miRNA-125b regulates TNF-α production in CD14+ neonatal monocytes via post-transcriptional regulation

Neonatal monocytes express lower miR‐125b, a negative regulator of TNF‐α expression, resulting in higher TNF‐α responses after LPS stimulation. Neonates, although deficient in cell immunity, frequently reveal sepsis with augmented proinflammatory reactions. Here, we found that neonatal monocytes produced significantly higher TNF‐α mRNA and protein than adult monocytes. Assessment of the transcriptional factor found no significant difference of NF‐κB p65 level between neonatal and adult monocytes. Addition of Act D to access the half‐life of TNF‐α mRNA revealed no significant difference of the LPS‐induced TNF‐α mRNA half‐life between them, whereas CHX increased neonatal TNF‐α mRNA significantly. This suggests that a post‐transcriptional mechanism involves the augmentation of TNF‐α production by neonatal monocytes. To examine whether miRNA was involved in the post‐transcriptional regulation, differential displays of miRNA array between neonatal and adult MNCs were performed, along with the discovery of hsa‐miR‐103, hsa‐miR‐125b, hsa‐miR‐130a, hsa‐miR‐454‐3p, and hsa‐miR‐542‐3p, which were greater than a twofold decrease or increase after LPS treatment for 4 h. The functional validation identified that miR‐125b decreased significantly in association with higher TNF‐α expression by neonatal monocytes after LPS stimulation. Transfection of the miR‐125b precursor into neonatal monocytes significantly repressed the TNF‐α mRNA and protein expression, suggesting that miR‐125b negatively regulates TNF‐α expression in neonatal monocytes. Modulation of miRNA expression may be used to regulate TNF‐α production in newborns with altered proinflammatory reactions.