When things go wrong: exploring possible mechanisms driving the progressive fibrosis phenotype in interstitial lung diseases

Outcomes and predictors of progression in progressive pulmonary fibrosis

BACKGROUND

Progressive pulmonary fibrosis (PPF) is a general term for a class of interstitial lung diseases (ILDs) characterized by a progressive fibrosing (PF) phenotype. Patients with PPF have decreased lung function, exercise ability, and quality of life. The purpose of this study was to investigate the clinical characteristics, potential associated factors for disease progression, and survival outcomes of patients in the PPF population.

METHODS

This study retrospectively reviewed the data of patients diagnosed with ILD between January 2011 and December 2022 at The First Affiliated Hospital of Ningbo University. A PF phenotype was defined based on the criteria that were used in the PPF clinical practice guidelines, which led to the identification of 92 patients with a PF phenotype among the 177 patients with fibrotic ILD. Baseline clinical information and laboratory parameters were collected and analysed in our cohort.

RESULTS

Patients in the PPF group had higher tumour marker levels and lower pulmonary function test results at baseline than did those in the non-PPF group. According to the multivariate logistic regression analysis, age >65 years (OR 2.71, 95% CI 1.26-5.89; p = 0.011), LDH >245 U/L (OR 3.07, 95% CI 1.39-6.78; p = 0.006), CA-153 > 35 U/mL (OR 3.16, 95% CI 1.25-7.97; p = 0.015), FVC <60% predicted (OR 4.82, 95% CI 1.60-14.51; p = 0.005), DLCO <50% predicted (OR 3.21, 95% CI 1.43-7.21; p = 0.005), and the UIP-like pattern on chest HRCT (OR 3.65, 95% CI 1.33-10.07; p = 0.012) were potentially associated with the progression of fibrotic interstitial lung diseases (f-ILDs) to PPF. Furthermore, the PPF group had a poorer survival rate than the non-PPF group (p = 0.0045). According to the multivariate Cox regression analysis, an SPAP ≥ 37 mmHg (HR 2.33, 95% CI 1.09-5.00; p = 0.030) and acute exacerbation (HR 2.88, 95% CI 1.26-6.59; p = 0.012) were identified as significant prognostic factors for mortality in patients with PPFs.

CONCLUSIONS

Patients who were older, had high CA-153 and LDH levels, had poor pulmonary function test results, or had a UIP-like pattern on chest HRCT were more likely to have indications for the progression of f-ILD to PPF. Increased SPAP and AE are independent risk factors for the prognosis of PPF patients, so additional attention should be given to such patients.

Pulmonary fibrosis: pathogenesis and therapeutic strategies

Pulmonary fibrosis (PF) is a chronic and progressive lung disease characterized by extensive alterations of cellular fate and function and excessive accumulation of extracellular matrix, leading to lung tissue scarring and impaired respiratory function. Although our understanding of its pathogenesis has increased, effective treatments remain scarce, and fibrotic progression is a major cause of mortality. Recent research has identified various etiological factors, including genetic predispositions, environmental exposures, and lifestyle factors, which contribute to the onset and progression of PF. Nonetheless, the precise mechanisms by which these factors interact to drive fibrosis are not yet fully elucidated. This review thoroughly examines the diverse etiological factors, cellular and molecular mechanisms, and key signaling pathways involved in PF, such as TGF-β, WNT/β-catenin, and PI3K/Akt/mTOR. It also discusses current therapeutic strategies, including antifibrotic agents like pirfenidone and nintedanib, and explores emerging treatments targeting fibrosis and cellular senescence. Emphasizing the need for omni-target approaches to overcome the limitations of current therapies, this review integrates recent findings to enhance our understanding of PF and contribute to the development of more effective prevention and management strategies, ultimately improving patient outcomes.

Lung imaging patterns in connective tissue disease-associated interstitial lung disease impact prognosis and immunosuppression response

OBJECTIVES

Interstitial lung disease (ILD) in CTDs has highly variable morphology. We aimed to identify imaging features and their impact on ILD progression, mortality, and immunosuppression response.

METHODS

Patients with CTD-ILD had high-resolution chest CT (HRCT) reviewed by expert radiologists blinded to clinical data for overall imaging pattern [usual interstitial pneumonia (UIP); non-specific interstitial pneumonia (NSIP); organizing pneumonia (OP); fibrotic hypersensitivity pneumonitis (fHP); and other]. Transplant-free survival and change in percent-predicted forced vital capacity (FVC) were compared using Cox and linear mixed-effects models adjusted for age, sex, smoking, and baseline FVC. FVC decline after immunosuppression was compared with pre-treatment.

RESULTS

Among 645 CTD-ILD patients, the most frequent CTDs were SSc (n = 215), RA (n = 127), and inflammatory myopathies (n = 100). NSIP was the most common pattern (54%), followed by UIP (20%), fHP (9%), and OP (5%). Compared with the case for patients with UIP, FVC decline was slower in patients with NSIP (by 1.1%/year, 95% CI 0.2, 1.9) or OP (by 3.5%/year, 95% CI 2.0, 4.9), and mortality was lower in patients with NSIP [hazard ratio (HR) 0.65, 95% CI 0.45, 0.93] or OP (HR 0.18, 95% CI 0.05, 0.57), but higher in fHP (HR 1.58, 95% CI 1.01, 2.40). The extent of fibrosis also predicted FVC decline and mortality. After immunosuppression, FVC decline was slower compared with pre-treatment in NSIP (by 2.1%/year, 95% CI 1.4, 2.8), with no change for UIP or fHP.

CONCLUSION

Multiple radiologic patterns are possible in CTD-ILD, including a fHP pattern. NSIP and OP were associated with better outcomes and response to immunosuppression, while fHP had worse survival compared with UIP.

