Thyroid regeneration: characterization of clear cells after partial thyroidectomy

Long-term biological effects after acute 131I-administration of two rat models (with and without thyroid)

PURPOSE

Radioiodine-131 (RAI or iodine-131) is one of the most frequently used radionuclides for diagnosis and therapy of thyroid diseases (90% of all therapies in nuclear medicine). In order to optimize the patient protection, it is important to evaluate the long-term biological effects of RAI therapy on non-target organs.

MATERIALS AND METHODS

An experimental animal model has been adopted, it consists on miming RAI therapy. An activity of RAI has been administrated in two models of Wistar rats: the first model with an intact thyroid gland (Thy + model), and the second one was thyroidectomized (Thy- model). For each model, 6 rats were orally contaminated with a solution 18.5 ± 1MBq of [131I]NaI and 6 others rats were used as controls. The 24 rats have been placed in individual cages for a period of 08 months then they were euthanized. The blood was collected by cardiac puncture and all organs were immediately removed. A fraction of thyroid, liver, kidneys and testicles was put in vials containing formaldehyde (10%) for histological investigation.

RESULTS

Histological observations show some liver disorders more accentuated in the case of the Thy- model, the appearance of kidney tissue effects (hemosiderin deposits, fibrosis and glomerular necrosis) for both models and an absence of any anomaly for the testicles slides. The disturbance of blood parameters specific to each organ has been revealed.

CONCLUSIONS

Long-term biological effect of 131I-administration shows the appearance of various histological disorders confirmed by disturbances in hepatic and renal functions.

Spatially resolved single-cell atlas of ascidian endostyle provides insight into the origin of vertebrate pharyngeal organs

The pharyngeal endoderm, an innovation of deuterostome ancestors, contributes to pharyngeal development by influencing the patterning and differentiation of pharyngeal structures in vertebrates; however, the evolutionary origin of the pharyngeal organs in vertebrates is largely unknown. The endostyle, a distinct pharyngeal organ exclusively present in basal chordates, represents a good model for understanding pharyngeal organ origins. Using Stereo-seq and single-cell RNA sequencing, we constructed aspatially resolved single-cell atlas for the endostyle of the ascidian Styela clava. We determined the cell composition of the hemolymphoid region, which illuminates a mixed ancestral structure for the blood and lymphoid system. In addition, we discovered a cluster of hair cell-like cells in zone 3, which has transcriptomic similarity with the hair cells of the vertebrate acoustico-lateralis system. These findings reshape our understanding of the pharynx of the basal chordate and provide insights into the evolutionary origin of multiplexed pharyngeal organs.

Progress Toward and Challenges Remaining for Thyroid Tissue Regeneration

Thyroid hormones play a pivotal role in diverse physiological processes, and insufficient synthesis of these hormones results in hypothyroidism, a prevalent disorder with a significant global impact. Research has shown that the residual thyroid tissue following surgery fails to fully regenerate the gland and restore normal function. The slow turnover rate of the thyroid gland and the presence of resident stem cells, which may contribute to regeneration within adult thyroid tissue, are topics of ongoing debate. This comprehensive review summarizes current research findings concerning the regeneration of the adult thyroid. Investigations have identified potential cellular mechanisms implicated in thyroid regeneration following partial tissue damage, including cells within microfollicles and a cluster of potential thyroid progenitors cells. Nevertheless, the exact mechanisms remain elusive. In cases of complete removal of the thyroid gland, regeneration does not occur, underscoring the necessity for an external source of thyroid tissue. The transplantation of thyroid organoids has emerged as a promising approach to restore thyroid function. Researchers have successfully derived thyroid organoids from various sources and demonstrated their functionality in both in vitro and in vivo animal models. Despite the challenges that still need to be addressed in achieving full maturation and functionality of human thyroid organoids, significant strides have been made in this regard. This review explores the potential of thyroid organoid transplantation and its implications for the field of regenerative medicine.

Engineering a functional thyroid as a potential therapeutic substitute for hypothyroidism treatment: A systematic review

Background

Hypothyroidism is a common hormone deficiency disorder. Although hormone supplemental therapy can be easily performed by daily levothyroxine administration, a proportion of patients suffer from persisting complaints due to unbalanced hormone levels, leaving room for new therapeutic strategies, such as tissue engineering and regenerative medicine.

