Emerging Evidence for the Use of Antidiabetic Drugs, Glucagon-like Peptide 1 Receptor Agonists, for the Treatment of Alzheimer's Disease.

From an epidemiological and pathophysiological point of view, Alzheimer's disease (AD) and type 2 diabetes (T2DM) should be considered 'sister' diseases. T2DM significantly increases the risk of developing AD, and the mechanisms of neuronal degeneration themselves worsen peripheral glucose metabolism in multiple ways. The pathophysiological links between the two diseases, particularly cerebral insulin resistance, which causes neuronal degeneration, are so close that AD is sometimes referred to as 'type 3 diabetes'. Although the latest news on the therapeutic front for AD is encouraging, no treatment has been shown to halt disease progression permanently. At best, the treatments slow down the progression; at worst, they are inactive, or cause worrying side effects, preventing their use on a larger scale. Therefore, it appears logical that optimizing the metabolic milieu through preventive or curative measures can also slow down the cerebral degeneration that characterizes AD. Among the different classes of hypoglycaemic drugs, glucagon-like peptide 1 receptor agonists, which are widely used in the treatment of T2DM, were shown to slow down, or even prevent, neuronal degeneration. Data from animal, preclinical, clinical phase II, cohort and large cardiovascular outcomes studies are encouraging. Of course, randomized clinical phase III studies, which are on-going, will be essential to verify this hypothesis. Thus, for once, there is hope for slowing down the neurodegenerative processes associated with diabetes, and that hope is the focus of this review.

Incretin-induced changes in the transcriptome of skeletal muscles of fa/fa Zucker rat (ZFR) with obesity, without diabetes.

INTRODUCTION: Glucagon-like peptide-1 receptor agonists (GLP-1ra) are increasingly used in treating type 2 diabetes and obesity. Exendin-4 (Ex-4), a long acting GLP-1ra, was previously reported to decrease oxidative stress in hepatocytes, adipocytes and skeletal muscle cells in obese nondiabetic fa/fa Zucker rats (ZFR), thereby improving insulin resistance. AIM: We aimed first to identify Ex-4-induced changes in the transcriptome of skeletal muscle cells in ZFR. RESULTS: Ontology analysis of differentially expressed genes (DEGs) in ZFR versus lean animals (LR) showed that the extracellular matrix (ECM) is the first most affected cellular compartment, followed by myofibrils and endoplasmic reticulum (ER). Interestingly, among 15 genes regulated in ZFR versus LR, 14 of them were inversely regulated by Ex-4, as further confirmed by RT-qPCR. Picro-Sirius red histological staining showed that decreased ECM fiber area in ZFR is partially restored by Ex-4. Ontology analysis of the myofibril compartment revealed that decreased muscle contractile function in ZFR is partially restored by Ex-4, as confirmed by Phalloidin histological staining that showed a partial restoration by Ex-4 of altered contractile apparatus in ZFR. Ontology analysis of ER DEGs in ZFR versus LR showed that some of them are related to the AMP-activated protein kinase (AMPK) signaling pathway. Phosphorylated AMPK levels were strongly increased in Ex-4-treated ZFR. CONCLUSION: Altogether, our results suggest that GLP-1ra strongly restructure ECM and reinforce contractile capabilities in ZFR, while optimizing the cellular metabolism through AMPK.

Modulation of VEGF Expression and Oxidative Stress Response by Iodine Deficiency in Irradiated Cancerous and Non-Cancerous Breast Cells.

Breast cancer remains a major concern and its physiopathology is influenced by iodine deficiency (ID) and radiation exposure. Since radiation and ID can separately induce oxidative stress (OS) and microvascular responses in breast, their combination could additively increase these responses. Therefore, ID was induced in MCF7 and MCF12A breast cell lines by medium change. Cells were then X-irradiated with doses of 0.05, 0.1, or 3 Gy. In MCF12A cells, both ID and radiation (0.1 and 3 Gy) increased OS and vascular endothelial growth factor (VEGF) expression, with an additive effect when the highest dose was combined with ID. However, in MCF7 cells no additive effect was observed. VEGF mRNA up-regulation was reactive oxygen species (ROS)-dependent, involving radiation-induced mitochondrial ROS. Results on total VEGF mRNA hold true for the pro-angiogenic isoform VEGF165 mRNA, but the treatments did not modulate the anti-angiogenic isoform VEGF165b. Radiation-induced antioxidant response was differentially regulated upon ID in both cell lines. Thus, radiation response is modulated according to iodine status and cell type and can lead to additive effects on ROS and VEGF. As these are often involved in cancer initiation and progression, we believe that iodine status should be taken into account in radiation prevention policies.

