Targeting transglutaminase 2 partially restores extracellular matrix structure but not alveolar architecture in experimental bronchopulmonary dysplasia

c-Myc Drives inflammation of the maternal-fetal interface, and neonatal lung remodeling induced by intra-amniotic inflammation

Background: Intra-amniotic inflammation (IAI) is associated with increased risk of preterm birth and bronchopulmonary dysplasia (BPD), but the mechanisms by which IAI leads to preterm birth and BPD are poorly understood, and there are no effective therapies for preterm birth and BPD. The transcription factor c-Myc regulates various biological processes like cell growth, apoptosis, and inflammation. We hypothesized that c-Myc modulates inflammation at the maternal-fetal interface, and neonatal lung remodeling. The objectives of our study were 1) to determine the kinetics of c-Myc in the placenta, fetal membranes and neonatal lungs exposed to IAI, and 2) to determine the role of c-Myc in modulating inflammation at the maternal-fetal interface, and neonatal lung remodeling induced by IAI. Methods: Pregnant Sprague-Dawley rats were randomized into three groups: 1) Intra-amniotic saline injections only (control), 2) Intra-amniotic lipopolysaccharide (LPS) injections only, and 3) Intra-amniotic LPS injections with c-Myc inhibitor 10058-F4. c-Myc expression, markers of inflammation, angiogenesis, immunohistochemistry, and transcriptomic analyses were performed on placenta and fetal membranes, and neonatal lungs to determine kinetics of c-Myc expression in response to IAI, and effects of prenatal systemic c-Myc inhibition on lung remodeling at postnatal day 14. Results: c-Myc was upregulated in the placenta, fetal membranes, and neonatal lungs exposed to IAI. IAI caused neutrophil infiltration and neutrophil extracellular trap (NET) formation in the placenta and fetal membranes, and neonatal lung remodeling with pulmonary hypertension consistent with a BPD phenotype. Prenatal inhibition of c-Myc with 10058-F4 in IAI decreased neutrophil infiltration and NET formation, and improved neonatal lung remodeling induced by LPS, with improved alveolarization, increased angiogenesis, and decreased pulmonary vascular remodeling. Discussion: In a rat model of IAI, c-Myc regulates neutrophil recruitment and NET formation in the placenta and fetal membranes. c-Myc also participates in neonatal lung remodeling induced by IAI. Further studies are needed to investigate c-Myc as a potential therapeutic target for IAI and IAI-associated BPD.

Perinatal origins of bronchopulmonary dysplasia-deciphering normal and impaired lung development cell by cell

Bronchopulmonary dysplasia (BPD) is a multifactorial disease occurring as a consequence of premature birth, as well as antenatal and postnatal injury to the developing lung. BPD morbidity and severity depend on a complex interplay between prenatal and postnatal inflammation, mechanical ventilation, and oxygen therapy as well as associated prematurity-related complications. These initial hits result in ill-explored aberrant immune and reparative response, activation of pro-fibrotic and anti-angiogenic factors, which further perpetuate the injury. Histologically, the disease presents primarily by impaired lung development and an arrest in lung microvascular maturation. Consequently, BPD leads to respiratory complications beyond the neonatal period and may result in premature aging of the lung. While the numerous prenatal and postnatal stimuli contributing to BPD pathogenesis are relatively well known, the specific cell populations driving the injury, as well as underlying mechanisms are still not well understood. Recently, an effort to gain a more detailed insight into the cellular composition of the developing lung and its progenitor populations has unfold. Here, we provide an overview of the current knowledge regarding perinatal origin of BPD and discuss underlying mechanisms, as well as novel approaches to study the perturbed lung development.