Lung Fibrosis Is Linked to Increased Endothelial Cell Activation and Dysfunctional Vascular Barrier Integrity

Pulmonary fibrosis (PF) can be a fatal disease characterized by progressive lung scarring. It is still poorly understood how the pulmonary endothelium is involved in the disease pathogenesis. Differences of the pulmonary vasculature between patients and donors were analyzed using transmission electron microscopy, immunohistochemistry, and single-cell RNA sequencing. Vascular barrier resistance, endothelial-immune cell adhesion, and sensitivity to an inflammatory milieu were studied in vitro. Integrity and activation markers were measured by ELISA in human plasma. Transmission electron microscopy demonstrated abnormally swollen endothelial cells (ECs) in fibrotic lungs compared with donors. A more intense CD31 and von Willebrand Factor (vWF) and patchy vascular endothelial (VE)-Cadherin staining in fibrotic lungs supported the presence of a dysregulated endothelium. Integrity markers CD31, VE-Cadherin, Thrombomodulin, and VEGFR-2 (vascular endothelial growth factor receptor-2) and activation marker vWF gene expression was increased in different endothelial subpopulations (e.g., arterial, venous, general capillary, aerocytes) in PF. This was associated with a heightened sensitivity of fibrotic ECs to TNF-α or IFN-γ and elevated immune cell adhesion. The barrier strength was overall reduced in ECs from fibrotic lungs. vWF and IL-8 were increased in the plasma of patients, whereas VE-Cadherin, Thrombomodulin, and VEGFR-2 were decreased. VE-Cadherin staining was also patchy in biopsy tissue and was decreased in plasma samples of patients with PF 6 months after the initial diagnosis. Our data demonstrate highly abnormal ECs in PF. The vascular compartment is characterized by hyperactivation and increased immune cell adhesion, as well as dysfunctional endothelial barrier function. Reestablishing EC homeostasis and function might represent a new therapeutic option for fibrotic lung diseases.

Emerging role of BMPs/BMPR2 signaling pathway in treatment for pulmonary fibrosis

Pulmonary fibrosis is a fatal and chronic lung disease that is characterized by accumulation of thickened scar in the lungs and impairment of gas exchange. The cases with unknown etiology are referred as idiopathic pulmonary fibrosis (IPF). There are currently no effective therapeutics to cure the disease; thus, the investigation of the pathogenesis of IPF is of great importance. Recent studies on bone morphogenic proteins (BMPs) and their receptors have indicated that reduction of BMP signaling in lungs may play a significant role in the development of lung fibrosis. BMPs are members of TGF-β superfamily, and they have been shown to play an anti-fibrotic role in combating TGF-β-mediated pathways. The impact of BMP receptors, in particular BMPR2, on pulmonary fibrosis is growing attraction to researchers. Previous studies on BMPR2 have often focused on pulmonary arterial hypertension (PAH). Given the strong clinical association between PAH and lung fibrosis, understanding BMPs/BMPR2-mediated signaling pathway is important for development of therapeutic strategies to treat IPF. In this review, we comprehensively review recent studies regarding the biological functions of BMPs and their receptors in lungs, especially focusing on their roles in the pathogenesis of pulmonary fibrosis and fibrosis resolution.

Evaluation of progressive pulmonary fibrosis in non-idiopathic pulmonary fibrosis-interstitial lung diseases: a cross-sectional study

BACKGROUND

Progressive pulmonary fibrosis is the symptomatic, physiological, and radiological progression of interstitial lung diseases. The aim of this study was to examine the relationship between progressive pulmonary fibrosis and demographic characteristics and to evaluate the effect on clinical outcomes and mortality.

METHODS

This cross-sectional study included 221 patients diagnosed with non-idiopathic pulmonary fibrosis interstitial lung diseases who were followed in the last 5 years. Patient symptoms, clinical, radiological, and demographic data were examined. Risk factors for the development of progressive pulmonary fibrosis and the relationship with clinical outcomes and mortality were examined.

RESULTS

Of the patients, 33.0% (n = 73) had fibrotic idiopathic nonspecific interstitial pneumonia (iNSIP), 35.7% (n = 79) had fibrotic hypersensitivity pneumonia (HP), 18.1% (n = 40) had fibrotic connective tissue disease (CTD) interstitial lung diseases (ILD), and 13.1% (n = 29) had postinfectious fibrotic ILD. The progressive pulmonary fibrosis development rates of the subtypes were 46.5% iNSIP (n = 34), 86.0% fibrotic HP (n = 68), 42.5% fibrotic CTD-ILD (n = 17), and 20.7% postinfectious ILD (n = 6). The presence of progressive pulmonary fibrosis was associated with the development of respiratory failure and mortality (odds ratio [OR]: 2.70, 95% CI: 1.04-7.05 and OR: 2.13, 95% CI: 1.23-3.69). Progressive pulmonary fibrosis development was higher in hypersensitivity pneumonia patients with farmer's lung (OR: 5.06, 95% CI: 1.02-25.18).

CONCLUSION

Progressive pulmonary fibrosis was more prevalent in older patients. Farming was an important risk factor in the development of hypersensitivity pneumonia-progressive pulmonary fibrosis. Respiratory failure and mortality were higher in those who developed progressive pulmonary fibrosis.

SFTPB in serum extracellular vesicles as a biomarker of progressive pulmonary fibrosis

Progressive pulmonary fibrosis (PPF), defined as the worsening of various interstitial lung diseases (ILDs), currently lacks useful biomarkers. To identify novel biomarkers for early detection of patients at risk of PPF, we performed a proteomic analysis of serum extracellular vesicles (EVs). Notably, the identified candidate biomarkers were enriched for lung-derived proteins participating in fibrosis-related pathways. Among them, pulmonary surfactant-associated protein B (SFTPB) in serum EVs could predict ILD progression better than the known biomarkers, serum KL-6 and SP-D, and it was identified as an independent prognostic factor from ILD-gender-age-physiology index. Subsequently, the utility of SFTPB for predicting ILD progression was evaluated further in 2 cohorts using serum EVs and serum, respectively, suggesting that SFTPB in serum EVs but not in serum was helpful. Among SFTPB forms, pro-SFTPB levels were increased in both serum EVs and lungs of patients with PPF compared with those of the control. Consistently, in a mouse model, the levels of pro-SFTPB, primarily originating from alveolar epithelial type 2 cells, were increased similarly in serum EVs and lungs, reflecting pro-fibrotic changes in the lungs, as supported by single-cell RNA sequencing. SFTPB, especially its pro-form, in serum EVs could serve as a biomarker for predicting ILD progression.

Interstitial Lung Disease Associated with Systemic Sclerosis

Systemic sclerosis (SSc) is a rare autoimmune disease characterized by a tripod combining vasculopathy, fibrosis, and immune-mediated inflammatory processes. The prevalence of interstitial lung disease (ILD) in SSc varies according to the methods used to detect it, ranging from 25 to 95%. The fibrotic and vascular pulmonary manifestations of SSc, particularly ILD, are the main causes of morbidity and mortality, contributing to 35% of deaths. Although early trials were conducted with cyclophosphamide, more recent randomized controlled trials have been performed to assess the efficacy and tolerability of several medications, mostly mycophenolate, rituximab, tocilizumab, and nintedanib. Although many uncertainties remain, expert consensus is emerging to optimize the therapeutic management and to provide clinicians with evidence-based clinical practice guidelines for patients with SSc-ILD. This article provides an overview, in the light of the latest advances, of the available evidence for the diagnosis and management of SSc-ILD.

