Deletion of the eNOS gene has a greater impact on the pulmonary circulation of male than female mice

Overview of Methamphetamine-Associated Pulmonary Arterial Hypertension

TOPIC IMPORTANCE

The global surge in methamphetamine use is a critical public health concern, particularly due to its robust correlation with methamphetamine-associated pulmonary arterial hypertension (MA-PAH). This association raises urgent alarms about the potential escalation of MA-PAH incidence, posing a significant and imminent challenge to global public health.

REVIEW FINDINGS

This comprehensive review meticulously explores MA-PAH, offering insights into its epidemiology, pathophysiology, clinical presentation, diagnostic intricacies, and management strategies. The pathogenesis, yet to be fully described, involves complex molecular interactions, including alterations in serotonin signaling, reduced activity of carboxylesterase 1, oxidative stress, and dysregulation of pulmonary vasoconstrictors and vasodilators. These processes culminate in the structural remodeling of the pulmonary vasculature, resulting in pulmonary arterial hypertension. MA-PAH exhibits a more severe clinical profile in functional class and hemodynamics compared with idiopathic pulmonary arterial hypertension. Management involves a multifaceted approach, integrating pulmonary vasodilators, cessation of methamphetamine use, and implementing social and rehabilitation programs. These measures aim to enhance patient outcomes and detect potential relapses for timely intervention.

SUMMARY

This review consolidates our understanding of MA-PAH, pinpointing knowledge gaps for future studies. Addressing these gaps is crucial for advancing diagnostic accuracy, unraveling mechanisms, and optimizing treatment for MA-PAH, thereby addressing the evolving landscape of this complex health concern.

Heterogeneity of cGMP signalling in tumour cells and the tumour microenvironment: Challenges and chances for cancer pharmacology and therapeutics

The second messenger cyclic guanosine monophosphate (cGMP) is an important regulator of human (patho-)physiology and has emerged as an attractive drug target. Currently, cGMP-elevating drugs are mainly used to treat cardiovascular diseases, but there is also increasing interest in exploring their potential for cancer prevention and therapy. In this review article, we summarise recent findings in cancer-related cGMP research, with a focus on melanoma, breast cancer, colorectal cancer, prostate cancer, glioma, and ovarian cancer. These studies indicate tremendous heterogeneity of cGMP signalling in tumour tissue. It appears that different tumour and stroma cells, and perhaps different sexes, express different cGMP generators, effectors, and degraders. Therefore, the same cGMP-elevating drug can lead to different outcomes in different tumour settings, ranging from inhibition to promotion of tumourigenesis or therapy resistance. These findings, together with recent evidence that increased cGMP signalling is associated with worse prognosis in several human cancers, challenge the traditional view that cGMP elevation generally has an anti-cancer effect. As cGMP pathways appear to be more stable in the stroma than in tumour cells, we suggest that cGMP-modulating drugs should preferentially target the tumour microenvironment. Indeed, there is evidence that phosphodiesterase 5 inhibitors like sildenafil enhance anti-tumour immunity by acting on immune cells. Moreover, many in vivo results obtained with cGMP-modulating drugs could be explained by effects on the tumour vasculature rather than on the tumour cells themselves. We therefore propose a model that incorporates the NO/cGMP signalling pathway in tumour vessels as a key target for cancer therapy. Deciphering the multifaceted roles of cGMP in cancer is not only a challenge for basic research, but also provides a chance to predict potential adverse effects of cGMP-modulating drugs in cancer patients and to develop novel anti-tumour therapies by precision targeting of the relevant cells and molecular pathways.

Sex Differences in Pulmonary Hypertension

Pulmonary hypertension (PH) includes multiple diseases that share as common characteristic an elevated pulmonary artery pressure and right ventricular involvement. Sex differences are observed in practically all causes of PH. The most studied type is pulmonary arterial hypertension (PAH) which presents a gender bias regarding its prevalence, prognosis, and response to treatment. Although this disease is more frequent in women, once affected they present a better prognosis compared to men. Even if estrogens seem to be the key to understand these differences, animal models have shown contradictory results leading to the birth of the estrogen paradox. In this review we will summarize the evidence regarding sex differences in experimental animal models and, very specially, in patients suffering from PAH or PH from other etiologies.

Sex, Gender, and Sex Hormones in Pulmonary Hypertension and Right Ventricular Failure

Pulmonary hypertension (PH) encompasses a syndrome of diseases that are characterized by elevated pulmonary artery pressure and pulmonary vascular remodeling and that frequently lead to right ventricular (RV) failure and death. Several types of PH exhibit sexually dimorphic features in disease penetrance, presentation, and progression. Most sexually dimorphic features in PH have been described in pulmonary arterial hypertension (PAH), a devastating and progressive pulmonary vasculopathy with a 3-year survival rate <60%. While patient registries show that women are more susceptible to development of PAH, female PAH patients display better RV function and increased survival compared to their male counterparts, a phenomenon referred to as the "estrogen paradox" or "estrogen puzzle" of PAH. Recent advances in the field have demonstrated that multiple sex hormones, receptors, and metabolites play a role in the estrogen puzzle and that the effects of hormone signaling may be time and compartment specific. While the underlying physiological mechanisms are complex, unraveling the estrogen puzzle may reveal novel therapeutic strategies to treat and reverse the effects of PAH/PH. In this article, we (i) review PH classification and pathophysiology; (ii) discuss sex/gender differences observed in patients and animal models; (iii) review sex hormone synthesis and metabolism; (iv) review in detail the scientific literature of sex hormone signaling in PAH/PH, particularly estrogen-, testosterone-, progesterone-, and dehydroepiandrosterone (DHEA)-mediated effects in the pulmonary vasculature and RV; (v) discuss hormone-independent variables contributing to sexually dimorphic disease presentation; and (vi) identify knowledge gaps and pathways forward. © 2020 American Physiological Society. Compr Physiol 10:125-170, 2020.

