Angiotensin II type 2 receptor ligand PD123319 attenuates hyperoxia-induced lung and heart injury at a low dose in newborn rats

An insight into the placental growth factor (PlGf)/angii axis in Covid-19: a detrimental intersection

Coronavirus disease 2019 (Covid-19) is a recent and current infectious pandemic caused by severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2). Covid-19 may lead to the development of acute lung injury (ALI), acute respiratory distress syndrome (ARDS), and extrapulmonary manifestations in severe cases. Down-regulation of angiotensin-converting enzyme (ACE2) by the SARS-CoV-2 increases the production of angiotensin II (AngII), which increases the release of pro-inflammatory cytokines and placental growth factor (PlGF). PlGF is a critical molecule involved in vasculogenesis and angiogenesis. PlGF is stimulated by AngII in different inflammatory diseases through a variety of signaling pathways. PlGF and AngII are interacted in SARS-CoV-2 infection resulting in the production of pro-inflammatory cytokines and the development of Covid-19 complications. Both AngII and PlGF are interacted and are involved in the progression of inflammatory disorders; therefore, we aimed in this review to highlight the potential role of the PlGF/AngII axis in Covid-19.

ACE2 Alleviates Endoplasmic Reticulum Stress and Protects against Pyroptosis by Regulating Ang1-7/Mas in Ventilator-Induced Lung Injury

BACKGROUND

Ventilator-induced lung injury (VILI) is a consequence of inflammation and increased alveolar-capillary membrane permeability due to alveolar hyperdistention or elevated intrapulmonary pressure, but the precise mechanisms remain unclear. The aim of the study was to analyze the mechanism by which angiotensin converting enzyme 2 (ACE2) alleviates endoplasmic reticulum stress (ERS) and protects alveolar cells from pyroptosis in VILI by regulating angiotensin (Ang)1-7/Mas.

METHODS

VILI was induced in mice by mechanical ventilation by regulating the tidal volume. The alveolar cell line, A549, mimics VILI in vitro by cyclic stretch (CS). Ang (1-7) (100 nmol/L) was added to the medium. ERS was induced in cells by stimulating with tunicamycin (TM, 2 μg/mL). ERS was inhibited by tracheal instillation of 4-phenylbutyric acid (4-PBA) (1 mg/kg). ACE2's enzymatic function was activated or inhibited by subcutaneous injection of resorcinolnaphthalein (RES, 20 μg/kg) or MLN-4760 (20 μg/kg). pGLV-EF1a-GFP-ACE2 was instilled into the trachea to increase the protein expression of ACE2. The Ang (1-7) receptor, Mas, was antagonized by injecting A779 subcutaneously (80 μg/kg).

RESULTS

ACE2 protein levels decreased after modeling. Ang (1-7) level was decreased and Ang II was accumulated. ERS was significantly induced in VILI mice, and pyroptosis was observed in cells. When ERS was inhibited, pyroptosis under the VILI condition was significantly inhibited. Ang (1-7) alleviated ERS and pyroptosis under CS. When ERS was continuously activated, the function of Ang (1-7) in inhibiting pyroptosis was blocked. Resorcinolnaphthalein (RES) effectively promoted Ang II conversion, alleviated the Ang (1-7) level in VILI, ameliorated lung injury, and inhibited ERS and cell pyroptosis. Inhibiting ACE2's function in VILI hindered the production of Ang (1-7), promoted the accumulation of Ang II, and exacerbated ERS and pyroptosis, along with lung injury. The Mas antagonist significantly blocked the inhibitory effects of ACE2 on ERS and pyroptosis in VILI.

CONCLUSIONS

Reduced ACE2 expression in VILI is involved in ERS and pyroptosis-related injury. ACE2 can alleviate ERS in alveolar cells by catalyzing the production of Ang (1-7), thus inhibiting pyroptosis in VILI.

Angiotensin II Type 2 Receptor Inhibits M1 Polarization and Apoptosis of Alveolar Macrophage and Protects Against Mechanical Ventilation-Induced Lung Injury

Angiotensin II (Ang II) is associated with macrophage polarization and apoptosis, but the role of the angiotensin type 2 receptor (AT2R) in these processes remains controversial. However, the effect of AT2Rs on alveolar macrophages and mechanical ventilation-induced lung injury has not been determined. Mechanical ventilation-induced lung injury in Sprague‒Dawley (SD) rats and LPS-stimulated rat alveolar macrophages (NR8383) were used to determine the effects of AT2Rs, selective AT2R agonists and selective AT1Rs or AT2R antagonists. Macrophage polarization, apoptosis, and related signaling pathways were assessed via western blotting, QPCR and flow cytometry. AT2R expression was decreased in LPS-stimulated rat alveolar macrophages (NR8383). Administration of the AT2R agonist CGP-42112 was associated with an increase in AT2R expression and M2 polarization, but no effect was observed upon administration of the AT2R antagonist PD123319 or the AT1R antagonist valsartan. In mechanical ventilation-induced lung injury in Sprague‒Dawley (SD) rats, the administration of the AT2R agonist C21 was associated with attenuation of the pathological damage score, lung wet/dry weight, cell count and protein content in BALF. C21 can significantly reduce proinflammatory factor TNF-α, IL-1β levels, increase anti-inflammatory factor IL-4, IL-10 levels in BALF, compared with the model group (p < 0.01). Similarly, compared with those at the same time points, the M1/M2 ratios in alveolar macrophages and apoptosis in peritoneal macrophages at 4 h, 6 h and 8 h in the mechanical ventilation models were lower after C21 administration. These findings indicated that the expression of AT2Rs in alveolar macrophages mediates M1 macrophage polarization and apoptosis and that AT2Rs play a protective role in mediating mechanical ventilation-induced lung injury.

