Involvement of RhoA/Rho kinase signaling in protection against monocrotaline-induced pulmonary hypertension in pneumonectomized rats by dehydroepiandrosterone

Pulmonary arterial hypertension: Sex matters

Pulmonary arterial hypertension (PAH) is a complex disease of multifactorial origin. While registries have demonstrated that women are more susceptible to the disease, females with PAH have superior right ventricle (RV) function and a better prognosis than their male counterparts, a phenomenon referred to as the 'estrogen paradox'. Numerous pre-clinical studies have investigated the involvement of sex hormones in PAH pathobiology, often with conflicting results. However, recent advances suggest that abnormal estrogen synthesis, metabolism and signalling underpin the sexual dimorphism of this disease. Other sex hormones, such as progesterone, testosterone and dehydroepiandrosterone may also play a role. Several non-hormonal factor including sex chromosomes and epigenetics have also been implicated. Though the underlying pathophysiological mechanisms are complex, several compounds that modulate sex hormones levels and signalling are under investigation in PAH patients. Further elucidation of the estrogen paradox will set the stage for the identification of additional therapeutic targets for this disease.

Serotonin and Pulmonary Hypertension; Sex and Drugs and ROCK and Rho

Serotonin is often referred to as a "happy hormone" as it maintains good mood, well-being, and happiness. It is involved in communication between nerve cells and plays a role in sleeping and digestion. However, too much serotonin can have pathogenic effects and serotonin synthesis is elevated in pulmonary artery endothelial cells from patients with pulmonary arterial hypertension (PAH). PAH is characterized by elevated pulmonary pressures, right ventricular failure, inflammation, and pulmonary vascular remodeling; serotonin has been shown to be associated with these pathologies. The rate-limiting enzyme in the synthesis of serotonin in the periphery of the body is tryptophan hydroxylase 1 (TPH1). TPH1 expression and serotonin synthesis are elevated in pulmonary artery endothelial cells in patients with PAH. The serotonin synthesized in the pulmonary arterial endothelium can act on the adjacent pulmonary arterial smooth muscle cells (PASMCs), adventitial macrophages, and fibroblasts, in a paracrine fashion. In humans, serotonin enters PASMCs cells via the serotonin transporter (SERT) and it can cooperate with the 5-HT1B receptor on the plasma membrane; this activates both contractile and proliferative signaling pathways. The "serotonin hypothesis of pulmonary hypertension" arose when serotonin was associated with PAH induced by diet pills such as fenfluramine, aminorex, and chlorphentermine; these act as indirect serotonergic agonists causing the release of serotonin from platelets and cells through the SERT. Here the role of serotonin in PAH is reviewed. Targeting serotonin synthesis or signaling is a promising novel alternative approach which may lead to novel therapies for PAH. © 2022 American Physiological Society. Compr Physiol 12: 1-16, 2022.

Endothelial cell ferroptosis mediates monocrotaline-induced pulmonary hypertension in rats by modulating NLRP3 inflammasome activation

Inflammation triggers pulmonary vascular remodelling. Ferroptosis, a nonapoptotic form of cell death that is triggered by iron-dependent lipid peroxidation and contributes to the pathogenesis of several inflammation-related diseases, but its role in pulmonary hypertension (PH) has not been studied. We examined endothelial cell ferroptosis in PH and the potential mechanisms. Pulmonary artery endothelial cells (PAECs) and lung tissues from monocrotaline (MCT)-induced PH rats were analysed for ferroptosis markers, including lipid peroxidation, the labile iron pool (LIP) and the protein expression of glutathione peroxidase 4 (GPX4), ferritin heavy chain 1 (FTH1) and NADPH oxidase-4 (NOX4). The effects of the ferroptosis inhibitor ferrostatin-1 (Fer-1) on endothelial cell ferroptosis and pulmonary vascular remodelling in MCT-induced rats were studied in vitro and in vivo. Ferroptosis was observed in PAECs from MCT-induced PH rats in vitro and in vivo and was characterized by a decline in cell viability accompanied by increases in the LIP and lipid peroxidation, the downregulation of GPX4 and FTH1 expression and the upregulation of NOX4 expression. High-mobility group box 1 (HMGB1)/Toll-like receptor 4 (TLR4)/NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome signalling was measured by western blotting. These changes were significantly blocked by Fer-1 administration in vitro and in vivo. These results suggest that Fer-1 plays a role in inhibiting ferroptosis-mediated PAEC loss during the progression of PH. The ferroptosis-induced inflammatory response depended on the activation of HMGB1/TLR4 signalling, which activated the NLRP3 inflammasome in vivo. We are the first to suggest that pulmonary artery endothelial ferroptosis triggers inflammatory responses via the HMGB1/TLR4/NLRP3 inflammasome signalling pathway in MCT-induced rats. Treating PH with a ferroptosis inhibitor and exploring new treatments based on ferroptosis regulation might be promising therapeutic strategies for PH.

Proteinase-activated receptor 1 antagonism ameliorates experimental pulmonary hypertension

AIMS

Pulmonary hypertension (PH) is characterized by progressive increases in pulmonary vascular resistance (PVR). Thrombotic lesions are common pathological findings. The pulmonary artery has a unique property regarding the vasoconstrictive response to thrombin, which is mediated by proteinase-activated receptor 1 (PAR1). We aim to elucidate the role of PAR1 in the development and progression of PH.

METHODS AND RESULTS

A rat model of monocrotaline-induced PH and a mouse model of hypoxia (Hx)-induced PH were used to investigate the effects of atopaxar (a PAR1 antagonist) and PAR1 knockout on haemodynamic parameters, right ventricular hypertrophy (RVH), vascular remodelling and survival. In perfused lung preparations, the pressor response to PAR1 agonist was significantly augmented in monocrotaline-induced PH. Both the preventive and therapeutic administration of atopaxar significantly inhibited the increase in PVR and the development of RVH and prolonged survival. A real-time PCR revealed that the level of PAR1 mRNA in the pulmonary artery was significantly higher than that in any of the systemic arteries examined in control rats, and the level was significantly up-regulated in monocrotaline-induced PH. PAR1 gene knockout significantly attenuated the haemodynamic and histological findings in the mouse model of Hx-induced PH.

CONCLUSION

The specific expression of PAR1 in the pulmonary artery and its up-regulation were suggested to play a critical role in the development and progression of experimental PH in murine models. PAR1 is a potential therapeutic target for the treatment of PH.

Hypoxia-inducible factor-1 α deletion in myeloid lineage attenuates hypoxia-induced pulmonary hypertension

Hypoxemia is seen in patients with pulmonary hypertension and hypoxic pulmonary vasoconstriction worsens their clinical condition. However, vasoconstriction is not the only aspect through which hypoxia induces the progression to pulmonary hypertension. Hypoxia‐inducible factor‐1α (HIF‐1α) is a transcription factor responding to hypoxic conditions by regulating hundreds of genes involved in angiogenesis, erythropoiesis, inflammation, and proliferation. We sought to determine the contribution of HIF‐1α in myeloid lineage cells to the pulmonary vascular response to chronic exposure to hypoxia. We generated myeloid‐specific HIF‐1α knockout (MyeHIF1KO) mice by using Cre‐lox P system, and exposed them to hypoxic conditions for 3 weeks to induce pulmonary hypertension. Macrophages from MyeHIF1KO and control mice were used for western blotting, RT‐qPCR, chemotaxis assay, and ATP assay. MyeHIF1KO mice exposed to hypoxia for 3 weeks exhibited a significant reduction in the right ventricular systolic pressure accompanied by a decrease in the ratio of the right ventricular weight to left ventricular weight, muscularization of the small pulmonary arteries, and infiltration of macrophages into the lung and right ventricle compared with control mice. HIF‐1α‐deficient peritoneal macrophages showed less migration toward monocyte chemoattractant protein‐1 and a decrease in intracellular ATP levels. These results indicate that HIF‐1α in macrophages contributes to the progression of pulmonary vascular remodeling and pulmonary hypertension induced by chronic exposure to hypoxic conditions. The inhibition of myeloid‐specific HIF‐1α may be a novel therapeutic strategy for the treatment of pulmonary hypertension.

