Endocrine Abstracts

Background: The expression of thyroid-specific genes [thyroglobulin (Tg) and sodium iodide symporter (NIS)] is modulated by several cytokines (IL-1, IFNγ, TGF-ß) and it is down-regulated in Hashimoto’s thyroiditis (HT). Also, lymphocytic infiltration and inflammation in HT results in intra-thyroidal accumulation of hyaluronan (HA). During inflammation, HA can be degraded into small fragments, able to up-regulate pro-inflammatory genes by stimulating the toll-like receptors (mostly TLR-4) and CD44, via NF-kB activation. The present study was aimed to evaluate the potential role of small HA fragments, as mediators of TLR-4 and CD44 activation, inIL-1-beta-induced inflammation in human thyrocytes in vitro.

Methods: Primary thyrocytes were obtained from patients undergone surgery for benign thyroid nodules. Cultured cells were treated for 24 h with IL-1β (5 ng/ml), with and without TLR-4 and CD44 blocking antibodies, and the hyaluronan binding protein (HABP), which inhibits HA activity. HA concentration was measured by ELISA, while molecular size was assayed by agarose gel electrophoresis. mRNA and related protein levels of TLR4, CD44, interleukin-6 (IL-6), matrix metalloproteinase-13 (MMP-13), thyroglobulin (Tg) and sodium iodide symporter (NIS)were evaluated by real-time PCR, Western Blot and ELISA, respectively. NF-kB activation was also assayed.

Results: IL-1beta induced an increase of HA production and accumulation, that primarily consisted of low molecular weight (LMW) fragments. TLR4 and CD44 levels were higher than controls in thyrocytes treated with IL-1beta. IL-1beta also induced NF-kB up-regulation and increased IL-6 and MMP-13, while reduced Tg and NIS expression. Treatment of thyrocytes exposed to IL-1beta with specific TLR-4 and CD44 blocking antibodies and/or HABP, reduces NF-kB activation and pro-inflammatory mediators production, while partially restore Tg and NIS levels. These findings suggest that IL-1beta exerts inflammatory activity in part via TLR-4 and CD44 by the mediation of small HA fragments derived from HA depolymerization.

Conclusion: In human thyrocytes, IL-1β promotes accumulation of LMW HA fragments anddown-regulate thyroid-specific genes expression via CD44/TLR-4/NF-kB signaling activation. Accumulation of HA pro-inflammatory fragments may play a role in the pathogenesis of thyroid inflammation and damage in autoimmune thyroid disease.