Directed differentiation of mouse embryonic stem cells into thyroid follicular cells

Translation of cell therapies to treat autoimmune disorders

Autoimmune diseases are a diverse and complex set of chronic disorders with a substantial impact on patient quality of life and a significant global healthcare burden. Current approaches to autoimmune disease treatment comprise broadly acting immunosuppressive drugs that lack disease specificity, possess limited efficacy, and confer undesirable side effects. Additionally, there are limited treatments available to restore organs and tissues damaged during the course of autoimmune disease progression. Cell therapies are an emergent area of therapeutics with the potential to address both autoimmune disease immune dysfunction as well as autoimmune disease-damaged tissue and organ systems. In this review, we discuss the pathogenesis of common autoimmune disorders and the state-of-the-art in cell therapy approaches to (1) regenerate or replace autoimmune disease-damaged tissue and (2) eliminate pathological immune responses in autoimmunity. Finally, we discuss critical considerations for the translation of cell products to the clinic.

Regeneration of Thyroid Glands in the Spleen Restores Homeostasis in Thyroidectomy Mice

Surgical removal of the thyroid gland (TG) for treating thyroid disorders leaves the patients on lifelong hormone replacement that partially compensates the physiological needs, but regenerating TG is challenging. Here, an approach is reported to regenerate TG within the spleen for fully restoring the thyroid's functions in mice, by transplanting thyroid tissue blocks to the spleen. Within 48 h, the transplanted tissue efficiently revascularizes, forming thyroid follicles similar to the native gland after 4 weeks. Structurally, the ectopically generated thyroid integrates with the surrounding splenic tissue while maintaining its integrity, separate from the lymphatic tissue. Functionally, it fully restores the native functions of the TG in hormone regulation in response to physiological stimuli, outperforming the established method of oral levothyroxine therapy in maintaining systemic homeostasis. The study demonstrates the full restoration of thyroid functions post-thyroidectomy by intrasplenic TG regeneration, providing fresh insights for designing novel therapies for thyroid-related disorders.

Thyroid Gland Organoids: Current models and insights for application in tissue engineering

The incidence of treatment of thyroid disease and consequential hypothyroidism has been increasing over the past few years. To maintain adequate thyroid hormone levels, these patients require daily supplementation with levothyroxine (L-T4) for the rest of their lives. However, a large part of these patients experiences difficulties due to the medication, which causes a decrease in their quality of life. Regenerative medicine through tissue engineering could provide a potential therapy by establishing tissue engineering models, such as those employing thyroid-derived organoids. The development of such treatment options may replace the need for additional hormonal replacement therapy. This review aims to highlight the current knowledge on thyroid regenerative medicine using organoids for tissue engineering, and to discuss insights into potential methods to optimize thyroid engineering culture systems. Finally, we will describe several challenges faced when utilising these models.

Stem cells therapy for thyroid diseases: progress and challenges

Background

Thyroid hormones are indispensable for organ development and maintaining homeostasis. Thyroid diseases, including thyroiditis and thyroid cancer, affect the normal secretion of hormones and result in thyroid dysfunction.

Objective

This review focuses on therapeutic applications of stem cells for thyroid diseases.

Methods

A literature search of Medline and PubMed was conducted (January 2000–July 2021) to identify recent reports on stem cell therapy for thyroid diseases.

Results

Stem cells are partially developed cell types. They have the capacity to form specialized cells. Besides embryonic stem cells and mesenchymal stem cells, organ resident stem cells and cancer stem cells are recently reported to have important roles in forming organ specific cells and cancers. Stem cells, especially mesenchymal stem cells, have anti-inflammatory and anticancer functions as well.

Conclusions

This review outlines the therapeutic potency of embryonic stem cells, mesenchymal stem cells, thyroid resident stem cells, and thyroid cancer stem cells in thyroid cells’ regeneration, thyroid function modulation, thyroiditis suppression, and antithyroid cancers. Stem cells represent a promising form of treatment for thyroid disorders.

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.

Modeling Human Organ Development and Diseases With Fetal Tissue-Derived Organoids

Recent advances in human organoid technology have greatly facilitated the study of organ development and pathology. In most cases, these organoids are derived from either pluripotent stem cells or adult stem cells for the modeling of developmental events and tissue homeostasis. However, due to the lack of human fetal tissue references and research model, it is still challenging to capture early developmental changes and underlying mechanisms in human embryonic development. The establishment of fetal tissue–derived organoids in rigorous time points is necessary. Here we provide an overview of the strategies and applications of fetal tissue–derived organoids, mainly focusing on fetal organ development research, developmental defect disease modeling, and organ–organ interaction study. Discussion of the importance of fetal tissue research also highlights the prospects and challenges in this field.

Generation and Differentiation of Adult Tissue-Derived Human Thyroid Organoids

Total thyroidectomy as part of thyroid cancer treatment results in hypothyroidism requiring lifelong daily thyroid hormone replacement. Unbalanced hormone levels result in persistent complaints such as fatigue, constipation, and weight increase. Therefore, we aimed to investigate a patient-derived thyroid organoid model with the potential to regenerate the thyroid gland. Murine and human thyroid-derived cells were cultured as organoids capable of self-renewal and which expressed proliferation and putative stem cell and thyroid characteristics, without a change in the expression of thyroid tumor-related genes. These organoids formed thyroid-tissue-resembling structures in culture. (Xeno-)transplantation of 600,000 dispersed organoid cells underneath the kidney capsule of a hypothyroid mouse model resulted in the generation of hormone-producing thyroid-resembling follicles. This study provides evidence that thyroid-lineage-specific cells can form organoids that are able to self-renew and differentiate into functional thyroid tissue. Subsequent (xeno-)transplantation of these thyroid organoids demonstrates a proof of principle for functional miniature gland formation.

Long Term Rescue of the TSH Receptor Knock-Out Mouse - Thyroid Stem Cell Transplantation Restores Thyroid Function

The synergistic activation of transcription factors can lead to thyroid progenitor cell speciation. We have previously shown in vitro that mouse or human stem cells, expressing the transcription factors NKx2-1 and Pax8, can differentiate into thyroid neo-follicular structures (TFS). We now show that syngeneic mouse TFS when implanted into hypothyroid TSH receptor knockout (TSHR-KO) mice can ameliorate the hypothyroid state for an extended period. ES cells derived from heterozygous TSHR-KO blastocysts were stably transfected with Nkx2-1-GFP and Pax8-mcherry constructs and purified into 91.8% double positive cells by flow cytometry. After 5 days of activin A treatment these double positive cells were then induced to differentiate into neo-follicles in Matrigel for 21 days in the presence of 500μU/mL of TSH. Differentiated TFS expressing thyroglobulin mRNA were implanted under the kidney capsule of 4-6 weeks old TSHR-KO mice (n=5) as well as hind limb muscle (n=2) and anterior chamber of one eye (n=2). Five of the mice tested after 4 weeks were all rendered euthyroid and all mice remained euthyroid at 20 weeks post implantation. The serum T4 fully recovered (pre-bleed 0.62 ± 0.03 to 8.40 ± 0.57 µg/dL) and the previously elevated TSH became normal or suppressed (pre-bleed 391 ± 7.6 to 4.34 ± 1.25 ng/dL) at the end of the 20 week observation period. The final histology obtained from the implanted kidney tissues showed only rudimentary thyroid follicular structures but which stained positive for thyroglobulin expression. The presence of only rudimentary structures at the site of implant on these extended animals suggested possible migration of cells from the site of implant or an inability of TFCs to maintain proper follicular morphology in these external sites for extended periods. However, there were no signs of tumor formation and no immune infiltration. These preliminary studies show that TSHR-KO mice are a useful model for orthotropic implantation of functional thyroid cells without the need for thyroidectomy, radioiodine ablation or anti thyroid drug control of thyroid function. This approach is also proof of principle that thyroid cells derived from mouse ES cells are capable of surviving as functional neo-follicles in vivo for an extended period of 20 weeks.

