Simone Magagnin Wajner

The Role of Thyroid Hormone in Testicular Development and Function

Thyroid hormone is a critical regulator of growth, development, and metabolism in virtually all tissues, and altered thyroid status affects many organs and systems. Although for many years testis has been regarded as a thyroid hormone unresponsive organ, it is now evident that thyroid hormone plays an important role in testicular development and function. A considerable amount of data show that thyroid hormone influences steroidogenesis as well as spermatogenesis. The involvement of tri-iodothyronine (T(3)) in the control of Sertoli cell proliferation and functional maturation is widely accepted, as well as its role in postnatal Leydig cell differentiation and steroidogenesis. The presence of thyroid hormone receptors in testicular cells throughout development and in adulthood implies that T(3) may act directly on these cells to bring about its effects. Several recent studies have employed different methodologies and techniques in an attempt to understand the mechanisms underlying thyroid hormone effects on testicular cells. The current review aims at presenting an updated picture of the recent advances made regarding the role of thyroid hormones in male gonadal function.

Increased Expression of Vascular Endothelial Growth Factor and Its Receptors, VEGFR-1 and VEGFR-2, in Medullary Thyroid Carcinoma

BACKGROUND Vascular endothelial growth factor (VEGF-A) expression is upregulated in the majority of human tumors, where it stimulates proliferation, migration, and survival of endothelial cells. Studies have suggested that VEGF inhibitors can be used as an alternative therapy in medullary thyroid carcinoma (MTC), but data about expression of VEGF-A and its receptor in this tumor are scarce. The aims of this study were to evaluate VEGF-A, VEGF receptor (VEGFR)-1, VEGFR-2, and microvessel density (MVD) expression in MTC samples and correlate it with clinical parameters. METHODS Paraffin-embedded samples from 38 MTC patients were evaluated for VEGF-A, VEGFR-1, VEGFR-2, and MVD expression by immunohistochemistry. Clinical data were retrospectively reviewed in medical records. RESULTS Thirty-eight patients aged 31.8 +/- 17.1 years were enrolled. Twenty-seven patients had hereditary disease (71.1%). Twenty-five of them were found to have multiple endocrine neoplasia (MEN) 2A and two were found to have MEN 2B. VEGF-A immunohistochemical staining was detected in 95% (36/38), VEGFR-1 in 96% (36/37), and VEGFR-2 in 91% (31/34) of MTC samples. Age at surgery was positively correlated with VEGFR-2 (p = 0.003). There was no correlation between VEGF-A, VEGFR-2, and tumor stage (tumor node metastasis). Nevertheless, VEGFR-1 was found to be inversely correlated with tumor node metastasis (p = 0.034). We also observed a trend toward an association between VEGFR-1 signal intensity and cure of disease, although this did not reach statistical significance (p = 0.054). Neither VEGF-A nor VEGFR-2 was associated with disease outcome after a median follow-up period of 5 years (p = 0.882 and p = 0.236, respectively). As expected, MVD was correlated with age at surgery (p = 0.005) and tumor size (p = 0.03). Patients with the hereditary form of the disease had a stronger intensity for VEGFR-1 (p = 0.039), whereas patients with sporadic disease displayed higher MVD counts (44 [27-63] vs. 21 [9-49], p = 0.018). CONCLUSION The VEGF-A, VEGFR-1, and VEGFR-2 immunoreactive proteins are overexpressed in MTC lesions and might be implicated in tumor progression. It is not clear, however, if expression of these molecules provides prognostic information regarding the spread or outcome of MTC.

Type 1 iodothyronine deiodinase in human physiology and disease Deiodinases: the balance of thyroid hormone

