Chronic administration of adrenomedullin attenuates hypoxic pulmonary vascular structural remodeling and inhibits proadrenomedullin N-terminal 20-peptide production in rats

Rieske iron-sulfur protein induces FKBP12.6/RyR2 complex remodeling and subsequent pulmonary hypertension through NF-κB/cyclin D1 pathway

Ca2+ signaling in pulmonary arterial smooth muscle cells (PASMCs) plays an important role in pulmonary hypertension (PH). However, the underlying specific ion channel mechanisms remain largely unknown. Here, we report ryanodine receptor (RyR) channel activity and Ca2+ release both are increased, and association of RyR2 by FK506 binding protein 12.6 (FKBP12.6) is decreased in PASMCs from mice with chronic hypoxia (CH)-induced PH. Smooth muscle cell (SMC)-specific RyR2 knockout (KO) or Rieske iron-sulfur protein (RISP) knockdown inhibits the altered Ca2+ signaling, increased nuclear factor (NF)-κB/cyclin D1 activation and cell proliferation, and CH-induced PH in mice. FKBP12.6 KO or FK506 treatment enhances CH-induced PH, while S107 (a specific stabilizer of RyR2/FKBP12.6 complex) produces an opposite effect. In conclusion, CH causes RISP-dependent ROS generation and FKBP12.6/RyR2 dissociation, leading to PH. RISP inhibition, RyR2/FKBP12.6 complex stabilization and Ca2+ release blockade may be potentially beneficial for the treatment of PH.

Up-regulation of caveolin-1 by DJ-1 attenuates rat pulmonary arterial hypertension by inhibiting TGFβ/Smad signaling pathway

Pulmonary arterial hypertension (PAH), characterized by excessive proliferation and apoptosis resistance of pulmonary artery smooth muscle cells (PASMCs), is closely associated with the imbalance in vasoactive mediators and massive remodeling of pulmonary vasculature. DJ-1/park7, a multifunctional protein, plays a critical defense role in several cytobiological activity, such as transcriptional regulation, anti-oxidative stress and tumor formation. In this study, we investigated the effects of DJ-1 on hypoxia-induced PAH model rats and PASMCs, as well as its possible molecular mechanism. First, the low expressions of DJ-1 and caveolin-1 (Cav-1) were synchronously detected in lung tissue of PAH model rats and hypoxia-induced PASMCs by Western blot. Then, the DJ-1 wild type (WT) or Knock out (KO) rats were exposed to chronic hypoxia to mimic a hypoxic PAH condition. The protein level of Cav-1 was markedly decreased in the tissue of DJ-1 KO rats, and additionally lower in tissue of the hypoxia group than that in the normoxia group for DJ-1 WT and KO rats. In vivo, hemodynamic data showed that the pulmonary arterial pressure (mPAP), right ventricle systolic pressure (RVSP) and pulmonary arterial systolic pressure (PASP), as well as the weight of the right ventricle/left ventricle plus septum (RV/LV+S) ratio of PAH model rats were higher in the DJ-1 KO group than those in the DJ-1 WT group. Moreover, knockout of DJ-1 also results in the phenotype switch from contractile to synthetic PASMC, which is reflected by reduced calponin and SM22α expressions. In vitro, DJ-1 overexpression reversed hypoxia-induced elevation of PASMC cell proliferation, migration and Ca²⁺ concentration, which were not obviously observed in Cav-1 shRNA (sh-Cav-1) and DJ-1 co-transfected cells. Then the increased levels of calponin and SM22α were detected in the DJ-1 group; similarly those levels were not changed in the DJ-1+sh-Cav-1 group. Finally, the expression of TGFβ1, p-Smad2 and p-Smad3 were obviously decreased in the ad-DJ-1 group, however those were all elevated in the DJ-1 and sh-Cav-1 co-transfected groups. In conclusion, these results indicate that DJ-1 may alleviate hypoxia-induced PASMCs injury by Cav-1 through inhibiting the TGFβ/Smad signaling pathway.

