The thyroid angiofollicular units, a biological model of functional and morphological integration

The fundamental role of the thyroid gland is to ensure the biosynthesis of thyroid hormones whose primary role during embryonic development and the maintenance of homeostasis after birth is well known. The challenge here is double, as the hormone synthesis depends on both potentially toxic biochemical processes, as long as they are not fully contained, and the availability of a trace element, iodine, whose uptake may be extremely variable depending on the geographical location and the physiological status of individuals. The squaring of the circle has been resolved by the thyroid gland during its phylogenetic maturation by setting up angiofollicular units, morphological entities whose the perfect functional coherence between the different compartments within them (epithelial, endothelial and interstitial) results from a high level three-dimensional assemblage. This morphological and functional integration warrants adequate supplies of thyroid hormones whose mobilization must be triggered at any time when necessary. This functional requirement finds its expression in the morphological heterogeneity that ultimately culminates in the formation of nodules. Each angiofollicular unit is an individualized entity with its own genotypic and phenotypic asset that runs on the extrinsic control of TSH and a host of autocrine and paracrine factors. But subtle intrinsic mechanisms of self-regulation, operating out of any outside influences, constantly adjust the availability of players involved in the hormonal synthesis (iodine, thyroglobulin) within a biochemical entity (the thyroxisome) that is perfectly suited for this synthesis taking place without prejudice to the thyrocyte. The hormonal synthesis generates oxygen-derived substances as oxidative load or stress, though perfectly controlled in healthy thyrocytes. Any injury related to the nature, the amount, or where in the cell oxygen-derived substances are produced, may lead to morphological and functional breakdowns responsible for various disease processes, including those of autoimmune or even neoplastic nature

Delta-like 4/Notch pathway is differentially regulated in benign and malignant thyroi tissues

BACKGROUND: Angiogenesis plays an essential role in embryonic and tumoral developments. Vascular endothelial growth factor (VEGF), one of the best known proangiogenic factors, is increased in thyroid cancers, especially in papillary carcinomas (PC). However, other regulating mechanisms refine VEGF-induced cellular changes, such as the Notch family of ligands and receptors. Their role has not yet been investigated in the thyroid. The purpose of our study was to analyze the expression of Notch1, Notch4, and Delta-like 4 (DLL4) in benign and malignant thyroid lesions. METHODS: The expression of Notch1, Notch4, and DLL4 was analyzed by immunohistochemistry, quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR), and Western-blot in normal thyroids (NTs), hyperplasic thyroids from patients with Graves' disease (GD), microcarcinomas, PC, and follicular carcinomas. RESULTS: The immunohistochemical expression of Notch1, Notch4, and DLL4 was highly variable in thyrocytes from NTs and GD. In contrast, the staining in tumors was homogeneous and often intense. The increased expression of Notch1, Notch4, and DLL4 in carcinomas compared with the neighboring normal tissue was confirmed by qRT-PCR and Western-blot. However, only capillary endothelial cells from GD samples were positive for DLL4, the expression being restricted to large vessels in carcinomas and NTs. CONCLUSIONS: The detection of Notch1, Notch4, and DLL4 in thyrocytes and their regulation in various pathologies suggest that this pathway may play a role in thyroid carcinogenesis and angiogenesis

Minimal oxidative load: a prerequisite for thyroid cell function

In addition to reactive oxygen species (ROS) produced by mitochondria during aerobic respiration, thyrocytes are continuously producing H2O2, a key element for hormonogenesis. Because nothing is known about ROS implication in normal non stimulated cells, we studied their possible involvement in thyrocytes incubated with a potent antioxidant, N-acetylcysteine (NAC). NAC, which blocked the production of intracellular ROS, also decreased dual oxidases, thyroperoxidase, pendrin and thyroglobulin protein and/or gene expression. By contrast, Na+/I- symporter mRNA expression was unaffected. Among antioxidant systems, peroxiredoxin5 expression was reduced by NAC, whereas peroxiredoxin3 increased and catalase remained unchanged. In vivo, the expression of both dual oxidases and peroxiredoxin5 proteins was also decreased by NAC. In conclusion, when intracellular ROS levels drop below a basal threshold, the expression of proteins involved in thyroid cell function is hampered. This suggests that keeping ROS at a minimal level is required for safeguarding thyrocyte function

Differential Interactions between Th1/Th2, Th1/Th3, and Th2/Th3 Cytokines in the Regulation of Thyroperoxidase and Dual Oxidase Expression, and of Thyroglobulin Secretion in Thyrocytes in Vitro

Hypothyroidism, together with glandular atrophy, is the usual outcome of destructive autoimmune thyroiditis. The impairment in the thyroid function results either from cell destruction or from Th1 cytokine-induced alteration in hormonogenesis. Here, we investigated the impact of the local immune context on the thyroid function. We used two rat thyroid cell lines (PCCL3 and FRTL-5) and human thyrocytes incubated with IL-1alpha/interferon (IFN) gamma together with IL-4, a Th2 cytokine, or with TGF-beta, or IL-10, two Th3 cytokines. We first observed that IL-4 totally blocked IL-1alpha/interferon gamma-induced alteration in dual oxidase and thyroperoxidase expression, and in thyroglobulin secretion. By contrast, TGF-beta and IL-10 had no such effect. They rather repressed thyrocyte function as do Th1 cytokines. In addition, IL-4 blocked IL-10-induced repression of thyrocyte function, but not that induced by TGF-beta. In conclusion, Th1 cytokine- and IL-10-induced local inhibitory actions on thyroid function can be totally overturned by Th2 cytokines. These data provide new clues about the influence of the immune context on thyrocyte function

Anti-TNF-alpha reduces the inflammatory reaction associated with cuff electrode implantation around the sciatic nerve.