Sex differences in pulmonary vascular control: focus on the nitric oxide pathway

Although the incidence of pulmonary hypertension is higher in females, the severity and prognosis of pulmonary vascular disease in both neonates and adults have been shown to be worse in male subjects. Studies of sex differences in pulmonary hypertension have mainly focused on the role of sex hormones. However, the contribution of sex differences in terms of vascular signaling pathways regulating pulmonary vascular function remains incompletely understood. Consequently, we investigated pulmonary vascular function of male and female swine in vivo, both at rest and during exercise, and in isolated small pulmonary arteries in vitro, with a particular focus on the NO‐cGMP‐PDE5 pathway. Pulmonary hemodynamics at rest and during exercise were virtually identical in male and female swine. Moreover, NO synthase inhibition resulted in a similar degree of pulmonary vasoconstriction in male and female swine. However, NO synthase inhibition blunted bradykinin‐induced vasodilation in pulmonary small arteries to a greater extent in male than in female swine. PDE5 inhibition resulted in a similar degree of vasodilation in male and female swine at rest, while during exercise there was a trend towards a larger effect in male swine. In small pulmonary arteries, PDE5 inhibition failed to augment bradykinin‐induced vasodilation in either sex. Finally, in the presence of NO synthase inhibition, the pulmonary vasodilator effect of PDE5 inhibition was significantly larger in female swine both in vivo and in vitro. In conclusion, the present study demonstrated significant sex differences in the regulation of pulmonary vascular tone, which may contribute to understanding sex differences in incidence, treatment response, and prognosis of pulmonary vascular disease.

The Role of Transient Receptor Potential Channel 6 Channels in the Pulmonary Vasculature

Canonical or classical transient receptor potential channel 6 (TRPC6) is a Ca²⁺-permeable non-selective cation channel that is widely expressed in the heart, lung, and vascular tissues. The use of TRPC6-deficient (“knockout”) mice has provided important insights into the role of TRPC6 in normal physiology and disease states of the pulmonary vasculature. Evidence indicates that TRPC6 is a key regulator of acute hypoxic pulmonary vasoconstriction. Moreover, several studies implicated TRPC6 in the pathogenesis of pulmonary hypertension. Furthermore, a unique genetic variation in the TRPC6 gene promoter has been identified, which might link the inflammatory response to the upregulation of TRPC6 expression and ultimate development of pulmonary vascular abnormalities in idiopathic pulmonary arterial hypertension. Additionally, TRPC6 is critically involved in the regulation of pulmonary vascular permeability and lung edema formation during endotoxin or ischemia/reperfusion-induced acute lung injury. In this review, we will summarize latest findings on the role of TRPC6 in the pulmonary vasculature.

Genotype-phenotype effects of Bmpr2 mutations on disease severity in mouse models of pulmonary hypertension

More than 350 mutations in the type-2 BMP (bone morphogenetic protein) receptor, BMPR2, have been identified in patients with heritable pulmonary arterial hypertension (HPAH). However, only 30% of BMPR2 mutation carriers develop PAH, and we cannot predict which of these carriers will develop clinical disease. One possibility is that the nature of the BMPR2 mutation affects disease severity. This hypothesis has been difficult to test clinically, given the rarity of HPAH and the complexity of the confounding genetic and environmental risk factors. To test this hypothesis, therefore, we evaluated the susceptibility to experimental pulmonary hypertension (PH) of mice carrying different HPAH-associated Bmpr2 mutations on otherwise identical genetic backgrounds. Mice with Bmpr2ΔEx4-5 mutations (Bmpr2^+/-), in which the mutant protein is not expressed, develop less severe PH in response to hypoxia or hypoxia with vascular endothelial growth factor receptor inhibition than mice with an extracellular-domain Bmpr2ΔEx2 mutation (Bmpr2^ΔEx2/+), in which the mutant protein is expressed. This was associated with a marked decrease in stabilizing phosphorylation of threonine 495 endothelial nitric oxide synthase (pThr495 eNOS) in Bmpr2^ΔEx2/+ compared to wild-type and Bmpr2^+/- mouse lungs. These findings provide the first experimental evidence that BMPR2 mutation types influence the severity of HPAH and suggest that patients with BMPR2 mutations who express mutant BMPR2 proteins by escaping non-sense-mediated messenger RNA decay (NMD- mutations) will develop more severe disease than HPAH patients with NMD+ mutations who do not express BMPR2 mutant proteins. Since decreased levels of pThr495 eNOS are associated with increased eNOS uncoupling, our data also suggest that this effect may result from defects in eNOS function.