Estradiol Metabolism: Crossroads in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a debilitating and progressive disease that predominantly develops in women. Over the past 15 years, cumulating evidence has pointed toward dysregulated metabolism of sex hormones in animal models and patients with PAH. 17β-estradiol (E2) is metabolized at positions C2, C4, and C16, which leads to the formation of metabolites with different biological/estrogenic activity. Since the first report that 2-methoxyestradiol, a major non-estrogenic metabolite of E2, attenuates the development and progression of experimental pulmonary hypertension (PH), it has become increasingly clear that E2, E2 precursors, and E2 metabolites exhibit both protective and detrimental effects in PH. Furthermore, both experimental and clinical data suggest that E2 has divergent effects in the pulmonary vasculature versus right ventricle (estrogen paradox in PAH). The estrogen paradox is of significant clinical relevance for understanding the development, progression, and prognosis of PAH. This review updates experimental and clinical findings and provides insights into: (1) the potential impacts that pathways of estradiol metabolism (EMet) may have in PAH; (2) the beneficial and adverse effects of estrogens and their precursors/metabolites in experimental PH and human PAH; (3) the co-morbidities and pathological conditions that may alter EMet and influence the development/progression of PAH; (4) the relevance of the intracrinology of sex hormones to vascular remodeling in PAH; and (5) the advantages/disadvantages of different approaches to modulate EMet in PAH. Finally, we propose the three-tier-estrogen effects in PAH concept, which may offer reconciliation of the opposing effects of E2 in PAH and may provide a better understanding of the complex mechanisms by which EMet affects the pulmonary circulation–right ventricular interaction in PAH.

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.

The Search for Disease-Modifying Therapies in Pulmonary Hypertension

Pulmonary hypertension (PH) and its severe subtype pulmonary arterial hypertension (PAH) encompass a set of multifactorial diseases defined by sustained elevation of pulmonary arterial pressure and pulmonary vascular resistance leading to right ventricular failure and subsequent death. Pulmonary hypertension is characterized by vascular remodeling in association with smooth muscle cell proliferation of the arterioles, medial thickening, and plexiform lesion formation. Despite our recent advances in understanding its pathogenesis and related therapeutic discoveries, PH still remains a progressive disease without a cure. Nevertheless, development of drugs that specifically target molecular pathways involved in disease pathogenesis has led to improvement in life quality and clinical outcomes in patients with PAH. There are presently more than 12 Food and Drug Administration-approved vasodilator drugs in the United States for the treatment of PAH; however, mortality with contemporary therapies remains high. More recently, there have been exuberant efforts to develop new pharmacologic therapies that target the fundamental origins of PH and thus could represent disease-modifying opportunities. This review aims to summarize recent developments on key signaling pathways and molecular targets that drive PH disease progression, with emphasis on new therapeutic options under development.

Dehydroepiandrosterone attenuates pulmonary artery and right ventricular remodeling in a rat model of pulmonary hypertension due to left heart failure

AIM

Pulmonary hypertension due to left heart failure (PH-LHF) is the most common cause of pulmonary hypertension. However, therapies for PH-LHF are lacking. Therefore, we investigated the effects and potential mechanism of dehydroepiandrosterone (DHEA) treatment in an experimental model of PH-LHF.

MAIN METHOD

PH-LHF was induced in rats via ascending aortic banding. The rats then received daily DHEA from Day 1 to Day 63 for the prevention protocol or from Day 49 to Day 63 for the reversal protocol. Other ascending aortic banding rats were left untreated to allow development of PH and right ventricular (RV) failure. Sham ascending aortic banding rats served as controls.

KEY FINDING

Significant increases in mean pulmonary arterial pressure (mPAP) and right ventricular end-diastolic diameter (RVEDD) were observed in the PH-LHF group. Therapy with DHEA prevented LHF-induced PH and RV failure by preserving mPAP and preventing RV hypertrophy and pulmonary artery remodeling. In preexisting severe PH, DHEA attenuated most lung and RV abnormalities. The beneficial effects of DHEA in PH-LHF seem to result from depression of the STAT3 signaling pathway in the lung.

SIGNIFICANT

DHEA not only prevents the development of PH-LHF and RV failure but also rescues severe preexisting PH-LHF.

Dehydroepiandrosterone: Molecular mechanisms and therapeutic implications in osteoarthritis

Dehydroepiandrosterone (DHEA), a 19-carbon steroid hormone primarily synthesized in the adrenal gland, exerts a chondroprotective effect against osteoarthritis (OA) and has been considered an effective candidate of disease-modifying OA drugs (DMOADs) that slow disease progression. We and others previously demonstrated that DHEA exerted a beneficial effect on osteoarthritic cartilage by positively modulating the balance between anabolic and catabolic factors (e.g., MMPs/TIMP-1, ADAMTS/TIMP-3 and cysteine proteinases/cystatin C), inhibiting catabolic signaling pathways (e.g., Wnt/β-catenin), and suppressing proinflammatory cytokines-mediated low-grade synovial inflammation (e.g., IL-1β). However, the full picture of the pharmacological molecular mechanism(s) underlying the activity of DHEA against OA is still incomplete, and a comprehensive and up-to-date review article in this field is unavailable. In this review, recent findings (apart from the well documented pathogenesis of OA) regarding disease-related mechanisms involving low grade synovial inflammation, cartilage matrix stiffness, chondrocyte autophagy and the roles of a variety of catabolic cellular signaling pathways are discussed. Moreover, the possible relationship between these disease-related mechanisms and DHEA action is discussed. Emerging evidence from in vivo and in vitro studies were scrutinized and are concisely presented to demonstrate the investigational and putative mechanisms underlying the anti-OA potential of DHEA.

Vasodilator effects of dehydroepiandrosterone (DHEA) on fetal pulmonary circulation: An experimental study in pregnant sheep

Persistent pulmonary hypertension (PPHN) remains a severe complication of the transition to extra-uterine life with significant morbidity and mortality in the newborns. Dehydroepiandrosterone (DHEA) represents a new pharmacological agent with vascular effects, including improvement of PPHN in several animal models. We hypothesized that DHEA could decrease pulmonary vascular resistance (PVR) in the pulmonary circulation of fetal sheep. We studied the effect of intravenous infusion of DHEA in fetal lambs using chronically instrumented sheep at 128 days of gestation. PVR was computed before and after intravenous infusion of increasing doses of DHEA. We assessed pre-treatment by L-nitroarginine, an inhibitor of NO production. Blood gases and doses of DHEA were measured in both sheep and fetus before/after DHEA infusion. Intravenous infusion of DHEA had a vasodilator effect with a significant decrease in PVR (respectively -11%, -14% and -36% after infusion of 6, 12 and 24 mg DHEA, p<0.01) without damaging effects on systemic circulation or on blood gases. The inhibitory effect of pre-treatment with L-nitroarginine resulted in a significant increase in PVR. We demonstrated a potent vasodilator effect of DHEA on fetal pulmonary circulation without deleterious effects. DHEA might represent a new treatment for PPHN.

