Danger-associated molecular patterns and danger signals in idiopathic pulmonary fibrosis

Circulating Mitochondrial DNA Is Associated With High Levels of Fatigue in Two Independent Sarcoidosis Cohorts

BACKGROUND

Patients with sarcoidosis who develop severe clinical phenotypes of pulmonary fibrosis or multiorgan disease experience debilitating symptoms, with fatigue being a common chief complaint. Studies that have investigated this patient-related outcome measure (PROM) have used the Fatigue Assessment Scale (FAS), a self-reported questionnaire that reflects mental and physical domains. Despite extensive work, its cause is unknown and treatment options remain limited. Previously, we showed that the plasma of patients with sarcoidosis with extrapulmonary disease endorsing fatigue was enriched for mitochondrial DNA (mtDNA), a ligand for the innate immune receptor toll-like receptor 9 (TLR9). Through our cross-disciplinary platform, we investigated a relationship between sarcoidosis-induced fatigue and circulating mtDNA.

RESEARCH QUESTION

Is there a psychobiologic mechanism that connects sarcoidosis-induced fatigue and mtDNA-mediated TLR9 activation?

STUDY DESIGN AND METHODS

Using a local cohort of patients at Yale (discovery cohort) and the National Institutes of Health-sponsored Genomic Research in Alpha-1 Antitrypsin Deficiency and Sarcoidosis study (validation cohort), we scored the FAS and quantified in the plasma, mtDNA concentrations, TLR9 activation, and cytokine levels.

RESULTS

Although FAS scores were independent of corticosteroid use and Scadding stage, we observed a robust association between FAS scores, which included mental and physical domains, and multiorgan sarcoidosis. Subsequently, we identified a significant correlation between plasma mtDNA concentrations and all domains of fatigue. Additionally, we found that TLR9 activation is associated with all aspects of the FAS and partially mediates this PROM through mtDNA. Last, we found that TLR9-associated soluble mediators in the plasma are independent of all facets of fatigue.

INTERPRETATION

Through our cross-disciplinary translational platform, we identified a previously unrecognized psychobiologic connection between sarcoidosis-induced fatigue and circulating mtDNA concentrations. Mechanistic work that investigates the contribution of mtDNA-mediated innate immune activation in this PROM and clinical studies with prospective cohorts has the potential to catalyze novel therapeutic strategies for this patient population and those with similar conditions.

Mitochondrial DNA Sensing Pathogen Recognition Receptors in Systemic Sclerosis Associated Interstitial Lung Disease: A Review

Purpose of the review

Systemic sclerosis (SSc) is a condition of dermal and visceral scar formation characterized by immune dysregulation and inflammatory fibrosis. Approximately 90% of SSc patients develop interstitial lung disease (ILD), and it is the leading cause of morbidity and mortality. Further understanding of immune-mediated fibroproliferative mechanisms has the potential to catalyze novel treatment approaches in this difficult to treat disease.

Recent findings

Recent advances have demonstrated the critical role of aberrant innate immune activation mediated by mitochondrial DNA (mtDNA) through interactions with toll-like receptor 9 (TLR9) and cytosolic cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS).

Summary

In this review, we will discuss how the nature of the mtDNA, whether oxidized or mutated, and its mechanism of release, either intracellularly or extracellularly, can amplify fibrogenesis by activating TLR9 and cGAS, and the novel insights gained by interrogating these signaling pathways. Because the scope of this review is intended to generate hypotheses for future research, we conclude our discussion with several important unanswered questions.

Targeting the NLRP3 inflammasome and associated cytokines in scleroderma associated interstitial lung disease

SSc-ILD (scleroderma associated interstitial lung disease) is a complex rheumatic disease characterized in part by immune dysregulation leading to the progressive fibrotic replacement of normal lung architecture. Because improved treatment options are sorely needed, additional study of the fibroproliferative mechanisms mediating this disease has the potential to accelerate development of novel therapies. The contribution of innate immunity is an emerging area of investigation in SSc-ILD as recent work has demonstrated the mechanistic and clinical significance of the NLRP3 inflammasome and its associated cytokines of TNFα (tumor necrosis factor alpha), IL-1β (interleukin-1 beta), and IL-18 in this disease. In this review, we will highlight novel pathophysiologic insights afforded by these studies and the potential of leveraging this complex biology for clinical benefit.

Elevated serum mitochondrial DNA levels were associated with the progression and mortality in idiopathic pulmonary fibrosis

Circulating mitochondrial DNA (mtDNA) was implicated in idiopathic pulmonary fibrosis (IPF), but the association between circulating mtDNA levels with clinical parameters in IPF was unclear. In this study, we investigate the relationship between serum mtDNA levels with the progression and mortality of IPF. Eighty-three patients with clinical diagnoses of IPF and fifty-three healthy controls were enrolled. Clinical data were collected and IPF patients were classified as stable disease (SD) and progressive disease (PD) based on the diagnostic criteria. Serum mtDNA levels were measured by real-time quantitative PCR and were compared between the two groups. Associations of the mtDNA levels with pulmonary function data and clinical parameters were assessed. Cox regression was performed to access the association between serum mtDNA levels with mortality in IPF. The serum mtDNA levels were significantly higher in IPF patients compared to those in healthy controls (P < 0.001), and further higher in patients with PD than those with SD (P < 0.001). Serum mtDNA levels were significantly inverse correlated with carbon monoxide diffusing capacity percent predicted (DLCO% predicted) (P = 0.030) and serum albumin levels (P = 0.008). During follow-up, 36 patients (43.4 %) died with a median survival of 46.00 (IQR: 25.00-69.75) months. Multivariate analysis showed that higher serum mtDNA levels were a significant predictor of mortality in IPF. In conclusion, elevated serum mtDNA levels were associated with the progression and mortality of IPF, which provided new insights that mitochondrial metabolism might have a potential role in the pathogenesis of IPF.

The Dual Role of the Airway Epithelium in Asthma: Active Barrier and Regulator of Inflammation

Chronic airway inflammation is the cornerstone on which bronchial asthma arises, and in turn, chronic inflammation arises from a complex interplay between environmental factors such as allergens and pathogens and immune cells as well as structural cells constituting the airway mucosa. Airway epithelial cells (AECs) are at the center of these processes. On the one hand, they represent the borderline separating the body from its environment in order to keep inner homeostasis. The airway epithelium forms a multi-tiered, self-cleaning barrier that involves an unstirred, discontinuous mucous layer, the dense and rigid mesh of the glycocalyx, and the cellular layer itself, consisting of multiple, densely interconnected cell types. On the other hand, the airway epithelium represents an immunologically highly active tissue once its barrier has been penetrated: AECs play a pivotal role in releasing protective immunoglobulin A. They express a broad spectrum of pattern recognition receptors, enabling them to react to environmental stressors that overcome the mucosal barrier. By releasing alarmins-proinflammatory and regulatory cytokines-AECs play an active role in the formation, strategic orientation, and control of the subsequent defense reaction. Consequently, the airway epithelium is of vital importance to chronic inflammatory diseases, such as asthma.

