Effect of thyroxine administration on the IGF/IGF binding protein system in neonatal and adult thyroidectomized rats

Multifactorial control of reproductive and growth axis in male goldfish: Influences of GnRH, GnIH and thyroid hormone

Reproduction and growth are under multifactorial control of neurohormones and peripheral hormones. This study investigated seasonally related effects of GnIH, GnRH, and T3 on the reproductive and growth axis in male goldfish at three stages of gonadal recrudescence. The effects of injection treatments with GnRH, GnIH and/or T3 were examined by measuring serum LH and GH levels, as well as peripheral transcript levels, using a factorial design. As expected, GnRH elevated serum LH and GH levels in a seasonally dependant manner, with maximal elevations of LH in late stages of gonadal recrudescence (Spring) and maximal increases in GH in the regressed gonadal stage (Summer). GnIH injection increased serum LH and GH levels only in fish at the regressed stage but exerted both stimulatory and inhibitory effects on GnRH-induced LH responses depending on season. T3 treatment mainly had stimulatory effects on circulating LH levels and inhibitory effects on serum GH concentrations. In the liver and testes, we observed seasonal differences in thyroid receptors, estrogen receptors, vitellogenin, follicle-stimulating hormone receptor, aromatase and IGF-I transcript levels that were tissue- and sex-specific. Generally, there were no clear correlation between circulating LH and GH levels and peripheral transcript levels, presumably due to time-related response and possible direct interaction of GnRH and GnIH at the level of liver and testis. The results support the hypothesis that GnRH and GnIH are important components of multifactorial mechanisms that work in concert with T3 to regulate reciprocal control of reproduction and growth in goldfish.

Effects of levothyroxine on growth hormone (gh) sensitivity in children with idiopathic short stature

BACKGROUND

The possible relationship between the circulating concentrations of T4 and GH sensitivity has not been elucidated.

OBJECTIVE

The aim of this study is to evaluate the effect of levothyroxine supplementation on GH sensitivity in prepubertal boys with idiopathic short stature (ISS).

METHODS

We selected 28 prepubertal boys with ISS (mean age 8.2±0.5years) and free T4 (Ft4) concentrations between the 3rd and the 25th percentiles (Ft4: 0.8-1.5ng/dl). They were randomly divided into two groups: Group A received thyroid supplementation (1-3μg/kg/day) for 120days, and Group B received placebo for the same period. To evaluate GH sensitivity, an IGF-I generation test (GH: 33μg/kg/day sc for 3days) was performed in both groups: under basal conditions, and after 120days of levothyroxine supplementation (or placebo).

RESULTS

After thyroid supplementation, Group A had higher Ft4 concentrations compared with Group B (2.14±0.06 vs 1.48±0.06ng/dl, p=0.01), their growth velocity was significantly higher (2.3±0.1 vs 1.5±0.2cm/4months), and they exhibited a greater increase in IGF-I after GH administration (Group A: 32.5±3.8% vs Group B 17.3±2.6%).

CONCLUSION

Supplementation with levothyroxine for 120days promotes an increase in growth velocity, and a greater IGF-I response to short-term GH administration in prepubertal boys with ISS and low-normal thyroid hormone concentrations.

Thyroid regeneration: how stem cells play a role?

Many tissues if not all are thought to contain stem cells that are responsible for regeneration and repair of the tissue after injury. Dysregulation of tissue regeneration may result in various pathological conditions, among which cancer is the most extensively studied. Notably, the so-called cancer stem cells or tumor-initiating cells, have been studied in order to understand the mechanisms of carcinogenesis and/or metastasis. However, the nature of cancer stem cells, let alone normal stem/progenitor cells, particularly those of the thyroid remains elusive. There remains a gap in knowledge between adult thyroid stem/progenitor cells and cancer stem cells of the thyroid, and if and/or how they are related to each other. Understanding of the mechanism for thyroid regeneration and mode of participation of normal adult thyroid stem/progenitor cells in this process will hopefully yield a more complete understanding of the nature of thyroid cancer stem cells, and/or help understand the pathogenesis of other thyroid diseases. This review summarizes the current understanding of adult thyroid stem/progenitor cells, with particular emphasis on how they contribute to thyroid regeneration.

