Identification of TLR2 and TLR4-induced microRNAs in human mesenchymal stem cells and their possible roles in regulating TLR signals

Toll-like receptors (TLRs) are expressed in human bone marrow-derived mesenchymal stromal cells (BM-MSCs), and the activation of TLRs is important in proliferation, differ- entiation, migration and hematopoiesis-supporting functions of BM-MSCs. However, the molecular mechanisms underlying these processes remain to be elucidated. MicroRNAs (miRNAs) are involved in various biological functions by mediating mRNA degradation or inhibiting translation of target genes. The present study aimed to identify whether TLRs regulate the expression of miRNAs in BM-MSCs and elucidate the regula- tory roles of miRNAs. Illumina high-throughput sequencing was used to profile miRNAs expressed in BM‑MSCs stimu - lated with TLR2 agonist, PAM3CSK4 (PM) or TLR4 agonist, lipopolysaccharides (LPS). A marked expression change upon PM or LPS treatment was observed for 164 known miRNAs and six novel miRNAs that were identified. The expression of six novel miRNAs and 40 randomly selected known miRNAs was further validated by reverse transcription-quantitative polymerase chain reaction. In addition, bioinformatic methods were used to predict the potential target genes of the abundant known miRNAs. The gene ontology analysis demonstrated that predicted targets were enriched in the regulation of signal transduction, cellular processes and macromolecule meta- bolic processes. Kyoto Encyclopedia of Genes and Genomes pathway analysis suggested that these potential targets were involved in numerous important pathways, predominantly including mitogen-activated protein kinase, phosphati- dylinositol-4,5-bisphosphate 3-kinase-Akt, neurotrophin and cancer-associated signaling pathways. The present study aimed to identify the global expression change of miRNAs in BM-MSCs stimulated with LPS and PM, providing the oppor- tunity to further elucidate the roles of miRNAs in mediating TLR signals to regulate the functions of BM-MSCs.