Thyroid hormone is essential for the normal function of virtually all tissues. The iodothyronine deiodinases catalyze the removal of an iodine residue from the pro-hormone thyroxine (T 4 ) molecule, thus producing either the active form triiodothyronine (T 3 ; activation) or inactive metabolites (reverse T 3 ; inactivation). Type I deiodinase (D1) catalyzes both reactions. Over the last years, several studies have attempted to understand the mechanisms of D1 function, underlying its effects on normal thyroid hormone metabolism and pathological processes. Although peripheral D1-generated T 3 production contributes to a portion of plasma T 3 in euthyroid state, pathologically increased thyroidal D1 activity seems to be the main cause of the elevated T 3 concentrations observed in hyperthyroid patients. On the other hand, D1-deficient mouse models show that, in the absence of D1, inactive and lesser iodothyronines are excreted in feces with the loss of associated iodine, demonstrating the scavenging function for D1 that might be particularly important in an iodine deficiency setting. Polymorphisms in the DIO1 gene have been associated with changes in serum thyroid hormone levels, whereas decreased D1 activity has been reported in the nonthyroid illness syndrome and in several human neoplasias. The current review aims at presenting an updated picture of the recent advances made in the biochemical and molecular properties of D1 as well as its role in human physiology.Thyroid hormone is essential for the normal function of virtually all tissues. The iodothyronine deiodinases catalyze the removal of an iodine residue from the pro-hormone thyroxine (T(4)) molecule, thus producing either the active form triiodothyronine (T(3); activation) or inactive metabolites (reverse T(3); inactivation). Type I deiodinase (D1) catalyzes both reactions. Over the last years, several studies have attempted to understand the mechanisms of D1 function, underlying its effects on normal thyroid hormone metabolism and pathological processes. Although peripheral D1-generated T(3) production contributes to a portion of plasma T(3) in euthyroid state, pathologically increased thyroidal D1 activity seems to be the main cause of the elevated T(3) concentrations observed in hyperthyroid patients. On the other hand, D1-deficient mouse models show that, in the absence of D1, inactive and lesser iodothyronines are excreted in feces with the loss of associated iodine, demonstrating the scavenging function for D1 that might be particularly important in an iodine deficiency setting. Polymorphisms in the DIO1 gene have been associated with changes in serum thyroid hormone levels, whereas decreased D1 activity has been reported in the nonthyroid illness syndrome and in several human neoplasias. The current review aims at presenting an updated picture of the recent advances made in the biochemical and molecular properties of D1 as well as its role in human physiology.

Deiodinases: the balance of thyroid hormone: type 1 iodothyronine deiodinase in human physiology and disease.

Thyroid hormone is essential for the normal function of virtually all tissues. The iodothyronine deiodinases catalyze the removal of an iodine residue from the pro-hormone thyroxine (T 4 ) molecule, thus producing either the active form triiodothyronine (T 3 ; activation) or inactive metabolites (reverse T 3 ; inactivation). Type I deiodinase (D1) catalyzes both reactions. Over the last years, several studies have attempted to understand the mechanisms of D1 function, underlying its effects on normal thyroid hormone metabolism and pathological processes. Although peripheral D1-generated T 3 production contributes to a portion of plasma T 3 in euthyroid state, pathologically increased thyroidal D1 activity seems to be the main cause of the elevated T 3 concentrations observed in hyperthyroid patients. On the other hand, D1-deficient mouse models show that, in the absence of D1, inactive and lesser iodothyronines are excreted in feces with the loss of associated iodine, demonstrating the scavenging function for D1 that might be particularly important in an iodine deficiency setting. Polymorphisms in the DIO1 gene have been associated with changes in serum thyroid hormone levels, whereas decreased D1 activity has been reported in the nonthyroid illness syndrome and in several human neoplasias. The current review aims at presenting an updated picture of the recent advances made in the biochemical and molecular properties of D1 as well as its role in human physiology.Thyroid hormone is essential for the normal function of virtually all tissues. The iodothyronine deiodinases catalyze the removal of an iodine residue from the pro-hormone thyroxine (T(4)) molecule, thus producing either the active form triiodothyronine (T(3); activation) or inactive metabolites (reverse T(3); inactivation). Type I deiodinase (D1) catalyzes both reactions. Over the last years, several studies have attempted to understand the mechanisms of D1 function, underlying its effects on normal thyroid hormone metabolism and pathological processes. Although peripheral D1-generated T(3) production contributes to a portion of plasma T(3) in euthyroid state, pathologically increased thyroidal D1 activity seems to be the main cause of the elevated T(3) concentrations observed in hyperthyroid patients. On the other hand, D1-deficient mouse models show that, in the absence of D1, inactive and lesser iodothyronines are excreted in feces with the loss of associated iodine, demonstrating the scavenging function for D1 that might be particularly important in an iodine deficiency setting. Polymorphisms in the DIO1 gene have been associated with changes in serum thyroid hormone levels, whereas decreased D1 activity has been reported in the nonthyroid illness syndrome and in several human neoplasias. The current review aims at presenting an updated picture of the recent advances made in the biochemical and molecular properties of D1 as well as its role in human physiology.

