Differentiation of PTH-Expressing Cells From Human Pluripotent Stem Cells.

Differentiation of pluripotent stem cells into functional parathyroid-like cells would accelerate development of important therapeutic options for subjects with parathyroid-related disorders, from the design and screening of novel pharmaceutical agents to the development of durable cellular therapies. We have established a highly reproducible directed differentiation approach leading to PTH-expressing cells from human embryonic stem cells and induced pluripotent stem cells. We accomplished this through the comparison of multiple different basal media, the inclusion of the CDK inhibitor PD0332991 in both definitive endoderm and anterior foregut endoderm stages, and a 2-stage pharyngeal endoderm series. This is the first protocol to reproducibly establish PTH-expressing cells from human pluripotent stem cells and represents a first step toward the development of functional parathyroid cells with broad applicability for medicinal and scientific investigation.

Parathyroidectomy Without the Utilisation of iPTH: The Gold Standard is Still a Good Operation-How Understanding the Anatomy and a Simple US Can Help.

Parathyroid surgery is frequently performed after at least two preoperative localisation studies, in addition to the use of intraoperative ioPTH. The key to performing a successful parathyroidectomy is reliant on the surgeon having an outstanding knowledge of parathyroid embryology and anatomy. With this, it is possible to undertake surgery with a simple neck ultrasound and without more expensive pre- and intraoperative localisation studies.

Parathyroid Pathology.

Proliferative pathologic lesions of parathyroid glands encompass a spectrum of entities ranging from benign hyperplastic processes to malignant neoplasia. This review article outlines the pathophysiologic classification of parathyroid disorders and describes histologic, immunohistochemical, and molecular features that can be assessed to render accurate diagnoses.

Deficiency in the secreted protein Semaphorin3d causes abnormal parathyroid development in mice.

Primary hyperparathyroidism (PHPT) is a common endocrinopathy characterized by hypercalcemia and elevated levels of parathyroid hormone. The primary cause of PHPT is a benign overgrowth of parathyroid tissue causing excessive secretion of parathyroid hormone. However, the molecular etiology of PHPT is incompletely defined. Here, we demonstrate that semaphorin3d (Sema3d), a secreted glycoprotein, is expressed in the developing parathyroid gland in mice. We also observed that genetic deletion of Sema3d leads to parathyroid hyperplasia, causing PHPT. In vivo and in vitro experiments using histology, immunohistochemistry, biochemical, RT-qPCR, and immunoblotting assays revealed that Sema3d inhibits parathyroid cell proliferation by decreasing the epidermal growth factor receptor (EGFR)/Erb-B2 receptor tyrosine kinase (ERBB) signaling pathway. We further demonstrate that EGFR signaling is elevated in Sema3d-/- parathyroid glands and that pharmacological inhibition of EGFR signaling can partially rescue the parathyroid hyperplasia phenotype. We propose that because Sema3d is a secreted protein, it may be possible to use recombinant Sema3d or derived peptides to inhibit parathyroid cell proliferation causing hyperplasia and hyperparathyroidism. Collectively, these findings identify Sema3d as a negative regulator of parathyroid growth.

Embryology of the Parathyroid Glands.

The parathyroid glands are essential for regulating calcium homeostasis in the body. The genetic programs that control parathyroid fate specification, morphogenesis, differentiation, and survival are only beginning to be delineated, but are all centered around a key transcription factor, GCM2. Mutations in the Gcm2 gene as well as in several other genes involved in parathyroid organogenesis have been found to cause parathyroid disorders in humans. Therefore, understanding the normal development of the parathyroid will provide insight into the origins of parathyroid disorders.

Cotton rats (Sigmodon hispidus) possess pharyngeal pouch remnants originating from different primordia.

Pharyngeal pouches in mammals develop into specific derivatives. If the differentiation of the pharyngeal pouches is anomalous, their remnants can result in cysts, sinuses, and fistulae in the differentiated organs or around the neck. In the present study, we found several pharyngeal pouch remnants, such as cystic structures in thymus and parathyroid gland and fossulae extended from the piriform fossa, in the inbred cotton rats maintained at Hokkaido Institute of Public Health (HIS/Hiph) and University of Miyazaki (HIS/Mz). In HIS/Hiph, the fossulae extended from the apex of the piriform fossa into the thyroid glands and were lined with stratified squamous and cuboidal epithelium. Calcitonin-positive C-cells were present within their epithelium in HIS/Hiph. In contrast, the fossulae of HIS/Mz ran outside the thyroid glands toward the parathyroid glands; they were lined with columnar ciliated epithelium and a few goblet cells, but had no C-cells, which was consistent with the cystic structures in the thymus and the parathyroid gland. These results indicated that the fossulae were a remnant of the ultimobranchial body in HIS/Hiph and of the thymopharyngeal duct in HIS/Mz. Thus, the fossulae of the piriform fossa resembled the piriform sinus fistula in human. In conclusion, cotton rats frequently possessed pharyngeal pouch remnants, including the piriform sinus fistula, and therefore, might serve as a novel model to elucidate the mechanisms of pharyngeal pouch development.