Acute iodine deficiency induces a transient VEGF-dependent microvascular response in mammary glands involving HIF-1, ROS, and mTOR.

Iodine deficiency (ID), which affects almost two billion people worldwide, is associated with breast pathologies such as fibrosis in human and induces breast atypia in animal models. Because ID induces vascular activation in the thyroid, another iodide-uptaking organ, and as breast is also sensitive to ID, we aimed to characterize ID-induced effects on the breast microvasculature in vivo and in two different breast cell lines in vitro. Virgin and lactating NMRI mice received an iodide-deficient diet and a Na+/I- symporter inhibitor for 1 to 20 days. Some virgin mice were treated with vascular endothelial growth factor A (VEGF) or VEGF receptor inhibitors. In vitro, ID was induced in MCF7 and MCF12A cells by replacing the iodide-containing medium by an iodide-deficient medium. In vivo, VEGF expression was increased following ID in mammary tissues. Consequently, ID induced a transient increase in mammary gland blood flow, measured after anesthesia, in virgin and lactating mice, which was repressed by VEGF or VEGF receptor inhibitors. In MCF7 cells, ID induced a transient increase in reactive oxygen species, followed by an increase in hypoxia-inducible factor-1α (HIF-1α) protein and VEGF mRNA expression. Antioxidant N-acetylcysteine and mammalian target of rapamycin (mTOR) inhibitor blocked ID-induced HIF-1α protein increase and VEGF transcription. However, mTOR activity was not inhibited by N-acetylcysteine. Similar responses were observed in MCF12A cells. These data indicate that ID activates the canonical VEGF pathway and mTOR in breast tissues, which provides new insights to better understand the correlation between ID, vascular activation, and breast pathologies.

The new FreeStyle libre flash glucose monitoring system improves the glycaemic control in a cohort of people with type 1 diabetes followed in real-life conditions over a period of one year.

AIMS: Using the novel FreeStyle Libre (FSL), glucose monitoring (FGM) system becomes increasingly popular among people with type 1 diabetes (T1D) and is associated with less and shorter hypoglycaemic events without deterioration of HbA1c. There are not yet data reporting the impact of FGM in people with T1D in real-life conditions. We sought of evaluating the tolerance, the acceptance and the efficacy of the FGM system in routine medical practice. METHODS: This 12-month observational study included 120 individuals with T1D evaluated every 3 months. After having been instructed about FGM utilization, participants were trained to optimize the glycaemic control. RESULTS: Participants stopped immediately of measuring capillary blood glucose (2.88 ± 0.12 per day) (mean ± SEM) after having received the first FSL device and the number of scans per day increased up to 8.87 ± 0.58 per day. HbA1c levels decreased from 8.51% ± 0.14% at baseline to 7.77% ± 0.09% after 3 months to slightly increase to 7.92% ± 0.09% at 12 months, in correlation with the number of scans per day. The number (but not the duration) of hypoglycaemic events slightly increased from 16.9 ± 1.44 per month at baseline to 24.0 ± 2.91 per month at 12 months, after reaching a peak of 26.4 ± 2.31 per month at 6 months. They were correlated with improved HbA1c. CONCLUSION: Our study shows that using the FGM system improves HbA1c levels in people with T1D along with a moderate increase in the number of mild hypoglycaemic events. The new FGM system facilitates the therapeutic empowerment of people with T1D, but in a context of structured education.

Extrapancreatic effects of incretin hormones: evidence for weight-independent changes in morphological aspects and oxidative status in insulin-sensitive organs of the obese nondiabetic Zucker rat (ZFR).