Hyperoxia-induced airflow restriction and Renin-Angiotensin System expression in a bronchopulmonary dysplasia mouse model

Mechanisms underlying hyperoxia-induced airflow restriction in the pediatric lung disease Bronchopulmonary dysplasia (BPD) are unclear. We hypothesized a role for Renin-Angiotensin System (RAS) activity in BPD. RAS is comprised of a pro-developmental pathway consisting of angiotensin converting enzyme-2 (ACE2) and angiotensin II receptor type 2 (AT2), and a pro-fibrotic pathway mediated by angiotensin II receptor type 1 (AT1). We investigated associations between neonatal hyperoxia, airflow restriction, and RAS activity in a BPD mouse model. C57 mouse pups were randomized to normoxic (FiO2  = 0.21) or hyperoxic (FiO2  = 0.75) conditions for 15 days (P1-P15). At P15, P20, and P30, we measured airflow restriction using plethysmography and ACE2, AT1, and AT2 mRNA and protein expression via polymerase chain reaction and Western Blot. Hyperoxia increased airflow restriction P15 and P20, decreased ACE2 and AT2 mRNA, decreased AT2 protein, and increased AT1 protein expression. ACE2 mRNA and protein remained suppressed at P20. By P30, airflow restriction and RAS expression did not differ between groups. Hyperoxia caused high airflow restriction, increased pulmonary expression of the pro-fibrotic RAS pathway, and decreased expression of the pro-developmental in our BPD mouse model. These associated findings may point to a causal role for RAS in hyperoxia-induced airflow restriction.

Evolving views on the first two ligands of the angiotensin II type 2 receptor. From putative antagonists to potential agonists?

The renin-angiotensin system is one of the most complex regulatory systems that controls multiple organ functions. One of its key components, angiotensin II (Ang II), stimulates two G-protein coupled class A receptors: the Ang II type 1 (AT1) receptor and the Ang II type 2 (AT2) receptor. While stimulation of the AT1 receptor causes G-protein-dependent signaling and arrestin recruitment, the AT2 receptor seems to have a constitutively active-like conformation and appears to act via G-protein-dependent and -independent pathways. Overstimulation of the AT1 receptor may lead to unwanted effects like inflammation and fibrosis. In contrast, stimulation of the AT2 receptor leads to opposite effects thus restoring the balance. However, the role of the AT2 receptor has become controversial due to beneficial effects of putative AT2 receptor antagonists. The two first synthetic AT2 receptor-selective ligands, peptide CGP42112 and small molecule PD123319, were initially both considered antagonists. CGP42112 was subsequently considered a partial agonist and it was recently demonstrated to be a full agonist. Based on the search-term PD123319 in Pubmed, 1652 studies have investigated putative AT2 receptor antagonist PD123319. Here, we put forward literature that shows beneficial effects of PD123319 alone, even at doses too low for antagonist efficacy. These beneficial effects appear compatible with agonist-like activity via the AT2 receptor. Taken together, a more consistent image of a therapeutic role of stimulated AT2 receptor emerges which may clarify current controversies.

The AT1/AT2 Receptor Equilibrium Is a Cornerstone of the Regulation of the Renin Angiotensin System beyond the Cardiovascular System

The AT₁ receptor has mainly been associated with the pathological effects of the renin-angiotensin system (RAS) (e.g., hypertension, heart and kidney diseases), and constitutes a major therapeutic target. In contrast, the AT₂ receptor is presented as the protective arm of this RAS, and its targeting via specific agonists is mainly used to counteract the effects of the AT₁ receptor. The discovery of a local RAS has highlighted the importance of the balance between AT₁/AT₂ receptors at the tissue level. Disruption of this balance is suggested to be detrimental. The fine tuning of this balance is not limited to the regulation of the level of expression of these two receptors. Other mechanisms still largely unexplored, such as S-nitrosation of the AT₁ receptor, homo- and heterodimerization, and the use of AT₁ receptor-biased agonists, may significantly contribute to and/or interfere with the settings of this AT₁/AT₂ equilibrium. This review will detail, through several examples (the brain, wound healing, and the cellular cycle), the importance of the functional balance between AT₁ and AT₂ receptors, and how new molecular pharmacological approaches may act on its regulation to open up new therapeutic perspectives.

Vascular and pulmonary effects of ibuprofen on neonatal lung development

BACKGROUND

Ibuprofen is a nonsteroidal anti-inflammatory drug that is commonly used to stimulate closure of a patent ductus arteriosus (PDA) in very premature infants and may lead to aberrant neonatal lung development and bronchopulmonary dysplasia (BPD).

