Prior hypoxia prevents downregulation of ACE-2 by hyperoxia in fetal human lung fibroblasts

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.

Angiotensin II can trigger HSC-LX2 pyroptosis through both classical and non-classical pathways

BACKGROUND

Current evidence suggests that liver fibrosis is reversible even at late stages. Pyroptosis is reportedly regulated by classical and non-classical pathways and is also involved in the activation of the human hepatic stellate cell line LX2. This study sought to identify regulatory pathways that pyroptosis of HSC during AngII-ROS-induced HSC activation and provides novel insights for anti-fibrosis therapy by targeting HSC.

MATERIALS AND METHODS

All experiments were conducted in HSC-LX2. The expressions of α-SMA, NLRP3, Caspases-1, -4, -5, ASC and GSDMD-N were detected in HSC-LX2 cells induced with AngII by Western blot and qRT-PCR. CCK8 was used to detect cell proliferation and activity. 2'-7'dichlorofluorescin diacetate (DCFH-DA) was used to measure ROS generation. An LDH assay kit was used to detect LDH released from damaged cells, and ELISA was used to quantify IL-18 and IL-1β levels.

RESULTS

After AngII stimulation, HSC-LX2 cell viability, ROS, LDH, IL-18, and IL-1β were increased compared with Control group. At the same time, the protein and mRNA levels of α-SMA, NLRP3, Caspases-1, -4, -5, ASC and GSDMD-N were increased. In addition, after NAC and NSA treatment, LDH, IL-18 and IL-1β levels and the protein and mRNA expression of α-SMA, Caspases-4 and -5, and GSDMD-N were decreased.

CONCLUSION

HSC-LX2 pyroptosis induced by AngII-ROS is mediated by the classical pathway involving NLRP3/Caspase-1 and the non-classical pathway involving Caspases-4 and -5. Our results provide compelling evidence that AngII could activate Caspases-4 and -5 by producing ROS.

Stem-Cell Therapy for Bronchopulmonary Dysplasia (BPD) in Newborns

Premature newborns are at a higher risk for the development of respiratory distress syndrome (RDS), acute lung injury (ALI) associated with lung inflammation, disruption of alveolar structure, impaired alveolar growth, lung fibrosis, impaired lung angiogenesis, and development of bronchopulmonary dysplasia (BPD) with severe long-term developmental adverse effects. The current therapy for BPD is limited to supportive care including high-oxygen therapy and pharmacotherapy. Recognizing more feasible treatment options to improve lung health and reduce complications associated with BPD is essential for improving the overall quality of life of premature infants. There is a reduction in the resident stem cells in lungs of premature infants with BPD, which strongly suggests a critical role of stem cells in BPD pathogenesis; this warrants the exploration of the potential therapeutic use of stem-cell therapy. Stem-cell-based therapies have shown promise for the treatment of many pathological conditions including acute lung injury and BPD. Mesenchymal stem cells (MSCs) and MSC-derived extracellular vesicles (EVs) including exosomes are promising and effective therapeutic modalities for the treatment of BPD. Treatment with MSCs and EVs may help to reduce lung inflammation, improve pulmonary architecture, attenuate pulmonary fibrosis, and increase the survival rate.

Alternative RAS in Various Hypoxic Conditions: From Myocardial Infarction to COVID-19

Alternative branches of the classical renin–angiotensin–aldosterone system (RAS) represent an important cascade in which angiotensin 2 (AngII) undergoes cleavage via the action of the angiotensin-converting enzyme 2 (ACE2) with subsequent production of Ang(1-7) and other related metabolites eliciting its effects via Mas receptor activation. Generally, this branch of the RAS system is described as its non-canonical alternative arm with counterbalancing actions to the classical RAS, conveying vasodilation, anti-inflammatory, anti-remodeling and anti-proliferative effects. The implication of this branch was proposed for many different diseases, ranging from acute cardiovascular conditions, through chronic respiratory diseases to cancer, nonetheless, hypoxia is one of the most prominent common factors discussed in conjugation with the changes in the activity of alternative RAS branches. The aim of this review is to bring complex insights into the mechanisms behind the various forms of hypoxic insults on the activity of alternative RAS branches based on the different duration of stimuli and causes (acute vs. intermittent vs. chronic), localization and tissue (heart vs. vessels vs. lungs) and clinical relevance of studied phenomenon (experimental vs. clinical condition). Moreover, we provide novel insights into the future strategies utilizing the alternative RAS as a diagnostic tool as well as a promising pharmacological target in serious hypoxia-associated cardiovascular and cardiopulmonary diseases.