Endothelial nitric oxide synthase deficient mice are protected from lipopolysaccharide induced acute lung injury

Lipopolysaccharide (LPS) derived from the outer membrane of gram-negative bacteria induces acute lung injury (ALI) in mice. This injury is associated with lung edema, inflammation, diffuse alveolar damage, and severe respiratory insufficiency. We have previously reported that LPS-mediated nitric oxide synthase (NOS) uncoupling, through increases in asymmetric dimethylarginine (ADMA), plays an important role in the development of ALI through the generation of reactive oxygen and nitrogen species. Therefore, the focus of this study was to determine whether mice deficient in endothelial NOS (eNOS^-/-) are protected against ALI. In both wild-type and eNOS^-/- mice, ALI was induced by the intratracheal instillation of LPS (2 mg/kg). After 24 hours, we found that eNOS^-/-mice were protected against the LPS mediated increase in inflammatory cell infiltration, inflammatory cytokine production, and lung injury. In addition, LPS exposed eNOS^-/- mice had increased oxygen saturation and improved lung mechanics. The protection in eNOS^-/- mice was associated with an attenuated production of NO, NOS derived superoxide, and peroxynitrite. Furthermore, we found that eNOS^-/- mice had less RhoA activation that correlated with a reduction in RhoA nitration at Tyr³⁴. Finally, we found that the reduction in NOS uncoupling in eNOS^-/- mice was due to a preservation of dimethylarginine dimethylaminohydrolase (DDAH) activity that prevented the LPS-mediated increase in ADMA. Together our data suggest that eNOS derived reactive species play an important role in the development of LPS-mediated lung injury.

Progress in solving the sex hormone paradox in pulmonary hypertension

Pulmonary arterial hypertension (PAH) is a devastating and progressive disease with marked morbidity and mortality. Even though being female represents one of the most powerful risk factors for PAH, multiple questions about the underlying mechanisms remain, and two "estrogen paradoxes" in PAH exist. First, it is puzzling why estrogens have been found to be protective in various animal models of PAH, whereas PAH registries uniformly demonstrate a female susceptibility to the disease. Second, despite the pronounced tendency for the disease to develop in women, female PAH patients exhibit better survival than men. Recent mechanistic studies in classical and in novel animal models of PAH, as well as recent studies in PAH patients, have significantly advanced the field. In particular, it is now accepted that estrogen metabolism and receptor signaling, as well as estrogen interactions with key pathways in PAH development, appear to be potent disease modifiers. A better understanding of these interactions may lead to novel PAH therapies. It is the purpose of this review to 1) review sex hormone synthesis, metabolism, and receptor physiology; 2) assess the context in which sex hormones affect PAH pathogenesis; 3) provide a potential explanation for the observed estrogen paradoxes and gender differences in PAH; and 4) identify knowledge gaps and future research opportunities. Because the majority of published studies investigated 17β-estradiol and/or its metabolites, this review will primarily focus on pulmonary vascular and right ventricular effects of estrogens. Data for other sex hormones will be discussed very briefly.

Congenital absence of nitric oxide synthase 3 potentiates cardiac dysfunction and reduces survival in doxorubicin- and trastuzumab-mediated cardiomyopathy

BACKGROUND

Doxorubicin (DOX) and trastuzumab (TRZ) are highly effective chemotherapeutic agents in the breast cancer setting, limited by their cardiotoxic side effects. Among the potential mechanisms for this drug-induced cardiomyopathy, increased production of oxidative stress (OS) through a nitric oxide synthase 3 (NOS3)-dependent pathway has gained recent attention. The objective of the study was to determine the role of NOS3 and OS in a clinically relevant female murine model of DOX- and TRZ-induced heart failure.

METHODS

A total of 120 female mice (60 wild-type [WT] and 60 NOS3 knockout [NOS3(-/-)]) were treated with either 0.9% saline, DOX, TRZ, or DOX with TRZ (DOX+TRZ). Serial echocardiography was performed for a total of 10 days, after which the mice were euthanized for histological and biochemical analyses.

RESULTS

In WT female mice receiving DOX+TRZ, left ventricular ejection fraction (LVEF) decreased from 75 ± 3% at baseline to 46 ± 2% at day 10 (P < 0.05). In the NOS3(-/-) group, LVEF decreased from 72 ± 3% at baseline to 35 ± 2% at day 10 (P < 0.05). LVEF was significantly lower in NOS3(-/-) female mice receiving DOX+TRZ than WT mice at day 10 (P < 0.05). Compared with WT, NOS3(-/-) female mice also demonstrated increased mortality after treatment with DOX+TRZ, corroborating the echocardiographic findings. Histological analysis demonstrated increased myofibrillar degradation and loss of cell integrity in NOS3(-/-) female mice treated with DOX+TRZ. There was increased generation of oxidized phosphatidylcholine, a marker of OS, in NOS3(-/-) female mice receiving DOX+TRZ compared with control mice.

CONCLUSIONS

Congenital absence of NOS3 potentiates the cardiotoxic side effects of DOX+TRZ in an acute female murine model of chemotherapy-induced cardiomyopathy.

