RFX1 downregulation contributes to TLR4 overexpression in CD14+ monocytes via epigenetic mechanisms in coronary artery disease

Abstract

Background: Toll-like receptor 4 (TLR4) expression is increased in activated monocytes, which play a critical role in the pathogenesis of coronary artery disease (CAD). However, the mechanism remains unclear. Regulatory factor X1 (RFX1) is a critical transcription factor regulating epigenetic modifications. In this study, we investigated whether RFX1 and epigenetic modifications mediated by RFX1 contributed to the overexpression of TLR4 in activated monocytes. Results: Compared with those of the controls, the mRNA and protein expression of RFX1 were downregulated and the mRNA expression of TLR4 was upregulated in CD14+ monocytes obtained from CAD patients and CD14+ monocytes obtained from healthy controls treated with low-density lipoprotein (LDL). The mRNA expression of RFX1 was negatively correlated with the mRNA expression of TLR4 in CD14+ monocytes. RFX1 knockdown led to the overexpression of TLR4 and the activation of CD14+ monocytes. In contrast, the overexpression of RFX1 inhibited TLR4 expression and the activation of CD14+ monocytes stimulated with LDL. Moreover, TLR4 was identified as a target gene of RFX1. The results indicated that RFX1 downregulation contributed to the decreased DNA methylation and histone H3 lysine 9 trimethylation and the increased H3 and H4 acetylation in the TLR4 promoter via the lack of recruitments of DNA methyltransferase 1 (DNMT1), histone deacetylase 1 (HDAC1), and histone-lysine N-methyltransferase SUV39H1 (SUV39H1), which were observed in CD14+ monocytes of CAD patients. Conclusions: Our results show that RFX1 expression deficiency leads to the overexpression of TLR4 and the activation of CD14+ monocytes in CAD patients by regulating DNA methylation and histone modifications, which highlights the vital role of RFX1 in the pathogenesis of CAD.