Fibrotic lung disease inhibits innate immune responses to Staphylococcal pneumonia via impaired neutrophil and macrophage function

High fat diet feeding impairs neutrophil phagocytosis, bacterial killing, and neutrophil-induced hematopoietic regeneration

The prevalence of obesity and metabolic diseases have risen significantly over the past decades. Chronic inflammation in obesity is a link between obesity and secondary disease. While macrophages and monocytes are known to contribute to metabolic disease risk during diet exposure, little is known about the contribution of neutrophils. We assessed the impact of obesity on neutrophils using a 16-week model of diet-induced obesity. Bone marrow (BM) neutrophils significantly expanded with chronic high-fat diet (HFD), significantly decreased TNFɑ protein release, and impaired neutrophil regenerative function compared to normal diet (ND) neutrophils. scRNAseq and flow cytometry demonstrated HFD neutrophil heterogeneity and validated that these cells do not have elevated expression of proinflammatory genes without secondary stimulation. HFD neutrophils showed elevated expression of genes associated with lipid metabolism-acyl-CoA thioesterase 1 (Acot1), carnitine palmitoyltransferase 1a (Cpt1a), and perilipin 2 (Plin2). Consistent with the importance of lipid metabolism in driving dysfunction, neutrophils from HFD-fed animals and neutrophils treated with palmitate had impaired bacterial phagocytosis and killing responses. These data shed light on the complex regulation of intracellular lipids and the role of metabolism on neutrophil function during homeostasis and disease.

Caveolin Scaffolding Domain (CSD) Peptide LTI-2355 Modulates the Phagocytic and Synthetic Activity of Lung-Derived Myeloid Cells in Idiopathic Pulmonary Fibrosis (IPF) and Post-Acute Sequelae of COVID Fibrosis (PASC-F)

Rationale: The role of the innate immune system in idiopathic pulmonary fibrosis (IPF) remains poorly understood. However, a functional myeloid compartment is required to remove dying cells and cellular debris, as well as to mediate innate immune responses against pathogens. Aberrant macrophage activity has been described in patients with post-acute sequelae of COVID fibrosis (PASC-F), and caveolin scaffolding domain (CSD) peptides have been found to attenuate inflammation and fibrosis in mouse lung injury models. Therefore, we examined, for the first time, the effects of CSD peptide LTI-2355 on the functional and synthetic properties of human myeloid cells isolated from lung explant tissue of donor lungs as well as IPF and PASC-F lung explant tissue. Methods and Results: CD45+ myeloid cells isolated from lung explant tissue from IPF and PASC-F patients exhibited an impaired capacity to clear autologous dead cells and cellular debris. The uptake of pathogen-coated bioparticles was impaired in myeloid cells from both fibrotic patient groups independent of the type of pathogen, highlighting an intrinsic functional cell impairment. LTI-2355 improved the phagocytic activity of both IPF and PASC-F myeloid cells, and this improvement was paired with decreased proinflammatory and pro-fibrotic synthetic activity. LTI-2355 was also shown to primarily target CD206-expressing IPF and PASC-F myeloid cells. Conclusions: Primary myeloid cells from IPF and PASC-F patients exhibit dysfunctional phagocytic and synthetic properties that are modulated by LTI-2355. LTI-2355 treatment of IPF myeloid cells resulted in significantly reduced sCD163, IFN-α2, IFN-γ, IL-2, IL-10, IL-12p40, and MMP-1 in the cell supernatant. This study highlights an additional mechanism of action of the CSD peptide in the treatment of IPF and progressive fibrotic lung disease.

Confined Mechanical Microenvironment Regulated Antibiotic Resistance in 3D Biofilm Aggregates Probed by Scanning Electrochemical Microscopy

