Intrinsic BMP inhibitor Gremlin regulates alveolar epithelial type II cell proliferation and differentiation

Type 1 alveolar epithelial cells (AT1s) and type 2 alveolar epithelial cells (AT2s) regulate the structural integrity and function of alveoli. AT1s mediate gas exchange, whereas AT2s serve multiple functions, including surfactant secretion and alveolar repair through proliferation and differentiation into AT1s as progenitors. However, mechanisms regulating AT2 proliferation and differentiation remain unclear. Here we demonstrate that Gremlin, an intrinsic inhibitor of bone morphogenetic protein (BMP), induces AT2 proliferation and differentiation. Transient overexpression of Gremlin in rat lungs by adenovirus vector delivery suppressed BMP signaling, induced proliferation of AT2s and the production of Bmp2, which in turn led to the recovery of BMP signaling and induced AT2 differentiation into AT1s. Bleomycin-induced lung injury upregulated Gremlin and showed a similar time course of biomarker expression comparable to the adenovirus model. TGF-β and IL-1β induced Gremlin expression in fibroblasts. Taken together, our findings implicate that Gremlin expression during lung injury leads to precisely timed inhibition of BMP signaling and activates AT2s, leading to alveolar repair.

Vascular-Parenchymal Crosstalk Promotes Lung Fibrosis Through BMPR2 Signaling

RATIONALE

Idiopathic pulmonary fibrosis (IPF) is a fatal lung disease characterized by progressive lung scarring. IPF-related pulmonary vascular remodeling and pulmonary hypertension (PH) result in particularly poor prognosis.

OBJECTIVES

To study the pathogenesis of vascular remodeling in fibrotic lungs and its contribution to progression of fibrosis.

METHODS

We used an experimental model of lung fibrosis associated with PH by transient overexpression of active TGF-β1. Samples from patients with fibrotic lung diseases were analyzed in-depth by immunostaining, gene expression, and gene mutations.

MEASUREMENTS AND MAIN RESULTS

We found a reduction in endothelial cells (ECs) and activation of vascular smooth muscle cells (VSMCs) in fibrotic lungs. Co-culturing fibroblasts with VSMCs or ECs from fibrotic lungs induced fibrotic phenotypes in fibroblasts. IPF fibroblasts induced EC death and activation of VSMCs in co-culture systems. Decreased levels of BMPR2 and its signaling were observed in ECs and VSMCs from fibrotic lungs in both rats and humans. On fibroblasts treated with media from VSMCs, BMPR2 suppression in VSMCs led to fibrogenic effects. Tacrolimus activated BMPR2 signaling and attenuated fibrosis and PH in rodent lungs. Whole exome sequencing revealed rare mutations in PH-related genes, including BMPR2, in IPF patients undergoing transplantation. A unique missense BMPR2 mutation (p.Q721R) was discovered to have dysfunctional effects on BMPR2 signaling.

CONCLUSIONS

Endothelial dysfunction and vascular remodeling in PH secondary to pulmonary fibrosis enhance fibrogenesis through impaired BMPR2 signaling. Tacrolimus may have value as treatment of advanced IPF and concomitant PH. Genetic abnormalities may determine the development of PH in advanced IPF.

