Cultured Pig Thyroid Follicular Cells: Electrical Evaluation of Epithelial Integrity

Thyroid epithelial cells organize as enclosed follicles containing thyroid hormone precursor, iodinated thyroglobulin, with lumina bordered by the cellular apices. Transepithelial transport determines composition of compartmental milieu essential for both prohormone formation and its downstream conversion to thyroxine. Hence, not only do follicular lumina function as storage vessels but also as physiological reaction chambers into which reactive components, together with the proper salts and water, are secreted. Polarized, two-dimensional cultures of pig thyroid epithelia, prepared using established protocols, provide a convenient system for assessing transport processes subserving hormone production. This chapter details established methods for growing and evaluating integrity of primary pig thyroid cultures for downstream analysis of transport and other key physiological functions.

Myeloid cells interact with a subset of thyrocytes to promote their migration and follicle formation through NF-κB

The pathogenesis of thyroid dysgenesis (TD) is not well understood. Here, using a combination of single-cell RNA and spatial transcriptome sequencing, we identify a subgroup of NF-κB-activated thyrocytes located at the center of thyroid tissues in postnatal mice, which maintained a partially mesenchymal phenotype. These cells actively protruded out of the thyroid primordium and generated new follicles in zebrafish embryos through continuous tracing. Suppressing NF-κB signaling affected thyrocyte migration and follicle formation, leading to a TD-like phenotype in both mice and zebrafish. Interestingly, during thyroid folliculogenesis, myeloid cells played a crucial role in promoting thyrocyte migration by maintaining close contact and secreting TNF-α. We found that cebpa mutant zebrafish, in which all myeloid cells were depleted, exhibited thyrocyte migration defects. Taken together, our results suggest that myeloid-derived TNF-α-induced NF-κB activation plays a critical role in promoting the migration of vertebrate thyrocytes for follicle generation.

Notch signaling in thyrocytes is essential for adult thyroid function and mammalian homeostasis

The thyroid functions as an apex endocrine organ that controls growth, differentiation and metabolism1, and thyroid diseases comprise the most common endocrine disorders2. Nevertheless, high-resolution views of the cellular composition and signals that govern the thyroid have been lacking3,4. Here, we show that Notch signalling controls homeostasis and thermoregulation in adult mammals through a mitochondria-based mechanism in a subset of thyrocytes. We discover two thyrocyte subtypes in mouse and human thyroids, identified in single-cell analyses by different levels of metabolic activity and Notch signalling. Therapeutic antibody blockade of Notch in adult mice inhibits a thyrocyte-specific transcriptional program and induces thyrocyte defects due to decreased mitochondrial activity and ROS production. Thus, disrupting Notch signalling in adult mice causes hypothyroidism, characterized by reduced levels of circulating thyroid hormone and dysregulation of whole-body thermoregulation. Inducible genetic deletion of Notch1 and 2 in thyrocytes phenocopies this antibody-induced hypothyroidism, establishing a direct role for Notch in adult murine thyrocytes. We confirm that hypothyroidism is enriched in children with Alagille syndrome, a genetic disorder marked by Notch mutations, suggesting that these findings translate to humans.

Thyroid-Disrupting Effects of Exposure to Fipronil and Its Metabolites from Drinking Water Based on Human Thyroid Follicular Epithelial Nthy-ori 3-1 Cell Lines

Fipronil is a broad-spectrum insecticide used for plants and poultry. Owing to its widespread use, fipronil and its metabolites (fipronil sulfone, fipronil desulfinyl, and fipronil sulfide), termed FPM, can be frequently detected in drinking water and food. Fipronil can affect the thyroid function of animals, but the effects of FPM on the human thyroid remain unclear. We employed human thyroid follicular epithelial Nthy-ori 3-1 cells to examine combined cytotoxic responses, thyroid-related functional proteins including the sodium-iodide symporter (NIS), thyroid peroxidase (TPO), deiodinases I-III (DIO I-III), and the nuclear factor erythroid-derived factor 2-related factor 2 (NRF2) pathway induced by FPM of 1-1000-fold concentrations detected in school drinking water collected from a heavily contaminated area of the Huai River Basin. Thyroid-disrupting effects of FPM were evaluated by examining biomarkers of oxidative stress and thyroid function and tetraiodothyronine (T4) levels secreted by Nthy-ori 3-1 cells after FPM treatment. FPM activated the expression of NRF2, HO-1 (heme oxygenase 1), TPO, DIO I, and DIO II but inhibited NIS expression and increased the T4 level of thyrocytes, indicating that FPM can disrupt the function of human thyrocytes through oxidative pathways. Given the adverse impact of low FPM concentrations on human thyrocytes, supportive evidence from rodent studies, and the critical importance of thyroid hormones on development, the effects of FPM on the neurodevelopment and growth of children warrant priority attention.