Is the ultimobranchial body a reality or myth: a study using serial sections of human embryos.

Reported morphologies of the ultimobranchial body had varied between researchers: a cluster of mitotic cells, a duct-like structure and a rosette-like cell mass. To clarify the true morphology, we studied tilted horizontal sections of 20 human embryos (crown-rump length 5-18 mm; 4-6 weeks). The sections displayed a ladder-like arrangement of the second to fourth endodermal pouches and, in 5 early embryos we found the fifth pouch attached to the fifth ectodermal groove near the fourth pharyngeal arch artery. The bilateral fifth pharyngeal pouches protruded anterolaterally to form a U-shaped lumen surrounding the arytenoid swelling. The third to fifth pouches were each characterized by a pedal-shaped inferior end. We identified several types of cell clusters as candidates for the ultimobranchial body, but morphologically most of them were, to various degrees, likely to correspond to the blind end of the lower pouch when cut tangentially. Because of the topographical relation to the common carotid artery, a cyst-like structure with a cell cluster seemed to be the most likely candidate of the ultimobranchial body (a common anlage of the thymus and parathyroid). However, we were not able to deny a possibility that a certain plane cutting the pouch end incidentally provided such a cyst-like structure in sections. At any stage, the ultimobranchial body might not appear as a definite structure that is discriminated from others with routine staining. A concept of the ultimobranchial body might be biased by comparative anatomy that shows the ultimobranchial gland in adult birds and reptiles.

Tissue-specific roles for sonic hedgehog signaling in establishing thymus and parathyroid organ fate.

The thymus and parathyroids develop from third pharyngeal pouch (3rd pp) endoderm. Our previous studies show that Shh null mice have smaller, aparathyroid primordia in which thymus fate specification extends into the pharynx. SHH signaling is active in both dorsal pouch endoderm and neighboring neural crest (NC) mesenchyme. It is unclear which target tissue of SHH signaling is required for the patterning defects in Shh mutants. Here, we used a genetic approach to ectopically activate or delete the SHH signal transducer Smo in either pp endoderm or NC mesenchyme. Although no manipulation recapitulated the Shh null phenotype, manipulation of SHH signaling in either the endoderm or NC mesenchyme had direct and indirect effects on both cell types during fate specification and organogenesis. SHH pathway activation throughout pouch endoderm activated ectopic Tbx1 expression and partially suppressed the thymus-specific transcription factor Foxn1, identifying Tbx1 as a key target of SHH signaling in the 3rd pp. However, ectopic SHH signaling was insufficient to expand the GCM2-positive parathyroid domain, indicating that multiple inputs, some of which might be independent of SHH signaling, are required for parathyroid fate specification. These data support a model in which SHH signaling plays both positive and negative roles in patterning and organogenesis of the thymus and parathyroids.

Notch and Hedgehog in the thymus/parathyroid common primordium: Crosstalk in organ formation.

The avian thymus and parathyroids (T/PT) common primordium derives from the endoderm of the third and fourth pharyngeal pouches (3/4PP). The molecular mechanisms that govern T/PT development are not fully understood. Here we study the effects of Notch and Hedgehog (Hh) signalling modulation during common primordium development using in vitro, in vivo and in ovo approaches. The impairment of Notch activity reduced Foxn1/thymus-fated and Gcm2/Pth/parathyroid-fated domains in the 3/4PP and further compromised the development of the parathyroid glands. When Hh signalling was abolished, we observed a reduction in the Gata3/Gcm2- and Lfng-expression domains at the median/anterior and median/posterior territories of the pouches, respectively. In contrast, the Foxn1 expression-domain at the dorsal tip of the pouches expanded ventrally into the Lfng-expression domain. This study offers novel evidence on the role of Notch signalling in T/PT common primordium development, in an Hh-dependent manner.

Temporal and spatial requirements for Hoxa3 in mouse embryonic development.

