Augmented interleukin 6 production by rat thyrocytes (FRTL5): effect of interleukin 1 beta and thyroid-stimulating hormone

Evaluation of hypothalamus-pituitary-thyroid axis function by chronic perchlorate exposure in male rats

Perchlorate is a widespread endocrine disruptor that was previously correlated with increased serum TSH levels and decreased thyroid hormones production both in animals and humans. Even so, the regulation of gene/protein expression in the hypothalamus, pituitary and thyroid by chronic perchlorate exposure was not completely elucidated. Therefore, this study aimed to investigate the underlying mechanisms involved in the disruption of hypothalamus-pituitary-thyroid axis by chronic perchlorate exposure. Male Wistar rats were treated or not with NaClO₄ in the drinking water (35 mg/Kg/day) for 60 days. Thereafter, hormone/cytokines serum levels were measured through multiplex assays; genes/proteins expression were investigated by qPCR/Western Blotting and thyroid morphology was evaluated through histological analysis. Serum TSH levels were increased and serum T₄ /T₃ levels were decreased in perchlorate-treated animals. This treatment also altered the thyrotropin-releasing hormone mRNA/protein content in the hypothalamus. Additionally, the expression of both subunits of TSH were increased in the pituitary of perchlorate-treated rats, which also presented significant alterations in the thyroid morphology/gene expression. Furthermore, perchlorate exposure reduced liver Dio1 mRNA expression and increased the content of pro-inflammatory cytokines in the thyroid and the serum. In conclusion, our study adds novel findings about the perchlorate-induced disruption of the hypothalamus-pituitary-thyroid axis gene/protein expression in male rats. The data presented herein also suggest that perchlorate induces thyroid and systemic inflammation through the increased production of cytokines. Taken together, our results suggest that perchlorate contamination should be monitored, especially in the individuals most susceptible to the deleterious effects of reduced levels of thyroid hormones.

Regulation of IL-1 receptor antagonist by TSH in fibrocytes and orbital fibroblasts

CONTEXT

The IL-1 family plays important roles in normal physiology and mediates inflammation. The actions of IL-1 are modulated by multiple IL-1 receptor antagonists (IL-1RA), including intracellular and secreted forms. IL-1 has been implicated in autoimmunity, such as that occurring in Graves' disease (GD) and its inflammatory orbital manifestation, thyroid-associated ophthalmopathy (TAO). We have previously reported that CD34(+) fibrocytes, monocyte-lineage bone marrow-derived cells, express functional TSH receptor, the central antigen in GD. When activated by TSH, they produce IL-6, IL-8, and TNF-α. Moreover, they infiltrate the orbit in TAO in which they transition into CD34(+) fibroblasts and comprise a population of orbital fibroblasts (OFs). Little is known currently about any relationship between TSH, TSH receptor, and the IL-1 pathway.

OBJECTIVE

The objective of the study was to determine whether TSH regulates IL-1RA in fibrocytes and OFs.

DESIGN/SETTING/PARTICIPANTS

Fibrocytes and OFs were collected and analyzed from healthy individuals and those with GD in an academic clinical practice.

MAIN OUTCOME MEASURES

Real-time PCR, Western blot analysis, reporter gene assays, and cell transfections were performed.

RESULTS

TSH induces the expression of IL-1RA in fibrocytes and GD-OFs. The patterns of induction diverge quantitatively and qualitatively in the two cell types. This results from relatively small effects on gene transcription-related events but a greater influence on secreted IL-1RA and intracellular IL-1RA mRNA stabilities. These actions of TSH are dependent on the intermediate induction of IL-1α and IL-1β.

CONCLUSIONS

Our findings for the first time directly link activities of the TSH and IL-1 pathways. Furthermore, they identify novel molecular interactions that could be targeted as therapy for TAO.

Activation of the cAMP pathway synergistically increases IL-1-induced IL-6 gene expression in FRTL-5 thyroid cells: involvement of AP-1 transcription factors

Interleukin-6 (IL-6) is a multifunctional cytokine involved in autoimmune thyroid diseases such as Hashimoto's thyroiditis and Graves' disease. IL-6 is produced by infiltrating immune cells and by thyrocytes. In the latter cell type, secretion of IL-6 is stimulated notably by interleukin-1 (IL-1), thyroid-stimulating hormone (TSH) or forskolin (Fk), a cAMP elevating agent. We report here that Fk and IL-1 synergistically enhance IL-6 mRNA expression in FRTL-5 thyroid cells by mechanisms involving the cAMP/PKA pathway, and both stabilization of the IL-6 mRNA and activation of the IL-6 promoter. Point mutations or deletions of the main transcription factor binding sites in the IL-6 promoter indicated that the synergistic effect was mainly mediated by the AP-1 site, and that the CRE site contributed to this effect. The DNA binding activity of AP-1 transcription factors and the expression of c-Fos and Fra-2 proteins, were all enhanced when the cAMP and IL-1 signalling pathways were both stimulated. These findings contribute to elucidating the synergistic mechanisms that regulate IL-6 secretion by thyroid cells, and suggest that such mechanisms may be involved in the development of thyroid autoimmune disorders.