Derivation of Thyroid Follicular Cells From Pluripotent Stem Cells: Insights From Development and Implications for Regenerative Medicine

Stem cell-based therapies to reconstitute in vivo organ function hold great promise for future clinical applications to a variety of diseases. Hypothyroidism resulting from congenital lack of functional thyrocytes, surgical tissue removal, or gland ablation, represents a particularly attractive endocrine disease target that may be conceivably cured by transplantation of long-lived functional thyroid progenitors or mature follicular epithelial cells, provided a source of autologous cells can be generated and a variety of technical and biological challenges can be surmounted. Here we review the emerging literature indicating that thyroid follicular epithelial cells can now be engineered in vitro from the pluripotent stem cells (PSCs) of mice, normal humans, or patients with congenital hypothyroidism. We review the in vivo embryonic development of the thyroid gland and explain how emerging discoveries in developmental biology have been utilized as a roadmap for driving PSCs, which resemble cells of the early embryo, into mature functional thyroid follicles in vitro. Finally, we discuss the bioengineering, biological, and clinical hurdles that now need to be addressed if the goals of life-long cure of hypothyroidism through cell- and/or gene-based therapies are to be attained.

Practical applications of studies on the TSH receptor and TSH receptor autoantibodies

Studies on the TSH receptor (TSHR) have numerous practical applications in vitro and in vivo. For example human monoclonal autoantibodies (MAbs) to the TSHR are useful reagents for in vitro diagnostics. Measurement of TSHR autoantibodies (TRAbs) is helpful in diagnosis and management of autoimmune thyroid disease. Currently available highly sensitive and specific assays to measure TRAbs use the human TSHR MAb M22 instead of the TSH. Furthermore, preparations of the human TSHR MAb M22 are useful as the World Health Organisation International Standard for thyroid stimulating antibody and for calibration of the assays for measuring TRAbs. Preparations of thermostabilised TSHR extracellular domain have recently become available and this is likely to have an impact on improvements in specificity testing for TRAb assays. In addition the stable TSHR preparations have practical application for specific immunoadsorption of patient serum TRAbs. Human TSHR MAbs also have promising prospects as new therapeutics. Autoantibodies with TSHR antagonistic activities are "natural" inhibitors of TSHR stimulation and are expected to be helpful in controlling TSHR activity in patients with Graves' disease, Graves' ophthalmopathy and thyroid cancer.

Generation of embryonic stem cells derived from the inner cell mass of blastocysts of outbred ICR mice

Embryonic stem cells (ESCs) derived from outbred mice which share several genetic characteristics similar to humans have been requested for developing stem cell-based bioengineering techniques directly applicable to humans. Here, we report the generation of ESCs derived from the inner cell mass of blastocysts retrieved from 9-week-old female outbred ICR mice mated with 9-week-old male outbred ICR mice (_ICRESCs). Similar to those from 129/Ola mouse blastocysts (_E14ESCs), the established _ICRESCs showed inherent characteristics of ESCs except for partial and weak protein expression and activity of alkaline phosphatase. Moreover, _ICRESCs were not originated from embryonic germ cells or pluripotent cells that may co-exist in outbred ICR strain-derived mouse embryonic fibroblasts (_ICRMEFs) used for deriving colonies from inner cell mass of outbred ICR mouse blastocysts. Furthermore, instead of outbred _ICRMEFs, hybrid _B6CBAF1MEFs as feeder cells could sufficiently support in vitro maintenance of _ICRESC self-renewal. Additionally, _ICRESC-specific characteristics (self-renewal, pluripotency, and chromosomal normality) were observed in _ICRESCs cultured for 40th subpassages (164 days) on _B6CBAF1MEFs without any alterations. These results confirmed the successful establishment of ESCs derived from outbred ICR mice, and indicated that self-renewal and pluripotency of the established _ICRESCs could be maintained on _B6CBAF1MEFs in culture.

Differentiation of human pluripotent stem cells toward pharyngeal endoderm derivatives: Current status and potential

The pharyngeal apparatus, a transient embryological structure, includes diverse cells from all three germ layers that ultimately contribute to a variety of adult tissues. In particular, pharyngeal endoderm produces cells of the inner ear, palatine tonsils, the thymus, parathyroid and thyroid glands, and ultimobranchial bodies. Each of these structures and organs contribute to vital human physiological processes, including central immune tolerance (thymus) and metabolic homeostasis (parathyroid and thyroid glands, and ultimobranchial bodies). Thus, improper development or damage to pharyngeal endoderm derivatives leads to complicated and severe human maladies, such as autoimmunity, immunodeficiency, hypothyroidism, and/or hypoparathyroidism. To study and treat such diseases, we can utilize human pluripotent stem cells (hPSCs), which differentiate into functionally mature cells in vitro given the proper developmental signals. Here, we discuss current efforts regarding the directed differentiation of hPSCs toward pharyngeal endoderm derivatives. We further discuss model system and therapeutic applications of pharyngeal endoderm cell types produced from hPSCs. Finally, we provide suggestions for improving hPSC differentiation approaches to pharyngeal endoderm derivatives with emphasis on current single cell-omics and 3D culture system technologies.

Generation of Thyroid Tissues From Embryonic Stem Cells via Blastocyst Complementation In Vivo

The generation of mature, functional, thyroid follicular cells from pluripotent stem cells would potentially provide a therapeutic benefit for patients with hypothyroidism, but in vitro differentiation remains difficult. We earlier reported the in vivo generation of lung organs via blastocyst complementation in fibroblast growth factor 10 (Fgf10), compound, heterozygous mutant (Fgf10 Ex1^mut/Ex3^mut) mice. Fgf10 also plays an essential role in thyroid development and branching morphogenesis, but any role thereof in thyroid organogenesis remains unclear. Here, we report that the thyroids of Fgf10 Ex1^mut/Ex3^mut mice exhibit severe hypoplasia, and we generate thyroid tissues from mouse embryonic stem cells (ESCs) in Fgf10 Ex1^mut/Ex3^mut mice via blastocyst complementation. The tissues were morphologically normal and physiologically functional. The thyroid follicular cells of Fgf10 Ex1^mut/Ex3^mut chimeric mice were derived largely from GFP-positive mouse ESCs although the recipient cells were mixed. Thyroid generation in vivo via blastocyst complementation will aid functional thyroid regeneration.