Methods

Electronic searches of databases for studies of thyroid regeneration or thyroid organoids were performed. A systematic review including both in vitro and in vivo models of thyroid regenerative medicine was conducted.

Results

Sixty-six independent studies published between 1959 and May 1st, 2022 were included in the current systematic review. Among these 66 studies, the most commonly involved species was human (19 studies), followed by mouse (18 studies), swine (14 studies), rat (13 studies), calf/bovine (4 studies), sheep/lamb (4 studies) and chick (1 study). In addition, in these experiments, the most frequently utilized tissue source was adult thyroid tissue (46 studies), followed by embryonic stem cells (ESCs)/pluripotent stem cells (iPSCs) (10 studies), rat thyroid cell lines (7 studies), embryonic thyroid tissue (2 studies) and newborn or fetal thyroid tissue (2 studies). Sixty-three studies reported relevant thyroid follicular regeneration experiments in vitro, while 21 studies showed an in vivo experiment section that included transplanting engineered thyroid tissue into recipients. Together, 12 studies were carried out using 2D structures, while 50 studies constructed 3D structures.

Conclusions

Each aspect of thyroid regenerative medicine was comprehensively described in this review. The recovery of optimal hormonal equilibrium by the transplantation of an engineered functional thyroid holds great therapeutic promise.

Adult mouse and human organoids derived from thyroid follicular cells and modeling of Graves' hyperthyroidism

The thyroid is essential for maintaining systemic homeostasis by regulating thyroid hormone concentrations in the bloodstream. This study describes an organoid-based model system to study mouse and human thyroid biology. Moreover, the study explores the potential of human organoids for modeling autoimmune disease, the anti-TSH receptor (TSHR) antibody-driven Graves’ hyperthyroidism.

The thyroid maintains systemic homeostasis by regulating serum thyroid hormone concentrations. Here we report the establishment of three-dimensional (3D) organoids from adult thyroid tissue representing murine and human thyroid follicular cells (TFCs). The TFC organoids (TFCOs) harbor the complete machinery of hormone production as visualized by the presence of colloid in the lumen and by the presence of essential transporters and enzymes in the polarized epithelial cells that surround a central lumen. Both the established murine as human thyroid organoids express canonical thyroid markers PAX8 and NKX2.1, while the thyroid hormone precursor thyroglobulin is expressed at comparable levels to tissue. Single-cell RNA sequencing and transmission electron microscopy confirm that TFCOs phenocopy primary thyroid tissue. Thyroid hormones are readily detectable in conditioned medium of human TFCOs. We show clinically relevant responses (increased proliferation and hormone secretion) of human TFCOs toward a panel of Graves’ disease patient sera, demonstrating that organoids can model human autoimmune disease.

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.

Long-term effects of in ovo exposure to an environmentally relevant dose of atrazine on the thyroid gland of Caiman latirostris

The increased incidence of human thyroid disorders, particularly in women, suggests that the exposure to endocrine-disrupting compounds (EDCs) together with sex-related factors could play a role in thyroid dysregulation. Since the herbicide atrazine (ATZ) is an environmental EDC suspected to behave as a thyroid disruptor, and Caiman latirostris is a crocodilian species highly sensitive to endocrine disruption that can be exposed to ATZ, this study aimed to describe the histoarchitecture and sexually dimorphic features of the thyroid gland of C. latirostris, and to determine the long-term effects of in ovo exposure to an environmentally relevant dose of ATZ (0.2 ppm) on its thyroid gland and growth. Control caimans showed no sexual dimorphisms. In contrast, ATZ-exposed caimans showed altered embryo growth but an unaltered temporal pattern of development and a sexually dimorphic response in the body condition index growth curves postnatally, which suggests a female-related increase in fat storage. Besides, both male and female exposed caimans showed increases in the size of the thyroid stromal compartment, content of interstitial collagen, and follicular hyperplasia, and decreases in the expression of androgen receptor in the follicular epithelium. ATZ-exposed females, but not males, also showed evidences of thyroid enlargement, colloid depletion, increased follicular epithelial height and increased presence of microfollicular structures. Our results demonstrate that prenatal exposure of caimans to ATZ causes thyroid disruption and that females were more vulnerable to ATZ than males. The effects were organizational and observed long after exposure ended. These findings alert on ATZ side-effects on the growth, metabolism, reproduction and development of non-target exposed organisms, particularly females.

