Targeting defective Toll-like receptor-3 function and idiopathic pulmonary fibrosis

The role of cGAS-STING signaling in pulmonary fibrosis and its therapeutic potential

Pulmonary fibrosis is a progressive and ultimately fatal lung disease, exhibiting the excessive production of extracellular matrix and aberrant activation of fibroblast. While Pirfenidone and Nintedanib are FDA-approved drugs that can slow down the progression of pulmonary fibrosis, they are unable to reverse the disease. Therefore, there is an urgent demand to develop more efficient therapeutic approaches for pulmonary fibrosis. The intracellular DNA sensor called cyclic guanosine monophosphate-adenosine monophosphate (cGAMP) synthase (cGAS) plays a crucial role in detecting DNA and generating cGAMP, a second messenger. Subsequently, cGAMP triggers the activation of stimulator of interferon genes (STING), initiating a signaling cascade that leads to the stimulation of type I interferons and other signaling molecules involved in immune responses. Recent studies have highlighted the involvement of aberrant activation of cGAS-STING contributes to fibrotic lung diseases. This review aims to provide a comprehensive summary of the current knowledge regarding the role of cGAS-STING pathway in pulmonary fibrosis. Moreover, we discuss the potential therapeutic implications of targeting the cGAS-STING pathway, including the utilization of inhibitors of cGAS and STING.

Acute Exacerbations of Interstitial Lung Diseases: Focus on Biomarkers

Interstitial lung diseases (ILDs) are a large group of pulmonary disorders characterized histologically by the cardinal involvement of the pulmonary interstitium. The prototype of ILDs is idiopathic pulmonary fibrosis (IPF), an incurable disease characterized by progressive distortion and loss of normal lung architecture through unchecked collagen deposition. Acute exacerbations are dramatic events during the clinical course of ILDs, associated with high morbidity and mortality. Infections, microaspiration, and advanced lung disease might be involved in the pathogenesis of acute exacerbations. Despite clinical scores, the prediction of the onset and outcome of acute exacerbations is still inaccurate. Biomarkers are necessary to characterize acute exacerbations better. We review the evidence for alveolar epithelial cell, fibropoliferation, and immunity molecules as potential biomarkers for acute exacerbations of interstitial lung disease.

Research Progress in the Molecular Mechanisms, Therapeutic Targets, and Drug Development of Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a fatal interstitial lung disease. Recent studies have identified the key role of crosstalk between dysregulated epithelial cells, mesenchymal, immune, and endothelial cells in IPF. In addition, genetic mutations and environmental factors (e.g., smoking) have also been associated with the development of IPF. With the recent development of sequencing technology, epigenetics, as an intermediate link between gene expression and environmental impacts, has also been reported to be implicated in pulmonary fibrosis. Although the etiology of IPF is unknown, many novel therapeutic targets and agents have emerged from clinical trials for IPF treatment in the past years, and the successful launch of pirfenidone and nintedanib has demonstrated the promising future of anti-IPF therapy. Therefore, we aimed to gain an in-depth understanding of the underlying molecular mechanisms and pathogenic factors of IPF, which would be helpful for the diagnosis of IPF, the development of anti-fibrotic drugs, and improving the prognosis of patients with IPF. In this study, we summarized the pathogenic mechanism, therapeutic targets and clinical trials from the perspective of multiple cell types, gene mutations, epigenetic and environmental factors.

Bacterial and viral coinfection in idiopathic pulmonary fibrosis patients: the prevalence and possible role in disease progression

Background

Idiopathic pulmonary fibrosis (IPF) is a progressive interstitial pneumonia of unknown aetiology with a mean survival rate of less than 3 years. No previous studies have been performed on the role of co-infection (viral and bacterial infection) in the pathogenesis and progression of IPF. In this study, we investigated the role of viral/bacterial infection and coinfection and their possible association with pathogenesis and progression of IPF.

Methods

We investigated the prevalence and impact of bacterial and viral coinfection in IPF patients (n = 67) in the context of pulmonary function (FVC, FEV₁ and DL_CO), disease status and mortality risk. Using principal component analysis (PCA), we also investigated the relationship between distribution of bacterial and viral co-infection in the IPF cohort.

Results

Of the 67 samples, 17.9% samples were positive for viral infection, 10.4% samples were positive for bacterial infection and 59.7% samples were positive coinfection. We demonstrated that IPF patients who were co-infected had a significantly increased risk of mortality compared (p = 0.031) with IPF patients who were non-infected [Hazard ratio: 8.12; 95% CI 1.3–26.9].

Conclusion

In this study, we report for the first time that IPF patients who were coinfected with bacterial and viral infection have significantly decreased FVC and DL_CO (% predicted). Besides, the results demonstrated the increased AE-IPF, increased incidence of death and risk of mortality in infected/coinfected patients compared to non-infected IPF patients.