Emerging therapeutics in pulmonary hypertension

Pulmonary hypertension (PH) is a progressive and often fatal illness presenting with nonspecific symptoms of dyspnea, lower extremity edema, and exercise intolerance. Pathologically, endothelial dysfunction leads to abnormal intimal and smooth muscle proliferation along with reduced apoptosis, resulting in increased pulmonary vascular resistance and elevated pulmonary pressures. PH is subdivided into five World Health Organization groups based on the disease pathology and specific cause. While there are Food and Drug Administration-approved medications for the treatment of pulmonary arterial hypertension (PAH; Group 1 PH), as well as for chronic thromboembolic PH (Group 4 PH), the morbidity and mortality remain high. Moreover, there are no approved therapies for other forms of PH (Groups 2, 3, and 5) at present. New research has identified molecular targets that mediate vasodilation, anti-inflammatory, and antifibrotic changes within the pulmonary vasculature. Given that PAH is the most commonly studied form of PH worldwide and because recent studies have led to better mechanistic understanding of this devastating disease, in this review we attempt to provide an updated overview of new therapeutic approaches under investigation for the treatment of PH, with a particular focus on PAH, as well as to offer guidelines for future investigations.

Role of P2X7R in the development and progression of pulmonary hypertension

BACKGROUND

Pulmonary arterial hypertension (PAH) is a devastating disease that lacks sufficient treatment. Studies have shown that the Nod-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome contributes to PAH pathogenesis, but the role of the upstream molecular P2X₇ receptor (P2X₇R) has remained unexplored. We investigated the role of P2X7R in the pathogenesis of PAH.

METHODS AND RESULTS

PH was induced by a single subcutaneous injection of monocrotaline (MCT) (60 mg/kg) on left pneumonectomised Sprague-Dawley rats, as validated by significant increases in pulmonary artery pressure and vessel wall thickness. Marked P2X₇R was detected by predominant PA immunostaining in lungs from PH rats. Western blot revealed a significant increase in the protein levels of P2X₇R as well as NLRP3 and caspase-1 in the diseased lung tissue compared with normal tissue. The rats received A-740003 (a selective P2X₇ receptor antagonist, 30 mg/kg) daily starting from 1 week before or 2 weeks after MCT injection. Consequently, A-740003 reversed the NLRP3 inflammasome upregulation, significantly decreased the mean right ventricular (RV) pressure and RV hypertrophy, and reversed pulmonary arterial remodelling 4 weeks after MCT injection, as both a pretreatment and rescue intervention. Notably, A-740003 significantly reduced macrophage and pro-inflammatory cytokine levels, as measured via bronchoalveolar lavage. The recruitment of macrophages as well as collagen fibre deposition in the perivascular areas were also reduced, as confirmed by histological staining.

CONCLUSIONS

P2X₇R contributes to the pathogenesis of PH, probably in association with activation of the NLRP3 inflammasome. Blockade of P2X7R might be applied as a novel therapeutic approach for the treatment of PAH.

Higher Estradiol and Lower Dehydroepiandrosterone-Sulfate Levels Are Associated with Pulmonary Arterial Hypertension in Men

RATIONALE

Recent studies have focused on the role of female sex and estradiol (E2) in pulmonary arterial hypertension (PAH), but it is not known whether sex hormones are risk factors for PAH in men.

OBJECTIVES

We performed a case-control study to determine whether hormone levels (E2, dehydroepiandrosterone-sulfate [DHEA-S], and testosterone) are associated with PAH in men.

METHODS

Plasma sex hormone levels in men with idiopathic, heritable, or connective tissue disease-associated PAH were compared with those from age- and body mass index-matched men without clinical cardiovascular disease.

MEASUREMENTS AND MAIN RESULTS

There were 23 cases with PAH (70% had idiopathic PAH, 65% were functional class III/IV) and 67 control subjects. Higher E2 and E2/testosterone levels were associated with the risk of PAH (odds ratio per 1 ln[E2:testosterone], 6.0; 95% confidence interval, 2.2-16.4; P = 0.001), whereas higher levels of DHEA-S were associated with a reduced risk (odds ratio per 1 ln[DHEA-S], 0.1; 95% confidence interval, 0.0-0.3; P = 0.001). E2 and DHEA-S levels were strong predictors of case status (C statistic for both, 0.82) but testosterone was not (C statistic, 0.53). Higher levels of E2 were associated with shorter 6-minute-walk distances (P = 0.03), whereas higher levels of DHEA-S were associated with lower right atrial pressure (P = 0.02) and pulmonary vascular resistance (P = 0.01) in men with PAH.

CONCLUSIONS

Higher levels of E2 and lower levels of DHEA-S were associated with PAH in men. Sex-based differences in sex hormone processing and signaling may contribute to unique phenotypes in pulmonary vascular disease.

Pulmonary Hypertension Associated with Idiopathic Pulmonary Fibrosis: Current and Future Perspectives

Pulmonary hypertension (PH) is commonly present in patients with chronic lung diseases such as Chronic Obstructive Pulmonary Disease (COPD) or Idiopathic Pulmonary Fibrosis (IPF) where it is classified as Group III PH by the World Health Organization (WHO). PH has been identified to be present in as much as 40% of patients with COPD or IPF and it is considered as one of the principal predictors of mortality in patients with COPD or IPF. However, despite the prevalence and fatal consequences of PH in the setting of chronic lung diseases, there are limited therapies available for patients with Group III PH, with lung transplantation remaining as the most viable option. This highlights our need to enhance our understanding of the molecular mechanisms that lead to the development of Group III PH. In this review we have chosen to focus on the current understating of PH in IPF, we will revisit the main mediators that have been shown to play a role in the development of the disease. We will also discuss the experimental models available to study PH associated with lung fibrosis and address the role of the right ventricle in IPF. Finally we will summarize the current available treatment options for Group III PH outside of lung transplantation.

Update on novel targets and potential treatment avenues in pulmonary hypertension

Pulmonary hypertension (PH) is a condition marked by a combination of constriction and remodeling within the pulmonary vasculature. It remains a disease without a cure, as current treatments were developed with a focus on vasodilatory properties but do not reverse the remodeling component. Numerous recent advances have been made in the understanding of cellular processes that drive pathologic remodeling in each layer of the vessel wall as well as the accompanying maladaptive changes in the right ventricle. In particular, the past few years have yielded much improved insight into the pathways that contribute to altered metabolism, mitochondrial function, and reactive oxygen species signaling and how these pathways promote the proproliferative, promigratory, and antiapoptotic phenotype of the vasculature during PH. Additionally, there have been significant advances in numerous other pathways linked to PH pathogenesis, such as sex hormones and perivascular inflammation. Novel insights into cellular pathology have suggested new avenues for the development of both biomarkers and therapies that will hopefully bring us closer to the elusive goal: a therapy leading to reversal of disease.

Rosuvastatin intensifies the beneficial effects of rho-kinase inhibitor in reversal of monocrotaline-induced pulmonary hypertension

INTRODUCTION

It remains controversial whether statins have a beneficial effect on pulmonary arterial hypertension (PAH). This study is intended to evaluate whether statin, co-administered with Rho-kinase inhibitor, could enhance its efficacy. Although Rho-kinase inhibitors, including fasudil, have been reported to improve pulmonary hypertension in experimental and clinical studies, the combination of these agents has not been tested in the treatment of pulmonary hypertension (PH).

MATERIAL AND METHODS

The effects of such a regimen on hemodynamics, right ventricle hypertrophy, and Rho-associated protein kinase (ROCK) activity in experimental monocrotaline (MCT)-induced pulmonary hypertension were examined. Fourteen days after monocrotaline injection (60 mg/kg), male rats were treated orally for another 14 days with fasudil (15 mg/kg per day), or with a combination of fasudil + rosuvastatin (10 mg/kg per day).

RESULTS

The drug combination reversed the MCT-induced increase in right ventricle pressure (RVP) and reduced right ventricular hypertrophy (RV/LV + S ratio) more than Rho kinase inhibitor alone. The simultaneous administration of fasudil and rosuvastatin caused a further decrease of RhoA kinase activity in isolated lung tissues as compared to fasudil alone.

