Consequences of Hypoxia for the Pulmonary Alveolar Epithelial Cell Innate Immune Response

Aryl Hydrocarbon Receptor Activation in Pulmonary Alveolar Epithelial Cells Limits Inflammation and Preserves Lung Epithelial Cell Integrity

The aryl hydrocarbon receptor (AHR) is a receptor/transcription factor widely expressed in the lung. The physiological roles of AHR expressed in the alveolar epithelium remain unclear. In this study, we tested the hypothesis that alveolar epithelial AHR activity plays an important role in modulating inflammatory responses and maintaining alveolar integrity during lung injury and repair. AHR is expressed in alveolar epithelial cells (AECs) and is active. AHR activation with the endogenous AHR ligand, FICZ (5,11-dihydroindolo[3,2-b] carbazole-6-carboxaldehyde), significantly suppressed inflammatory cytokine expression in response to inflammatory stimuli in primary murine AECs and in the MLE-15 epithelial cell line. In an LPS model of acute lung injury in mice, coadministration of FICZ with LPS suppressed protein leak, reduced neutrophil accumulation in BAL fluid, and suppressed inflammatory cytokine expression in lung tissue and BAL fluid. Relevant to healing following inflammatory injury, AHR activation suppressed TGF-β-induced expression of genes associated with epithelial-mesenchymal transition. Knockdown of AHR in primary AECs with shRNA or in CRISPR-Cas-9-induced MLE-15 cells resulted in upregulation of α-smooth muscle actin (αSma), Col1a1, and Fn1 and reduced expression of epithelial genes Col4a1 and Sdc1. MLE-15 clones lacking AHR demonstrated accelerated wound closure in a scratch model. AHR activation with FICZ enhanced barrier function (transepithelial electrical resistance) in primary murine AECs and limited decline of transepithelial electrical resistance following inflammatory injury. AHR activation in AECs preserves alveolar integrity by modulating inflammatory cytokine expression while enhancing barrier function and limiting stress-induced expression of mesenchymal genes.

Integrative transcriptome-proteome approach reveals key hypoxia-related features involved in the neuroprotective effects of Yang Xue oral liquid on Alzheimer's and Parkinson's disease

Introduction: This study investigates the role of hypoxia-related genes in the neuroprotective efficacy of Yang Xue oral liquid (YXKFY) in Alzheimer's disease (AD) and Parkinson's disease (PD). Methods and results: Using differential expression and weighted gene co-expression network analysis (WGCNA), we identified 106 and 9 hypoxia-associated genes in AD and PD, respectively, that are implicated in the transcriptomic and proteomic profiles. An artificial intelligence-driven hypoxia signature (AIDHS), comprising 17 and 3 genes for AD and PD, was developed and validated across nine independent cohorts (n = 1713), integrating 10 machine learning algorithms and 113 algorithmic combinations. Significant associations were observed between AIDHS markers and immune cells in AD and PD, including naive CD4+ T cells, macrophages, and neutrophils. Interactions with miRNAs (hsa-miR-1, hsa-miR-124) and transcription factors (USF1) were also identified. Single-cell RNA sequencing (scRNA-seq) data highlighted distinct expression patterns of AIDHS genes in various cell types, such as high expression of TGM2 in endothelial cells, PDGFRB in endothelial and mesenchymal cells, and SYK in microglia. YXKFY treatment was shown to repair cellular damage and decrease reactive oxygen species (ROS) levels. Notably, genes with previously dysfunctional expression, including FKBPL, TGM2, PPIL1, BLVRB, and PDGFRB, exhibited significant recovery after YXKFY treatment, associated with riboflavin and lysicamine. Conclusion: The above genes are suggested to be central to hypoxia and neuroinflammation responses in AD and PD, and are potential key mediators of YXKFY's neuroprotective action.

