Molecular mechanisms of thyroid hormone synthesis: from atoms to organoids

Thyroid hormones are iodinated compounds essential for vertebrate metabolism and their imbalance severely impacts human health. Thyroid hormones are synthesised in the natural bioreactor of the thyroid, which uptakes dietary iodine from the bloodstream and secretes back to it a highly regulated amount of hormones, which then reach several target organs. Despite extensive clinical investigations and studies in animal models, controlling hormone levels in vivo remains a major challenge. THYROMOL aims to reveal the molecular mechanisms that rule thyroid hormone homeostasis using an integrative structural biology approach, totally novel in the field. The THYROMOL team will combine electron cryo-microscopy (cryo-EM), light microscopy and biochemical tools to unravel key steps of the process of thyroid hormone regulation: aim 1) synthesis of the hormones aim 2) release of the hormones and aim 3) storage of the hormones in the gland. The strength and potential of the work relies in a “across scales” approach which spans from in vitro reconstituted systems to native thyroid organoids. We expect that these findings will make a major contribution to our detailed understanding of important macromolecular machines regulating thyroid function, informing new strategies to balance thyroid hormones in vivo. In addition, this study represents a starting point to explore the role of iodine across evolutionarily distant non-vertebrate species, an important question which is largely uncharted. Finally, the innovative methods established here may become general benchmarks in thyroid and structural biology laboratories as well as inspiring new diagnostic tools.

In the current reporting period, work has been done on all three project aims (1-3). The main results of this period are summarised in four publications, but most of the results are still in refinement and going to be shortly finalised. Overall, we have made great progress on aim 1, evaluating the impact of iodination on hormone synthesis and in this context, we have revealed that iodination may affect autoimmune response (Casula et al, 2023 Endocrine abstracts). Moreover, we have reviewed how not only iodination, but also other post-translational modifications of thyroglobulin can affect thyroid hormonogenesis and pathogenesis (Tosatto & Coscia, European Thyroid Journal 2022).
Towards aim 2, we used a plethora of biophysics, structural and cellular assays to unveil a pathway of thyroglobulin-mediated hormone release. These findings mark a good advancement on this part of the project, but more work is in progress to characterise other pathways. Branching from aim 2, we have also studied how mutations in the foxe1 transcription factor impact thyroglobulin gene expression and are related to disease phenotypes (Grassi et al, 2023, Frontiers in Endocrinology).
Regarding aim 3, we performed pioneering structural characterisation on thyroid cell models and tissues according to the proposal plan. We encountered unexpected challenges due to tissue instability and labelling. Nevertheless, we recently successfully produced a functional sample and obtained the first informative light microscopy images. In this context, we have participated to the development of a new method for imaging of tissues by in situ sectioning coupled to cryo electron tomography (cryoET) analysis, that we will soon apply to the thyroid samples (Perone, Nguyen et al, bioRxiv 2023.05.11.540146).

During the first reporting period the THYROMOL team has dissected and recapitulated some of the key steps of hormone production and release in a test tube, via development of assays which mimic the native hormone production (aim 1). Having molecular control on the system gives us a new lens on the relationship between thyroid hormone production and iodine diet. In this context we have also shown that iodine has an impact on the thyroid hormone precursor immunogenicity in patients with Hashimoto thyroiditis exposed to different amounts of iodine (Casula et al, 2023 Endocrine abstracts). Potentially, all the findings related to aim1 have great impact towards development of more sensitive diagnostics tools detecting hormone levels and thyroid hormone precursor title. In the near future, we plan to take into account the interplay between iodination and the many other post-translational modifications related to thyroid phenotype alterations. This hypothesis has been described in Tosatto & Coscia, European Thyroid Journal 2022. Regarding THYROMOL aim 2, in this first reporting period our team has started to reveal what is the mechanism by which hormones travel through thyroid follicles to be eventually released in the bloodstream. We clarified one of the hormone release pathways and we will tackle more thyroid hormone routes. A major but exciting challenge in the next reporting period will be to establish the interplay between these two or more pathways in balancing the overall hormone levels. Clarifying this molecular mechanism is key to act on specific steps of release, blocking or enhancing different hormone release pathways. The most ambitious aim 3 has been started with a few encouraging results on the characterisation of hormone storage in thyroid tissues. Whilst it remains arduous to handle thyroid tissues in a functional state for structural and dynamic studies, we have made progress in setting up our own pipelines, which require much further optimisation to be streamlined to a general method. Our major goal taking us beyond state-of-the-arts for the next reporting period will be to expand our skills on native thyroid tissues, to visualise single components of this complex sample and to reveal at the same time how storage and release are compensated in a healthy or altered thyroid system.

Periodic Reporting for period 1 - THYROMOL (Molecular mechanisms of thyroid hormone synthesis: from atoms to organoids)

Share this page

Download