Antibiotic resistance is a significant global concern. Clinical trials have highlighted discrepancies in antibiotic doses between in vivo three-dimensional (3D) biofilms and in vitro two-dimensional biofilm models. A critical factor often overlooked is the confined mechanical microenvironment (e.g., host extracellular matrix (ECM) stiffness) surrounding the in vivo biofilms, leading to inaccurate diagnosis and increased antibiotic resistance. Herein, we designed a 3D agarose-gel-based in vitro biofilm model and applied scanning electrochemical microscopy (SECM) to monitor the metabolic dynamics in situ, including cellular respiration and reactive oxygen species of an embedded single biofilm aggregate. We discovered distinct respiration patterns for biofilm aggregates embedded in stiff and soft gels at the single aggregate level, which was corroborated by transcriptional analysis. Our findings indicate that mechanical cues mediate antibiotic tolerance by reducing metabolic activity and increasing the production of extracellular polymeric substances (EPS). Additionally, we identified that metabolite glycine enhances the tricarboxylic acid cycle, suggesting its potential as an adjuvant to improve antibiotic efficacy. Knocking out the upregulated EPS-related gene (ΔyjbE) results in significantly reduced survival rates of ΔyjbE mutants in stiff agarose gels compared to the wild type, thereby enhancing antibiotic efficacy. Overall, our study demonstrates the versatility of the SECM-based strategy for investigating both metabolic dynamics and antibiotic resistance in biofilms and uncovers the role of ECM stiffness in mediating antibiotic resistance in 3D biofilms, paving the way for improved clinical strategies in antibiotic treatment.

Persistent microbial infections and idiopathic pulmonary fibrosis - an insight into non-typeable Haemophilus influenza pathogenesis

Interstitial lung disease (ILD) is characterized by chronic inflammation and scarring of the lungs, of which idiopathic pulmonary fibrosis (IPF) is the most devastating pathologic form. Idiopathic pulmonary fibrosis pathogenesis leads to loss of lung function and eventual death in 50% of patients, making it the leading cause of ILD-associated mortality worldwide. Persistent and subclinical microbial infections are implicated in the acute exacerbation of chronic lung diseases. However, while epidemiological studies have highlighted pollutants, gastric aspirate, and microbial infections as major causes for the progression and exacerbation of IPF, the role of persistent microbial infections in the pathogenesis of IPF remains unclear. In this review, we have focused on the role of persistent microbial infections, including viral, bacterial, and fungal infections, and their mechanisms of action in the pathogenesis of IPF. In particular, the mechanisms and pathogenesis of the Gram-negative bacteria Non-typeable Haemophilus influenzae (NTHi) in ILDs are discussed, along with growing evidence of its role in IPF, given its unique ability to establish persistent intracellular infections by leveraging its non-capsulated nature to evade host defenses. While antibiotic treatments are presumably beneficial to target the extracellular, interstitial, and systemic burden of pathogens, their effects are significantly reduced in combating pathogens that reside in the intracellular compartments. The review also includes recent clinical trials, which center on combinatorial treatments involving antimicrobials and immunosuppressants, along with antifibrotic drugs that help mitigate disease progression in IPF patients. Finally, future directions focus on mRNA-based therapeutics, given their demonstrated effectiveness across a wide range of clinical applications and feasibility in targeting intracellular pathogens.

RSV enhances Staphylococcus aureus bacterial growth in the lung

Patients coinfected with respiratory syncytial virus (RSV) and bacteria have longer hospital stays, higher risk of intensive care unit admission, and worse outcomes. We describe a model of RSV line 19F/methicillin-resistant Staphylococcus aureus (MRSA) USA300 coinfection that does not impair viral clearance, but prior RSV infection enhances USA300 MRSA bacterial growth in the lung. The increased bacterial burden post-RSV correlates with reduced accumulation of neutrophils and impaired bacterial killing by alveolar macrophages. Surprisingly, reduced neutrophil accumulation is likely not explained by reductions in phagocyte-recruiting chemokines or alterations in proinflammatory cytokine production compared with mice infected with S. aureus alone. Neutrophils from RSV-infected mice retain their ability to migrate toward chemokine signals, and neutrophils from the RSV-infected lung are better able to phagocytize and kill S. aureus ex vivo on a per cell basis. In contrast, while alveolar macrophages could ingest USA300 post-RSV, intracellular bacterial killing was impaired. The RSV/S. aureus coinfected lung promotes a state of overactivation in neutrophils, demonstrated by increased production of reactive oxygen species (ROS) that can drive formation of neutrophil extracellular traps (NETs), resulting in cell death. Mice with RSV/S. aureus coinfection had increased extracellular DNA and protein in bronchoalveolar lavage fluid and histological evidence confirmed NETosis in vivo. Taken together, these data highlight that prior RSV infection can prime the overactivation of neutrophils leading to cell death that impairs neutrophil accumulation in the lung. Additionally, alveolar macrophage killing of bacteria is impaired post-RSV. Together, these defects enhance USA300 MRSA bacterial growth in the lung post-RSV.

