Genetic predictors of systemic sclerosis-associated interstitial lung disease: a review of recent literature

The interplay between genetic and environmental factors is likely involved in the pathogenesis of systemic sclerosis (SSc). Interstitial lung disease associated in the context of SSc (SSc-ILD) is associated with significant morbidity, and is the leading cause of death in SSc. The spectrum of SSc-ILD severity is wide, ranging from patients with only limited and inherently stable pulmonary involvement, to those with extensive and progressive pulmonary fibrosis. In order to provide accurate prognostic information for patients, and to initiate appropriate monitoring and treatment regimens, the ability to identify patients at risk of developing severe ILD early in the disease course is crucial. Identification of genetic variants involved in disease pathogenesis can not only potentially provide diagnostic/prognostic markers, but can also highlight dysregulated molecular pathways for therapeutic targeting. A number of genetic associations have been established for susceptibility to SSc, but far fewer studies have investigated genetic susceptibility to SSc-ILD specifically. In this review we present a summary of the studies assessing genetic associations with SSc-ILD

Aetiology, Risk Factors, and Biomarkers in Systemic Sclerosis with Interstitial Lung Disease

Systemic sclerosis (SSc) is a complex, multi-organ, autoimmune disease. Lung fibrosis occurs in ~80% of patients with SSc; 25-30% develop progressive interstitial lung disease (ILD). The pathogenesis of fibrosis in SSc associated ILD (SSc-ILD) involves cellular injury, activation/differentiation of mesenchymal cells and morphological/biological changes in epithelial/endothelial cells. Risk factors for progressive SSc-ILD include older age, male sex, lung involvement on baseline high-resolution computed tomography, reduced diffusing capacity for carbon monoxide and reduced forced vital capacity. SSc-ILD is characterized by genetic risk architecture distinct from that associated with idiopathic pulmonary fibrosis (IPF). Presence of anti-Scl-70 antibodies and absence of anti-centromere antibodies indicate increased likelihood of progressive ILD. Elevated levels of serum Krebs von den Lungen-6 (KL6) and CRP are associated with SSc-ILD severity, although whether KL6 independently predicts SSc-ILD progression remains controversial. A promising prognostic indicator is serum chemokine (C-C motif) ligand 18. SSc-ILD shares similarities with IPF, although clear differences exist. Histologically, a non-specific interstitial pneumonia pattern is commonly observed in SSc-ILD, whereas IPF is defined by usual interstitial pneumonia. The course of SSc-ILD is variable, ranging from minor, stable disease to a progressive course, while all IPF patients experience progression of disease. Although appropriately treated SSc-ILD patients have better chances of stabilization and survival, a relentlessly progressive course, akin to IPF, is seen in a minority. Better understanding of cellular and molecular pathogenesis, genetic risk and distinctive features of SSc-ILD, and identification of robust prognostic biomarkers are needed for optimal disease management. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Serum C-reactive protein is associated with earlier mortality across different interstitial lung diseases

Background and Objective: The acute-phase protein C-reactive protein (CRP) is known to be associated with poor outcomes in cancer and cardiovascular disease, but there is limited evidence of its prognostic implications in interstitial lung diseases (ILDs). We therefore set out to test whether baseline serum CRP levels are associated with mortality in four different ILDs. Methods: In this retrospective study, clinically measured CRP levels, as well as baseline demographics and lung function measures, were collected for ILD patients first presenting to the Royal Brompton Hospital between January 2010 and December 2019. Cox regression analysis was used to determine the relationship with 5-year mortality. Results: Patients included in the study were: idiopathic pulmonary fibrosis (IPF) n = 422, fibrotic hypersensitivity pneumonitis (fHP) n = 233, rheumatoid arthritis associated ILD (RA-ILD) n = 111 and Systemic Sclerosis associated ILD (SSc-ILD) n = 86. Patients with a recent history of infection were excluded. Higher CRP levels were associated with shorter 5-year survival in all four disease groups on both univariable analyses, and after adjusting for age, gender, smoking history, immunosuppressive therapy and baseline disease severity (IPF: HR (95% CI): 1.3 (1.1–1.5), p = 0.003, fHP: 1.5 (1.2–1.9), p = 0.001, RA-ILD: 1.4 (1.1–1.84), p = 0.01 and SSc-ILD: 2.7 (1.6–4.5), p < 0.001). Conclusion: Higher CRP levels are independently associated with reduced 5-year survival in IPF, fHP, RA-ILD and SSc-ILD

Epigenetic regulation of cyclooxygenase-2 by methylation of c8orf4 in pulmonary fibrosis