CONCLUSIONS

The results indicate that rosuvastatin intensifies the beneficial effects of Rho-kinase inhibitor on the Rho/Rho-kinase pathway and such a combination may represent an option for the treatment of pulmonary arterial hypertension.

Involvement of gap junctions between smooth muscle cells in sustained hypoxic pulmonary vasoconstriction development: a potential role for 15-HETE and 20-HETE

In response to hypoxia, the pulmonary artery normally constricts to maintain optimal ventilation-perfusion matching in the lung, but chronic hypoxia leads to the development of pulmonary hypertension. The mechanisms of sustained hypoxic pulmonary vasoconstriction (HPV) remain unclear. The aim of this study was to determine the role of gap junctions (GJs) between smooth muscle cells (SMCs) in the sustained HPV development and involvement of arachidonic acid (AA) metabolites in GJ-mediated signaling. Vascular tone was measured in bovine intrapulmonary arteries (BIPAs) using isometric force measurement technique. Expression of contractile proteins was determined by Western blot. AA metabolites in the bath fluid were analyzed by mass spectrometry. Prolonged hypoxia elicited endothelium-independent sustained HPV in BIPAs. Inhibition of GJs by 18β-glycyrrhetinic acid (18β-GA) and heptanol, nonspecific blockers, and Gap-27, a specific blocker, decreased HPV in deendothelized BIPAs. The sustained HPV was not dependent on Ca(2+) entry but decreased by removal of Ca(2+) and by Rho-kinase inhibition with Y-27632. Furthermore, inhibition of GJs decreased smooth muscle myosin heavy chain (SM-MHC) expression and myosin light chain phosphorylation in BIPAs. Interestingly, inhibition of 15- and 20-hydroxyeicosatetraenoic acid (HETE) synthesis decreased HPV in deendothelized BIPAs. 15-HETE- and 20-HETE-stimulated constriction of BIPAs was inhibited by 18β-GA and Gap-27. Application of 15-HETE and 20-HETE to BIPAs increased SM-MHC expression, which was also suppressed by 18β-GA and by inhibitors of lipoxygenase and cytochrome P450 monooxygenases. More interestingly, 15,20-dihydroxyeicosatetraenoic acid and 20-OH-prostaglandin E2, novel derivatives of 20-HETE, were detected in tissue bath fluid and synthesis of these derivatives was almost completely abolished by 18β-GA. Taken together, our novel findings show that GJs between SMCs are involved in the sustained HPV in BIPAs, and 15-HETE and 20-HETE, through GJs, appear to mediate SM-MHC expression and contribute to the sustained HPV development.

Increased pulmonary RhoA expression in the nitrofen-induced congenital diaphragmatic hernia rat model

PURPOSE

Persistent pulmonary hypertension remains a major cause of mortality and morbidity in cases of congenital diaphragmatic hernia (CDH). Recently, RhoA/Rho-kinase-mediated vasoconstriction has been reported to be important in the pathogenesis of pulmonary hypertension (PH). Several recent reports have described that fasudil, a potent Rho-kinase inhibitor and vasodilator, could represent a potential therapeutic option for PH. We designed this study to investigate the hypothesis that the expression level of RhoA is increased in the nitrofen-induced CDH rat model. The expression level of Wnt11, an activator of RhoA, was also evaluated.

METHODS

Pregnant rats were treated with or without nitrofen on gestational day 9 (D9). Fetuses were sacrificed on D17, D19 and D21 and were divided into control and CDH groups. Quantitative real-time polymerase chain reaction was performed to determine the pulmonary gene expression levels of both Wnt11 and RhoA. An immunofluorescence study was also performed to evaluate the expression and localization of RhoA.

RESULTS

The relative mRNA expression levels of pulmonary Wnt11 and RhoA on D21 were significantly increased in the CDH group compared with the control group (p=0.016 and p=0.008, respectively). The immunofluorescence study confirmed the overexpression of RhoA in the pulmonary vessels of CDH rats on D21.

CONCLUSIONS

Our results provide evidence that the RhoA/Rho-kinase-mediated pathway is involved in the pathogenesis of PH in the nitrofen-induced CDH rat model. Our data also suggest that the fasudil, a Rho-kinase inhibitor, could represent a therapeutic option for the treatment of PH in CDH.

Statement on pregnancy in pulmonary hypertension from the Pulmonary Vascular Research Institute

Pregnancy outcomes in patients with pulmonary hypertension remain poor despite advanced therapies. Although consensus guidelines recommend against pregnancy in pulmonary hypertension, it may nonetheless occasionally occur. This guideline document sought to discuss the state of knowledge of pregnancy effects on pulmonary vascular disease and to define usual practice in avoidance of pregnancy and pregnancy management. This guideline is based on systematic review of peer-reviewed, published literature identified with MEDLINE. The strength of the literature was graded, and when it was inadequate to support high-level recommendations, consensus-based recommendations were formed according to prespecified criteria. There was no literature that met standards for high-level recommendations for pregnancy management in pulmonary hypertension. We drafted 38 consensus-based recommendations on pregnancy avoidance and management. Further, we identified the current state of knowledge on the effects of sex hormones during pregnancy on the pulmonary vasculature and right heart and suggested areas for future study. There is currently limited evidence-based knowledge about both the basic molecular effects of sex hormones and pregnancy on the pulmonary vasculature and the best practices in contraception and pregnancy management in pulmonary hypertension. We have drafted 38 consensus-based recommendations to guide clinicians in these challenging topics, but further research is needed in this area to define best practices and improve patient outcomes.

Rho-kinase as a therapeutic target in vascular diseases: striking nitric oxide signaling

Rho GTPases are a globular, monomeric group of small signaling G-protein molecules. Rho-associated protein kinase/Rho-kinase (ROCK) is a downstream effector protein of the Rho GTPase. Rho-kinases are the potential therapeutic targets in the treatment of cardiovascular diseases. Here, we have primarily discussed the intriguing roles of ROCK in cardiovascular health in relation to nitric oxide signaling. Further, we highlighted the biphasic effects of Y-27632, a ROCK inhibitor under shear stress, which acts as an agonist of nitric oxide production in endothelial cells. The biphasic effects of this inhibitor raised the question of safety of the drug usage in treating cardiovascular diseases.

PK10453, a nonselective platelet-derived growth factor receptor inhibitor, prevents the progression of pulmonary arterial hypertension

The platelet-derived growth factor (PDGF) signaling pathway has been found to be activated in human pulmonary arterial hypertension (PAH) and in animal models of the disease. Our study tested the hypothesis that a novel, nonselective inhaled PDGF receptor inhibitor, PK10453, would decrease pulmonary hypertension both in the rat monocrotaline (MCT) model and the rat MCT plus pneumonectomy (MCT+PN) model of PAH. PK10453, delivered by inhalation for 4 (D4)- and 8 (D8)-minute exposures 3 times a day for 2 weeks, decreased right ventricular systolic pressure (RVSP) in both the rat MCT and rat MCT+PN models: RVSP was 80.4 ± 2.6 mmHg in the vehicle MCT group (n = 6), 44.4 ± 5.8 mmHg in the D4 MCT group (n = 6), and 37.1 ± 4.5 mmHg in the D8 MCT group (n = 5; P < 0.001 vs. vehicle); RVSP was 75.7 ± 7.1 mmHg in the vehicle MCT+PN group (n = 9), 40.4 ± 2.7 mmHg in the D4 MCT+PN group (n = 10), and 43.0 ± 3.0 mmHg in the D8 MCT+PN group (n = 8; P < 0.001). In the rat MCT+PN model, continuous telemetry monitoring of pulmonary artery pressures also demonstrated that PK10453 prevented the progression of PAH. Imatinib given by inhalation was equally effective in the MCT model but was not effective in the MCT+PN model. Immunohistochemistry demonstrated increased activation of the PDGFβ receptor compared to the PDGFα receptor in neointimal and perivascular lesions found in the MCT+PN model. We show that imatinib is selective for the PDGFα receptor, whereas PK10453 has a lower half-maximal inhibitor concentration (IC50) for inhibition of kinase activity of both the PDGFα and PDGFβ receptors compared to imatinib. In conclusion, PK10453, when delivered by inhalation, significantly decreased the progression of PAH in the rat MCT and MCT+PN models. Nonselective inhibition of both the PDGFα and PDGFβ receptors may have a therapeutic advantage over selective PDGFα receptor inhibition in PAH.

