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EMT and interstitial lung disease: a mysterious relationship

imagePurpose of review: Pathogenesis of interstitial lung diseases (ILD) has largely been investigated in the context of the most frequent ILD, idiopathic pulmonary fibrosis (IPF). We review studies of epithelial-to-mesenchymal transition (EMT) and discuss its potential contribution to collagen-producing (myo)fibroblasts in IPF. Recent findings: Endoplasmic reticulum (ER) stress leading to epithelial apoptosis has been reported as a potential etiologic factor in fibrosis. Recent studies further suggest EMT as a link between ER stress and fibrosis. Combinatorial interactions among Smad3, β-catenin and other transcriptional co-activators at the α-smooth muscle actin (α-SMA) promoter provide direct evidence for crosstalk between transforming growth factor-β (TGFβ) and β-catenin pathways during EMT. Lineage tracing yielded conflicting results, with two recent studies supporting and one opposing a role for EMT in lung fibrosis.

Summary: Advances have been made in elucidating causes and mechanisms of EMT, potentially leading to new treatment options, although contributions of EMT to lung fibrosis in vivo remain controversial. In addition to EMT providing a direct source of (myo)fibroblasts, expression of mesenchymal markers may reflect epithelial injury, in which case inhibition of EMT might be deleterious. EMT-derived cells may also contribute to aberrant epithelial–mesenchymal crosstalk that promotes fibrogenesis.

Biomarkers in idiopathic pulmonary fibrosis

imagePurpose of review: This review examines the recent literature on molecular biomarkers of idiopathic pulmonary fibrosis (IPF). Specific attention is dedicated to the recent studies that identified the genes associated with IPF and the peripheral blood biomarkers that predict outcome in IPF.

Recent findings: Multiple studies attempted to identify diagnostic and predictive biomarkers in IPF. Until recently, these studies were limited in size and lacked replication, but still when taken together provided convincing evidence that changes in blood proteins (KL-6, SP-A, MMP-7, CCL-18, among others) or cells (fibrocytes and T-cell subpopulations) are indicative of the disease presence and outcome. More recently, larger studies have identified gene polymorphisms associated with IPF, as well as protein markers and integrated clinical and molecular prediction rules that accurately predict outcome in patients with IPF.

Summary: The peripheral blood contains disease presence and outcome relevant information, and suggests distinct biologically defined outcome trajectories in patients with IPF. Although recently identified biomarkers should still be validated in multiple clinical contexts, there is sufficient evidence to suggest that collection of peripheral blood biomarkers needs to be incorporated in the design of drug studies and that some of these markers be clinically evaluated in lung transplant prioritization.

Serologic evaluation in idiopathic interstitial pneumonias

imagePurpose of review: Diagnosis of idiopathic interstitial pneumonias (IIPs) requires the exclusion of, among others, concomitant connective tissue diseases (CTDs), which may present as interstitial lung disease (ILD). This review focuses on the evaluation required to separate these entities through serology, although not exclusively.

Recent findings: Several recent data suggest that patients diagnosed with IIPs can show evidence of CTDs on follow-up. This is especially true for nonspecific interstitial pneumonia but may also be seen with other forms of ILD.

Summary: ILDs may occur alone, IIPs, or in association with, among others, CTDs. In the latter case, they may present before, during or even several months or years after the fulfsuillment of undisputed criteria for CTDs. If present before, their presentation presupposes their occurrence in early undiagnosed, undefined or undifferentiated CTD, which occasionally indefinitely maintains this status of diagnostic uncertainty, especially if ILD is empirically treated by immunosuppressants. Serologic evaluation for autoantibodies assisted by serum inflammatory biomarkers, detailed search for clinical clues of CTDs and suggestive histopathologic features on lung specimens may provide a framework to build the correct diagnosis. Obtaining a diagnosis of ILD associated with CTD exceeds semantics as this subset of patients may present different natural history, pathobiology, treatment and prognosis.

The big clinical trials in idiopathic pulmonary fibrosis

imagePurpose of review: Since the late 1990 s, when a more uniform definition of idiopathic pulmonary fibrosis (IPF) was proposed, more than 3000 patients have been enrolled in clinical studies exploring novel therapies. Some of the most relevant trials have been published only recently. Recent findings: This review describes and comments on the randomized clinical trials in IPF published within the past 18 months, with emphasis on the studies evaluating pirfenidone, which at present is the only drug approved for IPF (at least in Europe and Japan), and bosentan. This latter represents the largest single trial performed in IPF so far.

Summary: Despite multiple clinical trials, there is no strong, definitive evidence in favor of any agent to treat IPF. On the other hand, the placebo arms of these large trials have provided us with important critical information on the natural history of this disease. Clinical heterogeneity represents a critical issue to be taken into account in designing future clinical trials. The limited effectiveness of current treatment regimes has fuelled the search for a variety of new therapeutic approaches.

Combined pulmonary fibrosis and emphysema in connective tissue disease

imagePurpose of review: This review discusses combined pulmonary fibrosis and emphysema (CPFE) in the setting of connective tissue disease. Recent findings: CPFE is a recently identified syndrome in smokers or ex-smokers characterized by dyspnea often severe, preserved lung volumes, severely impaired gas exchanges, and an increased risk of pulmonary hypertension associated with a dismal prognosis, and possibly lung cancer. It may be encountered in the setting of connective tissue diseases, especially rheumatoid arthritis and systemic sclerosis, with generally similar features as ‘idiopathic’ (tobacco-related) CPFE. The diagnosis is based on the presence of both emphysema predominating in the upper lobes and frequently paraseptal, and interstitial abnormalities suggesting pulmonary fibrosis in the lower lung zones with velcro crackles at auscultation.

Pathologic radiological correlations are difficult owing to various pathology and difficulties in identifying honeycombing at chest high-resolution computed tomography in the setting of coexistent emphysema. Tobacco smoking is associated with an increased risk of developing most of the individual components of the syndrome (i.e. emphysema, pulmonary fibrosis, pulmonary hypertension, rheumatoid arthritis, and pulmonary fibrosis among patients with rheumatoid arthritis). CPFE impacts modalities of follow-up for pulmonary function and detection of pulmonary hypertension especially in systemic sclerosis.

Summary: The syndrome of CPFE is a distinct pulmonary manifestation in the spectrum of lung diseases associated with connective tissue diseases, especially in smokers or ex-smokers.

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