α1 Adrenoreceptor antagonism mitigates extracellular mitochondrial DNA accumulation in lung fibrosis models and in patients with idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis is increasingly associated with nerve-driven processes and endogenous innate immune ligands such as mitochondrial DNA (mtDNA). Interestingly, a connection between these entities has not been explored. Here, we report that noradrenaline (NA) derived from the lung's adrenergic nerve supply drives α-smooth muscle actin (αSMA)-expressing fibroblast accumulation via mechanisms involving α1 adrenoreceptors and mtDNA. Using the bleomycin model, we compared ablation of the lung's adrenergic nerve supply with surgical adrenal resection and found that NA derived from local but not adrenal sources contributes to experimentally induced lung fibrosis and the emergence of an αSMA+ve fibroblast population expressing adrenoreceptor α-1D (ADRA1D). Therapeutic delivery of the α1 adrenoreceptor antagonist terazosin reversed these changes and suppressed extracellular mtDNA accumulation. Cultured normal human lung fibroblasts displayed α1 adrenoreceptors and in response to costimulation with TGFβ1 and NA adopted ACTA2 expression and extracellular mtDNA release. These findings were opposed by terazosin. Evaluation of a previously studied IPF cohort revealed that patients prescribed α1 adrenoreceptor antagonists for nonpulmonary indications demonstrated improved survival and reduced concentrations of plasma mtDNA. Our observations link nerve-derived NA, α1 adrenoreceptors, extracellular mtDNA, and lung fibrogenesis in mouse models, cultured cells, and humans with IPF. Further study of this neuroinnate connection may yield new avenues for investigation in the clinical and basic science realms.

Serum cold-inducible RNA-binding protein levels as a potential biomarker for systemic sclerosis-associated interstitial lung disease

Systemic sclerosis (SSc) is a complex autoimmune disease characterized by fibrotic, inflammatory, and vascular dysfunction. Danger-associated molecular patterns (DAMPs)-mediated inflammasome activation has been reported to be involved in the pathogenesis of SSc. Cold-inducible RNA-binding protein (CIRP) is newly identified as a DAMP. Here we examined the clinical significance of serum levels of CIRP in 60 patients with SSc and 20 healthy control patients (HCs) using an enzyme-linked immunosorbent assay. Serum CIRP levels in diffuse cutaneous SSc (dcSSc) patients were significantly increased compared with limited cutaneous SSc (lcSSc) patients or HCs. When examining the relationship with SSc-specific parameters, serum CIRP levels with the presence of interstitial lung disease (ILD) were higher than those without ILD. In detail, serum CIRP levels correlated negatively with the percent predicted diffusing capacity for carbon monoxide and positively with levels of Krebs von den Lungen-6. In addition, elevated serum CIRP levels declined along with decreased SSc-ILD activity in patients who received immunosuppressive therapy. These results suggest that CIRP may play a role in the development of ILD in SSc. Moreover, CIRP could serve as a useful serological marker of SSc-ILD in terms of disease activity and therapeutic effects.

Notch Blockade Specifically in Bone Marrow-Derived FSP-1-Positive Cells Ameliorates Renal Fibrosis

BACKGROUND

The infiltration of inflammatory cells during a kidney injury stimulates myofibroblast activation leading to kidney fibrosis. Fibroblast-specific protein 1 (FSP-1) positive cells have been reported as either myofibroblasts or monocytes during tissue fibrosis. The functions of FSP-1⁺ cells that are associated with the development of renal fibrosis and the signaling pathways that regulate FSP-1⁺ cell activation have not been well defined.

METHODS

In mice with unilateral ureteral obstruction (UUO), we characterized FSP-1⁺ cells and determined the role of the Notch signaling pathway in the activation of bone marrow-derived FSP-1⁺ cells during kidney fibrosis.

RESULTS

In kidneys from mice with UUO, the FSP-1⁺ cells accumulated significantly in the tubulointerstitial area. By using immunostaining and FSP-1 reporter mice, we found that FSP-1 was co-stained with inflammatory cell markers, but not myofibroblast markers. Results from mice with bone marrow transplantations showed that FSP-1⁺ cells in obstructed kidneys represent a bone marrow-derived population of inflammatory cells. In cultured FSP-1⁺ cells, the inhibition of Notch signaling suppressed the activation and cytokine secretion of FSP-1⁺ cells that were induced by LPS but not by IL-4. The specific KO or blockade of Notch signaling in bone marrow-derived FSP-1⁺ cells suppressed UUO-induced ECM deposition, the infiltration of FSP-1⁺ inflammatory cells, and cytokine production. These responses ameliorated myofibroblast accumulation and renal fibrosis in obstructed kidneys.

CONCLUSION

Our study reveals that most FSP-1⁺ cells in obstructed kidneys are activated macrophages that are derived from bone marrow and that Notch signaling activates the production of M1 cytokines in FSP-1⁺ monocytes/macrophages, which is important for renal inflammation and fibrosis.

Novel tracers for molecular imaging of interstitial lung disease: A state of the art review

Interstitial lung disease is an overarching term for a wide range of disorders characterized by inflammation and/or fibrosis in the lungs. Most prevalent forms, among others, include idiopathic pulmonary fibrosis (IPF) and connective tissue disease associated interstitial lung disease (CTD-ILD). Currently, only disease modifying treatment options are available for IPF and progressive fibrotic CTD-ILD, leading to reduction or stabilization in the rate of lung function decline at best. Management of these patients would greatly advance if we identify new strategies to improve (1) early detection of ILD, (2) predicting ILD progression, (3) predicting response to therapy and (4) understanding pathophysiology. Over the last years, positron emission tomography (PET) and single photon emission computed tomography (SPECT) have emerged as promising molecular imaging techniques to improve ILD management. Both are non-invasive diagnostic tools to assess molecular characteristics of an individual patient with the potential to apply personalized treatment. In this review, we encompass the currently available pre-clinical and clinical studies on molecular imaging with PET and SPECT in IPF and CTD-ILD. We provide recommendations for potential future clinical applications of these tracers and directions for future research.

In silico Prediction of Deleterious Single Nucleotide Polymorphism in S100A4 Metastatic Gene: Potential Early Diagnostic Marker

S100A4 protein overexpression has been reported in different types of cancer and plays a key role by interacting with the tumor suppressor protein Tp53. Single nucleotide polymorphisms (SNP) in S100A4 could directly influence the biomolecular interaction with the tumor suppressor protein Tp53 due to their aberrant conformations. Hence, the study was designed to predict the deleterious SNP and its effect on the S100A4 protein structure and function. Twenty-one SNP data sets were screened for nonsynonymous mutations and subsequently subjected to deleterious mutation prediction using different computational tools. The screened deleterious mutations were analyzed for their changes in functionality and their interaction with the tumor suppressor protein Tp53 by protein-protein docking analysis. The structural effects were studied using the 3DMissense mutation tool to estimate the solvation energy and torsion angle of the screened mutations on the predicted structures. In our study, 21 deleterious nonsynonymous mutations were screened, including F72V, E74G, L5P, D25E, N65S, A28V, A8D, S20L, L58P, and K26N were found to be remarkably conserved by exhibiting the interaction either with the EF-hand 1 or EF-hand 2 domain. The solvation and torsion values significantly deviated for the mutant-type structures with S20L, N65S, and F72L mutations and showed a marked reduction in their binding affinity with the Tp53 protein. Hence, these deleterious mutations might serve as prospective targets for diagnosing and developing personalized treatments for cancer and other related diseases.

