Thyroid hormone regulates the obesity gene tub

Acute exercise reduces feeding by activating IL-6/Tubby axis in the mouse hypothalamus

Background: Acute exercise contributes to decreased feeding through leptin and interleukin/Janus kinase 2/signal transducers and activators of transcription 3 (IL-6/JAK2/STAT3) signaling. Considering the pleiotropic use of substrates by JAK2 and that JAK2 can phosphorylate the Tubby protein (TUB) in CHO-IR cells, we speculated that acute exercise can activate the IL-6/JAK2/TUB pathway to decrease food intake.

Aims: We investigated whether acute exercise induced tyrosine phosphorylation and the association of TUB and JAK2 in the hypothalamus and if IL-6 is involved in this response, whether acute exercise increases the IL-6/TUB axis to regulate feeding, and if leptin has an additive effect over this mechanism.

Methods: We applied a combination of genetic, pharmacological, and molecular approaches.

Key findings: The in vivo experiments showed that acute exercise increased the tyrosine phosphorylation and association of JAK2/TUB in the hypothalamus, which reduced feeding. This response was dependent on IL-6. Leptin had no additive effect on this mechanism.

Significance: The results of this study suggest a novel hypothalamic pathway by which IL-6 released by exercise regulates feeding and reinforces the beneficial effects of exercise.

The Impact of Subclinical Hypothyroidism on Patients with Polycystic Ovary Syndrome: A Meta-Analysis

The association between subclinical hypothyroidism (SCH) and polycystic ovary syndrome (PCOS) has been shown in many studies. These findings are still controversial, however. It is unclear whether the co-incidence of subclinical hypothyroidism and polycystic ovary syndrome will affect the severity of metabolism. Therefore, we performed this meta-analysis to investigate the association. A comprehensive search strategy was developed to obtain all relevant studies published in PubMed, EMBASE, Cochrane Library, and Chinese Academic Journal Full-text Database (CNKI) up to 31 December 2020. We adopted the standardized mean difference (SMD) with 95% confidence intervals (CI) for evaluation, and sensitivity analysis was performed. Publication bias was analyzed and represented by a funnel plot, and funnel plot symmetry was assessed with Egger's test. Twenty-seven studies with 4821 participants (1300 PCOS patients with SCH, 3521 PCOS patients without SCH) were included in the present meta-analysis,among which 71.31% chinese patients out of the total. The results showed that PCOS patients with SCH had higher levels of HOMA-IR, TG, TC, LDL, FBG, FCP, PRL and lower levels of HDL, LH and T. It also recognized the limitation of the lack of a consistent definition of hypothyroidism in the 27 studies included. The results of this study indicated that SCH may aggravate lipid and glucose metabolism in patients with PCOS.

Promoting Effect of L-tyrosine Supplement on New Zealand Rabbit Bucks' Performance and Reproduction Through Upregulation of Steroidogenic Markers

Delayed puberty and lower fertility are among the most challenging concerns in rabbit development during the summer season. This study was, therefore, aimed at enhancing male NZ rabbits' performance by using L-tyrosine. Thirty male, New Zealand rabbits, were employed for this purpose at the age of 60 days. Rabbits were divided accidentally into two groups: a control group and another treated with L-tyrosine (100 mg/kg body weight). After 4 weeks, three bucks of each group were assassinated. A comparable oral dose of L-tyrosine was administered to half of the treated group left untreated during the second half. Weekly blood samples were assembled from each group for testosterone, T3, and T4 hormone testing. The results showed that body weight and serum testosterone, T3, and T4 increased exponentially with increasing age in both groups. L-tyrosine contributed to another vital rise in dose-dependence than control, in bodyweight, GSI, and testosterone, T3, and T4. At the end of the third month, tests fell in the scrotum, compared to 2 weeks before in the L-tyrosine group. In the middle of the fourth month, the semen evaluations were first carried out for the L-tyrosine group and 1 month after for the control group. L-tyrosine has contributed to a substantial upsurge in semen quality and motility, and abnormalities have reduced dramatically (P < 0.01). The L-tyrosine-treated group showed significantly increased mRNA expression of steroidogenesis markers STAR, CYP11A1, and 3B-HSD. Besides, free sperm in the seminiferous tubular lumen was discovered at the end of the third month. Nevertheless, it achieves only in control of the spermatocyte stage. The research suggests that L-tyrosine supplements promote puberty and improve male New Zealand rabbit fertility during high-temperature periods in the year.

