Experimental Biology 2010: Macrolide Repression Of MUC5AC Gene Expression In Human Lung Epithelial Cells

Purpose of Study: Overproduction of mucin glycoproteins (mucins) is a characteristic phenotype of chronic lung diseases. Inflammatory mediators upregulate mucin gene expression in vitro while glucocorticoids and macrolides repress mucin gene expression. Macrolide antibiotics have anti-microbial effects but also appear to have an anti-inflammatory role in chronic lung diseases. Whether their reported effect on mucin gene expression in lung epithelial cells is due to a direct effect on gene regulation or through an indirect effect on inflammatory mediators is unresolved. The purpose of this study is to evaluate the effects of two macrolides, azithromycin and erythromycin, on MUC5AC gene expression in lung epithelial cells in a concentration and time based manner and to determine whether macrolides, like glucocorticoids, transcriptionally repress MUC5AC gene expression.

Methods Used: Normal primary human bronchial epithelial (HBE) cells were cultured, differentiated under air-liquid interface conditions, and exposed in duplicate to azithromycin and erythromycin in concentration ranges from 10-4 to 10-7 M for 24 h. HBE cells were also exposed to 10-6 M macrolides for 1, 4, 8, and 24 h. MUC5AC mRNA levels were analyzed by real time RT-PCR and normalized to ß-actin. Transcriptional analysis of MUC5AC gene expression will be performed following transfection of MUC5AC promoter luciferase constructs into lung epithelial cells.

Summary of Results: MUC5AC mRNA levels had a decreasing trend with exposure to erythromycin at concentrations of 10-6 and 10-7 M (36% and 45% decrease, respectively) at 24 h. In contrast, MUC5AC mRNA levels decreased 24% at a concentration of 10-5 M of azithromycin. Experiments to determine the temporal effects of macrolides on MUC5AC gene repression are underway.

Conclusions: Erythromycin exhibited a more potent inhibition of MUC5AC gene expression than azithromycin in primary differentiated HBE cells in the absence of inflammatory mediators, indicating that macrolides, like glucocorticoids, directly repress MUC5AC gene expression. Future experiments will investigate mechanisms whereby macrolides regulate mucin gene expression.