Structure and composition of pulmonary arteries, capillaries, and veins

The pulmonary vasculature comprises three anatomic compartments connected in series: the arterial tree, an extensive capillary bed, and the venular tree. Although, in general, this vasculature is thin-walled, structure is nonetheless complex. Contributions to structure (and thus potentially to function) from cells other than endothelial and smooth muscle cells as well as those from the extracellular matrix should be considered. This review is multifaceted, bringing together information regarding (i) classification of pulmonary vessels, (ii) branching geometry in the pulmonary vascular tree, (iii) a quantitative view of structure based on morphometry of the vascular wall, (iv) the relationship of nerves, a variety of interstitial cells, matrix proteins, and striated myocytes to smooth muscle and endothelium in the vascular wall, (v) heterogeneity within cell populations and between vascular compartments, (vi) homo- and heterotypic cell-cell junctional complexes, and (vii) the relation of the pulmonary vasculature to that of airways. These issues for pulmonary vascular structure are compared, when data is available, across species from human to mouse and shrew. Data from studies utilizing vascular casting, light and electron microscopy, as well as models developed from those data, are discussed. Finally, the need for rigorous quantitative approaches to study of vascular structure in lung is highlighted.

FK506 activates BMPR2, rescues endothelial dysfunction, and reverses pulmonary hypertension

Dysfunctional bone morphogenetic protein receptor-2 (BMPR2) signaling is implicated in the pathogenesis of pulmonary arterial hypertension (PAH). We used a transcriptional high-throughput luciferase reporter assay to screen 3,756 FDA-approved drugs and bioactive compounds for induction of BMPR2 signaling. The best response was achieved with FK506 (tacrolimus), via a dual mechanism of action as a calcineurin inhibitor that also binds FK-binding protein-12 (FKBP12), a repressor of BMP signaling. FK506 released FKBP12 from type I receptors activin receptor-like kinase 1 (ALK1), ALK2, and ALK3 and activated downstream SMAD1/5 and MAPK signaling and ID1 gene regulation in a manner superior to the calcineurin inhibitor cyclosporine and the FKBP12 ligand rapamycin. In pulmonary artery endothelial cells (ECs) from patients with idiopathic PAH, low-dose FK506 reversed dysfunctional BMPR2 signaling. In mice with conditional Bmpr2 deletion in ECs, low-dose FK506 prevented exaggerated chronic hypoxic PAH associated with induction of EC targets of BMP signaling, such as apelin. Low-dose FK506 also reversed severe PAH in rats with medial hypertrophy following monocrotaline and in rats with neointima formation following VEGF receptor blockade and chronic hypoxia. Our studies indicate that low-dose FK506 could be useful in the treatment of PAH.

Female-specific hypertension loci on rat chromosome 13

A 3.7-Mb region of rat chromosome 13 (45.2-49.0 Mb) affects blood pressure (BP) in females only, indicating the presence of sex-specific BP loci in close proximity to the Renin locus. In the present study, we used a series of Dahl salt-sensitive/Mcwi-13 Brown Norway congenic rat strains to further resolve BP loci within this region. We identified 3 BP loci affecting female rats only, of which the 2 smaller loci (line9BP3 and line9BP4) were functionally characterized by sequence and expression analysis. Compared with SS (SS/HsdMcwiCrl), the presence of a 591-kb region of BN (BN/NHsdMcwi) chromosome 13 (line9BP3) significantly lowered BP by 21 mm Hg on an 8% NaCl diet (153 ± 7 versus 174 ± 5 mm Hg; P<0.001). Unexpectedly, the addition of 23 kb of Brown Norway chromosome 13 (line9BP4) completely erased the female-specific BP protection on 8% NaCl diet, suggesting that BN hypertensive allele(s) reside in this region. The congenic interval of the protective line 9F strain contains 3 genes (Optc, Prelp, and Fmod), and the hypertensive line 9E contains 1 additional gene (Btg2). Sequence analysis of the 2 BP loci revealed a total of 282 intergenic variants, with no coding variants. Analysis of gene expression by quantitative real-time polymerase chain reaction revealed strain- and sex-specific differences in Prelp, Fmod, and Btg2 expression, implicating these as novel candidate genes for female-specific hypertension.

Estrogen paradox in pulmonary hypertension: current controversies and future perspectives

Although the incidence of pulmonary hypertension is higher in female patients, numerous experimental studies have demonstrated better outcome in female animals, exacerbation of the disease after ovariectomy, and a strong protective effect of estrogen: a phenomenon known as the "estrogen paradox" of pulmonary hypertension. On the other hand, some clinical studies have indirectly linked estrogen to increased risk of portopulmonary hypertension, whereas others implicate increased estrogen metabolism and high levels of certain estrogen metabolites in promoting pulmonary vascular remodeling in familial pulmonary arterial hypertension. In this review we investigate the estrogen paradox through highlighting the differential receptor-mediated effects of estrogen. Although estrogen and estrogen receptor-based therapies have shown promise in rescuing preexisting pulmonary hypertension in animals, their role is yet to be defined in humans.

Sex differences in primary hypertension

Men have higher blood pressure than women through much of life regardless of race and ethnicity. This is a robust and highly conserved sex difference that it is also observed across species including dogs, rats, mice and chickens and it is found in induced, genetic and transgenic animal models of hypertension. Not only do the differences between the ovarian and testicular hormonal milieu contribute to this sexual dimorphism in blood pressure, the sex chromosomes also play a role in and of themselves. This review primarily focuses on epidemiological studies of blood pressure in men and women and experimental models of hypertension in both sexes. Gaps in current knowledge regarding what underlie male-female differences in blood pressure control are discussed. Elucidating the mechanisms underlying sex differences in hypertension may lead to the development of anti-hypertensives tailored to one's sex and ultimately to improved therapeutic strategies for treating this disease and preventing its devastating consequences.

