Aberrant cGMP signaling persists during recovery in mice with oxygen-induced pulmonary hypertension

Emerging role of metabolic reprogramming in hyperoxia-associated neonatal diseases

Oxygen therapy is common during the neonatal period to improve survival, but it can increase the risk of oxygen toxicity. Hyperoxia can damage multiple organs and systems in newborns, commonly causing lung conditions such as bronchopulmonary dysplasia and pulmonary hypertension, as well as damage to other organs, including the brain, gut, and eyes. These conditions are collectively referred to as newborn oxygen radical disease to indicate the multi-system damage caused by hyperoxia. Hyperoxia can also lead to changes in metabolic pathways and the production of abnormal metabolites through a process called metabolic reprogramming. Currently, some studies have analyzed the mechanism of metabolic reprogramming induced by hyperoxia. The focus has been on mitochondrial oxidative stress, mitochondrial dynamics, and multi-organ interactions, such as the lung-gut, lung-brain, and brain-gut axes. In this article, we provide an overview of the major metabolic pathway changes reported in hyperoxia-associated neonatal diseases and explore the potential mechanisms of metabolic reprogramming. Metabolic reprogramming induced by hyperoxia can cause multi-organ metabolic disorders in newborns, including abnormal glucose, lipid, and amino acid metabolism. Moreover, abnormal metabolites may predict the occurrence of disease, suggesting their potential as therapeutic targets. Although the mechanism of metabolic reprogramming caused by hyperoxia requires further elucidation, mitochondria and the gut-lung-brain axis may play a key role in metabolic reprogramming.

How lung injury and therapeutic oxygen could alter white matter development

Developmental brain injury describes a spectrum of neurological pathologies resulting from either antenatal or perinatal injury. This includes both cognitive and motor defects that affect patients for their entire lives. Developmental brain injury can be caused by a spectrum of conditions including stroke, perinatal hypoxia-ischemia, and intracranial hemorrhage. Additional risk factors have been identified including very low birth weight, mechanical ventilation, and oxygen (O2 ) supplementation. In fact, infants with bronchopulmonary dysplasia, an inflammatory disease associated with disrupted lung development, have been shown to have decreased cerebral white matter and decreased intracranial volumes. Thus, there appears to be a developmental link between the lung, O2 , and the brain that leads to proper myelination. Here, we will discuss what is currently known about the link between O2 and myelination and how scientists are exploring mechanisms through which supplemental O2 and/or lung injury can affect brain development. Consideration of a link between the diseased lung and developing brain will allow clinicians to fine tune their approaches in managing preterm lung disease in order to optimize brain health.

Hyperoxia Induced Bronchopulmonary Dysplasia-Like Inflammation via miR34a-TNIP2-IL-1β Pathway

Lung injury induced by oxygen is a key contributor to the pathogenesis of preterm infant bronchopulmonary dysplasia (BPD). To date, there are comprehensive therapeutic strategy for this disease, but the underlying mechanism is still in progress. By using lentivirus, we constructed microRNA34a (miR34a)-overexpressing or knockdown A549 cell lines, and exposure to hyperoxia to mimic oxygen induce lung injury. In this study, we investigated 4 proinflammatory cytokines, interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), angiopoietin-1 (Ang-1), and Cyclooxygenase-2 (COX-2) in the secreted sputum of infants who received mechanical ventilation, and found that IL-1β was substantially elevated in the first week after oxygen therapy and with no significant decrease until the fourth week, while TNF-α, Ang-1, and COX-2 were increased in the first week but decreased quickly in the following weeks. In addition, in vitro assay revealed that hyperoxia significantly increased the expression of miR-34a, which positively regulated the proinflammatory cytokine IL-1β in a time- and concentration-dependent manner in A549 cells. Overexpressing or knockdown miR34 would exacerbate or inhibit production of IL-1β and its upstream NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome signaling pathway. Mechanically, it's found that TNFAIP3 interacting protein 2 (TNIP2), an inhibitor of nuclear factor κB (NF-κB), is a direct target of miR34a, negatively regulated activation of NLRP3 inflammasome and the production of IL-1β. Overexpressing TNIP2 ameliorated hyperoxia-induced production of IL-1β and cell apoptosis. Our findings suggest that TNIP2 may be a potential clinical marker in the diagnosis of BPD.