A Stem Cell Surge During Thyroid Regeneration

BACKGROUND

Many tissues, including the thyroid, contain resident (adult) stem cells that are responsible for regeneration and repair after injury. The mechanisms of thyroid regeneration and the role of thyroid stem cells and thyroid progenitor cells in this process are not well understood. We have now used a new mouse thyroid injury model to gain insight into this phenomenon.

METHODS

Tamoxifen induced TPO-Cre mice (TPOCreER2) were crossed with inducible Diphtheria Toxin Receptor homozygous mice (ROSA26iDTR) to give rise to TPOCreER2/iDTR mice, allowing for the Cre-mediated expression of the DTR and rendering TPO expressing thyroid cells highly sensitive to diphtheria toxin (DT). This model of TPOCreER2/iDTR mice allowed us to study the repair/regeneration of thyroid follicles after diphtheria toxin induced thyroid damage by measuring serum thyroid hormones and cell fate.

RESULTS

In TPOCreER2/iDTR double transgenic mice we observed severe thyroid damage as early as 2 weeks after initiating intraperitoneal DT injections. There was marked thyroid tissue apoptosis and a ~50% drop in serum T4 levels (from 5.86 to 2.43 ug/dl) and a corresponding increase in serum TSH (from 0.18 to 8.39 ng/dl). In addition, there was a ~50% decrease in transcription of thyroid specific genes (thyroglobulin, TSH receptor, and sodium-iodide symporter). After suspending the DT administration, the thyroid rapidly recovered over a 4-week period during which we observed a transient surge in stem cell marker expression (including Oct4, Nanog, Sox2, and Rex1). In addition, cells immunostaining with stem cell markers Oct4 and Ssea-1 were found in clusters around new thyroid follicles in TPOCreER2/iDTR double transgenic mice. Furthermore, the presence of clusters of thyroid progenitor cells was also identified by Pax8 staining of thyroglobulin negative cells. This recovery of the injured gland was followed by a rapid and sequential restoration of thyroid function.

CONCLUSION

These data demonstrate that a new model of thyroid cell damage induced by DT can be used to study the mobilization of resident adult stem cells. Furthermore, the model clearly demonstrates the involvement of both stem and progenitor cells in the in vivo regeneration of the thyroid after severe destruction.

Stem Cells, Self-Renewal, and Lineage Commitment in the Endocrine System

The endocrine system coordinates a wide array of body functions mainly through secretion of hormones and their actions on target tissues. Over the last decades, a collective effort between developmental biologists, geneticists, and stem cell biologists has generated a wealth of knowledge related to the contribution of stem/progenitor cells to both organogenesis and self-renewal of endocrine organs. This review provides an up-to-date and comprehensive overview of the role of tissue stem cells in the development and self-renewal of endocrine organs. Pathways governing crucial steps in both development and stemness maintenance, and that are known to be frequently altered in a wide array of endocrine disorders, including cancer, are also described. Crucially, this plethora of information is being channeled into the development of potential new cell-based treatment modalities for endocrine-related illnesses, some of which have made it through clinical trials.

Functions of stem cells of thyroid glands in health and disease

Thyroid gland has been implicated in the regulation of many functions using endocrine, paracrine and autocrine signals. Functional thyroid follicular cells derived from stem cells attracted a great interest from researchers as a strategy for thyroid's regenerative therapy. Thyroid has a very low rate of turnover; however, studies showed that the regenerative ability is enhanced following diseases or thyroidectomy, which promotes the role of stem cell. The objective of this review is to summarize the morphological characterization and the expression of stem cell genes/markers in the thyroid. Also, to highlight the mechanisms of tumor formation in thyroid via its stem cells. The most important thyroid stem cell's markers are: stem cell antigen 1 (SCA-1), octamer-binding transcription 4 (OCT-4), p63, CD34+ CD45-, paired box gene 8 (PAX-8), thyroid transcription factor 1 (TTF-1), thyroid transcription factor 2 (TTF-2), hematopoietically expressed homeobox protein HHEX, the transcription factor GATA-4, hepatocyte nuclear factor 4-α (HNF-4-α) and homeobox transcription factor Nanog (hNanog). This review highlights the functional characterization describing the mechanisms of stem cell's differentiation into functional thyroid follicle and proposing mechanisms involving in cancer formation through one of these cell types: fetal cell, thyroblasts, prothyrocytes, certain genetic mutation in the mature thyroid cells or presence of a special type of cells (cancer stem cell) which are responsible for different types of cancer formation. Understanding the mechanisms of thyroid's stem cell in cancer formation and the expression of the biomarkers in normal and abnormal thyroid status are promising physiological tools in promoting thyroid regeneration and in provision management for thyroid cancer.