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.

Development of the thyroid gland

Thyroid hormones are crucial for organismal development and homeostasis. In humans, untreated congenital hypothyroidism due to thyroid agenesis inevitably leads to cretinism, which comprises irreversible brain dysfunction and dwarfism. Elucidating how the thyroid gland - the only source of thyroid hormones in the body - develops is thus key for understanding and treating thyroid dysgenesis, and for generating thyroid cells in vitro that might be used for cell-based therapies. Here, we review the principal mechanisms involved in thyroid organogenesis and functional differentiation, highlighting how the thyroid forerunner evolved from the endostyle in protochordates to the endocrine gland found in vertebrates. New findings on the specification and fate decisions of thyroid progenitors, and the morphogenesis of precursor cells into hormone-producing follicular units, are also discussed.

Regenerative therapy for hypothyroidism: Mechanisms and possibilities

The ability to derive functional thyroid follicular cells from embryonic stem cells (ESCs) or induced pluripotent stem cells (iPSCs) would provide potential therapeutic benefit for patients with congenital or post-surgical hypothyroidism. Furthermore, understanding the process by which thyroid follicular cells develop will also provide great insight into the key steps that regulate the development of other tissues derived from endoderm. Here we review the advances in our understanding of the process of thyroid follicular cell development including the creation of two models that have allowed for the rescue of hypothyroid mouse recipients through the transplantation of thyroid follicular cells derived from mouse ESCs. Rapid progress in the field suggests that the same success should be achievable with human ESCs or iPSCs in the near future. Additionally, the availability of ESC or iPSC-derived thyroid follicular cell models will provide ideal systems to explore how genetic mutations, drugs or illness impact thyroid function in a cell-autonomous fashion.

Functional Thyroid Follicular Cells Differentiation from Human-Induced Pluripotent Stem Cells in Suspension Culture

The replacement of regenerated thyroid follicular cells (TFCs) is a promising therapeutic strategy for patients with hypothyroidism. Here, we have succeeded in inducing functional TFCs from human-induced pluripotent stem cells (iPSCs) in scalable suspension culture. Differentiation of iPSCs with Activin A treatment produced Sox17- and FoxA2-expressing definitive endodermal cells that also expressed thyroid transcription factors Pax8 and Nkx2-1. Further treatment with thyroid-stimulating hormone (TSH) induced TFCs expressing various types of thyroid proteins including TSH receptor, sodium-iodide symporter, thyroglobulin, and thyroid peroxidase. Interestingly, differentiated cells secreted free thyroxine in vitro. These results indicate successful differentiation of human iPSCs to functional TFCs that may enable us to fabricate thyroid tissues for regenerative medicine and disease models.

Generation of Functional Thyroid Tissue Using 3D-Based Culture of Embryonic Stem Cells

During the last decade three-dimensional (3D) cultures of pluripotent stem cells have been intensively used to understand morphogenesis and molecular signaling important for the embryonic development of many tissues. In addition, pluripotent stem cells have been shown to be a valid tool for the in vitro modeling of several congenital or chronic human diseases, opening new possibilities to study their physiopathology without using animal models. Even more interestingly, 3D culture has proved to be a powerful and versatile tool to successfully generate functional tissues ex vivo. Using similar approaches, we here describe a protocol for the generation of functional thyroid tissue using mouse embryonic stem cells and give all the details and references for its characterization and analysis both in vitro and in vivo. This model is a valid approach to study the expression and the function of genes involved in the correct morphogenesis of thyroid gland, to elucidate the mechanisms of production and secretion of thyroid hormones and to test anti-thyroid drugs.

Microencapsulation of porcine thyroid cell organoids within a polymer microcapsule construct

Hypothyroidism is a common condition of hormone deficiency, and oral administration of thyroid hormones is currently the only available treatment option. However, there are some disadvantages with this treatment modality including compliance challenges to patients. Therefore, a physiologically based alternative therapy for hypothyroidism with little or no side-effects is needed. In this study, we have developed a method for microencapsulating porcine thyroid cells as a thyroid hormone replacement approach. The hybrid wall of the polymer microcapsules permits thyroid hormone release while preventing immunoglobulin antibodies from entry. This strategy could potentially enable implantation of the microcapsule organoids containing allogeneic or xenogeneic thyroid cells to secret hormones over time without the need for immunosuppression of recipients. Porcine thyroid cells were isolated and encapsulated in alginate-poly-L-ornithine-alginate microcapsules using a microfluidic device. The porcine thyroid cells formed three-dimensional follicular spheres in the microcapsules with decent cell viability and proliferation. Thyroxine release from the encapsulated cells was higher than from unencapsulated cells ( P < 0.05) and was maintained during the entire duration of experiment (>28 days). These results suggest that the microencapsulated thyroid cell organoids may have the potential to be used for therapy and/or drug screening.

ICRP Publication 131: Stem Cell Biology with Respect to Carcinogenesis Aspects of Radiological Protection

This report provides a review of stem cells/progenitor cells and their responses to ionising radiation in relation to issues relevant to stochastic effects of radiation that form a major part of the International Commission on Radiological Protection's system of radiological protection. Current information on stem cell characteristics, maintenance and renewal, evolution with age, location in stem cell 'niches', and radiosensitivity to acute and protracted exposures is presented in a series of substantial reviews as annexes concerning haematopoietic tissue, mammary gland, thyroid, digestive tract, lung, skin, and bone. This foundation of knowledge of stem cells is used in the main text of the report to provide a biological insight into issues such as the linear-no-threshold (LNT) model, cancer risk among tissues, dose-rate effects, and changes in the risk of radiation carcinogenesis by age at exposure and attained age. Knowledge of the biology and associated radiation biology of stem cells and progenitor cells is more developed in tissues that renew fairly rapidly, such as haematopoietic tissue, intestinal mucosa, and epidermis, although all the tissues considered here possess stem cell populations. Important features of stem cell maintenance, renewal, and response are the microenvironmental signals operating in the niche residence, for which a well-defined spatial location has been identified in some tissues. The identity of the target cell for carcinogenesis continues to point to the more primitive stem cell population that is mostly quiescent, and hence able to accumulate the protracted sequence of mutations necessary to result in malignancy. In addition, there is some potential for daughter progenitor cells to be target cells in particular cases, such as in haematopoietic tissue and in skin. Several biological processes could contribute to protecting stem cells from mutation accumulation: (a) accurate DNA repair; (b) rapidly induced death of injured stem cells; (c) retention of the DNA parental template strand during divisions in some tissue systems, so that mutations are passed to the daughter differentiating cells and not retained in the parental cell; and (d) stem cell competition, whereby undamaged stem cells outcompete damaged stem cells for residence in the niche. DNA repair mainly occurs within a few days of irradiation, while stem cell competition requires weeks or many months depending on the tissue type. The aforementioned processes may contribute to the differences in carcinogenic radiation risk values between tissues, and may help to explain why a rapidly replicating tissue such as small intestine is less prone to such risk. The processes also provide a mechanistic insight relevant to the LNT model, and the relative and absolute risk models. The radiobiological knowledge also provides a scientific insight into discussions of the dose and dose-rate effectiveness factor currently used in radiological protection guidelines. In addition, the biological information contributes potential reasons for the age-dependent sensitivity to radiation carcinogenesis, including the effects of in-utero exposure.