Hoxa3(null) mice have severe defects in the development of pharyngeal organs including athymia, aparathyroidism, thyroid hypoplasia, and ultimobranchial body persistence, in addition to defects of the throat cartilages and cranial nerves. Some of the structures altered in the Hoxa3(null) mutant embryos are anterior to the described Hoxa3 gene expression boundary: the thyroid, soft palate, and lesser hyoid horn. All of these structures develop over time and through the interactions of multiple cell types. To investigate the specific cellular targets for HOXA3 function in these structures across developmental time, we performed a comprehensive analysis of the temporal and tissue-specific requirements for Hoxa3, including a lineage analysis using Hoxa3(Cre). The combination of these approaches showed that HOXA3 functions in both a cell autonomous and non-cell autonomous manner during development of the 3rd and 4th arch derivatives, and functions in a neural crest cell (NCC)-specific, non-cell autonomous manner for structures that were Hoxa3-negative by lineage tracing. Our data indicate that HOXA3 is required for tissue organization and organ differentiation in endodermal cells (in the tracheal epithelium, thymus, and parathyroid), and contributes to organ migration and morphogenesis in NCCs. These data provide a detailed picture of where and when HOXA3 acts to promote the development of the diverse structures that are altered in the Hoxa3(null) mutant. Data presented here, combined with our previous studies, indicate that the regionally restricted defects in Hoxa3 mutants do not reflect a role in positional identity (establishment of cell or tissue fate), but instead indicate a wider variety of functions including controlling distinct genetic programs for differentiation and morphogenesis in different cell types during development.

Multiple roles for HOXA3 in regulating thymus and parathyroid differentiation and morphogenesis in mouse.

Hoxa3 was the first Hox gene to be mutated by gene targeting in mice and is required for the development of multiple endoderm and neural crest cell (NCC)-derived structures in the pharyngeal region. Previous studies have shown that the Hoxa3 null mutant lacks third pharyngeal pouch derivatives, the thymus and parathyroids by E18.5, and organ-specific markers are absent or downregulated during initial organogenesis. Our current analysis of the Hoxa3 null mutant shows that organ-specific domains did undergo initial patterning, but the location and timing of key regional markers within the pouch, including Tbx1, Bmp4 and Fgf8, were altered. Expression of the parathyroid marker Gcm2 was initiated but was quickly downregulated and differentiation failed; by contrast, thymus markers were delayed but achieved normal levels, concurrent with complete loss through apoptosis. To determine the cell type-specific roles of Hoxa3 in third pharyngeal pouch development, we analyzed tissue-specific mutants using endoderm and/or NCC-specific Cre drivers. Simultaneous deletion with both drivers resulted in athymia at E18.5, similar to the null. By contrast, the individual tissue-specific Hoxa3 deletions resulted in small, ectopic thymi, although each had a unique phenotype. Hoxa3 was primarily required in NCCs for morphogenesis. In endoderm, Hoxa3 temporally regulated initiation of the thymus program and was required in a cell-autonomous manner for parathyroid differentiation. Furthermore, Hoxa3 was required for survival of third pharyngeal pouch-derived organs, but expression in either tissue was sufficient for this function. These data show that Hoxa3 has multiple complex and tissue-specific functions during patterning, differentiation and morphogenesis of the thymus and parathyroids.

Parathyroid conditions in childhood.

This review of parathyroid surgery in children will briefly discuss parathyroid gland embryology and anatomy before focusing on the pathophysiology, clinical presentation, and treatment of hyperparathyroidism in children. Hyperparathyroidism (HPT) is the overproduction of PTH and it is rare in children, with an incidence of 2-5 per 100,000. This rarity means that the principles of caring for children with parathyroid disease are largely extrapolated from the richer adult experience; however, the unique pediatric aspects of parathyroid problems and their surgical treatment, including presentation, imaging, operative approach, and complications, will be considered.

Hes1 is required for the development of pharyngeal organs and survival of neural crest-derived mesenchymal cells in pharyngeal arches.