PGC-1β cooperating with FOXA2 inhibits proliferation and migration of breast cancer cells

Background

Breast cancer is one of the most common malignancy among females from the worldwide cancer incidence statistics. Peroxisome gamma coactivator-1β (PGC-1β) has long been identified to be involved in this type of tumorigenesis. However, the mechanisms of PGC-1β in human breast cancer have not been fully understood and the function requires to be further elucidated.

Methods

mRNA and protein expression of PGC-1β and FOXA2 in breast cancer tissues and cell lines were determined by qRT-PCR and Western Blotting, respectively. To further visualize the expression and localization of PGC-1β and FOXA2, immunochemistry and immunofluorescence staining methods were employed. The effect of PGC-1β and FOXA2 on cell proliferation and migration were evaluated by CCK8, clone formation, transwell and wound-healing assays, which has been done either with stable PGC-1β knockdown or FOXA2 overexpression in vitro. Xenografts model of nude mice were used to evaluate tumor growth in vivo. In addition, proteins expression of the PI3K-AKT-mTOR signaling pathway involved in the regulation of breast cancer were detected by Western Blotting.

Results

Our results showed that PGC-1β was upregulated and FOXA2 was downregulated in breast cancer tissues and cell lines. These two proteins can be interacted with each other to form the complex. Also, we found the combination of PGC-1β interference with FOXA2 overexpression significantly inhibited cell proliferation and migration in vitro as well as tumor growth in vivo. We further identified that PGC-1β and FOXA2 strongly correlated with the PI3K-AKT-mTOR signaling pathway, and they exerted their biological functions by activating this pathway.

Conclusions

We demonstrated that downregulation of PGC-1β combined with overexpression of FOXA2 obviously inhibited the function of breast cancer cells through regulating the PI3K-AKT-mTOR pathway.

Heterogeneity of Stem Cells in the Thyroid

Identification of thyroid stem cells in the past few years has made important contributions to our understanding of the cellular and molecular mechanisms that induce tissue regeneration and repair. Embryonic stem (ES) cells and induced-pluripotent stem cells have been used to establish reliable protocols to obtain mature thyrocytes and functional follicles for the treatment of thyroid diseases in mice. In addition, the discovery of resident thyroid progenitor cells, along with other sources of stem cells, has defined in detail the mechanisms responsible for tissue repair upon moderate or severe organ injury.In this chapter, we highlight in detail the current state of research on thyroid stem cells by focusing on (1) the description of the first experiments performed to obtain thyroid follicles from embryonic stem cells, (2) the identification of resident stem cells in the thyroid gland, and (3) the definition of the current translational in vivo and in vitro models used for thyroid tissue repair and regeneration.

Maternal smoking and high BMI disrupt thyroid gland development

BACKGROUND

Maternal lifestyle factors, including smoking and increased body weight, increase risks of adult diseases such as metabolic syndrome and infertility. The fetal thyroid gland is essential for the control of fetal metabolic rate, cardiac output, and brain development. Altered fetal thyroid function may contribute to increased disease onset later in life. Here, we investigated the impact of maternal smoking and high maternal weight on human fetal thyroid function during the second trimester.

METHODS

Thyroid glands and plasma were collected from fetuses electively terminated in the second trimester (normally progressing pregnancies). Plasma total triiodothyronine (T3) and total thyroxine (T4) were measured by solid-phase extraction-liquid chromatography-tandem mass spectrometry. Fetal plasma thyroid-stimulating hormone (TSH) levels were measured using a multiplex assay for human pituitary hormones. Histology and immunolocalization of thyroid developmental markers were examined in thyroid sections. Transcript levels of developmental, functional, apoptotic, and detoxification markers were measured by real-time PCR. Statistical analyses were performed using multivariate linear regression models with fetal age, sex, and maternal smoking or maternal body mass index (BMI) as covariates.