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.

Simvastatin treatment highlights a new role for the isoprenoid/cholesterol biosynthetic pathway in the modulation of emotional reactivity and cognitive performance in rats

The aim of the present work was to shed light on the role played by the isoprenoid/cholesterol biosynthetic pathway in the modulation of emotional reactivity and memory consolidation in rodents through the inhibition of the key and rate-limiting enzyme 3-hydroxy 3-methylglutaryl Coenzyme A reductase (HMGR) both in vivo and in vitro with simvastatin. Three-month-old male Wistar rats treated for 21 days with simvastatin or vehicle were tested in the social interaction, elevated plus-maze, and inhibitory avoidance tasks; after behavioral testing, the amygdala, hippocampus, prefrontal cortex, dorsal, and ventral striatum were dissected out for biochemical assays. In order to delve deeper into the molecular mechanisms underlying the observed effects, primary rat hippocampal neurons were used. Our results show that HMGR inhibition by simvastatin induces anxiogenic-like effects in the social interaction but not in the elevated plus-maze test, and improves memory consolidation in the inhibitory avoidance task. These effects are accompanied by imbalances in the activity of specific prenylated proteins, Rab3 and RhoA, involved in neurotransmitter release, and synaptic plasticity, respectively. Taken together, the present findings indicate that the isoprenoid/cholesterol biosynthetic pathway is critically involved in the physiological modulation of both emotional and cognitive processes in rodents.

Dehydroepiandrosterone promotes pulmonary artery relaxation by NADPH oxidation-elicited subunit dimerization of protein kinase G 1α

The activity of glucose-6-phosphate dehydrogenase (G6PD) controls a vascular smooth muscle relaxing mechanism promoted by the oxidation of cytosolic NADPH, which has been associated with activation of the 1α form of protein kinase G (PKG-1α) by a thiol oxidation-elicited subunit dimerization. This PKG-1α-activation mechanism appears to contribute to responses of isolated endothelium-removed bovine pulmonary arteries (BPA) elicited by peroxide, cytosolic NADPH oxidation resulting from G6PD inhibition, and hypoxia. Dehydroepiandrosterone (DHEA) is a steroid hormone with pulmonary vasodilator activity, which has beneficial effects in treating pulmonary hypertension. Because multiple mechanisms have been suggested for the vascular effects of DHEA and one of the known actions of DHEA is inhibiting G6PD, we investigated whether it promoted relaxation associated with NADPH oxidation, PKG-1α dimerization, and PKG activation detected by increased vasodilator-stimulated phosphoprotein (VASP) phosphorylation. Relaxation of BPA to DHEA under aerobic or hypoxic conditions was associated with NADPH oxidation, PKG-1α dimerization, and increased VASP phosphorylation. The vasodilator activity of DHEA was markedly attenuated in pulmonary arteries and aorta from a PKG knockin mouse containing a serine in place of a cysteine involved in PKG dimerization. DHEA promoted increased PKG dimerization in lungs from wild-type mice, which was not detected in the PKG knockin mouse model. Thus PKG-1α dimerization is a major contributing factor to the vasodilator actions of DHEA and perhaps its beneficial effects in treating pulmonary hypertension.

Crucial role of ROCK2 in vascular smooth muscle cells for hypoxia-induced pulmonary hypertension in mice

OBJECTIVE

Rho/Rho-kinase (ROCK) pathway in vascular smooth muscle cells (VSMCs) plays an important role in the pathogenesis of cardiovascular diseases, including pulmonary arterial hypertension (PAH). Rho-kinase has 2 isoforms, ROCK1 and ROCK2, with different functions in different cells; ROCK1 for circulating inflammatory cells and ROCK2 for the vasculature. In the present study, we aimed to examine whether ROCK2 in VSMC is involved in the pathogenesis of PAH.

APPROACH AND RESULTS

In patients with PAH, the expression of ROCK2 was increased in pulmonary arterial media and primary pulmonary arterial smooth muscle cells when compared with controls. To investigate the role of ROCK2 in VSMC, we generated VSMC-specific heterozygous ROCK2-deficient (ROCK2(+/-)) mice and VSMC-specific ROCK2-overexpressing transgenic (ROCK2-Tg) mice. The extent of hypoxia-induced pulmonary hypertension was reduced in ROCK2(+/-) mice and was enhanced in ROCK2-Tg mice compared with respective littermates. The protein expression of ROCK activity and phosphorylated extracellular signal-regulated kinase and the number of Ki67-positive proliferating cells in the lung were reduced in ROCK2(+/-) mice and were increased in ROCK2-Tg mice compared with respective littermates. In cultured mouse aortic VSMC, migration and proliferation activities were reduced in ROCK2(+/-) mice, and migration activity was increased in ROCK2-Tg mice compared with respective littermates. In addition, in primary pulmonary arterial smooth muscle cells from a patient with PAH, ROCK2 was required for migration and proliferation through ROCK and extracellular signal-regulated kinase activation.

CONCLUSIONS

ROCK2 in VSMC contributes to the pathogenesis of PAH.

Rho-kinase inhibitor Y-27632 attenuates pulmonary hypertension in hyperoxia-exposed newborn rats

AIM

To test the hypothesis that neonatal hyperoxia induced pulmonary hypertension accompanied by increased Rho-kinase expression in rat lungs and that Rho-kinase inhibitor could attenuate right ventricular hypertrophy and pulmonary arterial remodeling.

METHODS

Newborn rats were exposed to >95% O2 in the first week after birth, then to 60% O2 in the following 2 weeks. Control pups were exposed to room air over the same periods. The pups were injected with either Rho-kinase inhibitor Y-27632 (10 mg·kg(-1)·d(-1), ip) or vehicle from postnatal d 14 to 20. Lung and heart tissues were collected on postnatal d 7 and 21. Rho-kinase activity in lungs was measured using Western blotting and immunohistochemistry. The right ventricular hypertrophy and arterial medial wall thickness (MWT) were assessed morphologically.

RESULTS

Rho-kinase activity in lungs was comparable between the hyperoxic and control pups on postnatal d 7, but it had a more than 2-fold increase in the hyperoxic pups on postnatal d 21. Moreover, the hyperoxic exposure induced structural features of pulmonary hypertension, as shown by the right ventricular hypertrophy and significantly increased arterial MWT. Administration with Y-27632 effectively blocked the hyperoxia-induced increase of Rho-kinase activity in lungs, and attenuated the right ventricular hypertrophy.

CONCLUSION

Rho-kinase inhibitor may be a novel therapy for attenuating the hyperoxia-induced structural changes in pulmonary hypertension.

Beneficial effect of dehydroepiandrosterone on pulmonary hypertension in a rodent model of pulmonary hypertension in infants

BACKGROUND

Pulmonary hypertension (PH) is a disease that affects the adult or infant population. Dehydroepiandrosterone (DHEA), a steroid hormone, has been previously shown to prevent and to reverse PH in an adult rat model. We thus investigated its effect in a rat-pup model of chronic hypoxic PH.