Candidate variants in TUB are associated with familial tremor

Essential tremor (ET) is the most common adult-onset movement disorder. In the present study, we performed whole exome sequencing of a large ET-affected family (10 affected and 6 un-affected family members) and identified a TUB p.V431I variant (rs75594955) segregating in a manner consistent with autosomal-dominant inheritance. Subsequent targeted re-sequencing of TUB in 820 unrelated individuals with sporadic ET and 630 controls revealed significant enrichment of rare nonsynonymous TUB variants (e.g. rs75594955: p.V431I, rs1241709665: p.Ile20Phe, rs55648406: p.Arg49Gln) in the ET cohort (SKAT-O test p-value = 6.20e-08). TUB encodes a transcription factor predominantly expressed in neuronal cells and has been previously implicated in obesity. ChIP-seq analyses of the TUB transcription factor across different regions of the mouse brain revealed that TUB regulates the pathways responsible for neurotransmitter production as well thyroid hormone signaling. Together, these results support the association of rare variants in TUB with ET.

Essential tremor (ET) is the most common adult-onset movement disorder and in most affected families it appears to be inherited in an autosomal dominant pattern. The causes of essential tremor are unknown. Although many genetic studies in affected families and sporadic cases of ET have shown that genes may play a role, it has proven quite challenging to identify the specific genetic variants involved. Here, we use state-of-the-art technologies to identify the role of genetic variants on ET through exome sequencing of a large affected ET family and subsequent validation in a large population of cases and controls. We show that rare nonsynonymous variants of the TUB gene are significantly enriched in ET cases versus healthy controls. Further studies of biological pathways regulated by TUB in the mouse brain reveal key pathways related to ET. Our work expands our knowledge of the genetic basis of ET.

Relationship Between Hormonal Mechanisms of Diabetes Mellitus and Hypothyroidism Post-Bariatric Surgery

BACKGROUND

Obesity, diabetes mellitus may be related to the health, the relationship and the physiological capacity of the production of thyroid hormones (TH), triiodothyronine (T3) and thyroxine (T4).

OBJECTIVES

The main aims of this review are to describe the relationship between obesity, appetite, weight management, hormonal mechanisms of diabetes mellitus and hypothyroidism post-bariatric surgery.

METHODOLOGY

An in-depth literature search was conducted to identify scientific studies, which analyzed the correlation between diabetes mellitus and hypothyroidism post-bariatric surgery.

RESULTS

Bariatric surgery decreases hypothyroidism, reduces the need for pharmacological action (such as levothyroxine), controls the weight and body fat and increases the sensitivity to leptin and insulin.

CONCLUSION

The reduction of the stomach and intestine by bariatric surgery is an evolutionary and beneficial action, because it may lead to a drastic decrease on numbers of conditions such as diabetes, obesity, hypothyroidism, and others. Thus, new studies should also focus on patients' post-operatory conditions, such as lifetime, regulation and functioning of organs after reduced nutrition, and consumption and delivery of nutrients to health maintenance.

TUB gene expression in hypothalamus and adipose tissue and its association with obesity in humans

BACKGROUND/OBJECTIVES

Mutations in the Tubby gene (TUB) cause late-onset obesity and insulin resistance in mice and syndromic obesity in humans. Although TUB gene function has not yet been fully elucidated, studies in rodents indicate that TUB is involved in the hypothalamic pathways regulating food intake and adiposity. Aside from the function in central nervous system, TUB has also been implicated in energy metabolism in adipose tissue in rodents. We aimed to determine the expression and distribution patterns of TUB in man as well as its potential association with obesity.

SUBJECTS/METHODS

In situ hybridization was used to localize the hypothalamic regions and cells expressing TUB mRNA. Using RT-PCR, we determined the mRNA expression level of the two TUB gene alternative splicing isoforms, the short and the long transcript variants, in the hypothalami of 12 obese and 12 normal-weight subjects, and in biopsies from visceral (VAT) and subcutaneous (SAT) adipose tissues from 53 severely obese and 24 non-obese control subjects, and correlated TUB expression with parameters of obesity and metabolic health.

RESULTS

Expression of both TUB transcripts was detected in the hypothalamus, whereas only the short TUB isoform was found in both VAT and SAT. TUB mRNA was detected in several hypothalamic regions involved in body weight regulation, including the nucleus basalis of Meynert and the paraventricular, supraoptic and tuberomammillary nuclei. We found no difference in the hypothalamic TUB expression between obese and control groups, whereas the level of TUB mRNA was significantly lower in adipose tissue of obese subjects as compared to controls. Also, TUB expression was negatively correlated with indices of body weight and obesity in a fat-depot-specific manner.

CONCLUSIONS

Our results indicate high expression of TUB in the hypothalamus, especially in areas involved in body weight regulation, and the correlation between TUB expression in adipose tissue and obesity. These findings suggest a role for TUB in human obesity.

