Neonatal hyperoxia increases sensitivity of adult mice to bleomycin-induced lung fibrosis

FOXO4-D-Retro-Inverso targets extracellular matrix production in fibroblasts and ameliorates bleomycin-induced pulmonary fibrosis in mice

Pulmonary fibrosis (PF) occurs in various end stages of lung disease, and it is characterized by persistent scarring of the lung parenchyma with excessive deposition of extracellular matrix (ECM), leading to degressive quality of life and earlier mortality. FOXO4-D-Retro-Inverso (FOXO4-DRI), a synthesis peptide as a specific FOXO4 blocker, selectively induced dissociation of the FOXO4-p53 complex and nuclear exclusion of p53. Simultaneously, the p53 signaling pathway has been reported to activate in fibroblasts isolated from IPF fibrotic lung tissues and the p53 mutants cooperate with other factors that have the ability to disturb the synthesis of ECM. Yet, whether FOXO4-DRI influences the nuclear exclusion of p53 and then obstructs PF progress is still unknown. In this research, we explored the effect of FOXO4-DRI on bleomycin (BLM)-induced PF mouse model and activated fibroblasts model. The animal group of FOXO4-DRI therapeutic administration shows a milder pathologic change and less collagen deposition compared with the BLM-induced group. We also found the FOXO4-DRI resets the distribution of intranuclear p53 and concurrently decreased the total ECM proteins content. After further validation, FOXO4-DRI may well be a promising therapeutic approach to treating pulmonary fibrosis.

Low Dose Hyperoxia Primes Airways for Fibrosis in Mice after Influenza A Infection

It is well known that supplemental oxygen used to treat preterm infants in respiratory distress is associated with permanently disrupting lung development and the host response to influenza A virus (IAV). However, many infants who go home with normally functioning lungs are also at risk for hyperreactivity after a respiratory viral infection. We recently reported a new, low-dose hyperoxia mouse model (40% for 8 days; 40x8) that causes a transient change in lung function that resolves, rendering 40x8 adult animals functionally indistinguishable from room air controls. Here we reported that when infected with IAV, 40x8 mice display an early transient activation of TGFβ signaling and later airway hyperreactivity associated with peribronchial inflammation (profibrotic macrophages) and fibrosis compared to infected room air controls, suggesting neonatal oxygen induced hidden molecular changes that prime the lung for hyperreactive airways disease. While searching for potential activators of TGFβ signaling, we discovered that thrombospondin-1 (TSP-1) is elevated in naïve 40x8 mice compared to controls and localized to lung megakaryocytes and platelets before and during IAV infection. Elevated TSP-1 was also identified in human autopsy samples of former preterm infants with bronchopulmonary dysplasia. These findings reveal how low doses of oxygen that do not durably change lung function may prime it for hyperreactive airways disease by changing expression of genes, such as TSP-1, thus helping to explain why former preterm infants who have normal lung function are susceptible to airway obstruction and increased morbidity after viral infection.

Neonatal hyperoxia impairs adipogenesis of bone marrow-derived mesenchymal stem cells and fat accumulation in adult mice

Preterm birth is a risk factor for growth failure and development of respiratory disease in children and young adults. Their early exposure to oxygen may contribute to lung disease because adult mice exposed to hyperoxia as neonates display reduced lung function, changes in the host response to respiratory viral infections, and develop pulmonary hypertension and heart failure that shortens their lifespan. Here, we provide new evidence that neonatal hyperoxia also impairs growth by inhibiting fat accumulation. Failure to accumulate fat may reflect a systemic defect in adipogenic potential of stem cells because bone marrow-derived mesenchymal cells (BMSCs) isolated from the mice grew slower and were more oxidized compared to controls. They also displayed reduced capacity to accumulate lipid and differentiate into adipocytes. BMSCs from adult mice exposed to neonatal hyperoxia express lower levels of peroxisome proliferator-activated receptor gamma (PPARγ), a transcription factor that drives adipocyte differentiation. The defect in adipogenesis was rescued by expressing PPARγ in these cells. These findings reveal early life exposure to high levels of oxygen may suppresses fat accumulation and impair adipogenic differentiation upstream of PPARγ signaling, thus potentially contributing to growth failure seen in people born preterm.

