Butyrate Silences MUC5AC in Airway Epithelial Cells Through Histone Deacetylation at Its Promoter Region

Mucin 5AC (MUC5AC) is a mucin that forms a gel on the surface of the airway epithelium, and its hyperproduction plays a pathological role in chronic inflammatory airway diseases. Short-chain fatty acids (SCFAs), microbial fermentation products of dietary fiber in the gut, have been shown to significantly impact the development of allergic airway disease. Nonetheless, little is known about whether and how SCFAs influence the function of airway epithelial cells. In this study, we investigated the direct effects of SCFAs, especially butyrate, on MUC5AC production and the underlying mechanisms.

NCI-H292 cells and normal human bronchial epithelial cells were treated with inflammatory mediators and butyrate. MUC5AC expression, signal transduction pathways, and promoter histone acetylation were assessed using quantitative real-time polymerase chain reaction, immunoblotting, immunocytochemistry, and chromatin immunoprecipitation (ChIP) assays.

Among SCFAs, butyrate has a strong inhibitory effect on MUC5AC expression at low micromolar concentrations in airway epithelial cells. Butyrate abolished MUC5AC expression induced by various inflammatory mediators, including epidermal growth factor (EGF). In line, butyrate upregulated forkhead box protein A (FOXA) 2, which inhibits goblet cell differentiation, while it downregulated SAM-pointed domain-containing ETS transcription factor (SPDEF) and FOXA3, which promote goblet cell metaplasia. Interestingly, butyrate exerts its inhibitory effect independent of its receptors and does not interfere with the early phase of EGF receptor signaling pathway. ChIP analysis revealed that butyrate increased H3K27 acetylation in both the proximal and distal regions of the MUC5AC promoter at the late phase following EGF stimulation, but this acetylation returned to baseline in the presence of butyrate.

Our findings indicate that butyrate plays a critical role in reprogramming the transcriptional and epigenetic regulation of MUC5AC production. This may represent a general mechanism for controlling MUC5AC production in both healthy and diseased states.