Impact of Obesity on Serum Levels of Thyroid Hormones among Euthyroid Saudi Adults

AIM OF STUDY

To assess serum thyroid hormones levels among Saudi adults and to correlate participants' serum levels with their grades of body mass index (BMI).

METHODOLOGY

A total of 278 adult subjects were recruited. Participants were categorized according to their BMI grades into normal weight (BMI < 25 kg/m2), overweight (BMI 25-29.9 kg/m2), or obese (BMI ≥ 30 kg/m2). Serum thyroid hormones levels were assessed at the central laboratory of Aseer Central Hospital, Abha City, by chemiluminescence immunoassay.

RESULTS

More than three-fourths of participants were either overweight (31.3%) or obese (44.6%). Mean TSH serum levels showed a significantly increasing trend with increasing BMI (p < 0.001). A negative trend was observed regarding participants' mean serum levels of fT4 with their BMI, but there were no significant differences in mean serum fT4 levels according to BMI. Moreover, no significant differences were observed in serum fT3 levels according to BMI.

CONCLUSIONS

Mean TSH serum levels increase with BMI increase. Further largescale multicentric and longitudinal studies are necessary to prove the association between serum levels of thyroid hormones and BMI of euthyroid adults.

The link between metabolic features and TSH levels in polycystic ovary syndrome is modulated by the body weight: an euglycaemic-hyperinsulinaemic clamp study

OBJECTIVE

To evaluate the link among thyroid function, glucose/insulin metabolism and steroid hormones in women with polycystic ovary syndrome (PCOS), and to verify if the body mass index (BMI) might influence the interplay between PCOS features and subclinical hypothyroidism (SCH).

STUDY DESIGN

Case-control study conducted from January to December 2014.

METHODS

One-hundred fifty-four young women with PCOS, according to Rotterdam criteria, and 88 controls were enrolled in an academic research environment. Anthropometric evaluation, hormonal and lipid assays, oral glucose tolerance test (OGTT) and euglycaemic-hyperinsulinaemic clamp were performed. Hirsutism was assessed with the Ferriman-Gallwey (FG) score.

MAIN RESULTS

SCH was found in 14% of PCOS subjects and in 1% of controls (P < 0.01). In PCOS women, TSH levels were directly correlated with fasting glycaemia, but not with other hormonal and metabolic parameters. When PCOS patients were classified on the basis of BMI, TSH levels significantly correlated with insulin secretion, insulin resistance, DHEAS and cortisol levels in obese PCOS women. Inverse correlations were found between TSH and both oestradiol and SHBG in the same group. In nonobese PCOS patients, only waist-to-hip ratio values were correlated with TSH. The prevalence of SCH was not different between nonobese and obese PCOS groups (14 and 15% respectively). However, SCH was associated with higher levels of insulin, DHEAS, cortisol and FG score only in the obese subgroup.

CONCLUSIONS

Our data confirm that the prevalence of SCH is increased in PCOS women. The presence of SCH is associated with endocrine and metabolic imbalances of PCOS, and the excessive body weight seems to promote this interplay.

Insulin Phosphorylates Tyrosine Residue 464 of Tub and Translocates Tubby into the Nucleus in HIRcB Cells

BACKGROUND

The tubby protein has a motif that might be relevant for its action in the insulin signaling pathway. Previous studies have indicated that tubby undergoes phosphorylation on tyrosine residues in response to several stimuli and is known to localize in the nucleus as well as in the plasma membrane. However, the relationship between phosphorylation and nuclear translocation is not well understood. Here, we report that insulin directly phosphorylates tubby, which translocates into the nucleus.

METHODS

The effects of insulin on Tubby were performed with Western blot. The immunoprecipitation and confocal microscopy were performed to prove phosphorylation and nuclear translocation.

RESULTS

Mutation study reveals that tyrosine residue 464 of tubby gene (Tub) is a phosphorylation site activated by insulin. In addition, major portions of tubby protein in the plasma membrane are translocated into the nucleus after insulin treatment. Tyrosine kinase inhibitor pretreatment blocked insulin-induced tubby translocation, suggesting that phosphorylation is important for nuclear translocation. Moreover, mutant tyrosine residue 464 did not translocate into the nucleus in respond to insulin. These findings demonstrate that insulin phosphorylates tyrosine residue 464 of Tub, and this event is important for insulin-induced tubby nuclear translocation.

CONCLUSION

Insulin phosphorylates tyrosine residue 464 of Tub and translocates tubby into the nuclei of HIRcB cells.