Clocks, Viruses, and Immunity: Lessons for the COVID-19 Pandemic

Circadian rhythms are evolutionarily conserved anticipatory systems that allow the host to prepare and respond to threats in its environment. This article summarizes a European Biological Rhythms Society (EBRS) workshop held in July 2020 to review current knowledge of the interplay between the circadian clock and viral infections to inform therapeutic strategies against SARS-CoV-2 and COVID-19. A large body of work supports the role of the circadian clock in regulating various aspects of viral replication, host responses, and associated pathogenesis. We review the evidence describing the multifaceted role of the circadian clock, spanning host susceptibility, antiviral mechanisms, and host resilience. Finally, we define the most pressing research questions and how our knowledge of chronobiology can inform key translational research priorities.

Neonatal hyperoxia enhances age-dependent expression of SARS-CoV-2 receptors in mice

The severity of COVID-19 lung disease is higher in the elderly and people with pre-existing co-morbidities. People who were born preterm may be at greater risk for COVID-19 because their early exposure to oxygen (hyperoxia) at birth increases the severity of respiratory viral infections. Hyperoxia at birth increases the severity of influenza A virus infections in adult mice by reducing the number of alveolar epithelial type 2 (AT2) cells. Since AT2 cells express the SARS-CoV-2 receptors angiotensin converting enzyme (ACE2) and transmembrane protease/serine subfamily member 2 (TMPRSS2), their expression should decline as AT2 cells are depleted by hyperoxia. Instead, ACE2 was detected in airway Club cells and endothelial cells at birth, and then AT2 cells at one year of age. Neonatal hyperoxia stimulated expression of ACE2 in Club cells and in AT2 cells by 2 months of age. It also stimulated expression of TMPRSS2 in the lung. Increased expression of SARS-CoV-2 receptors was blocked by mitoTEMPO, a mitochondrial superoxide scavenger that reduced oxidative stress and DNA damage seen in oxygen-exposed mice. Our finding that hyperoxia enhances the age-dependent expression of SARS-CoV-2 receptors in mice helps explain why COVID-19 lung disease is greater in the elderly and people with pre-existing co-morbidities.

Oxygen Sensing and Viral Replication: Implications for Tropism and Pathogenesis

The ability to detect and respond to varying oxygen tension is an essential prerequisite to life. Several mechanisms regulate the cellular response to oxygen including the prolyl hydroxylase domain (PHD)/factor inhibiting HIF (FIH)-hypoxia inducible factor (HIF) pathway, cysteamine (2-aminoethanethiol) dioxygenase (ADO) system, and the lysine-specific demethylases (KDM) 5A and KDM6A. Using a systems-based approach we discuss the literature on oxygen sensing pathways in the context of virus replication in different tissues that experience variable oxygen tension. Current information supports a model where the PHD-HIF pathway enhances the replication of viruses infecting tissues under low oxygen, however, the reverse is true for viruses with a selective tropism for higher oxygen environments. Differences in oxygen tension and associated HIF signaling may play an important role in viral tropism and pathogenesis. Thus, pharmaceutical agents that modulate HIF activity could provide novel treatment options for viral infections and associated pathological conditions.

Early origins of lung disease: towards an interdisciplinary approach

The prenatal and perinatal environments can have profound effects on the development of chronic inflammatory diseases. However, mechanistic insight into how the early-life microenvironment can impact upon development of the lung and immune system and consequent initiation and progression of respiratory diseases is still emerging. Recent studies investigating the developmental origins of lung diseases have started to delineate the effects of early-life changes in the lung, environmental exposures and immune maturation on the development of childhood and adult lung diseases. While the influencing factors have been described and studied in mostly animal models, it remains challenging to pinpoint exactly which factors and at which time point are detrimental in lung development leading to respiratory disease later in life. To advance our understanding of early origins of chronic lung disease and to allow for proper dissemination and application of this knowledge, we propose four major focus areas: 1) policy and education; 2) clinical assessment; 3) basic and translational research; and 4) infrastructure and tools, and discuss future directions for advancement. This review is a follow-up of the discussions at the European Respiratory Society Research Seminar "Early origins of lung disease: towards an interdisciplinary approach" (Lisbon, Portugal, November 2019).

Bronchopulmonary dysplasia: what are its links to COPD?