METHODS

We investigated the effect of ibuprofen on angiogenesis in human umbilical cord vein endothelial cells (HUVECs) and the therapeutic potential of daily treatment with 50 mg/kg of ibuprofen injected subcutaneously in neonatal Wistar rat pups with severe hyperoxia-induced experimental BPD. Parameters investigated included growth, survival, lung histopathology and mRNA expression.

RESULTS

Ibuprofen inhibited angiogenesis in HUVECs, as shown by reduced tube formation, migration and cell proliferation via inhibition of the cell cycle S-phase and promotion of apoptosis. Treatment of newborn rat pups with ibuprofen reduced pulmonary vessel density in the developing lung, but also attenuated experimental BPD by reducing lung inflammation, alveolar enlargement, alveolar septum thickness and small arteriolar wall thickening.

CONCLUSIONS

In conclusion, ibuprofen has dual effects on lung development: adverse effects on angiogenesis and beneficial effects on alveolarization and inflammation. Therefore, extrapolation of the beneficial effects of ibuprofen to premature infants with BPD should be done with extreme caution.

Quantitative Phosphoproteomics of the Angiotensin AT 2 -Receptor Signaling Network Identifies HDAC1 (Histone-Deacetylase-1) and p53 as Mediators of Antiproliferation and Apoptosis

Background:

Angiotensin AT 2 -receptor signaling is atypical for a G-protein coupled receptor and incompletely understood. To obtain novel insights into AT 2 -receptor signaling, we mapped changes in the phosphorylation status of the entire proteome of human aortic endothelial cells in response to AT 2 -receptor stimulation.

Methods:

Phosphorylation status of human aortic endothelial cells after stimulation with C21 (1 µM; 0, 1, 3, 5, 20 minutes) was determined utilizing time-resolved quantitative phosphoproteomics. Specific changes in protein phosphorylation and acetylation were confirmed by Western Blotting. Functional tests included resazurin assay for cell proliferation, and caspase 3/7 luminescence assay or FACS analysis of annexin V expression for apoptosis.

Results:

AT 2 -receptor stimulation significantly altered the phosphorylation status of 172 proteins (46% phosphorylations, 54% dephosphorylations). Bioinformatic analysis revealed a cluster of phospho-modified proteins involved in antiproliferation and apoptosis. Among these proteins, HDAC1 (histone-deacetylase-1) was dephosphorylated at serine 421/423 involving serine/threonine phosphatases. Resulting HDAC1 inhibition led to p53 acetylation and activation. AT 2 -receptor stimulation induced antiproliferation and apoptosis, which were absent when cells were co-incubated with the p53 inhibitor pifithrin-α, thus indicating p53-dependence of these AT 2 -receptor mediated functions.

Conclusions:

Contrary to the prevailing view that AT 2 -receptor signaling largely involves phosphatases, our study revealed significant involvement of kinases. HDAC1 inhibition and resulting p53 activation were identified as novel, AT 2 -receptor coupled signaling mechanisms. Furthermore, the study created an openly available dataset of AT 2 -receptor induced phospho-modified proteins, which has the potential to be the basis for further discoveries of currently unknown, AT 2 -receptor coupled signaling mechanisms.

The Angiotensin AT2 Receptor: From a Binding Site to a Novel Therapeutic Target

Discovered more than 30 years ago, the angiotensin AT2 receptor (AT2R) has evolved from a binding site with unknown function to a firmly established major effector within the protective arm of the renin-angiotensin system (RAS) and a target for new drugs in development. The AT2R represents an endogenous protective mechanism that can be manipulated in the majority of preclinical models to alleviate lung, renal, cardiovascular, metabolic, cutaneous, and neural diseases as well as cancer. This article is a comprehensive review summarizing our current knowledge of the AT2R, from its discovery to its position within the RAS and its overall functions. This is followed by an in-depth look at the characteristics of the AT2R, including its structure, intracellular signaling, homo- and heterodimerization, and expression. AT2R-selective ligands, from endogenous peptides to synthetic peptides and nonpeptide molecules that are used as research tools, are discussed. Finally, we summarize the known physiological roles of the AT2R and its abundant protective effects in multiple experimental disease models and expound on AT2R ligands that are undergoing development for clinical use. The present review highlights the controversial aspects and gaps in our knowledge of this receptor and illuminates future perspectives for AT2R research. SIGNIFICANCE STATEMENT: The angiotensin AT2 receptor (AT2R) is now regarded as a fully functional and important component of the renin-angiotensin system, with the potential of exerting protective actions in a variety of diseases. This review provides an in-depth view of the AT2R, which has progressed from being an enigma to becoming a therapeutic target.

ASTHMA: ROLE OF THE ANGIOTENSIN-(1-7)/MAS PATHWAY IN PATHOPHYSIOLOGY AND THERAPY

The incidence of asthma is a global health problem, requiring studies aimed at developing new treatments to improve clinical management, thereby reducing personal and economic burdens on the health system. Therefore, the discovery of mediators that promote anti-inflammatory and pro-resolutive events are highly desirable to improve lung function and quality of life in asthmatic patients. In that regard, experimental studies have shown that the Angiotensin-(1-7)/Mas receptor of the renin-angiotensin system (RAS) is a potential candidate for the treatment of asthma. Therefore, we reviewed findings related to the function of the Angiotensin-(1-7)/Mas pathway in regulating the processes associated with inflammation and exacerbations in asthma, including leukocyte influx, fibrogenesis, pulmonary dysfunction and resolution of inflammation. Thus, knowledge of the role of the Angiotensin-(1-7)/Mas can help pave the way for the development of new treatments for this disease with high morbidity and mortality through new experimental and clinical trials.

