COX-2 expression is upregulated by DNA hypomethylation after hematopoietic stem cell transplantation.

Hematopoietic stem cell transplant therapy is limited by pulmonary infections. Mice with fully reconstituted hematopoietic compartments, including alveolar macrophages (AMs), after bone marrow transplantation (BMT) have impaired host defense against Gram-negative Pseudomonas aeruginosa. Impaired innate immunity is related to increased production of PGE(2) by AMs. Cyclooxygenase (COX)-2 is the rate-limiting enzyme for synthesis of PGE(2) from arachidonic acid, and COX-2 expression is elevated in AMs post-BMT. We hypothesized that epigenetic mechanisms may be responsible for upregulation of COX-2 in AMs. Using bisulfite sequencing, we observed the 5'-untranslated region and exon 1 of the COX-2 gene is hypomethylated in the AMs of BMT mice compared with control. COX-2 expression was increased in primary AMs and in the AM cell line (MHS) after treatment with 5-aza-2'-deoxycytidine (a methyltransferase inhibitor). Methylation by SssI methyltransferase of a 698-bp region of the COX-2 promoter including the beginning of exon 1 driving a luciferase reporter silenced luciferase expression. Because TGF-β1 is elevated in lungs post-BMT, we tested whether TGF-β1 could promote expression of COX-2 in a hypermethylated COX-2 vector, and observed TGF-β1-induced modest expression of COX-2, suggesting an ability to demethylate the promoter. Finally, BMTs performed with marrow from mice expressing a dominant-negative form of the TGF-βRII on CD11c-expressing cells (which includes AMs) demonstrated improved host defense and AM function. Our findings suggest impaired innate immunity and PGE(2) elevation post-BMT are due to hypomethylation of the COX-2 gene, which is at least partly regulated by TGF-β1.