Cell Growth Dynamics in Embryonic and Adult Mouse Thyroid Revealed by a Novel Approach to Detect Thyroid Gland Subpopulations

BACKGROUND

The thyroid is composed of endocrine epithelial cells, blood vessels, and mesenchyme. However, no data exist thus far on absolute cell numbers, relative distribution, and proliferation of the different cell populations in the developing and mature thyroid. The aim of this study was therefore to establish a flow cytometry protocol that allows detection and quantification of discrete cell populations in embryonic and adult murine thyroid tissues.

METHODS

Cell-type anti-mouse specific antibodies were used for erythroid cells (Ter119), hematopoietic cells (CD45), epithelial cells (EpCam/CD326, E-cadherin/CD324), thyroid follicular cells and C-cells (Nkx2-1), endothelial cells (Pecam/CD31, Icam-1/CD54), and fibroblasts (PDGFRa/CD140a). Proliferating cells were detected after labeling with 5-bromo-2'-deoxyuridine (BrdU). For flow cytometry analyses, micro-dissected embryonic (E) and adult thyroids were pooled (E13.5, n = 25; E15.5, n = 15; E17.5, n = 15; adult, n = 4) in one sample.

RESULTS

The absolute parenchymal cell numbers per mouse thyroid (M ± SD), excluding the large number of CD45(+) and Ter119(+) cells, increased from 7425 ± 1338 at E13.5 to 271,561 ± 22,325 in adult tissues. As expected, Nkx2-1(+) cells represented the largest cell population in adult tissues (61.2 ± 1.1%). Surprisingly, at all three embryonic stages analyzed, thyroid follicular cells and C-cells accounted only for a small percentage of the total thyroid cell mass (between 4.7 ± 0.4% and 9.4 ± 1.6%). In contrast, the largest cell population at all three embryonic stages was identified as PDGFRa/CD140a(+) fibroblasts (61.4 ± 0.4% to 77.3 ± 1.1%). However, these cells represented the smallest population in adult tissues (5.2 ± 0.8%). Pecam/CD31(+) endothelial cells increased from E13.5 to E15.5 from 3.7 ± 0.8% to 8.5 ± 3.0%, then remained stable at E17.5 and adult tissues. Proliferation rates were sizable during the entire organogenesis but differed between cell populations, with distinct proliferative peaks at E13.5 in epithelial cells (32.7 ± 0.6% BrdU(+) cells), and at E15.5 in endothelial cells (22.4 ± 2.4% BrdU(+) cells). Fibroblasts showed a constant proliferation rate in embryonic tissues. In adult tissues, BrdU(+) cells were between 0.1% and 0.4% in all cell types.

CONCLUSIONS

Using a novel flow cytometry-based method, a previously unobserved highly dynamic growth pattern of thyroid cell populations during embryogenesis was uncovered. This approach will provide a useful new tool for cell function analyses in murine thyroid disease models.

Regeneration of Thyroid Function by Transplantation of Differentiated Pluripotent Stem Cells

Differentiation of functional thyroid epithelia from pluripotent stem cells (PSCs) holds the potential for application in regenerative medicine. However, progress toward this goal is hampered by incomplete understanding of the signaling pathways needed for directed differentiation without forced overexpression of exogenous transgenes. Here we use mouse PSCs to identify key conserved roles for BMP and FGF signaling in regulating thyroid lineage specification from foregut endoderm in mouse and Xenopus. Thyroid progenitors derived from mouse PSCs can be matured into thyroid follicular organoids that provide functional secretion of thyroid hormones in vivo and rescue hypothyroid mice after transplantation. Moreover, by stimulating the same pathways, we were also able to derive human thyroid progenitors from normal and disease-specific iPSCs generated from patients with hypothyroidism resulting from NKX2-1 haploinsufficiency. Our studies have therefore uncovered the regulatory mechanisms that underlie early thyroid organogenesis and provide a significant step toward cell-based regenerative therapy for hypothyroidism.

Thyrostimulin Regulates Osteoblastic Bone Formation During Early Skeletal Development

The ancestral glycoprotein hormone thyrostimulin is a heterodimer of unique glycoprotein hormone subunit alpha (GPA)2 and glycoprotein hormone subunit beta (GPB)5 subunits with high affinity for the TSH receptor. Transgenic overexpression of GPB5 in mice results in cranial abnormalities, but the role of thyrostimulin in bone remains unknown. We hypothesized that thyrostimulin exerts paracrine actions in bone and determined: 1) GPA2 and GPB5 expression in osteoblasts and osteoclasts, 2) the skeletal consequences of thyrostimulin deficiency in GPB5 knockout (KO) mice, and 3) osteoblast and osteoclast responses to thyrostimulin treatment. Gpa2 and Gpb5 expression was identified in the newborn skeleton but declined rapidly thereafter. GPA2 and GPB5 mRNAs were also expressed in primary osteoblasts and osteoclasts at varying concentrations. Juvenile thyrostimulin-deficient mice had increased bone volume and mineralization as a result of increased osteoblastic bone formation. However, thyrostimulin failed to induce a canonical cAMP response or activate the noncanonical Akt, ERK, or mitogen-activated protein kinase (P38) signaling pathways in primary calvarial or bone marrow stromal cell-derived osteoblasts. Furthermore, thyrostimulin did not directly inhibit osteoblast proliferation, differentiation or mineralization in vitro. These studies identify thyrostimulin as a negative but indirect regulator of osteoblastic bone formation during skeletal development.

Human embryonic stem cells form functional thyroid follicles

OBJECTIVE

The molecular events that lead to human thyroid cell speciation remain incompletely characterized. It has been shown that overexpression of the regulatory transcription factors Pax8 and Nkx2-1 (ttf-1) directs murine embryonic stem (mES) cells to differentiate into thyroid follicular cells by initiating a transcriptional regulatory network. Such cells subsequently organized into three-dimensional follicular structures in the presence of extracellular matrix. In the current study, human embryonic stem (hES) cells were studied with the aim of recapitulating this scenario and producing functional human thyroid cell lines.

METHODS

Reporter gene tagged pEZ-lentiviral vectors were used to express human PAX8-eGFP and NKX2-1-mCherry in the H9 hES cell line followed by differentiation into thyroid cells directed by Activin A and thyrotropin (TSH).