Hypoxic Pulmonary Vasoconstriction

It has been known for more than 60 years, and suspected for over 100, that alveolar hypoxia causes pulmonary vasoconstriction by means of mechanisms local to the lung. For the last 20 years, it has been clear that the essential sensor, transduction, and effector mechanisms responsible for hypoxic pulmonary vasoconstriction (HPV) reside in the pulmonary arterial smooth muscle cell. The main focus of this review is the cellular and molecular work performed to clarify these intrinsic mechanisms and to determine how they are facilitated and inhibited by the extrinsic influences of other cells. Because the interaction of intrinsic and extrinsic mechanisms is likely to shape expression of HPV in vivo, we relate results obtained in cells to HPV in more intact preparations, such as intact and isolated lungs and isolated pulmonary vessels. Finally, we evaluate evidence regarding the contribution of HPV to the physiological and pathophysiological processes involved in the transition from fetal to neonatal life, pulmonary gas exchange, high-altitude pulmonary edema, and pulmonary hypertension. Although understanding of HPV has advanced significantly, major areas of ignorance and uncertainty await resolution.

Changes of pulmonary pathology and gene expressions after simvastatin treatment in the monocrotaline-induced pulmonary hypertension rat model

BACKGROUND AND OBJECTIVES

Simvastatin's properties are suggestive of a potential pathophysiologic role in pulmonary hypertension. The objectives of this study were to investigate changes of pulmonary pathology and gene expressions, including endothelin (ET)-1, endothelin receptor A (ERA), inducible nitric oxide synthase (NOS2), endothelial nitric oxide synthase (NOS3), matrix metalloproteinase (MMP) 2, tissue inhibitor of matrix metalloproteinases (TIMP) and caspase 3, and to evaluate the effect of simvastatin on monocrotaline (M)-induced pulmonary hypertension.

MATERIALS AND METHODS

Six week old male Sprague-Dawley rats were treated, as follows: control group, subcutaneous (sc) injection of saline; M group, sc injection of M (60 mg/kg); and simvastatin group, sc injection of M (60 mg/kg) plus 10 mg/kg/day simvastatin orally.

RESULTS

On day 28, right ventricular hypertrophy (RVH) significantly decreased in the simvastatin group compared to the M group. Similarly, right ventricular pressure significantly decreased in the simvastatin group on day 28. From day 7, the ratio of medial thickening of the pulmonary artery was significantly increased in the M group, but there was no significant change in the simvastatin group. The number of muscular pulmonary arterioles was significantly reduced in the simvastatin group. On day 5, gene expressions of ET-1, ERA, NOS2, NOS3, MMP and TIMP significantly decreased in the simvastatin group.

CONCLUSION

Administration of simvastatin exerted weak inhibitory effects on RVH and on the number of muscular pulmonary arterioles, during the development of M-induced pulmonary hypertension in rats. Simvastatin decreased gene expressions on day 5.

Serotonin transporter, sex, and hypoxia: microarray analysis in the pulmonary arteries of mice identifies genes with relevance to human PAH

Pulmonary arterial hypertension (PAH) is up to threefold more prevalent in women than men. Female mice overexpressing the serotonin transporter (SERT; SERT+ mice) exhibit PAH and exaggerated hypoxia-induced PAH, whereas male SERT+ mice remain unaffected. To further investigate these sex differences, microarray analysis was performed in the pulmonary arteries of normoxic and chronically hypoxic female and male SERT+ mice. Quantitative RT-PCR analysis was employed for validation of the microarray data. In relevant groups, immunoblotting was performed for genes of interest (CEBPβ, CYP1B1, and FOS). To translate clinical relevance to our findings, CEBPβ, CYP1B1, and FOS mRNA and protein expression was assessed in pulmonary artery smooth muscle cells (PASMCs) derived from idiopathic PAH (IPAH) patients and controls. In female SERT+ mice, multiple pathways with relevance to PAH were altered. This was also observed in chronically hypoxic female SERT+ mice. We selected 10 genes of interest for qRT-PCR analysis (FOS, CEBPβ, CYP1B1, MYL3, HAMP2, LTF, PLN, NPPA, UCP1, and C1S), and 100% concordance was reported. Protein expression of three selected genes, CEBPβ, CYP1B1, FOS, was also upregulated in female SERT+ mice. Serotonin and 17β-estradiol increased CEBPβ, CYP1B1, and FOS protein expression in PASMCs. In addition, CEBPβ, CYP1B1, and FOS mRNA and protein expression was also increased in PASMCs derived from IPAH patients. Here, we have identified a number of genes that may predispose female SERT+ mice to PAH, and these findings may also be relevant to human PAH.

Disruption of the apelin-APJ system worsens hypoxia-induced pulmonary hypertension

OBJECTIVE

The G-protein-coupled receptor APJ and its ligand apelin are highly expressed in the pulmonary vasculature, but their function in this vascular bed is unclear. We hypothesized that disruption of apelin signaling would lead to worsening of the vascular remodeling associated with pulmonary hypertension (PH).