CircRNA, lncRNA, and mRNA profiles of umbilical cord blood exosomes from preterm newborns showing bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) represents a multifactorial chronic pulmonary pathology and a major factor causing premature illness and death. The therapeutic role of exosomes in BPD has been feverishly investigated. Meanwhile, the potential roles of exosomal circRNAs, lncRNAs, and mRNAs in umbilical cord blood (UCB) serum have not been studied. This study aimed to detect the expression profiles of circRNAs, lncRNAs, and mRNAs in UCB-derived exosomes of infants with BPD. Microarray analysis was performed to compare the RNA profiles of UCB-derived exosomes of a preterm newborn with (BPD group) and without (non-BPD, NBPD group) BPD. Then, circRNA/lncRNA-miRNA-mRNA co-expression networks were built to determine their association with BPD. In addition, cell counting kit-8 (CCK-8) assay was used to evaluate the proliferation of lipopolysaccharide (LPS)-induced human bronchial epithelial cells (BEAS-2B cells) and human umbilical vein endothelial cells (HUVECs). The levels of tumor necrosis factor (TNF)-α and interleukin (IL)-1β in LPS-induced BEAS-2B cells and HUVECs were assessed through Western blot analysis. Then, quantitative reverse transcription-polymerase chain reaction assay was used to evaluate the expression levels of four differentially expressed circRNAs (hsa_circ_0086913, hsa_circ_0049170, hsa_circ_0087059, and hsa_circ_0065188) and two lncRNAs (small nucleolar RNA host gene 20 (SNHG20) and LINC00582) detected in LPS-induced BEAS-2B cells or HUVECs. A total of 317 circRNAs, 104 lncRNAs, and 135 mRNAs showed significant differential expression in UCB-derived exosomes of preterm infants with BPD compared with those with NBPD. Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were conducted to examine differentially expressed exosomal circRNAs, lncRNAs, and mRNAs. The results showed that the GO terms and KEGG pathways mostly involving differentially expressed exosomal RNAs were closely associated with endothelial or epithelial cell development. In vitro, CCK-8 and Western blot assays revealed that LPS remarkably inhibited the viability and promoted inflammatory responses (TNF-α and IL-1β) of BEAS-2B cells or HUVECs. The expression levels of circRNAs hsa_circ_0049170 and hsa_circ_0087059 were upregulated in LPS-induced BEAS-2B cells; the expression level of hsa_circ_0086913 was upregulated and that of hsa_circ_0065188 was downregulated in LPS-induced HUVECs. Moreover, the expression level of lncRNA SNHG20 was upregulated and that of LINC00582 was downregulated in LPS-induced BEAS-2B cells. Further, 455 circRNA/lncRNA-miRNA-mRNA interaction networks were predicted, including hsa_circ_0086913/hsa-miR-103a-3p/transmembrane 4 L six family member 1 (TM4SF1) and lncRNA-SNHG20/hsa-miR-6720-5p/spermine synthase (SMS) networks, which may take part in BPD.

CONCLUSION

This study provided a systematic perspective on UCB-derived exosomal circRNAs and lncRNAs and laid an important foundation for further investigating the potential biological functions of exosomal circRNAs and lncRNAs in BPD.

WHAT IS KNOWN

• BPD represents a multifactorial chronic pulmonary pathology and a major factor causing premature illness and death. • The therapeutic role of exosomes in BPD has been feverishly investigated, and exosomal RNAs were ignored.

WHAT IS NEW

• The profiles of UCB-derived exosomal circRNAs, lncRNAs, and mRNAs were performed. • Several differentially expressed circRNAs and lncRNAs were identified in LPS-induced BEAS-2B cells and HUVECs.

Comprehensive analysis of transglutaminase substrate preference by cDNA display coupled with next-generation sequencing and bioinformatics

cDNA display is an in vitro display technology based on a covalent linkage between a protein and its corresponding mRNA/cDNA, widely used for the selection of proteins and peptides from large libraries (10¹²) in a high throughput manner, based on their binding affinity. Here, we developed a platform using cDNA display and next-generation sequencing (NGS) for rapid and comprehensive substrate profiling of transglutaminase 2 (TG2), an enzyme crosslinking glutamine and lysine residues in proteins. After screening and selection of the control peptide library randomized at the reactive glutamine, a combinatorial library of displayed peptides randomized at positions - 1, + 1, + 2, and + 3 from the reactive glutamine was screened followed by NGS and bioinformatic analysis, which indicated a strong preference of TG2 towards peptides with glutamine at position - 1 (Gln-Gln motif), and isoleucine or valine at position + 3. The highly enriched peptides indeed contained the indicated sequence and showed a higher reactivity as TG2 substrates than the peptide previously selected by phage display, thus representing the novel candidate peptide probes for TG2 research. Furthermore, the obtained information on substrate profiling can be used to identify potential TG2 protein targets. This platform will be further used for the substrate profiling of other TG isozymes, as well as for the selection and evolution of larger biomolecules.