RESULTS

Maternal smoking was associated with significant changes in fetal plasma T4 and TSH levels during the second trimester. Smoke-exposed thyroids had reduced thyroid GATA6 and NKX2-1 transcript levels and altered developmental trajectories for ESR2 and AHR transcript levels. Maternal BMI > 25 was associated with increased fetal thyroid weight, increased plasma TSH levels, and abnormal thyroid histology in female fetuses. Normal developmental changes in AHR and ESR1 transcript expression were also abolished in fetal thyroids from mothers with BMI > 25.

CONCLUSIONS

For the first time, we show that maternal smoking and high maternal BMI are associated with disturbed fetal thyroid gland development and endocrine function in a sex-specific manner during the second trimester. These findings suggest that predisposition to post-natal disease is mediated, in part, by altered fetal thyroid gland development.

An in vivo model for thyroid regeneration and folliculogenesis

While thyroid is considered to be a dormant organ, when required, it can regenerate through increased cell proliferation. However, the mechanism for regeneration remains unknown. Nkx2-1(fl/fl);TPO-cre mouse thyroids exhibit a very disorganized appearance because their thyroids continuously degenerate and regenerate. In mouse thyroids, a cluster of cells are found near the tracheal cartilage and muscle, which are positive for expression of NKX2-1, the master transcription factor governing thyroid development and function. In the present study, we propose that this cluster of NKX2-1-positive cells may be the precursor cells that mature to become thyroid follicular cells, forming thyroid follicles. We also found that phosphorylation of AKT is induced by NKX2-1 in the proposed thyroid progenitor-like side-population cell-derived thyroid cell line (SPTL) cells, suggesting the possibility that NKX2-1 plays a role in differentiation through the modulation of AKT signaling. This study revealed that Nkx2-1(fl/fl);TPO-cre mice provide a suitable model to study in vivo regeneration and folliculogenesis of the thyroid.

Immunohistochemical profiling of the ultimobranchial remnants in the rat postnatal thyroid gland

Ultimobranchial (UB) remnants are a constant presence in the thyroid throughout rat postnatal life; however, the difficulty in identifying the most immature forms from the surrounding thyroid tissue prompted us to search for a specific marker. With that objective, we applied a panel of antibodies reported to be specific for their human counterpart, solid cell nests (SCNs), using double immunohistochemistry and immunofluorescence. Our results demonstrated that cytokeratin 34βE12 and p63 are highly sensitive markers for the immunohistologic screening of UB-remnants, independently of their maturity or size. Furthermore, rat UB-follicles (UBFs) coincided with human SCNs in the immunohistochemical pattern exhibited by both antigens. In contrast, the pattern displayed for calcitonin and thyroglobulin differs considerably but confirm the hypothesis that rat UB-cells can differentiate into both types of thyroid endocrine cells. This hypothesis agrees with recent findings that thyroid C-cells share an endodermic origin with follicular cells in rodents. We suggest that the persistence of p63-positive undifferentiated cells in UB-remnants may constitute a reservoir of basal/stem cells that persist beyond embryogenesis from which, in certain unknown conditions, differentiated thyroid cells or even unusual tumors may arise.

Regeneration of thyroid follicles from primordial cells in a murine thyroidectomized model

The functional unit of the thyroid gland, the thyroid follicle, dynamically responds to various stimuli to maintain thyroid hormone homeostasis. However, thyroid follicles in the adult human thyroid gland have a very limited regenerative capacity following partial resection of the thyroid gland. To gain insight into follicle regeneration in the adult thyroid gland, we observed the regeneration processes of murine thyroid follicles after partial resection of the lower third of the thyroid gland in 10-week-old male C57BL/6 mice. Based on sequential observation of the partially resected thyroid lobe, we found primitive follicles forming in the area corresponding to the central zone of the intact lateral thyroid lobe. The primitive thyroid follicles were multiciliated and had coarsely vacuolated cytoplasm and large vesicular nuclei. Consistently, these primitive follicular cells did not express the differentiation markers paired box gene-8 and thyroid transcription factor-1 (clone SPT24), but were positive for forkhead box protein A2 and leucine-rich repeat-containing G-protein-coupled receptor 4/GPR48. Follicles newly generated from the primitive follicles had clear or vacuolar cytoplasm with dense, darkly stained nuclei. At day 21 after partial thyroidectomy, the tall cuboidal follicular epithelial cells had clear or vacuolar cytoplasm, and the intraluminal colloid displayed pale staining. Smaller activated follicles were found in the central zone of the lateral lobe, whereas larger mature follicles were located in the peripheral zone. Based on these observations, we propose that the follicle regeneration process in the partially resected adult murine thyroid gland associated with the appearance of primitive follicular cells may be a platform for the budding of differentiated follicles in mice.

