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. 2022 Jul 1;13:929176. doi: 10.3389/fendo.2022.929176

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Copyright © 2022 Iannuzzo, Campanozzi, Trevisani, Rutigliano, Abate, Rendina and De Filippo

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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Schematic representation of the role of iodine in the biosynthesis of thyroid hormones. Thanks to the action of NIS, iodine is incorporated in the thyrocyte (1). The process is guaranteed by the Na+ electrochemical gradient generated by the Na+/K+ ATPase on the basolateral membrane (2). Iodine subsequently crosses the apical membrane carried by pendrine (3) – and probably also by other transporters, to reach the colloid. Thyroglobulin, synthesized in the rough endoplasmic reticulum, reaches the colloid through exocytosis (4). The iodine present in the colloid is oxidized and incorporated in thyroglobulin, through the enzymatic mechanism of TPO thanks to H2O2 generated by Duox2 (5) Iodized thyroglobulin is internalized with a mechanism of pinocytosis (6) and undergoes proteolysis (7) giving rise to the formation of T4 and T3 which are then conveyed to the bloodstream (8).