Developmentally Regulated Innate Immune NFκB Signaling Mediates IL-1α Expression in the Perinatal Murine Lung

Implications of neonatal absence of innate immune mediated NFκB/AP1 signaling in the murine liver

BACKGROUND

The developmental immaturity of the innate immune system helps explains the increased risk of infection in the neonatal period. Importantly, innate immune signaling pathways such as p65/NFκB and c-Jun/AP1 are responsible for the prevention of hepatocyte apoptosis in adult animals, yet whether developmental immaturity of these pathways increases the risk of hepatic injury in the neonatal period is unknown.

METHODS

Using a murine model of endotoxemia (LPS 5 mg/kg IP x 1) in neonatal (P3) and adult mice, we evaluated histologic evidence of hepatic injury and apoptosis, presence of p65/NFκB and c-Jun/AP1 activation and associated transcriptional regulation of apoptotic genes.

RESULTS

We demonstrate that in contrast to adults, endotoxemic neonatal (P3) mice exhibit a significant increase in hepatic apoptosis. This is associated with absent hepatic p65/NFκB signaling and impaired expression of anti-apoptotic target genes. Hepatic c-Jun/AP1 activity was attenuated in endotoxemic P3 mice, with resulting upregulation of pro-apoptotic factors.

CONCLUSIONS

These results demonstrate that developmental absence of innate immune p65/NFκB and c-Jun/AP1 signaling, and target gene expression is associated with apoptotic injury in neonatal mice. More work is needed to determine if this contributes to long-term hepatic dysfunction, and whether immunomodulatory approaches can prevent this injury.

IMPACT

Various aspects of developmental immaturity of the innate immune system may help explain the increased risk of infection in the neonatal period. In adult models of inflammation and infection, innate immune signaling pathways such as p65/NFκB and c-Jun/AP1 are responsible for a protective, pro-inflammatory transcriptome and regulation of apoptosis. We demonstrate that in contrast to adults, endotoxemic neonatal (P3) mice exhibit a significant increase in hepatic apoptosis associated with absent hepatic p65/NFκB signaling and c-Jun/AP1 activity. We believe that these results may explain in part hepatic dysfunction with neonatal sepsis, and that there may be unrecognized developmental and long-term hepatic implications of early life exposure to systemic inflammatory stress.

Integrated MicroRNA-mRNA Analyses of Distinct Expression Profiles in Hyperoxia-Induced Bronchopulmonary Dysplasia in Neonatal Mice

OBJECTIVE

Bronchopulmonary dysplasia (BPD) is a common chronic lung disease of preterm neonates; the underlying pathogenesis is not fully understood. Recent studies suggested microRNAs (miRNAs) may be involved in BPD.

STUDY DESIGN

miRNA and mRNA microarrays were performed to analyze the expression profiles of miRNA and mRNA in BPD and control lung tissues after oxygen and air exposure on day 21. Bioinformatics methods, including Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG), were performed to predict the potential functions of differentially expressed genes. Then, miRNA-mRNA regulatory network was constructed by protein-protein interaction (PPI) data and TarBase data.

RESULTS

Our results showed that a total of 192 differentially expressed miRNAs (74 downregulated and 118 upregulated) and 1,225 differentially expressed mRNAs (479 downregulated and 746 upregulated) were identified between BPD mice and normoxia-control mice. GO and KEGG analysis showed that for downregulated genes, the top significant enriched GO terms and KEGG pathways were both mainly related to immune and inflammation processes; for upregulated genes, the top significant enriched GO terms and KEGG pathways were both mainly related to extracellular matrix (ECM) remodeling. PPI network and miRNA-mRNA regulatory network construction revealed that the key genes and pathways associated with inflammation and immune regulation.

CONCLUSION

Our findings revealed the integrated miRNA-mRNA data of distinct expression profiles in hyperoxia-induced BPD mice, and may provide some clues of the potential biomarkers for BPD, and provide novel insights into the development of new promising biomarkers for the treatment of BPD.

KEY POINTS

· Integrated advanced bioinformatics methods may offer a better way to understand the molecular expression profiles involved in BPD.. · ECM remodeling, inflammation, and immune regulation may be essential to BPD.. · The miRNA-mRNA regulatory network construction may contribute to develop new biomarkers for the treatment of BPD..

Postnatal Sepsis and Bronchopulmonary Dysplasia in Premature Infants: Mechanistic Insights into "New BPD"

Bronchopulmonary dysplasia (BPD) is a debilitating disease in premature infants resulting from lung injury that disrupts alveolar and pulmonary vascular development. Despite the use of lung-protective ventilation and targeted oxygen therapy, BPD rates have not significantly changed over the last decade. Recent evidence suggests that sepsis and conditions initiating the systemic inflammatory response syndrome in preterm infants are key risk factors for BPD. However, the mechanisms by which sepsis-associated systemic inflammation and microbial dissemination program aberrant lung development are not fully understood. Progress has been made within the last 5 years with the inception of animal models allowing mechanistic investigations into neonatal acute lung injury and alveolar remodeling due to endotoxemia and NEC. These recent studies begin to unravel the pathophysiology of early endothelial immune activation via pattern recognition receptors such as Toll Like Receptor 4 and disruption of critical lung developmental processes such as angiogenesis, extracellular matrix deposition, and ultimately alveologenesis. Here we review scientific evidence from preclinical models of neonatal sepsis-induced lung injury to new data emerging from clinical literature.