The Intersection of Pulmonary Vascular Disease and Hypoxia-Inducible Factors

Hypoxia-inducible factors (HIFs) are a family of nuclear transcription factors that serve as the master regulator of the adaptive response to hypoxia. In the lung, HIFs orchestrate multiple inflammatory pathways and signaling. They have been reported to have a major role in the initiation and progression of acute lung injury, chronic obstructive pulmonary disease, pulmonary fibrosis, and pulmonary hypertension. Although there seems to be a clear mechanistic role for both HIF 1α and 2α in pulmonary vascular diseases including PH, a successful translation into a definitive therapeutic modality has not been accomplished to date.

Hypoxia-Inducible Factor 1α and Its Role in Lung Injury: Adaptive or Maladaptive

Hypoxia-inducible factors (HIFs) are transcription factors critical for the adaptive response to hypoxia. There is also an essential link between hypoxia and inflammation, and HIFs have been implicated in the dysregulated immune response to various insults. Despite the prevalence of hypoxia in tissue trauma, especially involving the lungs, there remains a dearth of studies investigating the role of HIFs in clinically relevant injury models. Here, we summarize the effects of HIF-1α on the vasculature, metabolism, inflammation, and apoptosis in the lungs and review the role of HIFs in direct lung injuries, including lung contusion, acid aspiration, pneumonia, and COVID-19. We present data that implicates HIF-1α in the context of arguments both in favor and against its role as adaptive or injurious in the propagation of the acute inflammatory response in lung injuries. Finally, we discuss the potential for pharmacological modulation of HIFs as a new class of therapeutics in the modern intensive care unit.

Single-cell transcriptome atlas reveals protective characteristics of COVID-19 mRNA vaccine

Messenger RNA (mRNA) vaccines are promising alternatives to conventional vaccines in many aspects. We previously developed a lipopolyplex (LPP)-based mRNA vaccine (SW0123) that demonstrated robust immunogenicity and strong protective capacity against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection in mice and rhesus macaques. However, the immune profiles and mechanisms of pulmonary protection induced by SW0123 remain unclear. Through high-resolution single-cell analysis, we found that SW0123 vaccination effectively suppressed SARS-CoV-2-induced inflammatory responses by inhibiting the recruitment of proinflammatory macrophages and increasing the frequency of polymorphonuclear myeloid-derived suppressor cells. In addition, the apoptotic process in both lung epithelial and endothelial cells was significantly inhibited, which was proposed to be one major mechanism contributing to vaccine-induced lung protection. Cell-cell interaction in the lung compartment was also altered by vaccination. These data collectively unravel the mechanisms by which the SW0123 protects against lung damage caused by SARS-CoV-2 infection.

Transcriptome sequencing reveals altered ciliogenesis under hypoxia in nasal epithelial cells from chronic rhinosinusitis with nasal polyps

Background

Hypoxia is considered a key factor in the pathogenesis of chronic rhinosinusitis with nasal polyps (CRSwNP). However, the specific mechanism driving polypogenesis under hypoxic conditions is unclear. This study aimed to explore hypoxia-induced alterations in the transcriptome of human nasal epithelial cells (HNECs) in vitro.

Methods

HNECs derived from the tissue of patients with CRSwNP were established as air-liquid interface (ALI) cultures. Confluent cultures were kept submerged or treated with cobalt chloride (CoCl2) to induce hypoxia. Transcriptome analysis was used to identify key mRNAs involved in this process. Real-time PCR (RT-PCR), Western blotting, and immunofluorescence were used to observe the effects of hypoxia on ciliogenesis.

Results

Numerous genes, biological processes and pathways were altered under submerged culture conditions or after CoCl2 treatment. Analysis of the results under both hypoxic conditions revealed that the transcriptional program responsible for ciliogenesis was significantly impaired. Downregulation of cilia-related genes and inhibition of ciliated cell differentiation under hypoxia were confirmed by RT-PCR, Western blot and immunofluorescence analyses.

Conclusion

Hypoxia impairs ciliogenesis and ciliary function in HNECs, which might play a role in the pathogenesis of CRSwNP.

