Histone deacetylase 7 promotes Toll-like Receptor 4-dependent pro-inflammatory gene expression in macrophages

Broad-spectrum inhibitors of histone deacetylases (HDACs) constrain Toll-like receptor (TLR)-inducible production of key pro-inflammatory mediators. Here we investigated HDAC-dependent inflammatory responses in mouse macrophages. Of the classical Hdacs, Hdac7 was expressed at elevated levels in inflammatory macrophages (thioglycollate-elicited peritoneal macrophages, TEPM), as compared to bone marrow-derived macrophages (BMM) and the RAW264 cell line. Over-expression of a specific alternatively spliced isoform of Hdac7 lacking the N-terminal 22 amino acids (Hdac7-u), but not the Refseq Hdac7 (Hdac7-s), promoted lipopolysaccharide (LPS)-inducible expression of Hdac-dependent genes (Edn1, Il-12p40, Il-6) in RAW264 cells. A novel class IIa selective HDAC inhibitor reduced recombinant human HDAC7 enzyme activity, as well as TLR-induced production of inflammatory mediators in TEPM. Both LPS and Hdac7-u upregulated the activity of the Edn1 promoter in an HDAC-dependent fashion in RAW264 cells. A hypoxia-inducible factor (HIF)-1 binding site in this promoter was required for HDAC-dependent TLR-inducible promoter activity and for Hdac7- and HIF-1α-mediated trans-activation. Co-immunoprecipitation assays showed that both Hdac7-u and Hdac7-s interacted with HIF-1α, whereas only Hdac7-s interacted with the transcriptional repressor CtBP1. Thus, Hdac7-u positively regulates HIF-1α-dependent TLR signalling in macrophages, whereas an interaction with CtBP1 likely prevents Hdac7-s from exerting this effect. Hdac7 may represent a potential inflammatory disease target.