METHODS

Animals were maintained for 3 wk in a hypobaric chamber to induce PH, with or without concomitant treatment with DHEA (30 mg/kg every alternate day).

RESULTS

DHEA significantly reduced mean pulmonary artery pressure (measured by right cardiac catheterization), pulmonary artery remodeling (evaluated by histology), and right-ventricular hypertrophy (measured by echography and by the Fulton index). At the level of the pulmonary artery smooth muscle cell (PASMC), DHEA increased activity and expression of the large-conductance Ca2+-activated potassium channel (BKCa) (assessed by means of the patch clamp technique). DHEA also inhibited both serotonin- and KCl-induced contraction and smooth muscle cell proliferation.

CONCLUSION

Collectively, these results indicate that DHEA prevents PH in infant rats and may therefore be clinically relevant for the management of PH in human infants.

The emergence of new therapeutic targets in pulmonary arterial hypertension: from now to the near future

Pulmonary arterial hypertension (PAH) is a vascular remodeling disease that pathologically increases pulmonary vascular resistance. Ultimately, this leads to right ventricular failure and premature death. Current therapeutic strategies are mainly designed to induce relaxation of the pulmonary arteries, but are not directly aimed to improve vascular remodeling that characterize PAH. Although these treatments modestly improve patient symptoms, pulmonary hemodynamics and survival, none of them are curative and approximately 15% of patients die within 1 year of medical follow-up despite treatment. Within the last 5 years, tremendous advances in our understanding of the PAH pathophysiology have arisen. These advances have a high potential for the development of better patient care by providing novel therapeutic targets. The goal of this report is to review the current PAH treatments, as well as novel therapies that will pave the future in this devastating disease.

The role of disturbed blood flow in the development of pulmonary arterial hypertension: lessons from preclinical animal models

Pulmonary arterial hypertension (PAH) is a progressive pulmonary vasoproliferative disorder characterized by the development of unique neointimal lesions, including concentric laminar intima fibrosis and plexiform lesions. Although the histomorphology of neointimal lesions is well described, the pathogenesis of PAH and neointimal development is largely unknown. After three decades of PAH pathobiology research the focus has shifted from vasoconstriction towards a mechanism of cancer-like angioproliferation. In this concept the role of disturbed blood flow is seen as an important trigger in the development of vascular remodeling. For instance, in PAH associated with congenital heart disease, increased pulmonary blood flow (i.e., systemic-to-pulmonary shunt) is an essential trigger for the occurrence of neointimal lesions and PAH development. Still, questions remain about the exact role of these blood flow characteristics in disease progression. PAH animal models are important for obtaining insight in new pathobiological processes and therapeutical targets. However, as for any preclinical model the pathophysiological mechanism and clinical course has to be comparable to the human disease that it mimics. This means that animal models mimicking human PAH ideally are characterized by: a hit recognized in human disease (e.g., altered pulmonary blood flow), specific vascular remodeling resembling human neointimal lesions, and disease progression that leads to right ventriclular dysfunction and death. A review that underlines the current knowledge of PAH due to disturbed flow is still lacking. In this review we will summarize the current knowledge obtained from PAH animal models associated with disturbed pulmonary blood flow and address questions for future treatment strategies for PAH.

Dehydroepiandrosterone restores right ventricular structure and function in rats with severe pulmonary arterial hypertension

Current therapy of pulmonary arterial hypertension (PAH) is inadequate. Dehydroepiandrosterone (DHEA) effectively treats experimental pulmonary hypertension in chronically hypoxic and monocrotaline-injected rats. Contrary to these animal models, SU5416/hypoxia/normoxia-exposed rats develop a more severe form of occlusive pulmonary arteriopathy and right ventricular (RV) dysfunction that is indistinguishable from the human disorder. Thus, we tested the effects of DHEA treatment on PAH and RV structure and function in this model. Chronic (5 wk) DHEA treatment significantly, but moderately, reduced the severely elevated RV systolic pressure. In contrast, it restored the impaired cardiac index to normal levels, resulting in an improved cardiac function, as assessed by echocardiography. Moreover, DHEA treatment inhibited RV capillary rarefaction, apoptosis, fibrosis, and oxidative stress. The steroid decreased NADPH levels in the RV. As a result, the reduced reactive oxygen species production in the RV of these rats was reversed by NADPH supplementation. Mechanistically, DHEA reduced the expression and activity of Rho kinases in the RV, which was associated with the inhibition of cardiac remodeling-related transcription factors STAT3 and NFATc3. These results show that DHEA treatment slowed the progression of severe PAH in SU5416/hypoxia/normoxia-exposed rats and protected the RV against apoptosis and fibrosis, thus preserving its contractile function. The antioxidant activity of DHEA, by depleting NADPH, plays a central role in these cardioprotective effects.

Gender, sex hormones and pulmonary hypertension

Most subtypes of pulmonary arterial hypertension (PAH) are characterized by a greater susceptibility to disease among females, although females with PAH appear to live longer after diagnosis. While this "estrogen paradoxȍ of enhanced female survival despite increased female susceptibility remains a mystery, recent progress has begun to shed light upon the interplay of sex hormones, the pathogenesis of pulmonary hypertension, and the right ventricular response to stress. For example, emerging data in humans and experimental models suggest that estrogens or differential sex hormone metabolism may modify disease risk among susceptible subjects, and that estrogens may interact with additional local factors such as serotonin to enhance the potentially damaging chronic effects of estrogens on the pulmonary vasculature. Regardless, it remains unclear why not all estrogenic compounds behave equally, nor why estrogens appear to be protective in certain settings but detrimental in others. The contribution of androgens and other compounds, such as dehydroepiandrosterone, to pathogenesis and possibly treatment must be considered as well. In this review, we will discuss the recent understandings on how estrogens, estrogen metabolism, dehydroepiandrosterone, and additional susceptibility factors may all contribute to the pathogenesis or potentially to the treatment of pulmonary hypertension, by evaluating current human, cell-based, and experimental model data.

Role of DHEA in cardiovascular diseases

Dehydroepiandrosterone (DHEA) is a steroid hormone derived from cholesterol synthesized by the adrenal glands. DHEA and its 3β-sulphate ester (DHEA-S) are the most abundant circulating steroid hormones. In human, there is a clear age-related decline in serum DHEA and DHEA-S and this has suggested that a relative deficiency in these steroids may be causally related to the development of a series of diseases associated with aging including cardiovascular diseases (CVD). This commentary aims to highlight the action of DHEA in CVD and its beneficial effect in therapy. We thus discuss the possible impact of serum DHEA decline and DHEA supplementation in diseases such as hypertension, coronary artery disease and atherosclerosis. More specifically, we provide evidence for a beneficial action of DHEA in the main disease of the pulmonary circulation: pulmonary hypertension. We also examine the potential cellular mechanism of action of DHEA in terms of receptors (membrane/nuclear) and associated signaling pathways (ion channels, calcium signaling, PI3K/AKT/eNos pathway, cGMP, RhoA/RhoK pathway). We show that DHEA acts as an anti-remodeling and vasorelaxant drug. Since it is a well-tolerated and inexpensive drug, DHEA may prove to be a valuable molecule in CVD but it deserves further studies both at the molecular level and in large clinical trials.