Type 2 Iodothyronine Deiodinase Levels Are Higher in Slow-Twitch than Fast-Twitch Mouse Skeletal Muscle and Are Increased in Hypothyroidism

Because of its large mass, relatively high metabolic activity and responsiveness to thyroid hormone, skeletal muscle contributes significantly to energy expenditure. Despite the presence of mRNA encoding the type 2 iodothyronine-deiodinase (D2), an enzyme that activates T(4) to T3, very low or undetectable activity has been reported in muscle homogenates of adult humans and mice. With a modified D2 assay, using microsomal protein, overnight incubation and protein from D2 knockout mouse muscle as a tissue-specific blank, we examined slow- and fast-twitch mouse skeletal muscles for D2 activity and its response to physiological stimuli. D2 activity was detectable in all hind limb muscles of 8- to 12-wk old C57/BL6 mice. Interestingly, it was higher in the slow-twitch soleus than in fast-twitch muscles (0.40 ± 0.06 vs. 0.076 ± 0.01 fmol/min · mg microsomal protein, respectively, P < 0.001). These levels are greater than those previously reported. Hypothyroidism caused a 40% (P < 0.01) and 300% (P < 0.001) increase in D2 activity after 4 and 8 wk treatment with antithyroid drugs, respectively, with no changes in D2 mRNA. Neither D2 mRNA nor activity increased after an overnight 4 C exposure despite a 10-fold increase in D2 activity in brown adipose tissue in the same mice. The magnitude of the activity, the fiber specificity, and the robust posttranslational response to hypothyroidism argue for a more important role for D2-generated T(3) in skeletal muscle physiology than previously assumed.

Is there a role for thyroid hormone on spermatogenesis

Appropriate level of thyroid hormone is essential for normal development and metabolism in most vertebrate tissues and altered thyroid status impacts adversely on them. For many years the testis was regarded as a thyroid hormone unresponsive organ, but consistent evidence accumulated in the past two decades has definitively changed this classical view. Currently, the concept that thyroid hormone plays a critical role in testis development, in rats and other vertebrate species, is clearly established. Although the effects of thyroid hormone on Sertoli and Leydig cells in the immature testis are well described, its role on the adult organ remains controversial. In this review, we summarize and discuss the recent development on the thyroid hormone effects in immature and adult testes. Particularly, we have attempted to address the role of thyroid hormone in the regulation of spermatogenesis, emphasizing recent data that suggest its involvement in germ cells differentiation and survival. Microsc. Res. Tech. 2009.

Clinical implications of altered thyroid status in male testicular function

Os hormonios da tireoide estao envolvidos virtualmente no desenvolvimento e na manutencao de todos os tecidos. As gonadas masculinas foram, por decadas, consideradas insensiveis aos hormonios tireoidianos. No entanto, estudos mais recentes tem demonstrado que disfuncoes tireoidianas estao associadas nao somente a anormalidades na morfologia e na funcao dos testiculos, mas tambem a diminuicao da fertilidade e alteracoes na atividade sexual masculina. Atualmente, o papel da triiodotironina (T3) no controle da proliferacao das celulas de Sertoli e Leydig, maturacao testicular e esteroidogenese e amplamente aceito, bem como a presenca de transportadores e receptores para o hormonio tireoidiano nos testiculos durante o periodo de desenvolvimento e a idade adulta. No entanto, apesar dos dados que indicam que o T3 atua diretamente nos testiculos humanos, persistem controversias em relacao ao impacto das doencas tireoidianas sobre a espermatogenese e a fertilidade, o que pode ser em parte devido a escassez de estudos clinicos nessa area. Essa revisao tem por objetivo apresentar um panorama de dados clinicos atualizados sobre o papel dos hormonios tireoidianos na funcao gonadal masculina.Thyroid hormones are involved in the development and maintenance of virtually all tissues. Although for many years the testis was thought to be a thyroid-hormone unresponsive organ, studies of the last decades have demonstrated that thyroid dysfunction is associated not only with abnormalities in morphology and function of testes, but also with decreased fertility and alterations of sexual activity in men. Nowadays, the participation of triiodothyronine (T3) in the control of Sertoli and Leydig cell proliferation, testicular maturation, and steroidogenesis is widely accepted, as well as the presence of thyroid hormone transporters and receptors in testicular cells throughout the development process and in adulthood. But even with data suggesting that T3 may act directly on these cells to bring about its effects, there is still controversy regarding the impact of thyroid diseases on human spermatogenesis and fertility, which can be in part due to the lack of well-controlled clinical studies. The current review aims at presenting an updated picture of recent clinical data about the role of thyroid hormones in male gonadal function.