Myeloid-specific deletion of activating transcription factor 6 alpha increases CD11b+ macrophage subpopulations and aggravates lung fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive, fibrotic interstitial lung disease of unknown etiology. The accumulation of macrophages is associated with disease pathogenesis. The unfolded protein response (UPR) has been linked to macrophage activation in pulmonary fibrosis. To date, the impact of activating transcription factor 6 alpha (ATF6α), one of the UPR mediators, on the composition and function of pulmonary macrophage subpopulations during lung injury and fibrogenesis is not fully understood. We began by examining the expression of Atf6α in IPF patients' lung single-cell RNA sequencing dataset, archived surgical lung specimens, and CD14⁺ circulating monocytes. To assess the impact of ATF6α on pulmonary macrophage composition and pro-fibrotic function during tissue remodelling, we conducted an in vivo myeloid-specific deletion of Atf6α. Flow cytometric assessments of pulmonary macrophages were carried out in C57BL/6 and myeloid specific ATF6α-deficient mice in the context of bleomycin-induced lung injury. Our results demonstrated that Atf6α mRNA was expressed in pro-fibrotic macrophages found in IPF patient lung and in CD14⁺ circulating monocytes obtained from IPF patient blood. After bleomycin administration, the myeloid-specific deletion of Atf6α altered pulmonary macrophage composition, expanding CD11b⁺ subpopulations with dual polarized CD38⁺ CD206⁺ expressing macrophages. Compositional changes were associated with an aggravation of fibrogenesis including increased myofibroblast and collagen deposition. Further mechanistic ex vivo investigation revealed that ATF6α was required for CHOP induction and the death of bone marrow-derived macrophages. Overall, our findings suggest a detrimental role for the ATF6α-deficient CD11b⁺ macrophages which had altered function during lung injury and fibrosis.

Medical treatments for idiopathic pulmonary fibrosis: a systematic review and network meta-analysis

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a respiratory disorder with a poor prognosis. Our objective is to assess the comparative effectiveness of 22 approved or studied IPF drug treatments.

METHODS

We searched MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials and clinicaltrials.gov from inception to 2 April 2021. We included randomised controlled trials (RCTs) for adult patients with IPF receiving one or more of 22 drug treatments. Pairs of reviewers independently identified randomised trials that compared one or more of the target medical treatments in patients with IPF. We assessed the certainty of evidence using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach for network meta-analysis. We calculated pooled relative risk (RR) ratios and presented direct or network estimates with 95% credibility intervals (95% CI), within the GRADE framework.

RESULTS

We identified 48 (10 326 patients) eligible studies for analysis. Nintedanib [RR 0.69 (0.44 to 1.1), pirfenidone [RR 0.63 (0.37 to 1.09); direct estimate), and sildenafil [RR (0.44 (0.16 to 1.09)] probably reduce mortality (all moderate certainty). Nintedanib (2.92% (1.51 to 4.14)), nintedanib+sildenafil (157 mL (-88.35 to 411.12)), pirfenidone (2.47% (-0.1 to 5)), pamrevlumab (4.3% (0.5 to 8.1)) and pentraxin (2.74% (1 to 4.83)) probably reduce decline of overall forced vital capacity (all moderate certainty). Only sildenafil probably reduces acute exacerbation and hospitalisations (moderate certainty). Corticosteroids+azathioprine+N-acetylcysteine increased risk of serious adverse events versus placebo (high certainty).

CONCLUSION AND RELEVANCE

Future guidelines should consider sildenafil for IPF and further research needs to be done on promising IPF treatments such as pamrevlumab and pentraxin as phase 3 trials are completed.

Neighborhood-level Disadvantage Impacts on Patients with Fibrotic Interstitial Lung Disease

RATIONALE

Fibrotic interstitial lung diseases (fILDs) represent a group of pathologic entities characterized by scarring of the lungs and high morbidity and mortality. Research investigating how socioeconomic and residential factors impact outcomes in patients with fILDs is lacking.

OBJECTIVES

To determine the association between neighborhood-level disadvantage and presentation severity, disease progression, lung transplant, and mortality in patients with fILD from the United States (U.S.) and Canada.

METHODS

Multi-center, international, prospective cohort study of 4729 patients with fILD from one U.S. and eight Canadian ILD registry sites. Neighborhood-level disadvantage was measured by the area deprivation index (ADI) in the U.S. and the Canadian Index of Multiple Deprivation (CIMD) in Canada.

MEASUREMENTS AND MAIN RESULTS

In the U.S., but not Canadian cohort, patients with fILD living in neighborhoods with the greatest disadvantage (top quartile) experience the highest risk of mortality (hazard ratio=1.51, p=0.002) and in subgroups of patients with idiopathic pulmonary fibrosis (IPF), the top quartile of disadvantage experienced the lowest odds of lung transplant (odds ratio=0.46, p=0.04). Greater disadvantage was associated with reduced baseline diffusion capacity for carbon monoxide (DLCO) in both cohorts, but it was not associated with baseline forced vital capacity (FVC) or FVC or DLCO decline in either cohort.

