The Airway in Idiopathic Pulmonary Fibrosis: Protecting the Lung or Promoting Disease?

Trends and hotspots in pulmonary fibrosis biomarker research: a bibliometric analysis

Background

Pulmonary fibrosis is a fatal disease characterized by progressive scarring of lung tissue, with a complex pathogenesis and limited therapeutic options. The identification of robust biomarkers is critical for addressing key clinical challenges, including delayed diagnosis and poor prognostic assessment.

Methods

This study systematically analyzes global research trends and emerging hotspots in pulmonary fibrosis biomarkers by examining literature from 2001 to 2024 indexed in the Web of Science Core Collection. Utilizing a suite of bibliometric tools including VOSviewer, CiteSpace, Bibliometrix, Scimago Graphica, and OriginPro 2021, this work provides the first comprehensive insight into the evolving landscape of biomarker research in pulmonary fibrosis.

Results

This study included a total of 2,519 articles and reviews related to pulmonary fibrosis biomarkers. Since 2005, publication trends in this field have steadily increased. Research on pulmonary fibrosis biomarkers has involved 71 countries, 3,036 institutions, 760 journals, and over 14,000 researchers. China produced the highest number of publications (n = 535, 21.2%, TLCS = 459), followed by the United States (n = 529, 21%, TLCS = 3,527) and Japan (n = 270, 10.7%, TLCS = 1,279), with the United States exerting the greatest influence. The UNIVERSITY OF CALIFORNIA SYSTEM (n = 164) and HARVARD UNIVERSITY (n = 141) contributed the largest bodies of work. The most prolific authors in this domain are BARGAGLI E (n = 45), MAHER TM (n = 42), and MARTINEZ FJ (n = 32). The AMERICAN JOURNAL OF RESPIRATORY AND CRITICAL CARE MEDICINE is widely regarded as the leading journal in this field. In recent years, research has increasingly focused on macrophages, computed tomography, and Muc5b promoter polymorphism, among other areas. The concept of "double blind" reflects the translational trend of biomarkers toward clinical applications, particularly their potential utility in acute exacerbations of pulmonary fibrosis, interstitial pulmonary fibrosis, cystic pulmonary fibrosis, and radiation-induced pulmonary fibrosis.

Conclusion

The clinical application of gene and imaging biomarkers achieved through the integration of multiple parameters and multi-omics fusion represents a promising future trend and emerging hotspot in pulmonary fibrosis biomarker research.

Quantitative assessment of airway wall thickness in COPD patients with interstitial lung abnormalities

Background

Whether the airway is involved in the pathogenesis of interstitial lung abnormalities (ILA) is not well understood. Also the impact of ILA on lung function in COPD patients remains controversial. We aimed to assess the quantitative CT measurements of airway wall thickness (AWT) and lung function according to ILA status in COPD patients.

Methods

157 COPD patients discharged from our hospital from August 1, 2019 through August 31, 2022 who underwent chest CT imagings and pulmonary function tests were retrospectively enrolled. Linear regression analysis and multiple models were used to analyze associations between quantitative assessment of airway wall changes and the presence of ILA.

Results

In 157 COPD patients, 23 patients (14.6%) had equivocal ILA, 42 patients (26.8%) had definite ILA. The definite ILA group had the highest measurements of Pi10 (square root of theoretical airway wall area with a lumen perimeter of 10 mm), segmental AWT and segmental WA% (percentage of wall area), whereas the no ILA group had the lowest measurements of Pi10, segmental AWT and segmental WA%. In the adjusted analyses (adjusted by age, sex, body mass index, smoking intensity, COPD GOLD stage, lung function, slice thickness and scanner type), compared to COPD patients without ILA, the measurements of Pi10, segmental AWT and segmental WA% were higher in definite ILA group with differences of 0.225 mm (p = 0.012), 0.152 mm (p < 0.001), 4.8% (p < 0.001) respectively. COPD patients with definite ILA tended to have higher FEV1% predicted, FVC% predicted and lower MMEF75/25% predicted, but there were no statistically differences among the three groups.

