Epigenetic regulation of MUC5AC in airway epithelial cells by butyrate

Abstract

MUC5AC is a mucin that forms a gel on the surface of airway epithelium and plays a crucial role in regulating mucociliary clearance and innate defense of the lung. Given incessant exposure to external and internal stimuli leading to mucus hyperproduction, there must be an endogenous mechanism to maintain and control this production under homeostasis and diseased condition. Here, I report that butyrate, a metabolite of gut microbiota, strongly suppresses MUC5AC production at its low micromolar concentrations in airway epithelial cells. Butyrate nearly completely abolishes MUC5AC expression induced by several inflammatory mediators, including EGF, LPS, PMA, ROS, and lipid mediator. In line, butyrate upregulates FOXA2, which inhibits goblet cell differentiation, while downregulating SPDEF and FOXA3, goblet cell metaplasia-promoting transcriptions factors. Butyrate exerts its inhibitory effect independent of its known receptors nor does it influence the EGFR signaling pathway. Chromatin immunoprecipitation analysis shows that histone H3K27 acetylation is increased at proximal and distal promoter regions of the MUC5AC gene in response to EGF, but returns to baseline in the presence of butyrate. Binding of Sp1, a transcription factor that mediates EGF-mediated activation of MUC5AC transcription, is also significantly reduced upon butyrate treatment. Furthermore, at the transcription start sites of SPDEF and FOXA2 butyrate counteracts their respective levels of H3K27 acetylation altered following EGF stimulation, suggesting that these genes are epigenetically linked to MUC5AC. As such, butyrate reprograms transcriptional and epigenetic regulation of MUC5AC production, which might be a general mechanism for controlling MUC5AC production in homeostasis and diseased states, given its natural occurrence in our bodies.

Running Title: Silencing of MUC5AC by butyrate