HIF-1α Stabilization in Flagellin-Stimulated Human Bronchial Cells Impairs Barrier Function

The respiratory epithelium provides a first line of defense against pathogens. Hypoxia-inducible factor (HIF)1α is a transcription factor which is stabilized in hypoxic conditions through the inhibition of prolyl-hydroxylase (PHD)2, the enzyme that marks HIF1α for degradation. Here, we studied the impact of HIF1α stabilization on the response of primary human bronchial epithelial (HBE) cells to the bacterial component, flagellin. The treatment of flagellin-stimulated HBE cells with the PHD2 inhibitor IOX2 resulted in strongly increased HIF1α expression. IOX2 enhanced the flagellin-induced expression of the genes encoding the enzymes involved in glycolysis, which was associated with the intracellular accumulation of pyruvate. An untargeted pathway analysis of RNA sequencing data demonstrated the strong inhibitory effects of IOX2 toward key innate immune pathways related to cytokine and mitogen-activated kinase signaling cascades in flagellin-stimulated HBE cells. Likewise, the cell-cell junction organization pathway was amongst the top pathways downregulated by IOX2 in flagellin-stimulated HBE cells, which included the genes encoding claudins and cadherins. This IOX2 effect was corroborated by an impaired barrier function, as measured by dextran permeability. These results provide a first insight into the effects associated with HIF1α stabilization in the respiratory epithelium, suggesting that HIF1α impacts properties that are key to maintaining homeostasis upon stimulation with a relevant bacterial agonist.

Hypoxia‐inducible factor (HIF)‐1α‐induced regulation of lung injury in pulmonary aspiration is mediated through NF‐kB

Aspiration‐induced lung injury is a common grievance encountered in the intensive care unit (ICU). It is a significant risk factor for improving ventilator‐associated pneumonia (VAP) and acute respiratory distress syndrome (ARDS). Hypoxia‐inducible factor (HIF)‐1α is one of the primary transcription factors responsible for regulating the cellular response to changes in oxygen tension. Here, we sought to determine the role of HIF‐1α and specifically the role of type 2 alveolar epithelial cells in generating the acute inflammatory response following acid and particles (CASP) aspiration. Previous studies show HIF‐1 α is involved in regulating the hypoxia‐stimulated expression of MCP‐1 in mice and humans. The CASP was induced in C57BL/6, ODD‐Luc, HIF‐1α (+/+) control, and HIF‐1α conditional knockout (HIF‐1α (−/−) mice). Following an injury in ODD mice, explanted organs were subjected to IVIS imaging to measure the degree of hypoxia. HIF‐1α expression, BAL albumin, cytokines, and histology were measured following CASP. In C57BL/6 mice, the level of HIF‐1α was increased at 1 h after CASP. There were significantly increased levels of albumin and cytokines in C57BL/6 and ODD‐Luc mice lungs following CASP. HIF‐1α (+/+) mice given CASP demonstrated a synergistic increase in albumin leakage, increased pro‐inflammatory cytokines, and worse injury. MCP‐1 antibody neutralized HIF‐1α (+/+) mice showed reduced granuloma formation. The NF‐κB expression was increased substantially in the HIF‐1α (+/+) mice following CASP compared to HIF‐1α (−/−) mice. Our data collectively identify that HIF‐1α upregulation of the acute inflammatory response depends on NF‐κB following CASP.

Alveolar macrophages rely on GM-CSF from alveolar epithelial type 2 cells before and after birth

Programs defining tissue-resident macrophage identity depend on local environmental cues. For alveolar macrophages (AMs), these signals are provided by immune and nonimmune cells and include GM-CSF (CSF2). However, evidence to functionally link components of this intercellular cross talk remains scarce. We thus developed new transgenic mice to profile pulmonary GM-CSF expression, which we detected in both immune cells, including group 2 innate lymphoid cells and γδ T cells, as well as AT2s. AMs were unaffected by constitutive deletion of hematopoietic Csf2 and basophil depletion. Instead, AT2 lineage-specific constitutive and inducible Csf2 deletion revealed the nonredundant function of AT2-derived GM-CSF in instructing AM fate, establishing the postnatal AM compartment, and maintaining AMs in adult lungs. This AT2-AM relationship begins during embryogenesis, where nascent AT2s timely induce GM-CSF expression to support the proliferation and differentiation of fetal monocytes contemporaneously seeding the tissue, and persists into adulthood, when epithelial GM-CSF remains restricted to AT2s.