The Acute Hepatic NF-κB-Mediated Proinflammatory Response to Endotoxemia Is Attenuated in Intrauterine Growth-Restricted Newborn Mice

Intrauterine growth restriction (IUGR) is a relevant predictor for higher rates of neonatal sepsis worldwide and is associated with an impaired neonatal immunity and lower immune cell counts. During the perinatal period, the liver is a key immunological organ responsible for the nuclear factor kappa B (NF-κB)-mediated innate immune response to inflammatory stimuli, but whether this role is affected by IUGR is unknown. Herein, we hypothesized that the newborn liver adapts to calorie-restriction IUGR by inducing changes in the NF-κB signaling transcriptome, leading to an attenuated acute proinflammatory response to intraperitoneal lipopolysaccharide (LPS). We first assessed the hepatic gene expression of key NF-κB factors in the IUGR and normally grown (NG) newborn mice. Real-time quantitative PCR (RT-qPCR) analysis revealed an upregulation of both IκB proteins genes (Nfkbia and Nfkbib) and the NF-κB subunit Nfkb1 in IUGR vs. NG. We next measured the LPS-induced hepatic expression of acute proinflammatory genes (Ccl3, Cxcl1, Il1b, Il6, and Tnf) and observed that the IUGR liver produced an attenuated acute proinflammatory cytokine gene response (Il1b and Tnf) to LPS in IUGR vs. unexposed (CTR). Consistent with these results, LPS-exposed hepatic tumor necrosis factor alpha (TNF-α) protein concentrations were lower in IUGR vs. LPS-exposed NG and did not differ from IUGR CTR. Sex differences at the transcriptome level were observed in the IUGR male vs. female. Our results demonstrate that IUGR induces key modifications in the NF-κB transcriptomic machinery in the newborn that compromised the acute proinflammatory cytokine gene and protein response to LPS. Our results bring novel insights in understanding how the IUGR newborn is immunocompromised due to fundamental changes in NF-κB key factors.

Interleukin 1α: a comprehensive review on the role of IL-1α in the pathogenesis and treatment of autoimmune and inflammatory diseases

The interleukin (IL)-1 family member IL-1α is a ubiquitous and pivotal pro-inflammatory cytokine. The IL-1α precursor is constitutively present in nearly all cell types in health, but is released upon necrotic cell death as a bioactive mediator. IL-1α is also expressed by infiltrating myeloid cells within injured tissues. The cytokine binds the IL-1 receptor 1 (IL-1R1), as does IL-1β, and induces the same pro-inflammatory effects. Being a bioactive precursor released upon tissue damage and necrotic cell death, IL-1α is central to the pathogenesis of numerous conditions characterized by organ or tissue inflammation. These include conditions affecting the lung and respiratory tract, dermatoses and inflammatory skin disorders, systemic sclerosis, myocarditis, pericarditis, myocardial infarction, coronary artery disease, inflammatory thrombosis, as well as complex multifactorial conditions such as COVID-19, vasculitis and Kawasaki disease, Behcet's syndrome, Sjogren Syndrome, and cancer. This review illustrates the clinical relevance of IL-1α to the pathogenesis of inflammatory diseases, as well as the rationale for the targeted inhibition of this cytokine for treatment of these conditions. Three biologics are available to reduce the activities of IL-1α; the monoclonal antibody bermekimab, the IL-1 soluble receptor rilonacept, and the IL-1 receptor antagonist anakinra. These advances in mechanistic understanding and therapeutic management make it incumbent on physicians to be aware of IL-1α and of the opportunity for therapeutic inhibition of this cytokine in a broad spectrum of diseases.

Maturation of the Acute Hepatic TLR4/NF-κB Mediated Innate Immune Response Is p65 Dependent in Mice

Compared to adults, neonates are at increased risk of infection. There is a growing recognition that dynamic qualitative and quantitative differences in immunity over development contribute to these observations. The liver plays a key role as an immunologic organ, but whether its contribution to the acute innate immune response changes over lifetime is unknown. We hypothesized that the liver would activate a developmentally-regulated acute innate immune response to intraperitoneal lipopolysaccharide (LPS). We first assessed the hepatic expression and activity of the NF-κB, a key regulator of the innate immune response, at different developmental ages (p0, p3, p7, p35, and adult). Ontogeny of the NF-κB subunits (p65/p50) revealed a reduction in Rela (p65) and Nfkb1 (p105, precursor to p50) gene expression (p0) and p65 subunit protein levels (p0 and p3) vs. older ages. The acute hepatic innate immune response to LPS was associated by the degradation of the NF-κB inhibitory proteins (IκBα and IκBβ), and nuclear translocation of the NF-κB subunit p50 in all ages, whereas nuclear translocation of the NF-κB subunit p65 was only observed in the p35 and adult mouse. Consistent with these findings, we detected NF-κB subunit p65 nuclear staining exclusively in the LPS-exposed adult liver compared with p7 mouse. We next interrogated the LPS-induced hepatic expression of pro-inflammatory genes (Tnf, Icam1, Ccl3, and Traf1), and observed a gradually increase in gene expression starting from p0. Confirming our results, hepatic NF-κB subunit p65 nuclear translocation was associated with up-regulation of the Icam1 gene in the adult, and was not detected in the p7 mouse. Thus, an inflammatory challenge induces an NF-κB-mediated hepatic innate immune response activation across all developmental ages, but nuclear translocation of the NF-κB subunit p65 and associated induction of pro-inflammatory genes occurred only after the first month of life. Our results demonstrate that the LPS-induced hepatic innate immune response is developmentally regulated by the NF-κB subunit p65 in the mouse.