Emerging evidence suggests that adverse early life events can affect long-term health trajectories throughout life. Preterm birth, in particular, is a significant early life event that affects approximately 10% of live births. Worldwide, prematurity is the number one cause of death in children less than 5 years of age and has been shown to disrupt normal lung development with lasting effects into adult life. Along with impaired lung development, interventions used to support gas exchange and other sequelae of prematurity can lead to the development of bronchopulmonary dysplasia (BPD). BPD is a chronic respiratory disease of infancy characterized by alveolar simplification, small airways disease, and pulmonary vascular changes. Although many survivors of BPD improve with age, survivors of BPD often have chronic lung disease characterized by airflow obstruction and intermittent pulmonary exacerbations. Long-term lung function trajectories as measured by FEV1 can be lower in children and adults with a history BPD. In this review, we discuss the epidemiology and manifestations of BPD and its long-term consequences throughout childhood and into adulthood. Available evidence suggests that disrupted lung development, genetic susceptibility and subsequent environment and infectious events that occur in prenatal and postnatal life likely increase the predisposition of children with BPD to develop early onset chronic obstructive pulmonary disease (COPD). The reviews of this paper are available via the supplemental material section.

Myeloid-derived Suppressor Cells Are Necessary for Development of Pulmonary Hypertension

Pulmonary hypertension (PH) complicates the care of patients with chronic lung disease, such as idiopathic pulmonary fibrosis (IPF), resulting in a significant increase in morbidity and mortality. Disease pathogenesis is orchestrated by unidentified myeloid-derived cells. We used murine models of PH and pulmonary fibrosis to study the role of circulating myeloid cells in disease pathogenesis and prevention. We administered clodronate liposomes to bleomycin-treated wild-type mice to induce pulmonary fibrosis and PH with a resulting increase in circulating bone marrow-derived cells. We discovered that a population of C-X-C motif chemokine receptor (CXCR) 2⁺ myeloid-derived suppressor cells (MDSCs), granulocytic subset (G-MDSC), is associated with severe PH in mice. Pulmonary pressures worsened despite improvement in bleomycin-induced pulmonary fibrosis. PH was attenuated by CXCR2 inhibition, with antagonist SB 225002, through decreasing G-MDSC recruitment to the lung. Molecular and cellular analysis of clinical patient samples confirmed a role for elevated MDSCs in IPF and IPF with PH. These data show that MDSCs play a key role in PH pathogenesis and that G-MDSC trafficking to the lung, through chemokine receptor CXCR2, increases development of PH in multiple murine models. Furthermore, we demonstrate pathology similar to the preclinical models in IPF with lung and blood samples from patients with PH, suggesting a potential role for CXCR2 inhibitor use in this patient population. These findings are significant, as there are currently no approved disease-specific therapies for patients with PH complicating IPF.

Quercetin attenuates the hyperoxic lung injury in neonatal mice: Implications for Bronchopulmonary dysplasia (BPD)

Quercetin (QU) is one of the most common flavonoids that are present in a wide variety of fruits, vegetables, and beverages. This compound possesses potent anti-inflammatory and anti-oxidant properties. Supplemental oxygen is routinely administered to premature infants with pulmonary insufficiency. However, hyperoxia is one of the major risk factors for the development of bronchopulmonary dysplasia (BPD), which is also termed chronic lung disease in premature infants. Currently, no preventive approaches have been reported against BPD. The treatment of BPD is notably limited to oxygen administration, ventilatory support, and steroids. Since QU has been shown to be effective in reducing inflammation and oxidative stress in various disease models, we hypothesized that the postnatal QU treatment of newborn mice will protect against hyperoxic lung injury by the upregulation of the phase I (CYP1A/B) and/or phase II, NADPH quinone reductase enzymes. Newborn C57BL/6J mice within 24 h of birth with the nursing dams were exposed to either 21% O₂ (air) and/or 85% O₂ (hyperoxia) for 7 days. The mice were treated, intraperitoneally (i.p.) once every other day with quercetin, at a concentration of 20 mg/kg, or saline alone from postnatal day (PND) 2-6. The mice were sacrificed on day 7, and lung and liver tissues were collected. The expression levels of CYP1A1, CYP1B1, NQO1 proteins and mRNA as well as the levels of MDA-protein adducts were analyzed in lung and liver tissues. The findings indicated that QU attenuated hyperoxia-mediated lung injury by reducing inflammation and improving alveolarization with decreased number of neutrophil and macrophage infiltration. The attenuation of this lung injury correlated with the upregulation of CYP1A1/CYP1B1/NQO1 mRNA, proteins and the down regulation of NF-kB levels and MDA-protein adducts in lung and liver tissues. The present study demonstrated the potential therapeutic value of quercetin in the prevention and/or treatment of BPD.