Staphylococcus aureus adapts to exploit collagen-derived proline during chronic infection

Staphylococcus aureus is a pulmonary pathogen associated with substantial human morbidity and mortality. As vaccines targeting virulence determinants have failed to be protective in humans, other factors are likely involved in pathogenesis. Here we analysed transcriptomic responses of human clinical isolates of S. aureus from initial and chronic infections. We observed upregulated collagenase and proline transporter gene expression in chronic infection isolates. Metabolomics of bronchiolar lavage fluid and fibroblast infection, growth assays and analysis of bacterial mutant strains showed that airway fibroblasts produce collagen during S. aureus infection. Host-adapted bacteria upregulate collagenase, which degrades collagen and releases proline. S. aureus then imports proline, which fuels oxidative metabolism via the tricarboxylic acid cycle. Proline metabolism provides host-adapted S. aureus with a metabolic benefit enabling out-competition of non-adapted strains. These data suggest that clinical settings characterized by airway repair processes and fibrosis provide a milieu that promotes S. aureus adaptation and supports infection.

DEFA1A3 DNA gene-dosage regulates the kidney innate immune response during upper urinary tract infection

Antimicrobial peptides (AMPs) are host defense effectors with potent neutralizing and immunomodulatory functions against invasive pathogens. The AMPs α-Defensin 1-3/DEFA1A3 participate in innate immune responses and influence patient outcomes in various diseases. DNA copy-number variations in DEFA1A3 have been associated with severity and outcomes in infectious diseases including urinary tract infections (UTIs). Specifically, children with lower DNA copy numbers were more susceptible to UTIs. The mechanism of action by which α-Defensin 1-3/DEFA1A3 copy-number variations lead to UTI susceptibility remains to be explored. In this study, we use a previously characterized transgenic knock-in of the human DEFA1A3 gene mouse to dissect α-Defensin 1-3 gene dose-dependent antimicrobial and immunomodulatory roles during uropathogenic Escherichia coli (UPEC) UTI. We elucidate the relationship between kidney neutrophil- and collecting duct intercalated cell-derived α-Defensin 1-3/DEFA1A3 expression and UTI. We further describe cooperative effects between α-Defensin 1-3 and other AMPs that potentiate the neutralizing activity against UPEC. Cumulatively, we demonstrate that DEFA1A3 directly protects against UPEC meanwhile impacting pro-inflammatory innate immune responses in a gene dosage-dependent manner.

TRPV4 Regulates the Macrophage Metabolic Response to Limit Sepsis-induced Lung Injury

Sepsis is a systemic inflammatory response that requires effective macrophage metabolic functions to resolve ongoing inflammation. Previous work showed that the mechanosensitive cation channel, transient receptor potential vanilloid 4 (TRPV4), mediates macrophage phagocytosis and cytokine production in response to lung infection. Here, we show that TRPV4 regulates glycolysis in a stiffness-dependent manner by augmenting macrophage glucose uptake by GLUT1. In addition, TRPV4 is required for LPS-induced phagolysosome maturation in a GLUT1-dependent manner. In a cecal slurry mouse model of sepsis, TRPV4 regulates sepsis-induced glycolysis as measured by BAL fluid (BALF) lactate and sepsis-induced lung injury as measured by BALF total protein and lung compliance. TRPV4 is necessary for bacterial clearance in the peritoneum to limit sepsis-induced lung injury. It is interesting that BALF lactate is increased in patients with sepsis compared with healthy control participants, supporting the relevance of lung cell glycolysis to human sepsis. These data show that macrophage TRPV4 is required for glucose uptake through GLUT1 for effective phagolysosome maturation to limit sepsis-induced lung injury. Our work presents TRPV4 as a potential target to protect the lung from injury in sepsis.

