Molecular mechanisms of thyroid hormone synthesis: from atoms to organoids

Metabolic functions in vertebrates are ruled by thyroid hormones, produced by the thyroid gland and secreted into the bloodstream. Thyroid hormone levels modulate growth, development and many other key processes across the lifespan, and their impairment severely affects human health. Despite extensive studies, controlling hormone levels in vivo remains a major challenge. Synthesis of thyroid hormones occurs extracellularly, via iodination of thyroglobulin. They must then undergo endocytosis before they can be released into the bloodstream. Yet, most thyroglobulin forms a colloid matrix within the gland, enabling iodine and hormone storage for the body. How these three mechanisms are balanced to provide physiological levels of hormones to the organism remains an outstanding question. Using an integrative structural biology approach, the proposed research will focus on unravelling the molecular mechanisms underlying the major checkpoints of thyroid hormone synthesis. My research group will combine electron cryo-microscopy with biochemical and light microscopy tools to study thyroid hormone regulation at different scales: from in vitro reconstituted systems to native thyroid organoids. First, we will elucidate how thyroglobulin iodination modulates hormone yields and modifies thyroglobulin structure. Second, we will determine the mechanism of thyroglobulin endocytosis regulated by two main receptors. Third, we will decipher the mechanism of storage and depletion of the thyroglobulin storage matrix. These approaches will allow us to reproduce the complexity of thyroid hormone synthesis at high resolution and in a native environment. My expertise in structural biology and my pioneering work on thyroglobulin puts me in an ideal position to carry out this work. The expected outcome and method development of this research will open a new front in thyroid structural biology and inspire alternative strategies for the control of thyroid hormone synthesis in vivo.