Inhibition of Rac1 Signaling Downregulates Inflammasome Activation and Attenuates Lung Injury in Neonatal Rats Exposed to Hyperoxia

Recent progress in neonatal hyperoxic lung injury

With the progress in neonatal intensive care, there has been an increase in the survival rates of premature infants. However, this has also led to an increased incidence of neonatal hyperoxia lung injury and bronchopulmonary dysplasia (BPD), whose pathogenesis is believed to be influenced by various prenatal and postnatal factors, although the exact mechanisms remain unclear. Recent studies suggest that multiple mechanisms might be involved in neonatal hyperoxic lung injury and BPD, with sex also possibly playing an important role, and numerous drugs have been proposed and shown promise for improving the treatment outcomes of hyperoxic lung injury. Therefore, this paper aims to analyze and summarize sex differences in neonatal hyperoxic lung injury, potential pathogenesis and treatment progress to provide new ideas for basic and clinical research in this field.

PHLDA1 promotes sevoflurane-induced pyroptosis of neuronal cells in developing rats through TRAF6-mediated activation of Rac1

Sevoflurane anesthesia induces neurocognitive impairment and pyroptosis in the developing brain. Pleckstrin homology-like domain, family A, member 1 (PHLDA1) was involved in neuronal apoptosis, oxidative stress and inflammation during ischemic stroke. The role of PHLDA1 in sevoflurane-induced pyroptosis in developing rats was investigated. Firstly, neonatal rats at day 7 was exposed to 2.0% sevoflurane for 6 h to induce neurotoxicity. Pathological analysis showed that sevoflurane anesthesia induced hippocampal injury and reduced the number of neurons. The expression of PHLDA1 was elevated in hippocampus of sevoflurane-treated rats. Secondly, sevoflurane anesthesia-treated neonatal rats were injected with adeno-associated virus serotype (AAV) to mediate knockdown of PHLDA1. Injection with AAV-shPHLDA1 ameliorated sevoflurane-induced hippocampal injury and neurocognitive impairment in rats. Moreover, knockdown of PHLDA1 increased the number of neurons in sevoflurane-treated rats. Silence of PHLDA1 suppressed neuronal apoptosis, and inhibited pyroptosis in sevoflurane-treated rats. Thirdly, PHLDA1 was also elevated in sevoflurane-treated primary neuronal cells. Loss of PHLDA1 also enhanced cell viability and suppressed pyroptosis of sevoflurane-treated primary neuronal cells. Lastly, silence of PHLDA1 reduced protein expression of TRAF6 and p-Rac1 in sevoflurane-treated rats and neuronal cells. Over-expression of TRAF6 attenuated PHLDA1 silence-induced increase of cell viability and decreased pyroptosis in neuronal cells. In conclusion, loss of PHLDA1 protected against sevoflurane-induced pyroptosis in developing rats through inhibition of TRAF6-mediated activation of Rac1.

Rac1 as a therapeutic anticancer target: Promises and limitations

Small molecule inhibitors of GTPases are increasingly considered for the treatment of multiple human pathologies. The GTPase Rac1 (Ras-related C3 botulinum toxin substrate 1) plays major roles in vital cellular processes, notably in the control cell motility and dynamic, the regulation of oxidative stress, and in inflammatory and immune surveillance. As such, Rac1 is viewed as a potential target to combat cancers but also diverse inflammatory, metabolic, neurodegenerative, respiratory, cardiovascular, viral, and parasitic diseases. Potent and selective Rac1 inhibitors have been identified and designed, such as compounds GYS32661 and MBQ-167 both in preclinical development for the treatment of advanced solid tumors. The pleiotropic roles and ubiquitous expression of the protein can be viewed as limitations for anticancer approaches. However, the frequent overexpression and/or hyperactivation of the Rac1 in difficult-to-treat chemoresistant cancers, make Rac1 an attractive target in oncology. The key roles of Rac1 in multiple cellular pathways, together with its major implications in carcinogenesis, tumor proliferation and metastasis, support the development of small molecule inhibitors. The challenge is high and the difficulty shall not be underestimated, but the target is innovative and promising in combination with chemo- and/or immuno-therapy. Opportunities and challenges associated with the targeting of Rac1 are discussed.