Conclusion

Our study demonstrates the higher AWT measures in COPD patients with ILA compared to the patients without ILA. These findings suggest that the airway may be involved in the pathogenesis of ILA.

Myeloid- and Epithelial-derived Heparin-Binding Epidermal Growth Factor-like Growth Factor Promotes Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a poorly understood, progressive lethal lung disease with no known cure. In addition to alveolar epithelial cell (AEC) injury and excessive deposition of extracellular matrix proteins, chronic inflammation is a hallmark of IPF. Literature suggests that the persistent inflammation seen in IPF primarily consists of monocytes and macrophages. Recent work demonstrates that monocyte-derived alveolar macrophages (moAMs) drive lung fibrosis, but further characterization of critical moAM cell attributes is necessary. Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is an important epidermal growth factor receptor ligand that has essential roles in angiogenesis, wound healing, keratinocyte migration, and epithelial-mesenchymal transition. Our past work has shown HB-EGF is a primary marker of profibrotic M2 macrophages, and this study seeks to characterize myeloid-derived HB-EGF and its primary mechanism of action in bleomycin-induced lung fibrosis using Hbegff/f;Lyz2Cre+ mice. Here, we show that patients with IPF and mice with pulmonary fibrosis have increased expression of HB-EGF and that lung macrophages and transitional AECs of mice with pulmonary fibrosis and humans all express HB-EGF. We also show that Hbegff/f;Lyz2Cre+ mice are protected from bleomycin-induced fibrosis and that this protection is likely multifactorial, caused by decreased CCL2-dependent monocyte migration, decreased fibroblast migration, and decreased contribution of HB-EGF from AEC sources when HB-EGF is removed under the Lyz2Cre promoter.

Ciliated (FOXJ1+) Cells Display Reduced Ferritin Light Chain in the Airways of Idiopathic Pulmonary Fibrosis Patients

Cell-based therapies hold great promise in re-establishing organ function for many diseases, including untreatable lung diseases such as idiopathic pulmonary fibrosis (IPF). However, many hurdles still remain, in part due to our lack of knowledge about the disease-driving mechanisms that may affect the cellular niche and thereby possibly hinder the function of any transplanted cells by imposing the disease phenotype onto the newly generated progeny. Recent findings have demonstrated increased ciliation of lung cells from IPF patients, but how this affects ciliated cell function and the airway milieu is not well-known. Here, we performed single-cell RNA sequencing on primary ciliated (FOJ1+) cells isolated from IPF patients and from healthy control donors. The sequencing identified multiple biological processes, such as cilium morphogenesis and cell signaling, that were significantly changed between IPF and healthy ciliated cells. Ferritin light chain (FTL) was downregulated in IPF, which suggests that iron metabolism may be affected in the IPF ciliated cells. The RNA expression was confirmed at the protein level with histological localization in lung tissue, prompting future functional assays to reveal the potential role of FTL. Taken together, our data demonstrate the importance of careful analyses in pure cell populations to better understand the IPF disease mechanism.

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.

The minor T allele of the MUC5B promoter rs35705950 associated with susceptibility to idiopathic pulmonary fibrosis: a meta-analysis