The role of eCIRP in bleomycin-induced pulmonary fibrosis in mice

OBJECTIVE AND DESIGN

We examined the role of eCIRP in the pathogenesis of bleomycin-induced pulmonary fibrosis (PF).

MATERIAL AND METHODS

Publicly available gene expression omnibus datasets were analyzed for the expression of CIRP in lung samples from patients with PF. Wild type (WT) or CIRP-/- mice received daily injections of 10 μg/g bleomycin for 10 days. A subset of bleomycin-injected WT mice was treated with the eCIRP antagonist C23 (8 μg/g/day) from day 10 to day 19. At three weeks, transthoracic echocardiography was performed to measure the degree of pulmonary hypertension, and lung tissues were collected and analyzed for markers of fibrosis.

RESULTS

Analysis of the mRNA data of human lung samples showed a significant positive correlation between CIRP and α-smooth muscle actin (α-SMA), an important marker of fibrosis. Moreover, the expression of CIRP was higher in patients with acute exacerbation of PF than in patients with stable PF. CIRP-/- mice showed attenuated induction of α-SMA and collagens (Col1a1, Col3a1), reduced hydroxyproline content, decreased histological fibrosis scores, and improved pulmonary hypertension as compared to WT mice. WT mice treated with C23 also had significant attenuation of the above endpoint measure.

CONCLUSIONS

Our study demonstrates that eCIRP plays a key role in promoting the development of PF, and blocking eCIRP with C23 can significantly attenuate this process.

The Role of Epithelial Damage in the Pulmonary Immune Response

Pulmonary epithelial cells are widely considered to be the first line of defence in the lung and are responsible for coordinating the innate immune response to injury and subsequent repair. Consequently, epithelial cells communicate with multiple cell types including immune cells and fibroblasts to promote acute inflammation and normal wound healing in response to damage. However, aberrant epithelial cell death and damage are hallmarks of pulmonary disease, with necrotic cell death and cellular senescence contributing to disease pathogenesis in numerous respiratory diseases such as idiopathic pulmonary fibrosis (IPF), chronic obstructive pulmonary disease (COPD) and coronavirus disease (COVID)-19. In this review, we summarise the literature that demonstrates that epithelial damage plays a pivotal role in the dysregulation of the immune response leading to tissue destruction and abnormal remodelling in several chronic diseases. Specifically, we highlight the role of epithelial-derived damage-associated molecular patterns (DAMPs) and senescence in shaping the immune response and assess their contribution to inflammatory and fibrotic signalling pathways in the lung.

Evolving Perspectives on Innate Immune Mechanisms of IPF

While epithelial-fibroblast interactions are viewed as the primary drivers of Idiopathic Pulmonary Fibrosis (IPF), evidence gleaned from animal modeling and human studies implicates innate immunity as well. To provide perspective on this topic, this review synthesizes the available data regarding the complex role of innate immunity in IPF. The role of substances present in the fibrotic microenvironment including pathogen associated molecular patterns (PAMPs) derived from invading or commensal microbes, and danger associated molecular patterns (DAMPs) derived from injured cells and tissues will be discussed along with the proposed contribution of innate immune populations such as macrophages, neutrophils, fibrocytes, myeloid suppressor cells, and innate lymphoid cells. Each component will be considered in the context of its relationship to environmental and genetic factors, disease outcomes, and potential therapies. We conclude with discussion of unanswered questions and opportunities for future study in this area.

The interplay of DAMPs, TLR4, and proinflammatory cytokines in pulmonary fibrosis

Pulmonary fibrosis is a chronic debilitating condition characterized by progressive deposition of connective tissue, leading to a steady restriction of lung elasticity, a decline in lung function, and a median survival of 4.5 years. The leading causes of pulmonary fibrosis are inhalation of foreign particles (such as silicosis and pneumoconiosis), infections (such as post COVID-19), autoimmune diseases (such as systemic autoimmune diseases of the connective tissue), and idiopathic pulmonary fibrosis. The therapeutics currently available for pulmonary fibrosis only modestly slow the progression of the disease. This review is centered on the interplay of damage-associated molecular pattern (DAMP) molecules, Toll-like receptor 4 (TLR4), and inflammatory cytokines (such as TNF-α, IL-1β, and IL-17) as they contribute to the pathogenesis of pulmonary fibrosis, and the possible avenues to develop effective therapeutics that disrupt this interplay.

S100A4 in Spinal Substantia Gelatinosa from Dorsal Root Ganglia Modulates Neuropathic Pain in a Rodent Spinal Nerve Injury Model

Purpose

To detect the spatio-temporal expression of S100A4 in a spinal nerve ligation (SNL) rat model. Also to figure out which other molecules directly interact with S100A4 to explore the possible mechanisms which might be involved in neuropathic pain.

Methods

Seven-week-old male SD rats were used for the SNL model construction. Immunofluorescence and Western blotting were used to detect the spatio-temporal expression of S100A4 in the model. S100A4 was co-labeled with a number of related molecules and marker molecules that can distinguish between cell types. After intrathecal injection of S100A4 neutralizing antibody, the behavioral changes of SNL rats were recorded, and molecular changes compared. The direct interaction between S100A4 and other related molecules was verified by co-immunoprecipitation (co-IP) to explore its possible mechanism.

Results

After spinal nerve ligation, the content of S100A4 in the dorsal root ganglion (DRG) and spinal dorsal horn increased significantly. Intrathecal injection of S100A4 neutralizing antibody could effectively relieve the mechanical pain in rats. co-IP revealed a direct interaction between S100A4 and RAGE.

Conclusion

The content of S100A4 in the DRG and spinal dorsal horn of SNL rats increased, compared with that of the control group. Intrathecal injection of S100A4 neutralizing antibody could effectively relieve the mechanical pain in SNL rats. S100A4 may be involved in the production of neuropathic pain through RAGE or other ways, but the specific mechanism needs to be further studied.

Multi-Modal Characterization of Monocytes in Idiopathic Pulmonary Fibrosis Reveals a Primed Type I Interferon Immune Phenotype

Idiopathic pulmonary fibrosis (IPF) is the most severe form of chronic lung fibrosis. Circulating monocytes have been implicated in immune pathology in IPF but their phenotype is unknown. In this work, we determined the immune phenotype of monocytes in IPF using multi-colour flow cytometry, RNA sequencing and corresponding serum factors, and mapped the main findings to amount of lung fibrosis and single cell transcriptomic landscape of myeloid cells in IPF lungs. We show that monocytes from IPF patients displayed increased expression of CD64 (FcγR1) which correlated with amount of lung fibrosis, and an amplified type I IFN response ex vivo. These were accompanied by markedly raised CSF-1 levels, IL-6, and CCL-2 in serum of IPF patients. Interrogation of single cell transcriptomic data from human IPF lungs revealed increased proportion of CD64hi monocytes and "transitional macrophages" with higher expression of CCL-2 and type I IFN genes. Our study shows that monocytes in IPF patients are phenotypically distinct from age-matched controls, with a primed type I IFN pathway that may contribute to driving chronic inflammation and fibrosis. These findings strengthen the potential role of monocytes in the pathogenesis of IPF.

