Evidence for processing of compact insoluble thyroglobulin globules in relation with follicular cell functional activity in the human and the mouse thyroid

Abstract

Objective: Thyroglobulin (Tg) is stored within the follicular lumen mainly in a soluble form, but globules made of insoluble multimers are also present and considered to be a mechanism to store prohormone at high concentration. We investigated the immunohistochemical properties of these intrafollicular globules and their possible processing by thyroid cells upon stimulation in the human and in the mouse. Design: Human thyroids (normal, Graves' disease and hot adenomas) and thyroids from old ICR mice without or with goitrogenic treatment were processed for light microscopy. Methods: Immunohistochemistry for Tg with a polyclonal antibody and two monoclonal antibodies, one specific for thyroxine-rich-iodinated Tg and the other recognizing Tg independently of its iodine level, staining with periodic-acid-schiff, and binding of lectins specific for mannose and sialic acid were performed on all tissue sections. Intrafollicular globules were quantified, with distinction between 'active' or 'hot' and 'hypofunctioning' or 'cold' follicles. Results: In normal human and old mouse thyroids, the intrafollicular globules were strongly stained with PAS, but negative for the three anti-Tg antibodies and the two lectin-binding assays, while the surrounding soluble Tg was positive. In normal human tissue, globules were more frequent in 'hypofunctioning' than in 'active' follicles. They were exceptional in Graves' disease and hot adenomas. In old mice, Tg globules were more frequent in 'cold' than in 'hot' follicles. Along with the goitrogen treatment, they became fewer, fragmented and more often present in follicles with a 'hot' aspect. Conclusions: Upon TSH stimulation, thyrocytes become able to process colloid globules suggesting that this stock of Tg can be used in vivo for thyroid hormone synthesis. 150 73-80 European Journal of Endocrinology

Suppressive effects of genistein and daidzein on pituitary–thyroid axis in orchidectomized middle-aged rats

“…27 For immunohistochemical studies of pituitary thyrotrophs, we applied the primary rabbit antisera directed against the rat TSH-b (generously received from Dr A F Parlow, NIH, Bethestda, MD, USA), while for thyroids we used the primary rabbit antisera directed against human thyroglobulin (Tg; Dakopatts, Glostrup, Denmark) that is not species specific. 28 In brief, endogenous peroxidase activity was blocked by incubation with 0.3% hydrogen peroxide in methanol for 15 min. The reduction of non-specific background staining was achieved by incubation with normal porcine serum (Dakopatts, Glostrup, Denmark) diluted 1:10, for 45 min.…”

Morphological and Functional Changes in the Thyroid Follicles of the Aged Murine and Humans

“…The size and shape of thyroid follicles and the height of the follicular epithelium vary depending on the thyroid’s functional activity. In addition, there is morphological heterogeneity of the intrafollicular colloid depending on the thyroid’s functional status [1]. …”

A Mouse Model Suggests Two Mechanisms for Thyroid Alterations in Infantile Cystinosis: Decreased Thyroglobulin Synthesis Due to Endoplasmic Reticulum Stress/Unfolded Protein Response and Impaired Lysosomal Processing

“…Tg is an oligomer of 330-kDa monomers, which assume a compact globular form stabilized by a huge number of disulfide bonds (Ͼ100/monomer) (17). Tg is dimerized in the endoplasmic reticulum (ER) and then undergoes compaction in the follicular lumen by intermolecular disulfide cross-linking to form insoluble thyroid globules for maximal storage (18,19). Luminal compaction is attributed to extrinsic [secreted protein disulfide isomerase (PDI)] and intrinsic disulfide bond exchange mechanisms [via well preserved thioredoxin (CXXC) motives] (20).…”

“…Luminal compaction is attributed to extrinsic [secreted protein disulfide isomerase (PDI)] and intrinsic disulfide bond exchange mechanisms [via well preserved thioredoxin (CXXC) motives] (20). The extent of luminal Tg cross-linking varies among species and is related to age and follicle activation state (18,19,21). Tg unfolding via disulfide bond reduction by lysosomal reducing equivalents thus appears necessary to expose cryptic peptides targeted by lysosomal proteases (22).…”