MUC5B promoter rs35705950 T/G gene polymorphism has been associated with the risk of IPF, but the influence of this relationship varies among different populations. In the past 2 years, there were new clinical studies with different results, but none of them reached unified conclusions. Therefore, this study further included the latest case-control studies, integrated their results and carried out meta-analysis on them to draw reliable conclusions. PubMed, EMBASE, CNKI, Wanfang database and VIP Chinese science were searched by a computer to collect the related literatures of MUC5B gene polymorphism and IPF susceptibility published before June 15, 2021. The first author, year of publication, diagnostic criteria and gene frequency were extracted after screened them. Forest plot was drawn and the trial sequential analysis (TSA) was carried out to confirm the stability of the meta-analysis results. Registration number: CRD42021272940. A total of 24 case-control studies (13 studies on the Caucasian, 7 studies on the Asian and 4 studies on the mixed population), and a total of 6749 IPF patients and 13,898 healthy controls were included in this study. The T vs.G, TT vs. GG, GT vs. GG, GT + TT vs. GG and TT vs. GG + GT genetic models of MUC5B promoter rs35705950 T/G polymorphism were associated with IPF risk in all populations, and the effect values were ([OR] 4.12, 95% CI [3.64, 4.67]), ([OR] 10.12, 95% CI [7.06, 14.49]), ([OR] 4.84, 95% CI [3.85, 6.08]), ([OR] 4.84, 95% CI [3.79, 6.19]) and ([OR] 5.11, 95% CI [4.02, 6.49]), respectively. The results of TSA confirmed the stability of the results. Subgroup analysis showed that T vs.G, TT vs. GG, GT vs. GG, GT + TT vs. GG and TT vs. GG + GT genetic models of MUC5B polymorphism were associated with IPF risk in Caucasian population. The effect values were ([OR] 4.50, 95% CI [3.93, 5.16]), ([OR] 10.98, 95% CI [7.59, 15.89]), ([OR] 6.27, 95% CI [5.37, 7.32]), ([OR] 6.30, 95% CI [5.19, 7.64]) and ([OR] 5.15, 95% CI [4.01, 6.61]), respectively. Similar results were also found in Asian and mixed populations. The association strength of the minor T allele in the Caucasian was more significant than that of the Asian population ([OR] 4.50 vs. [OR] 2.39), and the association strength of all genetic models carrying "T" was more significant than that of the Asian population ([OR] 10.98 vs. [OR] 4.29). In Caucasian, Asian and mixed populations, T minor allele carriers were more likely to be susceptible to pulmonary fibrosis, and TT genotype carriers were more likely to be susceptible to IPF than GT genotype carriers. The association between IPF and Caucasian population with minor T allele and all "T" genetic model was more significant than that of Asian population.

M2 macrophages have unique transcriptomes but conditioned media does not promote profibrotic responses in lung fibroblasts or alveolar epithelial cells in vitro

Macrophages are critical regulators of pulmonary fibrosis. Their plasticity, proximity, and ability to cross talk with structural cells of the lung make them a key cell type of interest in the regulation of lung fibrosis. Macrophages can express a variety of phenotypes, which have been historically represented through an "M1-like" to "M2-like" delineation. In this classification, M1-like macrophages are proinflammatory and have increased phagocytic capacity compared with alternatively activated M2-like macrophages that are profibrotic and are associated with wound healing. Extensive evidence in the field in both patients and animal models aligns pulmonary fibrosis with M2 macrophages. In this study, we performed RNA sequencing (RNAseq) to fully characterize M1- vs. M2-skewed bone marrow-derived macrophages (BMDMs) and investigated the profibrotic abilities of M2 BMDM conditioned media (CM) to promote fibroblast migration and proliferation, alveolar epithelial cell (AEC) apoptosis, and mRNA expression of key fibrotic genes in both fibroblasts and AECs. Although M2 CM-treated fibroblasts had increased migration and M2 CM-treated fibroblasts and AECs had increased expression of profibrotic proteins over M1 CM-treated cells, all differences can be attributed to M2 polarization reagents IL-4 and IL-13 also present in the CM. Collectively, these data suggest that the profibrotic effects associated with M2 macrophage CM in vitro are attributable to effects of polarization cytokines rather than additional factors secreted in response to those polarizing cytokines.

Increased Airway Wall Thickness in Interstitial Lung Abnormalities and Idiopathic Pulmonary Fibrosis

RATIONALE

There is increasing evidence that aberrant processes occurring in the airways may precede the development of idiopathic pulmonary fibrosis (IPF); however, there has been no prior confirmatory data derived from imaging studies.

OBJECTIVES

To assess quantitative measures of airway wall thickness (AWT) in populations characterized for interstitial lung abnormalities (ILA) and for IPF.