Fluoxetine inhibits monocrotaline-induced pulmonary arterial remodeling involved in inhibition of RhoA–Rho kinase and Akt signalling pathways in rats

Activation of the small GTPase Ras homolog gene family member A (RhoA) and Rho-associated kinase (ROCK) are important in the pathogenesis of pulmonary arterial hypertension (PAH). Selective serotonin reuptake inhibitors inhibit activation of RhoA and ROCK in vitro, and ameliorate PAH and pulmonary arterial remodeling in vivo. However, little is known about whether the RhoA–ROCK signalling pathway is involved in the treatment of PAH with fluoxetine in vivo. The aim of the present study was to investigate the involvement of the RhoA–ROCK signalling pathway in the protective effect of the selective serotonin reuptake inhibitor fluoxetine against monocrotaline (MCT)-induced pulmonary arterial remodeling. MCT was applied to establish PAH in male Wistar rats. Fluoxetine was administered by gastric gavage once a day for 21 d. The results showed that MCT induced pulmonary arterial remodeling, raised the serotonylation and membrane translocation of RhoA in the lungs, and increased serotonin transporter (5-HTT), RhoA, and ROCK2 expression, and extracellular signal-regulated kinase (ERK) and Akt phosphorylation in the pulmonary arteries and the lungs. Fluoxetine markedly inhibited these MCT-induced changes. The findings suggest that fluoxetine inhibits MCT-induced pulmonary arterial remodeling in rats by inhibition of the RhoA–ROCK and Akt signalling pathways.

[Pulmonary hypertension: from molecular pathophysiology to haemodynamic abnormalities]

Pulmonary hypertension (PH) is a complex disorder resulting from many etiologies that cause disturbances of normal pulmonary haemodynamics. Recent breakthroughs have led to a better understanding of the pathophysiology of the disease. In PH, haemodynamic disturbances are closely linked to structural changes and excessive remodeling of pulmonary vessels, leading to progressive narrowing of the pulmonary vascular lumen. Imbalances between pulmonary vasoconstrictors and vasodilators on the one hand, and factors favoring cell proliferation and apoptosis on the other hand, probably account for most cases of PH. This review aims to update readers with the current knowledge on the molecular physiopathology of PH and how this can progress the therapeutic of this disorder.

Glc-6-PD and PKG contribute to hypoxia-induced decrease in smooth muscle cell contractile phenotype proteins in pulmonary artery

Persistent hypoxic pulmonary vasoconstriction (HPV) plays a significant role in the pathogenesis of pulmonary hypertension, which is an emerging clinical problem around the world. We recently showed that hypoxia-induced activation of glucose-6-phosphate dehydrogenase (Glc-6-PD) in pulmonary artery smooth muscle links metabolic changes within smooth muscle cells to HPV and that inhibition of Glc-6PD reduces acute HPV. Here, we demonstrate that exposing pulmonary arterial rings to hypoxia (20-30 Torr) for 12 h in vitro significantly (P < 0.05) reduces (by 30-50%) SM22α and smooth muscle myosin heavy chain expression and evokes HPV. Glc-6-PD activity was also elevated in hypoxic pulmonary arteries. Inhibition of Glc-6-PD activity prevented the hypoxia-induced reduction in SM22α expression and inhibited HPV by 80-90% (P < 0.05). Furthermore, Glc-6-PD and protein kinase G (PKG) formed a complex in pulmonary artery, and Glc-6-PD inhibition increased PKG-mediated phosphorylation of VASP (p-VASP). In turn, increasing PKG activity upregulated SM22α expression and attenuated HPV evoked by Glc-6-PD inhibition. Increasing passive tension (from 0.8 to 3.0 g) in hypoxic arteries for 12 h reduced Glc-6-PD, increased p-VASP and SM22α levels, and inhibited HPV. The present findings indicate that increases in Glc-6-PD activity influence PKG activity and smooth muscle cell phenotype proteins, all of which affect pulmonary artery contractility and remodeling.

Dehydroepiandrosterone (DHEA) improves pulmonary hypertension in chronic obstructive pulmonary disease (COPD): a pilot study

OBJECTIVES

It was previously shown that dehydroepiandrosterone (DHEA) reverses chronic hypoxia-induced pulmonary hypertension (PH) in rats, but whether DHEA can improve the clinical and hemodynamic status of patients with PH associated to chronic obstructive pulmonary disease (PH-COPD) has not been studied whereas it is a very severe poorly treated disease.

PATIENTS AND METHODS

Eight patients with PH-COPD were treated with DHEA (200mg daily orally) for 3 months. The primary end-point was the change in the 6-minute walk test (6-MWT) distance. Secondary end-points included pulmonary hemodynamics, lung function tests and tolerance of treatment.

RESULTS

The 6-MWT increased in all cases, from 333m (median [IQR]) (257; 378) to 390m (362; 440) (P<0.05). Mean pulmonary artery pressure decreased from 26mmHg (25; 27) to 21.5mmHg (20; 25) (P<0.05) and pulmonary vascular resistance from 4.2UI (3.5; 4.4) to 2.6UI (2.5; 3.8) (P<0.05). The carbon monoxide diffusing capacity of the lung (DLCO % predicted) increased significantly from 27.4% (20.1; 29.3) to 36.4% (14.6; 39.6) (P<0.05). DHEA treatment did not change respiratory parameters of gas exchange and the 200mg per day of DHEA used was perfectly tolerated with no side effect reported.

CONCLUSION

DHEA treatment significantly improves 6-MWT distance, pulmonary hemodynamics and DLCO of patients with PH-COPD, without worsening gas exchange, as do other pharmacological treatments of PH (trial registration NCT00581087).

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.

Increased oxidative stress and severe arterial remodeling induced by permanent high-flow challenge in experimental pulmonary hypertension

BACKGROUND

Involvement of inflammation in pulmonary hypertension (PH) has previously been demonstrated and recently, immune-modulating dendritic cells (DCs) infiltrating arterial lesions in patients suffering from idiopathic pulmonary arterial hypertension (IPAH) and in experimental monocrotaline-induced PH have been reported. Occurrence of perivascular inflammatory cells could be linked to local increase of oxidative stress (OS), as it has been shown for systemic atherosclerosis. The impact of OS on vascular remodeling in PH is still to be determined. We hypothesized, that augmented blood-flow could increase OS and might thereby contribute to DC/inflammatory cell-recruitment and smooth-muscle-cell-proliferation.

METHODS

We applied a monocrotaline-induced PH-model and combined it with permanent flow-challenge. Thirty Sprague-Dawley rats were assigned to following groups: control, monocrotaline-exposure (MCT), monocrotaline-exposure/pneumonectomy (MCT/PE).

RESULTS

Hemodynamic exploration demonstrated most severe effects in MCT/PE, corresponding in histology to exuberant medial and adventitial remodeling of pulmonary muscular arteries, and intimal remodeling of smaller arterioles; lung-tissue PCR evidenced increased expression of DCs-specific fascin, CD68, proinflammatory cytokines (IL-6, RANTES, fractalkine) in MCT/PE and to a lesser extent in MCT. Major OS enzyme NOX-4 was maximal in MCT/PE. Antioxidative stress enzymes Mn-SOD and glutathion-peroxidase-1 were significantly elevated, while HO-1 showed maximal expression in MCT with significant decrease in MCT/PE. Catalase was decreased in MCT and MCT/PE. Expression of NOX-4, but also of MN-SOD in MCT/PE was mainly attributed to a highly increased number of interstitial and perivascular CXCR4/SDF1 pathway-recruited mast-cells. Stress markers malonedialdehyde and nitrotyrosine were produced in endothelial cells, medial smooth muscle and perivascular leucocytes of hypertensive vasculature. Immunolabeling for OX62, CD68 and actin revealed adventitial and medial DC- and monocyte-infiltration; in MCT/PE, medial smooth muscle cells were admixed with CD68+/vimentin+ cells.

CONCLUSION

Our experimental findings support a new concept of immunologic responses to increased OS in MCT/PE-induced PAH, possibly linking recruitment of dendritic cells and OS-producing mast-cells to characteristic vasculopathy.

