New insights into Glucocorticoid effect on T3 action in mice dendritic cells

MONTESINOS MM; ALAMINO VA; MASCANFRONI ID; SUSPERREGUY S; MASINI-REPISO AM; RABINOVICH GA; PELLIZAS CG

París

Congreso; 14th International Thyroid Congress; 2010

American Thyroid Association, European Thyroid Society, Latin American Thyroid Society, Assia and Oceania Thyroid Association

Abstract: Glucocorticoids (GC) are widely used as antiinflammatory and immunosuppressive agents in the therapy ofmany autoimmune and allergic diseases and in transplantation to prevent rejection. Several studies have indicated theimportant role of antigen-presenting cells(APC) in GC-mediated suppression of immunity. Among APC, dendritic cells(DC) are considered to be the most efficient and indispensable to stimulate naïve T cells and induce antigen-specificimmune responses (Guermonprez et al., 2002). Given the remarkable plasticity of these cells, manipulation of theirfunction to favor the induction of DC with immunogenic or tolerogenic properties could be exploited in order to stimulateor attenuate immune responses (Steinman & Banchereau, 2007). Mice DC are generated from bone marrow (immatureDC:iDC) and the exposure to pro-inflammatory stimuli (lipopolysaccharide,LPS) generates mature DC (mDC) thatstimulate T cells. We have provided evidence for thyroid hormone receptor (TR) b1 expression and triiodothyronine (T3)stimulatory action on DC (Mascanfroniet al, FASEB Journal, 2008) by a mechanism involving T3 binding to cytosolicTRb1 and a rapid and sustained Akt activation dependent on TRb1 and essential for supporting T3-induced DCmaturation and IL-12 production (Mascanfroni et al., J BiolChem, 2010). Recently, we demonstrated that Dexamethasone(Dex: synthetic GC) reduced TRb1 expression in DC by a mechanism that involved the glucocorticoid receptor (GR) (Montesinos et al., Arquivos Brasileiros de Endocrinologia & Metabologia, 2009). The aim of this study was to furtherevaluate the effect of Dex on T3 action in DC and to analyze the signalling pathway involved. Mice DC were cultured frombone marrow with GM-CSF for 7 days. Afterwards, iDC were pulsed with Dex 10 nM, LPS 100 ng/ml (positive control) orT3 5 nM for 18 h. After cell harvesting, DC surface phenotype was determined by flow cytometry and cytokine productionby ELISA. The ability of treated-DC to stimulate T cells was assessed in a mixed lymphocyte reaction (MLR). Wemeasured Akt-phosphorylation by Western Blot. Results: 1) the increment in DCmaturation markers and IL-12-producingDC induced by T3 and LPS was abolished by Dex by a mechanism that involved GR (it was prevented by a GRantagonist: RU486). Besides, Dex increase IL-10 levels in DC maturated with T3 and LPS. 2) Dex abolished T3-effectinducing DC able to stimulate IL-10 and toinhibit INFg production by T cells in a MLR. 3) T3-induced Akt phosphorylationwas inhibited by Dex. These results indicate that GC are able to act through GR on LPS and T3-activated DC byinhibiting production of the pro-inflammatory response by these cells. Moreover, GC prevent T cell activation induced byT3.  As the present work demonstrates that Dex prevented Akt activation induced by T3 by a mechanism that mayinvolvethe downregulation of TRβ1 induced by Dex, the findings achieved are of physiologic and therapeutic relevance asAkt activation has been shown to be of critical importance for promoting DC survival which is an essential requirement inDC-based tumor vaccines (Park et al., 2006). Hence, the use of GC in antitumor therapy should be reconsidered, mainlyin specific protocols involving DC directed to tumor antigen.