Increased miR‐223 expression in foetal organs is a signature of acute chorioamnionitis with systemic consequences

Acute chorioamnionitis, frequently observed in preterm placentas, is a major risk factor for the development of infection and non‐infection‐related adverse perinatal outcomes. MicroRNAs play important roles in immune cell development and function as well as in the development of cancers and neurologic diseases. We sought to investigate the changes in microRNA‐223 (miR‐223) expression and the functional significance of the changes in miR‐223 expression in foetal organs in the presence of acute chorioamnionitis. Using formalin‐fixed, paraffin‐embedded (FFPE) tissue samples from foetal or neonatal autopsy cases, which are the most practical option to study the changes in several organs simultaneously, miR‐223 expression profiles in foetal thymus, lung and liver were compared between cases with and without acute chorioamnionitis. Total RNA was extracted from FFPE specimens and qRT‐PCR was conducted. miR‐223‐3p expression levels in foetal thymus (2.55‐fold), lung (1.93‐fold) and liver (1.70‐fold) were significantly higher in cases with acute chorioamnionitis than in those without. Transfection of pre‐miR‐223‐3p in Jurkat cells and luciferase assay and ribonucleoprotein immunoprecipitation followed by qRT‐PCR analysis confirmed the binding of miR‐223 to the 3′ untranslated region (3′UTR) of forkhead box O1 (FoxO1) mRNA and the regulation of FoxO1 by miR‐223. We report for the first time that foetuses with inflammation in the chorioamniotic membranes show increased expression of miR‐223 in the thymus, lung and liver. Furthermore, FoxO1 is a target of miR‐223. These findings suggest that post‐transcriptional regulation of genes by miR‐223 is a component of the foetal inflammatory response, which has systemic consequences in the foetus.