METHODS AND RESULTS

We found that apelin-null mice developed more severe PH compared with wild-type mice when exposed to chronic hypoxia. Micro-computed tomography of the pulmonary arteries demonstrated significant pruning of the microvasculature in the apelin-null mice. Apelin-null mice had a significant reduction of serum nitrate levels. This was secondary to downregulation of endothelial nitric oxide synthase (eNOS), which was associated with reduced expression of Kruppel-like factor 2 (KLF2), a known regulator of eNOS expression. In vitro knockdown studies targeting apelin in human pulmonary artery endothelial cells demonstrated decreased eNOS and KLF2 expression, as well as impaired phosphorylation of AMP-activated kinase and eNOS. Moreover, serum apelin levels of patients with PH were significantly lower than those of controls.

CONCLUSIONS

These data demonstrate that disruption of apelin signaling can exacerbate PH mediated by decreased activation of AMP-activated kinase and eNOS, and they identify this pathway as a potentially important therapeutic target for treatment of this refractory human disease.

Distinct role and location of the endothelial isoform of nitric oxide synthase in regulating platelet aggregation in males and females in vivo

The role of endogenous nitric oxide in regulating platelet function in vivo is incompletely understood. The enzymic and anatomic sources of bioactive NO remain unclear and the consequences of the differences in endothelial function between males and females to platelet responsiveness are not known. We employed a mouse model of platelet thromboembolism to assess platelet aggregation in vivo along with supporting in vitro studies to investigate these issues. Pharmacological nitric oxide synthase (NOS) inhibition protracted the duration of thromboembolic responses to ADP (adenosine diphosphate) and enhanced in vivo platelet aggregation following activation of the coagulation cascade. Collagen induced in vivo platelet aggregation was enhanced in female eNOS(-/-) mice and the NOS inhibitor L-NAME (Nω-Nitro-l-arginine methyl ester hydrochloride) potentiated collagen induced thromboembolism although selective iNOS and nNOS antagonists had no effect. None of the NOS inhibitors tested had significant effects on platelet aggregation in isolated whole blood. In conclusion, endogenous NO derived from eNOS in the vascular endothelium is a critical regulator of platelet function in vivo in both males and females with negligible roles of iNOS and nNOS. Despite the expression of NOS enzymes in circulating blood elements, there is no evidence of a functional role of endogenous NO from these cells in regulating platelets. eNOS and its up- and down-stream mediators are therefore potential anti-thrombotic targets.

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.

Nitric oxide synthases in infants and children with pulmonary hypertension and congenital heart disease

Rationale

Nitric oxide is an important regulator of vascular tone in the pulmonary circulation. Surgical correction of congenital heart disease limits pulmonary hypertension to a brief period.

Objectives

The study has measured expression of endothelial (eNOS), inducible (iNOS), and neuronal nitric oxide synthase (nNOS) in the lungs from biopsies of infants with pulmonary hypertension secondary to cardiac abnormalities (n = 26), compared to a control group who did not have pulmonary or cardiac disease (n = 8).

Methods

eNOS, iNOS and nNOS were identified by immunohistochemistry and quantified in specific cell types.

Measurements and main results

Significant increases of eNOS and iNOS staining were found in pulmonary vascular endothelial cells of patients with congenital heart disease compared to control infants. These changes were confined to endothelial cells and not present in other cell types. Patients who strongly expressed eNOS also had strong expression of iNOS.

Conclusion

Upregulation of eNOS and iNOS occurs at an early stage of pulmonary hypertension, and may be a compensatory mechanism limiting the rise in pulmonary artery pressure.

Persistent eNOS activation secondary to caveolin-1 deficiency induces pulmonary hypertension in mice and humans through PKG nitration

Pulmonary hypertension (PH) is an unremitting disease defined by a progressive increase in pulmonary vascular resistance leading to right-sided heart failure. Using mice with genetic deletions of caveolin 1 (Cav1) and eNOS (Nos3), we demonstrate here that chronic eNOS activation secondary to loss of caveolin-1 can lead to PH. Consistent with a role for eNOS in the pathogenesis of PH, the pulmonary vascular remodeling and PH phenotype of Cav1-/- mice were absent in Cav1-/-Nos3-/- mice. Further, treatment of Cav1-/- mice with either MnTMPyP (a superoxide scavenger) or l-NAME (a NOS inhibitor) reversed their pulmonary vascular pathology and PH phenotype. Activation of eNOS in Cav1-/- lungs led to the impairment of PKG activity through tyrosine nitration. Moreover, the PH phenotype in Cav1-/- lungs could be rescued by overexpression of PKG-1. The clinical relevance of the data was indicated by the observation that lung tissue from patients with idiopathic pulmonary arterial hypertension demonstrated increased eNOS activation and PKG nitration and reduced caveolin-1 expression. Together, these data show that loss of caveolin-1 leads to hyperactive eNOS and subsequent tyrosine nitration-dependent impairment of PKG activity, which results in PH. Thus, targeting of PKG nitration represents a potential novel therapeutic strategy for the treatment of PH.