NLRP1 Inflammasomes: A Potential Target for the Treatment of Several Types of Brain Injury

NOD-like receptor (NLR) family pyrin domain-containing 1 (NLRP1) is a member of the NLR family. The NLRP1 inflammasome consists of the NLRP1 protein, the adaptor protein apoptosis-associated speck-like protein containing a CARD domain, and the effector molecule pro-caspase-1. When stimulated, the inflammasome initiates the cleavage of pro-caspase-1 and converts it into its active form, caspase-1; then, caspase-1 facilitates the cleavage of the proinflammatory cytokines interleukin-1β and interleukin-18 into their active and secreted forms. In addition, caspase-1 also mediates the cleavage of gasdermin D, which leads to pyroptosis, an inflammatory form of cell death. Pathological events that damage the brain and result in neuropathological conditions can generally be described as brain injury. Neuroinflammation, especially that driven by NLRP1, plays a considerable role in the pathophysiology of brain injury, such as early brain injury (EBI) of subarachnoid hemorrhage, ischemic brain injury during stroke, and traumatic brain injury (TBI). In this article, a thorough overview of NLRP1 is presented, including its structure, mechanism of activation, and role in neuroinflammation. We also present recent studies on NLRP1 as a target for the treatment of EBI, ischemic brain injury, TBI, and other types of brain injury, thus highlighting the perspective of NLRP1 as an effective mediator of catastrophic brain injury.

Simvastatin Inhibits NLRP3 Inflammasome Activation and Ameliorates Lung Injury in Hyperoxia-Induced Bronchopulmonary Dysplasia via the KLF2-Mediated Mechanism

Bronchopulmonary dysplasia (BPD) is a chronic lung disease commonly found in premature infants. Excessive inflammation and oxidative stress contribute to BPD occurrence and development. Simvastatin, as an inhibitor of HMG-CoA reductase, has been reported to have antioxidative and anti-inflammatory effects. However, its effect and possible mechanisms in hyperoxia-induced lung injury are rarely reported. In this study, in vivo and in vitro experiments were conducted to investigate whether simvastatin could ameliorate hyperoxia-induced lung injury and explore its potential mechanism. For the in vivo study, simvastatin could improve alveolar development after hyperoxic lung injury and reduce hyperoxic stress and inflammation. The in vitro study revealed that simvastatin can reduce inflammation in A549 cells after high-oxygen exposure. Simvastatin suppressed NLRP3 inflammasome activation and played anti-inflammatory and antioxidant roles by increasing KLF2 (Krüppel-like factor 2) expression. In vitro experiments also revealed that these effects of simvastatin were partially reversed by KLF2 shRNA, indicating that KLF2 was involved in simvastatin effects. In summary, our findings indicate that simvastatin could downregulate NLRP3 inflammasome activation and attenuate lung injury in hyperoxia-induced bronchopulmonary dysplasia via KLF2-mediated mechanism.

When inflammation meets lung development-an update on the pathogenesis of bronchopulmonary dysplasia

Even more than 50 years after its initial description, bronchopulmonary dysplasia (BPD) remains one of the most important and lifelong sequelae following premature birth. Tremendous efforts have been undertaken since then to reduce this ever-increasing disease burden but a therapeutic breakthrough preventing BPD is still not in sight. The inflammatory response provoked in the immature lung is a key driver of distorted lung development and impacts the formation of alveolar, mesenchymal, and vascular structures during a particularly vulnerable time-period. During the last 5 years, new scientific insights have led to an improved pathomechanistic understanding of BPD origins and disease drivers. Within the framework of current scientific progress, concepts involving disruption of the balance of key inflammatory and lung growth promoting pathways by various stimuli, take center stage. Still today, the number of efficient therapeutics available to prevent BPD is limited to a few, well-established pharmacological interventions including postnatal corticosteroids, early caffeine administration, and vitamin A. Recent advances in the clinical care of infants in the neonatal intensive care unit (NICU) have led to improvements in survival without a consistent reduction in the incidence of BPD. Our update provides latest insights from both preclinical models and clinical cohort studies and describes novel approaches to prevent BPD.