RESULTS

Both transcription factors were expressed efficiently in hES cells expressing either PAX8, NKX2-1, or in combination in the hES cells, which had low endogenous expression of these transcription factors. Further differentiation of the double transfected cells showed the expression of thyroid-specific genes, including thyroglobulin (TG), thyroid peroxidase (TPO), the sodium/iodide symporter (NIS), and the TSH receptor (TSHR) as assessed by reverse transcription polymerase chain reaction and immunostaining. Most notably, the Activin/TSH-induced differentiation approach resulted in thyroid follicle formation and abundant TG protein expression within the follicular lumens. On stimulation with TSH, these hES-derived follicles were also capable of dose-dependent cAMP generation and radioiodine uptake, indicating functional thyroid epithelial cells.

CONCLUSION

The induced expression of PAX8 and NKX2-1 in hES cells was followed by differentiation into thyroid epithelial cells and their commitment to form functional three-dimensional neo-follicular structures. The data provide proof of principal that hES cells can be committed to thyroid cell speciation under appropriate conditions.

Derivation of Endodermal Progenitors From Pluripotent Stem Cells

Stem and progenitor cells play important roles in organogenesis during development and in tissue homeostasis and response to injury postnatally. As the regenerative capacity of many human tissues is limited, cell replacement therapies hold great promise for human disease management. Pluripotent stem cells such as embryonic stem (ES) cells and induced pluripotent stem (iPS) cells are prime candidates for the derivation of unlimited quantities of clinically relevant cell types through development of directed differentiation protocols, that is, the recapitulation of developmental milestones in in vitro cell culture. Tissue-specific progenitors, including progenitors of endodermal origin, are important intermediates in such protocols since they give rise to all mature parenchymal cells. In this review, we focus on the in vivo biology of embryonic endodermal progenitors in terms of key transcription factors and signaling pathways. We critically review the emerging literature aiming to apply this basic knowledge to achieve the efficient and reproducible in vitro derivation of endodermal progenitors such as pancreas, liver and lung precursor cells.

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.

Generation of thyroid follicular cells from pluripotent stem cells: potential for regenerative medicine

Nearly 12% of the population in the United States will be afflicted with a thyroid related disorder during their lifetime. Common treatment approaches are tailored to the specific disorder and include surgery, radioactive iodine ablation, antithyroid drugs, thyroid hormone replacement, external beam radiation, and chemotherapy. Regenerative medicine endeavors to combat disease by replacing or regenerating damaged, diseased, or dysfunctional body parts. A series of achievements in pluripotent stem cell research have transformed regenerative medicine in many ways by demonstrating "repair" of a number of body parts in mice, of which, the thyroid has now been inducted into this special group. Seminal work in pluripotent cells, namely embryonic stem cells and induced pluripotent stem cells, have made possible their path to becoming key tools and biological building blocks for cell-based regenerative medicine to combat the gamut of human diseases, including those affecting the thyroid.

Metastatic mechanisms in follicular cell-derived thyroid cancer

Thyroid cancer incidence is rising annually largely related to enhanced detection and early stage well-differentiated primary tumors. The prognosis for patients with early stage thyroid cancer is outstanding with most patients being cured with surgery. In selected cases, I-131 is administered to treat known or suspected residual or metastatic disease. Even patients with loco-regional metastases typically have an outstanding long-term prognosis, albeit with monitoring and occasional intervention for residual or recurrent disease. By contrast, individuals with distant metastases from thyroid cancer, particularly older patients with larger metastatic burdens and those with poorly differentiated tumors, have a poor prognosis. Patients with metastatic anaplastic thyroid cancer have a particularly poor prognosis. Published clinical trials indicate that transient disease control and partial remissions can be achieved with kinase inhibitor therapy directed toward angiogenic targets and that in some cases I-131 uptake can be enhanced. However, the direct targets of activity in metastatic lesions are incompletely defined and clear evidence that these treatments increase the duration or quality of life of patients is lacking, underscoring the need for improved knowledge regarding the metastatic process to inform the development of new therapies. In this review, we will focus on current data and hypotheses regarding key regulators of metastatic dormancy, metastatic progression, and the role of putative cancer stem cells.

Thyroid follicle formation and thyroglobulin expression in multipotent endodermal stem cells

OBJECTIVE

The aim of this study was to assess the impact of transcriptional induction on thyroid follicular cell (TFC) differentiation from endodermally matured embryonic stem (ES) cells. The thyroid transcription factors-NKx2 homeobox 1 (NKx2-1, formerly called TTF-1) and Paired box gene 8 (Pax8)-are known to associate biochemically and synergistically in the activation of thyroid functional genes including the sodium/iodide symporter (NIS), thyrotropin (TSH) receptor (TSHR), thyroglobulin (Tg), and thyroid peroxidase (TPO) genes. In this study, we investigated the ability of ectopically expressed Pax8 and NKx2-1 to further the induction and differentiation of murine ES cells into potential TFCs.

METHODS

ES cells were stably transfected with either the Pax8 gene, the NKx2-1 gene, or both genes to study the induction of NIS, TSHR, Tg, and TPO genes as assessed using both quantitative reverse-transcription polymerase chain reaction (qRT-PCR) and protein expression. The derived cells were cultured with or without the presence of activin A to allow their differentiation into multipotent endodermal cells.

RESULTS

The four thyroid-specific genes NIS, TSHR, Tg, and TPO were all significantly activated by expressing both transcription factors within the same ES cell. In contrast, significant but much lower transcriptional activity of the TSHR, Tg, and TPO genes was detected in cells expressing just NKx2-1, and only the NIS and TSHR genes responded to Pax8 alone. No Tg protein expression could be detected prior to their development into endodermal derivatives. However, after further differentiation of postembryoid body ES cells with activin A and TSH into endodermal cell lines, those cells with dual transfection of Pax8 and NKx2-1 demonstrated greatly enhanced expression of the NIS, TSHR, Tg, and TPO genes to such a degree that it was similar to that found in control thyroid cells. Furthermore, these same cells formed three-dimensional neofollicles in vitro and expressed Tg protein, but these phenomena were absent from lines expressing only Pax8 or NKx2-1.

CONCLUSION

These findings provide further evidence that co-expression of Pax8 and NKx2-1 in murine ES cells may induce the differentiation of thyroid-specific gene expression within endodermally differentiated ES cells and commit them to form three-dimensional neofollicular structures.

Recent insights into the cell biology of thyroid angiofollicular units

In thyrocytes, cell polarity is of crucial importance for proper thyroid function. Many intrinsic mechanisms of self-regulation control how the key players involved in thyroid hormone (TH) biosynthesis interact in apical microvilli, so that hazardous biochemical processes may occur without detriment to the cell. In some pathological conditions, this enzymatic complex is disrupted, with some components abnormally activated into the cytoplasm, which can lead to further morphological and functional breakdown. When iodine intake is altered, autoregulatory mechanisms outside the thyrocytes are activated. They involve adjacent capillaries that, together with thyrocytes, form the angiofollicular units (AFUs) that can be considered as the functional and morphological units of the thyroid. In response to iodine shortage, a rapid expansion of the microvasculature occurs, which, in addition to nutrients and oxygen, optimizes iodide supply. These changes are triggered by angiogenic signals released from thyrocytes via a reactive oxygen species/hypoxia-inducible factor/vascular endothelial growth factor pathway. When intra- and extrathyrocyte autoregulation fails, other forms of adaptation arise, such as euthyroid goiters. From onset, goiters are morphologically and functionally heterogeneous due to the polyclonal nature of the cells, with nodules distributed around areas of quiescent AFUs containing globules of compact thyroglobulin (Tg) and surrounded by a hypotrophic microvasculature. Upon TSH stimulation, quiescent AFUs are activated with Tg globules undergoing fragmentation into soluble Tg, proteins involved in TH biosynthesis being expressed and the local microvascular network extending. Over time and depending on physiological needs, AFUs may undergo repetitive phases of high, moderate, or low cell and tissue activity, which may ultimately culminate in multinodular goiters.