New perspectives on angiotensin-converting enzyme 2 and its related diseases

Since the worldwide outbreak of coronavirus disease 2019, angiotensin-converting enzyme 2 (ACE2) has received widespread attention as the cell receptor of the severe acute respiratory syndrome coronavirus 2 virus. At the same time, as a key enzyme in the renin-angiotensin-system, ACE2 is considered to be an endogenous negative regulator of vasoconstriction, proliferation, fibrosis, and proinflammation caused by the ACE-angiotensin II-angiotensin type 1 receptor axis. ACE2 is now implicated as being closely connected to diabetes, cardiovascular, kidney, and lung diseases, and so on. This review covers the available information on the host factors regulating ACE2 and discusses its role in a variety of pathophysiological conditions in animal models and humans.

Regulation of ACE-2 enzyme by hyperoxia in lung epithelial cells by post-translational modification

BACKGROUND

Bronchopulmonary Dysplasia (BPD) occurs in premature neonates with respiratory distress who require supplemental oxygen in the first days after birth. BPD involves uniform arrest of alveolar development and variable interstitial cellularity and/or fibroproliferation. Previous studies by our lab showed that the enzyme, angiotensin converting enzyme-2 (ACE-2) and its product Ang1-7 exerting action on the receptor Mas oncogene in what is known as ACE-2/Mas axis is protective to lung cells. We also showed that ACE-2 is expressed in fetal human lung fibroblasts but is significantly decreased by hyperoxic gas lung injury, an effect caused by ACE-2 enzyme shedding mediated by TNF-alpha-converting enzyme (TACE/ADAM17). However, no reports yet exist about the regulation of ACE-2 in the alveolar epithelia in hyperoxic lung injury.

OBJECTIVE

In this study we aim to define the effects of hyperoxic lung injury on the protective ACE-2 enzyme in the human lung alveolar epithelial cell line A549.

DESIGN/METHODS

Cultured A549 cells were exposed to hyperoxia (95% O2) or normoxia (21% O2) for 3 or 7 days in serum-free nutrient media. Cells were lysed and culture media were collected to test for cellular ACE-2 enzymatic activity and for ACE-2, Mas receptor, TACE/ADAM17, and ubiquitin proteins abundance by immunoblotting. Cells were harvested in Trizol for RNA extraction and ACE-2 qRT-PCR. Whole cell extracts of A549 cell line was used for ACE-2 immunoprecipitation and subsequent ubiquitin immunoblotting.

RESULTS

Total ubiquitinated proteins were increased by hyperoxia treatment, while ACE-2 and Mas receptor proteins abundance and ACE-2 enzymatic activity were decreased significantly in A549 cells exposed to hyperoxia relative to the normoxia controls. The percent decrease in ACE-2 activity corresponded with increased time of hyperoxic gas exposure. However, in contrast to our data from lung fibroblasts, no significant change was noted in ACE-2 protein released into the media or in ACE-2 mRNA levels by the hyperoxic treatment. Ubiquitin immunoreactive bands were detectable in the ACE-2 immunoprecipitate.

CONCLUSIONS

These data suggest that hyperoxic exposure of the lung epithelial cells decreases the protective enzyme ACE-2 by cell type specific mechanisms independent of shedding by TACE/ADAM17. The data also suggest a regulatory level of ACE-2 downstream of transcription may involve ACE-2 ubiquitination and targeting for degradation.

