Expression Profiling and Functional Characterization of MicroRNAs in Apical Periodontitis.

ABSTRACT Introduction MicroRNAs (miRNAs) are evolutionarily conserved small non-coding RNAs that may orchestrate the pathogenesis of apical periodontitis (AP). This study aimed to identify differentially expressed miRNAs and investigate their target gene pathways in AP. Methods Total RNA was extracted from 10 human AP and 2 healthy apical tissues (controls) and subjected to miRNA sequencing for identification of differentially expressed miRNAs (>1.5-fold changes). The function of the most upregulated miRNA was further studied in vitro. MiR-10a-5p mimics and inhibitors were introduced to human stem cells from the apical papilla (SCAPs) and K-562 cells, challenged with lipopolysaccharide (LPS), and expressions of predicted target genes were examined via quantitative reverse transcription-polymerase chain reaction and RNA sequencing (RNA-seq). Results A total of 852 miRNAs were identified, of which 12 were significantly upregulated (1.54-8.44 fold), and 94 were significantly downregulated (0.14-0.67 fold) in AP. Predicted target genes of these miRNAs are involved in inflammation, pain, and related pathways. MiR-10a-5p showed the highest expression levels in AP. Overexpression of miR-10a-5p in LPS-challenged SCAPs resulted in downregulation of mRNA levels of TNFA and upregulation of interleukin IL10. RNA-sequencing of K-562 cells treated with miR-10a-5p mimics and inhibitors identified miR-10a-5p target genes associated with multiple pathways, including macrophage-mediated inflammation and coagulation pathways. Conclusions Over 100 miRNAs were differentially expressed in AP and appeared to be involved with modulation of genes in inflammatory and immune pathways. MiR-10a-5p was the most significantly upregulated miRNA in AP and may play a critical role in suppressing inflammation and promoting healing.