Introduction:
Procalcitonin (PCT) has been reported to function as a predictive biomarker of post-operative infection. In this study, we aimed to explore the mechanisms underlying the regulation of PCT expression.

Material and methods:
72 children diagnosed with post-operative infection and 58 children without post-operative infection were recruited in this study. Computational analysis, luciferase assay, real-time PCR, Western-blot analysis, and assays of post-operative C-reactive protein (CRP), erythrocyte sedimentation rate (ESR) and PCT were performed to investigate the mechanisms underlying the regulation of PCT expression.

Results:
MiR-125b was found to repress STAT3 expression with putative binding sites in 3’UTR of STAT3. The levels of PCT and miR-125b in non-infection group remained stable from day 0 to day 5, while the level of PCT was increased in the infection group along with a decreased level of miR-125b from day 1 to day 5. The post-operative levels of CRP and ESR in both non-infection and infection groups were evidently increased in a time-dependent manner, but the levels of miR-106b and miR-20a in both non-infection and infection groups remained stable. The area under the curve (AUC) values of PCT, CRP, ESR, miR-125b, miR-106b and miR-20a demonstrated that only miR-125b and PCT were involved in infection. Transfection with miR-125b reduced STAT3 expression, while the activation of STAT3 by lipopolysaccharide (LPS) treatment up-regulated PCT production. Finally, miR-125b down-regulated the expression of PCT by targeting STAT3.

Conclusions:
Taken together, we suggested that miR-125b was involved in the prognosis and diagnosis of poster-operative infection by modulating the signaling pathway of miR-125b/STAT3/PCT.