Progressive Pulmonary Fibrosis: Where Are We Now?

Interstitial lung diseases (ILDs) are a diverse collection of lung disorders sharing similar features, such as inflammation and fibrosis. The diagnosis and management of ILD require a multidisciplinary approach using clinical, radiological, and pathological evaluation. Progressive pulmonary fibrosis (PPF) is a distinct form of progressive and fibrotic disease, occurring in ILD cases other than in idiopathic pulmonary fibrosis (IPF). It is defined based on clinical symptoms, lung function, and chest imaging, regardless of the underlying condition. The progression to PPF must be monitored through a combination of pulmonary function tests (forced vital capacity [FVC] and diffusing capacity of the lung for carbon monoxide), an assessment of symptoms, and computed tomography scans, with regular follow-up. Although the precise mechanisms of PPF remain unclear, there is evidence of shared pathogenetic mechanisms with IPF, contributing to similar disease behavior and worse prognosis compared to non-PPF ILD. Pharmacological treatment of PPF includes immunomodulatory agents to reduce inflammation and the use of antifibrotics to target progressive fibrosis. Nintedanib, a known antifibrotic agent, was found to be effective in slowing IPF progression and reducing the annual rate of decline in FVC among patients with PPF compared to placebos. Nonpharmacological treatment, including pulmonary rehabilitation, supplemental oxygen therapy, and vaccination, also play important roles in the management of PPF, leading to comprehensive care for patients with ILD. Although there is currently no cure for PPF, there are treatments that can help slow the progression of the disease and improve quality of life.

Prediction of progressive fibrosing interstitial lung disease in patients with systemic sclerosis: insight from the CRDC cohort study

BACKGROUND

This study aims to establish a reliable prediction model of progressive fibrosing interstitial lung disease (PF-ILD) in patients with systemic sclerosis (SSc)-ILD, to achieve early risk stratification and to help better in preventing disease progression.

METHODS

304 SSc-ILD patients with no less than three pulmonary function tests within 6-24 months were included. We collected data at baseline and compared differences between SSc patients with and without PF-ILD. Least absolute shrinkage and selection operator regularisation regression and multivariable Cox regression were used to construct the prediction model, which were presented as nomogram and forest plot.

RESULTS

Among the 304 patients with SSc-ILD included, 92.1% were women, with a baseline average age of 46.7 years. Based on the 28 variables preselected by comparison between SSc patients without PF-ILD group (n=150) and patients with SSc PF-ILD group (n=154), a 9-variable prediction model was constructed, including age≥50 years (HR 1.8221, p=0.001), hyperlipidemia (HR 4.0516, p<0.001), smoking history (HR 3.8130, p<0.001), diffused cutaneous SSc subtype (HR 1.9753, p<0.001), arthritis (HR 2.0008, p<0.001), shortness of breath (HR 2.0487, p=0.012), decreased serum immunoglobulin A level (HR 2.3900, p=0.002), positive anti-Scl-70 antibody (HR 1.9573, p=0.016) and usage of cyclophosphamide/mycophenolate mofetil (HR 0.4267, p<0.001). The concordance index after enhanced bootstrap resampling adjustment was 0.874, while the optimism-corrected Brier Score was 0.144 in internal validation.

CONCLUSION

This study developed the first prediction model for PF-ILD in patients with SSc-ILD, and internal validation showed favourable accuracy and stability of the model.

Targeting Progression in Pulmonary Fibrosis: An Overview of Underlying Mechanisms, Molecular Biomarkers, and Therapeutic Intervention

Interstitial lung diseases comprise a heterogenous range of diffuse lung disorders, potentially resulting in pulmonary fibrosis. While idiopathic pulmonary fibrosis has been recognized as the paradigm of a progressive fibrosing interstitial lung disease, other conditions with a progressive fibrosing phenotype characterized by a significant deterioration of the lung function may lead to a burden of significant symptoms, a reduced quality of life, and increased mortality, despite treatment. There is now evidence indicating that some common underlying biological mechanisms can be shared among different chronic fibrosing disorders; therefore, different biomarkers for disease-activity monitoring and prognostic assessment are under evaluation. Thus, understanding the common pathways that induce the progression of pulmonary fibrosis, comprehending the diversity of these diseases, and identifying new molecular markers and potential therapeutic targets remain highly crucial assignments. The purpose of this review is to examine the main pathological mechanisms regulating the progression of fibrosis in interstitial lung diseases and to provide an overview of potential biomarker and therapeutic options for patients with progressive pulmonary fibrosis.

Key learnings from the INBUILD trial in patients with progressive pulmonary fibrosis

In a patient with interstitial lung disease (ILD) of known or unknown etiology other than idiopathic pulmonary fibrosis (IPF), progressive pulmonary fibrosis (PPF) is defined by worsening lung fibrosis on high-resolution computed tomography (HRCT), decline in lung function, and/or deterioration in symptoms. The INBUILD trial involved 663 patients with PPF who were randomized to receive nintedanib or placebo. The median exposure to trial medication was approximately 19 months. The INBUILD trial provided valuable learnings about the course of PPF and the efficacy and safety of nintedanib. The relative effect of nintedanib on reducing the rate of forced vital capacity decline was consistent across subgroups based on ILD diagnosis, HRCT pattern, and disease severity at baseline, and between patients who were and were not taking glucocorticoids or disease-modifying anti-rheumatic drugs and/or glucocorticoids at baseline. The adverse events most frequently associated with nintedanib were gastrointestinal, particularly diarrhea, but nintedanib was discontinued in only a minority of cases. The results of the INBUILD trial highlight the importance of prompt detection and treatment of PPF and the utility of nintedanib as a treatment option.

Decline in forced vital capacity as a surrogate for mortality in patients with pulmonary fibrosis

BACKGROUND AND OBJECTIVE

Surrogate endpoints enable determination of meaningful treatment effects more efficiently than applying the endpoint of ultimate interest. We used data from trials of nintedanib in subjects with pulmonary fibrosis to assess decline in forced vital capacity (FVC) as a surrogate for mortality.

METHODS

Data from the nintedanib and placebo groups of trials in subjects with idiopathic pulmonary fibrosis, other forms of progressive pulmonary fibrosis, and pulmonary fibrosis due to systemic sclerosis (NCT00514683, NCT01335464, NCT01335477, NCT01979952, NCT02999178, NCT02597933) were pooled. Using joint models for longitudinal and time-to-event data, we assessed the association between decline in FVC % predicted and time to death over 52 weeks. The rate of change in FVC % predicted and the current value of FVC % predicted were modelled longitudinally and estimates applied as predictors in time-to-event models.