Angiotensin II Type 2 Receptor: A Target for Protection Against Hypertension, Metabolic Dysfunction, and Organ Remodeling

The renin-angiotensin system is of vital significance not only in the maintenance of blood pressure but also because of its role in the pathophysiology of different organ systems in the body. Of the 2 Ang II (angiotensin II) receptors, the AT₁R (Ang II type 1 receptor) has been extensively studied for its role in mediating the classical functions of Ang II, including vasoconstriction, stimulation of renal tubular sodium reabsorption, hormonal secretion, cell proliferation, inflammation, and oxidative stress. The other receptor, AT₂R (Ang II type 2 receptor), is abundantly expressed in both immune and nonimmune cells in fetal tissue. However, its expression is increased under pathological conditions in adult tissues. The role of AT₂R in counteracting AT₁R function has been discussed in the past 2 decades. However, with the discovery of the nonpeptide agonist C21, the significance of AT₂R in various pathologies such as obesity, hypertension, and kidney diseases have been examined. This review focuses on the most recent findings on the beneficial effects of AT₂R by summarizing both gene knockout studies as well as pharmacological studies, specifically highlighting its importance in blood pressure regulation, obesity/metabolism, organ protection, and relevance in the treatment of coronavirus disease 2019 (COVID-19).

LP2, the first lanthipeptide GPCR agonist in a human pharmacokinetics and safety study

Introduction of a lanthionine into a peptide may enhance target affinity, target specificity and proteolytic resistance. This manuscript reports preclinical safety studies and the first-in-human study with the lanthipeptide AT₂R agonist LP2, a structural analog of cAng-(1-7), whose N-terminus was protected against aminopeptidases by the presence of a d-lysine. None of the preclinical studies, including an in vitro multitarget panel, behavioral, respiratory and cardiovascular measurements, genotoxicity and toxicity studies in rat and dog, posed any safety concern. Due to lack of toxicity the maximum tolerated dose was not reached neither in rat nor in dog. In the human dose escalation study, healthy male volunteers received a single 1 mL subcutaneous injection (0.001 mg, 0.01 mg or 0.1 mg) of LP2 or matching placebo. In contrast to angiotensin II which has a T_1/2 in plasma of < 1 min, LP2 has a T_1/2 of approximately 2.1-2.6 hours. The fraction of the dose excreted unchanged in urine ranged from 84.73 ± 10.4 % at a dose of 0.001 mg to 66.4 ± 3.9 % at 0.1 mg. There were no deaths, serious adverse events or subject withdrawals as a result of an adverse event. The incidence of adverse events was 16.7 %; each was mild in severity. One adverse event, peripheral coldness, was considered to be possibly related to LP2 at 0.001 mg LP2. None of the results was considered to pose a clinically relevant safety concern. This study supports the potential for the therapeutic use of lanthipeptides.

Severe Acute Respiratory Syndrome Coronavirus 2, COVID-19, and the Renin-Angiotensin System: Pressing Needs and Best Research Practices

The coronavirus disease 2019 (COVID-19) pandemic is associated with significant morbidity and mortality throughout the world, predominantly due to lung and cardiovascular injury. The virus responsible for COVID-19-severe acute respiratory syndrome coronavirus 2-gains entry into host cells via ACE2 (angiotensin-converting enzyme 2). ACE2 is a primary enzyme within the key counter-regulatory pathway of the renin-angiotensin system (RAS), which acts to oppose the actions of Ang (angiotensin) II by generating Ang-(1-7) to reduce inflammation and fibrosis and mitigate end organ damage. As COVID-19 spans multiple organ systems linked to the cardiovascular system, it is imperative to understand clearly how severe acute respiratory syndrome coronavirus 2 may affect the multifaceted RAS. In addition, recognition of the role of ACE2 and the RAS in COVID-19 has renewed interest in its role in the pathophysiology of cardiovascular disease in general. We provide researchers with a framework of best practices in basic and clinical research to interrogate the RAS using appropriate methodology, especially those who are relatively new to the field. This is crucial, as there are many limitations inherent in investigating the RAS in experimental models and in humans. We discuss sound methodological approaches to quantifying enzyme content and activity (ACE, ACE2), peptides (Ang II, Ang-[1-7]), and receptors (types 1 and 2 Ang II receptors, Mas receptor). Our goal is to ensure appropriate research methodology for investigations of the RAS in patients with severe acute respiratory syndrome coronavirus 2 and COVID-19 to ensure optimal rigor and reproducibility and appropriate interpretation of results from these investigations.