Dehydroepiandrosterone inhibits the Src/STAT3 constitutive activation in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is an obstructive vasculopathy characterized by enhanced pulmonary artery smooth muscle cell (PASMC) proliferation and suppressed apoptosis. This phenotype is sustained by the activation of the Src/signal transducer and activator of transcription 3 (STAT3) axis, maintained by a positive feedback loop involving miR-204 and followed by an aberrant expression/activation of its downstream targets such as Pim1 and nuclear factor of activated T-cells (NFATc2). Dehydroepiandrosterone (DHEA) is a steroid hormone shown to reverse vascular remodeling in systemic vessels. Since STAT3 has been described as modulated by DHEA, we hypothesized that DHEA reverses human pulmonary hypertension by inhibiting Src/STAT3 constitutive activation. Using PASMCs isolated from patients with PAH (n = 3), we demonstrated that DHEA decreases both Src and STAT3 activation (Western blot and nuclear translocation assay), resulting in a significant reduction of Pim1, NFATc2 expression/activation (quantitative RT-PCR and Western blot), as well as Survivin and upregulation of bone morphogenetic protein receptor 2 (BMPR2) and miR-204. Src/STAT3 axis inhibition by DHEA is associated with 1) mitochondrial membrane potential (tetramethylrhodamine methyl-ester perchlorate; n = 150; P < 0.05) depolarization increasing apoptosis by 25% (terminal deoxynucleotidyl transferase dUTP-mediated nick-end labeling; n = 150; P < 0.05); and 2) decreased intracellular Ca(2+) concentration (fluo-3 AM; n = 150; P < 0.05) and proliferation by 30% (PCNA). Finally, in vivo similarly to STAT3 inhibition DHEA improves experimental PAH (monocrotaline rats) by decreasing mean PA pressure and right ventricle hypertrophy. These effects were associated with the inhibition of Src, STAT3, Pim1, NFATc2, and Survivin and the upregulation of BMPR2 and miR-204. We demonstrated that DHEA reverses pulmonary hypertension in part by inhibiting the Src/STAT3.

Estrogen rescues preexisting severe pulmonary hypertension in rats

RATIONALE

Pulmonary hypertension (PH) is characterized by progressive increase in pulmonary artery pressure leading to right ventricular (RV) hypertrophy, RV failure, and death. Current treatments only temporarily reduce severity of the disease, and an ideal therapy is still lacking.

OBJECTIVES

Estrogen pretreatment has been shown to attenuate development of PH. Because PH is not often diagnosed early, we examined if estrogen can rescue preexisting advanced PH.

METHODS

PH was induced in male rats with monocrotaline (60 mg/kg). At Day 21, rats were either treated with 17-β estradiol or estrogen (E2, 42.5 μg/kg/d), estrogen receptor-β agonist (diarylpropionitrile, 850 μg/kg/d), or estrogen receptor α-agonist (4,4',4"-[4-Propyl-(1H)-pyrazole-1,3,5-triyl] trisphenol, 850 μg/kg/d) for 10 days or left untreated to develop RV failure. Serial echocardiography, cardiac catheterization, immunohistochemistry, Western blot, and real-time polymerase chain reaction were performed.

MEASUREMENTS AND MAIN RESULTS

Estrogen therapy prevented progression of PH to RV failure and restored lung and RV structure and function. This restoration was maintained even after removal of estrogen at Day 30, resulting in 100% survival at Day 42. Estradiol treatment restored the loss of blood vessels in the lungs and RV. In the presence of angiogenesis inhibitor TNP-470 (30 mg/kg) or estrogen receptor-β antagonist (PHTPP, 850 μg/kg/d), estrogen failed to rescue PH. Estrogen receptor-β selective agonist was as effective as estrogen in rescuing PH.

CONCLUSIONS

Estrogen rescues preexisting severe PH in rats by restoring lung and RV structure and function that are maintained even after removal of estrogen. Estrogen-induced rescue of PH is associated with stimulation of cardiopulmonary neoangiogenesis, suppression of inflammation, fibrosis, and RV hypertrophy. Furthermore, estrogen rescue is likely mediated through estrogen receptor-β.

Sex hormones are associated with right ventricular structure and function: The MESA-right ventricle study

RATIONALE

Sex hormones have effects on the left ventricle, but hormonal influences on the right ventricle (RV) are unknown.

OBJECTIVES

We hypothesized that sex hormones would be associated with RV morphology in a large cohort free of cardiovascular disease.

METHODS

Sex hormones were measured by immunoassay and RV ejection fraction (RVEF), stroke volume (RVSV), mass, end-diastolic volume, and end-systolic volume (RVESV) were measured by cardiac magnetic resonance imaging in 1,957 men and 1,738 postmenopausal women. The relationship between each hormone and RV parameter was assessed by multivariate linear regression.

MEASUREMENTS AND MAIN RESULTS

Higher estradiol levels were associated with higher RVEF (β per 1 ln[nmol/L], 0.88; 95% confidence interval [CI], 0.32 to 1.43; P = 0.002) and lower RVESV (β per 1 ln[nmol/L], -0.87; 95% CI, -1.67 to -0.08; P = 0.03) in women using hormone therapy. In men, higher bioavailable testosterone levels were associated with higher RVSV (β per 1 ln[nmol/L], 1.97; 95% CI, 0.20 to 3.73; P = 0.03) and greater RV mass and volumes (P ≤ 0.01). Higher dehydroepiandrosterone levels were associated with higher RVSV (β per 1 ln[nmol/L], 1.37; 95% CI, 0.15 to 2.59; P = 0.03) and greater RV mass (β per 1 ln[nmol/L], 0.25; 95% CI, 0.00 to 0.49; P = 0.05) and volumes (P ≤ 0.001) in women.

CONCLUSIONS

Higher estradiol levels were associated with better RV systolic function in women using hormone therapy. Higher levels of androgens were associated with greater RV mass and volumes in both sexes.

STIM2 Contributes to Enhanced Store-operated Ca Entry in Pulmonary Artery Smooth Muscle Cells from Patients with Idiopathic Pulmonary Arterial Hypertension

Pulmonary vasoconstriction and vascular remodeling are two major causes for elevated pulmonary vascular resistance and pulmonary arterial pressure in patients with idiopathic pulmonary arterial hypertension (IPAH). An increase in cytosolic free Ca²⁺concentration ([Ca²⁺]_cyt) in pulmonary artery smooth muscle cells (PASMC) is a major trigger for pulmonary vasoconstriction and an important stimulus for PASMC proliferation, which causes pulmonary vascular remodeling. Store-operated Ca²⁺ entry (SOCE), induced by depletion of stored Ca²⁺ in the sarcoplasmic reticulum (SR), can increase [Ca²⁺]_cyt in PASMC, independent of other means of Ca²⁺ entry. Stromal interaction molecule (STIM) proteins, STIM1 and STIM2, were both recently identified as sensors for store depletion and also signaling molecules to open store-operated Ca²⁺ channels. We previously reported that SOCE was significantly enhanced in PASMC from IPAH patients compared to PASMC from normotensive control subjects. Enhanced SOCE plays an important role in the pathophysiological changes in PASMC associated with pulmonary arterial hypertension. In this study, we examine whether the expression levels of STIM1 and STIM2 are altered in IPAH-PASMC compared to control PASMC, and whether these putative changes in the STIM1 and STIM2 expression levels are responsible for enhanced SOCE and proliferation in IPAH-PASMC. Compared to control PASMC, the protein expression level of STIM2 was significantly increased in IPAH-PASMC, whereas STIM1 protein expression was not significantly changed. In IPAH-PASMC, the small interfering RNA (siRNA)-mediated knockdown of STIM2 decreased SOCE and proliferation, while knockdown of STIM2 in control PASMC had no effect on either SOCE or proliferation. Overexpression of STIM2 in the control PASMC failed to enhance SOCE or proliferation. These data indicate that enhanced protein expression of STIM2 is necessary, but not sufficient, for enhanced SOCE and proliferation of IPAH-PASMC.