RESULTS

Among 2583 subjects with pulmonary fibrosis, both a greater rate of decline in FVC % predicted and a lower current value of FVC % predicted were associated with an increased risk of death over 52 weeks (HR 1.79 [95% CI: 1.57, 2.03] and HR 1.24 [1.17, 1.32] per 5-percentage point decrease, respectively). Associations between the rate of change in FVC % predicted and the risk of death were consistent between patients with IPF and other ILDs.

CONCLUSION

Data from clinical trials in subjects with pulmonary fibrosis of diverse aetiology demonstrate a strong association between decline in FVC % predicted and mortality over 52 weeks, supporting FVC decline as a surrogate for mortality in these patients.

Anti-fibrotic effects of nintedanib on lung fibroblasts derived from patients with Progressive Fibrosing Interstitial Lung Diseases (PF-ILDs)

The tyrosine kinase inhibitor nintedanib has been recently approved for the treatment of Interstitial Lung Diseases (ILDs) that manifest a progressive fibrosis phenotype other than Idiopathic pulmonary Fibrosis (IPF). Nintedanib reduces the development of lung fibrosis in various animal models resembling features of PF-ILD and in vitro, it inhibits the fibrosing phenotype of human lung fibroblasts (HLFs) isolated from patients with IPF. To get insight on the cellular and molecular mechanisms that drive the clinical efficiency of nintedanib in patients with non-IPF PF-ILD, we investigated its effects on the fibrosing functions of HLFs derived from patients with PF-hypersensitivity pneumonitis (PF-HP, n = 7), PF-sarcoidosis (n = 5) and pleuroparenchymal fibroelastosis (PPFE, n = 4). HLFs were treated with nintedanib (10 nM-1 μM) and then stimulated with PDGF-BB (25-50 ng/ml) or TGF-β1 (1 ng/ml) for 24-72 h to assess proliferation and migration or differentiation. At nanomolar concentrations, nintedanib reduced the levels of PDGF receptor and ERK1/2 phosphorylation, the proliferation and the migration of PF-HP, PF-sarcoidosis and PPFE HLFs stimulated with PDGF-BB. Moreover, nintedanib also attenuates the myofibroblastic differentiation driven by TGF-β1 but only when it is used at 1 μM. The drug reduced the phosphorylation of SMAD2/3 and decreased the induction of collagen, fibronectin and α-smooth muscle actin expression induced by TGF-β1. In conclusion, our results demonstrate that nintedanib counteracts fundamental fibrosing functions of lung fibroblasts derived from patients with PF-HP, PF-sarcoidosis and PPFE, at concentrations previously reported to inhibit control and IPF HLFs. Such effects may contribute to its clinical benefit in patients suffering from these irreversible ILDs.

Iron accumulation drives fibrosis, senescence and the senescence-associated secretory phenotype

Fibrogenesis is part of a normal protective response to tissue injury that can become irreversible and progressive, leading to fatal diseases. Senescent cells are a main driver of fibrotic diseases through their secretome, known as senescence-associated secretory phenotype (SASP). Here, we report that cellular senescence, and multiple types of fibrotic diseases in mice and humans are characterized by the accumulation of iron. We show that vascular and hemolytic injuries are efficient in triggering iron accumulation, which in turn can cause senescence and promote fibrosis. Notably, we find that senescent cells persistently accumulate iron, even when the surge of extracellular iron has subdued. Indeed, under normal conditions of extracellular iron, cells exposed to different types of senescence-inducing insults accumulate abundant ferritin-bound iron, mostly within lysosomes, and present high levels of labile iron, which fuels the generation of reactive oxygen species and the SASP. Finally, we demonstrate that detection of iron by magnetic resonance imaging might allow non-invasive assessment of fibrotic burden in the kidneys of mice and in patients with renal fibrosis. Our findings suggest that iron accumulation plays a central role in senescence and fibrosis, even when the initiating events may be independent of iron, and identify iron metabolism as a potential therapeutic target for senescence-associated diseases.

Effect of nintedanib in patients with progressive pulmonary fibrosis associated with rheumatoid arthritis: data from the INBUILD trial

OBJECTIVES

Some patients with rheumatoid arthritis develop interstitial lung disease (RA-ILD) that develops into progressive pulmonary fibrosis. We assessed the efficacy and safety of nintedanib versus placebo in patients with progressive RA-ILD in the INBUILD trial.

METHODS

The INBUILD trial enrolled patients with fibrosing ILD (reticular abnormality with traction bronchiectasis, with or without honeycombing) on high-resolution computed tomography of >10% extent. Patients had shown progression of pulmonary fibrosis within the prior 24 months, despite management in clinical practice. Subjects were randomised to receive nintedanib or placebo.

RESULTS

In the subgroup of 89 patients with RA-ILD, the rate of decline in FVC over 52 weeks was -82.6 mL/year in the nintedanib group versus -199.3 mL/year in the placebo group (difference 116.7 mL/year [95% CI 7.4, 226.1]; nominal p = 0.037). The most frequent adverse event was diarrhoea, which was reported in 61.9% and 27.7% of patients in the nintedanib and placebo groups, respectively, over the whole trial (median exposure: 17.4 months). Adverse events led to permanent discontinuation of trial drug in 23.8% and 17.0% of subjects in the nintedanib and placebo groups, respectively.

CONCLUSIONS

In the INBUILD trial, nintedanib slowed the decline in FVC in patients with progressive fibrosing RA-ILD, with adverse events that were largely manageable. The efficacy and safety of nintedanib in these patients were consistent with the overall trial population. A graphical abstract is available at: https://www.globalmedcomms.com/respiratory/INBUILD_RA-ILD . Key Points • In patients with rheumatoid arthritis and progressive pulmonary fibrosis, nintedanib reduced the rate of decline in forced vital capacity (mL/year) over 52 weeks by 59% compared with placebo. • The adverse event profile of nintedanib was consistent with that previously observed in patients with pulmonary fibrosis, characterised mainly by diarrhoea. • The effect of nintedanib on slowing decline in forced vital capacity, and its safety profile, appeared to be consistent between patients who were taking DMARDs and/or glucocorticoids at baseline and the overall population of patients with rheumatoid arthritis and progressive pulmonary fibrosis.