Persistent eNOS activation secondary to caveolin-1 deficiency induces pulmonary hypertension in mice and humans through PKG nitration

Pulmonary hypertension (PH) is an unremitting disease defined by a progressive increase in pulmonary vascular resistance leading to right-sided heart failure. Using mice with genetic deletions of caveolin 1 (Cav1) and eNOS (Nos3), we demonstrate here that chronic eNOS activation secondary to loss of caveolin-1 can lead to PH. Consistent with a role for eNOS in the pathogenesis of PH, the pulmonary vascular remodeling and PH phenotype of Cav1-/- mice were absent in Cav1-/-Nos3-/- mice. Further, treatment of Cav1-/- mice with either MnTMPyP (a superoxide scavenger) or l-NAME (a NOS inhibitor) reversed their pulmonary vascular pathology and PH phenotype. Activation of eNOS in Cav1-/- lungs led to the impairment of PKG activity through tyrosine nitration. Moreover, the PH phenotype in Cav1-/- lungs could be rescued by overexpression of PKG-1. The clinical relevance of the data was indicated by the observation that lung tissue from patients with idiopathic pulmonary arterial hypertension demonstrated increased eNOS activation and PKG nitration and reduced caveolin-1 expression. Together, these data show that loss of caveolin-1 leads to hyperactive eNOS and subsequent tyrosine nitration-dependent impairment of PKG activity, which results in PH. Thus, targeting of PKG nitration represents a potential novel therapeutic strategy for the treatment of PH.

Role of platelet-activating factor in pulmonary vascular remodeling associated with chronic high altitude hypoxia in ovine fetal lambs

Platelet-activating factor (PAF) is implicated in pathogenesis of chronic hypoxia-induced pulmonary hypertension in some animal models and in neonates. Effects of chronic hypoxia on PAF receptor (PAF-R) system in fetal pulmonary vasculature are unknown. We investigated the effect of chronic high altitude hypoxia (HAH) in fetal lambs [pregnant ewes were kept at 3,801 m (12,470 ft) altitude from ∼35 to 145 days gestation] on PAF-R-mediated effects in the pulmonary vasculature. Age-matched controls were kept at sea level. Intrapulmonary arteries were isolated, and smooth muscle cells (SMC-PA) were cultured from HAH and control fetuses. To determine presence of pulmonary vascular remodeling, lung tissue sections were subjected to morphometric analysis. Percentage medial wall thickness was significantly increased ( P < 0.05) in arteries at all levels in the HAH lambs. PAF-R protein expression studied by immunocytochemistry and Western blot analysis on lung tissue SMC-PA demonstrated greater PAF-R expression in HAH lambs. PAF-R binding (femtomoles per 106cells) in HAH SMC-PA was 90.3 ± 4.08 and 66% greater than 54.3 ± 4.9 in control SMC-PA. Pulmonary arteries from HAH fetuses synthesized >3-fold PAF than vessels from controls. Compared with controls SMC-PA of HAH lambs demonstrated 139% and 40% greater proliferation in 10% FBS alone and with 10 nM PAF, respectively. Our data demonstrate that exposure of ovine fetuses to HAH will result in significant upregulation of PAF synthesis, PAF-R expression, and PAF-R-mediated effects in pulmonary arteries. These findings suggest that increased PAF-R protein expression and increased PAF binding contribute to pulmonary vascular remodeling in these animals and may predispose them to persistent pulmonary hypertension after birth.

A neonatal mouse model of intestinal perforation: investigating the harmful synergism between glucocorticoids and indomethacin

BACKGROUND

Early postnatal steroids and indomethacin in combination have been shown to increase the risk of spontaneous intestinal perforation (SIP) in infants with extremely low birth weight (ELBW), but the mechanism behind this synergistic effect is unknown.

MATERIALS AND METHODS

Based on literature in a variety of models suggesting that glucocorticoids and nonsteroidal antiinflammatory agents diminish complementary isoforms of nitric oxide synthase (NOS), we hypothesized that perturbations in NO metabolism contribute to SIP.

RESULTS

Our results using newborn wild-type (WT) and endothelial NOS-knockout (eNOS KO) mice treated with dexamethasone and/or indomethacin indicate that indomethacin treatment diminishes ileal eNOS abundance; dexamethasone treatment diminishes ileal inducible NOS and neuronal NOS (nNOS); 100% of dexamethasone-treated eNOS KO mice die after 3 days; eNOS KO mice treated for 2 days with dexamethasone develop acute pyloric stenosis in association with reduced expression of pyloric nNOS; and isolated ileum from eNOS KO mice treated for 2 days with dexamethasone exhibit a significant decrease in spontaneous peristalsis, decreased circumference, and decreased capacitance for forced volume before ileal perforation compared with ileum from untreated controls.

CONCLUSIONS

Our findings suggest that eNOS and nNOS display functional overlap in the newborn mouse gastrointestinal tract and that simultaneous reduction in the activity of both NOS isoforms may be a risk factor for neonatal ileal perforation. If this holds true in human infants, then it provides a plausible etiologic explanation for the strong temporal association between SIP and the simultaneous treatment of ELBW infants with glucocorticoids and indomethacin.

Moderate Pulmonary Arterial Hypertension in Male Mice Lacking the Vasoactive Intestinal Peptide Gene

Background— Vasoactive intestinal peptide (VIP), a pulmonary vasodilator and inhibitor of vascular smooth muscle proliferation, has been reported absent in pulmonary arteries from patients with idiopathic pulmonary arterial hypertension (PAH). We have tested the hypothesis that targeted deletion of the VIP gene may lead to PAH with pulmonary vascular remodeling.