CONCLUSIONS

Patients with fILD who live in areas with greater neighborhood-level disadvantage in the U.S. experience higher mortality, and patients with IPF experience lower odds of lung transplant. These disparities are not seen in Canadian patients, which may indicate differences in access to care between the U.S. and Canada.

Connective-Tissue Growth Factor (CTGF/CCN2) Contributes to TGF-β1-Induced Lung Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a fatal lung disease characterized by progressive and excessive accumulation of myofibroblasts and extracellular matrix in the lung. Connective-tissue growth factor (CTGF) exacerbates pulmonary fibrosis in radiation-induced lung fibrosis, and in this study, we demonstrate upregulation of CTGF in a rat lung fibrosis model induced by an adenovirus vector encoding active TGF-β1 (AdTGF-β1). We show that CTGF is also upregulated in patients with IPF. Expression of CTGF was upregulated in vascular smooth muscle cells cultured from fibrotic lungs on days 7 and 14 as well as endothelial cells sorted from fibrotic lungs on days 14 and 28. These findings suggest contributions of different cells in maintaining the fibrotic phenotype during fibrogenesis. Treatment of fibroblasts with recombinant CTGF along with TGF-β increases pro-fibrotic markers in fibroblasts, confirming the synergistic effect of recombinant CTGF with TGF-β in inducing pulmonary fibrosis. Also, fibrotic extracellular matrix upregulated CTGF expression, compared with normal extracellular matrix, suggesting that not only profibrotic mediators, but also a profibrotic environment contributes to fibrogenesis. We also showed that pamrevlumab, a CTGF inhibitory antibody, partially attenuates fibrosis in the model. These results suggest that pamrevlumab could be an option for treatment of pulmonary fibrosis.

Emerging therapeutic targets for idiopathic pulmonary fibrosis: preclinical progress and therapeutic implications

INTRODUCTION

Idiopathic pulmonary fibrosis (IPF) is a chronic progressive lung disease with high associated morbidity and mortality. The therapeutic landscape has significantly changed in the last 20 years with two drugs currently approved that have demonstrated the ability to slow disease progression. Despite these developments, survival in IPF is limited, so there is a major interest in therapeutic targets which could serve to open up new therapeutic avenues.

AREAS COVERED

We review the most recent information regarding drug targets and therapies currently being investigated in preclinical and early-stage clinical trials.

EXPERT OPINION

The complex pathogenesis of IPF and variability in disease course and response to therapy highlights the importance of a precision approach to therapy. Novel technologies including transcriptomics and the use of serum biomarkers, will become essential tools to guide future drug development and therapeutic decision making particularly as it pertains to combination therapy.

Fibrotic extracellular matrix induces release of extracellular vesicles with pro-fibrotic miRNA from fibrocytes

RATIONALE

Extracellular vesicles (EVs) are small lipid vesicles, and EV-coupled microRNAs (miRNAs) are important modulators of biological processes. Fibrocytes are circulating bone marrow-derived cells that migrate into the injured lungs and contribute to fibrogenesis. The question of whether EV-coupled miRNAs derived from fibrocytes are able to regulate pulmonary fibrosis has not been addressed yet.

METHODS

Pulmonary fibrosis was induced in rats by intratracheal administration of an adenoviral gene vector encoding active transforming growth factor-β1 (TGF-β1) or control vector. Primary fibrocytes and fibroblasts were cultured from rat lungs and were sorted by anti-CD45 magnetic beads. Human circulating fibrocytes and fibrocytes in bronchoalveolar lavage fluid (BALF) were isolated by fibronectin-coated dishes. Fibrocytes were cultured on different stiffness plates or decellularised lung scaffolds. We also determined the effects of extracellular matrix (ECM) and recombinant TGF-β1 on the cellular and EV-coupled miRNA expression of fibrocytes.