Tub has a key role in insulin and leptin signaling and action in vivo in hypothalamic nuclei

Mutation of tub gene in mice induces obesity, suggesting that tub could be an important regulator of energy balance. In the current study, we investigated whether insulin, leptin, and obesity can modulate Tub in vivo in hypothalamic nuclei, and we investigated possible consequences on energy balance, neuropeptide expression, and hepatic glucose metabolism. Food intake, metabolic characteristics, signaling proteins, and neuropeptide expression were measured in response to fasting and refeeding, intracerebroventricular insulin and leptin, and Tub antisense oligonucleotide (ASO). Tub tyrosine phosphorylation (Tub-p-tyr) is modulated by nutritional status. Tub is a substrate of insulin receptor tyrosine kinase (IRTK) and leptin receptor (LEPR)-Janus kinase 2 (JAK2) in hypothalamic nuclei. After leptin or insulin stimulation, Tub translocates to the nucleus. Inhibition of Tub expression in hypothalamus by ASO increased food intake, fasting blood glucose, and hepatic glucose output, decreased O(2) consumption, and blunted the effect of insulin or leptin on proopiomelanocortin, thyroid-releasing hormone, melanin-concentrating hormone, and orexin expression. In hypothalamus of mice administered a high-fat diet, there is a reduction in leptin and insulin-induced Tub-p-tyr and nuclear translocation, which is reversed by reducing protein tyrosine phosphatase 1B expression. These results indicate that Tub has a key role in the control of insulin and leptin effects on food intake, and the modulation of Tub may contribute to insulin and leptin resistance in DIO mice.

The effect of n-3 long chain fatty acids supplementation on plasma peroxisome proliferator activated receptor gamma and thyroid hormones in obesity

BACKGROUND

Peroxisome proliferator-activated receptor gamma (PPAR γ) is a transcription factor, which is abundantly expressed in adipose tissue and has a direct link to adiposity. It seems that long-chain polyunsaturated fatty acids (LC-PUFAs) can regulate PPAR γ expression. The purpose of this study was to investigate the effects of n-3LC PUFA supplementation on plasma levels of PPAR γ and thyroid hormones in obesity.

MATERIALS AND METHODS

In a randomized double-blind controlled trial, 66 subjects with obesity were assigned to 2 groups. Participants in intervention group consumed omega3 capsules contained 1000 mg n-3 fatty acids (180 mg of eicosapentaenoic acid [EPA] and 120 mg of docosahexaenoic acid [DHA]) and placebo group consumed placebo capsules contained paraffin twice a day for 4 wk. Fasting blood samples and weight measurements were collected at the baseline and at the end of the trial. Plasma PPAR γ and thyroid hormones were measured by ELISA. Data were analyzed using a repeated measure model-two factor for comparing two groups in two times.

RESULTS

No significant changes were observed in PPAR γ levels between and within the groups after supplementation (P>0.05). N-3LC PUFA supplementation significantly increased T4 levels after 4 wk (P<0.05) but T3 and TSH did not change significantly.

CONCLUSION

Our study showed that n-3LC PUFAs supplementation increased T4 levels. However, no significant changes in T3, TSH and PPAR γ plasma levels were observed in obese adults.

Relationships between thyroid function and lipid status or insulin resistance in a pediatric population

BACKGROUND

In adults without thyroid disease, increasing levels of thyroid-stimulating hormone (TSH) within the range of that considered normal have been shown to be associated with increases in total cholesterol, low-density lipoprotein cholesterol, non-high-density lipoprotein cholesterol, and triglycerides, and with decreases in high-density lipoprotein cholesterol. Serum TSH has also been found to be positively associated with fasting and postload insulin concentrations and negatively associated with insulin sensitivity in euthyroid adults. We hypothesized that such relationships also exist in euthyroid children and adolescents.

METHODS

This was a retrospective record review of pediatric outpatients (ages 2-18 years) having measurements of TSH or free thyroxine (T4) and a concurrent lipid panel, fasting glucose, or fasting insulin. Pearson correlation coefficient was used to estimate the correlation between TSH or free T4 and logarithmic transformed lipid, plasma glucose, or insulin levels. Lipid levels, fasting plasma glucose, insulin, and homeostasis model assessment (HOMA) were also compared between subjects with TSH levels in the high normal range (2.5-5 mIU/L) and those with TSH in the low normal range (0.3-2.4 mIU/L).

RESULTS

TSH levels were positively correlated with triglyceride levels (r = 0.10, p = 0.001). Conversely, free T4 levels were inversely correlated with triglyceride levels (r = -0.10, p = 0.011). TSH levels were also positively correlated with fasting insulin (r = 0.26, p = 0.002) and with HOMA (r = 0.27, p = 0.001). These associations remained significant after adjustment for age, gender, and body mass index z-score. Children who had TSH levels between 2.5 and 5.0 mIU/L had higher triglycerides (p = 0.003), insulin levels (p = 0.040), and HOMA (p = 0.021) than those having TSH values between 0.3 and 2.4 mIU/L.