Alternative Progenitor Lineages Regenerate the Adult Lung Depleted of Alveolar Epithelial Type 2 Cells

An aberrant oxygen environment at birth increases the severity of respiratory viral infections later in life through poorly understood mechanisms. Here, we show that alveolar epithelial cell (AEC) 2 cells (AEC2s), progenitors for AEC1 cells, are depleted in adult mice exposed to neonatal hypoxia or hyperoxia. Airway cells expressing surfactant protein (SP)-C and ATP binding cassette subfamily A member 3, alveolar pod cells expressing keratin (KRT) 5, and pulmonary fibrosis were observed when these mice were infected with a sublethal dose of HKx31, H3N2 influenza A virus. This was not seen in infected siblings birthed into room air. Genetic lineage tracing studies in mice exposed to neonatal hypoxia or hyperoxia revealed pre-existing secretoglobin 1a1⁺ cells produced airway cells expressing SP-C and ATP binding cassette subfamily A member 3. Pre-existing Kr5⁺ progenitor cells produced squamous alveolar cells expressing receptor for advanced glycation endproducts, aquaporin 5, and T1α in alveoli devoid of AEC2s. They were not the source of KRT5⁺ alveolar pod cells. These oxygen-dependent changes in epithelial cell regeneration and fibrosis could be recapitulated by conditionally depleting AEC2s in mice using diphtheria A toxin and then infecting with influenza A virus. Likewise, airway cells expressing SP-C and alveolar cells expressing KRT5 were observed in human idiopathic pulmonary fibrosis. These findings suggest that alternative progenitor lineages are mobilized to regenerate the alveolar epithelium when AEC2s are severely injured or depleted by previous insults, such as an adverse oxygen environment at birth. Because these lineages regenerate AECs in spatially distinct compartments of a lung undergoing fibrosis, they may not be sufficient to prevent disease.

Adult Lysophosphatidic Acid Receptor 1-Deficient Rats with Hyperoxia-Induced Neonatal Chronic Lung Disease Are Protected against Lipopolysaccharide-Induced Acute Lung Injury

Aim: Survivors of neonatal chronic lung disease or bronchopulmonary dysplasia (BPD) suffer from compromised lung function and are at high risk for developing lung injury by multiple insults later in life. Because neonatal lysophosphatidic acid receptor-1 (LPAR1)-deficient rats are protected against hyperoxia-induced lung injury, we hypothesize that LPAR1-deficiency may protect adult survivors of BPD from a second hit response against lipopolysaccharides (LPS)-induced lung injury.

Methods: Directly after birth, Wistar control and LPAR1-deficient rat pups were exposed to hyperoxia (90%) for 8 days followed by recovery in room air. After 7 weeks, male rats received either LPS (2 mg kg⁻¹) or 0.9% NaCl by intraperitoneal injection. Alveolar development and lung inflammation were investigated by morphometric analysis, IL-6 production, and mRNA expression of cytokines, chemokines, coagulation factors, and an indicator of oxidative stress.

Results: LPAR1-deficient and control rats developed hyperoxia-induced neonatal emphysema, which persisted into adulthood, as demonstrated by alveolar enlargement and decreased vessel density. LPAR1-deficiency protected against LPS-induced lung injury. Adult controls with BPD exhibited an exacerbated response toward LPS with an increased expression of pro-inflammatory mRNAs, whereas LPAR1-deficient rats with BPD were less sensitive to this “second hit” with a decreased pulmonary influx of macrophages and neutrophils, interleukin-6 (IL-6) production, and mRNA expression of IL-6, monocyte chemoattractant protein-1, cytokine-induced neutrophil chemoattractant 1, plasminogen activator inhibitor-1, and tissue factor.

