Type 3 iodothyronine deiodinase is expressed in human induced pluripotent stem cell derived cardiomyocytes

Expression of genes involved in thyroid hormone action in human induced pluripotent stem cells during differentiation to insulin-producing cells: Effects of iopanoic acid on differentiation

AIMS

Type 3 iodothyronine deiodinase (Dio3) converts triiodothyronine (T3) to diiodothyronine, thereby reducing intracellular T3 levels. In this study, we investigated the potential roles of Dio3 in the differentiation of human pancreatic β cells, using β cells derived from human induced pluripotent stem cells (hiPSCs).

MAIN METHODS

hiPSCs were differentiated to β cells in a stepwise manner over 29 days. The differentiation medium was supplemented with B27, which contains T3 but not T4, instead of serum. The T3 levels in the differentiated cells were determined based on the amount of T3 supplied to the medium and the activity of Dio3 within the cells. Iopanoic acid (IOP) was used as the Dio3 inhibitor.

KEY FINDINGS

Dio3 expression is substantially altered during differentiation. IOP treatment reduced Dio3 activity on day 4 and increased T3 levels in the medium on day 29. To investigate the involvement of Dio3 during differentiation, we used IOP, in which cells differentiated in the presence of IOP (+IOP) were compared to those differentiated without IOP (-IOP). On day 29, the proportion of β cells expressing C-peptide, NKX6 homeobox 1, and both markers was considerably higher in the presence than in the absence of IOP. Furthermore, on day 29, the insulin content of differentiated + IOP cells was considerably higher than that of differentiated -IOP cells.

CONCLUSIONS

An increase in intracellular T3 content promoted via the inhibition of Dio3 activity by IOP from day 0-29 enhances the differentiation of hiPSCs to β cells.

Poorly Differentiated Thyroid Carcinoma Coexisting with Graves' Disease Involving T3 Thyrotoxicosis due to Increased D1 and D2 Activities

Background: Poorly differentiated thyroid carcinoma is rare and patients are typically euthyroid. We report a novel rare case of poorly differentiated thyroid carcinoma with triiodothyronine (T3) thyrotoxicosis. Patient's Findings: A 77-year-old man presented to Kuma Hospital due to a neck tumor. A thyroid ultrasonography revealed a 220-mL mass in the right lobe. Laboratory data showed low serum thyrotropin (TSH), low free thyroxine (fT4), and high free T3 (fT3) levels. Anti-TSH receptor antibodies and thyroid-stimulating antibodies were positive. 131I scintigraphy showed diffuse uptake only in the left thyroid lobe. The patient underwent a total thyroidectomy and histological examination identified as poorly differentiated thyroid carcinoma. He was diagnosed with poorly differentiated thyroid carcinoma coexisting with Graves' disease. The tumor showed elevated type 1 iodothyronine deiodinases (D1) and type 2 iodothyronine deiodinases (D2) activities compared with that of the left thyroid lobe. Summary and Conclusions: Increased D1 and D2 activities in poorly differentiated carcinoma resulted in T3 toxicosis with a high serum fT3/fT4 ratio.

Mass Spectrometry-Based Determination of Thyroid Hormones and Their Metabolites in Endocrine Diagnostics and Biomedical Research – Implications for Human Serum Diagnostics

The wide spectrum of novel applications for the LC-MS/MS-based analysis of thyroid hormone metabolites (THM) in blood samples and other biological specimen highlights the perspectives of this novel technology. However, thorough development of pre-analytical sample workup and careful validation of both pre-analytics and LC-MS/MS analytics, is needed, to allow for quantitative detection of the thyronome, which spans a broad concentration range in these biological samples.

This minireview summarizes recent developments in advancing LC-MS/MS-based analytics and measurement of total concentrations of THM in blood specimen of humans, methods in part further refined in the context of previous achievements analyzing samples derived from cell-culture or tissues. Challenges and solutions to tackle efficient pre-analytic sample extraction and elimination of matrix interferences are compared. Options for automatization of pre-analytic sample-preparation and comprehensive coverage of the wide thyronome concentration range are presented. Conventional immunoassay versus LC-MS/MS-based determination of total and free THM concentrations are briefly compared.

Paradigms of Dynamic Control of Thyroid Hormone Signaling

Thyroid hormone (TH) molecules enter cells via membrane transporters and, depending on the cell type, can be activated (i.e., T4 to T3 conversion) or inactivated (i.e., T3 to 3,3'-diiodo-l-thyronine or T4 to reverse T3 conversion). These reactions are catalyzed by the deiodinases. The biologically active hormone, T3, eventually binds to intracellular TH receptors (TRs), TRα and TRβ, and initiate TH signaling, that is, regulation of target genes and other metabolic pathways. At least three families of transmembrane transporters, MCT, OATP, and LAT, facilitate the entry of TH into cells, which follow the gradient of free hormone between the extracellular fluid and the cytoplasm. Inactivation or marked downregulation of TH transporters can dampen TH signaling. At the same time, dynamic modifications in the expression or activity of TRs and transcriptional coregulators can affect positively or negatively the intensity of TH signaling. However, the deiodinases are the element that provides greatest amplitude in dynamic control of TH signaling. Cells that express the activating deiodinase DIO2 can rapidly enhance TH signaling due to intracellular buildup of T3. In contrast, TH signaling is dampened in cells that express the inactivating deiodinase DIO3. This explains how THs can regulate pathways in development, metabolism, and growth, despite rather stable levels in the circulation. As a consequence, TH signaling is unique for each cell (tissue or organ), depending on circulating TH levels and on the exclusive blend of transporters, deiodinases, and TRs present in each cell. In this review we explore the key mechanisms underlying customization of TH signaling during development, in health and in disease states.

The Colorful Diversity of Thyroid Hormone Metabolites

Since the discovery of L-thyroxine, the main secretory product of the thyroid gland, and its major metabolite T3, which exerts the majority of thyroid hormone action via ligand-dependent modulation of the function of T3 receptors in nuclei, mitochondria, and other subcellular compartments, various other T4-derived endogenous metabolites have been identified in blood and tissues of humans, animals, and early protochordates. This review addresses major historical milestones and experimental findings resulting in the discovery of the key enzymes of thyroid hormone metabolism, the three selenoprotein deiodinases, as well as the decarboxylases and amine oxidases involved in formation and degradation of recently identified endogenous thyroid hormone metabolites, i.e. 3-iodothyronamine and 3-thyroacetic acid. The concerted action of deiodinases 2 and 3 in regulation of local T3 availability is discussed. Special attention is given to the role of the thyromimetic "hot" metabolite 3,5-T2 and the "cool" 3-iodothyronamine, especially after administration of pharmacological doses of these endogenous thyroid hormone metabolites in various animal experimental models. In addition, available information on the biological roles of the two major acetic acid derivatives of thyroid hormones, i.e. Tetrac and Triac, as well as sulfated metabolites of thyroid hormones is reviewed. This review addresses the consequences of the existence of this broad spectrum of endogenous thyroid hormone metabolites, the "thyronome," beyond the classical thyroid hormone profile comprising T4, T3, and rT3 for appropriate analytical coverage and clinical diagnostics using mass spectrometry versus immunoassays for determination of total and free concentrations of thyroid hormone metabolites in blood and tissues.