0 ng/ml (range 4.1 to 95.3, and SD 14.1). Infants born before 32 weeks’ gestation had increased odds of 25(OH)D levels < 20 ng/ml in unadjusted (OR 2.2, 95% CI 1.1, 4.3) and adjusted models (OR 2.4, 95% CI 1.2, 5.3) compared to more mature infants. Conclusion Infants born < 32 weeks’ gestation are at higher risk than more mature infants for low 25(OH)D levels. Further investigation of the relationships between low 25(OH)D levels and preterm birth and its sequelae is thus warranted.

The insulin-like growth factor (IGF) system is the dominant endocrine regulator of fetal growth, whereas insulin has a permissive role. Although a role for leptin in fetal growth has been suggested recently, the mechanism by which leptin may be related to fetal growth is not known; but leptin may interact with the IGF system in utero as it does in the extrauterine life. In the context of a hospital-based case control study, we collected anthropometric and demographic data and measured serum leptin, IGF-I, IGF-II, insulin, cortisol, and IGF binding protein 3 concentrations in 142 cord blood samples from full-term deliveries. Cord leptin, IGF-I, and insulin levels correlated positively with birth weight (r = 0.46, r = 0.41, and r = 0.21, respectively, P < 0.01) by univariate analysis and were significantly higher in large-for-gestational-age (LGA) infants, compared with appropriate-for-gestational-age (AGA) infants. Cord leptin concentrations correlated with insulin levels (r = 0.36, P < 0.01) but not with IGF-I levels (r = 0.20). Multiple linear and logistic regression analysis demonstrated an independent positive relationship of both leptin and IGF-I with birth weight and AGA/LGA status. The positive association of leptin levels with birth weight and AGA/LGA status cannot be attributed to IGF-I. This suggests the existence of alternative mechanisms underlying leptin's associations with fetal growth that should be further explored.