Biosynthesis of lanthionine-constrained agonists of G protein-coupled receptors

The conformation with which natural agonistic peptides interact with G protein-coupled receptor(s) (GPCR(s)) partly results from intramolecular interactions such as hydrogen bridges or is induced by ligand–receptor interactions. The conformational freedom of a peptide can be constrained by intramolecular cross-links. Conformational constraints enhance the receptor specificity, may lead to biased activity and confer proteolytic resistance to peptidic GPCR agonists. Chemical synthesis allows to introduce a variety of cross-links into a peptide and is suitable for bulk production of relatively simple lead peptides. Lanthionines are thioether bridged alanines of which the two alanines can be introduced at different distances in chosen positions in a peptide. Thioether bridges are much more stable than disulfide bridges. Biosynthesis of lanthionine-constrained peptides exploiting engineered Gram-positive or Gram-negative bacteria that contain lanthionine-introducing enzymes constitutes a convenient method for discovery of lanthionine-stabilized GPCR agonists. The presence of an N-terminal leader peptide enables dehydratases to dehydrate serines and threonines in the peptide of interest after which a cyclase can couple the formed dehydroamino acids to cysteines forming (methyl)lanthionines. The leader peptide also guides the export of the formed lanthionine-containing precursor peptide out of Gram-positive bacteria via a lanthipeptide transporter. An engineered cleavage site in the C-terminus of the leader peptide allows to cleave off the leader peptide yielding the modified peptide of interest. Lanthipeptide GPCR agonists are an emerging class of therapeutics of which a few examples have demonstrated high efficacy in animal models of a variety of diseases. One lanthipeptide GPCR agonist has successfully passed clinical Phase Ia.

Role of angiotensin II type 1 (AT1) and type 2 (AT2) receptors in airway reactivity and inflammation in an allergic mouse model of asthma

Objective: Angiotensin II (Ang II) exerts its effects through two G-protein coupled receptors: angiotensin II type 1 receptors (AT1) and type 2 receptors (AT2). Both these receptor subtypes are poorly understood in asthma. In this study, we investigated effects of AT1 receptor antagonist losartan, novel AT2 receptor agonist novokinin and AT2 receptor antagonist PD 123319 in a mouse model of asthma. Methods: Mice were divided into control (CON) and allergen sensitized (SEN) groups. SEN was sensitized with ovalbumin (OVA) on days 1 and 6 (30 μg; i.p.), followed by 5% OVA aerosol challenge (days 11-13). Treatments included (a) losartan (SEN + LOS; 20 mg/kg i.p., day 14), (b) novokinin (SEN + NOV; 0.3 mg/kg i.p., day 14), and (c) PD 123319 (SEN + PD; 5 mg/kg i.p., day 14). Experiments for airway responsiveness, bronchoalveolar lavage, and tracheal ring reactivity using isolated organ bath were performed. Results: Airway responsiveness to methacholine (MCh) (48 mg/mL) was significantly higher in SEN (563.71 ± 40% vs. 294.3 ± 123.84 in CON). This response was potentiated in SEN + PD group (757 ± 30%; p < .05 compared to SEN). SEN + LOS (247.61 ± 86.85%) and SEN + NOV (352 ± 11%) had significantly lower response compared to SEN. SEN + LOS (26.22 ± 0.29%) and SEN + NOV (46.20 ± 0.76%) treatment significantly (p < .001) attenuated total cell count and eosinophils compared to SEN group (69.38 ± 1.5%), while SEN + PD (73.04 ± 0.69%) had highest number of eosinophils. Tracheal response to MCh was significantly higher in SEN group compared to controls, and this response was significantly lowered with the losartan and novokinin treatments. Conclusions: These data suggest that AT1 and AT2 receptors have opposite effects in modulating airway hyperresponsiveness and inflammation in asthma.

Prevention of lipopolysaccharide-induced CD11b+ immune cell infiltration in the kidney: role of AT2 receptors

Immune cell infiltration plays a central role in mediating endotoxemic acute kidney injury (AKI). Recently, we have reported the anti-inflammatory and reno-protective role of angiotensin-II type-2 receptor (AT₂R) activation under chronic low-grade inflammatory condition in the obese Zucker rat model. However, the role of AT₂R activation in preventing lipopolysaccharide (LPS)-induced early infiltration of immune cells, inflammation and AKI is not known. Mice were treated with AT₂R agonist C21 (0.3 mg/kg), with and without AT₂R antagonist PD123319 (5 mg/kg) prior to or concurrently with LPS (5 mg/kg) challenge. Prior-treatment with C21, but not concurrent treatment, significantly prevented the LPS-induced renal infiltration of CD11b⁺ immune cells, increase in the levels of circulating and/or renal chemotactic cytokines, particularly interleukin-6 (IL-6) and monocyte chemoattractant protein-1 (MCP-1) and markers of renal dysfunction (blood urea nitrogen and albuminuria), while preserving anti-inflammatory interleukin-10 (IL-10) production. Moreover, C21 treatment in the absence of LPS increased renal and circulating IL-10 levels. To investigate the role of IL-10 in a cross-talk between epithelial cells and monocytes, we performed in vitro conditioned media (CM) studies in human kidney proximal tubular epithelial (HK-2) cells and macrophages (differentiated human monocytes, THP-1 cells). These studies revealed that the conditioned-media derived from the C21-treated HK-2 cells reduced LPS-induced THP-1 tumor necrosis factor-α (TNF-α) production via IL-10 originating from HK-2 cells. Our findings suggest that prior activation of AT₂R is prophylactic in preventing LPS-induced renal immune cell infiltration and dysfunction, possibly via IL-10 pathway.