Molecular pathways and role of epigenetics in the idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a fatal lung disease with unknown etiological factors that can progress to other dangerous diseases like lung cancer. Environmental and genetic predisposition are the two major etiological or risk factors involved in the pathology of the IPF. Among the environmental risk factors, smoking is one of the major causes for the development of IPF. Epigenetic pathways like nucleosomes remodeling, DNA methylation, histone modifications and miRNA mediated genes play a crucial role in development of IPF. Mutations in the genes make the epigenetic factors as important drug targets in IPF. Transcriptional changes due to environmental factors are also involved in the progression of IPF. The mutations in human telomerase reverse transcriptase (hTERT) have shown decreased life expectancy in IPF patients. The TERT-gene is highly expressed in chronic smokers and makes the role of epigenetics evident. Drug like nintedanib acts through vascular endothelial growth factor receptors (VEGFR), while drug pirfenidone acts through transforming growth factor (TGF), which is useful in IPF. Gefitinib, a tyrosine kinase inhibitor of EGFR, is useful as an anti-fibrosis agent in preclinical models. Newer drugs such as Celgene-CC90001 and FibroGen-FG-3019 are currently under investigations acts through the modulating epigenetic mechanisms. Thus, the study on epigenetics opens a wide window for the discovery of newer drugs. This study provides an elementary analysis of multiple regulators of epigenetics and their roles associated with the pathology of IPF. Further, this review also includes epigenetic drugs under development in preclinical and clinical stages.

Synthesis, activity and mechanism for double-ring conjugated enones

The relationship between TLR4 and inflammation-related diseases has been paid more and more attention. The studies have shown that TLR4/NF-κB signaling pathway plays an important role in the transmission of inflammatory signals. A large number of pro-inflammatory factors, chemokines, adhesion factors, TLR4 and its ligands interact with each other, and jointly promote the development of diseases. In this work, 8 target compounds were synthesized to screen the inhibitory activity of TLR4 in vitro. The results of TLR4 inhibition test in vitro showed that the double-ring conjugated enones had a good inhibitory activity, and the IC₅₀ value of compound 4f was 0.56 ± 0.10 μM, and it was superior to the positive control methotrexate. To further study the anti-inflammatory effect and mechanism of double-ring conjugated enones by using LPS induced rat synovial cell inflammation model. The results of the mechanism test showed that compound 4f could effectively promote the apoptosis of rat synovial cells, and the mechanism might be related to the up-regulation of the expression of apoptosis-related protein Caspase-3. In addition, compound 4f could significantly inhibit the increase of inflammatory factors TNF-α, IL-1β and IL-6 in rat synovial cells induced by LPS, showing a good anti-inflammatory activity. In the TLR4/NF-κB signaling pathway test of rat synovial cells, compound 4f can effectively regulate the expression levels of TLR4, MyD88, NF-κB and IκB related proteins in TLR4/NF-κB signaling pathway, which may be due to its inhibition of LPS-induced inflammation in rat synovial cells. At the same time, it inhibits the abnormal proliferation of cells and its important mechanism promoted of apoptosis.

Molecular Biomarkers in Idiopathic Pulmonary Fibrosis: State of the Art and Future Directions

Idiopathic pulmonary fibrosis (IPF), the most lethal form of interstitial pneumonia of unknown cause, is associated with a specific radiological and histopathological pattern (the so-called "usual interstitial pneumonia" pattern) and has a median survival estimated to be between 3 and 5 years after diagnosis. However, evidence shows that IPF has different clinical phenotypes, which are characterized by a variable disease course over time. At present, the natural history of IPF is unpredictable for individual patients, although some genetic factors and circulating biomarkers have been associated with different prognoses. Since in its early stages, IPF may be asymptomatic, leading to a delayed diagnosis. Two drugs, pirfenidone and nintedanib, have been shown to modify the disease course by slowing down the decline in lung function. It is also known that 5-10% of the IPF patients may be affected by episodes of acute and often fatal decline. The acute worsening of disease is sometimes attributed to identifiable conditions, such as pneumonia or heart failure; but many of these events occur without an identifiable cause. These idiopathic acute worsenings are termed acute exacerbations of IPF. To date, clinical biomarkers, diagnostic, prognostic, and theranostic, are not well characterized. However, they could become useful tools helping facilitate diagnoses, monitoring disease progression and treatment efficacy. The aim of this review is to cover molecular mechanisms underlying IPF and research into new clinical biomarkers, to be utilized in diagnosis and prognosis, even in patients treated with antifibrotic drugs.

