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

Area of Science:

• Immunology
• Epigenetics
• Pulmonary Medicine

Background:

• Hematopoietic stem cell transplantation (HSCT) is crucial but complicated by pulmonary infections.
• Alveolar macrophages (AMs) in mice post-HSCT exhibit impaired defense against Pseudomonas aeruginosa.
• This immune deficit is linked to elevated prostaglandin E2 (PGE2) production by AMs.

Purpose of the Study:

• To investigate the epigenetic mechanisms underlying the upregulation of Cyclooxygenase-2 (COX-2) in AMs following bone marrow transplantation (BMT).
• To explore the role of transforming growth factor-beta 1 (TGF-β1) in regulating COX-2 expression and its epigenetic status in AMs post-BMT.

Main Methods:

• Bisulfite sequencing to analyze DNA methylation patterns in the COX-2 gene promoter region of AMs from BMT mice.
• In vitro experiments using primary AMs and an AM cell line treated with a methyltransferase inhibitor (5-aza-2'-deoxycytidine).
• Reporter assays to assess the impact of COX-2 promoter methylation and TGF-β1 on gene expression.
• In vivo studies using genetically modified mice undergoing BMT.

Main Results:

• The 5'-untranslated region and exon 1 of the COX-2 gene were hypomethylated in AMs of BMT mice compared to controls.
• COX-2 expression increased in AMs treated with a methyltransferase inhibitor, confirming the role of methylation.
• TGF-β1 showed a modest ability to induce COX-2 expression in a hypermethylated vector, suggesting a demethylating effect.
• BMT in mice with a dominant-negative TGF-β receptor in AMs improved host defense and AM function.

Conclusions:

• Impaired innate immunity and elevated PGE2 levels post-BMT are attributed to the hypomethylation of the COX-2 gene in AMs.
• TGF-β1 plays a role in regulating COX-2 gene methylation and expression in AMs following BMT.
• Targeting epigenetic modifications of COX-2 may offer therapeutic strategies to enhance host defense after HSCT.