To study the capacity of butyrate to inhibit production of tumor necrosis factor alpha (TNFalpha) in macrophage-like synoviocytes (MLS) from patients with rheumatoid arthritis (RA), in human peripheral monocytes, and in murine RAW264.7 macrophages.
The concentrations of TNFalpha in culture supernatants of these cells were measured using enzyme-linked immunosorbent assay. The expression levels of various messenger RNAs (mRNA), such as those for TNFalpha, the mRNA-binding protein TIS11B, and luciferase, were measured using real-time quantitative polymerase chain reaction. The in vitro effects of butyrate on transcriptional regulation were evaluated by transfection with various reporter plasmids in RAW264.7 macrophages. The effects of TIS11B on TNFalpha expression were examined using an overexpression model of TIS11B in RAW264.7 cells.
Butyrate suppressed TNFalpha protein and mRNA production in MLS and monocytes, but paradoxically enhanced transactivation of the TNFalpha promoter. Expression of the AU-rich element (ARE)-binding protein TIS11B was up-regulated by butyrate. Induction of TNFalpha mRNA by lipopolysaccharide was significantly inhibited when TIS11B was overexpressed. Butyrate facilitated the degradation of luciferase transcripts containing the 3'-untranslated region (3'-UTR) of TNFalpha, and this effect was dependent on the ARE in the 3'-UTR that is known to be involved in the regulation of mRNA degradation.
These results indicate that butyrate suppresses TNFalpha expression by facilitating mRNA degradation mediated through a cis-acting ARE. Butyrate has the ability to regulate TNFalpha at the mRNA level and is therefore a potential therapeutic drug for RA patients.