Incretin-based therapies are widely used to treat type 2 diabetes. Although hypoglycemic actions of incretins are mostly due to their insulinotropic/glucagonostatic effects, they may also influence extrapancreatic metabolism. We administered exendin-4 (Ex-4), a long-acting glucagon-like peptide receptor agonist, at low dose (0.1 nmol/kg/day) for a short period (10 days), in obese nondiabetic fa/fa Zucker rats (ZFRs). Ex-4-treated ZFRs were compared to vehicle (saline)-treated ZFRs and vehicle- and Ex-4-treated lean rats (LRs). Blood glucose levels were measured at days 0, 9, and 10. Ingested food and animal weight were recorded daily. On the day of sacrifice (d10), blood was sampled along with liver, epididymal, subcutaneous, brown adipose, and skeletal muscle tissues from animals fasted for 24 h. Plasma insulin and blood glucose levels, food intake, and body and epididymal fat weight were unchanged, but gross morphological changes were observed in insulin-sensitive tissues. The average size of hepatocytes was significantly lower in Ex-4-treated ZFRs, associated with decreased number and size of lipid droplets and 4-hydroxy-2-nonenal (HNE) staining, a marker of oxidative stress (OS). Myocytes, which were smaller in ZFRs than in LRs, were significantly enlarged and depleted of lipid droplets in Ex-4-treated ZFRs. Weak HNE staining was increased by Ex-4. A similar observation was made in brown adipose tissue, whereas the elevated HNE staining observed in epididymal adipocytes of ZFRs, suggestive of strong OS, was decreased by Ex-4. These results suggest that incretins by acting on OS in insulin-sensitive tissues may contribute to weight-independent improvement in insulin sensitivity.

Iodine deficiency induces a VEGF-dependent microvascular response in salivary glands and in the stomach.

Despite efforts to optimize iodine supply in iodine deficient countries, iodine deficiency (ID) remains a global problem worldwide. Activation of the local microvasculature by ID in the thyroid gland aims at improving the local supply of iodide. For this purpose, the thyrocytes secrete vascular endothelial growth factor (VEGF) that acts on adjacent capillaries, via a reactive oxygen species (ROS)/Hypoxia Inducible factor (HIF)-dependent pathway. Beside the thyroid, other organs including salivary glands and the stomach do express the sodium/iodide symporter (NIS) and are able to take iodide up, potentially rendering them sensitive to ID. To verify this hypothesis, ID-induced effects on the local microvasculature were studied in salivary glands and in the stomach. ID was induced by feeding young mice with an iodide-deficient diet and NIS inhibitor perchlorate in the drinking water. In salivary glands, ID induced a transient increase in HIF-1α protein expression accompanied by a transient, VEGF-dependent increase in blood flow. In the gastric mucosa, ID transiently increased VEGF expression in the mucin-secreting epithelium and in ghrelin-secreting endocrine cells. These observations suggest that microvascular changes in response to ID occur in NIS-expressing tissues other than the thyroid. NIS expressing cells could be viewed as iodide sensors that respond to ID by inducing vascular changes, probably to optimize iodide bioavailability at regional or systemic levels.

The expression of dual oxidase, thyroid peroxidase, and caveolin-1 differs according to the type of immune response (TH1/TH2) involved in thyroid autoimmune disorders.

CONTEXT: Hashimoto's thyroiditis (HT) and Graves' disease (GD) are thyroid autoimmune disorders driven by Th1 and Th2 immune responses, respectively. Caveolin-1 (Cav-1), thyroid peroxidase (TPO), and dual oxidase (DUOX) are thought to be part of the thyroxisome, which is essential to maintain thyroid hormone synthesis, at the apical membrane. OBJECTIVES: To analyze the thyroxisome in HT and GD thyroids, we investigated Cav-1, DUOX, and TPO expression as well as markers of oxidative stress (OS), cell proliferation, apoptosis, and antioxidant defenses. The effects of cytokines on Cav-1 expression were analyzed in vitro. RESULTS: In HT, the decrease in Cav-1, DUOX, and TPO expression was marked in follicles having the morphological aspect of active follicles in normal glands and thus called active-like follicles. T4 was not detected in the colloid but in the cytoplasm as well as DUOX and TPO. These abnormalities were associated with increased OS and cell damage. In the hypofunctioning follicles of HT and normal thyroids, Cav-1, DUOX, and TPO were not expressed. In GD, they were expressed at the apical pole of thyrocytes, and T4 accumulated in the colloid of all follicles. Th1 cytokines IL-1α/interferonγ decreased Cav-1 expression in vitro, whereas the Th2 cytokine IL-4 had no effect. CONCLUSION: Th1 cytokine-induced down-regulation of Cav-1 could be responsible for intracytoplasmic T4 synthesis and mislocalization of DUOX and TPO, suggesting an important role for Cav-1 in the preservation of thyroxisome integrity. The thyroxisome's disruption, leading to uncontrolled OS and cell apoptosis, is a key, event in HT pathogenesis.