Expression of peptide fragments from proADM and involvement of mitogen-activated protein kinase signaling pathways in pulmonary remodeling induced by high pulmonary blood flow

Pulmonary arterial hypertension (PAH) is a life-threatening disease characterized by progressive pulmonary arterial remodeling and right ventricular failure. Despite recent advances in pathophysiological mechanism exploration and new therapeutic approaches, PAH remains a challenging condition. In this study, we investigated the roles of the peptide fragments from proadrenomedullin (proADM) such as adrenomedullin (ADM), adrenotensin (ADT), and proadrenomedullin N-terminal 20 peptide (PAMP) during pulmonary remodeling caused by high pulmonary blood flow, and probed the possible involvement of mitogen-activated protein kinase (MAPK) signal transduction pathways. Sixteen rat models of PAH were artificially established by surgically connecting the left common carotid artery to the external jugular vein. We subcutaneously injected an extracellular signal-regulated protein kinase (ERK1/2) inhibitor, PD98059, in eight rats, treated another eight rats with an equal volume of saline. Eight rats without connections served as the control group. We observed that mRNA expression levels of ADM, stress-activated protein kinase (SAPK), and ERK1/2 were significantly elevated in the shunted rats; furthermore, ERK1/2 levels were significantly inhibited by PD98059. Protein levels of ADM, PAMP, p-SAPK, and p-ERK1/2 were significantly higher ADT was lower, and p-p38 remained unchanged in the rat models compared with the controls. However, the protein expression of both ADM and p-ERK1/2 was significantly inhibited by PD98059. Our results suggest that levels of ADM, ADT, and PAMP respond to pulmonary remodeling, and that activation of the SAPK and ERK1/2 signaling pathways is involved in pulmonary hypertension and artery remodeling caused by high pulmonary blood flow.

Prospective evaluation of biomarkers for prediction of quality of life in community-acquired pneumonia

Background:

Most clinical research investigated prognostic biomarkers for their ability to predict cardiovascular events or mortality. It is unknown whether biomarkers allow prediction of quality of life (QoL) after survival of the acute event. Herein, we investigated the prognostic potential of well-established inflammatory/cardiovascular blood biomarkers including white blood cells (WBC), C-reactive protein (CRP), procalcitonin (PCT), pro-adrenomedullin (proADM) and pro-atrial natriuretic peptide (proANP) in regard to a decline in QoL in a well-defined cohort of patients with community-acquired pneumonia (CAP).

Methods:

Within this secondary analysis including 753 patients with a final inpatient diagnosis of CAP from a multicenter trial, we investigated associations between admission biomarker levels and decline in QoL assessed by the EQ-5D health questionnaire from admission to day 30 and after 6 years.

Results:

Admission proADM and proANP levels significantly predicted decline of the weighted EQ-5D index after 30 days (n=753) with adjusted odds ratios (ORs) of 2.0 ([95% CI 1.1–3.8]; p=0.027) and 3.7 ([95% CI 2.2–6.0]; p<0.001). Results for 6-year outcomes (n=349) were similar with ORs of 3.3 ([95% CI 1.3–8.3]; p=0.012) and 6.2 ([95% CI 2.7–14.2]; p<0.001). The markers were associated with most of the different QoL dimensions including mobility, self-care, and usual activities, but not pain/discomfort and to a lesser degree anxiety/depression and the visual analogue scale (VAS). Initial WBC, PCT and CRP values did not well predict QoL at any time point.

Conclusions:

ProADM and proANP accurately predict short- and long-term decline in QoL across most dimensions in CAP patients. It will be interesting to reveal underlying physiopathology in future studies.

Bench-to-bedside pharmacology of adrenomedullin

The bioactive peptide adrenomedullin (AM) exerts pleiotropic actions in various organs and tissues. In the heart, AM has an inhibitory effect on ventricular remodeling, suppressing cardiomyocyte hypertrophy and the proliferation of cardiac fibroblasts. This pharmacological property was shown not only in rat models of acute myocardial infarction, but also clinically in patients with this cardiac disease. An originally characterized feature of AM was a potent vasodilatory effect, but this peptide was found to be important for vascular integrity and angiogenesis. AM-induced angiogenesis is involved in tumor growth, while AM inhibits apoptosis of some types of tumor cell. A unique pharmacological property is anti-inflammatory activity, which has been characterized in sepsis and inflammatory bowel diseases; thus, there is an ongoing clinical trial to test the efficacy of AM for patients with intractable ulcerative colitis. These activities are assumed to be mediated via the specific receptor formed by calcitonin receptor-like receptor and receptor activity-modifying protein 2 or 3, while some questions remain to be answered about the molecular mechanisms of this signal transduction system. Taking these findings together, AM is a bioactive peptide with pleiotropic effects, with potential as a therapeutic tool for a wide range of human diseases from myocardial infarction to malignant tumors or inflammatory bowel diseases.

Exertional hypoxemia in stable COPD is common and predicted by circulating proadrenomedullin

BACKGROUND

The prevalence of exertional hypoxemia in unselected patients with COPD is unknown. Intermittent hypoxia leads to adrenomedullin (ADM) upregulation through the hypoxia-inducible factor-1 pathway. We aimed to assess the prevalence and the annual probability to develop exertional hypoxemia in stable COPD. We also hypothesized that increased ADM might be associated with exertional hypoxemia and envisioned that adding ADM to clinical variables might improve its prediction in COPD.