Generation of functional thyroid from embryonic stem cells

The primary function of the thyroid gland is to metabolize iodide by synthesizing thyroid hormones, which are critical regulators of growth, development and metabolism in almost all tissues. So far, research on thyroid morphogenesis has been missing an efficient stem-cell model system that allows for the in vitro recapitulation of the molecular and morphogenic events regulating thyroid follicular-cell differentiation and subsequent assembly into functional thyroid follicles. Here we report that a transient overexpression of the transcription factors NKX2-1 and PAX8 is sufficient to direct mouse embryonic stem-cell differentiation into thyroid follicular cells that organize into three-dimensional follicular structures when treated with thyrotropin. These in vitro-derived follicles showed appreciable iodide organification activity. Importantly, when grafted in vivo into athyroid mice, these follicles rescued thyroid hormone plasma levels and promoted subsequent symptomatic recovery. Thus, mouse embryonic stem cells can be induced to differentiate into thyroid follicular cells in vitro and generate functional thyroid tissue.

Thyroid regeneration: characterization of clear cells after partial thyroidectomy

Although having the capacity to grow in response to a stimulus that perturbs the pituitary-thyroid axis, the thyroid gland is considered not a regenerative organ. In this study, partial thyroidectomy (PTx) was used to produce a condition for thyroid regeneration. In the intact thyroid gland, the central areas of both lobes served as the proliferative centers where microfollicles, and bromodeoxyuridine (BrdU)-positive and/or C cells, were localized. Two weeks after PTx, the number of BrdU-positive cells and cells with clear or faintly eosinophilic cytoplasm were markedly increased in the central area and continuous to the cut edge. Clear cells were scant in the cytoplasm, as determined by electron microscopy; some retained the characteristics of calcitonin-producing C cells by having neuroendocrine granules, whereas others retained follicular cell-specific features, such as the juxtaposition to a lumen with microvilli. Some cells were BrdU-positive and expressed Foxa2, the definitive endoderm lineage marker. Serum TSH levels drastically changed due to the thyroidectomy-induced acute reduction in T(4)-generating tissue, resulting in a goitrogenesis setting. Microarray followed by pathway analysis revealed that the expression of genes involved in embryonic development and cancer was affected by PTx. The results suggest that both C cells and follicular cells may be altered by PTx to become immature cells or immature cells that might be derived from stem/progenitor cells on their way to differentiation into C cells or follicular cells. These immature clear cells may participate in the repair and/or regeneration of the thyroid gland.

Efficient derivation of purified lung and thyroid progenitors from embryonic stem cells

Two populations of Nkx2-1(+) progenitors in the developing foregut endoderm give rise to the entire postnatal lung and thyroid epithelium, but little is known about these cells because they are difficult to isolate in a pure form. We demonstrate here the purification and directed differentiation of primordial lung and thyroid progenitors derived from mouse embryonic stem cells (ESCs). Inhibition of TGFβ and BMP signaling, followed by combinatorial stimulation of BMP and FGF signaling, can specify these cells efficiently from definitive endodermal precursors. When derived using Nkx2-1(GFP) knockin reporter ESCs, these progenitors can be purified for expansion in culture and have a transcriptome that overlaps with developing lung epithelium. Upon induction, they can express a broad repertoire of markers indicative of lung and thyroid lineages and can recellularize a 3D lung tissue scaffold. Thus, we have derived a pure population of progenitors able to recapitulate the developmental milestones of lung/thyroid development.

Identifying thyroid stem/progenitor cells: advances and limitations

Continuing advances in stem cell science have prompted researchers to envisage the potential application of stem cells for the management of several debilitating disorders, thus raising the expectations of transplant clinicians. In particular, in order to find a source of adult stem cells alternative to embryonic stem cells (ESCs) for the exploration of novel strategies in regenerative medicine, researchers have attempted to identify and characterise adult stem/progenitor cells resident in compact organs, since these populations appear to be responsible for physiological tissue renewal and regeneration after injury. In particular, recent studies have also reported evidence for the existence of adult stem/progenitor cell populations in both mouse and human thyroids. Here, I provide a review of published findings about ESC lines capable of generating thyroid follicular cells, thyroid somatic stem cells and cancer stem cells within the thyroid. The three subjects are analysed by also considering the criticism recently raised against their existence and potential utility. I comment specifically on the significance of resident thyroid stem cells in the developmental biology of the gland and their putative role in the pathogenesis of thyroid disorders and on the protocols employed for their identification. I finally provide my opinion on whether from basic science results obtained to date it is possible to extrapolate any convincing basic for future treatment of thyroid disorders.

Stimulation of cultured h9 human embryonic stem cells with thyroid stimulating hormone does not lead to formation of thyroid-like cells

The sodium-iodine symporter (NIS) is expressed on the cell membrane of many thyroid cancer cells, and is responsible for the radioactive iodine accumulation. However, treatment of anaplastic thyroid cancer is ineffective due to the low expression of NIS on cell membranes of these tumor cells. Human embryonic stem cells (ESCs) provide a potential vehicle to study the mechanisms of NIS expression regulation during differentiation. Human ESCs were maintained on feeder-independent culture conditions. RT-qPCR and immunocytochemistry were used to study differentiation marker expression, ¹²⁵I uptake to study NIS function. We designed a two-step protocol for human ESC differentiation into thyroid-like cells, as was previously done for mouse embryonic stem cells. First, we obtained definitive endoderm from human ESCs. Second, we directed differentiation of definitive endoderm cells into thyroid-like cells using various factors, with thyroid stimulating hormone (TSH) as the main differentiating factor. Expression of pluripotency, endoderm and thyroid markers and ¹²⁵I uptake were monitored throughout the differentiation steps. These approaches did not result in efficient induction of thyroid-like cells. We conclude that differentiation of human ESCs into thyroid cells cannot be induced by TSH media supplementation alone and most likely involves complicated developmental patterns that are yet to be understood.

Role of the wnt pathway in thyroid cancer

Aberrant activation of Wnt signaling is involved in the development of several epithelial tumors. Wnt signaling includes two major types of pathways: (i) the canonical or Wnt/β-catenin pathway; and (ii) the non-canonical pathways, which do not involve β-catenin stabilization. Among these pathways, the Wnt/β-catenin pathway has received most attention during the past years for its critical role in cancer. A number of publications emphasize the role of the Wnt/β-catenin pathway in thyroid cancer. This pathway plays a crucial role in development and epithelial renewal, and components such as β-catenin and Axin are often mutated in thyroid cancer. Although it is accepted that altered Wnt signaling is a late event in thyroid cell transformation that affects anaplastic thyroid tumors, recent data suggest that it is also altered in papillary thyroid carcinoma (PTC) with RET/PTC mutations. Therefore, the purpose of this review is to summarize the main relevant data of Wnt signaling in thyroid cancer, with special emphasis on the Wnt/β-catenin pathway.