Early weaning PCB 95 exposure alters the neonatal endocrine system: thyroid adipokine dysfunction

Polychlorinated biphenyls (PCBs) are persistent environmental pollutants that can severely disrupt the endocrine system. In the present study, early-weaned male rats were administered a single dose of 2,3,6-2',5'-pentachlorinated biphenyl (PCB 95; 32 mg/kg per day, by i.p. injection) for two consecutive days (postnatal days (PNDs) 15 and 16) and killed 24 and 48 h after the administration of the last dose. Compared with the control group, administration of PCB 95 induced a reduction (P<0.01) in serum concentrations of thyroxine, triiodothyronine, and GH and an increase (P<0.01) in the serum concentration of TSH at PNDs 17 and 18. These conspicuous perturbations led to some histopathological deterioration in the thyroid gland characterized by follicular degeneration, edema, fibrosis, hemorrhage, luminal obliteration, and hypertrophy with reduced colloidal contents at PND 18. The dyshormonogenesis and thyroid dysgenesis may be attributed to the elevation of DNA fragmentation at PNDs 17 and 18. Furthermore, this hypothyroid state revealed higher (P<0.01) serum concentrations of leptin, adiponectin, and tumor necrosis factor and lower (P<0.01) serum concentrations of IGF1 and insulin at both PNDs compared with the control group. Interestingly, the body weight of the neonates in the PCB 95 group exhibited severe decreases throughout the experimental period in relation to that of the control group. These results imply that PCB 95 may act as a disruptor of the developmental hypothalamic-pituitary-thyroid axis. Hypothyroidism caused by PCB 95 may impair the adipokine axis, fat metabolism, and in general postnatal development. Thus, further studies need to be carried out to understand this concept.

Thyroid regeneration: characterization of clear cells after partial thyroidectomy

Although having the capacity to grow in response to a stimulus that perturbs the pituitary-thyroid axis, the thyroid gland is considered not a regenerative organ. In this study, partial thyroidectomy (PTx) was used to produce a condition for thyroid regeneration. In the intact thyroid gland, the central areas of both lobes served as the proliferative centers where microfollicles, and bromodeoxyuridine (BrdU)-positive and/or C cells, were localized. Two weeks after PTx, the number of BrdU-positive cells and cells with clear or faintly eosinophilic cytoplasm were markedly increased in the central area and continuous to the cut edge. Clear cells were scant in the cytoplasm, as determined by electron microscopy; some retained the characteristics of calcitonin-producing C cells by having neuroendocrine granules, whereas others retained follicular cell-specific features, such as the juxtaposition to a lumen with microvilli. Some cells were BrdU-positive and expressed Foxa2, the definitive endoderm lineage marker. Serum TSH levels drastically changed due to the thyroidectomy-induced acute reduction in T(4)-generating tissue, resulting in a goitrogenesis setting. Microarray followed by pathway analysis revealed that the expression of genes involved in embryonic development and cancer was affected by PTx. The results suggest that both C cells and follicular cells may be altered by PTx to become immature cells or immature cells that might be derived from stem/progenitor cells on their way to differentiation into C cells or follicular cells. These immature clear cells may participate in the repair and/or regeneration of the thyroid gland.