Caveolin scaffolding domain (CSD) peptide LTI-2355 modulates the phagocytic and synthetic activity of lung derived myeloid cells in Idiopathic Pulmonary Fibrosis (IPF) and Post-acute sequelae of COVID-fibrosis (PASC-F)

Rationale

The role of the innate immune system in Idiopathic Pulmonary Fibrosis (IPF) remains poorly understood. However, a functional myeloid compartment is required to remove dying cells and cellular debris, and to mediate innate immune responses against pathogens. Aberrant macrophage activity has been described in patients with Post-acute sequelae of COVID fibrosis (PASC-F). Therefore, we examined the functional and synthetic properties of myeloid cells isolated from normal donor lung and lung explant tissue from both IPF and PASC-F patients and explored the effect of LTI-2355, a Caveolin Scaffolding Domain (CSD) peptide, on these cells.

Methods & Results

CD45 + myeloid cells isolated from lung explant tissue from IPF and PASC-F patients exhibited an impaired capacity to clear autologous dead cells and cellular debris. Uptake of pathogen-coated bioparticles was impaired in myeloid cells from both fibrotic patient groups independent of type of pathogen highlighting a cell intrinsic functional impairment. LTI-2355 improved the phagocytic activity of both IPF and PASC-F myeloid cells, and this improvement was paired with decreased pro-inflammatory and pro-fibrotic synthetic activity. LTI-2355 was also shown to primarily target CD206-expressing IPF and PASC-F myeloid cells.

Conclusions

Primary myeloid cells from IPF and PASC-F patients exhibit dysfunctional phagocytic and synthetic properties that are reversed by LTI-2355. Thus, these studies highlight an additional mechanism of action of a CSD peptide in the treatment of IPF and progressive fibrotic lung disease.

Macrophages in Lung Repair and Fibrosis

Macrophages are key regulators of tissue repair and fibrosis. Following injury, macrophages undergo marked phenotypic and functional changes to play crucial roles throughout the phases of tissue repair. Idiopathic Pulmonary Fibrosis, which is the most common fibrosing lung disease, has been described as an aberrant reparative response to repetitive alveolar epithelial injury in a genetically susceptible aging individual. The marked destruction of the lung architecture results from the excessive secretion of extracellular matrix by activated fibroblasts and myofibroblasts. Accumulating evidence suggests that macrophages have a pivotal regulatory role in pulmonary fibrosis. The origins and characteristics of macrophages in the lung and their role in regulating lung homeostasis, repair, and fibrosis are reviewed herein. We discuss recent studies that have employed single-cell RNA-sequencing to improve the identification and characterization of macrophage populations in the context of homeostatic and fibrotic conditions. We also discuss the current understanding of the macrophage-mediated mechanisms underlying the initiation and progression of pulmonary fibrosis, with a focus on the phenotypic and functional changes that aging macrophages acquire and how these changes ultimately contribute to age-related chronic lung diseases.

Horizontal transmission of gut microbiota attenuates mortality in lung fibrosis

Pulmonary fibrosis is a chronic and often fatal disease. The pathogenesis is characterized by aberrant repair of lung parenchyma, resulting in loss of physiological homeostasis, respiratory failure, and death. The immune response in pulmonary fibrosis is dysregulated. The gut microbiome is a key regulator of immunity. The role of the gut microbiome in regulating the pulmonary immunity in lung fibrosis is poorly understood. Here, we determine the impact of gut microbiota on pulmonary fibrosis in substrains of C57BL/6 mice derived from different vendors (C57BL/6J and C57BL/6NCrl). We used germ-free models, fecal microbiota transplantation, and cohousing to transmit gut microbiota. Metagenomic studies of feces established keystone species between substrains. Pulmonary fibrosis was microbiota dependent in C57BL/6 mice. Gut microbiota were distinct by β diversity and α diversity. Mortality and lung fibrosis were attenuated in C57BL/6NCrl mice. Elevated CD4+IL-10+ T cells and lower IL-6 occurred in C57BL/6NCrl mice. Horizontal transmission of microbiota by cohousing attenuated mortality in C57BL/6J mice and promoted a transcriptionally altered pulmonary immunity. Temporal changes in lung and gut microbiota demonstrated that gut microbiota contributed largely to immunological phenotype. Key regulatory gut microbiota contributed to lung fibrosis, generating rationale for human studies.