Idiopathic pulmonary fibrosis: current diagnosis and treatment

Idiopathic pulmonary fibrosis (IPF) is a devastating chronic lung disease without a clear recognizable cause. IPF has been at the forefront of new diagnostic algorithms and treatment developments that led to a shift in patients' care in the past decade, indeed influencing the management of fibrotic interstitial lung diseases other than IPF itself. Clinical presentation, pathophysiology, and diagnostic criteria are briefly addressed in this review article. Additionally, evidence regarding the use of antifibrotics beyond the settings of clinical trials, impact of comorbidities, and therapeutic approaches other than pharmacological treatments are discussed in further detail.

The endothelium in lung fibrosis: a core signaling hub in disease pathogenesis?

Pulmonary fibrosis (PF) is a progressive chronic lung disease characterized by excessive deposition of extracellular matrix (ECM) and structural destruction, associated with a severe 5-year mortality rate. The onset of the disease is thought to be triggered by chronic damage to the alveolar epithelium. Since the pulmonary endothelium is an important component of the alveolar-capillary niche, it is also affected by the initial injury. In addition to ensuring proper gas exchange, the endothelium has critical functional properties, including regulation of vascular tone, inflammatory responses, coagulation, and maintenance of vascular homeostasis and integrity. Recent single-cell analyses have shown that shifts in endothelial cell (EC) subtypes occur in PF. Furthermore, the increased vascular remodeling associated with PF leads to deteriorated outcomes for patients, underscoring the importance of the vascular bed in PF. To date, the causes and consequences of endothelial and vascular involvement in lung fibrosis are poorly understood. Therefore, it is of great importance to investigate the involvement of EC and the vascular system in the pathogenesis of the disease. In this review, we will outline the current knowledge on the role of the pulmonary vasculature in PF, in terms of abnormal cellular interactions, hyperinflammation, vascular barrier disorders, and an altered basement membrane composition. Finally, we will summarize recent advances in extensive therapeutic research and discuss the significant value of novel therapies targeting the endothelium.

Prediction of progressive pulmonary fibrosis in patients with anti-synthetase syndrome-associated interstitial lung disease

OBJECTIVE

Interstitial lung disease (ILD) is a common extramuscular manifestation of the anti-synthetase syndrome (ASS). Patients with ASS-ILD are at risk in developing a progressive fibrosing phenotype despite appropriate treatments. This study investigated the risk factors and the predictive value of multiple risk factors for progressive pulmonary fibrosis (PPF) in patients with ASS-ILD.

METHODS

Ninety patients with a diagnosis of ASS and evidence of ILD on high-resolution computed tomography (HRCT) were recruited. Among them, 72 participants completed follow-up for more than 12 months. These patients were further divided into a PPF-ASS group (n = 18) and a non-PPF-ASS group (n = 54). Logistic regression analysis was performed to investigate the risk factors for PPF. The predictive value of the combined risk factors for predicting PPF were analyzed by a ROC curve.

RESULTS

The PPF-ASS group had a higher rate of positive non-Jo-1 antibodies, a significantly higher neutrophil-to-lymphocyte ratio (NLR) and serum lactate dehydrogenase (LDH), and a significantly lower PaO2/FiO2 ratio and diffusing capacity for carbon monoxide (DLCO%pred) than the non-PPF-ASS group. In addition, elevated serum Krebs von den Lungen-6 (KL-6) level and reticular opacities were significantly more common, and corticosteroid monotherapy at onset was administered more frequently in the PPF-ASS group. The median duration of follow-up was 37.4 months, survival was poorer in the PPF-ASS group, and the overall survival was 88.9%. Multivariate regression analysis further revealed that positive non-Jo-1 antibodies, NLR, and KL-6 were independent risk factors for PPF. These combined indexes had good accuracy (area under the curve = 0.874) in predicting PPF in patients with ASS-ILD.

CONCLUSION

Positive non-Jo-1 antibodies, NLR, and serum KL-6 are independent risk factors for PPF in patients with ASS-ILD. Monitoring these markers can potentially predict PPF in this group of patients. Key Points • Positive non-Jo-1 antibodies, NLR, and serum KL-6 are independent risk factors associated with PPF in patients with ASS-ILD. • Monitoring non-Jo-1 antibodies, NLR, and serum KL-6 can potentially predict PPF in patients with ASS-ILD.

Genetics in Idiopathic Pulmonary Fibrosis: A Clinical Perspective

BACKGROUND

Unraveling the genetic background in a significant proportion of patients with both sporadic and familial IPF provided new insights into the pathogenic pathways of pulmonary fibrosis.

AIM

The aim of the present study is to overview the clinical significance of genetics in IPF.

PERSPECTIVE

It is fascinating to realize the so-far underestimated but dynamically increasing impact that genetics has on aspects related to the pathophysiology, accurate and early diagnosis, and treatment and prevention of this devastating disease. Genetics in IPF have contributed as no other in unchaining the disease from the dogma of a "a sporadic entity of the elderly, limited to the lungs" and allowed all scientists, but mostly clinicians, all over the world to consider its many aspects and "faces" in all age groups, including its co-existence with several extra pulmonary conditions from cutaneous albinism to bone-marrow and liver failure.

CONCLUSION

By providing additional evidence for unsuspected characteristics such as immunodeficiency, impaired mucus, and surfactant and telomere maintenance that very often co-exist through the interaction of common and rare genetic variants in the same patient, genetics have created a generous and pluralistic yet unifying platform that could lead to the understanding of the injurious and pro-fibrotic effects of many seemingly unrelated extrinsic and intrinsic offending factors. The same platform constantly instructs us about our limitations as well as about the heritability, the knowledge and the wisdom that is still missing.

Hypersensitivity Pneumonitis: A Pictorial Review Based on the New ATS/JRS/ALAT Clinical Practice Guideline for Radiologists and Pulmonologists

Hypersensitivity pneumonitis (HP) is a complicated and heterogeneous interstitial lung disease (ILD) caused by an excessive immune response to an inhaled antigen in susceptible individuals. Accurate diagnosis of HP is difficult and necessitates a detailed exposure history, as well as a multidisciplinary discussion of clinical, histopathologic, and radiologic data. We provide a pictorial review based on the latest American Thoracic Society (ATS)/Japanese Respiratory Society (JRS)/Asociación Latinoamericana del Tórax (ALAT) guidelines for diagnosing HP through demonstrating new radiologic terms, features, and a new classification of HP which will benefit radiologists and pulmonologists.