Cystic Fibrosis Disease Modifiers: Complex Genetics Defines the Phenotypic Diversity in a Monogenic Disease

In many respects, genetic studies in cystic fibrosis (CF) serve as a paradigm for a human Mendelian genetic success story. From recognition of the condition as a heritable pathological entity to implementation of personalized treatments based on genetic findings, this multistep pathway of progress has focused on the genetic underpinnings of CF clinical disease. Along this path was the recognition that not all CFTR gene mutations produce the same disease and the recognition of the complex, multifactorial nature of CF genotype–phenotype relationships. The non- CFTR genetic components (gene modifiers) that contribute to variation in phenotype are the focus of this review. A multifaceted approach involving candidate gene studies, genome-wide association studies, and gene expression studies has revealed significant gene modifiers for multiple CF phenotypes. The bold challenges for the future are to integrate the findings into our understanding of CF pathogenesis and to use the knowledge to develop novel therapies.

Human mesenchymal stem cells attenuate hyperoxia-induced lung injury through inhibition of the renin-angiotensin system in newborn rats

Hyperoxia induces activation of the renin-angiotensin system (RAS) in newborn rat lungs. This study investigated the therapeutic effects of human mesenchymal stem cells (MSCs) on lung development and RAS expression in neonatal rats exposed to hyperoxia. Sprague-Dawley rat pups were exposed to either room air (RA) or oxygen-enriched atmosphere (O2) treatment from postnatal days 1 to 14. Human MSCs (1 × 105 cells) in 0.03 mL of normal saline (NS) were administered intratracheally on postnatal day 5, and four study groups were obtained: RA + NS, RA + MSCs, O2 + NS, and O2 + MSCs. The lungs were excised for cytokine, expression of RAS components, and histological analyses on postnatal day 14. Body and lung weights were significantly lower in rats reared in hyperoxia than in those reared in RA. The rats reared in hyperoxia and treated with NS exhibited significantly higher tumor necrosis factor (TNF)-α and interleukin (IL)-6 levels, mean linear intercept (MLI), and expression of angiotensin II, angiotensin II type 1 receptor, and angiotensin-converting enzyme than those reared in RA and treated with NS or MSCs did. Administering MSC to hyperoxia-exposed rats reduced TNF-α and IL-6 levels, improved MLI, and decreased expression of angiotensin II, angiotensin II type 1 receptor, and angiotensin-converting enzyme to normoxic levels. Thus, human MSCs attenuated hyperoxia-induced lung injury through inhibition of the RAS in newborn rats.

AGTR2 absence or antagonism prevents cystic fibrosis pulmonary manifestations

BACKGROUND

Pulmonary disease remains the primary cause of morbidity and mortality for individuals with cystic fibrosis (CF). Variants at a locus on the X-chromosome containing the type 2 angiotensin II receptor gene (AGTR2) were identified by a large GWAS as significantly associating with lung function in CF patients. We hypothesized that manipulating the angiotensin-signaling pathway may yield clinical benefit in CF.

METHODS

Genetic subset analysis was conducted on a local CF cohort to extend the GWAS findings. Next, we evaluated pulmonary function in CF mice with a deleted AGTR2 gene, and in those who were given subcutaneous injections of PD123,319, a selective AGTR2 antagonist for 12 weeks beginning at weaning.

RESULTS

The genetic subset analysis replicated the initial GWAS identified association, and confirmed the association of this locus with additional lung function parameters. Studies in genetically modified mice established that absence of the AGTR2 gene normalized pulmonary function indices in two independent CF mouse models. Further, we determined that pharmacologic antagonism of AGTR2 improved overall pulmonary function in CF mice to near wild-type levels.

CONCLUSIONS

These results identify that reduced AGTR2 signaling is beneficial to CF lung function, and suggest the potential of manipulating the angiotensin-signaling pathway for treatment and/or prevention of CF pulmonary disease. Importantly, the beneficial effects were not CF gene mutation dependent, and were able to be reproduced with pharmacologic antagonism. As there are clinically approved drugs available to target the renin-angiotensin signaling system, these findings may be quickly translated to human clinical trials.

Elevated potassium outward currents in hyperoxia treated atrial cardiomyocytes

Supplementation of 100% oxygen is a very common intervention in intensive care units (ICU) and critical care centers for patients with dysfunctional lung and lung disorders. Although there is advantage in delivering sufficient levels of oxygen, hyperoxia is reported to be directly associated with increasing in-hospital deaths. Our previous studies reported ventricular and electrical remodeling in hyperoxia treated mouse hearts, and in this article, for the first time, we are investigating the effects of hyperoxia on atrial electrophysiology using whole-cell patch-clamp electrophysiology experiments along with assessment of Kv1.5, Kv4.2, and KChIP2 transcripts and protein profiles using real-time quantitative RT-PCR and Western blotting. Our data showed that induction of hyperoxia for 3 days in mice showed larger outward potassium currents with shorter action potential durations (APD). This increase in current densities is due to significant increase in ultrarapid delayed rectifier outward K⁺ currents (I_Kur ) and rapidly activating, rapidly inactivating transient outward K+ current (I_to ) densities. We also observed a significant increase in both transcripts and protein levels of Kv1.5 and KChIP2 in hyperoxia treated atrial cardiomyocytes, whereas no significant change was observed in Kv4.2 transcripts or protein. The data presented here further support our previous findings that hyperoxia induces not only ventricular remodeling, but also atrial electrical remodeling.

