Altered miR-146a expression in Sjögren's syndrome and its functional role in innate immunity.

MicroRNAs (miRNAs), small non-coding RNA molecules that post-transcriptionally regulate gene expression, are known to play key roles in regulating immune responses and autoimmunity. We investigated miR-146a expression in Sjögren's syndrome (SjS) patients as well as in the SjS-prone C57BL/6.NOD-Aec1Aec2 mouse model, to elucidate its involvement in SjS pathogenesis. Expression of miR-146a was examined in the PBMCs of 25 SjS patients and ten healthy donors, as well as in PBMCs, salivary and lacrimal glands of SjS-prone mice and WT C57BL/6J mice. Functional assays using THP-1 human monocytes were conducted to determine the biological roles of miR-146a in innate immunity. Expression of miR-146a was significantly increased in SjS patients compared with healthy controls, and was upregulated in the salivary glands and PBMCs of the SjS-prone mouse at both 8 wk (prior to disease onset) and 20 wk (full-blown disease) of age. More importantly, functional analysis revealed roles for miR-146a in increasing phagocytic activity and suppressing inflammatory cytokine production while migration, nitric oxide production and expression of antigen-presenting/costimulatory molecules are not affected in human monocytic THP-1 cells. Taken together, our data suggest that abnormal expression/regulation of microRNAs in innate immunity may contribute to, or be indicative of, the initiation and progression of SjS.