CONCLUSIONS

In euthyroid children without a history of hypo- or hyperthyroidism, increasing levels of TSH and decreasing levels of free T4 are associated with higher triglyceride levels and elevated markers of insulin resistance. Whether these findings carry implications regarding optimal TSH levels in children at increased risk for cardiovascular disease awaits further study.

Expression and modulation of TUB by insulin and thyroid hormone in primary rat and murine 3T3-L1 adipocytes

tub encodes a protein of poorly understood function, but one implicated strongly in the control of energy balance and insulin sensitivity. Whilst tub expression is particularly prominent in neurones it is also detectable in extraneuronal tissues. We show here, for the first time, expression of TUB protein in rat adipocytes and the murine adipocyte model 3T3-L1 and demonstrate that insulin induces its tyrosine phosphorylation and association with the insulin receptor. TUB expression is regulated developmentally during adipogenic differentiation of 3T3-L1 cells and in response to cell treatment with thyroid hormone or induction of insulin resistance. TUB was upregulated 5- to 10-fold in adipocytes from obese Zucker rats and 3T3-L1 adipocytes that had been rendered insulin resistant, a response that could be antagonised by rosiglitasone, an insulin-sensitising drug. Our data are consistent with a previously unforeseen role for TUB in insulin signalling and fuel homeostasis in adipocytes.

Unconventional secretion of tubby and tubby-like protein 1

Tubby-like proteins (Tulps) with no signal peptide have been characterized as cytoplasmic proteins with various intracellular functions, including binding to phosphatidylinositol-4,5-bisphosphate [PI(4,5)P(2)]. PI(4,5)P(2) has been implicated in unconventional secretion of fibroblast growth factor-2 without a signal peptide. Here, we show that all Tulps are expressed intracellularly and extracellularly. Tubby secretion is partially dependent on its PI(4,5)P(2)-binding activity with an essential secretory signal in the N-terminus. Pathogenic mutation in Tubby mice has no impact on tubby extracellular trafficking. Moreover, unconventional secretion of tubby and Tulp1 is independent of endoplasmic reticulum-Golgi pathway. These data implicate that Tulps may function extracellularly as well.

Microarray analysis of differentially expressed genes in the brains of tubby mice

The tubby mouse is characterized by progressive retinal and cochlear degeneration and late-onset obesity. These phenotypes are caused by a loss-of-function mutation in the tub gene and are shared with several human syndromes, suggesting the importance of tubby protein in central nervous system (CNS) functioning. Although evidence suggests that tubby may act as a transcription factor mediating G-protein coupled receptor (GPCR) signaling, any downstream gene regulated by tubby has yet to be identified. To explore potential target genes of tubby with region-specific transcription patterns in the brain, we performed a microarray analysis using the cerebral cortex and hypothalamus of tubby mice. We also validated the changes of gene expression level observed with the microarray analysis using real-time RT-PCR. We found that expression of erythroid differentiation factor 1 (Erdr1) and caspase 1 (Casp1) increased, while p21-activated kinase 1 (Pak1) and cholecystokinin 2 receptor (Cck2r) expression decreased in the cerebral cortex of tubby mice. In the hypothalamic region, Casp 1 was up-regulated and micro-crystallin (CRYM) was down-regulated. Based on the reported functions of the differentially expressed genes, these individual or grouped genes may account for the phenotype of tubby mice. We discussed how altered expression of genes in tubby mice might be understood as the underlying mechanism behind tubby phenotypes.

DISP3, a sterol-sensing domain-containing protein that links thyroid hormone action and cholesterol metabolism

In the body, the brain is the most cholesterol-rich organ. Despite this, remarkably little is known about the mechanisms in the brain that regulate cholesterol homeostasis. Due to the blood-brain barrier, plasma lipoproteins are unable to traverse, and instead cholesterol must be synthesized de novo from within the central nervous system. Thyroid hormone receptors, activated in response to thyroid hormone (T(3)), are known to modulate the level of serum cholesterol via complex regulatory pathways. By screening for T(3)-regulated genes we have identified Disp3, a sterol-sensing domain-containing protein that is related to the Dispatched family of proteins. Analysis by RT-PCR and immunohistochemistry demonstrated that DISP3 is predominately expressed in specific cell types of the brain, retina, and testis. Using the model of hyperthyroidism in vivo, we observed the modulation of Disp3 expression in the retina. Furthermore, in vitro analysis of Disp3 expression in cells treated with T(3) revealed both positive and negative regulation. DISP3 localizes within the endoplasmic reticulum and was further found to colocalize with cholesterol. Ectopic expression of DISP3 in fibroblasts resulted in elevated cholesterol levels combined with an altered cholesterol distribution. Given that DISP3 is highly expressed in Purkinje cells, hippocampal neurons, and retinal ganglion cells and that its overexpression results in increased cholesterol levels, it is tempting to postulate that DISP3 may contribute to cholesterol homeostasis in neural cell types. Taken together, we propose that DISP3 represents a new molecular link between thyroid hormone and cholesterol metabolism.