Clinical review: The emerging cell biology of thyroid stem cells

CONTEXT

Stem cells are undifferentiated cells with the property of self-renewal and give rise to highly specialized cells under appropriate local conditions. The use of stem cells in regenerative medicine holds great promise for the treatment of many diseases, including those of the thyroid gland.

EVIDENCE ACQUISITION

This review focuses on the progress that has been made in thyroid stem cell research including an overview of cellular and molecular events (most of which were drawn from the period 1990-2011) and discusses the remaining problems encountered in their differentiation.

EVIDENCE SYNTHESIS

Protocols for the in vitro differentiation of embryonic stem cells, based on normal developmental processes, have generated thyroid-like cells but without full thyrocyte function. However, agents have been identified, including activin A, insulin, and IGF-I, which are able to stimulate the generation of thyroid-like cells in vitro. In addition, thyroid stem/progenitor cells have been identified within the normal thyroid gland and within thyroid cancers.

CONCLUSIONS

Advances in thyroid stem cell biology are providing not only insight into thyroid development but may offer therapeutic potential in thyroid cancer and future thyroid cell replacement therapy.

The influence of thyroid-stimulating hormone and thyroid-stimulating hormone receptor antibodies on osteoclastogenesis

BACKGROUND

We have shown that thyroid-stimulating hormone (TSH) has a direct inhibitory effect on osteoclastic bone resorption and that TSH receptor (TSHR) null mice display osteoporosis. To determine the stage of osteoclast development at which TSH may exert its effect, we examined the influence of TSH and agonist TSHR antibodies (TSHR-Ab) on osteoclast differentiation from murine embryonic stem (ES) cells to gain insight into bone remodeling in hyperthyroid Graves' disease.

METHODS

Osteoclast differentiation was initiated in murine ES cell cultures through exposure to macrophage colony stimulation factor, receptor activator of nuclear factor кB ligand, vitamin D, and dexamethasone.

RESULTS

Tartrate resistant acid phosphatase (TRAP)-positive osteoclasts formed in ~12 days. This coincided with the expected downregulation of known markers of self renewal and pluripotency (including Oct4, Sox2, and REX1). Both TSH and TSHR-Abs inhibited osteoclastogenesis as evidenced by decreased development of TRAP-positive cells (~40%-50% reduction, p = 0.0047), and by decreased expression, in a concentration-dependent manner, of osteoclast differentiation markers (including the calcitonin receptor, TRAP, cathepsin K, matrix metallo-proteinase-9, and carbonic anhydrase II). Similar data were obtained using serum immunoglobulin-Gs (IgGs) from patients with hyperthyroid Graves' disease and known TSHR-Abs. TSHR stimulators inhibited tumor necrosis factor-alpha mRNA and protein expression, but increased the expression of osteoprotegerin (OPG), an antiosteoclastogenic human soluble receptor activator of nuclear factor кB ligand receptor. Neutralizing antibody to OPG reversed the inhibitory effect of TSH on osteoclast differentiation evidencing that the TSH effect was at least in part mediated by increased OPG.

CONCLUSION

These data establish ES-derived osteoclastogenesis as an effective model system to study the regulation of osteoclast differentiation in early development. The results support the observations that TSH has a bone protective action by negatively regulating osteoclastogenesis. Further, our results implicate TSHR-Abs in offering skeletal protection in hyperthyroid Graves' disease, even in the face of high thyroid hormone and low TSH levels.

Differentiation of E14 mouse embryonic stem cells into thyrocytes in vitro

BACKGROUND

If methods of differentiating stem cells into thyrocytes can be perfected, they may provide a ready source of normal thyrocytes for basic research and clinical application. We developed a novel culture method capable of differentiating mouse embryonic stem (ES) cells into thyroid follicular cells.

METHODS

E14 mouse ES cells were allowed to differentiate into embryoid bodies and then stimulated with thyroid-stimulating hormone, insulin, and potassium iodide. The resulting differentiated cells were observed for expression of thyrocyte-specific mRNA transcripts with reverse transcriptase (RT)-polymerase chain reaction. To definitively identify thyrocytes, we simultaneously observed the thyrocyte-specific proteins, thyroid transcription factor-1 and PAX-8, with dual-color immunofluorescent labeling. The cells were further characterized by electron microscopy.

RESULTS

The ES cells were successfully differentiated into thyrocytes. Differentiated cells expressed PAX-8, thyroid-stimulating hormone receptor, sodium/iodide symporter, thyroperoxidase, and thyroglobulin mRNAs, and coexpressed thyroid transcription factor-1 and PAX-8 proteins. The extent of differentiation was further explored by electron microscopy, which showed that differentiated cells had ultrastructural features similar to adult human thyrocytes, whereas the cells from unstimulated cultures were mostly disintegrated and lacked developed organelle structures.

CONCLUSIONS

These data show that E14 mouse ES cells can be differentiated into thyrocytes by culturing with thyroid-stimulating hormone, insulin, and potassium iodide. The development of reliable methods to produce thyroid cells from ES cells is important to future research in thyroid biology and medical applications.

Differentiation of synovial CD-105(+) human mesenchymal stem cells into chondrocyte-like cells through spheroid formation

Mesenchymal stem cells (MSCs) have the capacity to differentiate into several cell lineages, some of which can generate bone, cartilage, or adipose tissue. The presence of MSCs in the synovial membrane was recently reported. Data from comparative studies of MSCs derived from various mesenchymal tissues suggest that MSCs from synovial membranes have a superior chondrogenesis capacity. Previous chondrogenic differentiation studies have used the total population of MSCs, including cells with several MSC markers, such as CD44, CD90, CD105, or CD73. However the chondrogenic capacity of an individual population of MSCs has not been examined. Our aim was to study the chondrogenic capacity of the cellular MSC subset, CD105(+), derived from synovial membrane tissues of patients with osteoarthritis (OA) and normal donors. The tissues were digested with a cocktail of collagenase/dispase and the isolated MSCs were seeded into plates. The subpopulation of CD105(+)-MSCs was separated using a magnetic separator. The MSCs were then differentiated towards chondrocyte-like cells using a specific medium to promote spheroid formation. Spheroids were collected after 14, 28, and 46 days in chondrogenic medium and stained with hematoxylin, eosin, Safranin O or Alcian blue to evaluate the extracellular matrix. Immunohistochemistry was performed to study collagen types I (COLI) and II (COLII) and aggrecan expression. Phenotypic characterization of the isolated CD105(+)-MSCs shows that these cells are also positive for CD90 and CD44, but negatives for CD34 and CD45. In addition, this cellular subset expressed Sox-9. Spheroids appeared after 7 days in culture in the presence of chondrogenic medium. Our studies show no differences between MSCs obtained from OA and normal synovial membranes during chondrogenesis. The morphological analysis of spheroids revealed characteristics typical of chondrocyte cells. The intensity of Safranin O, Alcian blue and aggrecan staining was positive and constant throughout the culture period. However, the intensity of COL2 staining was higher at 28 days (84.29 +/- 0.1 U) than at 46 days (61.28 +/- 01 U), while COL1 staining was not detected in any samples analyzed. These results were confirmed by reverse transcriptase-polymerase chain reaction assays. We conclude that the cellular subset of CD105(+)-MSCs has chondrogenic capacity. The study also show the similar chondrogenic capacity of CD105(+)-MSCs cultured from normal and OA synovial membranes.