Differential regulation of the production of reactive oxygen species in Th1 cytokine-treated thyroid cells.

BACKGROUND: Th1 cytokines exert pleiotropic effects in Hashimoto's thyroiditis. Previous studies reported a downregulation of thyroperoxidase and dual oxidase (DUOX) protein and mRNA expression in thyroid cells treated with Th1 cytokines. Although this effect is partially mediated by intracellular reactive oxygen species (ROS) and reactive nitrogen species, the nature and the source of the ROS involved are currently unknown. The aim of this study was to examine further the nature and source of the ROS produced in response to Th1 cytokines. METHODS: Two rat thyroid cell lines (PCCL3 and FRTL-5) and human thyrocytes were incubated with Th1 cytokines (interleukin [IL]-1α and interferon-γ) in the presence or absence of the Th2 cytokine IL-4, the nitric oxide synthase inhibitor N-nitroso-L-arginine methyl ester (L-NAME), or the synthetic antioxidant N-acetylcysteine. The nature and source of the intracellular and extracellular ROS produced were determined. RESULTS: A rapid increase in intracellular ROS was observed in cells incubated with Th1 cytokines. This increase was not caused by extracellular hydrogen peroxide (H2O2) produced by DUOX because both DUOX expression and extracellular H2O2 synthesis were decreased by Th1 cytokines. Confocal colocalization experiments showed that the Th1 cytokine-triggered ROS were not produced from mitochondria. Electron paramagnetic resonance investigations of PCCL3 cells indicated that the highly reactive hydroxyl radical was not involved in the response to Th1 cytokines. NOX2 mRNA expression was significantly increased in PCCL3 cells incubated with Th1 cytokines, as was the expression of the protein in the thyroid of Hashimoto's thyroiditis patients. NOX4 expression was by contrast unaffected. These results suggest that at least superoxide could be produced after exposure of thyroid cells to Th1 cytokines. The effects of L-NAME and IL-4, both of which partially or totally reverse Th1 cytokine-induced effects, on ROS release were also analyzed. L-NAME and IL-4 significantly reduced the Th1 cytokine-induced surge of intracellular ROS in PCCL3 and human thyroid cells. CONCLUSION: The data presented here reinforce the idea that ROS, other than extracellular H2O2 produced by DUOX, are released from NOX2 after exposure of thyroid cells to Th1 cytokines. ROS/reactive nitrogen species act as important, but as further explained, not exclusive intracellular mediators of Th1 cytokine-induced effects in thyroid cells.

Recent insights into the cell biology of thyroid angiofollicular units.

In thyrocytes, cell polarity is of crucial importance for proper thyroid function. Many intrinsic mechanisms of self-regulation control how the key players involved in thyroid hormone (TH) biosynthesis interact in apical microvilli, so that hazardous biochemical processes may occur without detriment to the cell. In some pathological conditions, this enzymatic complex is disrupted, with some components abnormally activated into the cytoplasm, which can lead to further morphological and functional breakdown. When iodine intake is altered, autoregulatory mechanisms outside the thyrocytes are activated. They involve adjacent capillaries that, together with thyrocytes, form the angiofollicular units (AFUs) that can be considered as the functional and morphological units of the thyroid. In response to iodine shortage, a rapid expansion of the microvasculature occurs, which, in addition to nutrients and oxygen, optimizes iodide supply. These changes are triggered by angiogenic signals released from thyrocytes via a reactive oxygen species/hypoxia-inducible factor/vascular endothelial growth factor pathway. When intra- and extrathyrocyte autoregulation fails, other forms of adaptation arise, such as euthyroid goiters. From onset, goiters are morphologically and functionally heterogeneous due to the polyclonal nature of the cells, with nodules distributed around areas of quiescent AFUs containing globules of compact thyroglobulin (Tg) and surrounded by a hypotrophic microvasculature. Upon TSH stimulation, quiescent AFUs are activated with Tg globules undergoing fragmentation into soluble Tg, proteins involved in TH biosynthesis being expressed and the local microvascular network extending. Over time and depending on physiological needs, AFUs may undergo repetitive phases of high, moderate, or low cell and tissue activity, which may ultimately culminate in multinodular goiters.