METHODS

A total of 1,233 6-min walk tests and circulating proadrenomedullin (proADM) levels from 574 patients with clinically stable, moderate to very severe COPD enrolled in a multinational cohort study and followed up for 2 years were concomitantly analyzed.

RESULTS

The prevalence of exertional hypoxemia was 29.1%. In a matrix derived from a fitted-multistate model, the annual probability to develop exertional hypoxemia was 21.6%. Exertional hypoxemia was associated with greater deterioration of specific domains of health-related quality of life, higher severe exacerbation, and death annual rates. In the logistic linear and conditional Cox regression multivariable analyses, both FEV1% predicted and proADM proved independent predictors of exertional hypoxemia (P < .001 for both). Adjustment for comorbidities, including cardiovascular disorders, and exacerbation rate did not influence results. Relative to using FEV1% predicted alone, adding proADM resulted in a significant improvement of the predictive properties (P = .018). Based on the suggested nonlinear nomogram, patients with moderate COPD (FEV1% predicted = 50%) but high proADM levels (> 2 nmol/L) presented increased risk (> 30%) for exertional desaturation.

CONCLUSIONS

Exertional desaturation is common and associated with poorer clinical outcomes in COPD. ADM improves prediction of exertional desaturation as compared with the use of FEV1% predicted alone.

TRIAL REGISTRY

ISRCTN Register; No.: ISRCTN99586989; URL: www.controlled-trials.com.

Mortality risk prediction in COPD by a prognostic biomarker panel

Chronic obstructive pulmonary disease (COPD) is a complex disease with various phenotypes. The simultaneous determination of multiple biomarkers reflecting different pathobiological pathways could be useful in identifying individuals with an increased risk of death.

We derived and validated a combination of three biomarkers (adrenomedullin, arginine vasopressin and atrial natriuretic peptide), assessed in plasma samples of 385 patients, to estimate mortality risk in stable COPD. Biomarkers were analysed in combination and defined as high or low.

In the derivation cohort (n = 142), there were 73 deaths during the 5-year follow-up. Crude hazard ratios for mortality were 3.0 (95% CI 1.8–5.1) for one high biomarker, 4.8 (95% CI 2.4–9.5) for two biomarkers and 9.6 (95% CI 3.3–28.3) for three high biomarkers compared with no elevated biomarkers. In the validation cohort (n = 243), 87 individuals died. Corresponding hazard ratios were 1.9 (95% CI 1.1–3.3), 3.1 (95% CI 1.8–5.4) and 5.4 (95% CI 2.5–11.4). Multivariable adjustment for clinical variables as well as the BODE (body mass index, airflow obstruction, dyspnoea, exercise capacity) index and stratification by the Global Initiative for Chronic Obstructive Lung Disease stages provided consistent results. The addition of the panel of three biomarkers to the BODE index generated a net reclassification improvement of 57.9% (95% CI 21.7–92.4%) and 45.9% (95% CI 13.9–75.7%) at 3 and 5 years, respectively.

Simultaneously elevated levels of adrenomedullin, arginine vasopressin and atrial natriuretic peptide are associated with increased risk of death in patients with stable COPD.

Adrenomedullin alleviates pulmonary artery collagen accumulation in rats with pulmonary hypertension induced by high blood flow

Collagen accumulation is one of the important pathologic changes in the development of pulmonary hypertension. Previous research showed that adrenomedullin (ADM) mitigates the development of pulmonary hypertension. The present study explored the role of ADM in the development of pulmonary artery collagen accumulation induced by high pulmonary blood flow, by investigating the effect of ADM [1.5 μg/(kg h)] subcutaneously administered by mini-osmotic pump on pulmonary hemodynamics, pulmonary vascular structure and pulmonary artery collagen accumulation and synthesis in rats with high pulmonary blood flow induced by aortocaval shunting. The results showed that ADM significantly decreased mean pulmonary artery pressure (mPAP) and the ratio of right ventricular mass to left ventricular plus septal mass [RV/(LV+SP)], attenuated the muscularization of small pulmonary vessels and relative medial thickness (RMT) of pulmonary arteries in rats with high pulmonary blood flow. Meanwhile, ADM ameliorated pulmonary artery collagen deposition represented by a decrease in lung tissue hydroxyproline, collagens I and III content and pulmonary artery collagens I and III expression, reduced collagen synthesis represented by a decrease in lung tissue procollagens I and III mRNA expression. The results suggest that ADM plays a protective role in the development of pulmonary hypertension induced by high blood flow, by inhibiting pulmonary procollagen synthesis and alleviating pulmonary artery collagen accumulation.

