Background: microRNAs (miRNAs) are a class of small (1825 nucleotides), non-coding RNA molecules. They play an important role in the regulation of gene expression by either suppressing translation of genes or inducing their mRNA degradation. Several miRNA species are expressed in adipose tissue and involved in adipocyte function.
Objective and hypotheses: Obesity leads to the infiltration of macrophages into adipose tissue causing local inflammation. In an Affymetrix miRNA array we found miR-146a expression strongly upregulated in adipocytes under inflammatory conditions. The aim of this project was to elucidate the biological function of miR146a in adipocytes.
Method: SGBS adipocytes were cultured with human THP-1 macrophage conditioned medium (MacCM) to mimic adipose tissue inflammation. Gain-of-function experiments were performed by transfection of miR146a mimics into SGBS adipocytes.
Results: miR146a is down-regulated during adipogenic differentiation of SGBS cells as well as human primary preadipocytes. However, the expression of miR146a was significantly upregulated in SGBS adipocytes treated with 10% MacCM (24 h: 16.9-fold vs vehicle control). Transfection of miR146a mimic into adipocytes resulted in a down-regulation of IRAK1 and TRAF6 expression, two known target genes of miR146a. Upon MacCM stimulation adipocytes transfected with miR146a mimic showed a significantly reduced activation of the NFkB signalling pathway and a reduced upregulation of IL-8 secretion (24 h, ctrl+MacCM: 7.0 ng/ml, miR-146a mimic+MacCM: 3.1 ng/ml).
Conclusion: miR146 is a fine tuner of immune responses in many cell types. We show here for the first time that miR146a operates in a negative feedback loop in adipocytes to control the inflammatory response caused by macrophage-secreted factors.
Funding: This work was supported by an ESPE-RU collaborative project grant.
01 Oct 2015 - 03 Oct 2015