Extracellular Matrix Stiffness in Lung Health and Disease

The extracellular matrix (ECM) provides structural support and imparts a wide variety of environmental cues to cells. In the past decade, a growing body of work revealed that the mechanical properties of the ECM, commonly known as matrix stiffness, regulate the fundamental cellular processes of the lung. There is growing appreciation that mechanical interplays between cells and associated ECM are essential to maintain lung homeostasis. Dysregulation of ECM-derived mechanical signaling via altered mechanosensing and mechanotransduction pathways is associated with many common lung diseases. Matrix stiffening is a hallmark of lung fibrosis. The stiffened ECM is not merely a sequelae of lung fibrosis but can actively drive the progression of fibrotic lung disease. In this article, we provide a comprehensive view on the role of matrix stiffness in lung health and disease. We begin by summarizing the effects of matrix stiffness on the function and behavior of various lung cell types and on regulation of biomolecule activity and key physiological processes, including host immune response and cellular metabolism. We discuss the potential mechanisms by which cells probe matrix stiffness and convert mechanical signals to regulate gene expression. We highlight the factors that govern matrix stiffness and outline the role of matrix stiffness in lung development and the pathogenesis of pulmonary fibrosis, pulmonary hypertension, asthma, chronic obstructive pulmonary disease (COPD), and lung cancer. We envision targeting of deleterious matrix mechanical cues for treatment of fibrotic lung disease. Advances in technologies for matrix stiffness measurements and design of stiffness-tunable matrix substrates are also explored. © 2022 American Physiological Society. Compr Physiol 12:3523-3558, 2022.

Inducible factors and interaction of pulmonary fibrosis induced by prenatal dexamethasone exposure in offspring rats

This study aimed to investigate the correlation between prenatal dexamethasone exposure (PDE) and susceptibility to pulmonary fibrosis in offspring. Healthy female Wistar rats were given dexamethasone (0.2 mg/kg.d) or an equal volume of normal saline subcutaneously from 9 to 20 days after conception. Some of their female offspring underwent ovariectomy (OV) at 22 weeks after birth. All animals were euthanized at 28 weeks after birth. The morphological changes related to pulmonary fibrosis and extracellular matrix-related gene expression were detected, and Two-way ANOVA analyzed the interaction between PDE and OV. The results showed that adult offspring rats in FD group (female rats with PDE treatment) had early pulmonary fibrosis changes, such as pulmonary interstitial thickening, and increased expression of type IV collagen (COL4), α -smooth muscle actin (α-SMA) and fibronectin (FN) in lung tissues compared with those in FC group (female rats with saline treatment). In addition, adult offspring rats in FDO group (female rats with PDE and OV treatment) showed signs of pulmonary fibrosis, including apparent extracellular matrix deposition, increased lung injury scores (P＜0.01, P＜0.05), and extracellular matrix related gene expression (P＜0.01, P＜0.05), compared with rats in FDS (female rats with PDE treatment alone) or rats in FCO group (female rats with OV treatment alone). Moreover, PDE and OV had an interactive effect on the development of pulmonary fibrosis in female adult offspring. This study first reported the correlation between PDE and susceptibility to pulmonary fibrosis in female offspring rats, as well as the synergistic effect of PDE and OV in this pathological event, which provided a basis for further understanding of the pathogenesis of fetal originated pulmonary fibrosis.

Lysyl oxidase regulation and protein aldehydes in the injured newborn lung

During newborn lung injury, excessive activity of lysyl oxidases (LOXs) disrupts extracellular matrix (ECM) formation. Previous studies indicate that TGFβ activation in the O₂-injured mouse pup lung increases lysyl oxidase (LOX) expression. But how TGFβ regulates this, and whether the LOXs generate excess pulmonary aldehydes are unknown. First, we determined that O₂-mediated lung injury increases LOX protein expression in TGFβ-stimulated pup lung interstitial fibroblasts. This regulation appeared to be direct; this is because TGFβ treatment also increased LOX protein expression in isolated pup lung fibroblasts. Then using a fibroblast cell line, we determined that TGFβ stimulates LOX expression at a transcriptional level via Smad2/3-dependent signaling. LOX is translated as a pro-protein that requires secretion and extracellular cleavage before assuming amine oxidase activity and, in some cells, reuptake with nuclear localization. We found that pro-LOX is processed in the newborn mouse pup lung. Also, O₂-mediated injury was determined to increase pro-LOX secretion and nuclear LOX immunoreactivity particularly in areas populated with interstitial fibroblasts and exhibiting malformed ECM. Then, using molecular probes, we detected increased aldehyde levels in vivo in O₂-injured pup lungs, which mapped to areas of increased pro-LOX secretion in lung sections. Increased activity of LOXs plays a critical role in the aldehyde generation; an inhibitor of LOXs prevented the elevation of aldehydes in the O₂-injured pup lung. These results reveal new mechanisms of TGFβ and LOX in newborn lung disease and suggest that aldehyde-reactive probes might have utility in sensing the activation of LOXs in vivo during lung injury.