Extraneural cuff electrodes have been extensively used to investigate the nervous system. Their implantation is, however, associated with epineurial fibrosis, fiber loss, limited reproducibility of recordings and variability in stimulating conditions. It has recently been shown that TNF-alpha is involved in nerve alterations after electrode implantation. This study investigated whether a peri-operative anti-TNF-alpha treatment could modify the inflammation and fibrosis associated with cuff electrode implantation. Morphometrical and immunohistochemical methods were used to show that a single systemic injection of TNF-alpha neutralizing antibodies is sufficient to reduce the early inflammatory events, but not the long lasting fibrotic reaction

Detection and identification of endothelin-1 immunoreactivity in rat and porcine thyroid follicular cells.

Endothelin-1 immunoreactivity (irET-1) was observed in rat and porcine thyroid glands. Using a radioimmunoassay for endothelin-1, the mean concentration in extracts of rat and porcine thyroid glands were 0.75 pg/mg +/- 0.03 (n = 4) and 1.5 pg/mg +/- 0.2 (n = 8) (mean +/- SE) respectively. Gel-filtration and reverse-phase HPLC showed that ir ET-1 eluted in a position identical to synthetic endothelin-1. In addition, immunohistochemical study showed that irET-1 is located within epithelial follicular cells. No immunostaining was seen in parafollicular C-cells nor in parathyroid

Time course of tissue remodelling and electrophysiology in the rat sciatic nerve after spiral cuff electrode implantation.

Implantation of nerve cuff electrodes induces inflammatory cell infiltration and loose connective tissue accumulation. Along with time, morphological changes evolve towards a thicker epi/perineurium as part of mechanisms that protect nerve functionality when a foreign body is wrapped around it. The rise in electrode impedance is linked to the nature of the epineurial tissue. Changes involve an increased expression of neuroprotective factors that is stronger in the endoneurium with axonal degeneration. Our data indicate that epineurial and endoneurial changes after electrode cuff implantation are part of axonal protection mechanisms. Their control is important to improve the yield of FES applications

Direct toxic effect of iodide in excess on iodine-deficient thyroid glands: epithelial necrosis and inflammation associated with lipofuscin accumulation.

Involution of thyroid hyperplasia (induced by a low iodine diet and a goitrogen, propylthiouracil, PTU) was obtained in mice by administering a high or a moderate dose of iodide (HID or MID, respectively). In HID involuting glands, vasoconstriction was observed after 12 hr whereas necrosis and inflammation were very abundant as early as after 6 hr and maximal after 48 hr. They were not prevented by papaverine by which vasoconstriction was inhibited, but were inhibited by the continuation of PTU by which iodide oxidation and organification were inhibited. Lipofuscin inclusions in thyroid and inflammatory cells were always associated with necrosis. On the contrary, when involution was induced by MID or by HID + triiodothyronine (T3), or by T3 alone, neither necrosis nor inflammation occurred and apoptosis was the only mode of cell deletion. No lipofuscin inclusion occurred. Our results demonstrate that iodide in excess, after being oxidized or organified, is directly toxic for iodine-deficient thyroid cells. The presence of lipofuscin suggests that its toxicity is mediated by lipid peroxidation, a consequence of production of free radicals in excess

Expression of TPO and ThOXs in human thyrocytes is downregulated by IL-1alpha/IFN-gamma, an effect partially mediated by nitric oxide

Morphological and functional alterations in Hashimoto's thyroiditis (HT) are predominantly mediated by Th1 cytokines through apoptotic cell death. This ultimate step could be preceded by functional injuries in thyroid hormone synthesis. The action of two Th1 cytokines (IL-1alpha/IFN-gamma) on thyroperoxidase (TPO) and thyroid oxidase (ThOXs) expression was tested in human thyrocytes isolated from normal tissues, Graves' disease (GD) tissues, and autonomous toxic nodules. There was no evidence of cell death. Nitric oxide (NO) release was induced by cytokines but was absent when NG-nitro-L-arginine methyl ester (L-NAME) was coincubated. When thyrotropin (TSH)-incubated normal and GD thyrocytes were treated with IL-1alpha/IFN-gamma, TPO and ThOXs protein and mRNA expression dropped, a decrease partially prevented by L-NAME, suggesting that NO acts as a mediator of Th1 effects. In thyrocytes from autonomous toxic nodules, the high level of TPO and ThOXs protein expression was not influenced by TSH or by cytokines, a finding partially reproduced when normal thyrocytes were treated with increasing concentrations of TSH. In conclusion, incubation of normal or GD thyrocytes with Th1 cytokines induces a significant reduction in TSH-increased expression of both TPO and ThOXs, an effect partially mediated by NO. The thyroid cell function can therefore be severely affected in HT, even when cells remain viable. In autonomous toxic nodules, cells become partially insensitive to exogenous Th1 cytokines