Partial thyrocyte-specific Gαs deficiency leads to rapid-onset hypothyroidism, hyperplasia, and papillary thyroid carcinoma-like lesions in mice

Congenital Hypothyroidism and Hyperthyroidism Alters Adrenal Gene Expression, Development, and Function

Background: The human adrenal cortex undergoes several rapid remodeling steps during its lifetime. In rodents, similar remodeling occurs postnatally in the "X-zone" layer through unknown mechanisms. Furthermore, little is known regarding the impact of thyroid hormone (TH) on adrenal glands in humans. Methods: To investigate the impact of TH on adrenal pathophysiology, we created two genetic murine models mimicking human nonautoimmune hypothyroidism and hyperthyroidism. Moreover, we analyzed serum thyrotropin (TSH) and steroid hormone concentrations in patients diagnosed with congenital hypothyroidism and premature adrenarche (PA). Results: We found that TH receptor beta-mediated hypertrophy of the X-zone significantly elevated the adrenal weights of hyperthyroid women. In the hypothyroid model, the X-zone was poorly developed in both sexes. Moreover, large reciprocal changes in the expression levels of genes that regulate adrenal cortical function were observed with both models. Unexpectedly, up- and downregulation of several genes involved in catecholamine synthesis were detected in the adrenal glands of the hypothyroid and hyperthyroid models, respectively. Furthermore, TSH and adrenal steroid concentrations correlated positively in pediatric patients with congenital hypothyroidism and PA. Conclusions: Our results revealed that congenital hypothyroidism and hyperthyroidism functionally affect adrenal gland development and related steroidogenic activity, as well as the adrenal medulla.

The paradoxical lean phenotype of hypothyroid mice is marked by increased adaptive thermogenesis in the skeletal muscle

Obesity is a major health problem worldwide, given its growing incidence and its association with a variety of comorbidities. Weight gain results from an increase in energy intake without a concomitant increase in energy expenditure. To combat the obesity epidemic, many studies have focused on the pathways underlying satiety and hunger signaling, while other studies have concentrated on the mechanisms involved in energy expenditure, most notably adaptive thermogenesis. Hypothyroidism in humans is typically associated with a decreased basal metabolic rate, lower energy expenditure, and weight gain. However, hypothyroid mouse models have been reported to have a leaner phenotype than euthyroid controls. To elucidate the mechanism underlying this phenomenon, we used a drug-free mouse model of hypothyroidism: mice lacking the sodium/iodide symporter (NIS), the plasma membrane protein that mediates active iodide uptake in the thyroid. In addition to being leaner than euthyroid mice, owing in part to reduced food intake, these hypothyroid mice show signs of compensatory up-regulation of the skeletal-muscle adaptive thermogenic marker sarcolipin, with an associated increase in fatty acid oxidation (FAO). Neither catecholamines nor thyroid-stimulating hormone (TSH) are responsible for sarcolipin expression or FAO stimulation; rather, thyroid hormones are likely to negatively regulate both processes in skeletal muscle. Our findings indicate that hypothyroidism in mice results in a variety of metabolic changes, which collectively lead to a leaner phenotype. A deeper understanding of these changes may make it possible to develop new strategies against obesity.

Nevirapine Increases Sodium/Iodide Symporter-Mediated Radioiodide Uptake by Activation of TSHR/cAMP/CREB/PAX8 Signaling Pathway in Dedifferentiated Thyroid Cancer

Nevirapine has been proved to be effective in inducing re-differentiation and suppressing tumor growth in several tumor cells. This study aims to investigate the therapeutic potential of nevirapine in dedifferentiated thyroid cancer (DeTC), which refractory to radioiodine treatment and the underlying mechanisms. The results indicated that nevirapine significantly inhibited the proliferation and increased the expressions of thyroid differentiation-related genes, thyroid stimulating hormone receptor (TSHR), sodium/iodide symporter (NIS), thyroid peroxidase (TPO), and transcriptional factor paired box 8 (PAX8) in dedifferentiated thyroid cancer cells (WRO 82-1 and dFTC-133). Furthermore, nevirapine also enhanced radioiodide uptake significantly both in vitro and in vivo, and inhibited the growth of xenograft tumors. Nevirapine might improve radioiodine sensitivity via the activation of TSHR/cAMP/CREB/PAX8 signaling pathway. This study demonstrates that nevirapine could be potentially used to improve radioiodine therapeutic efficacy in dedifferentiated thyroid cancer patients.