Induction of epithelial-mesenchymal transition in thyroid follicular cells is associated with cell adhesion alterations and low-dose hyper-radiosensitivity

BACKGROUND

Epithelial-mesenchymal transition (EMT) is associated with altered cellular adhesion. We previously demonstrated that cellular adhesion influences Low-dose Hyper-Radiosensitivity (HRS) in a variety of tumor cells. However, the relationship of low-dose HRS with the phenotypic plasticity incurred by EMT during the neoplastic transformation remains to be elucidated.

OBJECTIVE

To investigate whether acquisition of EMT phenotype during progressive neoplastic transformation may affect low-dose radiation sensitivity.

METHODS

Primary thyroid cells obtained from a human cystic thyroid nodule were first subjected to nutritional stress. This yielded immortalized INM-Thy1 cell strain, which was further treated with either multiple γ-radiation fractions (1.5 Gy each) or repetitive cycles of 3-methylcholanthrene and phorbol-12-myristate-13-acetate, yielding two progressive transformants, viz., INM-Thy1R and INM-Thy1C. Morphological alterations, chromosomal double-minutes, cell adhesion proteins, anchorage dependency, tumorigenicity in nude mice and cellular radiosensitivity were studied in these strains.

RESULTS

Both transformants (INM-Thy1R, INM-Thy1C) displayed progressive tumorigenic features, viz., soft agar colony growth and solid tumor growth in nude mice, coupled with features of epithelial-mesenchymal transition and activated Wnt pathway. Incidentally, the chemical-induced transformant (INM-Thy1C) displayed a prominent HRS (αs/αr = 29.35) which remained unaffected at high cell density. However, the parental (INM-Thy1) cell line as well as radiation-induced transformant (INM-Thy1R) failed to show this hypersensitivity.

CONCLUSION

The study shows that induction of EMT in thyroid follicular cells may accompany increased susceptibility to low-dose ionizing radiation, which was attenuated by adaptive resistance acquired during radiation-induced transformation.

Nickel Sulfate Induces Autophagy in Human Thyroid Follicular Epithelial Cells

Nickel is an industrial and environmental toxic metal, which is toxic to humans in certain forms at high doses. Here, we investigated the cytotoxic effects of nickel sulfate (NiSO₄) exposure on the human thyroid follicular epithelial cells (Nthy-ori 3-1) and its underlying toxicological mechanisms. The results showed that NiSO₄ reduced the cell viability of Nthy-ori 3-1 cells in a dose- and time-dependent manner, inducing S and G2/M phases cell-cycle arrest and apoptosis. Electron microscopy demonstrated that abundant autophagic vacuoles were found in Nthy-ori 3-1 cells after NiSO₄ treatment. Accordingly, exposure of Nthy-ori 3-1 cells to NiSO₄ resulted in a dose-dependent increase of LC3II/I ratio, an induction of Beclin-1 expression, and a decrease in p62 levels. Blockade of autophagy with 3-methyladenine (3-MA) potentiated the NiSO₄-induced apoptotic cell death, while induction of autophagy significantly alleviated toxicity of NiSO₄. From a molecular standpoint, NiSO₄ markedly promoted the activation of p38 and IKKβ by increasing their phosphorylation. In conclusion, we showed that autophagy was induced to protect thyroid cells from Ni²⁺ mediated apoptosis, thus providing rational strategy to prevent against nickel toxicity in the thyroid.

Single-cell transcriptome analysis reveals thyrocyte diversity in the zebrafish thyroid gland

The thyroid gland regulates growth and metabolism via production of thyroid hormone in follicles composed of thyrocytes. So far, thyrocytes have been assumed to be a homogenous population. To uncover heterogeneity in the thyrocyte population and molecularly characterize the non-thyrocyte cells surrounding the follicle, we developed a single-cell transcriptome atlas of the region containing the zebrafish thyroid gland. The 6249-cell atlas includes profiles of thyrocytes, blood vessels, lymphatic vessels, immune cells, and fibroblasts. Further, the thyrocytes show expression heterogeneity, including bimodal expression of the transcription factor pax2a. To validate thyrocyte heterogeneity, we generated a CRISPR/Cas9-based pax2a knock-in line that monitors pax2a expression in the thyrocytes. A population of pax2a-low mature thyrocytes interspersed in individual follicles can be distinguished. We corroborate heterogeneity within the thyrocyte population using RNA sequencing of pax2a-high and pax2a-low thyrocytes, which demonstrates 20% differential expression in transcriptome between the two subpopulations. Our results identify and validate transcriptional differences within the presumed homogenous thyrocyte population.