Escherichia coli infection activates the production of IFN-α and IFN-β via the JAK1/STAT1/2 signaling pathway in lung cells

Escherichia coli infections can result in lung injury, which may be closely linked to the induction of interferon secretion. The Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway is one of most important pathways that regulate interferon production. Thus, the present study aimed to dissect whether E. coli infections can regulate interferon production and the underlying mechanisms. For this aim, two lung cell lines, a human bronchial epithelial cell line transformed with Ad12-SV40 2B (BEAS-2b) and a human fetal lung fibroblast (HFL1) cell line, were used. The effects of E. coli infections on interferon production were studied using qRT-PCR, Western blot, and siRNA knockdown assays. E. coli infections remarkably promoted the expression levels of IFN-α, IFN-β, and ISGs. Major components of the JAK/STAT pathway, including JAK1, STAT1, and STAT2, were demonstrated to be regulated by E. coli infections. Importantly, knockdown of JAK1, STAT1, and STAT2 abolished the induction of IFN-α, IFN-β, and ISGs by E. coli. Therefore, experiments in the present study demonstrated that E. coli infections remarkably promoted interferon production in lung cells, which was closely regulated by the JAK/STAT signaling pathway. The findings in the present study are useful for further understanding the pathogenesis of E. coli infections in the lung and finding novel therapies to treat E. coli-induced lung injury.

A Machine-Generated View of the Role of Blood Glucose Levels in the Severity of COVID-19

SARS-CoV-2 started spreading toward the end of 2019 causing COVID-19, a disease that reached pandemic proportions among the human population within months. The reasons for the spectrum of differences in the severity of the disease across the population, and in particular why the disease affects more severely the aging population and those with specific preconditions are unclear. We developed machine learning models to mine 240,000 scientific articles openly accessible in the CORD-19 database, and constructed knowledge graphs to synthesize the extracted information and navigate the collective knowledge in an attempt to search for a potential common underlying reason for disease severity. The machine-driven framework we developed repeatedly pointed to elevated blood glucose as a key facilitator in the progression of COVID-19. Indeed, when we systematically retraced the steps of the SARS-CoV-2 infection, we found evidence linking elevated glucose to each major step of the life-cycle of the virus, progression of the disease, and presentation of symptoms. Specifically, elevations of glucose provide ideal conditions for the virus to evade and weaken the first level of the immune defense system in the lungs, gain access to deep alveolar cells, bind to the ACE2 receptor and enter the pulmonary cells, accelerate replication of the virus within cells increasing cell death and inducing an pulmonary inflammatory response, which overwhelms an already weakened innate immune system to trigger an avalanche of systemic infections, inflammation and cell damage, a cytokine storm and thrombotic events. We tested the feasibility of the hypothesis by manually reviewing the literature referenced by the machine-generated synthesis, reconstructing atomistically the virus at the surface of the pulmonary airways, and performing quantitative computational modeling of the effects of glucose levels on the infection process. We conclude that elevation in glucose levels can facilitate the progression of the disease through multiple mechanisms and can explain much of the differences in disease severity seen across the population. The study provides diagnostic considerations, new areas of research and potential treatments, and cautions on treatment strategies and critical care conditions that induce elevations in blood glucose levels.