Serum IGF-1 and IGFBP-3 levels in subclinical hypothyroid women

Thyroid status is known to influence growth in mammals. The aim of this study is to investigate the possible relationship between autoimmune subclinical hypothyroidism and growth hormone (GH), insulin-like growth factor-1(IGF-1) and insulin-like growth factor binding protein-3(IGFBP-3) levels. Thirty-five women with autoimmune subclinical hypothyroidism, 33 years of age, were used as controls and enrolled in the study. Free triiodothyronin (FT3), free thyroxin(FT4), thyrotropin(TSH), anti-thyroid peroxidase(Anti-TPO), anti-thyroglobuline(Anti-Tg), GH, IGF-1 and IGFBP-3 levels were measured in blood samples and correlations among these parameters were evaluated. We found no significant differences in GH, IGF-1 or IGFBP-3 between patients and controls. In patients and controls, there were no correlations among thyroid hormones and IGF-1 or IGFBP-3 levels, but GH levels were correlated with FT3, FT4 and TSH only in patients’ group. In controls, only IGF-1 and IGFBP-3 levels were correlated. The present study suggests that subclinical hypothyroidism with high TSH and antibody status does not affect IGF-1 and IGFBP-3 levels in adult women. To our knowledge, this is the first study concerning the relationship between autoimmune subclinical hypothyroidism and IGF-1 and IGFBP-3 levels.

Live prey enrichment, with particular emphasis on HUFAs, as limiting factor in false percula clownfish (Amphiprion ocellaris, Pomacentridae) larval development and metamorphosis: molecular and biochemical implications

In fast growing organisms, like fish larvae, fatty acids provided through live prey are essential to satisfy high energy demand and are required to promote growth. Therefore, in recent decades, a great amount of research has been directed towards the development of lipid enrichment in order to improve larval fish survival and growth. However, in fish, the biochemical and molecular processes related to highly unsaturated fatty acid (HUFA) administration are still poorly understood. In the current study, the false percula clownfish, a short larval phase marine species, was used as an experimental model and the effects of a standard and a HUFAs-enriched diet were tested through a molecular, biochemical, ultrastructural and morphometric approach. Our results support the hypothesis that HUFA administration may improve larval development through the presence of better structured mitochondria, a higher synthesis of energy compounds and coenzymes with a central position in the metabolism, with respect to controls. This higher energy status was confirmed by better growth performance and a shorter larval phase in larvae fed with an enriched diet with respect to the control. This strategy of rapid growth and early energy storage may be considered positively adaptive and beneficial to the survival of this species.

Insulin-like growth factor-I gene and insulin-like growth factor binding protein-3 polymorphism in patients with thyroid dysfunction

BACKGROUND AND AIMS

Thyroid hormones have important roles in normal growth and skeletal muscle development. IGF-I is one of the most important growth factors and is needed for the proliferation and development of thyroid cells. It stimulates fibroblasts, follicular and endothelia cells in thyroid gland. It has been shown that thyroid hormones play an important role in the regulation of IGF-I and IGFBP-3. In this study we proposed that IGF-I (CA)(19) and IGFBP-3-202 A/C gene polymorphism may affect thyroid functions. For this purpose, frequency of IGF-I (CA)(19) and IGFBP-3-202 A/C gene polymorphism in hypo- and hyperthyroid patients and possible role of these polymorphism in thyroid functions were investigated.

METHODS

This study was performed on 37 volunteer hyperthyroid and 76 hypothyroid patients as well as with 50 healthy subjects as controls. DNA isolation was applied in peripheral blood samples obtained from patients and controls. Required areas were amplified with PCR by using proper primers belonging to these gene areas from the isolated DNA samples. The products were evaluated with visualization by UV gel documentation system.

RESULTS

Frequency of IGF-I (CA)(19) gene polymorphism among hypothyroidism patients, hyperthyroidism patients and controls were statistically significant (chi(2) = 11.55, df = 4, p = 0.021). Genotypic variations between hyper- and hypothyroid patients were significant (chi(2) = 11.39, df = 2, p = 0.003), whereas there was no difference in IGF-I (CA)(19) gene polymorphism between the patients and controls. Differences in the IGFBP-3-202 A/C gene polymorphism between controls and hypo- as well as hyperthyroid patients were not significant. But IGFBP-3-202 A/C gene polymorphism genotype frequencies showed a significant difference between hypo- and hyperthyroid patients (chi(2) = 6.24, df = 2, p = 0.044).

CONCLUSIONS

These findings suggests that IGF-I (CA)(19) and IGFBP-3-202 A/C gene polymorphisms may be a risk factor for hypothyroidism.