Thyrotropin modifies activation of nuclear factor kappaB by tumour necrosis factor alpha in rat thyroid cell line

We have recently demonstrated that nuclear factor kappaB (NF-kappaB) mediates the tumour necrosis factor alpha (TNF-alpha)-dependent expression of the gene encoding interleukin 6 (IL-6) in rat thyroid FRTL-5 cells cultured in the presence of thyrotropin (TSH). In the present study we investigated how TSH is involved in the activation of NF-kappaB by TNF-alpha in the cells. Electrophoretic mobility-shift assay revealed that, in the absence of TSH, TNF-alpha activated a single protein-DNA complex containing the p50 subunit but not other NF-kappaB subunits such as p65. In contrast, two distinct protein-DNA complexes were activated in the presence of TSH: the faster-migrating complex contained only p50 subunit; the slower-migrating complex consisted of p65-p50 heterodimer. This TSH effect was mimicked by forskolin and thyroid-stimulating antibodies obtained from patients with Graves's disease, suggesting that an increase in intracellular cAMP is responsible for the induction of different NF-kappaBs by TNF-alpha. A transient transfection study with a luciferase reporter gene driven by multimerized NF-kappaB sites demonstrated that TNF-alpha increased the luciferase activities only in the presence of TSH, and that this increase was inhibited by the co-transfection of mutant p65, which prevented the function of wild-type p65 in a dominant-negative manner. Accordingly, TNF-alpha activated the expression of the IL-6 gene in the presence of TSH but not in its absence. Although the expression of the p105 gene, another known target for NF-kappaB, was increased by TNF-alpha in the absence of TSH, the presence of TSH further increased the mRNA level. Taken together, these observations indicate that the presence of TSH is crucial for the NF-kappaB-mediated actions of TNF-alpha on thyroid follicular cells.

Interleukin-6 levels are not increased in women with postpartum thyroid dysfunction

Postpartum thyroid dysfunction (PPTD) is an autoimmune-mediated thyroid destructive process. Human interleukin-6 (IL-6) is a cytokine found to be increased in subacute thyroiditis, amiodarone-induced thyrotoxicosis, Graves' disease, and other thyroid destructive processes. We report serum IL-6 levels in PPTD in two independent studies. New York Study: In a previous prospective study we demonstrated that PPTD occurred in 25% (7/28) of women with type 1 diabetes mellitus. IL-6 determinations were made on the frozen serum samples of these 28 women during each trimester of their pregnancy and at 1.5, 3, 6, 9, and 12 months postpartum. IL-6 levels were found to be similar in women with PPTD compared with women without PPTD (mean 3.06+/-2.25 vs. 2.51+/-2.21 pg/mL; p = 0.15). No difference in IL-6 levels was found between the pre- and the postpartum periods (mean 2.67+/-1.82 vs. 3.04+/-2.44 pg/mL; p = 0.30) in all 28 women. Cardiff Study: Serum IL-6 levels were measured on frozen serum samples of 30 women with PPTD. IL-6 levels were below the detection limit (25 fmol/L or 0.65 pg/mL) in 94 (67%) of these samples. No significant difference in the mean serum IL-6 levels were found between any time points in the study. There was no correlation between serum IL-6 levels, thyroid peroxidase (TPO)- antibodies and serum thyrotropin (TSH) levels at any time point. IL-6 levels during pregnancy or postpartum were not found to be significantly different in women with PPTD compared with women without PPTD.

Cytokines and thyroid function

Cytokines play a crucial role in autoimmune thyroid disease (ATD) through various mechanisms. They are produced in the thyroid by intrathyroidal inflammatory cells, in particular lymphocytes, as well as by the thyroid follicular cells (TFC) themselves and may thus act in a cascade to enhance the autoimmune process (Fig. 1). Cytokines upregulate the inflammatory reaction through stimulation of both T and B cells, resulting in antibody production and tissue injury. In addition, intrathyroidal cytokines induce immunological changes in TFC including enhancement of both major histocompatibility complex (MHC) class I and class II molecule expression, and upregulation of adhesion and complement regulatory molecule expression. Cytokines can also modulate both growth and function of TFC and have a role in extrathyroidal complications of ATD, most importantly thyroid-associated ophthalmopathy (TAO), where they induce fibroblast proliferation and enhance the production of glycosaminoglycans (GAG), resulting in proptosis and the other clinical features of the disease. In addition to these effects, exogenous administration of cytokines has been associated with impairment of thyroid function ranging from the appearance of autoantibodies alone to the development of frank thyroid dysfunction. Cytokines have also been implicated in subacute thyroiditis (SAT) and amiodarone-induced thyroid dysfunction, as well as in thyroid function abnormalities occurring in patients with non-thyroidal illnesses (NTI). Genetic variations in cytokine genes represent potential risk factors for ATD, and disease associations have been described for polymorphisms in IL-1ra and TNF beta genes. Recent experimental evidence suggests the possibility of novel cytokine-based therapeutic approaches for ATD and its complications, in particular TAO.