Conclusion: LPAR1-deficient rats have increased hyperoxia-induced BPD survival rates and, despite the presence of neonatal emphysema, are less sensitive to an aggravated “second hit” than Wistar controls with BPD. Intervening in LPA-LPAR1-dependent signaling may not only have therapeutic potential for neonatal chronic lung disease, but may also protect adult survivors of BPD from sequelae later in life.

The Oxygen Environment at Birth Specifies the Population of Alveolar Epithelial Stem Cells in the Adult Lung

Alveolar epithelial type II cells (AEC2) maintain pulmonary homeostasis by producing surfactant, expressing innate immune molecules, and functioning as adult progenitor cells for themselves and alveolar epithelial type I cells (AEC1). How the proper number of alveolar epithelial cells is determined in the adult lung is not well understood. Here, BrdU labeling, genetic lineage tracing, and targeted expression of the anti-oxidant extracellular superoxide dismutase in AEC2s are used to show how the oxygen environment at birth influences postnatal expansion of AEC2s and AEC1s in mice. Birth into low (12%) or high (≥60%) oxygen stimulated expansion of AEC2s through self-renewal and differentiation of the airway Scgb1a1 + lineage. This non-linear or hormesis response to oxygen was specific for the alveolar epithelium because low oxygen stimulated and high oxygen inhibited angiogenesis as defined by changes in V-cadherin and PECAM (CD31). Although genetic lineage tracing studies confirmed adult AEC2s are stem cells for AEC1s, we found no evidence that postnatal growth of AEC1s were derived from self-renewing Sftpc + or the Scbg1a1 + lineage of AEC2s. Taken together, our results show how a non-linear response to oxygen at birth promotes expansion of AEC2s through two distinct lineages. Since neither lineage contributes to the postnatal expansion of AEC1s, the ability of AEC2s to function as stem cells for AEC1s appears to be restricted to the adult lung. Stem Cells 2016;34:1396-1406.

Affect of Early Life Oxygen Exposure on Proper Lung Development and Response to Respiratory Viral Infections

Children born preterm often exhibit reduced lung function and increased severity of response to respiratory viruses, suggesting that premature birth has compromised proper development of the respiratory epithelium and innate immune defenses. Increasing evidence suggests that premature birth promotes aberrant lung development likely due to the neonatal oxygen transition occurring before pulmonary development has matured. Given that preterm infants are born at a point of time where their immune system is also still developing, early life oxygen exposure may also be disrupting proper development of innate immunity. Here, we review current literature in hopes of stimulating research that enhances understanding of how the oxygen environment at birth influences lung development and host defense. This knowledge may help identify those children at risk for disease and ideally culminate in the development of novel therapies that improve their health.

Activin A contributes to the development of hyperoxia-induced lung injury in neonatal mice

BACKGROUND

Bronchopulmonary dysplasia (BPD) is one of the leading causes of morbidity and mortality in babies born prematurely, yet there is no curative treatment. In recent years, a number of inhibitors against TGFβ signaling have been tested for their potential to prevent neonatal injury associated with hyperoxia, which is a contributing factor of BPD. In this study, we assessed the contribution of activin A-a member of the TGFβ superfamily-to the development of hyperoxia-induced lung injury in neonatal mice.

METHODS

We placed newborn C57Bl6 mouse pups in continuous hyperoxia (85% O2) to mimic many aspects of BPD including alveolar simplification and pulmonary inflammation. The pups were administered activin A receptor type IIB-Fc antagonist (ActRIIB-Fc) at 5 mg/kg or follistatin at 0.1 mg/kg on postnatal days 4, 7, 10, and 13.

RESULTS

Treatment with ActRIIB-Fc and follistatin protected against hyperoxia-induced growth retardation. ActRIIB-Fc also reduced pulmonary leukocyte infiltration, normalized tissue: airspace ratio and increased septal crest density. These findings were associated with reduced phosphorylation of Smad3 and decreased matrix metalloproteinase (MMP)-9 activity.

CONCLUSION

This study suggests that activin A signaling may contribute to the pathology of bronchopulmonary dysplasia.