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.

Long Noncoding RNA and mRNA Expression Profiles in the Thyroid Gland of Two Phenotypically Extreme Pig Breeds Using Ribo-Zero RNA Sequencing

The thyroid gland is an important endocrine organ modulating development, growth, and metabolism, mainly by controlling the synthesis and secretion of thyroid hormones (THs). However, little is known about the pig thyroid transcriptome. Long non-coding RNAs (lncRNAs) regulate gene expression and play critical roles in many cellular processes. Yorkshire pigs have a higher growth rate but lower fat deposition than that of Jinhua pigs, and thus, these species are ideal models for studying growth and lipid metabolism. This study revealed higher levels of THs in the serum of Yorkshire pigs than in the serum of Jinhua pigs. By using Ribo-zero RNA sequencing—which can capture both polyA and non-polyA transcripts—the thyroid transcriptome of both breeds were analyzed and 22,435 known mRNAs were found to be expressed in the pig thyroid. In addition, 1189 novel mRNAs and 1018 candidate lncRNA transcripts were detected. Multiple TH-synthesis-related genes were identified among the 455 differentially-expressed known mRNAs, 37 novel mRNAs, and 52 lncRNA transcripts. Bioinformatics analysis revealed that differentially-expressed genes were enriched in the microtubule-based process, which contributes to THs secretion. Moreover, integrating analysis predicted 13 potential lncRNA-mRNA gene pairs. These data expanded the repertoire of porcine lncRNAs and mRNAs and contribute to understanding the possible molecular mechanisms involved in animal growth and lipid metabolism.

Normal vs cancer thyroid stem cells: the road to transformation

Recent investigations in thyroid carcinogenesis have led to the isolation and characterisation of a subpopulation of stem-like cells, responsible for tumour initiation, progression and metastasis. Nevertheless, the cellular origin of thyroid cancer stem cells (SCs) remains unknown and it is still necessary to define the process and the target population that sustain malignant transformation of tissue-resident SCs or the reprogramming of a more differentiated cell. Here, we will critically discuss new insights into thyroid SCs as a potential source of cancer formation in light of the available information on the oncogenic role of genetic modifications that occur during thyroid cancer development. Understanding the fine mechanisms that regulate tumour transformation may provide new ground for clinical intervention in terms of prevention, diagnosis and therapy.

Expression of stanniocalcin 1 in thyroid side population cells and thyroid cancer cells

BACKGROUND

Mouse thyroid side population (SP) cells consist of a minor population of mouse thyroid cells that may have multipotent thyroid stem cell characteristics. However the nature of thyroid SP cells remains elusive, particularly in relation to thyroid cancer. Stanniocalcin (STC) 1 and 2 are secreted glycoproteins known to regulate serum calcium and phosphate homeostasis. In recent years, the relationship of STC1/2 expression to cancer has been described in various tissues.

METHOD

Microarray analysis was carried out to determine genes up- and down-regulated in thyroid SP cells as compared with non-SP cells. Among genes up-regulated, stanniocalcin 1 (STC1) was chosen for study because of its expression in various thyroid cells by Western blotting and immunohistochemistry.

RESULTS

Gene expression analysis revealed that genes known to be highly expressed in cancer cells and/or involved in cancer invasion/metastasis were markedly up-regulated in SP cells from both intact as well as partial thyroidectomized thyroids. Among these genes, expression of STC1 was found in five human thyroid carcinoma-derived cell lines as revealed by analysis of mRNA and protein, and its expression was inversely correlated with the differentiation status of the cells. Immunohistochemical analysis demonstrated higher expression of STC1 in the thyroid tumor cell line and thyroid tumor tissues from humans and mice.

CONCLUSION

These results suggest that SP cells contain a population of cells that express genes also highly expressed in cancer cells including Stc1, which warrants further study on the role of SP cells and/or STC1 expression in thyroid cancer.

