Epigenetic Regulation of Interleukin 6 by Histone Acetylation in Macrophages and Its Role in Paraquat-Induced Pulmonary Fibrosis

Abstract

Overexpression of interleukin 6 (<i>IL-6</i>) has been proposed to contribute to pulmonary fibrosis and other fibrotic diseases. However, the regulatory mechanisms and the role of <i>IL-6</i> in fibrosis remain poorly understood. Epigenetics refers to alterations of gene expression without changes in the DNA sequence. Alternation of chromatin accessibility by histone acetylation acts as a critical epigenetic mechanism to regulate various gene transcriptions. The goal of this study was to determine the impact of <i>IL-6</i> in paraquat (PQ)-induced pulmonary fibrosis and to explore whether the epigenetic regulations may play a role in transcriptional regulation of <i>IL-6</i>. In PQ-treated lungs and macrophages, we found that the mRNA and protein expression of <i>IL-6</i> was robustly increased in a time-dependent and a dose-dependent manner. Our data demonstrated that PQ-induced <i>IL-6</i> expression in macrophages plays a central role in pulmonary fibrosis through enhanced epithelial-to-mesenchymal transition (EMT). <i>IL-6</i> expression and its role to enhance PQ-induced pulmonary fibrosis were increased by histone deacetylase (HDAC) inhibition and prevented by histone acetyltransferase (HAT) inhibition. In addition, the ability of CRISPR-ON transcription activation system (CRISPR-ON) to promote transcription of <i>IL-6</i> was enhanced by HDAC inhibitor and blocked by HAT inhibitor. Chromatin immunoprecipitation experiments revealed that HDAC inhibitor increased histones activation marks H3K4me3 and H3K9ac at <i>IL-6</i> promoter regions. In conclusion, <i>IL-6</i> functioning through EMT in PQ-induced pulmonary fibrosis was regulated dynamically by HDAC and HAT both <i>in vitro</i> and <i>in vivo via</i> epigenetically regulating chromatin accessibility.