Thyroid hormone receptor and IGF1/IGFR systems: Possible relations in the human heart

Thyroid hormone (TH) and insulin growth factor 1 (IGF1) systems both play crucial roles in the regulation of cardiac remodeling and hypertrophy processes. The mediation of this regulation is attributed to specific thyroid hormone receptors (TRs) and to the IGF1 receptor (IGF1R). In humans, two TR genes are expressed in the heart, TRalpha and TRbeta. Each gene generates two isoforms: TRalpha1, TRalpha2 and TRbeta1, TRbeta2. The aim of the present work was to study the local thyroid hormone and IGF1 signaling in human myocardium through the evaluation of the gene expression of TRalpha1, TRalpha2, TRbeta1 and IGF1R among atrial and ventricular biopsies obtained from patients undergoing cardiac surgery. Moreover, we evaluated possible correlations between TR and IGF1/IGF1R systems. Eighteen clinically and biochemically euthyroid patients (aged 68.3+/-3.2years, mean+/-SEM) without overt heart failure (Ejection Fraction (EF), 46.4+/-2.8%; Left Ventricular End Diastolic Diameter (LVEDD), 54.3+/-1.2mm, mean+/-SEM; NYHA I-II) were enrolled in the study: 13 undergoing aorto-coronary bypass and 5 undergoing valve replacement (aortic/mitral valve). The examination of total RNA, using real time PCR (LightCycler Technology) confirmed the expression of specific mRNAs encoding TRalpha1, TRalpha2, TRbeta1 and both IGF1 and IGF1R. We found that the three TR genes are co-expressed in the human atrium and ventricle. The finding of a strong correlation among IGF1R and the three TR genes expressed in the atrium (p<0.001) and among the three TRs in the atrium (p<0.001) suggests the interesting possibility that the two systems, TRs and IGF1R could also be functionally associated.

Manipulation of thyroid status and/or GH injection alters hepatic gene expression in the juvenile chicken

Both thyroid hormone (T3) and growth hormone (GH) are important regulators of somatic growth in birds and mammals. Although T3-mediated gene transcription is well known, the molecular basis of T3 interaction with GH on growth and development of birds remains unknown. In earlier studies, we discovered that exogenous GH alone increased accumulation of visceral fat in young chickens, while the combination of GH injections and dietary T3 worked synergistically to deplete body fat. In the present study, cDNA microarray and quantitative RT-PCR analyses enabled us to examine hepatic gene expression in young chickens after chronic manipulation of thyroid status and GH injection alone or in combination with T3. Thyroid status modulates expression of common and unique sets of genes involved in a wide range of molecular functions (i.e., energy metabolism, storage and transport, signal transduction, protein turnover and drug detoxification). Hepatic expression of 35 genes was altered by hypothyroidism (e.g., ADFP, ANGPTL3, GSTalpha, CAT, PPARG, HMGCL, GHR, IGF1, STAT3, THRSPalpha), whereas hyperthyroidism affected expression of another cluster of 13 genes (e.g., IGFBP1, KHK, LDHB, BAIA2L1, SULT1B, TRIAD3). Several genes were identified which have not been previously ascribed as T3 responsive (e.g., DEFB9, EPS8L2, ARHGAP1, LASS2, INHBC). Exogenous GH altered expression of 17 genes (e.g., CCAR1, CYP2C45, GYS2, ENOB, HK1, FABP1, SQLE, SOCS2, UPG2). The T3+GH treatment depleted the greatest amount of body fat, where 34 differentially expressed genes were unique to this group (e.g., C/EBP, CDC42EP1, SYDE2, PCK2, PIK4CA, TH1L, GPT2, BHMT). The marked reduction in body fat brought about by the T3+GH synergism could involve modulation of hormone signaling via altered activity of the Ras superfamily of molecular switches, which control diverse biological processes. In conclusion, this study provides the first global analysis of endocrine (T3 and GH) regulation of hepatic gene transcription in the chicken.