Oxygen Toxicity to the Immature Lung-Part I: Pathomechanistic Understanding and Preclinical Perspectives

In utero, the fetus and its lungs develop in a hypoxic environment, where HIF-1α and VEGFA signaling constitute major determinants of further development. Disruption of this homeostasis after preterm delivery and extrauterine exposure to high fractions of oxygen are among the key events leading to bronchopulmonary dysplasia (BPD). Reactive oxygen species (ROS) production constitutes the initial driver of pulmonary inflammation and cell death, altered gene expression, and vasoconstriction, leading to the distortion of further lung development. From preclinical studies mainly performed on rodents over the past two decades, the deleterious effects of oxygen toxicity and the injurious insults and downstream cascades arising from ROS production are well recognized. This article provides a concise overview of disease drivers and different therapeutic approaches that have been successfully tested within experimental models. Despite current studies, clinical researchers are still faced with an unmet clinical need, and many of these strategies have not proven to be equally effective in clinical trials. In light of this challenge, adapting experimental models to the complexity of the clinical situation and pursuing new directions constitute appropriate actions to overcome this dilemma. Our review intends to stimulate research activities towards the understanding of an important issue of immature lung injury.

Hyperoxia-activated circulating extracellular vesicles induce lung and brain injury in neonatal rats

Hyperoxia-induced lung injury plays a key role in the development of bronchopulmonary dysplasia (BPD), characterized by inflammatory injury and impaired lung development in preterm infants. Although BPD is a predictor of poor neurodevelopmental outcomes, currently it is uncertain how lung injury contributes to brain injury in preterm infants. Extracellular vesicles (EVs) are a heterogeneous group of cell-derived membranous structures that regulate intercellular and inter-organ communications. Gasdermin D (GSDMD) has emerged as a key executor of inflammasome-mediated cell death and inflammation. In this study, we utilized a neonatal rat model of BPD to assess if hyperoxia stimulates lung release of circulating EVs and if these EVs induce lung and brain injury. We found that hyperoxia-exposed rats had elevated numbers of plasma-derived EVs compared to rats maintained in room air. These EVs also had increased cargos of surfactant protein C, a marker of type II alveolar epithelial cells (AEC), and the active (p30) form of GSDMD. When these EVs were adoptively transferred into normal newborn rats via intravenous injection, they were taken up both by lung and brain tissues. Moreover, EVs from hyperoxic animals induced not only the pathological hallmarks of BPD, but also brain inflammatory injury in recipient rats, as well as inducing cell death in cultured pulmonary vascular endothelial cells and neural stem cells (NSC). Similarly, hyperoxia-exposed cultured AEC-like cells released EVs that also contained increased GSDMD-p30 and these EVs induced pyroptotic cell death in NSC. Overall, these data indicate that hyperoxia-activated circulating EVs mediate a lung to brain crosstalk resulting in brain injury and suggest a mechanism that links lung injury and neurodevelopmental impairment in BPD infants.