Protective Role of the Nucleic Acid Sensor STING in Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is the most common and severe type of interstitial lung disease for which current treatments display limited efficacy. IPF is largely driven by host-derived danger signals released upon recurrent local tissue damage. Here we explored the roles of self-DNA and stimulator of interferon genes (STING), a protein belonging to an intracellular DNA sensing pathway that leads to type I and/or type III interferon (IFN) production upon activation. Using a mouse model of IPF, we report that STING deficiency leads to exacerbated pulmonary fibrosis with increased collagen deposition in the lungs and excessive remodeling factors expression. We further show that STING-mediated protection does not rely on type I IFN signaling nor on IL-17A or TGF-β modulation but is associated with dysregulated neutrophils. Together, our data support an unprecedented immunoregulatory function of STING in lung fibrosis.

The self-fulfilling prophecy of pulmonary fibrosis: a selective inspection of pathological signalling loops

Pulmonary fibrosis is a devastating, progressive disease and carries a prognosis worse than most cancers. Despite ongoing research, the mechanisms that underlie disease pathogenesis remain only partially understood. However, the self-perpetuating nature of pulmonary fibrosis has led several researchers to propose the existence of pathological signalling loops. According to this hypothesis, the normal wound-healing process becomes corrupted and results in the progressive accumulation of scar tissue in the lung. In addition, several negative regulators of pulmonary fibrosis are downregulated and, therefore, are no longer capable of inhibiting these feed-forward loops. The combination of pathological signalling loops and loss of a checks and balances system ultimately culminates in a process of unregulated scar formation. This review details specific signalling pathways demonstrated to play a role in the pathogenesis of pulmonary fibrosis. The evidence of detrimental signalling loops is elucidated with regard to epithelial cell injury, cellular senescence and the activation of developmental and ageing pathways. We demonstrate where these loops intersect each other, as well as common mediators that may drive these responses and how the loss of pro-resolving mediators may contribute to the propagation of disease. By focusing on the overlapping signalling mediators among the many pro-fibrotic pathways, it is our hope that the pulmonary fibrosis community will be better equipped to design future trials that incorporate the redundant nature of these pathways as we move towards finding a cure for this unrelenting disease.

Bioactive Plasma Mitochondrial DNA Is Associated With Disease Progression in Scleroderma-Associated Interstitial Lung Disease

OBJECTIVE

Systemic sclerosis-associated interstitial lung disease (SSc-ILD) is characterized by variable clinical outcomes, activation of innate immune pattern-recognition receptors (PRRs), and accumulation of α-smooth muscle actin (α-SMA)-expressing myofibroblasts. The aim of this study was to identify an association between these entities and mitochondrial DNA (mtDNA), an endogenous ligand for the intracellular DNA-sensing PRRs Toll-like receptor 9 (TLR-9) and cyclic GMP-AMP synthase/stimulator of interferon genes (cGAS/STING), which has yet to be determined.

METHODS

Human lung fibroblasts (HLFs) from normal donors and SSc-ILD explants were treated with synthetic CpG DNA and assayed for α-SMA expression and extracellular mtDNA using quantitative polymerase chain reaction for the human MT-ATP6 gene. Plasma MT-ATP6 concentrations were evaluated in 2 independent SSc-ILD cohorts and demographically matched controls. The ability of SSc-ILD and control plasma to induce TLR-9 and cGAS/STING activation was evaluated with commercially available HEK 293 reporter cells. Plasma concentrations of type I interferons (IFNs), interleukin-6 (IL-6), and oxidized DNA were measured using electrochemiluminescence and enzyme-linked immunosorbent assay-based methods. Extracellular vesicles (EVs) precipitated from plasma were evaluated for MT-ATP6 concentrations and proteomics via liquid chromatography mass spectrometry.

RESULTS

Normal HLFs and SSc-ILD fibroblasts developed increased α-SMA expression and MT-ATP6 release following CpG stimulation. Plasma mtDNA concentrations were increased in the 2 SSc-ILD cohorts, reflective of ventilatory decline, and were positively associated with both TLR-9 and cGAS/STING activation as well as type I IFN and IL-6 expression. Plasma mtDNA was not oxidized and was conveyed by EVs displaying a proteomics profile consistent with a multicellular origin.

CONCLUSION

These findings demonstrate a previously unrecognized connection between EV-encapsulated mtDNA, clinical outcomes, and intracellular DNA-sensing PRR activation in SSc-ILD. Further study of these interactions could catalyze novel mechanistic and therapeutic insights into SSc-ILD and related disorders.

Regulation of cellular senescence by extracellular matrix during chronic fibrotic diseases

The extracellular matrix (ECM) is a complex network of macromolecules surrounding cells providing structural support and stability to tissues. The understanding of the ECM and the diverse roles it plays in development, homoeostasis and injury have greatly advanced in the last three decades. The ECM is crucial for maintaining tissue homoeostasis but also many pathological conditions arise from aberrant matrix remodelling during ageing. Ageing is characterised as functional decline of tissue over time ultimately leading to tissue dysfunction, and is a risk factor in many diseases including cardiovascular disease, diabetes, cancer, dementia, glaucoma, chronic obstructive pulmonary disease (COPD) and fibrosis. ECM changes are recognised as a major driver of aberrant cell responses. Mesenchymal cells in aged tissue show signs of growth arrest and resistance to apoptosis, which are indicative of cellular senescence. It was recently postulated that cellular senescence contributes to the pathogenesis of chronic fibrotic diseases in the heart, kidney, liver and lung. Senescent cells negatively impact tissue regeneration while creating a pro-inflammatory environment as part of the senescence-associated secretory phenotype (SASP) favouring disease progression. In this review, we explore and summarise the current knowledge around how aberrant ECM potentially influences the senescent phenotype in chronic fibrotic diseases. Lastly, we will explore the possibility for interventions in the ECM-senescence regulatory pathways for therapeutic potential in chronic fibrotic diseases.

Spliceosome-associated protein 130: a novel biomarker for idiopathic pulmonary fibrosis

Background

Spliceosome-associated protein 130 (SAP130), a novel danger-associated molecular pattern (DAMP), is involved in inflammatory disease. However, no data are available about SAP130 in idiopathic pulmonary fibrosis (IPF). Our study aimed to investigate SAP130 in the serum and lung tissue of patients with IPF and to determine its clinical significance.

Methods

SAP130 levels in the serum of 83 IPF patients and 38 healthy subjects were measured. Additionally, immunohistochemical staining for SAP130 was performed in lung specimens of IPF patients and control subjects. Correlation between serum SAP130 levels and clinical parameters were investigated.

Results

Serum SAP130 levels were elevated in IPF patients compared with healthy controls. In parallel, the expression of SAP130 in lung tissue was elevated in IPF. SAP130 levels were higher in patients with acute exacerbation of idiopathic pulmonary fibrosis (AE-IPF) than patients with stable IPF (P=0.0144). The area under curve (AUC) of the ROC curve for the diagnosis of IPF was 0.944 (95% CI, 0.810–0.997) for SAP130. The sensitivity (92.1%) and specificity (69.9%) were obtained for the cutoff value of 643.87 pg/mL. In patients with stable IPF, the SAP130 level correlated positively with fibrosis on high-resolution CT (HRCT) (r=0.4164, P=0.0029) and serum KL-6 (r=0.4564, P=0.0010), and inversely with FEV1 (r=−0.3562, P=0.0120) and DLCO (r=−0.5550, P<0.0001). In patients with AE-IPF, the SAP130 level correlated positively with fibrosis (r=0.3735, P=0.0296) and ground-glass opacity (r=0.4697, P=0.0051) on HRCT and serum Krebs von den Lungen 6 (KL-6) (r=0.5470, P= 0.0008).