Inhibition of FABP4 attenuates hyperoxia-induced lung injury and fibrosis via inhibiting TGF-β signaling in neonatal rats

Bronchopulmonary dysplasia (BPD) is a chronic lung disease characterized by interrupted alveologenesis and alveolar simplification caused by oxygen therapy in premature infants. Metabolic dysfunction is involved in the pathogenesis of BPD. Fatty acid-binding protein 4 (FABP4) is significantly increased in specific lung tissues in patients with BPD. Therefore, we investigated whether BMS309403, an FABP4 inhibitor that can mitigate tissue fibrosis, can regulate pulmonary fibrotic processes in newborn rats exposed to hyperoxia. Newborn rat pups were exposed to room air (RA; 21% O₂ ) or 85% O₂ from 5 to 14 days of age and were then allowed to recover in RA until 29 days of age. They received intraperitoneal injection with placebo (phosphate-buffered saline [PBS]) or BMS 309403 (0.5 mg or 1.0 mg kg^-1 d^-1 ) every other day from 4 to 14 days of age then were divided into O₂ plus PBS or low dose or high dose and RA plus PBS or low dose or high dose groups. We assessed lung histology and evaluated lung collagen I, FABP4 as well as TGF-β1 expression at 14 and 29 days of age. In the hyperoxia injury-recovery model, prophylactic BMS309403 treatment reduced mean linear intercept values and FABP4 expression (p < 0.001). Prophylactic BMS309403 treatment mitigated pulmonary fibrosis and TGF-β1 expression immediately after hyperoxia exposure (p < 0.05). The attenuation of hyperoxia-induced alveolar developmental impairment and pulmonary fibrosis by FABP4 inhibition indicated that such inhibition has potential clinical and therapeutic applications.

Neonatal Extracellular Superoxide Dismutase Knockout Mice Increase Total Superoxide Dismutase Activity and VEGF Expression after Chronic Hyperoxia

Bronchopulmonary dysplasia (BPD) is a common lung disease affecting premature infants that develops after exposure to supplemental oxygen and reactive oxygen intermediates. Extracellular superoxide dismutase (SOD3) is an enzyme that processes superoxide radicals and has been shown to facilitate vascular endothelial growth factor (VEGF) and nitric oxide (NO) signaling in vascular endothelium. We utilized a mouse model of neonatal hyperoxic lung injury and SOD3 knockout (KO) mice to evaluate its function during chronic hyperoxia exposure. Wild-type age-matched neonatal C57Bl/6 (WT) and SOD3^−/− (KO) mice were placed in normoxia (21% FiO₂, RA) or chronic hyperoxia (75% FiO₂, O₂) within 24 h of birth for 14 days continuously and then euthanized. Lungs were harvested for histologic evaluation, as well as comparison of antioxidant enzyme expression, SOD activity, VEGF expression, and portions of the NO signaling pathway. Surprisingly, KO-O₂ mice survived without additional alveolar simplification, microvascular remodeling, or nuclear oxidation when compared to WT-O₂ mice. KO-O₂ mice had increased total SOD activity and increased VEGF expression when compared to WT-O₂ mice. No genotype differences were noted in intracellular antioxidant enzyme expression or the NO signaling pathway. These results demonstrate that SOD3 KO mice can survive prolonged hyperoxia without exacerbation of alveolar or vascular phenotype.

Exploration of the effect of pulmonary fibrosis on erectile function in rats: A study based on bioinformatics and experimental research

First, the bioinformatics database was used to predict the potential targets and signaling pathways of pulmonary fibrosis (PF) leading to erectile dysfunction (ED), and bleomycin sulfate was used to create a PF rat model. Then, enzyme-linked immunosorbent assay (ELISA), Western blotting, Real-time fluorescent quantitative reverse transcription polymerase chain reaction (RT-qPCR) were used to detect the expression of sex hormones and related proteins and mRNA, and Hematoxylin and eosin (H&E) staining was used to compare the pathological changes of penile tissue. The results showed that, compared with group A, cyclic guanosine phosphate (cGMP) content in group B decreased, protein kinase CGMP-dependent 1(PKG1) and nitric oxide synthase 3 (eNOS) protein and mRNA expression were down-regulated, and phosphodiesterase 5A (PDE5A) protein and mRNA expression was up-regulated (p < .05); the penile tissue of rats in group B had pathological damage. And there was no change in sex hormone-related indicators in the two groups (p > .05). Therefore, PF inhibits erectile function by inhibiting the cGMP-PKG pathway and reducing the expression of eNOS and PKG1 protein and mRNA. And by up-regulating the expression of PDE5A to impair erectile function.

Repurposing of the PDE5 Inhibitor Sildenafil for the Treatment of Persistent Pulmonary Hypertension in Neonates

Nitric oxide (NO), an important endogenous signaling molecule released from vascular endothelial cells and nerves, activates the enzyme soluble guanylate cyclase to catalyze the production of cyclic guanosine monophosphate (cGMP) from guanosine triphosphate. cGMP, in turn, activates protein kinase G to phosphorylate a range of effector proteins in smooth muscle cells that reduce intracellular Ca²⁺ levels to inhibit both contractility and proliferation. The enzyme phosphodiesterase type 5 (PDE5) curtails the actions of cGMP by hydrolyzing it into inactive 5'-GMP. Small molecule PDE5 inhibitors (PDE5is), such as sildenafil, prolong the availability of cGMP and therefore, enhance NO-mediated signaling. PDE5is are the first-line treatment for erectile dysfunction but are also now approved for the treatment of pulmonary arterial hypertension (PAH) in adults. Persistent pulmonary hypertension in neonates (PPHN) is currently treated with inhaled NO, but this is an expensive option and around 1/3 of newborns are unresponsive, resulting in the need for alternative approaches. Here the development, chemistry and pharmacology of PDE5is, the use of sildenafil for erectile dysfunction and PAH, are summarized and then current evidence for the utility of further repurposing of sildenafil, as a treatment for PPHN, is critically reviewed.