Hes genes are required to maintain diverse progenitor cell populations during embryonic development. Loss of Hes1 results in a spectrum of malformations of pharyngeal endoderm-derived organs, including the ultimobranchial body (progenitor of C cells), parathyroid, thymus and thyroid glands, together with highly penetrant C-cell aplasia (81%) and parathyroid aplasia (28%). The hypoplastic parathyroid and thymus are mostly located around the pharyngeal cavity, even at embryonic day (E) 15.5 to E18.5, indicating the failure of migration of the organs. To clarify the relationship between these phenotypes and neural crest cells, we examine fate mapping of neural crest cells colonized in pharyngeal arches in Hes1 null mutants by using the Wnt1-Cre/R26R reporter system. In null mutants, the number of neural crest cells labeled by X-gal staining is markedly decreased in the pharyngeal mesenchyme at E12.5 when the primordia of the thymus, parathyroid and ultimobranchial body migrate toward their destinations. Furthermore, phospho-Histone-H3-positive proliferating cells are reduced in number in the pharyngeal mesenchyme at this stage. Our data indicate that the development of pharyngeal organs and survival of neural-crest-derived mesenchyme in pharyngeal arches are critically dependent on Hes1. We propose that the defective survival of neural-crest-derived mesenchymal cells in pharyngeal arches directly or indirectly leads to deficiencies of pharyngeal organs.

Ectopic parathyroid glands and their anatomical, clinical and surgical implications.

Ectopic parathyroid glands result from aberrant migration during early stages of development and lack of successful identification may lead to lack of success in parathyroid surgery. They constitute a common etiology of persistent or recurrent hyperparathyroidism, when they are missed at initial diagnosis. Their prevalence is about 2-43% in anatomical series and up to 16% and 14% in patients with primary and secondary hyperparathyroidism, respectively. Ectopic inferior parathyroids are most frequently found in the anterior mediastinum, in association with the thymus or the thyroid gland, while the most common position for ectopic superior parathyroids is the tracheoesophageal groove and retroesophageal region. Neck ultrasound and 99mTc Sestamibi scan are first-line imaging modalities, although with low sensitivity and specificity. However, their combination with modern techniques, such as single photon emission computed tomography (SPECT) alone or in combination with CT (SPECT/CT) increases their diagnostic accuracy. Fine needle-aspiration cytology of a lesion suspicious for parathyroid tissue and measurement of parathyroid hormone (PTH) in the aspired material further assist to the successful preoperative localization of ectopic glands. Common sites for surgical investigation are the upper thyroid pole and the upper vascular thyroid stalk behind the hypopharynx and cervical esophagus for the superior parathyroids, and the carotid artery bifurcation and the thymic tongue, for the inferior parathyroids. Radioguided minimally invasive parathyroidectomy after successful localization, assisted by rapid PTH measurement postoperatively, significantly improves surgical outcomes in patients with ectopic parathyroid adenomas.

Localised inhibition of FGF signalling in the third pharyngeal pouch is required for normal thymus and parathyroid organogenesis.

The thymus and parathyroid glands are derived from the third pharyngeal pouch endoderm. The mechanisms that establish distinct molecular domains in the third pouch and control the subsequent separation of these organ primordia from the pharynx are poorly understood. Here, we report that mouse embryos that lack two FGF feedback antagonists, Spry1 and Spry2, display parathyroid and thymus hypoplasia and a failure of these organ primordia to completely separate from the pharynx. We show that FGF ligands and downstream reporter genes are expressed in highly regionalised patterns in the third pouch and that sprouty gene deletion results in upregulated FGF signalling throughout the pouch endoderm. As a consequence, the initiation of markers of parathyroid and thymus fate is altered. In addition, a normal apoptotic programme that is associated with the separation of the primordia from the pharynx is disrupted, resulting in the maintenance of a thymus-pharynx attachment and a subsequent inability of the thymus to migrate to its appropriate position above the heart. We demonstrate that the sprouty genes function in the pharyngeal endoderm itself to control these processes and that the defects in sprouty-deficient mutants are, at least in part, due to hyper-responsiveness to Fgf8. Finally, we provide evidence to suggest that parathyroid hypoplasia in these mutants is due to early gene expression defects in the third pouch, whereas thymus hypoplasia is caused by reduced proliferation of thymic epithelial cells in the thymus primordium.

Modulation of Bmp4 signalling in the epithelial-mesenchymal interactions that take place in early thymus and parathyroid development in avian embryos.

