• Nicola Dalbeth, Bregina Pool, Odette M Shaw, Jacquie L Harper, Paul Tan, Christopher Franklin, Meaghan E House, Jillian Cornish, and Dorit Naot.
• Bone and Joint Research Group, Department of Medicine, University of Auckland, Auckland, New Zealand.
• Ann. Rheum. Dis. 2015 Apr 1; 74 (4): 786-90.

ObjectivesMicroRNAs (miRNA) are small non-coding RNAs that function as post-transcriptional repressors of gene expression. We hypothesised that miRNA regulate gene expression of proinflammatory cytokines in response to monosodium urate (MSU) crystals.MethodsWe stimulated human monocytic THP-1 cells with MSU crystals and examined miRNA and proinflammatory cytokine gene expression. The effects of miR-146a overexpression were examined by transfecting THP-1 cells with miR-146a precursor. miR-146a expression was examined in the urate peritonitis model, in peripheral blood mononuclear cells from people with gout and control participants, and in gouty tophus samples.ResultsMSU crystals increased miR-146a expression in THP-1 cells, but not other miRNA implicated in interleukin (IL)-1β regulation. Overexpression of miR-146a expression reduced MSU crystal-induced IL-1β, tumour necrosis factor-α (TNFα), monocyte chemoattractant protein-1 (MCP-1) and IL-8 gene expression. In the urate peritonitis model, reduced miR-146a expression was observed during the acute inflammatory response to MSU crystal injection. In people with intercritical gout, peripheral blood mononuclear cells expressed significantly higher levels of miR-146a, compared with normouricaemic and hyperuricaemic control participants and those with acute gout flares. Expression of miR-146a was also observed in all tophus samples.ConclusionsCollectively, these data suggest that miR-146a is a transcriptional brake that is lost during the acute inflammatory response to MSU crystals.Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.

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