Corrigendum: Thyroid Hormone Action on Innate Immunity

[This corrects the article DOI: 10.3389/fendo.2019.00350.].

Thyroid Hormone Action on Innate Immunity

The interplay between thyroid hormone action and the immune system has been established in physiological and pathological settings. However, their connection is complex and still not completely understood. The thyroid hormones (THs), 3,3',5,5' tetraiodo-L-thyroxine (T4) and 3,3',5-triiodo-L-thyronine (T3) play essential roles in both the innate and adaptive immune responses. Despite much research having been carried out on this topic, the available data are sometimes difficult to interpret or even contradictory. Innate immune cells act as the first line of defense, mainly involving granulocytes and natural killer cells. In turn, antigen presenting cells, macrophages and dendritic cells capture, process and present antigens (self and foreign) to naïve T lymphocytes in secondary lymphoid tissues for the development of adaptive immunity. Here, we review the cellular and molecular mechanisms involved in T4 and T3 effects on innate immune cells. An overview of the state-of-the-art of TH transport across the target cell membrane, TH metabolism inside these cells, and the genomic and non-genomic mechanisms involved in the action of THs in the different innate immune cell subsets is included. The present knowledge of TH effects as well as the thyroid status on innate immunity helps to understand the complex adaptive responses achieved with profound implications in immunopathology, which include inflammation, cancer and autoimmunity, at the crossroads of the immune and endocrine systems.

Nitric oxide-repressed Forkhead factor FoxE1 expression is involved in the inhibition of TSH-induced thyroid peroxidase levels

Thyroid peroxidase (TPO) is essential for thyroid hormone synthesis mediating the covalent incorporation of iodine into tyrosine residues of thyroglobulin process known as organification. Thyroid-stimulating hormone (TSH) via cAMP signaling is the main hormonal regulator of TPO gene expression. In thyroid cells, TSH-stimulated nitric oxide (NO) production inhibits TSH-induced thyroid-specific gene expression, suggesting a potential autocrine role of NO in modulating thyroid function. Indeed, NO donors downregulate TSH-induced iodide accumulation and organification in thyroid cells. Here, using FRTL-5 thyroid cells as model, we obtained insights into the molecular mechanism underlying the inhibitory effects of NO on iodide organification. We demonstrated that NO donors inhibited TSH-stimulated TPO expression by inducing a cyclic guanosine monophosphate-dependent protein kinase-mediated transcriptional repression of the TPO gene. Moreover, we characterized the FoxE1 binding site Z as mediator of the NO-inhibited TPO expression. Mechanistically, we demonstrated that NO decreases TSH-induced FoxE1 expression, thus repressing the transcripcional activation of TPO gene. Taken together, we provide novel evidence reinforcing the inhibitory role of NO on thyroid cell function, an observation of potential pathophysiological relevance associated with human thyroid pathologies that come along with changes in the NO production.

S-Nitrosylation of NF-κB p65 Inhibits TSH-Induced Na(+)/I(-) Symporter Expression

Nitric oxide (NO) is a ubiquitous signaling molecule involved in a wide variety of cellular physiological processes. In thyroid cells, NO-synthase III-endogenously produced NO reduces TSH-stimulated thyroid-specific gene expression, suggesting a potential autocrine role of NO in modulating thyroid function. Further studies indicate that NO induces thyroid dedifferentiation, because NO donors repress TSH-stimulated iodide (I(-)) uptake. Here, we investigated the molecular mechanism underlying the NO-inhibited Na(+)/I(-) symporter (NIS)-mediated I(-) uptake in thyroid cells. We showed that NO donors reduce I(-) uptake in a concentration-dependent manner, which correlates with decreased NIS protein expression. NO-reduced I(-) uptake results from transcriptional repression of NIS gene rather than posttranslational modifications reducing functional NIS expression at the plasma membrane. We observed that NO donors repress TSH-induced NIS gene expression by reducing the transcriptional activity of the nuclear factor-κB subunit p65. NO-promoted p65 S-nitrosylation reduces p65-mediated transactivation of the NIS promoter in response to TSH stimulation. Overall, our data are consistent with the notion that NO plays a role as an inhibitory signal to counterbalance TSH-stimulated nuclear factor-κB activation, thus modulating thyroid hormone biosynthesis.

Control of dendritic cell maturation and function by triiodothyronine

Accumulating evidence indicates a functional crosstalk between immune and endocrine mechanisms in the modulation of innate and adaptive immunity. However, the impact of thyroid hormones (THs) in the initiation of adaptive immune responses has not yet been examined. Here we investigated the presence of thyroid hormone receptors (TRs) and the impact of THs in the physiology of mouse dendritic cells (DCs), specialized antigen-presenting cells with the unique capacity to fully activate naive T cells and orchestrate adaptive immunity. Both immature and lipopolysaccharide-matured bone marrow-derived DCs expressed TRs at mRNA and protein levels, showing a preferential cytoplasmic localization. Remarkably, physiological levels of triiodothyronine (T3) stimulated the expression of DC maturation markers (major histocompatibility complex II, CD80, CD86, and CD40), markedly increased the secretion of interleukin-12, and stimulated the ability of DCs to induce naive T cell proliferation and IFN-gamma production in allogeneic T cell cultures. Analysis of the mechanisms involved in these effects revealed the ability of T3 to influence the cytoplasmic-nuclear shuttling of nuclear factor-kappaB on primed DCs. Our study provides the first evidence for the presence of TRs on bone marrow-derived DCs and the ability of THs to regulate DC maturation and function. These results have profound implications in immunopathology, including cancer and autoimmune manifestations of the thyroid gland at the crossroads of the immune and endocrine systems.