Thyroid hormone action in the adult brain: gene expression profiling of the effects of single and multiple doses of triiodo-L-thyronine in the rat striatum

Thyroid hormones have profound effects on mood and behavior, but the molecular basis of thyroid hormone action in the adult brain is relatively unknown. In particular, few thyroid hormone-dependent genes have been identified in the adult brain despite extensive work carried out on the developing brain. In this work we performed global analysis of gene expression in the adult rat striatum in search for genomic changes taking place after administration of T(3) to hypothyroid rats. The hormone was administered in two different schedules: 1) a single, large dose of 25 microg per 100 g body weight (SD) or 2) 1.5 microg per 100 g body weight once daily for 5 d (RD). Twenty-four hours after the single or last of multiple doses, gene expression in the striatum was analyzed using Codelink microarrays. SD caused up-regulation of 149 genes and down-regulation of 88 genes. RD caused up-regulation of 18 genes and down-regulation of one gene. The results were confirmed by hybridization to Affymetrix microarrays and by TaqMan PCR. Among the genes identified are genes involved in circadian regulation and the regulation of signaling pathways in the striatum. These results suggest that thyroid hormone is involved in regulation of striatal physiology at multiple control points. In addition, they may explain the beneficial effects of large doses of thyroid hormone in bipolar disorders.

Reduced activity without hyperphagia contributes to obesity in Tubby mutant mice

The Tub gene was originally identified as a spontaneous mutation in C57Bl/6J mice, and associated with adult-onset obesity (Tub MUT mice). Although the original Tub MUT mouse was identified over 15 years ago, there have been few reports on the animal's food intake, body fat percentage or energy expenditure. In this study, we report food intake, body weight from 5-20 weeks, body fat, body temperature and three different measures of physical activity behavior. Tub MUT mice display reduced food intake, uncharacteristic of many obese mouse models, and reduced voluntary wheel running with normal home cage ambulatory behavior. We conclude that motivation for food and exercise is an underlying defect in TUB MUT mice.

Influence of obesity and surgical weight loss on thyroid hormone levels

BACKGROUND

The pathophysiologic relationship between morbid obesity and thyroid hormones is not well understood. The goal of this study was to evaluate the influence of obesity and weight reduction after bariatric surgery on thyroid hormone levels.

METHODS

Patients who underwent gastric bypass or adjustable gastric banding at our institution, had no previous diagnosis of thyroid disorder, were not taking medication that could affect the thyroid function evaluation, and who were nonsmokers were included in this retrospective evaluation. The association between the thyroid-stimulating hormone (TSH) and free thyroxine (T(4)) levels and body mass index (BMI), and the influence of weight loss after bariatric surgery on these hormones were investigated at different points (preoperatively and 6 and 12 months after bariatric surgery).

RESULTS

A total of 86 patients met the study criteria. The TSH levels correlated positively with BMI (P <.001, r = .91) within the BMI range of 30-67 kg/m(2). The mean BMI change from 49 to 32 kg/m(2) after bariatric surgery was associated with a mean reduction in the TSH level from 4.5 to 1.9 microU/mL. Free T(4) showed no association with BMI and was not significantly influenced by weight loss. Before bariatric surgery, 10.5% of the subjects had laboratory values consistent with subclinical hypothyroidism. After bariatric surgery, 100% of these patients experienced significant weight reduction with simultaneous resolution of their subclinical hypothyroidism.

CONCLUSION

The results of our study have demonstrated a statistically significant positive association between serum TSH within the normal range and BMI. No association was found between BMI and free T(4) serum levels. The prevalence of subclinical hypothyroidism in study group was 10.5%. Weight loss after bariatric surgery improved or normalized thyroid hormone levels.

Lower serum free thyroxine levels are associated with metabolic syndrome in a Chinese population