Nevirapine inhibits migration and invasion in dedifferentiated thyroid cancer cells

Background

Metastatic or recurrent thyroid cancer often behaves aggressively, and approximately two‐thirds of patients present with radioiodine resistance. Effective therapies to suppress thyroid cancer metastasis are urgently needed. Nevirapine has been proved to suppress tumor growth and induce differentiation in several tumor cells, but has not previously been evaluated in metastasis of thyroid cancer. The present study aimed to investigate the effect of nevirapine on migration and invasion in dedifferentiated thyroid cancer cells.

Methods

Human dedifferentiated thyroid cancer cell line (WRO 82‐1) was subject to real‐time quantitative PCR, western blot and transwell migration/invasion assays. The liver metastasis in tumor xenografts of nude mice was subject to hematoxylin‐eosin (HE) staining.

Results

Nevirapine significantly repressed cell migration and invasion in WRO 82‐1 cells, and surprisingly significantly decreased liver metastatic tumor in the nude mouse model of dedifferentiated thyroid cancer compared with that of the control. Moreover, nevirapine significantly decreased the expression of IL‐6 mRNA and phosphorylation of JAK2 (Y1007+Y1008) and STAT3 (Tyr 705) in WRO 82‐1 cells compared with those in control cells.

Conclusion

Our findings suggest that nevirapine significantly repressed migration and invasion/metastasis in WRO 82‐1 cells and tumor xenografts, which may be related to inhibition of IL‐6/STAT3 signaling pathway. It promises great potential as a novel therapy for thyroid cancer, especially for those patients with metastasis.

The role of thyroglobulin in thyroid hormonogenesis

In humans, the thyroid hormones T₃ and T₄ are synthesized in the thyroid gland in a process that crucially involves the iodoglycoprotein thyroglobulin. The overall structure of thyroglobulin is conserved in all vertebrates. Upon thyroglobulin delivery from thyrocytes to the follicular lumen of the thyroid gland via the secretory pathway, multiple tyrosine residues can become iodinated to form mono-iodotyrosine (MIT) and/or di-iodotyrosine (DIT); however, selective tyrosine residues lead to preferential formation of T₄ and T₃ at distinct sites. T₄ formation involves oxidative coupling between two DIT side chains, and de novo T₃ formation involves coupling between an MIT donor and a DIT acceptor. Thyroid hormone synthesis is stimulated by TSH activating its receptor (TSHR), which upregulates the activity of many thyroid gene products involved in hormonogenesis. Additionally, TSH regulates post-translational changes in thyroglobulin that selectively enhance its capacity for T₃ formation - this process is important in iodide deficiency and in Graves disease. 167 different mutations, many of which are newly discovered, are now known to exist in TG (encoding human thyroglobulin) that can lead to defective thyroid hormone synthesis, resulting in congenital hypothyroidism.

Thyrocyte-specific deletion of insulin and IGF-1 receptors induces papillary thyroid carcinoma-like lesions through EGFR pathway activation

Insulin and insulin-like growth factor (IGF)-1 signaling in the thyroid are thought to be permissive for the coordinated regulation by thyroid-stimulating hormone (TSH) of thyrocyte proliferation and hormone production. However, the integrated role of insulin receptor (IR) and IGF-1 receptor (IGF-1R) in thyroid development and function has not been explored. Here, we generated thyrocyte-specific IR and IGF-1R double knockout (DTIRKO) mice to precisely evaluate the coordinated functions of these receptors in the thyroid of neonates and adults. Neonatal DTIRKO mice displayed smaller thyroids, paralleling defective folliculogenesis associated with repression of the thyroid-specific transcription factor Foxe1. By contrast, at postnatal day 14, absence of IR and IGF-1R paradoxically induced thyrocyte proliferation, which was mediated by mTOR-dependent signaling pathways. Furthermore, we found elevated production of TSH during the development of follicular hyperplasia at 8 weeks of age. By 50 weeks, all DTIRKO mice developed papillary thyroid carcinoma (PTC)-like lesions that correlated with induction of the ErbB pathway. Taken together, these data define a critical role for IR and IGF-1R in neonatal thyroid folliculogenesis. They also reveal an important reciprocal relationship between IR/IGF-1R and TSH/ErbB signaling in the pathogenesis of thyroid follicular hyperplasia and, possibly, of papillary carcinoma.