Conclusions

The study suggested that SAP130 was a potential noninvasive biomarker that correlates well with disease severity of IPF. A prospective, multicentre study is required to validate the clinical and pathophysiological utility of SAP130 in IPF.

More Than Just a Barrier: The Immune Functions of the Airway Epithelium in Asthma Pathogenesis

Allergic bronchial asthma is a chronic disease of the airways that is characterized by symptoms like respiratory distress, chest tightness, wheezing, productive cough, and acute episodes of broncho-obstruction. This symptom-complex arises on the basis of chronic allergic inflammation of the airway wall. Consequently, the airway epithelium is central to the pathogenesis of this disease, because its multiple abilities directly have an impact on the inflammatory response and thus the formation of the disease. In turn, its structure and functions are markedly impaired by the inflammation. Hence, the airway epithelium represents a sealed, self-cleaning barrier, that prohibits penetration of inhaled allergens, pathogens, and other noxious agents into the body. This barrier is covered with mucus that further contains antimicrobial peptides and antibodies that are either produced or specifically transported by the airway epithelium in order to trap these particles and to remove them from the body by a process called mucociliary clearance. Once this first line of defense of the lung is overcome, airway epithelial cells are the first cells to get in contact with pathogens, to be damaged or infected. Therefore, these cells release a plethora of chemokines and cytokines that not only induce an acute inflammatory reaction but also have an impact on the alignment of the following immune reaction. In case of asthma, all these functions are impaired by the already existing allergic immune response that per se weakens the barrier integrity and self-cleaning abilities of the airway epithelium making it more vulnerable to penetration of allergens as well as of infection by bacteria and viruses. Recent studies indicate that the history of allergy- and pathogen-derived insults can leave some kind of memory in these cells that can be described as imprinting or trained immunity. Thus, the airway epithelium is in the center of processes that lead to formation, progression and acute exacerbation of asthma.

Redox Imbalance in Idiopathic Pulmonary Fibrosis: A Role for Oxidant Cross-Talk Between NADPH Oxidase Enzymes and Mitochondria

Significance: Idiopathic pulmonary fibrosis (IPF) is a progressive age-related lung disease with a median survival of only 3 years after diagnosis. The pathogenic mechanisms behind IPF are not clearly understood, and current therapeutic approaches have not been successful in improving disease outcomes. Recent Advances: IPF is characterized by increased production of reactive oxygen species (ROS), primarily by NADPH oxidases (NOXes) and mitochondria, as well as altered antioxidant defenses. Recent studies have identified the NOX isoform NOX4 as a key player in various important aspects of IPF pathology. In addition, mitochondrial dysfunction is thought to enhance pathological features of IPF, in part by increasing mitochondrial ROS (mtROS) production and altering cellular metabolism. Recent findings indicate reciprocal interactions between NOX enzymes and mitochondria, which affect regulation of NOX activity as well as mitochondrial function and mtROS production, and collectively promote epithelial injury and profibrotic signaling. Critical Issues and Future Directions: The precise molecular mechanisms by which ROS from NOX or mitochondria contribute to IPF pathology are not known. This review summarizes the current knowledge with respect to the various aspects of ROS imbalance in the context of IPF and its proposed roles in disease development, with specific emphasis on the importance of inappropriate NOX activation, mitochondrial dysfunction, and the emerging evidence of NOX-mitochondria cross-talk as important drivers in IPF pathobiology.

Plasma mitochondrial DNA is associated with extrapulmonary sarcoidosis

Sarcoidosis is an unpredictable granulomatous disease in which African Americans disproportionately experience aggressive phenotypes. Mitochondrial DNA (mtDNA) released by cells in response to various stressors contributes to tissue remodelling and inflammation. While extracellular mtDNA has emerged as a biomarker in multiple diseases, its relevance to sarcoidosis remains unknown. We aimed to define an association between extracellular mtDNA and clinical features of sarcoidosis.Extracellular mtDNA concentrations were measured using quantitative PCR for the human MT-ATP6 gene in bronchoalveolar (BAL) and plasma samples from healthy controls and patients with sarcoidosis from The Yale Lung Repository; associations between MT-ATP6 concentrations and Scadding stage, extrapulmonary disease and demographics were sought. Results were validated in the Genomic Research in Alpha-1 Antitrypsin Deficiency and Sarcoidosis cohort.Relative to controls, MT-ATP6 concentrations in sarcoidosis subjects were robustly elevated in the BAL fluid and plasma, particularly in the plasma of patients with extrapulmonary disease. Relative to Caucasians, African Americans displayed excessive MT-ATP6 concentrations in the BAL fluid and plasma, for which the latter compartment correlated with significantly higher odds of extrapulmonary disease.Enrichments in extracellular mtDNA in sarcoidosis are associated with extrapulmonary disease and African American descent. Further study into the mechanistic basis of these clinical findings may lead to novel pathophysiologic and therapeutic insights.

The Role of Immunity and Inflammation in IPF Pathogenesis

IPF is thought to be a consequence of repetitive micro-injury to ageing alveolar epithelium by factors including tobacco smoke, environmental exposures, microbial colonisation/infection, microaspiration, endoplasmic reticulum stress and oxidative stress, with resultant aberrant wound healing. Though partially effective antifibrotic therapies have focused attention away from older inflammation-based hypotheses for IPF pathogenesis, innate and adaptive immune cells and processes may play roles potentially in initiation and/or disease progression in IPF and/or in IPF acute exacerbations, based on multiple lines of evidence. Members of the Toll-like family of innate immune receptors have been implicated in IPF pathogenesis, including a potential modulatory role for the lung microbiome. A variety of chemokines are associated with the presence of IPF, and an imbalance of angiogenic chemokines has been linked to vascular remodelling in the disease. Subsets of circulating monocytes, including fibrocytes and segregated-nucleus-containing atypical monocytes (SatM), have been identified that may facilitate progression of fibrosis, and apoptosis-resistant pulmonary macrophages have been shown to demonstrate pro-fibrotic potential. Inflammatory cells that have been somewhat dismissed as irrelevant to IPF pathogenesis are being re-evaluated in light of new mechanistic data, such as activated neutrophils which release their chromatin in a process termed NETosis, which appears to mediate age-related murine lung fibrosis. A greater understanding is needed of the role of lymphoid aggregates, a histologic feature of IPF lungs found in close proximity to fibroblastic foci and highly suggestive of the presence of chronic immune responses in IPF, as are well-characterised activated circulating T lymphocytes and distinct autoantibodies that have been observed in IPF. There is a pressing need to discern whether or not the indisputably present immune dysregulation of IPF constitutes cause or effect in the ongoing search for more effective therapeutic strategies.