Fibroblasts derived from the lungs of patients with idiopathic pulmonary fibrosis (IPF) and systemic sclerosis (SSc) produce low levels of prostaglandin (PG) E(2), due to a limited capacity to up-regulate cyclooxygenase-2 (COX-2). This deficiency contributes functionally to the fibroproliferative state, however the mechanisms responsible are incompletely understood. In the present study, we examined whether the reduced level of COX-2 mRNA expression observed in fibrotic lung fibroblasts is regulated epigenetically. The DNA methylation inhibitor, 5-aza-2′-deoxycytidine (5AZA) restored COX-2 mRNA expression by fibrotic lung fibroblasts dose dependently. Functionally, this resulted in normalization of fibroblast phenotype in terms of PGE(2) production, collagen mRNA expression and sensitivity to apoptosis. COX-2 methylation assessed by bisulfite sequencing and methylation microarrays was not different in fibrotic fibroblasts compared with controls. However, further analysis of the methylation array data identified a transcriptional regulator, chromosome 8 open reading frame 4 (thyroid cancer protein 1, TC-1) (c8orf4), which is hypermethylated and down-regulated in fibrotic fibroblasts compared with controls. siRNA knockdown of c8orf4 in control fibroblasts down-regulated COX-2 and PGE(2) production generating a phenotype similar to that observed in fibrotic lung fibroblasts. Chromatin immunoprecipitation demonstrated that c8orf4 regulates COX-2 expression in lung fibroblasts through binding of the proximal promoter. We conclude that the decreased capacity of fibrotic lung fibroblasts to up-regulate COX-2 expression and COX-2-derived PGE(2) synthesis is due to an indirect epigenetic mechanism involving hypermethylation of the transcriptional regulator, c8orf4

Defining genetic risk factors for scleroderma-associated interstitial lung disease

Although several genetic associations with scleroderma (SSc) are defined, very little is known on genetic susceptibility to SSc-associated interstitial lung disease (SSc-ILD). A number of common polymorphisms have been associated with SSc-ILD, but most have not been replicated in separate populations. Four SNPs in IRF5, and one in each of STAT4, CD226 and IRAK1, selected as having been previously the most consistently associated with SSc-ILD, were genotyped in 612 SSc patients, of European descent, of whom 394 had ILD. The control population (n = 503) comprised individuals of European descent from the 1000 Genomes Project. After Bonferroni correction, two of the IRF5 SNPs, rs2004640 (OR (95% CI)1.30 (1.10–1.54), p^{corr} = 0.015) and rs10488631 (OR 1.48 (1.14–1.92), p^{corr} = 0.022), and the STAT4 SNP rs7574865 (OR 1.43 (1.18–1.73), p^{corr} = 0.0015) were significantly associated with SSc compared with controls. However, none of the SNPs were significantly different between patients with SSc-ILD and controls. Two SNPs in IRF5, rs10488631 (OR 1.72 (1.24–2.39), p^{corr} = 0.0098), and rs2004640 (OR 1.39 (1.11–1.75), p^{corr} = 0.03), showed a significant difference in allele frequency between controls and patients without ILD, as did STAT4 rs7574865 (OR 1.86 (1.45–2.38), p^{corr} = 6.6 × 10^{-6}). A significant difference between SSc with and without ILD was only observed for STAT4 rs7574865, being less frequent in patients with ILD (OR 0.66 (0.51–0.85), p^{corr} = 0.0084). In conclusion, IRF5 rs2004640 and rs10488631, and STAT4 rs7574865 were significantly associated with SSc as a whole. Only STAT4 rs7574865 showed a significant difference in allele frequency in SSc-ILD, with the T allele being protective against ILD

Pulmonary hypertension in interstitial lung disease: Limitations of echocardiography compared to cardiac catheterization

BACKGROUND AND OBJECTIVE: In interstitial lung disease (ILD), pulmonary hypertension (PH) is a major adverse prognostic determinant. Transthoracic echocardiography (TTE) is the most widely used tool when screening for PH, although discordance between TTE and right heart catheter (RHC) measured pulmonary haemodynamics is increasingly recognized. We evaluated the predictive utility of the updated European Society of Cardiology/European Respiratory Society (ESC/ERS) TTE screening recommendations against RHC testing in a large, well-characterized ILD cohort. METHODS: Two hundred and sixty-five consecutive patients with ILD and suspected PH underwent comprehensive assessment, including RHC, between 2006 and 2012. ESC/ERS recommended tricuspid regurgitation (TR) velocity thresholds for assigning high (>3.4 m/s), intermediate (2.9-3.4 m/s) and low (3.4 m/s, and excluded PH in 60% of ILD subjects with a TR velocity <2.8 m/s. Thus, the ESC/ERS guidelines misclassified 40% of subjects as 'low probability' of PH, when PH was confirmed on subsequent RHC. Evaluating alternative TR velocity thresholds for assigning a low probability of PH did not significantly improve the ability of TR velocity to exclude a diagnosis of PH. CONCLUSION: In patients with ILD and suspected PH, currently recommended ESC/ERS TR velocity screening thresholds were associated with a high positive predictive value (86%) for confirming PH, but were of limited value in excluding PH, with 40% of patients misclassified as low probability when PH was confirmed at subsequent RHC