Regulation of the angiotensin II-p22phox-reactive oxygen species signaling pathway, apoptosis and 8-oxoguanine-DNA glycosylase 1 retrieval in hyperoxia-induced lung injury and fibrosis in rats

The present study was designed to explore the impact of hyperoxia on lung injury and fibrosis via the angiotensin II (AngII)-p22phox-reactive oxygen species (ROS) signaling pathway, apoptosis and 8-oxoguanine-DNA glycosylase 1 (OGG1) repair enzyme. Newborn Sprague-Dawley rats were randomly divided in the newborn air group, newborn hyperoxia group and newborn intervention group, the latter of which was administered the chymotrypsin inhibitor, 2-(5-formylamino-6-oxo-2-phenyl-1, 6-dihydropyrimidine-1-yl)-N-[4-dioxo-1-phenyl-7-(2-pyridyloxy)] 2-heptyl-acetamide (NK3201). A group of adult rats also received hyperoxic treatment. Histomorphological changes in lung tissues were dynamically observed. AngII, ROS, angiotensin type 1 receptor (AT₁R) and p22phox messenger RNA (mRNA) levels, and OGG1 and peroxisome proliferator-activated receptor-γ (PPARγ) protein levels in the lung tissues were detected at various times after hyperoxia. Hyperoxia led to traumatic changes in the lungs of newborn rats that resulted in decreased viability, increased mortality, morphological changes and the apoptosis of alveolar type II epithelial cells (AT-II), as well as increased expression levels of AngII, AT₁R and p22phox, which would ultimately lead to secondary diseases. NK3201 significantly inhibited the hyperoxia-induced increased expression of AngII, AT₁R and p22phox and further promoted OGG1 and PPARγ protein expression, thus reducing the intrapulmonary ROS level, the apoptotic index and caspase-3 levels. However, the adult hyperoxia group only exhibited tachypnea and reduced viability. This study suggested that the AngII-p22phox-ROS signaling pathway, PPARγ and OGG1 together contributed to the hyperoxia-induced lung injury and that NK3201 was able to reverse the effects of hyperoxia.

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.

The Succinate Receptor GPR91 Is Involved in Pressure Overload-Induced Ventricular Hypertrophy

Background

Pulmonary arterial hypertension is characterized by increased pressure overload that leads to right ventricular hypertrophy (RVH). GPR91 is a formerly orphan G-protein-coupled receptor (GPCR) that has been characterized as a receptor for succinate; however, its role in RVH remains unknown.

Methods and Results

We investigated the role of succinate-GPR91 signaling in a pulmonary arterial banding (PAB) model of RVH induced by pressure overload in SD rats. GPR91 was shown to be located in cardiomyocytes. In the sham and PAB rats, succinate treatment further aggravated RVH, up-regulated RVH-associated genes and increased p-Akt/t-Akt levels in vivo. In vitro, succinate treatment up-regulated the levels of the hypertrophic gene marker anp and p-Akt/t-Akt in cardiomyocytes. All these effects were inhibited by the PI3K antagonist wortmannin both in vivo and in vitro. Finally, we noted that the GPR91-PI3K/Akt axis was also up-regulated compared to that in human RVH.

Conclusions

Our findings indicate that succinate-GPR91 signaling may be involved in RVH via PI3K/Akt signaling in vivo and in vitro. Therefore, GPR91 may be a novel therapeutic target for treating pressure overload-induced RVH.

Mechanical Stress and the Induction of Lung Fibrosis via the Midkine Signaling Pathway

RATIONALE

Lung-protective ventilatory strategies have been widely used in patients with acute respiratory distress syndrome (ARDS), but the ARDS mortality rate remains unacceptably high and there is no proven pharmacologic therapy.

OBJECTIVES

Mechanical ventilation can induce oxidative stress and lung fibrosis, which may contribute to high dependency on ventilator support and increased ARDS mortality. We hypothesized that the novel cytokine, midkine (MK), which can be up-regulated in oxidative stress, plays a key role in the pathogenesis of ARDS-associated lung fibrosis.

METHODS

Blood samples were collected from 17 patients with ARDS and 10 healthy donors. Human lung epithelial cells were challenged with hydrogen chloride followed by mechanical stretch for 72 hours. Wild-type and MK gene-deficient (MK(-/-)) mice received two-hit injury of acid aspiration and mechanical ventilation, and were monitored for 14 days.

MEASUREMENTS AND MAIN RESULTS

Plasma concentrations of MK were higher in patients with ARDS than in healthy volunteers. Exposure to mechanical stretch of lung epithelial cells led to an epithelial-mesenchymal transition profile associated with increased expression of angiotensin-converting enzyme, which was attenuated by silencing MK, its receptor Notch2, or NADP reduced oxidase 1. An increase in collagen deposition and hydroxyproline level and a decrease in lung tissue compliance seen in wild-type mice were largely attenuated in MK(-/-) mice.

CONCLUSIONS

Mechanical stretch can induce an epithelial-mesenchymal transition phenotype mediated by the MK-Notch2-angiotensin-converting enzyme signaling pathway, contributing to lung remodeling. The MK pathway is a potential therapeutic target in the context of ARDS-associated lung fibrosis.