Recombinant Human Elafin Ameliorates Chronic Hyperoxia-Induced Lung Injury by Inhibiting Nuclear Factor-Kappa B Signaling in Neonatal Mice

The study aimed to investigate whether recombinant human elafin can prevent hyperoxia-induced pulmonary inflammation in newborn mice, and to explore the mechanism underlying the inhibitory effects of elafin on nuclear factor-kappa B (NF-κB) signaling pathway. Neonatal C57BL/6J mice were exposed to 85% O₂ for 1, 3, 7, 14, or 21 days. Then, elafin was administered daily for 20 days through intraperitoneal injection. After treatment, morphometric analysis, quantitative real-time polymerase chain reaction, terminal deoxynucleotidyl transferase dUTP nick end labeling staining, and Western blotting were carried out to determine the key markers involved in inflammatory process and the potential signaling pathways in hyperoxia-exposed newborn mice treated with elafin. In neonatal bronchopulmonary dysplasia (BPD) mice, hyperoxia induced apoptosis by increasing Bcl-2-associated X protein expression, and triggered inflammation by upregulating the expression levels of interleukin (IL)-1β, IL-6, IL-8, and tumor necrosis factor-α. Moreover, hyperoxia activated NF-κB signaling pathway by promoting the nuclear translocation of p65 in lung tissue. However, all these changes could be inhibited or reversed by elafin at least partially. Elafin reduced apoptosis, suppressed inflammation cytokines, and improved NF-κB p65 nuclear accumulation in hyperoxia-exposed neonatal mice, indicating that this recombinant protein can serve as a novel target for the treatment of BPD.

CpG-ODN-mediated TLR9 innate immune signalling and calcium dyshomeostasis converge on the NFκB inhibitory protein IκBβ to drive IL1α and IL1β expression

Sterile inflammation contributes to many pathological states associated with mitochondrial injury. Mitochondrial injury disrupts calcium homeostasis and results in the release of CpG-rich mitochondrial DNA. The role of CpG-stimulated TLR9 innate immune signalling and sterile inflammation is well studied; however, how calcium dyshomeostasis affects this signalling is unknown. Therefore, we interrogated the relationship beτween intracellular calcium and CpG-induced TLR9 signalling in murine macrophages. We found that CpG-ODN-induced NFκB-dependent IL1α and IL1β expression was significantly attenuated by both calcium chelation and calcineurin inhibition, a finding mediated by inhibition of degradation of the NFκB inhibitory protein IκBβ. In contrast, calcium ionophore exposure increased CpG-induced IκBβ degradation and IL1α and IL1β expression. These results demonstrate that through its effect on IκBβ degradation, increased intracellular Ca²⁺ drives a pro-inflammatory TLR9-mediated innate immune response. These results have implications for the study of innate immune signalling downstream of mitochondrial stress and injury.

Toxic Acetaminophen Exposure Induces Distal Lung ER Stress, Proinflammatory Signaling, and Emphysematous Changes in the Adult Murine Lung

Clinical studies have demonstrated a strong association between both acute toxic exposure and the repetitive, chronic exposure to acetaminophen (APAP) with pulmonary dysfunction. However, the mechanisms underlying this association are unknown. Preclinical reports have demonstrated that significant bronchiolar injury occurs with toxic APAP exposure, but very little information exists on how the distal lung is affected. However, cells in the alveolar space, including the pulmonary epithelium and resident macrophages, express the APAP-metabolizing enzyme CYP2E1 and are a potential source of toxic metabolites and subsequent distal lung injury. Thus, we hypothesized that distal lung injury would occur in a murine model of toxic APAP exposure. Following exposure of APAP (280 mg/kg, IP), adult male mice were found to have significant proximal lung histopathology as well as distal lung inflammation and emphysematous changes. Toxic APAP exposure was associated with increased CYP2E1 expression in the distal lung and accumulation of APAP-protein adducts. This injury was associated with distal lung activation of oxidant stress, endoplasmic reticulum stress, and inflammatory stress response pathways. Our findings confirm that following toxic APAP exposure, distal lung CYP2E1 expression is associated with APAP metabolism, tissue injury, and oxidant, inflammatory, and endoplasmic reticulum signaling. This previously unrecognized injury may help improve our understanding of the relationship between APAP and pulmonary-related morbidity.

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.