Iodine-deficiency-induced long lasting angiogenic reaction in thyroid cancers occurs via a vascular endothelial growth factor-hypoxia inducible factor-1-dependent, but not a reactive oxygen species-dependent, pathway.

BACKGROUND: In the thyroid, iodine deficiency (ID) induces angiogenesis via a tightly controlled reactive oxygen species (ROS)-hypoxia inducible factor-1 (HIF-1)-vascular endothelial growth factor (VEGF) dependent pathway (ROS-HIF-VEGF). Deficient iodine intake may be associated with increased thyroid cancer incidence. The hypothesis of this work is to test whether ID affects the angiogenic processes in thyroid malignant cells by altering the ROS-HIF-VEGF pathway. METHODS: Goiters were obtained in RET/PTC3 transgenic and wild-type (wt) mice and ID was induced in three thyroid carcinoma cell lines (TPC-1, 8305c, and R082-w1). Thyroid blood flow, VEGF mRNA and protein, and HIF-1α protein expression were measured. The role of HIF-1 and of ROS was assessed using echinomycin and N-acetylcysteine (NAC), respectively. RESULTS: The goitrogen treatment increased the thyroid blood flow in wt and RET/PTC3 mice. Compared with wt mice, basal VEGF expression was higher in RET/PTC3 mice and increased with goitrogen treatment. In the three cell lines, ID induced marked increases in VEGF mRNA, and moderate increases in HIF-1α protein expression that were not transient as in normal cells. ID-induced VEGF mRNA expression was fully (8305c), partially (TPC-1), or not (R082-w1) blocked by echinomycin. NAC had no effect on ID-induced VEGF mRNA and HIF-1α protein expression in the three cell lines. CONCLUSIONS: ID induces a long lasting angiogenic phenotype in thyroid cancer cells that occurs through VEGF induction via a pathway partially mediated by HIF-1, but not by ROS. These results suggest that, in contrast with normal cells, ID-induced angiogenesis in cancer cells occurs via alternative and likely less controlled routes, thereby leading to uncontrolled growth.

The vitamin d receptor in thyroid development and function.

BACKGROUND AND OBJECTIVE: Vitamin D is known to modulate thyroid neoplastic and autoimmune disease. We investigated the role of the vitamin D receptor (VDR) in normal thyroid development and function (thyrocytes and C cells). METHODS: The thyroid phenotype of VDR knockout mice was studied in comparison to wild-type controls. The mice were fed a normal diet or a calcium-rich diet to circumvent effects induced by hypocalcemia. RESULTS: Thyroid morphology was unaltered in VDR knockout mice. Also, expression of different parameters of thyrocyte function was comparable (immunohistochemistry). C cell physiology was, however, affected in the absence of the VDR, resulting in increased thyroidal calcitonin expression (immunohistochemistry), paralleled by increased serum calcitonin levels, but only in normocalcemic mice. To study a possible effect of vitamin D status on basal calcitonin levels in humans, serum calcitonin concentrations were compared between vitamin D-deficient and -sufficient patients (serum 25-OH vitamin D3 ≤10 and ≥40 ng/ml, respectively), but no difference was observed. CONCLUSIONS: In mice, the VDR is redundant for normal thyrocyte function, but not for C cell function, where it mediates the negative control of calcitonin by 1,25-dihydroxyvitamin D3. In patients, vitamin D status does not affect basal serum calcitonin levels. A study in healthy individuals is needed to confirm these findings.

Delta-like 4/Notch pathway is differentially regulated in benign and malignant thyroid 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.

A coherent organization of differentiation proteins is required to maintain an appropriate thyroid function in the Pendred thyroid.

CONTEXT: Pendred syndrome is caused by mutations in the gene coding for pendrin, an apical Cl-/I- exchanger. OBJECTIVE: To analyze intrathyroidal compensatory mechanisms when pendrin is lacking, we investigated the thyroid of a patient with Pendred syndrome. The expression of proteins involved in thyroid hormone synthesis, markers of oxidative stress (OS), cell proliferation, apoptosis, and antioxidant enzymes were analyzed. RESULTS: Three morphological zones were identified: nearly normal follicles with iodine-rich thyroglobulin in the colloid (zone 1.a), small follicles without iodine-rich thyroglobulin in lumina (zone 1.b), and destroyed follicles (zone 2). In zones 1.a, dual oxidase (Duox) and thyroid peroxidase (TPO) were localized at the apical pole, OS and cell apoptosis were absent, but ClC-5 expression was strongly increased. In zones 1.b, Duox and TPO were aberrantly present and increased in the cytosol and associated with high OS, apoptosis, cell proliferation, and increased expression of peroxiredoxin-5, catalase, and dehalogenase-1 but moderate ClC-5 expression. CONCLUSION: In conclusion, the absence of pendrin is accompanied by increased ClC-5 expression that may transiently compensate for apical iodide efflux. In more affected follicles, Duox and TPO are relocated in the cytosol, leading to abnormal intracellular thyroid hormone synthesis, which results in cell destruction presumably because intracellular OS cannot be buffered by antioxidant defenses.