Epithelial-mesenchymal interactions are crucial for the development of the endoderm of the pharyngeal pouches into the epithelia of thymus and parathyroid glands. Here we investigated the dynamics of epithelial-mesenchymal interactions that take place at the earliest stages of thymic and parathyroid organogenesis using the quail-chick model together with a co-culture system capable of reproducing these early events in vitro. The presumptive territories of thymus and parathyroid epithelia were identified in three-dimensionally preserved pharyngeal endoderm of embryonic day 4.5 chick embryos on the basis of the expression of Foxn1 and Gcm2, respectively: the thymic rudiment is located in the dorsal domain of the third and fourth pouches, while the parathyroid rudiment occupies a more medial/anterior pouch domain. Using in vitro quail-chick tissue associations combined with in ovo transplantations, we show that the somatopleural but not the limb bud mesenchyme, can mimic the role of neural crest-derived pharyngeal mesenchyme to sustain development of these glands up to terminal differentiation. Furthermore, mesenchymal-derived Bmp4 appears to be essential to promote early stages of endoderm development during a short window of time, irrespective of the mesenchymal source. In vivo studies using the quail-chick system and implantation of growth factor soaked-beads further showed that expression of Bmp4 by the mesenchyme is necessary during a 24 h-period of time. After this period however, Bmp4 is no longer required and another signalling factor produced by the mesenchyme, Fgf10, influences later differentiation of the pouch endoderm. These results show that morphological development and cell differentiation of thymus and parathyroid epithelia require a succession of signals emanating from the associated mesenchyme, among which Bmp4 plays a pivotal role for triggering thymic epithelium specification.

Anatomy of thyroid and parathyroid glands and neurovascular relations.

Historically, thyroid surgery has been fraught with complications. Injury to the recurrent laryngeal nerve, superior laryngeal nerve, or the parathyroid glands may result in profound life-long consequences for the patient. To minimize the morbidity of the operation, a surgeon must have an in-depth understanding of the anatomy of the thyroid and parathyroid glands and be able to apply this information to perform a safe and effective operation. This article will review the pertinent anatomy and embryology of the thyroid and parathyroid glands and the critical structures that lie in their proximity. This information should aid the surgeon in appropriate identification and preservation of the function of these structures and to avoid the pitfalls of the operation.

Endocrine disorders in pregnancy: physiological and hormonal aspects of pregnancy.

The endocrinology of pregnancy involves endocrine and metabolic changes as a consequence of physiological alterations at the foetoplacental boundary between mother and foetus. The vast changes in maternal hormones and their binding proteins complicate assessment of the normal level of most hormones during gestation. The neuroendocrine events and their timing in the placental, foetal and maternal compartments are critical for initiation and maintenance of pregnancy, for foetal growth and development, and for parturition. As pregnancy advances, the relative number of trophoblasts increase and the foeto-maternal exchange begins to be dominated by secretory function of the placenta. As gestation progresses toward term, the number of cytotrophoblasts again declines and the remaining syncytial layer becomes thin and barely visible. This arrangement facilitates transport of compounds including hormones and their precursors across the foeto-maternal interface. The endocrine system is the earliest system developing in foetal life, and it is functional from early intrauterine existence through old age. Regulation of the foetal endocrine system relies, to some extent, on precursors secreted by placenta and/or mother.

MafB interacts with Gcm2 and regulates parathyroid hormone expression and parathyroid development.

Serum calcium and phosphate homeostasis is critically regulated by parathyroid hormone (PTH) secreted by the parathyroid glands. Parathyroid glands develop from the bilateral parathyroid-thymus common primordia. In mice, the expression of transcription factor Glial cell missing 2 (Gcm2) begins in the dorsal/anterior part of the primordium on embryonic day 9.5 (E9.5), specifying the parathyroid domain. The parathyroid primordium then separates from the thymus primordium and migrates to its adult location beside the thyroid gland by E15.5. Genetic ablation of gcm2 results in parathyroid agenesis in mice, indicating that Gcm2 is essential for early parathyroid organogenesis. However, the regulation of parathyroid development at later stages is not well understood. Here we show that transcriptional activator v-maf musculoaponeurotic fibrosarcoma oncogene homologue B (MafB) is developmentally expressed in parathyroid cells after E11.5. MafB expression was lost in the parathyroid primordium of gcm2 null mice. The parathyroid glands of mafB(+/-) mice were mislocalized between the thymus and thyroid. In mafB(-/-) mice, the parathyroid did not separate from the thymus. Furthermore, in mafB(-/-) mice, PTH expression and secretion were impaired; expression levels of renal cyp27b1, one of the target genes of PTH, was decreased; and bone mineralization was reduced. We also demonstrate that although Gcm2 alone does not stimulate the PTH gene promoter, it associates with MafB to synergistically activate PTH expression. Taken together, our results suggest that MafB regulates later steps of parathyroid development, that is, separation from the thymus and migration toward the thyroid. MafB also regulates the expression of PTH in cooperation with Gcm2.