DOCK2 contributes to endotoxemia-induced acute lung injury in mice by activating proinflammatory macrophages

Dedicator of cytokinesis 2 (DOCK2), an atypical Rac activator, has important anti-inflammatory properties in blepharitis, enteric bacterial infection and colitis. However, the roles of DOCK2 in macrophage activation and acute lung injury (ALI) are still poorly elucidated. In vitro studies demonstrated that DOCK2 was essential for the nucleotide-sensing Toll-like receptor (TLR) 4-mediated inflammatory response in macrophages. We also confirmed that exposure of macrophages to LPS induced Rac activation through a TLR4-independent, DOCK2-dependent mechanism. Phosphorylation of IκB kinase (IKK) β and nuclear translocation of transcription factor nuclear factor kappa B (NF-κB) were impaired in Ad-shDOCK2-expressing macrophages, resulting in a decreased inflammatory response. Similar results were obtained when EHop-016 (a Rac inhibitor) was used to treat uninfected macrophages. In summary, these data indicate that the DOCK2-Rac signaling pathway acts in parallel with TLR4 engagement to control IKKβ activation for inflammatory cytokine release. Next, we investigated whether pharmacological inhibition of DOCK2 protects against endotoxemia-induced lung injury in mice. Treatment with 4-[3'-(2″-chlorophenyl)-2'-propen-1'-ylidene]-1-phenyl-3,5-pyrazolidinedione (CPYPP), a small-molecule inhibitor of DOCK2, reduced the severity of lung injury, as indicated by decreases in the lung injury score and myeloperoxidase (MPO) activity. Moreover, CPYPP attenuated LPS-induced proinflammatory cytokine release in mice. Our studies suggest that inhibition of DOCK2 may suppress LPS-induced macrophage activation and that DOCK2 may be a novel target for treating endotoxemia-related ALI.

Phenotypes of Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia (BPD) is the most common chronic morbidity in preterm infants. In the absence of effective interventions, BPD is currently a major therapeutic challenge. Several risk factors are known for this multifactorial disease that results in disrupted lung development. Inflammation plays an important role and leads to persistent airway and pulmonary vascular disease. Since corticosteroids are potent anti-inflammatory agents, postnatal corticosteroids have been used widely for BPD prevention and treatment. However, the clinical responses vary to a great degree across individuals, and steroid-related complications remain major concerns. Emerging studies on the molecular mechanism of lung alveolarization during inflammatory stress will elucidate the complicated pathway and help discover novel therapeutic targets. Moreover, with the advances in metabolomics, there are new opportunities to identify biomarkers for early diagnosis and prognosis prediction of BPD. Pharmacometabolomics is another novel field aiming to identify the metabolomic changes before and after a specific drug treatment. Through this "metabolic signature," a more precise treatment may be developed, thereby avoiding unnecessary drug exposure in non-responders. In the future, more clinical, genetic, and translational studies would be required to improve the classification of BPD phenotypes and achieve individualized care to enhance the respiratory outcomes in preterm infants.

Caffeine prevents hyperoxia-induced lung injury in neonatal mice through NLRP3 inflammasome and NF-κB pathway

Background

Bronchopulmonary dysplasia (BPD) is a common chronic lung disease in premature infants and hyperoxia exposure is a major cause. In hyperoxic lung injury animal model, alveolar simplification and pro-inflammatory cells infiltration are the main pathophysiologic changes. Caffeine is a drug used to treat apnea in premature infants. Early use of caffeine can decrease the rate and the severity of BPD while the mechanisms are still unclear. The purpose of this study was to evaluate the effects of caffeine on inflammation and lung development in neonatal mice with hyperoxic lung injury and to explore the possible mechanism.

Methods

Following 14 d of 75% oxygen exposure in newborn mouse, the BPD model was established. Caffeine at a dose of 1 g/L was added in drinking water to nursing mouse. We measured the concentration of caffeine in serum and oxidative stress in lung by commercially available kits. Adenosine 2A receptor (A_2AR) expression and lung inflammation were measured by Immunohistochemistry and western blotting. Apoptosis and surfactant protein-C (SFTPC) levels were measured by immunofluorescence. The inflammasome and NF-κB pathway proteins were assessed by western blotting.

