Antioxidant Defense Capacity Is Reduced in Thyroid Stem/Precursor Cells Compared to Differentiated Thyrocytes.

There is much evidence linking oxidative stress to thyroid cancer, and stem cells are thought to play a key role in the tumor-initiating mechanism. Their vulnerability to oxidative stress is unexplored. This study aimed to comparatively evaluate the antioxidant capacity of stem/precursor thyroid cells and mature thyrocytes. Human stem/precursor cells and mature thyrocytes were exposed to increasing concentrations of menadione, an oxidative-stress-producing agent, and reactive oxygen species (ROS) production and cell viability were measured. The expression of antioxidant and detoxification genes was measured via qPCR as well as the total antioxidant capacity and the content of glutathione. Menadione elevated ROS generation in stem/precursor thyroid cells more than in mature thyrocytes. The ROS increase was inversely correlated (p = 0.005) with cell viability, an effect that was partially prevented by the antioxidant curcumin. Most thyroid antioxidant defense genes, notably those encoding for the glutathione-generating system and phase I detoxification enzymes, were significantly less expressed in stem/precursor thyroid cells. As a result, the glutathione level and the total antioxidant capacity in stem/precursor thyroid cells were significantly decreased. This reduced antioxidant defense may have clinical implications, making stem/precursor thyroid cells critical targets for environmental conditions that are not detrimental for differentiated thyrocytes.

Heavy Metals in the Environment and Thyroid Cancer.

In recent decades, the incidence of thyroid cancer has increased more than most other cancers, paralleling the generalized worldwide increase in metal pollution. This review provides an overview of the evidence supporting a possible causative link between the increase in heavy metals in the environment and thyroid cancer. The major novelty is that human thyroid stem/progenitor cells (thyrospheres) chronically exposed to different metals at slightly increased environmentally relevant concentrations show a biphasic increase in proliferation typical of hormesis. The molecular mechanisms include, for all metals investigated, the activation of the extracellular signal-regulated kinase (ERK1/2) pathway. A metal mixture, at the same concentration of individual metals, was more effective. Under the same conditions, mature thyrocytes were unaffected. Preliminary data with tungsten indicate that, after chronic exposure, additional abnormalities may occur and persist in thyrocytes derived from exposed thyrospheres, leading to a progeny population of transformation-prone thyroid cells. In a rat model predisposed to develop thyroid cancer, long-term exposure to low levels of metals accelerated and worsened histological signs of malignancy in the thyroid. These studies provide new insight on metal toxicity and carcinogenicity occurring in thyroid cells at a low stage of differentiation when chronically exposed to metal concentrations that are slightly increased, albeit still in the "normal" range.

Thyroid Stem Cells But Not Differentiated Thyrocytes Are Sensitive to Slightly Increased Concentrations of Heavy Metals.

Thyroid cancer incidence is markedly increased in volcanic areas where residents are biocontaminated by chronic lifelong exposure to slightly increased metals in the environment. Metals can influence the biology of living cells by a variety of mechanisms, depending not only on the dose and length of exposure but also on the type and stage of differentiation of target cells. We explored the effect of five heavy metals (Cu, Hg, Pd, W and Zn) at nanomolar concentrations (the biocontamination level in residents of the volcanic area in Sicily where thyroid cancer is increased) on stimulating the proliferation of undifferentiated (thyrospheres) and differentiated human thyroid cells. Thyrosphere proliferation was significantly increased after exposure to each individual metal and a greater stimulating effect was observed when a mixture of the examined metals was used. No effect was seen in differentiated thyrocytes. For all metals, the dose-response curve followed a biphasic pattern that is typical of hormesis. Thyrosphere growth concerned the size rather than number, except with the metal mixture. An altered morphology was also observed in metal-treated thyrospheres. Metal-induced proliferation was due to activation of the ERK1/2 pathway, as confirmed by growth inhibition when ERK1/2 signaling was blocked. These studies show that stem/precursor thyroid cells are sensitive to small increases in environmental metal concentrations that are harmless for differentiated thyrocytes.

The Transient Human Thyroid Progenitor Cell: Examining the Thyroid Continuum from Stem Cell to Follicular Cell.

Background: The development of the thyroid follicular cell has been well characterized as it progresses from the original stem cell, either embryonic or adult, through a series of transitions to form a differentiated and functional thyroid cell. Summary: In this review, we briefly outline what is known about this transitional process with emphasis on characterizing the thyroid progenitor stem cell by using data obtained from both in vitro and in vivo studies and both mouse and human cells. It is of particular importance to note the influence of independent factors that guide the transcriptional control of the developing thyroid cell as it is subjected to extracellular signals, often working via epigenetic changes, and initiating intrinsic transcriptional changes leading to a functional cell. Conclusion: Thyroid stem cells fall into the category of dispositional stem cells and are greatly influenced by their environment.

Effect of low-dose tungsten on human thyroid stem/precursor cells and their progeny.