Neonatal hyperoxia stimulates the expansion of alveolar epithelial type II cells

Supplemental oxygen used to treat infants born prematurely disrupts angiogenesis and is a risk factor for persistent pulmonary disease later in life. Although it is unclear how neonatal oxygen affects development of the respiratory epithelium, alveolar simplification and depletion of type II cells has been observed in adult mice exposed to hyperoxia between postnatal Days 0 and 4. Because hyperoxia inhibits cell proliferation, we hypothesized that it depleted the adult lung of type II cells by inhibiting their proliferation at birth. Newborn mice were exposed to room air (RA) or hyperoxia, and the oxygen-exposed mice were recovered in RA. Hyperoxia stimulated mRNA expressed by type II (Sftpc, Abca3) and type I (T1α, Aquaporin 5) cells and inhibited Pecam expressed by endothelial cells. 5-Bromo-2'-deoxyuridine labeling and fate mapping with enhanced green fluorescence protein controlled statically by the Sftpc promoter or conditionally by the Scgb1a1 promoter revealed increased Sftpc and Abca3 mRNA seen on Day 4 reflected an increase in expansion of type II cells shortly after birth. When mice were returned to RA, this expanded population of type II cells was slowly depleted until few were detected by 8 weeks. These findings reveal that hyperoxia stimulates alveolar epithelial cell expansion when it disrupts angiogenesis. The loss of type II cells during recovery in RA may contribute to persistent pulmonary diseases such as those reported in children born preterm who were exposed to supplemental oxygen.

Oxygen, gastrin-releasing Peptide, and pediatric lung disease: life in the balance

Excessive oxygen (O2) can cause tissue injury, scarring, aging, and even death. Our laboratory is studying O2-sensing pulmonary neuroendocrine cells (PNECs) and the PNEC-derived product gastrin-releasing peptide (GRP). Reactive oxygen species (ROS) generated from exposure to hyperoxia, ozone, or ionizing radiation (RT) can induce PNEC degranulation and GRP secretion. PNEC degranulation is also induced by hypoxia, and effects of hypoxia are mediated by free radicals. We have determined that excessive GRP leads to lung injury with acute and chronic inflammation, leading to pulmonary fibrosis (PF), triggered via ROS exposure or by directly treating mice with exogenous GRP. In animal models, GRP-blockade abrogates lung injury, inflammation, and fibrosis. The optimal time frame for GRP-blockade and the key target cell types remain to be determined. The concept of GRP as a mediator of ROS-induced tissue damage represents a paradigm shift about how O2 can cause injury, inflammation, and fibrosis. The host PNEC response in vivo may depend on individual ROS sensing mechanisms and subsequent GRP secretion. Ongoing scientific and clinical investigations promise to further clarify the molecular pathways and clinical relevance of GRP in the pathogenesis of diverse pediatric lung diseases.

Neonatal hyperoxia alters the host response to influenza A virus infection in adult mice through multiple pathways

Exposing preterm infants or newborn mice to high concentrations of oxygen disrupts lung development and alters the response to respiratory viral infections later in life. Superoxide dismutase (SOD) has been separately shown to mitigate hyperoxia-mediated changes in lung development and attenuate virus-mediated lung inflammation. However, its potential to protect adult mice exposed to hyperoxia as neonates against viral infection is not known. Here, transgenic mice overexpressing extracellular (EC)-SOD in alveolar type II epithelial cells are used to test whether SOD can alleviate the deviant pulmonary response to influenza virus infection in adult mice exposed to hyperoxia as neonates. Fibrotic lung disease, observed following infection in wild-type (WT) mice exposed to hyperoxia as neonates, was prevented by overexpression of EC-SOD. However, leukocyte recruitment remained excessive, and levels of monocyte chemoattractant protein (MCP)-1 remained modestly elevated following infection in EC-SOD Tg mice exposed to hyperoxia as neonates. Because MCP-1 is often associated with pulmonary inflammation and fibrosis, the host response to infection was concurrently evaluated in adult Mcp-1 WT and Mcp-1 knockout mice exposed to neonatal hyperoxia. In contrast to EC-SOD, excessive leukocyte recruitment, but not lung fibrosis, was dependent upon MCP-1. Our findings demonstrate that neonatal hyperoxia alters the inflammatory and fibrotic responses to influenza A virus infection through different pathways. Therefore, these data suggest that multiple therapeutic strategies may be needed to provide complete protection against diseases attributed to prematurity and early life exposure to oxygen.