Mucins as a New Frontier in Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is the most common idiopathic interstitial pulmonary disease with a median survival of 3–5 years after diagnosis. Recent evidence identifies mucins as key effectors in cell growth and tissue remodeling processes compatible with the processes observed in IPF. Mucins are classified in two groups depending on whether they are secreted (secreted mucins) or tethered to cell membranes (transmembrane mucins). Secreted mucins (MUC2, MUC5AC, MUC5B, MUC6-8 and MUC19) are released to the extracellular medium and recent evidence has shown that a promoter polymorphism in the secreted mucin MUC5B is associated with IPF risk. Otherwise, transmembrane mucins (MUC1, MUC3, MUC4, MUC12-17 and MUC20) have a receptor-like structure, sensing the external environment and activating intracellular signal transduction pathways essential for mucosal maintenance and damage repair. In this context, the extracellular domain can be released to the external environment by metalloproteinase action, increased in IPF, thus activating fibrotic processes. For example, several studies have reported increased serum extracellular secreted KL6/MUC1 during IPF acute exacerbation. Moreover, MUC1 and MUC4 overexpression in the main IPF cells has been observed. In this review we summarize the current knowledge of mucins as promising druggable targets for IPF.

Biomarkers in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic, debilitating, fibrotic lung disease leading to respiratory failure and ultimately to death. Being the prototype of interstitial lung diseases, IPF is characterized by marked heterogeneity regarding its clinical course. Despite significant progress in the understanding of its pathogenesis, we still cannot reliably predict the course of the disease and the response to treatment of an individual patient. Non-invasive biomarkers, in particular serum biomarkers, for the (early) diagnosis, differential diagnosis, prognosis and prediction of therapeutic response are urgently needed. Numerous molecules involved in alveolar epithelial cell injury, fibroproliferation and matrix remodeling as well as immune regulation have been proposed as potential biomarkers. Furthermore, genetic variants of TOLLIP, MUC5B, and other genes are associated with a differential response to treatment and with the development and/or the prognosis of IPF. Additionally, the bacterial signature in IPF lungs, as shown from microbiome analyses, as well as mitochondrial DNA seem to have promising roles as biomarkers. Moreover, combination of multiple biomarkers may identify comprehensive biomarker signatures in IPF patients. However, there is still a long way until these potential biomarkers complete or substitute for the clinical and functional parameters currently available for IPF.

Modeling DNA damage-induced pneumopathy in mice: insight from danger signaling cascades

Radiation-induced pneumonitis and fibrosis represent severe and dose-limiting side effects in the radiotherapy of thorax-associated neoplasms leading to decreased quality of life or - as a consequence of treatment with suboptimal radiation doses - to fatal outcomes by local recurrence or metastatic disease. It is assumed that the initial radiation-induced damage to the resident cells triggers a multifaceted damage-signalling cascade in irradiated normal tissues including a multifactorial secretory program. The resulting pro-inflammatory and pro-angiogenic microenvironment triggers a cascade of events that can lead within weeks to a pronounced lung inflammation (pneumonitis) or after months to excessive deposition of extracellular matrix molecules and tissue scarring (pulmonary fibrosis).The use of preclinical in vivo models of DNA damage-induced pneumopathy in genetically modified mice has helped to substantially advance our understanding of molecular mechanisms and signalling molecules that participate in the pathogenesis of radiation-induced adverse late effects in the lung. Herein, murine models of whole thorax irradiation or hemithorax irradiation nicely reproduce the pathogenesis of the human disease with respect to the time course and the clinical symptoms. Alternatively, treatment with the radiomimetic DNA damaging chemotherapeutic drug Bleomycin (BLM) has frequently been used as a surrogate model of radiation-induced lung disease. The advantage of the BLM model is that the symptoms of pneumonitis and fibrosis develop within 1 month.Here we summarize and discuss published data about the role of danger signalling in the response of the lung tissue to DNA damage and its cross-talk with the innate and adaptive immune systems obtained in preclinical studies using immune-deficient inbred mouse strains and genetically modified mice. Interestingly we observed differences in the role of molecules involved in damage sensing (TOLL-like receptors), damage signalling (MyD88) and immune regulation (cytokines, CD73, lymphocytes) for the pathogenesis and progression of DNA damage-induced pneumopathy between the models of pneumopathy induced by whole thorax irradiation or treatment with the radiomimetic drug BLM. These findings underline the importance to pursue studies in the radiation model(s) if we are to unravel the mechanisms driving radiation-induced adverse late effects.A better understanding of the cross-talk of danger perception and signalling with immune activation and repair mechanisms may allow a modulation of these processes to prevent or treat radiation-induced adverse effects. Vice-versa an improved knowledge of the normal tissue response to injury is also particularly important in view of the increasing interest in combining radiotherapy with immune checkpoint blockade or immunotherapies to avoid exacerbation of radiation-induced normal tissue toxicity.

