XBP1S Regulates MUC5B in a Promoter Variant-Dependent Pathway in Idiopathic Pulmonary Fibrosis Airway Epithelia

CXCR4+ cells are increased in lung tissue of patients with idiopathic pulmonary fibrosis

BACKGROUND

CXCR4, a transmembrane-receptor located on epithelial cells that is activated by CXCL12, may have a role in IPF via migration of CXCR4⁺ fibrocytes to the lung. However, its expression has not been fully characterised in idiopathic pulmonary fibrosis (IPF) or other fibrotic interstitial lung diseases (ILDs). CXCL12 is constitutively expressed in the bone marrow, and levels of CXCR4 regulate control of this signalling pathway. The aim of this study was to profile the expression of CXCR4 in lung tissue and peripheral circulation of patients with IPF and other fibrotic ILDs.

METHODS

Expression of CXCR4 on peripheral blood mononuclear cells (PBMCs) was examined by flow cytometry in 20 patients with IPF and 10 age-matched non-disease control (NDC) donors. Levels of CXCL12 in human plasma were measured by ELISA. Expression of CXCR4, CXCL12, CD45, and e-cadherin was assessed in IPF (n = 10), other fibrotic ILD (n = 8) and NDC (n = 10) lung tissue by multiplex immunohistochemistry (OPAL) and slides were scanned using a Vectra 3 scanner. Cells were quantified with computer automated histological analysis software (HALO).

RESULTS

In blood, the number of CXCR4⁺ cells was lower but the level of CXCL12 was higher in patients with IPF compared to NDC donors. Elevated CXCR4 expression was detected in lung tissue from patients with IPF and other fibrotic ILDs compared to NDC. There were higher levels of CXCR4⁺/e-cadherin⁺/CXCL12⁺ (epithelial) cells in IPF lung tissue compared to NDC, but there was no difference in the numbers of CXCR4⁺/CD45⁺/CXCL12⁺ (myeloid) cells between the two groups.

CONCLUSIONS

This report demonstrates that CXCR4 is overexpressed not only in IPF but also in other ILDs and expression is particularly prominent within both honeycomb cysts and distal airway epithelium. This observation supports the hypothesis that CXCR4 may drive tissue fibrosis through binding its specific ligand CXCL12. Although CXCR4 expressing cells could be either of epithelial or myeloid origin it appears that the former is more prominent in IPF lung tissue. Further characterization of the cells of the honeycomb cyst may lead to a better understanding of the fibrogenic processes in IPF and other end-stage fibrotic ILDs.

The contribution of animal models to understanding the role of the immune system in human idiopathic pulmonary fibrosis

Pulmonary fibrosis occurs in a heterogeneous group of lung disorders and is characterised by an excessive deposition of extracellular matrix proteins within the pulmonary interstitium, leading to impaired gas transfer and a loss of lung function. In the past 10 years, there has been a dramatic increase in our understanding of the immune system and how it contributes to fibrogenic processes within the lung. This review will compare some of the models used to investigate the pathogenesis and treatment of pulmonary fibrosis, in particular those used to study immune cell pathogenicity in idiopathic pulmonary fibrosis, highlighting their advantages and disadvantages in dissecting human disease.

IL-1β dominates the promucin secretory cytokine profile in cystic fibrosis

Cystic fibrosis (CF) lung disease is characterized by early and persistent mucus accumulation and neutrophilic inflammation in the distal airways. Identification of the factors in CF mucopurulent secretions that perpetuate CF mucoinflammation may provide strategies for novel CF pharmacotherapies. We show that IL-1β, with IL-1α, dominated the mucin prosecretory activities of supernatants of airway mucopurulent secretions (SAMS). Like SAMS, IL-1β alone induced MUC5B and MUC5AC protein secretion and mucus hyperconcentration in CF human bronchial epithelial (HBE) cells. Mechanistically, IL-1β induced the sterile α motif-pointed domain containing ETS transcription factor (SPDEF) and downstream endoplasmic reticulum to nucleus signaling 2 (ERN2) to upregulate mucin gene expression. Increased mRNA levels of IL1B, SPDEF, and ERN2 were associated with increased MUC5B and MUC5AC expression in the distal airways of excised CF lungs. Administration of an IL-1 receptor antagonist (IL-1Ra) blocked SAMS-induced expression of mucins and proinflammatory mediators in CF HBE cells. In conclusion, IL-1α and IL-1β are upstream components of a signaling pathway, including IL-1R1 and downstream SPDEF and ERN2, that generate a positive feedback cycle capable of producing persistent mucus hyperconcentration and IL-1α and/or IL-1β-mediated neutrophilic inflammation in the absence of infection in CF airways. Targeting this pathway therapeutically may ameliorate mucus obstruction and inflammation-induced structural damage in young CF children.

Towards the Essence of Progressiveness: Bringing Progressive Fibrosing Interstitial Lung Disease (PF-ILD) to the Next Stage

Although only recently introduced in the ILD community, the concept of progressive fibrosing interstitial lung disease (PF-ILD) has rapidly acquired an important place in the management of non-idiopathic pulmonary fibrosis fibrosing ILD (nonIPF fILD) patients. It confirms a clinical gut feeling that an important subgroup of nonIPF fILD portends a dismal prognosis despite therapeutically addressing the alleged triggering event. Due to several recently published landmark papers showing a treatment benefit with currently available antifibrotic drugs in PF-ILD patients, endorsing a PF-ILD phenotype has vital therapeutic consequences. Importantly, defining progressiveness is based on former progression, which has proven to be a rather moderate predictor of future progression. As fibrosis extent >20% and the presence of honeycombing have superior predictive properties regarding future progression, we advocate immediate initiation of antifibrotic treatment in the presence of these risk factors. In this perspective, we describe the historical context wherein PF-ILD has emerged, determine the currently employed PF-ILD criteria and their inherent limitations and propose new directions to mature its definition. Finally, while ascertaining progression in a nonIPF fILD patient clearly demonstrates the need for (additional) therapy, in the future, therapeutic decisions should be taken after assessing which pathway is ultimately driving the progression. Although not readily available, pathophysiological insight and diagnostic means are emergent to go full steam ahead in this novel direction.

Update on the role of endoplasmic reticulum stress in asthma

Asthma has long attracted extensive attention because of its recurring symptoms of reversible airflow obstruction, airway hyperresponsiveness (AHR) and airway inflammation. Although accumulating evidence has enabled gradual increases in understanding of the pathogenesis of asthma, many questions regarding the mechanisms underlying asthma onset and progression remain unanswered. Recent advances delineating the potential functions of endoplasmic reticulum (ER) stress in meeting the need for an airway hypersensitivity response have revealed critical roles of unfolded protein response (UPR) pathways in asthma. In this review, we highlight the roles of ER stress and UPR activation in the etiology, pathogenesis and treatment of asthma and discuss whether the related mechanisms could be targets for therapeutic strategies.

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.