Angiotensin Converting Enzyme-2 (ACE-2) role in disease and future in research

Coronavirus Disease 2019 (COVID-19) is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Like the 2002-2003 epidemic severe acute respiratory syndrome coronavirus (SARS-CoV), angiotensin converting enzyme-2 (ACE-2) has been identified as the SARS-CoV-2 receptor.^1-3 The virus docks into host cell via its spike protein binding to ACE-2 and undergoes proteolytic cleavage by TMPRSS2 protease to facilitate membrane fusion. The spike protein binding to ACE-2 has been shown to be stronger in the novel SARS-CoV-2 virus.¹ This review will present an overview of ACE-2 biology.

Geographic components of SARS-CoV-2 expansion: a hypothesis

The emergence of COVID-19 infection (caused by the SARS-CoV-2 virus) in Wuhan, China in the latter part of 2019 has, within a relatively short time, led to a global pandemic. Amidst the initial spread of SARS-CoV-2 across Asia, an epidemiologic trend emerged in relation to high altitude (HA) populations. Compared with the rest of Asia, SARS-CoV-2 exhibited attenuated rates of expansion with limited COVID-19 infection severity along the Tibetan plateau. These characteristics were soon evident in additional HA regions across Bolivia, central Ecuador, Nepal, Bhutan, and the Sichuan province of mainland China. This mini-review presents a discussion surrounding attributes of the HA environment, aspects of HA physiology, as well as, genetic variations among HA populations which may provide clues for this pattern of SARS-CoV-2 expansion and COVID-19 infection severity. Explanations are provided in the hypothetical, albeit relevant historical evidence is provided to create a foundation for future research.

Application of System Biology to Explore the Association of Neprilysin, Angiotensin-Converting Enzyme 2 (ACE2), and Carbonic Anhydrase (CA) in Pathogenesis of SARS-CoV-2

BACKGROUND

Coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) appears with common symptoms including fever, dry cough, and fatigue, as well as some less common sysmptoms such as loss of taste and smell, diarrhea, skin rashes and discoloration of fingers. COVID-19 patients may also suffer from serious symptoms including shortness of breathing, chest pressure and pain, as well as loss of daily routine habits, pointing out to a sever reduction in the quality of life. COVID-19 has afftected almost all countries, however, the United States contains the highest number of infection (> 1,595,000 cases) and deaths cases (> 95,000 deaths) in the world until May 21, 2020. Finding an influential treatment strategy against COVID-19 can be facilitated through better understanding of the virus pathogenesis and consequently interrupting the biochemical pathways that the virus may play role in human body as the current reservoir of the virus.

RESULTS

In this study, we combined system biology and bioinformatic approaches to define the role of coexpression of angiotensin-converting enzyme 2 (ACE2), neprilysin or membrane metallo-endopeptidase (MME), and carbonic anhydrases (CAs) and their association in the pathogenesis of SARS-CoV-2. The results revealed that ACE2 as the cellular attachment site of SARS-CoV-2, neprilysin, and CAs have a great contribution together in the renin angiotensin system (RAS) and consequently in pathogenesis of SARS-CoV-2 in the vital organs such as respiratory, renal, and blood circulation systems. Any disorder in neprilysin, ACE2, and CAs can lead to increase of CO2 concentration in blood and respiratory acidosis, induction of pulmonary edema and heart and renal failures.

CONCLUSIONS

Due to the presence of ACE2-Neprilysin-CA complex in most of vital organs and as a receptor of COVID-19, it is expected that most organs are affected by SARS-CoV-2 such as inflammation and fibrosis of lungs, which may conversely affect their vital functions, temporary or permanently, sometimes leading to death. Therefore, ACE2-Neprilysin-CA complex could be the key factor of pathogenesis of SARS-CoV-2 and may provide us useful information to find better provocative and therapeutic strategies against COVID-19.