Patho-mechanisms of the origins of bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) continues to be one of the most common complications of prematurity, despite significant advancement in neonatology over the last couple of decades. The new BPD is characterized histopathologically by impaired lung alveolarization and dysregulated vascularization. With the increased survival of extremely preterm infants, the risk for the development of BPD remains high, emphasizing the continued need to understand the patho-mechanisms that play a role in the development of this disease. This brief review summarizes recent advances in our understanding of the maldevelopment of the premature lung, highlighting recent research in pathways of oxidative stress-related lung injury, the role of placental insufficiency, growth factor signaling, the extracellular matrix, and microRNAs.

A Novel UPLC-MS/MS Method Identifies Organ-Specific Dipeptide Profiles

BACKGROUND

Amino acids have a central role in cell metabolism, and intracellular changes contribute to the pathogenesis of various diseases, while the role and specific organ distribution of dipeptides is largely unknown.

METHOD

We established a sensitive, rapid and reliable UPLC-MS/MS method for quantification of 36 dipeptides. Dipeptide patterns were analyzed in brown and white adipose tissues, brain, eye, heart, kidney, liver, lung, muscle, sciatic nerve, pancreas, spleen and thymus, serum and urine of C57BL/6N wildtype mice and related to the corresponding amino acid profiles.

RESULTS

A total of 30 out of the 36 investigated dipeptides were detected with organ-specific distribution patterns. Carnosine and anserine were most abundant in all organs, with the highest concentrations in muscles. In liver, Asp-Gln and Ala-Gln concentrations were high, in the spleen and thymus, Glu-Ser and Gly-Asp. In serum, dipeptide concentrations were several magnitudes lower than in organ tissues. In all organs, dipeptides with C-terminal proline (Gly-Pro and Leu-Pro) were present at higher concentrations than dipeptides with N-terminal proline (Pro-Gly and Pro-Leu). Organ-specific amino acid profiles were related to the dipeptide profile with several amino acid concentrations being related to the isomeric form of the dipeptides. Aspartate, histidine, proline and serine tissue concentrations correlated with dipeptide concentrations, when the amino acids were present at the C- but not at the N-terminus.

CONCLUSION

Our multi-dipeptide quantification approach demonstrates organ-specific dipeptide distribution. This method allows us to understand more about the dipeptide metabolism in disease or in healthy state.

Hyperoxia and Lungs: What We Have Learned From Animal Models

Although oxygen (O₂) is essential for aerobic life, it can also be an important source of cellular damage. Supra-physiological levels of O₂ determine toxicity due to exacerbated reactive oxygen species (ROS) production, impairing the homeostatic balance of several cellular processes. Furthermore, injured cells activate inflammation cascades, amplifying the tissue damage. The lung is the first (but not the only) organ affected by this condition. Critically ill patients are often exposed to several insults, such as mechanical ventilation, infections, hypo-perfusion, systemic inflammation, and drug toxicity. In this scenario, it is not easy to dissect the effect of oxygen toxicity. Translational investigations with animal models are essential to explore injuring stimuli in controlled experimental conditions, and are milestones in understanding pathological mechanisms and developing therapeutic strategies. Animal models can resemble what happens in critical care or anesthesia patients under mechanical ventilation and hyperoxia, but are also critical to explore the effect of O₂ on lung development and the role of hyperoxic damage on bronchopulmonary dysplasia. Here, we set out to review the hyperoxia effects on lung pathology, contributing to the field by describing and analyzing animal experimentation's main aspects and its implications on human lung diseases.