Pulmonary immunity and extracellular matrix interactions

The lung harbors a complex immune system composed of both innate and adaptive immune cells. Recognition of infection and injury by receptors on lung innate immune cells is crucial for generation of antigen-specific responses by adaptive immune cells. The extracellular matrix of the lung, comprising the interstitium and basement membrane, plays a key role in the regulation of these immune systems. The matrix consists of several hundred assembled proteins that interact to form a bioactive scaffold. This template, modified by enzymes, acts to facilitate cell function and differentiation and changes dynamically with age and lung disease. Herein, we explore relationships between innate and adaptive immunity and the lung extracellular matrix. We discuss the interactions between extracellular matrix proteins, including glycosaminoglycans, with prominent effects on innate immune signaling effectors such as toll-like receptors. We describe the relationship of extracellular matrix proteins with adaptive immunity and leukocyte migration to sites of injury within the lung. Further study of these interactions will lead to greater knowledge of the role of matrix biology in lung immunity. The development of novel therapies for acute and chronic lung disease is dependent on a comprehensive understanding of these complex matrix-immunity interactions.

Danger-Associated Molecular Patterns (DAMPs): the Derivatives and Triggers of Inflammation

PURPOSE OF REVIEW

Allergen is an umbrella term for irritants of diverse origin. Along with other offenders such as pathogens, mutagens, xenobiotics, and pollutants, allergens can be grouped as inflammatory agents. Danger-associated molecular patterns (DAMPs) are altered metabolism products of necrotic or stressed cells, which are deemed as alarm signals by the innate immune system. Like inflammation, DAMPs play a role in correcting the altered physiological state, but in excess, they can be lethal due to their signal transduction roles. In a vicious loop, inflammatory agents are DAMP generators and DAMPs create a pro-inflammatory state. Only a handful of DAMPs such as uric acid, mtDNA, extracellular ATP, HSPs, amyloid β, S100, HMGB1, and ECM proteins have been studied till now. A large number of DAMPs are still obscure, in need to be unveiled. The identification and functional characterization of those DAMPs in inflammation pathways can be insightful.

RECENT FINDINGS

As inflammation and immune activation have been implicated in almost all pathologies, studies on them have been intensified in recent times. Consequently, the pathologic mechanisms of various DAMPs have emerged. Following PRR ligation, the activation of inflammasome, MAPK, and NF-kB is some of the common pathways. The limited number of recognized DAMPs are only a fraction of the vast array of other DAMPs. In fact, any misplaced or abnormal level of metabolite can be a DAMP. Sophisticated analysis studies can reveal the full profile of the DAMPs. Lowering the level of DAMPs is useful therapeutic intervention but certainly not as effective as avoiding the DAMP generators, i.e., the inflammatory agents. So, rather than mitigating DAMPs, efforts should be focused on the elimination of inflammatory agents.

Helicobacter Pylori Infection and Lung Cancer: New Insights and Future Challenges

Helicobacter pylori (H. pylori) is the causative agent of chronic gastritis and peptic ulcer diseases and is an important risk factor for the development functional dyspepsia, peptic ulceration, gastric adenocarcinoma and mucosa-associated lymphoid tissue lymphoma. H. pylori has very high rates of infection in human populations, and it is estimated that over 50% of the world population is infected. Recently, certain extra-gastric manifestations, linked to H. pylori infection, have been widely investigated. Noteworthy, a growing body of evidences supports an association between H. pylori infection with lung cancer. The present review intend to highlight not only the most recent evidences supporting this association, but also some missed points, which must be considered to validate this emerging association.

Toll-Like Receptor Agonists Modulate Wound Regeneration in Airway Epithelial Cells

Background: Impaired regeneration of airway epithelium may lead to persistence of inflammation and remodelling. Regeneration of injured epithelium is a complex phenomenon and the role of toll-like receptors (TLRs) in the stimulation of respiratory virus products in this process has not been established. Objective: This study was undertaken to test the hypothesis that the wound repair process in airway epithelium is modulated by microbial products via toll-like receptors. Methods: Injured and not-injured bronchial epithelial cells (ECs) (BEAS-2B line) were incubated with the TLR agonists poly(I:C), lipopolisacharide (LPS), allergen Der p1, and supernatants from virus-infected epithelial cells, either alone or in combination with TLR inhibitors. Regeneration and immune response in injured and not-injured cells were studied. Results: Addition of either poly(I:C) or LPS to ECs induced a marked inhibition of wound repair. Supernatants from RV1b-infected cells also decreased regeneration. Preincubation of injured and not-injured ECs with TLR inhibitors decreased LPS and poly(I:C)-induced repair inhibition. TGF-β and RANTES mRNA expression was higher in injured ECs and IFN-α, IFN-β, IL-8, and VEGF mRNA expression was lower in damaged epithelium as compared to not-injured. Stimulation with poly(I:C) increased IFN-α and IFN-β mRNA expression in injured cells, and LPS stimulation decreased interferons mRNA expression both in not-injured and injured ECs. Conclusion: Regeneration of the airway epithelium is modulated by microbial products via toll-like receptors.

Evaluation of 99mTc-rhAnnexin V-128 SPECT/CT as a diagnostic tool for early stages of interstitial lung disease associated with systemic sclerosis

Background

Given the need for early detection of organ involvement in systemic sclerosis, we evaluated ^99mTc-rhAnnexin V-128 for the detection of early stages of interstitial lung disease (ILD) in respective animal models using single photon emission computed tomography (SPECT/CT).

Methods

In bleomycin (BLM)-challenged mice, fos-related antigen 2 (Fra-2) transgenic (tg) mice and respective controls, lung injury was evaluated by analysis of hematoxylin and eosin (HE) and Sirius red staining, with semi-quantification of fibrosis by the Ashcroft score. Apoptotic cells were identified by TUNEL assay, cleaved caspase 3 staining and double staining with specific cell markers. To detect early stages of lung remodeling by visualization of apoptosis, mice were injected intravenously with ^99mTc-rhAnnexin V-128 and imaged by small animal SPECT/CT. For confirmation, biodistribution and ex vivo autoradiography studies were performed.

Results

In BLM-induced lung fibrosis, inflammatory infiltrates occurred as early as day 3 with peak at day 7, whereas pulmonary fibrosis developed from day 7 and was most pronounced at day 21. In accordance, the number of apoptotic cells was highest at day 3 compared with saline controls and then decreased over time. Epithelial cells (E-cadherin+) and inflammatory cells (CD45+) were the primary cells undergoing apoptosis in the earliest remodeling stages of experimental ILD. This was also true in the pathophysiologically different Fra-2 tg mice, where apoptosis of CD45+ cells occurred in the inflammatory stage. In accordance with the findings on tissue level, at day 3 in the BLM and at week 16 in the Fra-2 tg model, biodistribution and/or ex vivo autoradiography showed increased pulmonary uptake of ^99mTc-rhAnnexin V-128 compared with controls. However, accumulation of the radiotracer and thus the signal intensity in lungs was too low to allow the differentiation of healthy and injured lungs in vivo.

Conclusion

At the tissue level, ^99mTc-rhAnnexin V-128 successfully demonstrated early stages of ILD in two animal models by detection of apoptotic epithelial and/or inflammatory cells. In vivo, however, we did not detect early lung injury. It remains to be investigated whether the same applies to human ILD.

Electronic supplementary material

The online version of this article (10.1186/s13075-018-1681-1) contains supplementary material, which is available to authorized users.