A persistent neutrophil-associated immune signature characterizes post-COVID-19 pulmonary sequelae

Interstitial lung disease and associated fibrosis occur in a proportion of individuals who have recovered from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection through unknown mechanisms. We studied individuals with severe coronavirus disease 2019 (COVID-19) after recovery from acute illness. Individuals with evidence of interstitial lung changes at 3 to 6 months after recovery had an up-regulated neutrophil-associated immune signature including increased chemokines, proteases, and markers of neutrophil extracellular traps that were detectable in the blood. Similar pathways were enriched in the upper airway with a concomitant increase in antiviral type I interferon signaling. Interaction analysis of the peripheral phosphoproteome identified enriched kinases critical for neutrophil inflammatory pathways. Evaluation of these individuals at 12 months after recovery indicated that a subset of the individuals had not yet achieved full normalization of radiological and functional changes. These data provide insight into mechanisms driving development of pulmonary sequelae during and after COVID-19 and provide a rational basis for development of targeted approaches to prevent long-term complications.

Effects of nintedanib on disease progression and safety in Japanese patients with progressive fibrosing interstitial lung diseases: Further subset analysis from the whole INBUILD trial

BACKGROUND

A previous subgroup analysis of data from the INBUILD trial showed that nintedanib reduced the annual rate of decline in forced vital capacity (FVC) in Japanese patients with progressive fibrosing interstitial lung diseases (PF-ILDs). The safety profile of nintedanib over 52 weeks in Japanese patients was similar to that of the overall population.

METHODS

Using data from 108 Japanese patients with PF-ILDs who had received at least 1 dose of study medication in the INBUILD trial, we evaluated the effect of nintedanib on disease progression and assessed the safety profile over the whole trial period (i.e., a longer duration than the prior analysis) compared with placebo. ILD progression was defined as an absolute decline in FVC ≥10% predicted vs baseline.

RESULTS

Over the whole trial, in Japanese patients with PF-ILDs, nintedanib numerically lowered the risk of progression of ILD or death (hazard ratio [HR], 0.66; 95% confidence intervals [CI]: 0.37, 1.16), acute exacerbation of ILD or death (HR, 0.28; 95% CI: 0.09, 0.83), and death (HR, 0.41; 95% CI: 0.11, 1.51). The most common adverse event over the whole trial in nintedanib-treated Japanese patients was diarrhea, which was manageable for most patients by dose reduction and interruption. The safety profile of nintedanib in this longer duration analysis was consistent with that previously reported.

CONCLUSIONS

In this analysis of data from Japanese patients with PF-ILDs, nintedanib nominally reduced the risk of clinically meaningful outcomes reflecting disease progression, including death, over the whole trial, and no new safety concerns were observed.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov NCT02999178.

Prevalence and characteristics of progressive fibrosing interstitial lung disease in a prospective registry

BACKGROUND

Progressive fibrosing interstitial lung disease (PF-ILD) is characterised by progressive physiological, symptomatic and/or radiographic worsening. The real-world prevalence and characteristics of PF-ILD remain uncertain.

METHODS

Patients were enrolled from the Canadian Registry for Pulmonary Fibrosis between 2015 and 2020. PF-ILD was defined as a relative forced vital capacity (FVC) decline ≥10%, death, lung transplantation or any two of: relative FVC decline ≥5% and <10%, worsening respiratory symptoms or worsening fibrosis on computed tomography of the chest, all within 24 months of diagnosis. Time-to-event analysis compared progression between key diagnostic subgroups. Characteristics associated with progression were determined by multivariable regression.

RESULTS

Of 2746 patients with fibrotic ILD (mean±sd age 65±12 years; 51% female), 1376 (50%) met PF-ILD criteria in the first 24 months of follow-up. PF-ILD occurred in 427 (59%) patients with idiopathic pulmonary fibrosis (IPF), 125 (58%) with fibrotic hypersensitivity pneumonitis (HP), 281 (51%) with unclassifiable ILD (U-ILD) and 402 (45%) with connective tissue disease-associated ILD (CTD-ILD). Compared with IPF, time to progression was similar in patients with HP (hazard ratio (HR) 0.96, 95% CI 0.79-1.17), but was delayed in patients with U-ILD (HR 0.82, 95% CI 0.71-0.96) and CTD-ILD (HR 0.65, 95% CI 0.56-0.74). Background treatment varied across diagnostic subtypes, with 66% of IPF patients receiving antifibrotic therapy, while immunomodulatory therapy was utilised in 49%, 61% and 37% of patients with CHP, CTD-ILD and U-ILD, respectively. Increasing age, male sex, gastro-oesophageal reflux disease and lower baseline pulmonary function were independently associated with progression.

CONCLUSIONS

Progression is common in patients with fibrotic ILD, and is similarly prevalent in HP and IPF. Routinely collected variables help identify patients at risk for progression and may guide therapeutic strategies.

Epidemiology and real-life experience in progressive pulmonary fibrosis

PURPOSE OF REVIEW

Idiopathic pulmonary fibrosis (IPF), characterized by relentless disease progression from the time of diagnosis, is part of a larger group of chronic fibrosing interstitial lung diseases (ILDs). A proportion of patients with non-IPF ILDs may develop, despite conventional treatment, a progressive pulmonary fibrosis (PPF), also referred to as ILD with a progressive fibrosing phenotype (PF-ILD). These patients experience worsening of respiratory symptoms, decline in lung function, and early mortality. The goal of this review is to describe the epidemiology and recent real-life cohorts of PF-ILD, with implications for management.

RECENT FINDINGS

The relatively new concept of PF-ILD has aroused active clinical research over the past years. To understand risk factors for progression and the real burden of the disease is crucial to improve management. In the last 2 years, different cohort studies have addressed these questions. They showed that almost one-third of the non-IPF fibrotic ILD patients develop PF-ILD or PPF.

SUMMARY

Emerging data show similarities in prognosis between patients with IPF or with non-IPF PF-ILD patients. Early detection and appropriate treatment of this group of patients is a priority. Further research is needed to identify risk factors of progression, to clarify the assessment of progression in clinical practice, for a better management of patients with PF-ILD in a real-world setting.

Meta-Analysis of Effect of Nintedanib on Reducing FVC Decline Across Interstitial Lung Diseases

INTRODUCTION

The effect of nintedanib on slowing the rate of decline in forced vital capacity (FVC) has been investigated in randomized placebo-controlled trials in subjects with idiopathic pulmonary fibrosis (IPF), other progressive fibrosing interstitial lung diseases (ILDs), and ILD associated with systemic sclerosis (SSc-ILD). We assessed the consistency of the effect of nintedanib on the rate of decline in FVC over 52 weeks across four placebo-controlled phase III trials.