FOXA2 attenuates the epithelial to mesenchymal transition by regulating the transcription of E-cadherin and ZEB2 in human breast cancer

The Forkhead Box A2 (FOXA2) transcription factor is required for embryonic development and for normal functions of multiple adult tissues, in which the maintained expression of FOXA2 is usually related to preventing the progression of malignant transformation. In this study, we found that FOXA2 prevented the epithelial to mesenchymal transition (EMT) in human breast cancer. We observed a strong correlation between the expression levels of FOXA2 and the epithelial phenotype. Knockdown of FOXA2 promoted the mesenchymal phenotype, whereas stable overexpression of FOXA2 attenuated EMT in breast cancer cells. FOXA2 was found to endogenously bind to and stimulate the promoter of E-cadherin that is crucial for epithelial phenotype of the tumor cells. Meanwhile, FOXA2 prevented EMT of breast cancer cells by repressing the expression of EMT-related transcription factor ZEB2 through recruiting a transcriptional corepressor TLE3 to the ZEB2 promoter. The stable overexpression of FOXA2 abolished metastasis of breast cancer cells in vivo. This study confirmed that FOXA2 inhibited EMT in breast cancer cells by regulating the transcription of EMT-related genes such as E-cadherin and ZEB2.

Cancer etiology. Variation in cancer risk among tissues can be explained by the number of stem cell divisions

Some tissue types give rise to human cancers millions of times more often than other tissue types. Although this has been recognized for more than a century, it has never been explained. Here, we show that the lifetime risk of cancers of many different types is strongly correlated (0.81) with the total number of divisions of the normal self-renewing cells maintaining that tissue's homeostasis. These results suggest that only a third of the variation in cancer risk among tissues is attributable to environmental factors or inherited predispositions. The majority is due to "bad luck," that is, random mutations arising during DNA replication in normal, noncancerous stem cells. This is important not only for understanding the disease but also for designing strategies to limit the mortality it causes.

Thyroid C-Cell Biology and Oncogenic Transformation

The thyroid parafollicular cell, or commonly named "C-cell," functions in serum calcium homeostasis. Elevations in serum calcium trigger release of calcitonin from the C-cell, which in turn functions to inhibit absorption of calcium by the intestine, resorption of bone by the osteoclast, and reabsorption of calcium by renal tubular cells. Oncogenic transformation of the thyroid C-cell is thought to progress through a hyperplastic process prior to malignancy with increasing levels of serum calcitonin serving as a biomarker for tumor burden. The discovery that multiple endocrine neoplasia type 2 is caused by activating mutations of the RET gene serves to highlight the RET-RAS-MAPK signaling pathway in both initiation and progression of medullary thyroid carcinoma (MTC). Thyroid C-cells are known to express RET at high levels relative to most cell types; therefore, aberrant activation of this receptor is targeted primarily to the C-cell, providing one possible cause of tissue-specific oncogenesis. The role of RET signaling in normal C-cell function is unknown though calcitonin gene transcription appears to be sensitive to RET activation. Beyond RET, the modeling of oncogenesis in animals and screening of human tumors for candidate gene mutations have uncovered mutation of RAS family members and inactivation of Rb1 regulatory pathway as potential mediators of C-cell transformation. A growing understanding of how RET interacts with these pathways, both in normal C-cell function and during oncogenic transformation, will help in the development of novel molecular-targeted therapies.

Detection of thyroid cancer stem cells in papillary thyroid carcinoma

CONTEXT

Special populations of cells that can efficiently initiate tumor growth have been characterized, and this feature supports the cancer stem cell theory. These cancer stem cell populations have been identified with CD44 and POU5F1. Most cancer stem cells express high levels of CD44 and low levels of CD24. In thyroid lesions, cancer stem cells have been detected in anaplastic carcinoma. However, little is known about the presence of cancer stem cells in papillary thyroid carcinoma (PTC), especially in recurrent PTC.

OBJECTIVE AND DESIGN

PTC cells were labeled and sorted by flow cytometry to obtain two populations. Total RNA was prepared from cells with high CD44 and CD24 expressions (CD44+CD24+) and from cells with high CD44 and low CD24 expressions (CD44+CD24-). The expressions of the stem cell marker POU5F1 and several differentiated thyroid markers were measured via real-time PCR.

RESULTS

CD44+CD24- cells were present in all PTCs tested, and the percentage of these cells was higher in clinically aggressive recurrent PTC than in less aggressive primary PTCs. Higher expression of POU5F1 was found in CD44+CD24- cells compared with that of CD44+CD24+ cells. The expression of POU5F1 was higher in thyrospheroids grown in serum-free condition than in cells grown in the presence of serum from the same patient, and the tumor was initiated in mice using thyrospheroids.