The Role of Immune and Inflammatory Cells in Idiopathic Pulmonary Fibrosis

The contribution of the immune system to idiopathic pulmonary fibrosis (IPF) remains poorly understood. While most sources agree that IPF does not result from a primary immunopathogenic mechanism, evidence gleaned from animal modeling and human studies suggests that innate and adaptive immune processes can orchestrate existing fibrotic responses. This review will synthesize the available data regarding the complex role of professional immune cells in IPF. The role of innate immune populations such as monocytes, macrophages, myeloid suppressor cells, and innate lymphoid cells will be discussed, as will the activation of these cells via pathogen-associated molecular patterns derived from invading or commensural microbes, and danger-associated molecular patterns derived from injured cells and tissues. The contribution of adaptive immune responses driven by T-helper cells and B cells will be reviewed as well. Each form of immune activation will be discussed in the context of its relationship to environmental and genetic factors, disease outcomes, and potential therapies. We conclude with discussion of unanswered questions and opportunities for future study in this area.

Extracellular Mitochondrial DNA Is Generated by Fibroblasts and Predicts Death in Idiopathic Pulmonary Fibrosis

RATIONALE

Idiopathic pulmonary fibrosis (IPF) involves the accumulation of α-smooth muscle actin-expressing myofibroblasts arising from interactions with soluble mediators such as transforming growth factor-β1 (TGF-β1) and mechanical influences such as local tissue stiffness. Whereas IPF fibroblasts are enriched for aerobic glycolysis and innate immune receptor activation, innate immune ligands related to mitochondrial injury, such as extracellular mitochondrial DNA (mtDNA), have not been identified in IPF.

OBJECTIVES

We aimed to define an association between mtDNA and fibroblast responses in IPF.

METHODS

We evaluated the response of normal human lung fibroblasts (NHLFs) to stimulation with mtDNA and determined whether the glycolytic reprogramming that occurs in response to TGF-β1 stimulation and direct contact with stiff substrates, and spontaneously in IPF fibroblasts, is associated with excessive levels of mtDNA. We measured mtDNA concentrations in bronchoalveolar lavage (BAL) from subjects with and without IPF, as well as in plasma samples from two longitudinal IPF cohorts and demographically matched control subjects.

MEASUREMENTS AND MAIN RESULTS

Exposure to mtDNA augments α-smooth muscle actin expression in NHLFs. The metabolic changes in NHLFs that are induced by interactions with TGF-β1 or stiff hydrogels are accompanied by the accumulation of extracellular mtDNA. These findings replicate the spontaneous phenotype of IPF fibroblasts. mtDNA concentrations are increased in IPF BAL and plasma, and in the latter compartment, they display robust associations with disease progression and reduced event-free survival.

CONCLUSIONS

These findings demonstrate a previously unrecognized and highly novel connection between metabolic reprogramming, mtDNA, fibroblast activation, and clinical outcomes that provides new insight into IPF.

Role of metastasis-induced protein S100A4 in human non-tumor pathophysiologies

S100A4, an important member of the S100 family of proteins, is best known for its significant role in promoting cancer progression and metastasis. In addition to its expression in tumors, upregulation of S100A4 expression has been associated with various non-tumor pathophysiology processes. However, the mechanisms underlying the role of S100A4 remain unclear. Activated “host” cells (fibroblasts, immunocytes, vascular cells, among others) secrete S100A4 into the extracellular space in various non-tumor human disorders, where it executes its biological functions by interacting with intracellular target proteins. However, the exact molecular mechanisms underlying these interactions in different non-tumor pathophysiologies vary, and S100A4 is likely one of the cross-linking factors that acts as common intrinsic constituents of biological mechanisms. Numerous studies have indicated that the S100A4-mediated epithelial–mesenchymal transition plays a vital role in the occurrence and development of various non-tumor pathophysiologies. Epithelial–mesenchymal transition can be categorized into three general subtypes based on the phenotype and function of the output cells. S100A4 regulates tissue fibrosis associated with the type II epithelial–mesenchymal transition via various signaling pathways. Additionally, S100A4 stimulates fibroblasts to secrete fibronectin and collagen, thus forming the structural components of the extracellular matrix (ECM) and stimulating their deposition in tissues, contributing to the formation of a pro-inflammatory niche. Simultaneously, S100A4 enhances the motility of macrophages, neutrophils, and leukocytes and promotes the recruitment and chemotaxis of these inflammatory cells to regulate inflammation and immune functions. S100A4 also exerts a neuroprotective pro-survival effect on neurons by rescuing them from brain injury and participates in angiogenesis by interacting with other target molecules. In this review, we summarize the role of S100A4 in fibrosis, inflammation, immune response, neuroprotection, angiogenesis, and some common non-tumor diseases as well as its possible involvement in molecular pathways and potential clinical value.

Frontline Science: Multiple cathepsins promote inflammasome-independent, particle-induced cell death during NLRP3-dependent IL-1β activation

Sterile particles cause several chronic, inflammatory diseases, characterized by repeating cycles of particle phagocytosis and inflammatory cell death. Recent studies have proposed that these processes are driven by the NLRP3 inflammasome, a platform activated by phagocytosed particles, which controls both caspase-1-dependent cell death (pyroptosis) and mature IL-1β secretion. After phagocytosis, particles can disrupt lysosomes, and inhibitor studies have suggested that the resulting release of a lysosomal protease-cathepsin B-into the cytosol somehow activates NLRP3. However, using primary murine macrophages, we found that particle-induced cell death occurs independent of NLRP3/caspase-1 and depends instead on multiple, redundant cathepsins. In contrast, nigericin, a soluble activator of NLRP3 inflammasomes, induced cell death that was dependent on the NLRP3. Interestingly, nigericin-induced cell death depended partly on a single cathepsin, cathepsin X. By inhibiting or silencing multiple cathepsins in macrophages, several key proinflammatory events induced by sterile particles are blocked, including cell death, pro-IL-1β production, and IL-1β secretion. These data suggest that cathepsins might be potential therapeutic targets in particulate-mediated inflammatory disease. In support of this concept, we find that a broad-spectrum cathepsin inhibitor can suppress particle-induced IL-1-dependent peritonitis.

Calcium-binding protein S100A4 confers mesenchymal progenitor cell fibrogenicity in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive disease with a prevalence of 1 million persons worldwide. The fibrosis spreads from affected alveoli into contiguous alveoli and leads to death by asphyxiation. We previously discovered that the IPF lung harbors fibrogenic mesenchymal progenitor cells (MPCs) that serve as a cell of origin for disease-mediating myofibroblasts. In a prior genomewide transcriptional analysis, we found that IPF MPCs displayed increased expression of S100 calcium-binding A4 (S100A4), a protein linked to cancer cell proliferation and invasiveness. Here, we have examined whether S100A4 mediates MPC fibrogenicity. Ex vivo analysis revealed that IPF MPCs had increased levels of nuclear S100A4, which interacts with L-isoaspartyl methyltransferase to promote p53 degradation and MPC self-renewal. In vivo, injection of human IPF MPCs converted a self-limited bleomycin-induced mouse model of lung fibrosis to a model of persistent fibrosis in an S100A4-dependent manner. S100A4 gain of function was sufficient to confer fibrotic properties to non-IPF MPCs. In IPF tissue, fibroblastic foci contained cells expressing Ki67 and the MPC markers SSEA4 and S100A4. The expression colocalized in an interface region between myofibroblasts in the focus core and normal alveolar structures, defining this region as an active fibrotic front. Our findings indicate that IPF MPCs are intrinsically fibrogenic and that S100A4 confers MPCs with fibrogenicity.