METHODS

We used data on FVC decline from the INPULSIS-1 and INPULSIS-2 trials in subjects with IPF, the INBUILD trial in subjects with progressing fibrosing ILDs other than IPF, and the SENSCIS trial in subjects with SSc-ILD. In each trial, the primary endpoint was the annual rate of decline in FVC (mL/year) assessed over 52 weeks. We performed fixed effect and random effects meta-analyses based on the relative treatment effect of nintedanib versus placebo on the rate of decline in FVC (mL/year) over 52 weeks. Heterogeneity of the relative treatment effect of nintedanib across populations was assessed using the I2 statistic, τ2 and corresponding p value from a Q test for heterogeneity.

RESULTS

The combined analysis comprised 1257 subjects treated with nintedanib and 1042 subjects who received placebo. Nintedanib reduced the rate of decline in FVC (mL/year) over 52 weeks by 51.0% (95% CI 39.1, 63.0) compared with placebo. The relative effect (95% CI) was the same using the fixed effect and random effects models. There was no evidence of heterogeneity in the relative treatment effect of nintedanib across the populations studied (I2 = 0%, τ2 = 0, p = 0.93).

CONCLUSIONS

A meta-analysis of data from four placebo-controlled trials demonstrated that nintedanib approximately halved the rate of decline in FVC over 52 weeks across subjects with different forms of pulmonary fibrosis, with no evidence of heterogeneity in its relative treatment effect across patient populations.

From COVID to fibrosis: lessons from single-cell analyses of the human lung

The increased resolution of single-cell RNA-sequencing technologies has led to major breakthroughs and improved our understanding of the normal and pathologic conditions of multiple tissues and organs. In the study of parenchymal lung disease, single-cell RNA-sequencing has better delineated known cell populations and identified novel cells and changes in cellular phenotypes and gene expression patterns associated with disease. In this review, we aim to highlight the advances and insights that have been made possible by applying these technologies to two seemingly very different lung diseases: fibrotic interstitial lung diseases, a group of relentlessly progressive lung diseases leading to pulmonary fibrosis, and COVID-19 pneumonia, an acute viral disease with life-threatening complications, including pulmonary fibrosis. We discuss changes in cell populations and gene expression, highlighting potential common features, such as alveolar cell epithelial injury and aberrant repair and monocyte-derived macrophage populations, as well as relevance and implications to mechanisms of disease and future directions.

Idiopathic Pulmonary Fibrosis (an Update) and Progressive Pulmonary Fibrosis in Adults: An Official ATS/ERS/JRS/ALAT Clinical Practice Guideline

Background: This American Thoracic Society, European Respiratory Society, Japanese Respiratory Society, and Asociación Latinoamericana de Tórax guideline updates prior idiopathic pulmonary fibrosis (IPF) guidelines and addresses the progression of pulmonary fibrosis in patients with interstitial lung diseases (ILDs) other than IPF. Methods: A committee was composed of multidisciplinary experts in ILD, methodologists, and patient representatives. 1) Update of IPF: Radiological and histopathological criteria for IPF were updated by consensus. Questions about transbronchial lung cryobiopsy, genomic classifier testing, antacid medication, and antireflux surgery were informed by systematic reviews and answered with evidence-based recommendations using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) approach. 2) Progressive pulmonary fibrosis (PPF): PPF was defined, and then radiological and physiological criteria for PPF were determined by consensus. Questions about pirfenidone and nintedanib were informed by systematic reviews and answered with evidence-based recommendations using the GRADE approach. Results:1) Update of IPF: A conditional recommendation was made to regard transbronchial lung cryobiopsy as an acceptable alternative to surgical lung biopsy in centers with appropriate expertise. No recommendation was made for or against genomic classifier testing. Conditional recommendations were made against antacid medication and antireflux surgery for the treatment of IPF. 2) PPF: PPF was defined as at least two of three criteria (worsening symptoms, radiological progression, and physiological progression) occurring within the past year with no alternative explanation in a patient with an ILD other than IPF. A conditional recommendation was made for nintedanib, and additional research into pirfenidone was recommended. Conclusions: The conditional recommendations in this guideline are intended to provide the basis for rational, informed decisions by clinicians.

Diagnosis, course and management of hypersensitivity pneumonitis

Hypersensitivity pneumonitis (HP) is a complex and heterogeneous interstitial lung disease (ILD) that occurs when susceptible individuals develop an exaggerated immune response to an inhaled antigen. In this review, we discuss the latest guidelines for the diagnostic evaluation of patients with suspected HP, the importance of identifying patients with fibrotic and progressive disease, and the evidence supporting the drugs commonly used in the treatment of HP. Differential diagnosis of HP can be challenging and requires a thorough exposure history, multidisciplinary discussion of clinical and radiologic data, and, in some cases, assessment of bronchoalveolar lavage lymphocytosis and histopathologic findings. Patients with HP may be categorised as having non-fibrotic or fibrotic HP. The presence of fibrosis is associated with worse outcomes. A proportion of patients with fibrotic HP develop a progressive phenotype, characterised by worsening fibrosis, decline in lung function and early mortality. There are no established guidelines for the treatment of HP. Antigen avoidance should be implemented wherever possible. Immunosuppressants are commonly used in patients with HP but have not been shown to slow the worsening of fibrotic disease. Nintedanib, a tyrosine kinase inhibitor, has been approved by the US Food and Drug Administration for slowing the progression of chronic fibrosing ILDs with a progressive phenotype, including progressive fibrotic HP. Non-pharmacological interventions, such as oxygen therapy, pulmonary rehabilitation and supportive care, may be important components of the overall care of patients with progressive HP.

The role of precision medicine in interstitial lung disease

The management of interstitial lung disease (ILD) may benefit from a conceptual shift. Increased understanding of this complex and heterogeneous group of disorders over the past 20 years has highlighted the need for individualised treatment strategies that encompass diagnostic classification and disease behaviour. Biomarker-based approaches to precision medicine hold the greatest promise. Robust, large-scale biomarker-based technologies supporting ILD diagnosis have been developed, and future applications relating to staging, prognosis and assessment of treatment response are emerging. Artificial intelligence may redefine our ability to base prognostic evaluation on both diagnosis and underlying disease processes, sharpening individualised treatment algorithms to a level not previously achieved. Compared with therapeutic areas such as oncology, precision medicine in ILD is still in its infancy. However, the heterogeneous nature of ILD suggests that many relevant molecular, environmental and behavioural targets may serve as useful biomarkers if we are willing to invest in their identification and validation.