Results

We found that the caffeine concentration in plasma at present dose significantly decreased the expression of A_2AR protein in mice lung. Caffeine treatment significantly reduced oxidative stress, improved weight gain, promoted alveolar development, attenuated inflammatory infiltration and lung injury in hyperoxia-induced lung injury mice. Moreover, caffeine decreased the cell apoptosis in lung tissues, especially the Type II alveolar epithelial cell. The expression of NLRP3 inflammasome protein and NF-κB pathway were significantly inhibited by caffeine treatment.

Conclusion

Caffeine treatment can protect hyperoxia-induced mice lung from oxidative injury by inhibiting NLRP3 inflammasome and NF-κB pathway.

Deconvolution of RNA-Seq Analysis of Hyperbaric Oxygen-Treated Mice Lungs Reveals Mesenchymal Cell Subtype Changes

Hyperbaric oxygen (HBO) is widely applied to treat several hypoxia-related diseases. Previous studies have focused on the immediate effect of HBO-exposure induced oxidative stress on the lungs, but knowledge regarding the chronic effects from repetitive HBO exposure is limited, especially at the gene expression level. We found that repetitive HBO exposure did not alter the morphology of murine lungs. However, by deconvolution of RNA-seq from those mice lungs using CIBERSORTx and the expression profile matrices of 8 mesenchymal cell subtypes obtained from bleomycin-treated mouse lungs, we identify several mesenchymal cell subtype changes. These include increases in Col13a1 matrix fibroblasts, mesenchymal progenitors and mesothelial cell populations and decreases in lipofibroblasts, endothelial and Pdgfrb high cell populations. Our data suggest that repetitive HBO exposure may affect biological processes in the lungs such as response to wounding, extracellular matrix, vasculature development and immune response.

Acetate Downregulates the Activation of NLRP3 Inflammasomes and Attenuates Lung Injury in Neonatal Mice With Bronchopulmonary Dysplasia

Background: Bronchopulmonary dysplasia (BPD) is a common pulmonary complication in preterm infants. Acetate is a metabolite produced by the gut microbiota, and its anti-inflammatory function is well known. The role of acetate in BPD has not been studied. Here, we investigate the effects of acetate on lung inflammation and damage in mice model of BPD. Objective: To investigate the role of acetate in the development of BPD. Methods: C57BL/6 mice were randomly divided into three groups on the 3rd day after birth: room air group, hyperoxia group, and hyperoxia + acetate (250 mM, 0.02 ml/g) group. The expression of inflammatory factors was determined by ELISA and RT-PCR, and NLRP3 and caspase-1 were detected by Western blot. High-throughput sequencing was used to detect bacterial communities in the mice intestines. Results: After acetate treatment, the expression levels of TNF-α, IL-1β, IL-18, NLRP3, and caspase-1 were significantly reduced, while the expression of GPR43 was increased. In the BPD mice treated with acetate, the proportion of Escherichia-Shigella was lower than in placebo-treated BPD mice, while the abundance of Ruminococcus was increased. Conclusions: These results indicate that acetate may regulate intestinal flora and reduce inflammatory reactions and lung injury in BPD. Therefore, acetate may be an effective drug to protect against neonatal BPD.

TREM-1 Attenuates RIPK3-mediated Necroptosis in Hyperoxia-induced Lung Injury in Neonatal Mice