Analysis of Microarray-Identified Genes and MicroRNAs Associated with Idiopathic Pulmonary Fibrosis

The aim of this study was to identify potential microRNAs and genes associated with idiopathic pulmonary fibrosis (IPF) through web-available microarrays. The microRNA microarray dataset GSE32538 and the mRNA datasets GSE32537, GSE53845, and GSE10667 were downloaded from the Gene Expression Omnibus (GEO) database. Differentially expressed miRNAs (DE-miRNAs)/genes (DEGs) were screened with GEO2R, and their associations with IPF were analyzed by comprehensive bioinformatic analyses. A total of 45 DE-microRNAs were identified between IPF and control tissues, whereas 67 common DEGs were determined to exhibit the same expression trends in all three microarrays. Furthermore, functional analysis indicated that microRNAs in cancer and ECM-receptor interaction were the most significant pathways and were enriched by the 45 DE-miRNAs and 67 common DEGs. Finally, we predicted potential microRNA-target interactions between 17 DE-miRNAs and 17 DEGs by using at least three online programs. A microRNA-mediated regulatory network among the DE-miRNAs and DEGs was constructed that might shed new light on potential biomarkers for the prediction of IPF progression.

Real-time imaging of mechanically and chemically induced ATP release in human lung fibroblasts

Extracellular adenosine 5'-triphosphate (ATP) acts as an inflammatory mediator of pulmonary fibrosis. We investigated the effects of mechanical and chemical stimuli on ATP release from primary normal human lung fibroblasts. We visualized the ATP release from fibroblasts in real time using a luminescence imaging system while acquiring differential interference contrast cell images with infrared optics. Immediately following a single uniaxial stretch for 1s, ATP was released from a certain population of cells and spread to surrounding spaces. Hypotonic stress, which causes plasma membrane stretching, also induced the ATP release. Compared with the effects of mechanical stretch, ATP-induced release sites were homogeneously distributed. In contrast to the effects of mechanical stimuli, application of platelet-derived growth factor caused ATP release from small numbers of the cells. Our real-time ATP imaging demonstrates that there is a heterogeneous nature of ATP release from lung fibroblasts in response to mechanical and chemical stimuli.

Pulmonary fibrosis, part I: epidemiology, pathogenesis, and diagnosis

INTRODUCTION

Many forms of interstitial lung disease (ILD) can progress to extensive fibrosis and respiratory failure. Idiopathic pulmonary fibrosis (IPF), which generally has a poor prognosis, has been thoroughly studied over the past two decades, and many important discoveries have been made that pertain to genetic predisposition, epidemiology, disease pathogenesis, diagnosis, and management. Additionally, non-IPF forms of ILD can have radiologic and histopathologic manifestations that mimic IPF, and making an accurate diagnosis is key to providing personalized medicine to patients with pulmonary fibrosis. Areas covered: This manuscript discusses current knowledge pertaining to the genetics, epidemiology, pathogenesis, and diagnosis of pulmonary fibrosis with an emphasis on IPF. The material upon which this discussion is based was obtained from various published texts and manuscripts identified via literature searching (e.g. PubMed). Expert commentary: Many genetic variants have been identified that are associated with risk of developing pulmonary fibrosis, and an improved understanding of the influence of both genomic and epigenomic factors in the development of pulmonary fibrosis is rapidly evolving. Because many forms of fibrosing ILD can have similar radiologic and histopathologic patterns yet have different responses to therapeutic interventions, making an accurate diagnosis of specific forms of pulmonary fibrosis is increasingly important.

The Role of Infection in Interstitial Lung Diseases: A Review

Interstitial lung disease (ILD) comprises an array of heterogeneous parenchymal lung diseases that are associated with a spectrum of pathologic, radiologic, and clinical manifestations. There are ILDs with known causes and those that are idiopathic, making treatment strategies challenging. Prognosis can vary according to the type of ILD, but many exhibit gradual progression with an unpredictable clinical course in individual patients, as seen in idiopathic pulmonary fibrosis and the phenomenon of "acute exacerbation"(AE). Given the often poor prognosis of these patients, the search for a reversible cause of respiratory worsening remains paramount. Infections have been theorized to play a role in ILDs, both in the pathogenesis of ILD and as potential triggers of AE. Research efforts thus far have shown the highest association with viral pathogens; however, fungal and bacterial organisms have also been implicated. This review aims to summarize the current knowledge on the role of infections in the setting of ILD.

Macrophage and Innate Lymphoid Cell Interplay in the Genesis of Fibrosis

Fibrosis is a characteristic pathological feature of an array of chronic diseases, where development of fibrosis in tissue can lead to marked alterations in the architecture of the affected organs. As a result of this process of sustained attrition to organs, many diseases that involve fibrosis are often progressive conditions and have a poor long-term prognosis. Inflammation is often a prelude to fibrosis, with innate and adaptive immunity involved in both the initiation and regulation of the fibrotic process. In this review, we will focus on the emerging roles of the newly described innate lymphoid cells (ILCs) in the generation of fibrotic disease with an examination of the potential interplay between ILC and macrophages and the adaptive immune system.

Respiratory epithelial cells orchestrate pulmonary innate immunity

The epithelial surfaces of the lungs are in direct contact with the environment and are subjected to dynamic physical forces as airway tubes and alveoli are stretched and compressed during ventilation. Mucociliary clearance in conducting airways, reduction of surface tension in the alveoli, and maintenance of near sterility have been accommodated by the evolution of a multi-tiered innate host-defense system. The biophysical nature of pulmonary host defenses are integrated with the ability of respiratory epithelial cells to respond to and 'instruct' the professional immune system to protect the lungs from infection and injury.

The role of toll-like receptor 4 in corneal epithelial wound healing

PURPOSE

We evaluated the role of Toll-like receptor 4 (TLR4) in corneal epithelial wound healing.

METHODS

The expression of TLR4 during in vivo corneal epithelial wound healing was examined by immunostaining in mice. The expression and activation of TLR4 was studied in primary or telomerase-immortalized human corneal epithelial cells (HCEC). Scratch assay was performed to evaluate in vitro wound closure using live time-lapse microscopy. Transwell migration assay and Ki67 immunostaining were done to evaluate migration and proliferation, respectively. Lipopolysaccharide (LPS) was used to activate TLR4, whereas CLI-095 was used for its inhibition. The expression of inflammatory cytokines was determined by RT-PCR and ELISA. The activation of p42/44 and p38 was determined by immunoblotting.

RESULTS

In the murine model, TLR4 immunostaining was noted prominently in the epithelium 8 hours after wounding. There was a 4-fold increase in the expression of TLR4 6 hours after in vitro scratch wounding (P < 0.001). Confocal microscopy confirmed the membrane localization of TLR4/MD2 complex. There was a significant increase in migration, proliferation, and wound closure in HCEC treated with LPS (P < 0.05), while there was significant decrease with TLR4 inhibition (P < 0.05). Addition of LPS to wounded HCEC resulted in a significant increase in the expression of IL-6, TNF-α, CXCL8/IL8, and CCL5/RANTES at the mRNA and protein levels. Likewise, LPS increased the activation of p42/44 and p38 in wounded HCEC.

CONCLUSIONS

These results suggest that epithelial wounding induces the expression of functional TLR4. Toll-like receptor 4 signaling appears to contribute to early corneal epithelial wound repair by enhancing migration and proliferation.