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.

1. Interstitial lung disease is a common complication of systemic sclerosis. The mechanism by which excess collagen is deposited in the lung is poorly understood, but is thought to involve release of mediators which activate lung fibroblasts. In this study we investigated and partially characterized the fibroblast proliferative activity of bronchoalveolar lavage fluid from 29 patients with systemic sclerosis, 19 with and 10 without evidence of lung disease assessed by thin-section computed tomography. 2. Bronchoalveolar lavage fluid from both groups of patients stimulated fibroblast proliferation compared with control subjects: systemic sclerosis with normal computed tomography, 27.7 (range 10.5–57.9)% above control; systemic sclerosis with abnormal computed tomography, 26.7 (range 5.0–47.8)% above control, P < 0.02 in both cases. 3. The activity was reduced by about one-third by neutralizing antibodies to insulin-like growth factor-1 but not platelet-derived growth factor. Levels of insulin-like growth factor-1 of bronchoalveolar fluid were increased in patients with systemic sclerosis [2.10 (range 1.10–3.48) ng/ml of bronchoalveolar lavage fluid] compared with controls [1.45 (range 1.10–2.05) ng/ml; P < 0.01]. When patients were subdivided into those with abnormal computed tomography [2.10 (range 1.20–3.48) ng/ml] and those with normal computed tomography [1.85 (range 1.10–2.90) ng/ml] only the values for the group with evidence of lung disease were increased compared with control subjects ( P < 0.02). Platelet-derived growth factor could not be detected in bronchoalveolar lavage fluid from any group. Fractionation of bronchoalveolar lavage fluid demonstrated activity in several fractions consistent with the molecular masses of insulin-like growth factor-1 associated with binding proteins. 4. We conclude that bronchoalveolar lavage fluid from patients with systemic sclerosis contains increased levels of insulin-like growth factor-1 and this contributes to the increased fibroblast-growth-promoting activity of this fluid. The data also suggest that other mitogens are involved, but we were unable to demonstrate a role for platelet-derived growth factor.