Hyperoxia-induced injury to the developing lung, impaired alveolarization, and dysregulated vascularization are critical factors in the pathogenesis of bronchopulmonary dysplasia (BPD); however, mechanisms for hyperoxia-induced development of BPD are not fully known. In this study, we show that TREM-1 (triggering receptor expressed on myeloid cells 1) is upregulated in hyperoxia-exposed neonatal murine lungs as well as in tracheal aspirates and lungs of human neonates with respiratory distress syndrome and BPD as an adaptive response to survival in hyperoxia. Inhibition of TREM-1 function using an siRNA approach or deletion of the Trem1 gene in mice showed enhanced lung inflammation, alveolar damage, and mortality of hyperoxia-exposed neonatal mice. The treatment of hyperoxia-exposed neonatal mice with agonistic TREM-1 antibody decreased lung inflammation, improved alveolarization, and was associated with diminished necroptosis-regulating protein RIPK3 (receptor-interacting protein kinase 3). Mechanistically, we show that TREM-1 activation alleviates lung inflammation and improves alveolarization through downregulating RIPK3-mediated necroptosis and NLRP3 (nucleotide-binding oligomerization domain-like receptor containing pyrin domain 3) inflammasome activation in hyperoxia-exposed neonatal mice. These data show that activating TREM-1, enhancing angiopoietin 1 signaling, or blocking the RIPK3-mediated necroptosis pathway may be used in new therapeutic interventions to control adverse effects of hyperoxia in the development of BPD.

8-Aminoguanine Induces Diuresis, Natriuresis, and Glucosuria by Inhibiting Purine Nucleoside Phosphorylase and Reduces Potassium Excretion by Inhibiting Rac1

Background 8-Aminoguanosine and 8-aminoguanine are K⁺-sparing natriuretics that increase glucose excretion. Most effects of 8-aminoguanosine are due to its metabolism to 8-aminoguanine. However, the mechanism by which 8-aminoguanine affects renal function is unknown and is the focus of this investigation. Methods and Results Because 8-aminoguanine has structural similarities with inhibitors of the epithelial sodium channel (ENaC), Na⁺/H⁺ exchangers, and adenosine A₁ receptors, we examined the effects of 8-aminoguanine on EN aC activity in mouse collecting duct cells, on intracellular pH of human proximal tubular epithelial cells, on responses to a selective A₁-receptor agonist in vivo, and on renal excretory function in A₁-receptor knockout rats. These experiments showed that 8-aminoguanine did not block EN aC, Na⁺/H⁺ exchangers, or A₁ receptors. Because Rac1 enhances activity of mineralocorticoid receptors and some guanosine analogues inhibit Rac1, we examined the effects of 8-aminoguanine on Rac1 activity in mouse collecting duct cells. Rac1 activity was significantly inhibited by 8-aminoguanine. Because in vitro 8-aminoguanine is a purine nucleoside phosphorylase ( PNP ase) inhibitor, we examined the effects of a natriuretic dose of 8-aminoguanine on urinary excretion of PNP ase substrates and products. 8-Aminoguanine increased and decreased, respectively, urinary excretion of PNP ase substrates and products. Next we compared in rats the renal effects of intravenous doses of 9-deazaguanine ( PNP ase inhibitor) versus 8-aminoguanine. 8-Aminoguanine and 9-deazaguanine induced similar increases in urinary Na⁺ and glucose excretion, yet only 8-aminoguanine reduced K⁺ excretion. Nsc23766 (Rac1 inhibitor) mimicked the effects of 8-aminoguanine on K⁺ excretion. Conclusions 8-Aminoguanine increases Na⁺ and glucose excretion by blocking PNP ase and decreases K⁺ excretion by inhibiting Rac1.

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.

Rac1 GTPase Inhibition Blocked Podocyte Injury and Glomerular Sclerosis during Hyperhomocysteinemia via Suppression of Nucleotide-Binding Oligomerization Domain-Like Receptor Containing Pyrin Domain 3 Inflammasome Activation

