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

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

París

Congreso; 14th International Thyroid Congress; 2010

Sociedad Europea de Tiroides

Glucocorticoids (GCs) are widely used as antiinflammatory and immunosuppressive agents in the therapy of many autoimmune and allergic diseases and in transplantation to prevent rejection. Several studies have indicated the important 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-specific immune responses (Guermonprez et al., 2002). Given the remarkable plasticity of these cells, manipulation of their function to favor the induction of DC with immunogenic or tolerogenic properties could be exploited in order to stimulate or attenuate immune responses (Steinman & Banchereau, 2007). Mice DC are generated from bone marrow (immature DC:iDC) and the exposure to pro-inflammatory stimuli (lipopolysaccharide,LPS) generates mature DC (mDC) that stimulate T cells. We have provided evidence for thyroid hormone receptor (TR) 1 expression and triiodothyronine (T3) stimulatory action on DC (Mascanfroni et al, FASEB Jounal, 2008) by a mechanism involving T3 binding to cytosolic TR1 and Akt activation (Mascanfroni, Montesinos, et al., JBC,2010). Recently, we demonstrated that Dexamethasone (Dex: synthetic GC) reduced TR1 expression in DC by a mechanism that involved the glucocorticoid receptor (GR). The aim of this study was to further evaluate the effect of Dex on T3 action in DC and to analyze the signalling pathway involved. Mice DC were cultured from bone marrow with GM-CSF for 7 days. Afterwards, iDC were pulsed with Dex 10 nM, LPS 100 ng/ml (positive control) or T3 5 nM for 18 h. After cell harvesting, DC surface phenotype was determined by flow cytometry and cytokine production by ELISA. The ability of treated-DC to stimulate T cells was assessed in a mixed lymphocyte reaction (MLR). We measured Akt-phosphorylation by Western Blot. Results 1) the increment in maturation markers and IL-12-producing DC induced by T3 and LPS was abolished by Dex by a mechanism that involved GR (it was prevented by a GR antagonist: RU486). Besides, Dex increase Il-10 levels in DC maturated with T3 and LPS. 2) Dex abolished T3-effect inducing DC able to stimulate Il-10 and inhibited INF production by T cells in a MLR. 3) T3-induced Akt phosphorylation was inhibited by Dex. These results indicate that GC are able to act through GR on LPS and T3-activated DC by inhibiting production of the pro-inflammatory response by these cells. Moreover, GC prevent T cell activation induced by T3. Recently, we provide evidence that the exposure of DC to T3 resulted in rapid and sustained increase in Akt phosphorylation dependent on TRβ1, which was essential for supporting T3-induced DC maturation and IL-12 production. In this regard, in the present study Dex prevented Akt activation induced by T3, probably because of the downregulation of TRβ1 induced by Dex. This finding is of physiologic and therapeutic relevance as Akt activation has been shown to be of critical importance for promoting DC survival which is an essential characteristic in DC-based tumor vaccines (Park et al., 2006). Hence, the use of GC in antitumor therapy should be reconsidered because they could affect the survival of DC directed to tumor antigen.