Endothelial to mesenchymal transition during neonatal hyperoxia-induced pulmonary hypertension

Bronchopulmonary dysplasia (BPD), a chronic lung disease in premature infants, results from mechanical ventilation and hyperoxia, amongst other factors. Although most BPD survivors can be weaned from supplemental oxygen, many show evidence of cardiovascular sequelae in adulthood, including pulmonary hypertension and pulmonary vascular remodeling. Endothelial-mesenchymal transition (EndoMT) plays an important role in mediating vascular remodeling in idiopathic pulmonary arterial hypertension. Whether hyperoxic exposure, a known mediator of BPD in rodent models, causes EndoMT resulting in vascular remodeling and pulmonary hypertension remains unclear. We hypothesized that neonatal hyperoxic exposure causes EndoMT, leading to the development of pulmonary hypertension in adulthood. To test this hypothesis, newborn mice were exposed to hyperoxia and then allowed to recover in room air until adulthood. Neonatal hyperoxic exposure gradually caused pulmonary vascular and right ventricle remodeling as well as pulmonary hypertension. Male mice were more susceptible to developing pulmonary hypertension compared to female mice, when exposed to hyperoxia as newborns. Hyperoxic exposure induced EndoMT in mouse lungs as well as in cultured lung microvascular endothelial cells (LMVECs) isolated from neonatal mice and human fetal donors. This was augmented in cultured LMVECs from male donors compared to those from female donors. Using primary mouse LMVECs, hyperoxic exposure increased phosphorylation of both Smad2 and Smad3, but reduced Smad7 protein levels. Treatment with a selective TGF-β inhibitor SB431542 blocked hyperoxia-induced EndoMT in vitro. Altogether, we show that neonatal hyperoxic exposure caused vascular remodeling and pulmonary hypertension in adulthood. This was associated with increased EndoMT. These novel observations provide mechanisms underlying hyperoxia-induced vascular remodeling and potential approaches to prevent BPD-associated pulmonary hypertension by targeting EndoMT. © 2020 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Therapies that enhance pulmonary vascular NO-signaling in the neonate

There are several pulmonary hypertensive diseases that affect the neonatal population, including persistent pulmonary hypertension of the newborn (PPHN) and bronchopulmonary dysplasia (BPD)-associated pulmonary hypertension (PH). While the indication for inhaled nitric oxide (iNO) use is for late-preterm and term neonates with PPHN, there is a suboptimal response to this pulmonary vasodilator in ~40% of patients. Additionally, there are no FDA-approved treatments for BPD-associated PH or for preterm infants with PH. Therefore, investigating mechanisms that alter the nitric oxide-signaling pathway has been at the forefront of pulmonary vascular biology research. In this review, we will discuss the various mechanistic pathways that have been targets in neonatal PH, including NO precursors, soluble guanylate cyclase modulators, phosphodiesterase inhibitors and antioxidants. We will review their role in enhancing NO-signaling at the bench, in animal models, as well as highlight their role in the treatment of neonates with PH.

Recent advances in our understanding of the mechanisms of lung alveolarization and bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is the most common cause of morbidity and mortality in preterm infants. A key histopathological feature of BPD is stunted late lung development, where the process of alveolarization-the generation of alveolar gas exchange units-is impeded, through mechanisms that remain largely unclear. As such, there is interest in the clarification both of the pathomechanisms at play in affected lungs, and the mechanisms of de novo alveoli generation in healthy, developing lungs. A better understanding of normal and pathological alveolarization might reveal opportunities for improved medical management of affected infants. Furthermore, disturbances to the alveolar architecture are a key histopathological feature of several adult chronic lung diseases, including emphysema and fibrosis, and it is envisaged that knowledge about the mechanisms of alveologenesis might facilitate regeneration of healthy lung parenchyma in affected patients. To this end, recent efforts have interrogated clinical data, developed new-and refined existing-in vivo and in vitro models of BPD, have applied new microscopic and radiographic approaches, and have developed advanced cell-culture approaches, including organoid generation. Advances have also been made in the development of other methodologies, including single-cell analysis, metabolomics, lipidomics, and proteomics, as well as the generation and use of complex mouse genetics tools. The objective of this review is to present advances made in our understanding of the mechanisms of lung alveolarization and BPD over the period 1 January 2017-30 June 2019, a period that spans the 50th anniversary of the original clinical description of BPD in preterm infants.