RESULTS

The EVs of fibrocytes derived from fibrotic lungs significantly upregulated the expression of col1a1 of fibroblasts. Culturing on rigid plates or fibrotic decellularised lung scaffolds increased miR-21-5 p expression compared with soft plates or normal lung scaffolds. Dissolved ECM collected from fibrotic lungs and recombinant TGF-β1 increased miR-21-5 p expression on fibrocytes, and these effects were attenuated on soft plates. Fibrocytes from BALF collected from fibrotic interstitial pneumonia patients showed higher miR-21-5 p expression than those from other patients.

CONCLUSIONS

Our results indicate that ECM contributes to fibrogenesis through biomechanical and biochemical effects on miRNA expression in fibrocytes.

Minimum important difference of the EQ-5D-5L and EQ-VAS in fibrotic interstitial lung disease

RATIONALE

The European Quality of Life 5-Dimensions 5-Levels questionnaire (EQ-5D-5L) is a multidimensional patient-reported questionnaire that supports calculation of quality-adjusted life-years. Our objectives were to demonstrate feasibility of use and to calculate the minimum important difference (MID) of the EQ-5D-5L and its associated visual analogue scale (EQ-VAS) in patients with fibrotic interstitial lung disease (ILD).

METHODS

Patients who completed the EQ-5D-5L were identified from the prospective multicentre CAnadian REgistry for Pulmonary Fibrosis. Validity, internal consistency and responsiveness of the EQ-5D-5L were assessed, followed by calculation of the MID for the EQ-5D-5L and EQ-VAS. Anchor-based methods used an unadjusted linear regression against pulmonary function tests (PFTs) and dyspnoea and other quality of life questionnaires. Distribution-based method used one-half SD and SE measurement (SEM) calculations.

RESULTS

1816 patients were analysed, including 472 (26%) with idiopathic pulmonary fibrosis. EQ-5D-5L scores were strongly correlated with the dyspnoea and other quality of life questionnaires and weakly associated with PFTs. The estimated MID for EQ-5D-5L ranged from 0.0050 to 0.054 and from 0.078 to 0.095 for the anchor-based and distribution-based methods, respectively. The MID for EQ-VAS ranged from 0.5 to 5.0 and from 8.0 to 9.7 for the anchor-based and distribution-based methods. Findings were similar across ILD subtypes, sex and age.

CONCLUSION

We used a large and diverse cohort of patients with a variety of fibrotic ILD subtypes to suggest validity and MID of both the EQ-5D-5L and EQ-VAS. These findings will assist in designing future clinical trials and supporting cost-effectiveness analyses of potential treatments for patients with fibrotic ILD.

Treatment of idiopathic pulmonary fibrosis with Nintedanib: an update

Introduction: Idiopathic pulmonary fibrosis (IPF) is an incurable, progressive and debilitating disease. Nintedanib is one of two anti-fibrotic therapies available for the treatment of IPF and has been approved since 2014. Together with pirfenidone and antacid medications it has received a conditional recommendation for the treatment for IPF by international clinical practice guidelines.Areas covered: The authors review the mechanisms of action, pharmacological profile and update scientific data and our opinions on efficacy, safety profile and tolerability of nintedanib.Expert opinion: Nintedanib significantly slows disease progression in IPF patients with tolerable and manageable side effects. Its potential future role in the treatment of progressive fibrosing interstitial lung diseases other than IPF is challenging.

The FMS-like tyrosine kinase-3 ligand/lung dendritic cell axis contributes to regulation of pulmonary fibrosis

RATIONALE

Dendritic cells (DC) accumulate in the lungs of patients with idiopathic lung fibrosis, but their pathogenetic relevance is poorly defined.

OBJECTIVES

To assess the role of the FMS-like tyrosine kinase-3 ligand (Flt3L)-lung dendritic cell axis in lung fibrosis.