Thyroid cancer incidence is increased in volcanic areas where environment pollution biocontaminates residents. Tungsten (W) is the most increased heavy metal in drinking water of Mount Etna volcanic area where it exceeds the normal range in the urine of 27% inhabitants. The possible connection between increased tungsten and thyroid cancer has never been studied. We investigated in vitro the effect tungsten on both human thyrocytes in primary culture, thyrospheres (aggregates of stem/precursor thyroid cells) and thyrocytes differentiated from tungsten-exposed thyrospheres. Chronic exposure to low-dose (nanomolar range, as in the urines of volcanic area residents) soluble tungsten had major biological effects on thyroid stem/precursor cells, promoting growth with a biphasic (hormetic) dose-response and reducing apoptosis. No such effects were observed in mature thyrocytes. In addition, tungsten-exposed thyrospheres had abnormal expression of genes commonly altered also in thyroid cancer and increased activation of the DNA-repair proteins H2AX and 53BP1. Moreover, exposure to tungsten decreased thyrosphere differentiation, as indicated by the reduced expression of thyroid-specific genes in derived thyrocytes that also showed preneoplastic changes such as increased anchorage-independent growth, clonogenic growth and migration capacity. The mechanism of action of tungsten on thyroid stem/precursor cells is unclear but involves membrane G-proteins and activation of the ERK signaling pathway. These data indicate that chronic exposure to slightly increased tungsten, harmless for mature thyrocytes, importantly affects the biology of stem/precursor thyroid cells and of their progeny, inducing characteristics of preneoplastic transformation.

An Adult Mouse Thyroid Side Population Cell Line that Exhibits Enriched Epithelial-Mesenchymal Transition.

BACKGROUND: Studies of thyroid stem/progenitor cells have been hampered due to the small organ size and lack of tissue, which limits the yield of these cells. A continuous source that allows the study and characterization of thyroid stem/progenitor cells is desired to push the field forward. METHOD: A cell line was established from Hoechst-resistant side population cells derived from mouse thyroid that were previously shown to contain stem/progenitor-like cells. Characterization of these cells were carried out by using in vitro two- and three-dimensional cultures and in vivo reconstitution of mice after orthotopic or intravenous injection, in conjunction with quantitative reverse transcription polymerase chain reaction, Western blotting, immunohisto(cyto)chemistry/immunofluorescence, and RNA seq analysis. RESULTS: These cells were named SPTL (side population cell-derived thyroid cell line). Under low serum culturing conditions, SPTL cells expressed the thyroid differentiation marker NKX2-1, a transcription factor critical for thyroid differentiation and function, while no expression of other thyroid differentiation marker genes were observed. SPTL cells formed follicle-like structures in Matrigel® cultures, which did not express thyroid differentiation marker genes. In mouse models of orthotopic and intravenous injection, the latter following partial thyroidectomy, a few SPTL cells were found in part of the follicles, most of which expressed NKX2-1. SPTL cells highly express genes involved in epithelial-mesenchymal transition, as demonstrated by RNA seq analysis, and exhibit a gene-expression pattern similar to anaplastic thyroid carcinoma. CONCLUSION: These results demonstrate that SPTL cells have the capacity to differentiate into thyroid to a limited degree. SPTL cells may provide an excellent tool to study stem cells, including cancer stem cells of the thyroid.

Effect of 17β-estradiol on proliferation of human thyroid stem cells / 中华内分泌代谢杂志

Objective To investigate the effect of 17β-estradiol on the proliferation of thyroid stem/ progenitor cells.Methods In thyroid stem/progenitor cells derived from nodular goiters,the effects of 17 β-estradiol on thyrosphere formation,estrogen receptor (ER) expression,cyclin D1 expression,and mitogen activated protein kinase (MPAK) pathway were analysed by BrdU ELISA,conventional and realtime PCR,immunofluorensence staining,and Western blot.Results 17β-estradiol induced thyrosphere formation and proliferation of thyroid stem/ progenitor cells.ER-α and ER-β were expressed in thyroid stem and progenitor cells with higher mRNA expression level of ER-α compared to differentiated thyrocytes (8.85-±0.81 vs 1.10 ±0.35,P＜0.01).Stimulation by 1 mmol/L 17β-estradiol increased cyclin D1 mRNA expression and ERK phosphorylation levels,which was blocked by an ER antagonist,ICI 182780.Conclusion Estrogen stimulated the growth of stem cells derived from thyroid nodules via estrogen receptor,suggesting the relevance of increased thyroid stem cell proliferation with higher prevalence of thyroid nodules in women.

Oestrogen action on thyroid progenitor cells: relevant for the pathogenesis of thyroid nodules?

Benign and malignant thyroid nodules are more prevalent in females than in males. Experimental data suggest that the proliferative effect of oestrogen rather than polymorphisms is responsible for this gender difference. This study analysed whether both differentiated thyroid cells and thyroid stem and progenitor cells are targets of oestrogen action. In thyroid stem/progenitor cells derived from nodular goitres, the ability of 17ß-oestradiol (E2) to induce the formation of thyrospheres and the expression of oestrogen receptors (ERs) and the effect of E2 on the growth and expression of markers of stem cells and thyroid differentiation (TSH receptor, thyroperoxidase, thyroglobulin and sodium iodide symporter (NIS)) were analysed. E2 induced thyrosphere formation, albeit to a lower extent than other growth factors. Thyroid stem and progenitor cells expressed ERα (ESR1) and ERß (ESR2) with eight times higher expression levels of ERα mRNA compared with the differentiated thyrocytes. E2 was a potent stimulator of the growth of thyroid stem/progenitor cells. In contrast, TSH-induced differentiation of progenitor cells, in particular, the expression of NIS, was significantly inhibited by E2. In conclusion, oestrogen stimulated the growth and simultaneously inhibited the differentiation of thyroid nodule-derived stem/progenitor cells. From these data and based on the concept of cellular heterogeneity, we hypothesize a supportive role of oestrogen in the propagation of thyroid stem/progenitor cells leading to the selection of a progeny of growth-prone cells with a decreased differentiation. These cells may be the origin of hypofunctioning or non-functioning thyroid nodules in females.