The causal relationship between physical activity, sedentary time and idiopathic pulmonary fibrosis risk: a Mendelian randomization study

BACKGROUND

Several observational studies have found that physical inactivity and sedentary time are associated with idiopathic pulmonary fibrosis (IPF) risk. However, the causality between them still requires further investigation. Therefore, our study aimed to investigate the causal effect of physical activity (PA) and sedentary time on the risk of IPF via two-sample Mendelian randomization (MR) analysis.

METHODS

Multiple genome-wide association study (GWAS) data involving individuals of European ancestry were analyzed. The datasets encompassed published UK Biobank data (91,105-377,234 participants) and IPF data (2018 cases and 373,064 controls) from FinnGen Biobank. The inverse variance weighting (IVW) method was the primary approach for our analysis. Sensitivity analyses were implemented with Cochran's Q test, MR-Egger regression, MR-PRESSO global test, and leave-one-out analysis.

RESULTS

Genetically predicted self-reported PA was associated with lower IPF risk [OR = 0.27; 95% CI 0.09-0.82; P = 0.02]. No causal effects of accelerometry-based PA or sedentary time on the risk of IPF were observed.

CONCLUSIONS

Our findings supported a protective relationship between self-reported PA and the risk for IPF. The results suggested that enhancing PA may be an effective preventive strategy for IPF.

Pre-Existing Interstitial Lung Abnormalities in Patients with Head and Neck Squamous Cell Carcinoma and Their Follow Up after Therapy

Interstitial lung abnormalities (ILAs) are incidentally found nondependent parenchymal abnormalities affecting more than 5% of any lung zone and are potentially related to interstitial lung disease and worsening post-treatment outcomes in malignancies and infectious diseases. The aim of this study was to determine the prevalence and type of ILA changes in patients with head and neck squamous cell carcinoma (HNSCC) and their change in the follow-up period. This retrospective single-center study included 113 patients with newly diagnosed HNSCC who underwent lung MSCT prior to treatment. ILAs were reported in 13.3% of patients on pretreatment MSCT. Patients with ILAs were significantly older (median 75 vs. 67 years). ILAs were most prevalent in lower zones (73.3%) (p = 0.0045). The most reported ILA subtype was subpleural non-fibrotic (60%) (p = 0.0354). Reticulations were the most frequently described pattern (93.3%) (p < 0.0001). Progression of ILAs was reported in almost 30% of patients after receiving therapy. Patients with pre-existing ILAs were more likely to develop radiation-induced lung fibrosis after adjuvant radiotherapy (p = 0.0464). In conclusion, ILA's incidence, distribution and presentation were similar to previous research conducted in other special cohorts. Our research suggests a possible association of more frequent radiation pneumonitis with ILA changes in patients with HNSCC, which should be further investigated.

Identification of immune biomarkers associated with basement membranes in idiopathic pulmonary fibrosis and their pan-cancer analysis

Idiopathic pulmonary fibrosis (IPF) is a chronic progressive interstitial lung disease of unknown etiology, characterized by diffuse alveolitis and alveolar structural damage. Due to the short median survival time and poor prognosis of IPF, it is particularly urgent to find new IPF biomarkers. Previous studies have shown that basement membranes (BMs) are associated with the development of IPF and tumor metastasis. However, there is still a lack of research on BMs-related genes in IPF. Therefore, we investigated the expression level of BMs genes in IPF and control groups, and explored their potential as biomarkers for IPF diagnosis. In this study, the GSE32537 and GSE53845 datasets were used as training sets, while the GSE24206, GSE10667 and GSE101286 datasets were used as validation sets. In the training set, seven immune biomarkers related to BMs were selected by differential expression analysis, machine learning algorithm (LASSO, SVM-RFE, Randomforest) and ssGSEA analysis. Further ROC analysis confirmed that seven BMs-related genes played an important role in IPF. Finally, four immune-related Hub genes (COL14A1, COL17A1, ITGA10, MMP7) were screened out. Then we created a logistic regression model of immune-related hub genes (IHGs) and used a nomogram to predict IPF risk. The nomogram model was evaluated to have good reliability and validity, and ROC analysis showed that the AUC value of IHGs was 0.941 in the training set and 0.917 in the validation set. Pan-cancer analysis showed that IHGs were associated with prognosis, immune cell infiltration, TME, and drug sensitivity in 33 cancers, suggesting that IHGs may be potential targets for intervention in human diseases including IPF and cancer.