N-acetylcysteine and 15 deoxy-{delta}12,14-prostaglandin J2 exert a protective effect against autoimmune thyroid destruction in vivo but not against interleukin-1{alpha}/interferon {gamma}-induced inhibitory effects in thyrocytes in vitro.

Reactive oxygen species (ROS) are crucial for thyroid hormonogenesis, and their production is kept under tight control. Oxidative stress (OS) is toxic for thyrocytes in an inflammatory context. In vitro, Th1 pro-inflammatory cytokines have already been shown to decrease thyroid-specific protein expression. In the present study, OS level and its impact on thyroid function were analyzed in vitro in Th1 cytokine (interleukin [IL]-1alpha/interferon [IFN] gamma)-incubated thyrocytes (rat and human), as well as in vivo in thyroids from nonobese diabetic mice, a model of spontaneous autoimmune thyroiditis. N-acetylcysteine (NAC) and prostaglandin, 15 deoxy-(Delta12,14)-prostaglandinJ2 (15dPGJ2), were used for their antioxidant and anti-inflammatory properties, respectively. ROS production and OS were increased in IL-1alpha/IFNgamma-incubated thyrocytes and in destructive thyroiditis. In vitro, NAC not only reduced ROS production below control levels, but further decreased the expression of thyroid-specific proteins in addition to IL-1alpha/IFNgamma-inhibitory effects. Thus, besides ROS, other intracellular intermediaries likely mediate Th1 cytokine effects. In vivo, NAC and 15dPGJ2 reduced OS and the immune infiltration, thereby leading to a restoration of thyroid morphology. It is therefore likely that NAC and 15dPGJ2 mainly exert their protective effects by acting on infiltrating inflammatory cells rather than directly on thyrocytes.

Oxidative stress: a required condition for thyroid cell proliferation.

Goiter is associated with increased oxidative stress (OS). We studied the effects of an anti-inflammatory agent, 15 deoxy-Delta12,14-prostaglandin J2 (15dPGJ2) and an antioxidant, N-acetylcysteine (NAC), on OS, thyroid function, and goiter expansion in a model of goiter induced by propylthiouracil (PTU) or perchlorate. OS was assessed by the immunodetection of 4-hydroxynonenal, thyroid function by measuring thyroxin (T4) and thyrotropin (TSH) plasma levels and detecting T4-rich thyroglobulin (Tg-I), and goiter expansion by weighing the thyroids and measuring cell proliferation (PCNA and cyclin D1 immunodetection). In both PTU and perchlorate-induced goiters, OS, TSH plasma levels, thyroid weight, and cell proliferation were strongly enhanced, whereas Tg-I expression was negative. All these parameters were reversed by NAC and 15dPGJ2 in PTU-goiters. In perchlorate-goiters, TSH plasma levels remained elevated and Tg-I-negative after NAC or 15dPGJ2 treatment. OS was reduced by NAC, but not by 15dPGJ2. In addition, NAC reduced PCNA and cyclin D1 immunostainings, as well as thyroid weight, whereas 15dPGJ2 influenced neither thyroid weight nor cell proliferation. In conclusion, NAC and 15dPGJ2 overcome PTU- but not perchlorate-induced effects. The retrieval of hormonal synthesis may result from direct chemical interactions between PTU and NAC/15dPGJ2. Although 15dPGJ2 has no effect in perchlorate-goiters, the reduction of OS by NAC is associated with altered goiter development, making OS a required condition for the growth of the thyroid gland.

Role of caveolin-1 in thyroid phenotype, cell homeostasis, and hormone synthesis: in vivo study of caveolin-1 knockout mice.