Oxygen injury in neonates: which is worse? hyperoxia, hypoxia, or alternating hyperoxia/hypoxia

Premature birth results in an increased risk of respiratory distress and often requires oxygen therapy. While the supplemental oxygen has been implicated as a cause of bronchopulmonary dysplasia (BPD), in clinical practice this supplementation usually only occurs after the patient's oxygen saturation levels have dropped. The effect of hyperoxia on neonates has been extensively studied. However, there is an unanswered fundamental question: which has the most impact-hyperoxia, hypoxia or fluctuating oxygen levels? In this review, we will summarize the reported effect of hypoxia, hyperoxia or a fluctuation of oxygen levels (hypoxia/hyperoxia cycling) in preterm neonates, with special emphasis on the lungs.

Activation of mas restores hyperoxia-induced loss of lung epithelial barrier function through inhibition of apoptosis

BACKGROUND

Neonatal therapy with a high concentration of oxygen (hyperoxia) is a known cause of bronchopulmonary dysplasia (BPD). BPD is characterized by increased pulmonary permeability and diffuse infiltration of various inflammatory cells. Disruption of the epithelial barrier may lead to altered pulmonary permeability and airways fluid accumulation. Mas receptor is a component of the renin angiotensin system and is the receptor for the protective endogenous peptide angiotensin 1-7. The activation of the Mas receptor was previously shown to have protective pulmonary responses. However, the effect of Mas receptor activation on epithelial barrier integrity has not been tested.

OBJECTIVE

To determine the effects of hyperoxia with or without Mas receptor activation on epithelial cell barrier integrity.

DESIGN/METHODS

Human epithelial cell line A549 was cultured on transwell polycarbonate porous membrane to confluence and treated with 95% oxygen (hyperoxia) for 72 hours with or without the Mas receptor agonist (AVE0991), or the apoptotic inhibitors Z-VAD-FMK or aurintricarboxylic acid. The cells were then challenged with Rhodamine labeled bovine serum albumin (Rh-BSA) on one side of the membrane. Fluorescent quantitation of Rh-BSA (albumin flux) was performed on the media in the other side of the membrane 3 hours later and was compared with 21% oxygen (Normoxia) control group. A549 cells were also cultured with or without AVE0991 in hyperoxia or normoxia and used for nuclear fragmentation apoptosis assay using propidium iodide staining.

RESULTS

Hyperoxia induced an increase in albumin flux that was significantly prevented by AVE0991 treatment and by the apoptosis inhibitors. AVE0991 also significantly decreased the hyperoxia-induced nuclear fragmentation.

CONCLUSION

These results suggest that hyperoxia causes a disruption in the epithelial barrier integrity, and that this disruption is inhibited by the Mas receptor agonist AVE0991 through inhibition of epithelial apoptosis. These results reveal a novel potential drug for BPD and pulmonary edema treatment.

Degradation of Lung Protective Angiotensin Converting Enzyme-2 by Meconium in Human Alveolar Epithelial Cells: A Potential Pathogenic Mechanism in Meconium Aspiration Syndrome

BACKGROUND

Pancreatic digestive enzymes present in meconium might be responsible for meconium-induced lung injury. The local Renin Angiotensin System plays an important role in lung injury and inflammation. Particularly, angiotensin converting enzyme-2 (ACE-2) has been identified as a protective lung enzyme against the insult. ACE-2 converts pro-apoptotic Angiotensin II to anti-apoptotic Angiotensin 1-7. However, the effect of meconium on ACE-2 has never been studied before.

OBJECTIVE

To study the effect of meconium on ACE-2, and whether inhibition of proteolytic enzymes present in the meconium reverses its effects on ACE-2.

METHODS

Alveolar epithelial A549 cells were exposed to F-12 medium, 2.5% meconium, meconium + a protease inhibitor cocktail (PIc) and PIc alone for 16 h. At the end of incubation, apoptosis was measured with a nuclear fragmentation assay and cell lysates were collected for ACE-2 immunoblotting and enzyme activity.

RESULTS

Meconium caused a fourfold increase in apoptotic nuclei (p < 0.001). The pro-apoptotic effect of meconium can be reversed by PIc. Meconium reduced ACE-2 enzyme activity by cleaving ACE-2 into a fragment detected at ~ 37 kDa by immunoblot. PIc prevented the degradation of ACE-2 and restored 50% of ACE-2 activity (p < 0.05).