Regulation of galanin-like peptide gene expression by pituitary hormones and their downstream targets

Galanin-like peptide (GALP) mRNA is expressed in neurones of the hypothalamic arcuate nucleus and within pituicytes in the neurohypophysis. Several neuropeptides that are expressed in the arcuate nucleus participate in the neuroendocrine regulation of pituitary hormone secretion. Our objective was to determine the extent to which GALP might be a target for regulation by pituitary hormones or their downstream targets in the rat. The expression of GALP mRNA in the arcuate nucleus was reduced by hypophysectomy as determined by in situ hybridization. However, this did not appear to be attributable to the loss of either gonadal or adrenal steroids because castrated, ovariectomized and adrenalectomized rats had GALP mRNA expression that was indistinguishable from their respective controls. Next, we investigated the effects of growth hormone deficiency on GALP mRNA expression by studying dwarf rats and found that GALP gene expression was not different between dwarf rats and controls. We found that thyroidectomy led to a significant reduction in GALP mRNA expression compared to intact controls, and thyroidectomized rats implanted with thyroxine pellets had GALP mRNA expression that was similar to intact controls. Thus, the reduction of GALP mRNA expression seen in hypophysectomized animals may reflect, in part, a selective loss of thyroid hormone. We also found that the expression of GALP mRNA was increased in the neurohypophysis of lactating rats compared to nonlactating rats, whereas GALP mRNA expression in the arcuate nucleus was unaffected by lactation. This suggests that the induction of GALP gene expression in pituicytes is physiologically associated with activation of oxytocin and vasopressin secretion during lactation.

Age-dependent adaptation of the liver thyroid status and recovery of serum levels and hepatic insulin-like growth factor-I expression in neonatal and adult diabetic rats

The effect of treatment with thyroxine (T(4)) on the hepatic deiodinase (5'D-I) activity and triiodothyronine (T(3)) content and on insulin-like growth factor-I (IGF-I) secretion and mRNA hepatic expression were studied in neonatal and adult diabetic (D) rats and compared with 4 thyroidectomized (Tx) groups: neonatal and adult Tx rats treated or not with T(4). Serum T(3) and T(4) decreased by 92% in both Tx populations and by 80% to 70% in D adults according to the severity of diabetes: -70 mg/kg body weight (BW) (D(70)) or 50 mg/kg BW (D(50)) of streptozotocin (STZ) injected, whereas only a 30% to 33% decrease was found in D neonates. A similar decrease of liver 5'D-I activity and T(3) concentrations was found in neonatal and adult Tx rats, whereas a significant reduction in those parameters was observed only in adult diabetics, either D(70) or D(50), but not in D neonates. Serum levels and liver mRNA expression of IGF-I determined by ribonuclease protection assay, plasma and pituitary growth hormone (GH), plasma insulin, and glycemia were also measured in both D populations. A decrease in circulating IGF-I, previously reported for Tx adult rats, was also found in both D populations. T(4) treatment recovered IGF-I and liver T(3) in both Tx groups and D neonates, but not in D adults. These results show an age-dependent adaptation of the liver thyroid economy in diabetes, as hepatic 5'D-I does not respond to diabetes in neonates and IGF-I is insensitive to T(4) treatment in adult diabetics and suggest a positive correlation between hepatic T(3) content and IGF-I expression in conditions of diabetes and Tx.

Recombinant human growth hormone increases thyroid hormone-binding sites in recovering severely burned children