Elevated homocysteine (Hcy) levels have been shown to activate nucleotide-binding oligomerization domain-like receptor containing pyrin domain 3 (NLRP3) inflammasome leading to podocyte dysfunction and glomerular injury. However, it remains unclear how this inflammasome activation in podocytes is a therapeutic target for reversal of glomerular injury and ultimate sclerosis. The present study tested whether inhibition of Rac1 GTPase activity suppresses NLRP3 inflammation activation and thereby blocks podocyte injury induced by elevated Hcy. In cultured podocytes, we found that L-Hcy (the active Hcy form) stimulated the NLRP3 inflammasome formation, as shown by increased colocalization of NLRP3 with apoptosis-associated speck-like protein (ASC) or caspase-1, which was accompanied by increased interleukin-1β production and caspase-1 activity, indicating NLRP3 inflammasome activation. Rac1 activator, uridine triphosphate (UTP), mimicked L-Hcy-induced NLRP3 inflammasome activation, while Rac1 inhibitor NSC23766 blocked it. This Rac1 inhibition also prevented L-Hcy-induced podocyte dysfunction. All these effects were shown to be mediated via lipid raft redox signaling platforms with nicotinamide adenine dinucleotide phosphate oxidase subunits and consequent O₂⁻ production. In animal studies, hyperhomocysteinemia (hHcy) induced by folate-free diet was shown to induce NLRP3 inflammasome formation and activation in glomeruli, which was also mimicked by UTP and inhibited by NSC23766 to a comparable level seen in Nlrp3 gene knockout mice. These results together suggest that Rac1 inhibition protects the kidney from hHcy-induced podocyte injury and glomerular sclerosis due to its action to suppress NLRP3 inflammasome activation in podocytes.

Recent advances in the pathogenesis of BPD

Bronchopulmonary dysplasia (BPD) continues to be one of the most common complications of preterm birth and is characterized histopathologically by impaired lung alveolarization. Extremely preterm born infants remain at high risk for the development of BPD, highlighting a pressing need for continued efforts to understand the pathomechanisms at play in affected infants. This brief review summarizes recent progress in our understanding of the how the development of the newborn lung is stunted, highlighting recent reports on roles for growth factor signaling, oxidative stress, inflammation, the extracellular matrix and proteolysis, non-coding RNA, and fibroblast and epithelial cell plasticity. Additionally, some concerns about modeling BPD in experimental animals are reviewed, as are new developments in the in vitro modeling of pathophysiological processes relevant to impaired lung alveolarization in BPD.

Riociguat prevents hyperoxia-induced lung injury and pulmonary hypertension in neonatal rats without effects on long bone growth

Bronchopulmonary dysplasia (BPD) remains the most common and serious chronic lung disease of premature infants. Severe BPD complicated with pulmonary hypertension (PH) increases the mortality of these infants. Riociguat is an allosteric soluble guanylate cyclase stimulator and is approved by the FDA for treating PH in adults. However, it has not been approved for use in neonates due to concern for adverse effects on long bone growth. To address this concern we investigated if administration of riociguat is beneficial in preventing hyperoxia-induced lung injury and PH without side effects on long bone growth in newborn rats. Newborn rats were randomized to normoxia (21% O₂) or hyperoxia (85% O₂) exposure groups within 24 hours of birth, and received riociguat or placebo by once daily intraperitoneal injections during continuous normoxia or hyperoxia exposure for 9 days. In the hyperoxia control group, radial alveolar count, mean linear intercept and vascular density were significantly decreased, the pathological hallmarks of BPD, and these were accompanied by an increased inflammatory response. There was also significantly elevated vascular muscularization of peripheral pulmonary vessels, right ventricular systolic pressure and right ventricular hypertrophy indicating PH. However, administration of riociguat significantly decreased lung inflammation, improved alveolar and vascular development, and decreased PH during hyperoxia by inducing cGMP production. Additionally, riociguat did not affect long bone growth or structure. These data indicate that riociguat is beneficial in preventing hyperoxia-induced lung injury and PH without affecting long bone growth and structure and hence, suggests riociguat may be a potential novel agent for preventing BPD and PH in neonates.