Differentiation of murine embryonic stem cells to thyrocytes requires insulin and insulin-like growth factor-1

The mechanisms controlling thyrocyte development during embryonic stem (ES) cell differentiation have only been partially elucidated, although previous studies have suggested the participation of thyroid stimulating hormone (TSH) in these processes. To further define the role of TSH in this context, we have studied a murine ES cell line in which green fluorescent protein (GFP) cDNA is targeted to the TSH receptor (TSHR) gene, linking the expression of GFP to the transcription of the endogenous TSHR gene. We demonstrate that, in the initial stages of embryoid body formation, activin A and TSH induce the differentiation of definitive endoderm and thyrocyte progenitors expressing Sox17, Foxa2, and TSHR. These thyrocyte progenitors are then converted into cellular aggregates that, in the presence of insulin and IGF-1, further differentiate into mature thyroglobulin-expressing thyrocytes. Our data suggest that, despite the fact that TSH is important for the induction and specification of thyrocytes from ES cells, insulin and IGF-1 are crucial for thyrocyte maturation. Our method provides a powerful in vitro differentiation model for studying the mechanisms of early thyrocyte lineage development.

Thyrotropin-independent induction of thyroid endoderm from embryonic stem cells by activin A

To model the differentiation of thyroid epithelial cells, we examined embryoid bodies derived from undifferentiated murine embryonic stem cells treated with activin A to induce endoderm differentiation, the germ layer from which thyroid cells occur. The resulting endodermal cells were then further exposed to TSH and/or IGF-I for up to 21 d. Oct-4 and REX1 expression, required to sustain stem cell self-renewal and pluripotency, were appropriately down-regulated, whereas GATA-4, and alpha-fetoprotein, both endodermal-specific markers, increased as the embryonic stem cells were exposed to activin A. By d 5 culture, TSH receptor (TSHR) and sodium iodide symporter (NIS) gene and protein expression were markedly induced. Cells isolated by the fluorescence-activated cell sorter simultaneously expressed not only TSHR and NIS proteins but also PAX8 mRNA, an expression pattern unique to thyroid cells and expected in committed thyroid progenitor cells. Such expression continued until d 21 with no influence seen by the addition of TSH or IGF-I. The sequence of gene expression changes observed in these experiments demonstrated the emergence of definitive thyroid endoderm. The activin A induction of thyroid-specific markers, NIS and TSHR, occurred in the absence of TSH stimulation, and, therefore, the emergence of thyroid endoderm in vitro paralleled the emergence of thyroid cells in TSHR-knockout mice. Activin A is clearly a major regulator of thyroid endoderm.

TSH signalling and cancer

Thyroid cancers are the most frequent endocrine neoplasms and mutations in the thyrotropin receptor (TSHR) are unusually frequent. Here we present the state-of-the-art concerning the role of TSHR in thyroid cancer and discuss it in light of the cancer stem cell theory or the classical view. We briefly review the gene and protein structure updating the cancer related TSHR mutations database. Intriguingly, hyperfunctioning TSHR mutants characterise differentiated cancers in contrast to undifferentiated thyroid cancers which very often bear silenced TSHR. It remains unclear whether TSHR alterations in thyroid cancers play a role in the onset or they appear as a consequence of genetic instability during evolution, but the presence of functional TSHR is exploited in therapy. We outline the signalling network build up in the thyrocyte between TSHR/PKA and other proliferative pathways such as Wnt, PI3K and MAPK. This networks integrity surely plays a role in the onset/evolution of thyroid cancer and needs further research. Lastly, future investigation of epigenetic events occurring at the TSHR and other loci may give better clues for molecular based therapy of undifferentiated thyroid carcinomas. Targeted demethylating agents, histone deacetylase inhibitors combined with retinoids and specific RNAis may help treatment in the future.

Thyroid-stimulating hormone/cAMP-mediated proliferation in thyrocytes

Current research on thyrotropin-activated proliferation in the thyrocyte needs to be aimed at a better understanding of crosstalk and negative-feedback mechanisms with other proliferative pathways, especially the insulin/IGF-1-induced phosphoinositol-3 kinase pathway and the serum-induced MAPK or Wnt pathways. Convergence of proliferative pathways in mTOR is a hotspot of current research, and combined treatment using double class inhibitors for thyroid cancer may bring some success. New thyroid-stimulating hormone receptor (TSHR)-interacting proteins, a better picture of cAMP targets, a deeper knowledge of the action of the protein kinase A regulatory subunits, especially their interactions with the replication machinery, and a further understanding of mechanisms that lead to cell cycle progression through G₁/S and G₂/M checkpoints are areas that need further elucidation. Finally, massive information coming from microarray data analysis will prompt our understanding of thyroid-stimulating hormone-promoted thyrocyte proliferation in health and disease.

Real-time microfluidic system for studying mammalian cells in 3D microenvironments

We describe a microfluidic system that can control, in real time, the microenvironments of mammalian cells in naturally derived 3D extracellular matrix (ECM). This chip combines pneumatically actuated valves with an individually addressable array of 3D cell-laden ECM; actuation of valves determines the pathways for delivering reagents through the chip and for exchanging diffusible factors between cell chambers. To promote rapid perfusion of reagents through 3D gels (with complete exchange of reagents within the gel in seconds), we created conduits above the gels for fluid flow, and microposts to stabilize the gels under high perfusion rates. As a biological demonstration, we studied spatially segregated mouse embryonic stem cells and mouse embryonic fibroblasts embedded in 3D Matrigel over days of culture. Overall, this system may be useful for high-throughput screening, single-cell analysis and studies of cell-cell communication, where rapid control of 3D cellular microenvironments is desired.

Thyroid stem cells: lessons from normal development and thyroid cancer

Ongoing advances in stem cell research have opened new avenues for therapy for many human disorders. Until recently, however, thyroid stem cells have been relatively understudied. Here, we review what is known about thyroid stem cells and explore their utility as models of normal and malignant biological development. We also discuss the cellular origin of thyroid cancer stem cells and explore the clinical implications of cancer stem cells in the thyroid gland. Since thyroid cancer is the most common form of endocrine cancer and that thyroid hormone is needed for the growth and metabolism of each cell in the body, understanding the molecular and the cellular aspects of thyroid stem cell biology will ultimately provide insights into mechanisms underlying human disease.