Role of microRNAs in immunoregulatory functions of epithelial cells.

Epithelial cells (ECs) provide the first line of defense against microbial threats and environmental challenges. They participate in the host's immune responses via the expression and secretion of various immune-related molecules such as cytokines and chemokines, as well as interaction with immune cells. A growing body of evidence suggests that the dysregulated function of ECs can be involved in the pathophysiology of a broad range of infectious, autoimmune, and inflammatory diseases, including inflammatory bowel disease (IBD), asthma, multiple sclerosis, and rheumatoid arthritis. To maintain a substantial immunoregulatory function of ECs, precise expression of different molecules and their regulatory effects are indispensable. MicroRNAs (miRNAs, miRs) are small non-coding RNAs that regulate gene expression commonly at post-transcriptional level through degradation of target messenger RNAs (mRNAs) or suppression of protein translation. MiRNAs implicate as critical regulators in many cellular processes, including apoptosis, growth, differentiation, and immune response. Due to the crucial roles of miRNAs in such a vast range of biological processes, they have become the spotlight of biological research for more than two decades, but we are still at the beginning stages of the use of miRNA-based therapies in the improvement of human health. Hence, in the present paper, attempts are made to provide a comprehensive overview with regard to the roles of miRNAs in the immunoregulatory functions of ECs. A better understanding of the molecular mechanisms through which immunoregulatory properties of ECs are manifested, could aid the development of efficient strategies to prevent and treat multiple human diseases.