Minoxidil Cannot Be Used To Target Lysyl Hydroxylases during Postnatal Mouse Lung Development: A Cautionary Note

The lysyl hydroxylases (procollagen-lysine 5-dioxygenases) PLOD1, PLOD2, and PLOD3 have been proposed as pathogenic mediators of stunted lung development in bronchopulmonary dysplasia (BPD), a common complication of preterm birth. In affected infants, pulmonary oxygen toxicity stunts lung development. Mice lacking Plod1 exhibit 15% mortality, and mice lacking Plod2 or Plod3 exhibit embryonic lethality. Therefore, to address any pathogenic role of lysyl hydroxylases in stunted lung development associated with BPD, minoxidil was administered to newborn mice in an oxygen toxicity-based BPD animal model. Minoxidil, which has attracted much interest in the management of systemic hypertension and androgenetic alopecia, can also be used to reduce lysyl hydroxylase activity in cultured cells. An in vivo pilot dosing study established 50 mg⋅kg^-1⋅day^-1 as the maximum possible minoxidil dose for intraperitoneal administration in newborn mouse pups. When administered at 50 mg⋅kg^-1⋅day^-1 to newborn mouse pups, minoxidil was detected in the lungs but did not impact lysine hydroxylation, collagen crosslinking, or lysyl hydroxylase expression in the lungs. Consistent with no impact on mouse lung extracellular matrix structures, minoxidil administration did not alter the course of normal or stunted lung development in newborn mice. At doses of up to 50 mg⋅kg⋅day^-1, pharmacologically active concentrations of minoxidil were not achieved in neonatal mouse lung tissue; thus, minoxidil cannot be used to attenuate lysyl hydroxylase expression or activity during mouse lung development. These data also highlight the need for new and specific lysyl hydroxylase inhibitors. SIGNIFICANCE STATEMENT: Extracellular matrix crosslinking is mediated by lysyl hydroxylases, which generate hydroxylated lysyl residues in procollagen peptides. Deregulated collagen crosslinking is a pathogenic component of a spectrum of diseases, and thus, there is interest in validating lysyl hydroxylases as pathogenic mediators of disease and potential "druggable" targets. Minoxidil, administered at the maximum possible dose, did not inhibit lysyl hydroxylation in newborn mouse lungs, suggesting that minoxidil was unlikely to be of use in studies that pharmacologically target lysyl hydroxylation in vivo.

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.

Mouse genetic background impacts susceptibility to hyperoxia-driven perturbations to lung maturation

BACKGROUND

The laboratory mouse is widely used in preclinical models of bronchopulmonary dysplasia, where lung alveolarization is stunted by exposure of pups to hyperoxia. Whether the diverse genetic backgrounds of different inbred mouse strains impacts lung development in newborn mice exposed to hyperoxia has not been systematically assessed.

METHODS

Hyperoxia (85% O₂ , 14 days)-induced perturbations to lung alveolarization were assessed by design-based stereology in C57BL/6J, BALB/cJ, FVB/NJ, C3H/HeJ, and DBA/2J inbred mouse strains. The expression of components of the lung antioxidant machinery was assessed by real-time reverse transcriptase polymerase chain reaction and immunoblot.

RESULTS

Hyperoxia-reduced lung alveolar density in all five mouse strains to different degrees (C57BL/6J, 64.8%; FVB/NJ, 47.4%; BALB/cJ, 46.4%; DBA/2J, 45.9%; and C3H/HeJ, 35.9%). Hyperoxia caused a 94.5% increase in mean linear intercept in the C57BL/6J strain, whilst the C3H/HeJ strain was the least affected (31.6% increase). In contrast, hyperoxia caused a 65.4% increase in septal thickness in the FVB/NJ strain, where the C57BL/6J strain was the least affected (30.3% increase). The expression of components of the lung antioxidant machinery in response to hyperoxia was strain dependent, with the C57BL/6J strain exhibiting the most dramatic engagement. Baseline expression levels of components of the lung antioxidant systems were different in the five mouse strains studied, under both normoxic and hyperoxic conditions.

CONCLUSION

The genetic background of laboratory mouse strains dramatically influenced the response of the developing lung to hyperoxic insult. This might be explained, at least in part, by differences in how antioxidant systems are engaged by different mouse strains after hyperoxia exposure.

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.