Function of interleukin-6 as an inhibitor of meiotic DNA synthesis in the rat seminiferous epithelium

Interleukin-6 bioactivity (IL-6) has been shown to be present in Sertoli cells. To further characterize the IL-6 in the seminiferous epithelium, the IL-6 like-antigen was detected, stage-specific basal distribution of IL-6-like bioactivity and its regulation by FSH, cAMP and TPA was characterized in isolated, rat seminiferous tubule segments. In addition, the effects of human recombinant IL-6 on stage-specific DNA synthesis was investigated. Both monoclonal and polyclonal antibodies recognized M(r) 22 and 23 kDa of IL-6 like immunoreactivity in the seminiferous epithelium. The basal IL-6 production showed high levels during stages XIII-XIV-I-V, low during VII and VIII. FSH stimulated IL-6 production at nearly all stages and most significantly at stage VII of the cycle. Human recombinant IL-6 dose-dependently inhibited the onset of meiotic DNA synthesis of preleptotene spermatocytes, and a minor inhibition was found on advanced (A3-type B) spermatogonia. These results support the hypothesis that IL-6 is a stage-specific paracrine regulator of the seminiferous epithelium exerting a specific inhibitory action on meiotic DNA synthesis.

Relationship of the increased serum interleukin-6 concentration to changes of thyroid function in nonthyroidal illness

Variations in the serum concentration of interleukin-6 (IL-6) have been reported concomitantly with thyroid dysfunction: increased serum IL-6 levels have been found in patients with thyroidal destructive processes, such as subacute thyroiditis, some forms of amiodarone-induced thyrotoxicosis, or after percutaneous ethanol injection into "hot" thyroid nodules, as a result of the cytokine release from the damaged thyrocyte. In addition, recent in vitro evidence suggests that IL-6 might account, at least in part, for changes of thyroid economy found in nonthyroidal illness (NTI). In this cross-sectional study we addressed this problem by measuring serum IL-6 levels in 71 patients with NTI, due to neoplasia (n = 25), chronic liver disease (n = 9), chronic renal failure (n = 28), or other chronic nonthyroidal disorders (n = 9). These patients had reduced mean serum total T3 (TT3) and free T3 (FT3) concentrations, normal total and free T4 levels, normal TSH values, and increased serum reverse T3 (rT3) concentration (with the exception of chronic renal failure patients, who had normal rT3 levels). Serum IL-6 concentration was increased above normal (i.e. > 100 fmol/L) in almost all NTI patients, especially in those with low T3 values (median value: 258 fmol/L, range 73-3210, vs 152 fmol/L, range < 12.5-460, in patients with normal TT3 values, p < 0.001). Serum IL-6 values in NTI patients were negatively correlated with serum FT3 values (r = 0.56, p < 0.001), and positively correlated with serum rT3 values (r = 0.78, p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Increased serum interleukin-6 concentration in patients with subacute thyroiditis: relationship with concomitant changes in serum T4-binding globulin concentration

Interleukin-6 (IL-6) is the main mediator of the acute phase response. Increased serum concentrations of the cytokine have been found in patients with nonthyroidal inflammatory disorders and infections. In 18 patients with subacute thyroiditis (SAT) evaluated within 1-2 weeks after the onset of the disease, serum IL-6 values, as assessed by an ELISA method having a limit of detection of 25 fmol/L, ranged 139.2-543.9 fmol/L (mean +/- SE, 287.2 +/- 28.2 fmol/L). These values were significantly higher than those of 25 normal healthy controls (mean +/- SE, 26.2 +/- 5.5 fmol/L, range < 25-99.4), 18 of whom had serum IL-6 values below the detection limit. The increase in serum IL-6 levels in SAT patients appeared to be related to the inflammatory disorder and not to thyrotoxicosis, because 18 Graves' disease patients and 13 patients with toxic adenoma or toxic multinodular goiter had significantly lower serum IL-6 concentrations (101.7 +/- 35.2 fmol/L, range < 25-251, for Graves' disease, 79.6 +/- 41.4 fmol/L, range < 25-168.5, for toxic adenoma, p < 0.001 vs SAT for both groups) despite the markedly higher levels of total and free thyroid hormones. Neither free T4 nor free T3 values were correlated with serum IL-6 levels both in SAT and Graves' patients. Twelve SAT patients were reevaluated 3-4 months later, after remission of the disease and at least one month after glucocorticoid withdrawal. At the final observation, all SAT patients showed a normalization of IL-6 concentration, which was undetectable in 8/12 (mean +/- SE, 22.8 +/- 5.4 fmol/L, p < 0.001 vs acute phase values).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of interleukin-1 on the thyroid gland

The inhibitory effect of interleukin (IL)-1 on thyroid cell functions, including cAMP and thyroglobulin production, is well documented. Recently, IL-1 was shown to enhance the production of IL-6 from thyrocytes, and IL-1 receptors were demonstrated on normal thyroid cells. The origin of IL-1 could be from infiltrating monocytes/-macrophages, endothelial cells as well as from the thyrocytes themselves. Thus, IL-1 activated thyrocyte may participate directly in the immunological process by reacting to and producing immunoinflammatory cytokines.