Thyroxine (T4), Tri-iodothyronine (T3), and total serum protein levels are reduced in severely burned children. T4 and T3 are carried on serum transport proteins via thyroid hormone-binding sites (THBS). Treatment of bums with recombinant human growth hormone (rhGH) increases albumin (Alb) and prealbumin (PreAlb), which bind nearly 30% of circulating T4 and T3. This study investigated the effect of rhGH on THBS sites in burned children. Records of 11 acutely burned children with a total body surface area burned >40% who were randomized to either a daily subcutaneous injection of rhGH at 0.05 mg/kg/day or placebo for 6 months after discharge from hospital were reviewed. Thyroxine uptake percentage (TU%), Total T4 levels (TT4), free thyroxine index, Alb and PreAlb, and height and weight measurements taken at discharge and 6 months later were compared in both groups. In the six children who received rhGH, mean TU% had decreased from 41 +/- 1 to 33 +/- 1% by 6 months postdischarge, (P < 0.001), mean TT4 increased from 5.8 +/- 0.3 to 8.1 +/- 0.8 microg/dL, (P < 0.02), mean Alb increased from 2.0 +/- (0.6) to 3.5 +/- (0.1) g/dL (P < 0.0001), and mean PreAlb increased from 8.7 +/- 0.7 to 16.5 +/- 2.1 mg/dL, (P < 0.006). There were no significant changes in the five children in the placebo (control group), and height and weight did not significantly change in either group. rhGH significantly increases THBS in severely burned children, possibly through increases in serum Alb and PreAlb. The increases in circulating thyroxine observed in this group may be involved in the attenuation of growth arrest.

Local insulin-like growth factor-II mediates prolactin-induced mammary gland development

Prolactin (PRL) is a major determinant of mammary epithelial cell proliferation during alveolar development in sexually mature and pregnant mice. To date, it has not been clear whether PRL effects these responses alone or by also invoking the action of autocrine/paracrine growth factors. In this study, we provide evidence that part of the effect of PRL on mammary gland growth is mediated by IGF-II. During sexual maturity and in early pregnancy, the level of IGF-II mRNA in the mammary gland was increased concurrent with increased PRL receptor expression. The level of IGF-II mRNA was reduced in mammary tissue from PRL receptor-/- mice during early pregnancy, and explants of mouse mammary gland and HC11 mammary epithelial cells both increased their expression of IGF-II after exposure to PRL in vitro. These findings coincided with the demonstration that IGF-II stimulated alveolar development in mammary glands in whole organ culture. PRL was most efficacious in stimulating IGF-II gene transcription from promoter 3 of the mouse IGF-II gene in vitro. Insight into the mechanism by which PRL induced IGF-II expression was provided by the fact that it was blocked by the Jak2 inhibitor AG490 and the MAPK inhibitor PD98059. Finally, induction of insulin receptor substrate (IRS)-1 in the mammary glands of PRL-treated mice and induction of IRS-1 and IRS-2 after treatment with PRL plus progesterone indicates that these molecules are induced by PRL as potential signaling intermediates downstream from IGF-I/insulin receptors. Together, these data demonstrate a role for IGF-II as a mediator of PRL action in the mouse mammary gland during ductal branching and alveolar development.

Different role of insulin in GLUT-1 and -4 regulation in heart and skeletal muscle during perinatal hypothyroidism

Two groups of hypothyroid rats were used; one group was given 2-mercapto-1-methylimidazole (MMI) treatment in the drinking water of the mothers and was killed at 2 and 4 days of life, and the other group was given similar MMI treatment and then was thyroidectomized at 5 days of life and killed at 8 or 20 days. Serum insulin, growth hormone (GH), and insulin-like growth factor I (IGF-I) were decreased in MMI-treated rats but increased in MMI-treated plus thyroidectomized rats. No significant reduction of thyroid hormones was observed in 2-day-old MMI rats. Protein and mRNA expression of GLUT-1 increased, and those of GLUT-4 decreased, in the heart in all populations independent of changes in insulin, GH, and IGF-I levels. However, GLUT-4 protein and mRNA expression in quadriceps and gastrocnemius skeletal muscles decreased at 4 days and increased at 8 and 20 days of life in parallel with insulin, GH, and IGF-I levels. GLUT-1 in the skeletal muscles seemed regulated posttranscriptionally and presented a decrease of mRNA expression in all stages studied. A differential sensitivity to insulin regulation of GLUT-1 and GLUT-4 glucose transporters seems to be one of the causes for the tissue-specific regulation of these glucose transporters in heart and skeletal muscles during the perinatal period.