In human thyroid, caveolin-1 is localized at the apex of thyrocytes, but its role there remains unknown. Using immunohistochemistry, (127)I imaging, transmission electron microscopy, immunogold electron microscopy, and quantification of H(2)O(2), we found that in caveolin-1 knockout mice thyroid cell homeostasis was disrupted, with evidence of oxidative stress, cell damage, and apoptosis. An even more striking phenotype was the absence of thyroglobulin and iodine in one-half of the follicular lumina and their presence in the cytosol, suggesting that the iodide organification and binding to thyroglobulin were intracellular rather than at the apical membrane/extracellular colloid interface. The latter abnormality may be secondary to the observed mislocalization of the thyroid hormone synthesis machinery (dual oxidases, thyroperoxidase) in the cytosol. Nevertheless, the overall uptake of radioiodide, its organification, and secretion as thyroid hormones were comparable to those of wild-type mice, suggesting adequate compensation by the normal TSH retrocontrol. Accordingly, the levels of free thyroxine and TSH were normal. Only the levels of free triiodothyronine showed a slight decrease in caveolin-1 knockout mice. However, when TSH levels were increased through low-iodine chow and sodium perchlorate, the induced goiter was more prominent in caveolin-1 knockout mice. We conclude that caveolin-1 plays a role in proper thyroid hormone synthesis as well as in cell number homeostasis. Our study demonstrates for the first time a physiological function of caveolin-1 in the thyroid gland. Because the expression and subcellular localization of caveolin-1 were similar between normal human and murine thyroids, our findings in caveolin-1 knockout mice may have direct relevance to the human counterpart.

Iodide deficiency-induced angiogenic stimulus in the thyroid occurs via HIF- and ROS-dependent VEGF-A secretion from thyrocytes.

Vascular supply is an obvious requirement for all organs. In addition to oxygen and nutrients, blood flow also transports essential trace elements. Iodine, which is a key element in thyroid hormone synthesis, is one of them. An inverse relationship exists between the expansion of the thyroid microvasculature and the local availability of iodine. This microvascular trace element-dependent regulation is unique and contributes to keep steady the iodide delivery to the thyroid. Signals involved in this regulation, such as VEGF-A, originate from thyrocytes as early TSH-independent responses to iodide scarcity. The question raised in this paper is how thyrocytes, facing an acute drop in intracellular stores of iodine, generate angiogenic signals acting on adjacent capillaries. Using in vitro models of rat and human thyroid cells, we show for the first time that the deficit in iodine is related to the release of VEGF-A via a reactive oxygen species/hypoxia-inducible factor-1-dependent pathway.

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 H(2)O(2), 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, peroxiredoxin (PRDX) five expression was reduced by NAC, whereas peroxiredoxin three increased and catalase remained unchanged. In vivo, the expression of both dual oxidases and peroxiredoxin five 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.

Iodine deficiency induces a thyroid stimulating hormone-independent early phase of microvascular reshaping in the thyroid.

Expansion of the thyroid microvasculature is the earliest event during goiter formation, always occurring before thyrocyte proliferation; however, the precise mechanisms governing this physiological angiogenesis are not well understood. Using reverse transcriptase-polymerase chain reaction and immunohistochemistry to measure gene expression and laser Doppler to measure blood flow in an animal model of goitrogenesis, we show that thyroid angiogenesis occurred into two successive phases. The first phase lasted a week and involved vascular activation; this process was thyroid-stimulating hormone (TSH)-independent and was directly triggered by expression of vascular endothelial growth factor (VEGF) by thyrocytes as soon as the intracellular iodine content decreased. This early reaction was followed by an increase in thyroid blood flow and endothelial cell proliferation, both of which were mediated by VEGF and inhibited by VEGF-blocking antibodies. The second, angiogenic, phase was TSH-dependent and was activated as TSH levels increased. This phase involved substantial up-regulation of the major proangiogenic factors VEGF-A, fibroblast growth factor-2, angiopoietin 1, and NG2 as well as their receptors Flk-1/VEGFR2, Flt-1/VEGFR1, and Tie-2. In conclusion, goiter-associated angiogenesis promotes thyroid adaptation to iodine deficiency. Specifically, as soon as the iodine supply is limited, thyrocytes produce proangiogenic signals that elicit early TSH-independent microvascular activation; if iodine deficiency persists, TSH plasma levels increase, triggering the second angiogenic phase that supports thyrocyte proliferation.