Phycocyanin attenuates pulmonary fibrosis via the TLR2-MyD88-NF-κB signaling pathway

Our aim was to investigate the effects of phycocyanin (PC) on bleomycin (BLM)-induced pulmonary fibrosis (PF). In this study, C57 BL/6 wild-type (WT) mice and toll-like receptor (TLR) 2 deficient mice were treated with PC for 28 days following BLM exposure. Serum and lung tissues were collected on days 3, 7 and 28. Data shows PC significantly decreased the levels of hydroxyproline (HYP), vimentin, surfactant-associated protein C (SP-C), fibroblast specific protein-1 (S100A4) and α-smooth muscle actin (α-SMA) but dramatically increased E-cadherin and podoplanin (PDPN) expression on day 28. Moreover, PC greatly decreased the levels of interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) and myeloperoxidase (MPO) at the earlier time. Reduced expression of key genes in the TLR2 pathway was also detected. Compared with WT mice, TLR2-deficient mice exhibited less injury, and the protective effect of PC was partly diminished in this background. These data indicate the anti-fibrotic effects of PC may be mediated by reducing W/D ratio, MPO, IL-6, TNF-α, protecting type I alveolar epithelial cells, inhibiting fibroblast proliferation, attenuating epithelial-mesenchymal transitions (EMT) and reducing oxidative stress. The TLR2-MyD88-NF-κB pathway plays an important role in PC-mediated reduction in pulmonary fibrosis.

Deficiency of α7 nicotinic acetylcholine receptor attenuates bleomycin-induced lung fibrosis in mice

α7 nicotinic acetylcholine receptor (α7 nAChR, coded by Chrna7) is indispensible in dampening proinflammatory responses. However, whether α7 nAChR would play a role in regulating bleomycin (BLM)-induced lung fibrosis is less investigated. Here, we intratracheally challenged wildtype and Chrna7^-/- mice with BLM to elicit lung fibrosis. Taken advantage of this model, we measured body weight loss, lung fibrogenic genes (Acta2, Col1a1, Fsp1, and Fstl1), histology, Masson's trichrome staining, hydroxyproline levels, and expression of α-SMA at protein levels in the BLM-challenged lung for evaluating severity of lung fibrosis. We also pretreated human fibroblasts (MRC5 cell line) and isolated mouse lung fibroblasts with GTS-21 (an α7 nAChR agonist) to study its effects on TGF-β-stimulated profibrotic profiles. We found that lung Chrna7 expression and CD4⁺CHAT⁺ (Choline acetyltransferase, an enzyme for local acetylcholine synthesis) cells were 12-fold and 4.5-fold respectively elevated in the early stage of lung fibrosis. Deletion of Chrna7 prevented body weight loss and reduced lung fibrogenic genes (Acta2, Col1a1, Fsp1, and Fstl1) and Arg 1 (coding arginase 1). Deletion of Chrna7 attenuated lung arginase 1⁺Ly6C⁺ cells, Masson's trichrome staining, hydroxyproline levels, and expression of α-SMA at protein levels in BLM-challenged mice. Mechanistically, activation of α7 nAChR in human fibroblasts increased TGF-β-induced phosphorylation of Smad2/3 and transcription of fibrogenic genes (Acta2, Col1a1). In isolated mouse lung fibroblasts, activation of α7 nAChR also enhanced TGF-β induced-transcription of fibrogenic genes; however, deletion of Chrna7 diminished these effects. Taken together, deficiency of α7 nAChR could suppress the development of BLM-induced lung fibrosis. Thus, α7 nAChR might be a novel therapeutic target for treating lung fibrosis.

Personalized medicine in idiopathic pulmonary fibrosis: facts and promises

PURPOSE OF REVIEW

In this article, we summarize and discuss the most recent literature on personalized medicine in idiopathic pulmonary fibrosis (IPF), a chronic progressive and almost invariably lethal disease of unknown cause. This review is timely as major advances in our understanding of disease pathobiology and improvements in molecular techniques have recently led to the identification of potential surrogates of diagnosis, prognosis and response to treatment.

RECENT FINDINGS

The most promising and advanced candidate biomarkers are presented based on their proposed mechanistic pathways (e.g. alveolar epithelial cell dysfunction, immune dysregulation, microbiome, extracellular matrix remodeling and fibroproliferation, epigenetic markers and metabolomics). Recent data suggest that components of the immune system may contribute to the development of IPF. A potential role for infections as a cofactor in disease development and progression or as a trigger in disease exacerbation has also recently been proposed.

SUMMARY

Clinical management of IPF is unsatisfactory because of limited availability of truly effective therapies, lack of accurate predictors of disease behavior and absence of simple short-term measures of therapeutic response. A number of putative biomarkers have been identified in patients with IPF, although none has been validated to the standard necessary for their use in either therapeutic trials or clinical practice. Currently, ongoing prospective longitudinal studies will hopefully permit such validation.