The Burden of Progressive-Fibrosing Interstitial Lung Diseases

Despite conventional treatment, a proportion of interstitial lung disease (ILD) patients develop a progressive phenotype known as "fibrosing ILD with a progressive phenotype" (PF-ILD), characterized by worsening respiratory symptoms, decline in lung function, and early mortality. This review describes the epidemiology, and the humanistic and economic burden of PF-ILDs other than idiopathic pulmonary fibrosis (non-IPF PF-ILD). A structured review of the literature was conducted, using predefined search strategies in Ovid MEDLINE and EMBASE, and supplemented with gray literature searches. The search identified 3,002 unique articles and an additional 3 sources were included from the gray literature; 21 publications were included. The estimated prevalence of non-IPF PF-ILD ranges from 6.9 to 70.3/100,000 persons and the estimated incidence from 2.1 to 32.6/100,000 person-years. Limited evidence demonstrates that PF-ILD has a significant impact on patients' quality of life, affecting their daily lives, psychological well-being, careers, and relationships. PF-ILD is also associated with significant economic burden, demonstrating higher healthcare resource use and direct costs compared with the non-progressive phenotype, and indirect costs, which include job losses. This review indicates that PF-ILD places a considerable humanistic burden on both patients and caregivers, and a substantial economic burden on healthcare systems, patients, and society.

Treatment of fibrotic interstitial lung disease: current approaches and future directions

Fibrotic interstitial lung disease (ILD) represents a large group of pulmonary disorders that are often progressive and associated with high morbidity and early mortality. Important advancements in the past 10 years have enabled a better understanding, characterisation, and treatment of these diseases. This Series paper summarises the current approach to treatment of fibrotic ILDs, both pharmacological and non-pharmacological, including recent discoveries and practice-changing clinical trials. We further outline controversies and challenges, with discussion of evolving concepts and future research directions.

Disease pathology in fibrotic interstitial lung disease: is it all about usual interstitial pneumonia?

The interstitial pneumonias comprise a diverse group of diseases that are typically defined by their cause (either idiopathic or non-idiopathic) and their distinct histopathological features, for which radiology, in the form of high-resolution CT, is often used as a surrogate. One trend, fuelled by the failure of conventional therapies in a subset of patients and the broad-spectrum use of antifibrotic therapies, has been the focus on the progressive fibrosing phenotype of interstitial lung disease. The histological pattern, known as usual interstitial pneumonia, is the archetype of progressive fibrosis. However, it is clear that progressive fibrosis is not exclusive to this histological entity. Techniques including immunohistochemistry and single-cell RNA sequencing are providing pathogenetic insights and, if integrated with traditional histopathology, are likely to have an effect on the pathological classification of interstitial lung disease. This review, which focuses on the histopathology of interstitial lung disease and its relationship with progressive fibrosis, asks the question: is it all about usual interstitial pneumonia?

Hypersensitivity Pneumonitis: Diagnostic and Therapeutic Challenges

Hypersensitivity pneumonitis (HP) is one of the most common interstitial lung diseases (ILD), that presents unique challenges for a confident diagnosis and limited therapeutic options. The disease is triggered by exposure to a wide variety of inciting antigens in susceptible individuals which results in T-cell hyperactivation and bronchioloalveolar inflammation. However, the genetic risk and the pathogenic mechanisms remain incompletely elucidated. Revised diagnostic criteria have recently been proposed, recommending to classify the disease in fibrotic and non-fibrotic HP which has strong therapeutic and outcome consequences. Confident diagnosis depends on the presence of clinical features of ILD, identification of the antigen(s), typical images on high-resolution computed tomography (HRCT), characteristic histopathological features, and lymphocytosis in the bronchoalveolar lavage. However, identifying the source of antigen is usually challenging, and HRCT and histopathology are often heterogeneous and not typical, supporting the notion that diagnosis should include a multidisciplinary assessment. Antigen removal and treating the inflammatory process is crucial in the progression of the disease since chronic persistent inflammation seems to be one of the mechanisms leading to lung fibrotic remodeling. Fibrotic HP has a few therapeutic options but evidence of efficacy is still scanty. Deciphering the molecular pathobiology of HP will contribute to open new therapeutic avenues and will provide vital insights in the search for novel diagnostic and prognostic biomarkers.

The justification for the progressive fibrotic phenotype

PURPOSE OF REVIEW

Describe the concept and recent data for the concept of progressive fibrotic interstitial lung disease (ILD).

RECENT FINDINGS

Making an accurate diagnosis is critical to help determine appropriate therapy and predict prognosis. This is certainly true in the field of ILD where a diagnosis of idiopathic pulmonary fibrosis (IPF) leads a clinician to consider initiation of antifibrotic therapy, and avoidance of immunosuppression due to possible harm, at the time of diagnosis due to the high probability of disease progression. In other types of ILD immunosuppression may be helpful such as those associated with a connective tissue disease or in combination with antigen avoidance in hypersensitivity pneumonia. It is also recognized that despite initial approaches to therapy some non-IPF ILDs will develop progressive fibrosis leading to increased symptoms, decreased quality of life and early mortality. Once fibrosis is present, the biologic pathways responsible for progression can be redundant and respond in a similar fashion to antifibrotic therapy independent of the underlying disease.

SUMMARY

There are clinical and biological rationale for the justification of a progressive fibrotic phenotype that complements the therapeutic decisions and prognosis provided by initial diagnosis.

Metabolic changes induced by TGF-β1 via reduced expression of phosphatidylserine decarboxylase during myofibroblast transition

Metabolic alteration is increasingly recognized as an important pathogenic process that underlies fibrosis across many organ types, and metabolically targeted therapies could become important strategies for reducing fibrosis. In present study, target enzymes that are involved in changes in phospholipid metabolism during fibroblast-to-myofibroblast transition induced by transforming growth factor beta 1 (TGF-β1) were examined. Different amounts of phospholipids were found in the 2 groups. In response to TGF-β1 stimulation, 17 lipids decreased and 17 increased. The latter included the phospholipids phosphatidylcholine (PC), phosphatidylserine (PS), and phosphatidylethanolamine (PE). Furthermore, among the rate-limiting enzymes that regulate these phospholipids, phosphatidylserine decarboxylase (PISD), which controls conversion of PS to PE and is localized in mitochondria, decreased in response to TGF-β1. Knockdown of PISD alone without TGF-β1 stimulation increased expression of α-smooth muscle actin mRNA and production of total collagen. Taken together, these results indicate that PISD is involved in the mechanism of fibrogenesis by regulating phospholipid metabolism.