CONCLUSION

These data suggest that meconium causes degradation of lung protective ACE-2 by proteolytic enzymes present in meconium, since the effects of meconium can be reversed by PIc.

The renin angiotensin system in liver and lung: impact and therapeutic potential in organ fibrosis

Liver and lung fibrosis are two main organ diseases that are of particular importance in both Egypt and the US. Hepatitis C Virus "HCV" infection and idiopathic pulmonary fibrosis (IPF) are fibrotic diseases of the liver and lung respectively. The liver and lung are reported in literature to share many immune/inflammatory responses to damage through the lung-liver axis. Most importantly, HCV was shown to enhance the development of IPF and is considered one of the risk factors for IPF. The renin angiotensin system (RAS) plays a critical role in the fibrogenesis and inflammation damage of many organs including liver and lung. The relatively recently identified component of RAS, angiotensin converting enzyme-2 (ACE-2), has shown a promising therapeutic potential in models of liver and pulmonary fibrosis. This article reviews the role of RAS in organ fibrosis with focus on role of ACE-2 in fibrotic diseases of the liver and the lung.

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.

Roles of the Angiotensin System in Neonatal Lung Injury and Disease

The renin-angiotensin system (RAS) has long been known as a regulator of blood pressure and fluid homeostasis. In past several decades, local renin-angiotensin systems have been discovered in various tissues and novel actions of angiotensin II (ANGII) have emerged as an immunomodulator and profibrotic molecule. The enzyme responsible for its synthesis, angiotensin-converting-enzyme (ACE), is present in high concentrations in lung tissue. ACE cleaves angiotensin I (ANG I) to generate angiotensin II (ANGII), whereas ACE2 inactivates ANGII and is a negative regulator of the system. The RAS has been implicated in the pathogenesis of pulmonary hypertension, acute lung injury and experimental lung fibrosis. Recent studies in animal and humans indicate that the RAS also plays a critical role in fetal and neonatal lung diseases. Further investigations are needed to better understand the role of RAS, ACE and ACE-2 in neonatal lung injury. With more clarity and understanding, the RAS and/or ACE-2 may ultimately prove to constitute potential therapeutic targets for the treatment of neonatal lung diseases. This manuscript reviews the evidence supporting a role for RAS in neonatal lung injury and discusses new possibilities for therapeutic approaches.

The unfolded protein response controls ER stress-induced apoptosis of lung epithelial cells through angiotensin generation

Recent work from this laboratory showed that endoplasmic reticulum (ER) stress-induced apoptosis of alveolar epithelial cells (AECs) is regulated by the autocrine angiotensin (ANG)II/ANG1-7 system. The proteasome inhibitor MG132 or surfactant protein C (SP-C) BRICHOS domain mutation G100S induced apoptosis in human AECs by activating the proapoptotic cathepsin D and reducing antiapoptotic angiotensin converting enzyme-2 (ACE-2). This study tested the hypothesis that ER stress-induced apoptosis of human AECs might be mediated by influence of the unfolded protein response (UPR) on the autocrine ANGII/ANG1-7 system. A549 cells were challenged with MG132 or SP-C BRICHOS domain mutant G100S to induce ER stress and activation of UPR pathways. The results showed that either MG132 or G100S SP-C mutation activated all three canonical pathways of the UPR (IRE1/XBP1, ATF6, and PERK/eIF2α), which led to a significant increase in cathepsin D or in TACE (an ACE-2 ectodomain shedding enzyme) and eventually caused AEC apoptosis. However, ER stress-induced AEC apoptosis could be prevented by chemical chaperone or by UPR blockers. It is also suggested that ATF6 and IRE1 pathways might play important role in regulation of angiotensin system. These data demonstrate that ER stress induces apoptosis in human AECs through mediation of UPR pathways, which in turn regulate the autocrine ANGII/ANG1-7 system. They also demonstrated that ER stress-induced AEC apoptosis can be blocked by inhibition of UPR signaling pathways.