A novel standalone microfluidic device for local control of oxygen tension for intestinal-bacteria interactions

The intestinal environment is unique because it supports the intestinal epithelial cells under a normal oxygen environment and the microbiota under an anoxic environment. Due to importance of understanding the interactions between the epithelium and the microbiota, there is a strong need for developing representative and simple experimental models. Current approaches do not capture the partitioned oxygen environment, require external anaerobic chambers, or are complex. Another major limitation is that with the solutions that can mimic this oxygen environment, the oxygenation level of the epithelial cells is not known, raising the question whether the cells are hypoxic or not. We report standalone microfluidic devices that form a partitioned oxygen environment without the use of an external anaerobic chamber or oxygen scavengers to coculture intestinal epithelial and bacterial cells. By changing the thickness of the device cover, the oxygen tension in the chamber was modulated. We verified the oxygen levels using several tests: microscale oxygen sensitive sensors which were integrated within the devices, immunostaining of Caco-2 cells to determine hypoxia levels, and genetically encoded bacteria to visualize the growth. Collectively, these methods monitored oxygen concentrations in the devices more comprehensively than previous reports and allowed for control of oxygen tension to match the requirements of both intestinal cells and anaerobic bacteria. Our experimental model is supported by the mathematical model that considered diffusion of oxygen into the top chamber. This allowed us to experimentally determine the oxygen consumption rate of the intestinal epithelial cells under perfusion.

Hypoxia induces expression of angiotensin-converting enzyme II in alveolar epithelial cells: Implications for the pathogenesis of acute lung injury in COVID-19

SARS-CoV-2 uptake by lung epithelial cells is a critical step in the pathogenesis of COVID-19. Viral entry is dependent on the binding of the viral spike protein to the angiotensin converting enzyme II protein (ACE2) on the host cell surface, followed by proteolytic cleavage by a host serine protease such as TMPRSS2. Infection of alveolar epithelial cells (AEC) in the distal lung is a key feature in progression to the acute respiratory distress syndrome (ARDS). We hypothesized that AEC expression of ACE2 is induced by hypoxia. In a murine model of hypoxic stress (12% FiO2), the total lung Ace2 mRNA and protein expression was significantly increased after 24 hours in hypoxia compared to normoxia (21% FiO2). In experiments with primary murine type II AEC, we found that exposure to hypoxia either in vivo (prior to isolation) or in vitro resulted in greatly increased AEC expression of both Ace2 (mRNA and protein) and of Tmprss2. However, when isolated type II AEC were maintained in culture over 5 days, with loss of type II cell characteristics and induction of type I cell features, Ace2 expression was greatly reduced, suggesting that this expression was a feature of only this subset of AEC. Finally, in primary human small airway epithelial cells (SAEC), ACE2 mRNA and protein expression were also induced by hypoxia, as was binding to purified spike protein. Hypoxia-induced increase in ACE2 expression in type II AEC may provide an explanation of the extended temporal course of human patients who develop ARDS in COVID-19.

Influence of Hypoxia on the Epithelial-Pathogen Interactions in the Lung: Implications for Respiratory Disease

Under normal physiological conditions, the lung remains an oxygen rich environment. However, prominent regions of hypoxia are a common feature of infected and inflamed tissues and many chronic inflammatory respiratory diseases are associated with mucosal and systemic hypoxia. The airway epithelium represents a key interface with the external environment and is the first line of defense against potentially harmful agents including respiratory pathogens. The protective arsenal of the airway epithelium is provided in the form of physical barriers, and the production of an array of antimicrobial host defense molecules, proinflammatory cytokines and chemokines, in response to activation by receptors. Dysregulation of the airway epithelial innate immune response is associated with a compromised immunity and chronic inflammation of the lung. An increasing body of evidence indicates a distinct role for hypoxia in the dysfunction of the airway epithelium and in the responses of both innate immunity and of respiratory pathogens. Here we review the current evidence around the role of tissue hypoxia in modulating the host-pathogen interaction at the airway epithelium. Furthermore, we highlight the work needed to delineate the role of tissue hypoxia in the pathophysiology of chronic inflammatory lung diseases such as asthma, cystic fibrosis, and chronic obstructive pulmonary disease in addition to novel respiratory diseases such as COVID-19. Elucidating the molecular mechanisms underlying the epithelial-pathogen interactions in the setting of hypoxia will enable better understanding of persistent infections and complex disease processes in chronic inflammatory lung diseases and may aid the identification of novel therapeutic targets and strategies.