CONCLUSIONS

The percentage of CD44+CD24- cells varied from tumor to tumor. Our findings suggest that cancer stem cells are present in PTC.

Thyroid regeneration: how stem cells play a role?

Many tissues if not all are thought to contain stem cells that are responsible for regeneration and repair of the tissue after injury. Dysregulation of tissue regeneration may result in various pathological conditions, among which cancer is the most extensively studied. Notably, the so-called cancer stem cells or tumor-initiating cells, have been studied in order to understand the mechanisms of carcinogenesis and/or metastasis. However, the nature of cancer stem cells, let alone normal stem/progenitor cells, particularly those of the thyroid remains elusive. There remains a gap in knowledge between adult thyroid stem/progenitor cells and cancer stem cells of the thyroid, and if and/or how they are related to each other. Understanding of the mechanism for thyroid regeneration and mode of participation of normal adult thyroid stem/progenitor cells in this process will hopefully yield a more complete understanding of the nature of thyroid cancer stem cells, and/or help understand the pathogenesis of other thyroid diseases. This review summarizes the current understanding of adult thyroid stem/progenitor cells, with particular emphasis on how they contribute to thyroid regeneration.

Stem cell antigen 1-positive mesenchymal cells are the origin of follicular cells during thyroid regeneration

Many tissues are thought to contain adult stem/progenitor cells that are responsible for repair of the tissue where they reside upon damage and/or carcinogenesis, conditions when cellular homeostasis becomes uncontrolled. While the presence of stem/progenitor cells of the thyroid has been suggested, how these cells contribute to thyroid regeneration remains unclear. Here we show the origin of thyroid follicular cells and the process of their maturation to become follicular cells during regeneration. By using β-galactosidase (β-gal) reporter mice in conjunction with partial thyroidectomy as a model for thyroid regeneration, and bromodeoxyuridine (BrdU) long label-retaining cell analysis, we demonstrated that stem cell antigen 1 (Sca1) and BrdU-positive, but β-gal and NKX2-1 negative cells were found in the non-follicular mesenchymal area 7 days after partial thyroidectomy. They temporarily co-expressed cytokeratin 14, and were observed in part of follicles by day 35 post-partial thyroidectomy. Sca1, BrdU, β-gal, and NKX2-1-positive cells were found 120 days post-partial thyroidectomy. These results suggested that Sca1 and BrdU positive cells may participate in the formation of new thyroid follicles after partial thyroidectomy. The process of thyroid follicular cell regeneration was recapitulated in ex vivo thyroid slice collagen gel culture studies. These studies will facilitate research on thyroid stem/progenitor cells and their roles in thyroid diseases, particularly thyroid carcinomas.

Stem cells and cancer stem-like cells in endocrine tissues

Cancer stem-like cells are a subpopulation of self-renewing cells that are more resistant to chemotherapy and radiation therapy than the other surrounding cancer cells. The cancer stem cell model predicts that only a subset of cancer cells possess the ability to self-renew and produce progenitor cells that can reconstitute and sustain tumor growth. Evidence supporting the existence of cancer stem-like cells in the thyroid, pituitary, and in other endocrine tissues is rapidly accumulating. These cells have been studied using specific biomarkers including: CD133, CD44, Nestin, Nanog, and aldehyde dehydrogenase enzyme. Putative cancer stem-like cells can be studied in vitro using serum-free media supplemented with basic fibroblast growth factor and epidermal growth factor grown in low attachment plates or in extracellular matrix leading to sphere formation in vitro. Cancer stem-like cells can also be separated by fluorescent cell sorting and used for in vitro or in vivo studies. Injection of enriched populations of cancer stem-like cells (also referred to as tumor initiating cells) into immunodeficient mice results in growth of xenografts which express cancer stem-like biomarkers. Human cancer stem-like cells have been identified in thyroid cancer cell lines, in primary thyroid cancers, in normal pituitary, and in pituitary tumors. Other recent studies suggest the existence of stem cells and cancer stem-like cells in endocrine tumors of the gastrointestinal tract, pancreas, lungs, adrenal, parathyroid, and skin. New discoveries in this field may lead to more effective therapies for highly aggressive and lethal endocrine cancers.