Thyroid hormones play an important role in regulating energy homeostasis and lipid and glucose metabolism. This study assessed the relationship between free thyroxine and clinical features of metabolic syndrome (MS). A total of 4,938 Taiwanese subjects (2,891 men and 2,047 women with a mean age of 50.1+/-12.6 years) with normal serum free thyroxine levels were enrolled. A modified National Cholesterol Education Program definition of MS was adopted substituting body mass index (BMI) for waist circumference. Serum free thyroxine concentrations were determined by immunoassay. Overall, 14% of subjects had a high fasting glucose, 27% had high blood pressure, 14% had high serum total triglyceride, 8% had low high-density lipoprotein cholesterol, and 18% were obese. The serum free thyroxine concentrations showed a statistically significant correlation with triglyceride and body mass index, respectively (P<.01), but not with blood pressure, glucose level, or high-density lipoprotein cholesterol level. According to the presence of 0, 1, 2, and 3 or more features of MS, age and sex-adjusted means of serum free thyroxine were 17.8+/-3.7, 17.6+/-3.7, 17.5+/-3.7, and 17.1+/-3.3 pmol/L, respectively, with a modest, but statistically significant, decreasing trend (P<.05). When comparing subjects in the highest and lowest quartile of free thyroxine, the former group demonstrated a 2-fold decrease in the odds ratio for MS with 3 or more metabolic features. Low circulating free thyroxine levels, albeit normal, were associated with MS in a Chinese population. Further study is necessary to document the role of thyroid hormones in metabolic abnormalities of MS.

Catabolic action of insulin in rat arcuate nucleus is not enhanced by exogenous "tub" expression

The central nervous system (CNS) protein "tub" has been identified from the genetically obese "tubby" mouse. Although the native function of tub in situ is not understood, cell-based studies suggest that one of its roles may be as an intracellular signaling target for insulin. In normal animals, insulin acts at the hypothalamic arcuate nucleus (ARC) to regulate energy balance. Here we used a Herpes Simplex viral expression system to evaluate whether tub overexpression in the ARC of normal rats enhances this action of insulin. In chow-fed rats, tub overexpression had no effect on insulin action. In rats fed a high-fat diet snack in addition to chow, simulating the diet of Westernized societies, the body weight regulatory action of insulin was impaired, and tub overexpression further impaired insulin action. Thus an excess of tub at the ARC does not enhance the in vivo effectiveness of insulin and is not able to compensate for the "downstream" consequences of a high-fat diet to impair CNS body weight regulatory mechanisms.

Tubby proteins: the plot thickens

The tubby mouse, which shows late-onset obesity and neurosensory deficits, arises from a mutation in the Tub gene. Tub shares homology with the genes for tubby-like proteins Tulp1, Tulp2 and Tulp3. Ablation of Tub, Tulp1 or Tulp3 causes disease phenotypes that are indicative of their importance in nervous-system function and development. Despite this importance, the biochemical functions of tubby-like proteins are only now beginning to be understood. At present, data indicate that tubby-like proteins might function as heterotrimeric-G-protein-responsive intracellular signalling factors, although an array of data also implicates them in other processes.

The thyroid hormone receptor beta gene: structure and functions in the brain and sensory systems

Thyroid hormone profoundly influences the development of the vertebrate nervous system. The thyroid hormone receptor beta gene (Thrb) is a key mediator of many of these actions. The Thrb gene is complex, spanning up to 400 kb in mammals, and differentially expresses distinct receptor subtypes through independent tissue-specific promoters and alternative splicing. These receptors serve a range of functions in the brain as well as particularly sensitive functions in the auditory and visual sensory systems. The Thrb gene illustrates how versatility in neurodevelopmental control can be achieved at the receptor level.

SW. Thyroid dysfunction and their relation to cardiovascular risk factors such as lipid profile, hsCRP, and waist hip ratio in Korea

BACKGROUND

Thyroid abnormalities affect a considerable portion of the population, and overt hypothyroidism is associated with an elevated risk of cardiovascular disease and adverse changes in blood lipids. Subclinical hypothyroidism is also associated with an increase risk of cardiovascular disease. So, we undertook this study to investigate the prevalence of overt and subclinical thyroid disorders and their associations with cardiovascular risk factors.

METHODS

This study involved 66,260 subjects (43,588 men, 22,672 women; between 20-80 years of age, mean age 41.5 +/- 9.6). Serum free thyroxine (FT4), thyroid stimulating hormone (TSH), total cholesterol, low density lipoprotein cholesterol (LDL-C), and high density lipoprotein cholesterol (HDL-C) were measured by RIA using commercial kits. High sensitivity C-reactive protein (hsCRP) levels were determined by nephelometry.

RESULTS

The prevalences of overt thyrotoxicosis, subclinical thyrotoxicosis, overt hypothyroidism and subclinical hypothyroidism were 5/1000 (334 subjects), 6.4/1000 (426 subjects), 1.6/1000 (108 subjects), and 6.4/1000 (375 subjects). Mean plasma total cholesterol and LDL-C were elevated in overt hypothyroidism than in normal controls (202.1 mg/dL and 121.8 mg/dL versus 197.1 mg/dL and 120.1 mg/dL, respectively) (p < 0.05). In subclinical hypothyroidism, mean total cholesterol and LDL-C levels were also elevated (201.9 mg/dL and 123.7 mg/dL) (p = 0.015, p = 0.047). Waist-to-hip ratio (WHR) was lower in overt thyrotoxicosis and higher in hypothyroidism.