Transgelin as a therapeutic target to prevent hypoxic pulmonary hypertension

We previously observed that transgelin was preferentially expressed in human pulmonary arterial smooth muscle cells (PAMSCs) under hypoxia and that the upregulation of transgelin was independent of hypoxia-inducible factor 1α (HIF-1α). Reduced transgelin expression was accompanied by significantly impaired migration ability in vitro. However, the regulation mechanism of transgelin and its function in preventing hypoxic pulmonary hypertension (HPH) was unclear. In the present study, RNA interference with hypoxia-inducible factor 2α (HIF-2α) was employed in human PASMCs. Transgelin expression was diminished in HIF-2α-siRNA-treated cells at both the mRNA and protein levels under hypoxia. However, HIF-2α did not transactivate the transgelin promoter directly. TGF-β1 concentration in human PASMCs culture medium was higher under hypoxia, and the accumulated TGF-β1 under hypoxia was regulated by HIF-2α. Furthermore, luciferase and chromatin immunoprecipitation assays indicated that TGF-β1/Smad3 could bind to the transgelin promoter, resulting in increased transgelin expression. In addition to nonintact cellular migration, inhibition of transgelin expression resulted in impaired proliferation in vitro under hypoxia. A lentiviral vector used to inhibit transgelin expression was constructed and intratracheally instilled in rats 3 wk prior to hypoxia treatment. Our final results indicated that inhibition of transgelin expression locally could attenuate increased right ventricular systolic pressure and its associated cardiac and pulmonary vessel remodeling under hypoxia. Our findings indicate that HIF-2α upregulates transgelin indirectly and that accumulated TGF-β1 is a mediator in the upregulation of transgelin by HIF-2α under hypoxia. Inhibition of transgelin expression locally could prevent HPH and pulmonary vascular remodeling in vivo.

Adrenomedullin and adrenotensin regulate collagen synthesis and proliferation in pulmonary arterial smooth muscle cells

To understand the pathophysiological mechanisms of pulmonary arterial smooth muscle cell (PASMC) proliferation and extracellular-matrix accumulation in the development of pulmonary hypertension and remodeling, this study determined the effects of different doses of adrenomedullin (ADM) and adrenotensin (ADT) on PASMC proliferation and collagen synthesis. The objective was to investigate whether extracellular signal-regulated kinase (ERK1/2) signaling was involved in ADM- and ADT-stimulated proliferation of PASMCs in 4-week-old male Wistar rats (body weight: 100-150 g, n=10). The proliferation of PASMCs was examined by 5-bromo-2-deoxyuridine incorporation. A cell growth curve was generated by the Cell Counting Kit-8 method. Expression of collagen I, collagen III, and phosphorylated ERK1/2 (p-ERK1/2) was evaluated by immunofluorescence. The effects of different concentrations of ADM and ADT on collagen I, collagen III, and p-ERK1/2 protein expression were determined by immunoblotting. We also investigated the effect of PD98059 inhibition on the expression of p-ERK1/2 protein by immunoblotting. ADM dose-dependently decreased cell proliferation, whereas ADT dose-dependently increased it; and ADM and ADT inhibited each other with respect to their effects on the proliferation of PASMCs. Consistent with these results, the expression of collagen I, collagen III, and p-ERK1/2 in rat PASMCs decreased after exposure to ADM but was upregulated after exposure to ADT. PD98059 significantly inhibited the downregulation by ADM and the upregulation by ADT of p-ERK1/2 expression. We conclude that ADM inhibited, and ADT stimulated, ERK1/2 signaling in rat PASMCs to regulate cell proliferation and collagen expression.

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.

New perspectives for the treatment of pulmonary hypertension

Pulmonary hypertension (PH) is a debilitating disease with a poor prognosis. Therapeutic options remain limited despite the introduction of prostacyclin analogues, endothelin receptor antagonists and phosphodiesterase 5 inhibitors within the last 15 years; these interventions address predominantly the endothelial and vascular dysfunctionS associated with the condition, but simply delay progression of the disease rather than offer a cure. In an attempt to improve efficacy, emerging approaches have focused on targeting the pro-proliferative phenotype that underpins the pulmonary vascular remodelling in the lung and contributes to the impaired circulation and right heart failure. Many novel targets have been investigated and validated in animal models of PH, including modulation of guanylate cyclases, phosphodiesterases, tyrosine kinases, Rho kinase, bone morphogenetic proteins signalling, 5-HT, peroxisome proliferator activator receptors and ion channels. In addition, there is hope that combinations of such treatments, harnessing and optimizing vasodilator and anti-proliferative properties, will provide a further, possibly synergistic, increase in efficacy; therapies directed at the right heart may also offer an additional benefit. This overview highlights current therapeutic options, promising new therapies, and provides the rationale for a combination approach to treat the disease.

