Correlation between miRNA-126 expression abnormality and hypo-methylation of DNA in T cells of rheumatoid arthritis patients with respiratory failure

Rheumatoid arthritis is frequently complicated with respiratory failure, thus threatening patients’ lives. Hypo-methylation of T cells plays a critical role in multiple diseases. DNMT1 is important for gene methylation and is the target gene of microRNA (miR)-126, which thus might regulate T cell gene methylation. This study, therefore, examined the expression of miR-126 during DNG hypo-methylation in T cells from rheumatoid arthritis patients, to illustrate the relationship between two factors. 33 rheumatoid arthritis patients complicated with respiratory failure were recruited based on ACR criteria, in parallel with 33 healthy individuals. 5 ml venous blood samples were collected to sort out T cells, whose RNA was extracted to quantify miR-126 and DNMT1 expression by qRT-PCR. Methylation test kit was used to reveal the change of methylation level of EGFL7 in T cells. T cell sorting had higher than 98% of purity in this study. Expression of miR-126 in study group was about 3.32 folds of control group, with significant difference (P<0.05). DNMT1 expression was remarkably lower than control group (P<0.05), and was negatively correlated with miR-126 expression (r=0.643, P=0.021). Methylation level of EGFL7 in disease group was significantly decreased compared to control group. Disease group showed lower DNA methylation level in T cells. In rheumatoid arthritis patients, miR-126 expression is negatively correlated with T cell methylation, probably via inhibition on DNMT1 expression after miR-126 up-regulation, causing hypo-methylation of T cell DNA. Elevated EGFL7 methylation further caused hypo-methylation of T cells via up-regulating miR-126.