New insights toward the acute non-thyroidal illness syndrome

The non-thyroidal illness syndrome (NTIS) refers to changes in serum thyroid hormone levels observed in critically ill patients in the absence of hypothalamic–pituitary–thyroid primary dysfunction. Affected individuals have low T3, elevated rT3, and inappropriately normal TSH levels. The pathophysiological mechanisms are poorly understood but the acute and chronic changes in pituitary–thyroid function are probably the consequence of the action of multiple factors. The early phase seems to reflect changes occurring primarily in the peripheral thyroid hormone metabolism, best seen in humans since 80–90% of the circulating T3 are derived from the pro-hormone T4. The conversion of T4 to T3 is catalyzed by type 1 (D1) and type 2 (D2) deiodinases via outer-ring deiodination. In contrast, type 3 deiodinase (D3) catalyzes the inactivation of both T4 and T3. Over the last decades, several studies have attempted to elucidate the mechanisms underlying the changes on circulating thyroid hormones in NTIS. Increased inflammatory cytokines, which occurs in response to virtually any illness, has long been speculated to play a role in derangements of deiodinase expression. On the other hand, oxidative stress due to augmented reactive oxygen species (ROS) generation is characteristic of many diseases that are associated with NTIS. Changes in the intracellular redox state may disrupt deiodinase function by independent mechanisms, which might include depletion of the as yet unidentified endogenous thiol cofactor. Here we aim to present an updated picture of the advances in understanding the mechanisms that result in the fall of thyroid hormone levels in the acute phase of NTIS.

Type 2 iodothyronine deiodinase is highly expressed in germ cells of adult rat testis

The testis has been classically described as a thyroid hormone unresponsive tissue, but recent studies indicate that these hormones might play an important role in developing testes. We have previously demonstrated that type 2 iodothyronine deiodinase (D2), a thyroid hormone-activating enzyme, is expressed in adult rodent testis and that its activity is induced by hypothyroidism. Nevertheless, the precise location of D2 in testis is not known. The aim of the present work was to determine the testicular cell types in which D2 is expressed using real-time PCR analysis, in situ hybridization histochemistry, and determination of D2 activity in cell fractions isolated from adult euthyroid and/or hypothyroid rat testis. The D2 mRNA levels in germ cells were higher than those from somatic cells (6.94 +/- 1.49 vs 2.32 +/- 0.79 arbitrary units (au); P = 0.017). Hypothyroidism increased D2 expression in germ cells (6.94 +/- 1.49 vs 8.78 +/- 5.43 au, P = 0.002) but did not change D2 transcripts in somatic cells significantly (2.12 +/- 0.79 vs 2.88 +/- 1.39 au, P = 0.50). In situ hybridization analysis showed that D2 mRNA is specifically present in elongated spermatids undergoing differentiation, whereas other germ cell types and Sertoli cells of seminiferous epithelium and the interstitial cells were virtually negative for this enzyme. The enzyme activity measured in germ and somatic isolated cell fractions (0.23 +/- 0.003 vs 0.02 +/- 0.013 fmol/min per mg protein respectively; P < 0.001) further confirmed the real-time PCR and in situ hybridization results. Hence, our findings demonstrated that D2 is predominantly expressed in elongated spermatids, suggesting that thyroid hormone might have a direct effect on spermatogenesis in the adult rats.

Signaling pathways in follicular cell-derived thyroid carcinomas (review).

Thyroid carcinoma is the most common malignant endocrine neoplasia. Differentiated thyroid carcinomas (DTCs) represent more than 90% of all thyroid carcinomas and comprise the papillary and follicular thyroid carcinoma subtypes. Anaplastic thyroid carcinomas correspond to less than 1% of all thyroid tumors and can arise de novo or by dedifferentiation of a differentiated tumor. The etiology of DTCs is not fully understood. Several genetic events have been implicated in thyroid tumorigenesis. Point mutations in the BRAF or RAS genes or rearranged in transformation (RET)/papillary thyroid carcinoma (PTC) gene rearrangements are observed in approximately 70% of papillary cancer cases. Follicular carcinomas commonly harbor RAS mutations and paired box gene 8 (PAX8)-peroxisome proliferator-activated receptor γ (PPARγ) rearrangements. Anaplastic carcinomas may have a wide set of genetic alterations, that include gene effectors in the mitogen-activated protein kinase (MAPK), phosphatidylinositol 3-kinase (PI3K) and/or β-catenin signaling pathways. These distinct genetic alterations constitutively activate the MAPK, PI3K and β-catenin signaling pathways, which have been implicated in thyroid cancer development and progression. In this context, the evaluation of specific genes, as well as the knowledge of their effects on thyroid carcinogenesis may provide important information on disease presentation, prognosis and therapy, through the development of specific tyrosine kinase targets. In this review, we aimed to present an updated and comprehensive review of the recent advances in the understanding of the genetic basis of follicular cell-derived thyroid carcinomas, as well as the molecular mechanisms involved in tumor development and progression.