MEASUREMENTS AND MAIN RESULTS

We demonstrate in a model of adenoviral gene transfer of active TGF-β1 that established lung fibrosis was accompanied by elevated serum Flt3L levels and subsequent accumulation of CD11b^pos DC in the lungs of mice. Patients with idiopathic pulmonary fibrosis also demonstrated increased levels of Flt3L protein in serum and lung tissue and accumulation of lung DC in explant subpleural lung tissue specimen. Mice lacking Flt3L showed significantly reduced lung DC along with worsened lung fibrosis and reduced lung function relative to wild-type (WT) mice, which could be inhibited by administration of recombinant Flt3L. Moreover, therapeutic Flt3L increased numbers of CD11b^pos DC and improved lung fibrosis in WT mice exposed to AdTGF-β1. In this line, RNA-sequencing analysis of CD11b^pos DC revealed significantly enriched differentially expressed genes within extracellular matrix degrading enzyme and matrix metalloprotease gene clusters. In contrast, the CD103^pos DC subset did not appear to be involved in pulmonary fibrogenesis.

CONCLUSIONS

We show that Flt3L protein and numbers of lung DC are upregulated in mice and humans during pulmonary fibrogenesis, and increased mobilisation of lung CD11b^pos DC limits the severity of lung fibrosis in mice. The current study helps to inform the development of DC-based immunotherapy as a novel intervention against lung fibrosis in humans.

GRP78 and CHOP modulate macrophage apoptosis and the development of bleomycin-induced pulmonary fibrosis

Endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) have been associated with fibrotic lung disease, although exactly how they modulate this process remains unclear. Here we investigated the role of GRP78, the main UPR regulator, in an experimental model of lung injury and fibrosis. Grp78(+/-) , Chop(-/-) and wild type C57BL6/J mice were exposed to bleomycin by oropharyngeal intubation and lungs were examined at days 7 and 21. We demonstrate here that Grp78(+/-) mice were strongly protected from bleomycin-induced fibrosis, as shown by immunohistochemical analysis, collagen content and lung function measurements. In the inflammatory phase of this model, a reduced number of lung macrophages associated with an increased number of TUNEL-positive cells were observed in Grp78(+/-) mice. Dual immunohistochemical and in situ hybridization experiments showed that the macrophage population from the protected Grp78(+/-) mice was also strongly positive for cleaved caspase-3 and Chop mRNA, respectively. In contrast, the administration of bleomycin to Chop(-/-) mice resulted in increased quasi-static elastance and extracellular matrix deposition associated with an increased number of parenchymal arginase-1-positive macrophages that were negative for cleaved caspase-3. The data presented indicate that the UPR is activated in fibrotic lung tissue and strongly localized to macrophages. GRP78- and CHOP-mediated macrophage apoptosis was found to protect against bleomycin-induced fibrosis. Overall, we demonstrate here that the fibrotic response to bleomycin is dependent on GRP78-mediated events and provides evidence that macrophage polarization and apoptosis may play a role in this process. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Update on models of pulmonary fibrosis therapy for preclinical drug research

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a disease with high morbidity and mortality for which current medications are not effective. Therefore, identification of potential therapies is of paramount importance. The preclinical evaluation of novel compounds in animal models represents a critical step in drug development.

OBJECTIVE

To describe features and limitations of common animal models of pulmonary fibrosis and discuss relevant preclinical and clinical data on novel potential IPF therapies.

METHODS

Review of the existing literature on such models with a special focus on the bleomycin model and its usefulness for the IPF preclinical drug testing.

CONCLUSIONS

The model of bleomycin-induced pulmonary fibrosis has the advantages of being well established, reproducible and both time- and cost-efficient. However, it has major limitations as it only mimics some features of human IPF. Most importantly, it is initiated by acute lung injury and is at least partially reversible, which is strikingly different from IPF. The failure in establishing effective IPF therapies despite strong efforts in the last decade is partly attributable to our uncritical trust in the models of lung fibrosis and the false belief that they truly reflect what is going on in human disease.