Time Dependent Pathway Activation of Signalling Cascades in Rat Organs after Short-Term Hyperoxia

Administration of oxygen is one of the most common interventions in medicine. Previous research showed that differential regulated proteins could be linked to hyperoxia-associated signaling cascades in different tissues. However, it still remains unclear which signaling pathways are activated by hyperoxia. The present study analyses hyperoxia-induced protein alterations in lung, brain, and kidney tissue using a proteomic and bioinformatic approach. Pooled data of 36 Wistar rats exposed to hyperoxia were used. To identify possible hyperoxia biomarkers, and to evaluate the relationship between protein alterations in hyperoxia affected organs and blood, proteomics data from brain, lung, and kidney were analyzed. Functional network analyses (IPA^®, PathwaysStudio^®, and GENEmania^®) in combination with hierarchical cluster analysis (Perseus^®) was used to identify relevant pathways and key proteins. Data of 54 2D-gels with more than 2500 significantly regulated spots per gel were collected. Thirty-eight differentially expressed proteins were identified and consecutively analyzed by bioinformatic methods. Most differences between hyperoxia and normoxia (21 proteins up-regulated, 17 proteins down-regulated) were found immediately after hyperoxia (15 protein spots), followed by day 3 (13 spots), and day 7 (10 spots). A highly significant association with inflammation and the inflammatory response was found. Cell proliferation, oxidative stress, apoptosis and cell death as well as cellular functions were revealed to be affected. Three hours of hyperoxia resulted in significant alterations of protein expression in different organs (brain, lung, kidney) up to seven days after exposure. Further studies are required to interpret the relevance of protein alterations in signaling cascades during/after hyperoxia.

Recombinant CCN1 prevents hyperoxia-induced lung injury in neonatal rats

BackgroundCystein-rich protein 61 (Cyr61/CCN1) is a member of the CCN family of matricellular proteins that has an important role in tissue development and remodeling. However, the role of CCN1 in the pathogenesis of bronchopulmonary dysplasia (BPD) is unknown. Accordingly, we have investigated the effects of CCN1 on a hyperoxia-induced lung injury model in neonatal rats.MethodsIn experiment 1, newborn rats were randomized to room air (RA) or 85% oxygen (O₂) for 7 or 14 days, and we assessed the expression of CCN1. In experiment 2, rat pups were exposed to RA or O₂ and received placebo or recombinant CCN1 by daily intraperitoneal injection for 10 days. The effects of CCN1 on hyperoxia-induced lung inflammation, alveolar and vascular development, vascular remodeling, and right ventricular hypertrophy (RVH) were observed.ResultsIn experiment 1, hyperoxia downregulated CCN1 expression. In experiment 2, treatment with recombinant CCN1 significantly decreased macrophage and neutrophil infiltration, reduced inflammasome activation, increased alveolar and vascular development, and reduced vascular remodeling and RVH in the hyperoxic animals.ConclusionThese results demonstrate that hyperoxia-induced lung injury is associated with downregulated basal CCN1 expression, and treatment with CCN1 can largely reverse hyperoxic injury.

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

The objective of lung development is to generate an organ of gas exchange that provides both a thin gas diffusion barrier and a large gas diffusion surface area, which concomitantly generates a steep gas diffusion concentration gradient. As such, the lung is perfectly structured to undertake the function of gas exchange: a large number of small alveoli provide extensive surface area within the limited volume of the lung, and a delicate alveolo-capillary barrier brings circulating blood into close proximity to the inspired air. Efficient movement of inspired air and circulating blood through the conducting airways and conducting vessels, respectively, generates steep oxygen and carbon dioxide concentration gradients across the alveolo-capillary barrier, providing ideal conditions for effective diffusion of both gases during breathing. The development of the gas exchange apparatus of the lung occurs during the second phase of lung development-namely, late lung development-which includes the canalicular, saccular, and alveolar stages of lung development. It is during these stages of lung development that preterm-born infants are delivered, when the lung is not yet competent for effective gas exchange. These infants may develop bronchopulmonary dysplasia (BPD), a syndrome complicated by disturbances to the development of the alveoli and the pulmonary vasculature. It is the objective of this review to update the reader about recent developments that further our understanding of the mechanisms of lung alveolarization and vascularization and the pathogenesis of BPD and other neonatal lung diseases that feature lung hypoplasia.