Muscle stimulation in advanced idiopathic pulmonary fibrosis: A randomised placebo-controlled feasibility study

Objectives To assess the acceptability of neuromuscular electrical stimulation (NMES) of the quadriceps muscles in people with idiopathic pulmonary fibrosis (IPF) and to identify whether a future definitive trial is feasible. Design A randomised, parallel, two-group, participant and assessor-blinded, placebo-controlled feasibility trial with embedded qualitative interviews. Setting Outpatient department, Royal Brompton and Harefield Hospitals. Participants Twenty-two people with IPF: median (25th, 75th centiles) age 76 (74, 82) years, forced vital capacity 62 (50, 75) % predicted, 6min walk test distance 289 (149, 360) m. Interventions Usual care (home-based exercise, weekly telephone support, breathlessness management leaflet) with either placebo or active NMES for 6weeks, with follow-up at 6 and 12 weeks. Primary outcome measures Feasibility of recruitment and retention, treatment uptake and adherence, outcome assessments, participant and outcome assessor blinding and adverse events related to interventions. Secondary outcome measures Outcome measures with potential to be primary or secondary outcomes in a definitive clinical trial. In addition, purposively sampled participants were interviewed to capture their experiences and acceptability of the trial. Results Out of 364 people screened, 23 were recruited: 11 were allocated to each group and one was withdrawn prior to randomisation. Compared with the control group, a greater proportion of the intervention group completed the intervention, remained in the trial blinded to group allocation and experienced intervention-related adverse events. Assessor blinding was maintained. The secondary outcome measures were feasible with most missing data associated with the accelerometer. Small participant numbers precluded identification of an outcome measure suitable for a definitive trial. Qualitative findings demonstrated that trial process and active NMES were acceptable but there were concerns about the credibility of placebo NMES. Conclusions Primarily owing to recruitment difficulties, a definitive trial using the current protocol to evaluate NMES in people with IPF is not feasible. Trial registration number NCT03499275.British Lung Foundation IPF Project Grant (grant number IPF/PG/17-15

Short-term lung function changes predict mortality in patients with fibrotic hypersensitivity pneumonitis

Background and objective A proportion of patients with fibrotic hypersensitivity pneumonitis (fHP) follow a progressive disease course despite immunosuppressive treatment. Little is known about predictors of mortality in fHP. We aimed to investigate the impact of short-term lung function changes in fHP on mortality. Methods Baseline demographics for 145 consecutive patients with a multi-disciplinary team diagnosis of fHP, as well as baseline and 1-year follow-up of lung function, baseline echocardiographic findings, bronchoalveolar lavage (BAL) cellularity and all-cause mortality were recorded. Changes in forced vital capacity (FVC) ≥ 5% and ≥10%, and diffusion capacity of the lung for carbon monoxide (DLCO) ≥ 10% and ≥15% at 1 year were calculated. Cox proportional hazards analysis was performed to test for associations with mortality. Results Baseline lung function severity, age, presence of honeycombing on computed tomography (CT) and echocardiographic pulmonary arterial systolic pressure (PASP) ≥ 40 mm Hg were associated with early mortality, while BAL lymphocytosis was associated with improved survival. A decline in FVC ≥ 5% (hazard ratio [HR]: 3.10, 95% CI: 2.00–4.81, p < 0.001), FVC ≥ 10% (HR: 3.11, 95% CI: 1.94–4.99, p < 0.001), DLCO ≥ 10% (HR: 2.80, 95% CI: 1.78–4.42, p < 0.001) and DLCO ≥ 15% (HR: 2.92, 95% CI: 1.18–4.72, p < 0.001) at 1 year was associated with markedly reduced survival on univariable and multivariable analyses after correcting for demographic variables, disease severity, honeycombing on CT and treatment, as well as BAL lymphocytosis and PASP ≥ 40 mm Hg on echocardiography, in separate models. Conclusion Worsening in FVC and DLCO at 1 year, including a marginal decline in FVC ≥ 5% and DLCO ≥ 10%, is predictive of markedly reduced survival in fHP