MicroRNA-21 Negatively Regulates Treg Cells Through a TGF-β1/Smad-Independent Pathway in Patients with Coronary Heart Disease

Background: CD4+CD25+FoxP3+ regulatory T cells (Treg cells) play a protective role against the development and progression of the inflammatory disease atherosclerosis (AS). MicroRNA-21 (miR-21) is expressed in Treg cells and is up-regulated in the context of AS and other inflammatory diseases. Aims: This study aimed to determine the role of miR21 in Treg cell regulation and gene expression during the development of AS in patients with coronary heart disease (CHD). Methods and Results: MiR-21 expression in peripheral blood mononuclear cells (PBMCs) was significantly up-regulated in patients with CHD (acute myocardial infarction (AMI) group, n=24; unstable angina (UA) group, n=21; stable angina (SA) group, n=24) compared with patients with chest pain syndrome (CPS, n=27), and miR21 expression showed an increasing trend from SA to UA to AMI patients. Moreover, flow cytometry analysis indicated that the frequencies of circulating Treg cells decreased in a manner proportionate opposite with the level of miR-21. Quantitative real-time PCR (qRTPCR) revealed a decrease in mRNA expression of forkhead box P3 (foxp3), transforming cell growth factor beta 1(TGF-beta 1) and smad7 (a known target gene of miR-21).ELISA analysis revealed a decrease in TGF-beta 1 secreted into the plasma. In addition, we transfected PBMCs with a miRNA negative control (NS-m), a miR-21 mimic (miR-21-m), a miRNA inhibitor negative control (NS-i),or a miR-21 inhibitor(miR-21-i). Up-regulation of miR-21 decreased the frequency of circulating Treg cells, decreased the expression levels of foxp3, TGF-p1 and smad7, and decreased the amount of TGF-beta 1 secreted into the plasma. Consistent with these observations, miR-21 down-regulation increased the frequency of circulating Treg cells, increased the expression of foxp3, TGF-beta 1 and smad7, and increased the amount of TGF-beta 1 secreted into the plasma. Conclusions: Because the smad7 expression pattern was similar to that of TGF-p, our study suggests that miR-21 can negatively regulate the frequency of circulating Treg cells through a TGF-p1/smad-independent signaling pathway in PBMCs. Copyright (C) 2015 S. Karger AG, Basel