METHODS

Computed tomographic imaging of the chest and measures of AWT were available for 6,073, 615, 1,167, and 38 participants from COPDGene (Genetic Epidemiology of COPD study), ECLIPSE (Evaluation of COPD Longitudinally to Identify Predictive Surrogate Endpoints study), and the Framingham Heart Study (FHS) and in patients with IPF from the Brigham and Women's Hospital Herlihy Registry, respectively. To evaluate these associations, we used multivariable linear regression to compare a standardized measure of AWT (the square root of AWT for airways with an internal perimeter of 10 mm [Pi10]) and characterizations of ILA and IPF by computed tomographic imaging of the chest.

RESULTS

In COPDGene, ECLIPSE, and FHS, research participants with ILA had increased measures of Pi10 compared with those without ILA. Patients with IPF had mean measures of Pi10 that were even greater than those noted in research participants with ILA. After adjustment for important covariates (e.g., age, sex, race, body mass index, smoking behavior, and chronic obstructive pulmonary disease severity when appropriate), research participants with ILA had increased measures of Pi10 compared with those without ILA (0.03 mm in COPDGene, 95% confidence interval [CI], 0.02-0.03; P < 0.001; 0.02 mm in ECLIPSE, 95% CI, 0.005-0.04; P = 0.01; 0.07 mm in FHS, 95% CI, 0.01-0.1; P = 0.01). Compared with COPDGene participants without ILA older than 60 years of age, patients with IPF were also noted to have increased measures of Pi10 (2.0 mm, 95% CI, 2.0-2.1; P < 0.001). Among research participants with ILA, increases in Pi10 were correlated with reductions in lung volumes in some but not all populations.

CONCLUSIONS

These results demonstrate that measurable increases in AWT are consistently noted in research participants with ILA and in patients with IPF. These findings suggest that abnormalities of the airways may play a role in, or be correlated with, early pathogenesis of pulmonary fibrosis.

The Possible Pathogenesis of Idiopathic Pulmonary Fibrosis considering MUC5B

Background

Overexpression of the MUC5B protein is associated with idiopathic pulmonary fibrosis (IPF), but little information is available regarding the pathogenic effects and regulatory mechanisms of overexpressed MUC5B in IPF.

Main Body

The overexpression of MUC5B in terminal bronchi and honeycomb cysts produces mucosal host defensive dysfunction in the distal airway which may play an important role in the development of IPF. This review addresses the possible association of overexpression of MUC5B, with MUC5B promoter polymorphism, MUC5B gene epigenetic changes, effects of some transcriptional factors, and inflammatory mediators in IPF. In addition, the associated signaling pathways which may influence the expression of MUC5B are also discussed.

Conclusion

This work has important implications for further exploration of the mechanisms of overexpression of MUC5B in IPF, and future personalized treatment.

A role for telomere length and chromosomal damage in idiopathic pulmonary fibrosis

BACKGROUND

Idiopathic pulmonary fibrosis is a fatal lung disease characterized by a progressive formation of fibroblastic foci in the interstitium. This disease is strongly associated with telomere dysfunction but the extent of telomere shortening and consequent chromosomal damage within IPF lungs and with regional disease severity remains unknown.

METHODS

Explanted IPF lungs (n = 10) were collected from transplant surgeries with six samples per lung analysed to capture the regional heterogeneity ranging from mild to severe disease. Non-used donor lungs (n = 6) were collected as "healthy" controls. Structural changes related to disease severity (microCT surface density), relative telomere length (real-time qPCR), and quantitative histology of chromosomal damage (γ-H2A.X) and extracellular matrix (elastin, total collagen, collagen 1, and collagen 3) were measured. A multivariate linear mixed-effects model controlling for subject was used to identify association of disease severity or fibrotic markers with telomere length and chromosomal damage.

RESULTS

We observed shorter telomere length (p = 0.001) and increased chromosomal damage (p = 0.018) in IPF lungs compared to controls. In IPF lungs, telomere length was associated with total collagen (p < 0.001) but not with structural changes of disease severity. Chromosomal damage was positively associated with increased elastin (p = 0.006) and negatively with structural disease severity (p = 0.046). Extensive γ-H2A.X staining was also present in airway epithelial cells.

CONCLUSIONS

Telomere length and chromosomal damage are involved in IPF with regional variation in telomere length and chromosomal damage associated with pathological changes in tissue structure and the extracellular matrix.