Methods and Results— We examined VIP knockout (VIP −/− ) mice for evidence of PAH, right ventricular (RV) hypertrophy, and pulmonary vascular remodeling. Relative to wild-type control mice, VIP −/− mice showed moderate RV hypertension, RV hypertrophy confirmed by increased ratio of RV to left ventricle plus septum weight, and enlarged, thickened pulmonary artery and smaller branches with increased muscularization and narrowed lumen. Lung sections also showed perivascular inflammatory cell infiltrates. No systemic hypertension and no arterial hypoxemia existed to explain the PAH. The condition was associated with increased mortality. Both the vascular remodeling and RV remodeling were attenuated after a 4-week treatment with VIP.

Conclusions— Deletion of the VIP gene leads to spontaneous expression of moderately severe PAH in mice during air breathing. Although not an exact model of idiopathic PAH, the VIP −/− mouse should be useful for studying molecular mechanisms of PAH and evaluating potential therapeutic agents. VIP replacement therapy holds promise for the treatment of PAH, and mutations of the VIP gene may be a factor in the pathogenesis of idiopathic PAH.

Role of the endothelium in pulmonary arterial hypertension

Pulmonary hypertension represents a significant disease burden in both the developed and developing worlds. Certain forms of pulmonary hypertension are more common in some countries than others but people of all races, all ages and both sexes are affected. Treatment options are limited and expensive. The development of new therapies will be determined by improved understanding of endothelial cell biology.

Mediators and modulators of pulmonary arterial hypertension

Pulmonary hypertension (PH), defined as a mean pulmonary arterial (PA) pressure of >25 mmHg at rest or >30 mmHg during exercise, is characterized by a progressive and sustained increase in pulmonary vascular resistance that eventually leads to right ventricular failure. Clinically, PH may result from a variety of underlying diseases (Table 1 and Refs. 50, 113, 124). Pulmonary arterial hypertension (PAH) may be familial (FPAH) or sporadic (idiopathic, IPAH), formerly known as primary pulmonary hypertension, i.e., for which there is no demonstrable cause. More often, PAH is due to a variety of identifiable diseases including scleroderma and other collagen disorders, liver disease, human immunodeficiency virus, and the intake of appetite-suppressant drugs such as phentermine and fenfluramine (72). Other, more common, causes of PAH include left ventricular failure (perhaps the most common cause), valvular lesions, chronic pulmonary diseases, sleep-disordered breathing, and prolonged residence at high altitude. This classification, now widely accepted, was first proposed at a meeting in Evian, France, in 1998, and modified in Venice, Italy, in 2003 (124).

Perinatal changes in pulmonary vascular endothelial function

The pulmonary endothelium plays a crucial role in lung development and function during the perinatal period. Its 2 most important functions at this time are to help reduce pulmonary vascular resistance (PVR) in order to permit the entire cardiac output to pass through the lungs for the first time and to facilitate the clearance of lung fluid. In response to changes in environmental factors such as oxygen tension, blood flow, circulating cytokines, and growth factors, the endothelium synthesizes and/or extracts many vasoactive mediators such as endothelin-1 (ET-1), norepinephrine, angiotensin 1, thromboxane, prostacyclin (PGI(2)), and the endothelial-derived relaxing factor nitric oxide (NO). The endothelium acts as a transducer conveying information about environmental changes to the underlying smooth muscle cells (SMCs), which helps regulate their reactivity and pulmonary vascular tone. The endothelial layer also acts as a barrier, regulating the exchange of fluids and nutrients between blood components and the surrounding tissues. The purpose of this review is to demonstrate the importance of structural and functional changes in the pulmonary endothelium during the perinatal period and explain their role in the regulation of the pulmonary circulation in health and disease. We also highlight signalling pathways of some of the most important endothelium-derived factors and indicate potential targets for pharmacological intervention.

Statin protects endothelial nitric oxide synthase activity in hypoxia-induced pulmonary hypertension

OBJECTIVE

We investigated the effects of fluvastatin on hypoxia-induced (1 to 3 weeks, 10% O2) pulmonary hypertension with focus on endothelial nitric oxide synthase (eNOS) activity.

METHODS AND RESULTS

Oral fluvastatin treatment (1 mg/kg daily) prevented the causing and progression of pulmonary hypertension as determined by the right ventricular pressure, right ventricular hypertrophy, and muscularization of pulmonary artery. We also revealed that fluvastatin treatments prevented the hypoxia-induced decrease in cGMP production in the rat lung and restored the endothelium-dependent relaxation in the pulmonary artery. We revealed that this beneficial effect was not dependent on the increase in eNOS mRNA or protein expression, but was dependent on the inhibition of the eNOS-tight coupling with caveolin-1, the eNOS dissociation from heat shock protein 90, and the decrease in eNOS Ser1177-phosphorylation induced by hypoxia. Furthermore, in a whole-mount immunostaining the hypoxia-induced eNOS protein condensation with caveolin-1 of pulmonary endothelial cells was restored by the fluvastatin-treatment.

CONCLUSIONS

These results suggest that the fluvastatin exerts beneficial effects on chronic hypoxia-induced pulmonary hypertension by protecting against the eNOS activity at the post-transcriptional level.