New therapies for pulmonary arterial hypertension: an update on current bench to bedside translation

IMPORTANCE OF THE FIELD

Treatments of pulmonary arterial hypertension (PAH) that have so far proven efficacious are all based on the restoration of endothelium control of pulmonary vascular tone and structure, by administration of prostacyclins, endothelin receptor antagonists and phosphodiesterase-5 inhibitors. However, results remain unsatisfactory, with persistent high mortality, insufficient clinical improvement and no convincing report of any reversal of the disease process.

AREAS COVERED IN THIS REVIEW

New antiproliferative approaches that aim to actively limit pulmonary vascular remodeling are being sought. Several such treatments have shown promise in experimental models and in preliminary clinical studies. Noteworthy among these are dichloroacetate, survivin antagonists, nuclear factor of activated T-cell inhibitors, PPAR-gamma agonists, tyrosine kinase inhibitors, Rho-kinase inhibitors, statins, vasoactive intestinal peptide, soluble guanylate cyclase stimulators/activators, adrenomedullin, elastase inhibitors, serotonin reuptake inhibitors, anti-inflammatory agents, and bone marrow-derived progenitor cells.

WHAT THE READER WILL GAIN

Update on various strategies targeting proliferative, inflammatory and regenerating processes currently under evaluation in patients with PAH.

TAKE HOME MESSAGE

In spite of favorable results in experimental models, none of these strategies has achieved the ultimate goal of curing PAH. Further developments will depend on progress made in our pathobiological understanding of the disease and carefully designed randomized, controlled trials.

Up-regulation of two actin-associated proteins prompts pulmonary artery smooth muscle cell migration under hypoxia

Hypoxia stimulates the migration of pulmonary artery smooth muscle cells (PASMCs), which contributes to the pathogenesis of pulmonary vessel structural remodeling in hypoxic pulmonary hypertension (HPH). In the present study, we found, using a proteomics-based method, that gelsolin-like actin-capping protein (CapG) and transgelin were preferentially expressed in human (h)PAMSCs under hypoxia compared with normoxia. These two actin-associated proteins, modulate a variety of physiologic processes, including motility of cells, by interacting differently with the actin cytoskeleton. Our study showed that these two genes were up-regulated at both mRNA and protein levels under hypoxia in hPASMCs. As a key transcriptional regulation factor under hypoxia, hypoxia-inducible factor 1alpha (HIF-1alpha) up-regulated CapG protein expression under normoxia, and knockdown of HIF-1alpha expression in hPASMCs also inhibited hypoxia induced CapG up-regulation. However, HIF-1alpha could not regulate transgelin expression. Reduction of CapG or transgelin expression in hPASMCs by RNA interference was accompanied by significantly impaired migration ability in vitro, especially under hypoxia. Our study demonstrates that CapG and transgelin were preferentially expressed in hPAMSCs under hypoxia compared with normoxia. Hypoxia stimulates expression of these two actin-associated proteins via HIF-1alpha-dependent and -independent pathways, respectively. The up-regulation of these two proteins may contribute to the increased motility of hPASMCs under hypoxia. These findings may contribute to the understanding of the pathogenesis of HPH.

Therapeutic targets in pulmonary arterial hypertension

Pulmonary arterial hypertension is a progressive, fatal disease. Current treatments including prostanoids, endothelin-1 (ET-1) antagonists, and phosphodiesterase (PDE) inhibitors, have sought to address the pulmonary vascular endothelial dysfunction and vasoconstriction associated with the condition. These treatments may slow the progression of the disease but do not afford a cure. Future treatments must target more directly the structural vascular changes that impair blood flow through the pulmonary circulation. Several novel therapeutic targets have been proposed and are under active investigation, including soluble guanylyl cyclase, phosphodiesterases, tetrahydrobiopterin, 5-HT2B receptors, vasoactive intestinal peptide, receptor tyrosine kinases, adrenomedullin, Rho kinase, elastases, endogenous steroids, endothelial progenitor cells, immune cells, bone morphogenetic protein and its receptors, potassium channels, metabolic pathways, and nuclear factor of activated T cells. Tyrosine kinase inhibitors, statins, 5-HT2B receptor antagonists, EPCs and soluble guanylyl cyclase activators are among the most advanced, having produced encouraging results in animal models, and human trials are underway. This review summarises the current research in this area and speculates on their likely success.