Fibroblasts derived from the lungs of patients with idiopathic pulmonary fibrosis and systemic sclerosis produce low levels of prostaglandin E2, due to a limited capacity to up-regulate cyclooxygenase-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 cyclooxygenase-2 mRNA expression observed in fibrotic lung fibroblasts is regulated epigenetically. The DNA methylation inhibitor, 5 Aza-2'-deoxycytidine restored cyclooxygenase-2 mRNA expression by fibrotic lung fibroblasts dose dependently. Functionally, this resulted in normalization of fibroblast phenotype in terms of prostaglandin E2 production, collagen mRNA expression and sensitivity to apoptosis. Cyclooxygenase-2 methylation assessed by bisulphite 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, c8orf4, which is hypermethylated and down-regulated in fibrotic fibroblasts compared with controls. siRNA knock-down of c8orf4 in control fibroblasts down-regulated cyclooxygenase-2 and prostaglandin E2 production generating a phenotype similar to that observed in fibrotic lung fibroblasts. Chromatin immunoprecipitation demonstrated that c8orf4 regulates cyclooxygenase-2 expression in lung fibroblasts through binding of the proximal promoter.We conclude that the decreased capacity of fibrotic lung fibroblasts to up-regulate cyclooxygenase-2 expression and cyclooxygenase-2 derived prostaglandin E2 synthesis is due to an indirect epigenetic mechanism involving hypermethylation of the transcriptional regulator, c8orf4.