DIO2 modifies inflammatory responses in chondrocytes

Objective: Selenium neutralizes interleukin-1 beta (IL-1 beta) induced inflammatory responses in chondrocytes. We investigated potential mechanisms for this through in vitro knock down of three major selenoproteins, Iodothyronine Deiodinase-2 (DIO2), Glutathione Peroxidase-1 (GPX1), and Thioredoxin Reductase-1 (TR1) in primary human chondrocytes. Methods: Primary human chondrocytes were transfected with scrambled small interfering ribonucleic acid (siRNA) or siRNA specific for DIO2, GPX1 and TR1. After 48 h, transfected cells were cultured in serum free media for 48 h, with or without 10 pg/ml IL-1 beta for the final 24 h. The efficiency of siRNAs was confirmed by quantitative Real Time-Polymerase Chain Reaction (qRT-PCR) and Western blot analysis. The gene expression, by qRT-PCR, of cyclooxygenase-2 (COX2), IL-1 beta, and Liver X receptor (LXR) alpha and beta was evaluated to determine the impact of selenoprotein knockdown on inflammatory responses in chondrocytes. Results: The messenger RNA (mRNA) expression of DIO2, GPX1, and TR1 was significantly decreased by the specific siRNAs (reduced 56%, P = 0.0004; 96%, P < 0.0001; and 66%, P < 0.0001, respectively). Suppression of DIO2, but not GPX1 or TR1, significantly increased (similar to 2-fold) both basal (P = 0.0005) and IL-1 beta induced (P < 0.0001) COX2 gene expression. Similarly, suppression of DIO2 significantly increased (similar to 9-fold) IL-1 beta induced IL-1 beta gene expression (P = 0.0056) and resulted in a 32% (P = 0.0044) decrease in LXR alpha gene expression but no effect on LXR beta. Conclusions: Suppression of the selenoprotein DIO2 resulted in strong pro-inflammatory effects with increased expression of inflammatory mediators, IL-1 beta and COX2, and decreased expression of LXRa suggesting that this may be the upstream target through which the anti-inflammatory effects of DIO2 are mediated. (C) 2012 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.