Therapeutic potential of soluble guanylate cyclase modulators in neonatal chronic lung disease

Supplemental oxygen after premature birth results in aberrant airway, alveolar, and pulmonary vascular development with an increased risk for bronchopulmonary dysplasia, and development of wheeze and asthma, pulmonary hypertension, and chronic obstructive pulmonary disease in survivors. Although stimulation of the nitric oxide (NO)-soluble guanylate cyclase (sGC)-cGMP signal transduction pathway has significant beneficial effects on disease development in animal models, so far this could not be translated to the clinic. Oxidative stress reduces the NO-sGC-cGMP pathway by oxidizing heme-bound sGC, resulting in inactivation or degradation of sGC. Reduced sGC activity and/or expression is associated with pathology due to premature birth, oxidative stress-induced lung injury, including impaired alveolar maturation, smooth muscle cell (SMC) proliferation and contraction, impaired airway relaxation and vasodilation, inflammation, pulmonary hypertension, right ventricular hypertrophy, and an aggravated response toward hyperoxia-induced neonatal lung injury. Recently, Britt et al. (10) demonstrated that histamine-induced Ca(2+) responses were significantly elevated in hyperoxia-exposed fetal human airway SMCs compared with normoxic controls and that this hyperoxia-induced increase in the response was strongly reduced by NO-independent stimulation and activation of sGC. These recent studies highlight the therapeutic potential of sGC modulators in the treatment of preterm infants for respiratory distress with supplemental oxygen. Such treatment is aimed at improving aberrant alveolar and vascular development of the neonatal lung and preventing the development of wheezing and asthma in survivors of premature birth. In addition, these studies highlight the suitability of fetal human airway SMCs as a translational model for pathological airway changes in the neonate.

Genome-wide association meta-analysis identifies five modifier loci of lung disease severity in cystic fibrosis

The identification of small molecules that target specific CFTR variants has ushered in a new era of treatment for cystic fibrosis (CF), yet optimal, individualized treatment of CF will require identification and targeting of disease modifiers. Here we use genome-wide association analysis to identify genetic modifiers of CF lung disease, the primary cause of mortality. Meta-analysis of 6,365 CF patients identifies five loci that display significant association with variation in lung disease. Regions on chr3q29 (MUC4/MUC20; P=3.3 × 10(-11)), chr5p15.3 (SLC9A3; P=6.8 × 10(-12)), chr6p21.3 (HLA Class II; P=1.2 × 10(-8)) and chrXq22-q23 (AGTR2/SLC6A14; P=1.8 × 10(-9)) contain genes of high biological relevance to CF pathophysiology. The fifth locus, on chr11p12-p13 (EHF/APIP; P=1.9 × 10(-10)), was previously shown to be associated with lung disease. These results provide new insights into potential targets for modulating lung disease severity in CF.

A review of recent developments and applications of morphometry/stereology in lung research

Design-based stereology is the gold standard of morphometry in lung research. Here, we analyze the current use of morphometric and stereological methods in lung research and provide an overview on recent methodological developments and biological observations made by the use of stereology. Based on this analysis we hope to provide useful recommendations for a good stereological practice to further the use of advanced and unbiased stereological methods.

Recent advances in the mechanisms of lung alveolarization and the pathogenesis of bronchopulmonary dysplasia

Alveolarization is the process by which the alveoli, the principal gas exchange units of the lung, are formed. Along with the maturation of the pulmonary vasculature, alveolarization is the objective of late lung development. The terminal airspaces that were formed during early lung development are divided by the process of secondary septation, progressively generating an increasing number of alveoli that are of smaller size, which substantially increases the surface area over which gas exchange can take place. Disturbances to alveolarization occur in bronchopulmonary dysplasia (BPD), which can be complicated by perturbations to the pulmonary vasculature that are associated with the development of pulmonary hypertension. Disturbances to lung development may also occur in persistent pulmonary hypertension of the newborn in term newborn infants, as well as in patients with congenital diaphragmatic hernia. These disturbances can lead to the formation of lungs with fewer and larger alveoli and a dysmorphic pulmonary vasculature. Consequently, affected lungs exhibit a reduced capacity for gas exchange, with important implications for morbidity and mortality in the immediate postnatal period and respiratory health consequences that may persist into adulthood. It is the objective of this Perspectives article to update the reader about recent developments in our understanding of the molecular mechanisms of alveolarization and the pathogenesis of BPD.

Animal models of bronchopulmonary dysplasia. The term rat models

Bronchopulmonary dysplasia (BPD) is the chronic lung disease of prematurity that affects very preterm infants. Although advances in perinatal care have enabled the survival of infants born as early as 23-24 wk of gestation, the challenge of promoting lung growth while protecting the ever more immature lung from injury is now bigger. Consequently, BPD remains one of the most common complications of extreme prematurity and still lacks specific treatments. Progress in our understanding of BPD and the potential of developing therapeutic strategies have arisen from large (baboons, sheep, and pigs) and small (rabbits, rats, and mice) animal models. This review focuses specifically on the use of the rat to model BPD and summarizes how the model is used in various research studies and the advantages and limitations of this particular model, and it highlights recent therapeutic advances in BPD by using this rat model.