Human airway and lung microbiome at the crossroad of health and disease (Review)

The evolving field of the microbiome and microbiota has become a popular research topic. The human microbiome is defined as a new organ and is considered a living community of commensal, symbiotic and pathogenic microorganisms within a certain body space. The term 'microbiome' is used to define the entire genome of the microbiota. Bacteria, archaea, fungi, algae and small protists are all members of the microbiota, followed by phages, viruses, plasmids and mobile genetic elements. The composition, heterogeneity and dynamics of microbiomes in time and space, their stability and resistance, essential characteristics and key participants, as well as interactions within the microbiome and with the host, are crucial lines of investigation for the development of successful future diagnostics and therapies. Standardization of microbiome studies and harmonized comparable methodologies are required for the transfer of knowledge from fundamental science into the clinic. Human health is dependent on microbiomes and achieved by nurturing beneficial resident microorganisms and their interplay with the host. The present study reviewed scientific knowledge on the major components of the human respiratory microbiome, i.e. bacteria, viruses and fungi, their symbiotic and parasitic roles, and, also, major diseases of the human respiratory tract and their microbial etiology. Bidirectional relationships regulate microbial ecosystems and host susceptibility. Moreover, environmental insults render host tissues and microbiota disease-prone. The human respiratory microbiome reflects the ambient air microbiome. By understanding the human respiratory microbiome, potential therapeutic strategies may be proposed.

Fibrotic Lung Disease Alters Neutrophil Trafficking and Promotes Neutrophil Elastase and Extracellular Trap Release

Idiopathic pulmonary fibrosis (IPF) is a progressive, irreversible disease characterized by collagen deposition within the interstitium of the lung. This impairs gas exchange and results in eventual respiratory failure. Clinical studies show a correlation between elevated neutrophil numbers and IPF disease progression; however, the mechanistic roles neutrophils play in this disease are not well described. In the present study, we describe alterations to the trafficking and function of neutrophils after the development of fibrosis. We observed increased numbers of total and aged neutrophils in peripheral tissues of fibrotic mice. This appeared to be driven by an upregulation of neutrophil chemokine Cxcl2 by lung cells. In addition, neutrophil recruitment back to the bone marrow for clearance appeared to be impaired, because we saw decreased aged neutrophils in the bone marrow of fibrotic mice. Neutrophils in fibrosis were activated, because ex vivo assays showed increased elastase and extracellular trap release by neutrophils from fibrotic mice. This likely mediated disease exacerbation, because mice exhibiting a progressive disease phenotype with greater weight loss and mortality had more activated neutrophils and increased levels of extracellular DNA present in their lungs than did mice with a nonprogressive disease phenotype. These findings further our understanding of the dynamics of neutrophil populations and their trafficking in progressive fibrotic lung disease and may help inform treatments targeting neutrophil function for patients with IPF experiencing disease exacerbation in the future.

The role of immune response in the pathogenesis of idiopathic pulmonary fibrosis: far beyond the Th1/Th2 imbalance

INTRODUCTION

. Idiopathic pulmonary fibrosis (IPF) is a chronic disease of unknown origin characterized by progressive scarring of the lung leading to irreversible loss of function. Despite the availability of two drugs that are able to slow down disease progression, IPF remains a deadly disease. The pathogenesis of IPF is poorly understood, but a dysregulated wound healing response following recurrent alveolar epithelial injury is thought to be crucial. Areas covered. In the last few years, the role of the immune system in IPF pathobiology has been reconsidered; indeed, recent data suggest that a dysfunctional immune system may promote and unfavorable interplay with pro-fibrotic pathways thus acting as a cofactor in disease development and progression. In this article, we review and critically discuss the role of T cells in the pathogenesis and progression of IPF in the attempt to highlight ways in which further research in this area may enable the development of targeted immunomodulatory therapies for this dreadful disease.

EXPERT OPINION

A better understanding of T cells interactions has the potential to facilitate the development of immune modulators targeting multiple T cell-mediated pathways thus halting disease initiation and progression.