Epigenetics and expression of key genes associated with cardiac fibrosis: NLRP3, MMP2, MMP9, CCN2/CTGF, and AGT

Abstract

Excessive inflammatory signaling and pathological remodeling of the extracellular matrix are important contributors to cardiac fibrosis and involve major changes in gene expression. We examined the relationships between tissue-specific expression and the epigenetics of five genes involved in these pathways, NLRP3, MMP2, MMP9, CCN2/CTGF, and AGT. The proteins encoded by these genes play major fibrosis-related roles in inflammasome formation, degradation of extracellular matrix proteins and remodeling of the extracellular matrix and vasculature, autocrine regulation of fibrosis, or cell signaling. Our analyses showed that the first four of these genes had super-enhancers (unusually strong enhancer clusters) that correlate with their very high expression in monocytes, neutrophils, fibroblasts, or venous cells. Expression of the gene encoding miR-223, a micro-RNA that plays an important role in downregulating NLRP3 protein levels, is also probably driven by the super-enhancer in which it is embedded. Enhancer chromatin for all these genes was inside as well as outside the gene body. While AGT, which encodes precursors of angiotensin II, lacked a super-enhancer, its tissue-specific expression profile correlates with the tissue-specific enhancer chromatin extending into its distant silent gene neighbor (CAPN9). Tissue-specific peaks of DNA hypomethylation, open chromatin (DNaseI hypersensitivity), and transcription factor binding were detected in subregions of these super-enhancers/enhancers that are likely to be the main drivers of expression of their associated gene. We found that CCN2/CTGF is co-expressed with its far-upstream neighbor LINC01013, a noncoding RNA gene, specifically in vein endothelial cells (HUVEC) and chondrocytes. Evidence from chromatin looping profiling (Hi-C) suggests coregulation of these genes in HUVEC. Our findings indicate the importance of understanding the often-overlooked roles of enhancers and their hypomethylated, transcription factor-binding subregions in the regulation of expression of fibrosis-related genes in normal and fibrotic tissue.