CONCLUSION

The prevalence of thyroid dysfunction in Korea is not significantly different from that reported by other countries. It was also age dependent and higher in women, but this elevation in women was lower than expected. Patients with hypothyroidism exhibited higher waist-to-hip ratios, an index of obesity. Patients with subclinical hypothyroidism exhibited elevated atherogenic parameters (Total cholesterol, LDL-C). Therefore screening and treatment for subclinical hypothyroidism may be warranted due to its adverse effects on lipid metabolism.

Microarray analysis of knockout mice identifies cyclin D2 as a possible mediator for the action of thyroid hormone during the postnatal development of the cerebellum

Thyroid hormone is a major regulator of postnatal brain development, but the precise molecular mechanisms underlying its action in this organ remain poorly understood. We used microarray analysis to identify new target genes in brain. Thyroid hormone treatment of hypothyroid Pax8(-/-) knockout mice, which lack thyroid follicular cells, had a very limited global effect on brain transcripts. This analysis mainly identified cyclin D2 as a new thyroid hormone target gene in the cerebellum of hypothyroid mice. Thyroid hormone receptor (TRalpha and/or TRbeta) knockout mice studies provided further genetic evidence that cyclin D2 is likely to mediate the antiapoptotic effect exerted by thyroid hormone on the cerebellum external granular layer neuroblasts but that this transcriptional activation is not directly exerted by the thyroid hormone receptors.

Neuropeptides, food intake and body weight regulation: a hypothalamic focus

Energy homeostasis is controlled by a complex neuroendocrine system consisting of peripheral signals like leptin and central signals, in particular, neuropeptides. Several neuropeptides with anorexigenic (POMC, CART, and CRH) as well as orexigenic (NPY, AgRP, and MCH) actions are involved in this complex (partly redundant) controlling system. Starvation as well as overfeeding lead to changes in expression levels of these neuropeptides, which act downstream of leptin, resulting in a physiological response. In this review the role of several anorexigenic and orexigenic (hypothalamic) neuropeptides on food intake and body weight regulation is summarized.

Thyroid hormones before and after weight loss in obesity

BACKGROUND

Little is known about changes in thyroid function in obese children. An influence of leptin on thyroid hormone synthesis has been proposed.

AIMS

To examine thyroid function and leptin concentrations in obese children.

METHODS

Triiodothyronine (T3), thyroxine (T4), thyroid stimulating hormone (TSH), and leptin were measured in 118 obese children (aged 4.5-16 years); thyroid function was also determined in 107 healthy children of normal weight. T3, T4, and TSH were analysed in 55 obese children who had achieved weight reduction and in 13 obese children who had not achieved weight reduction after one year based on normal energy diet.

RESULTS

TSH, T3, and T4 were significantly higher in obese children compared to those of normal weight. Twelve per cent of the obese children had TSH, 15% had T3, and 11% had T4 concentrations above the twofold standard deviation of normal weight children. The degree of overweight correlated with T3, T4, and TSH. Thyroid hormones did not correlate significantly with leptin. A reduction in overweight showed a significant decrease in T3, T4, and leptin serum concentrations, but there was no significant change in TSH.

CONCLUSION

Peripheral thyroid hormones (T3, T4) and TSH are moderately increased in obese children; weight reduction leads to a long term decrease in the peripheral thyroid hormones but not in TSH. There is no necessity to treat the increased serum TSH.

Structure and expression patterns of Drosophila TULP and TUSP, members of the tubby-like gene family

Tubby is a mouse gene that may provide a model for adult-onset obesity in humans. It is a member of a four gene family in mammals that collectively encode the Tubby-like proteins (TULPs), putative transcription factors which share similar 260 amino acid 'tubby domains' at their C-termini. The mammalian genome also encodes distant relatives of TULPs, which have been called TUSPs (tubby domain superfamily proteins). We have characterized the transcription unit of the single Drosophila TULP homolog, analyzed the expression pattern of the Drosophila TULP and TUSP genes, and determined the evolutionary relationships between the Drosophila proteins and members of the tubby domain superfamily in other organisms. Interestingly, like its mammalian homologs, Drosophila TULP is principally expressed in the embryonic central and peripheral nervous systems. This suggests that mammalian and Drosophila TULPs may possess some conserved functional properties in the nervous system. The Drosophila TUSP gene is also expressed in the central nervous system and olfactory organ but in few other peripheral sensory organs.

Neurodevelopmental control by thyroid hormone receptors

Recent studies have provided insights into the neurodevelopmental functions of thyroid hormone signaling. The nuclear thyroid hormone receptors (TRs) are ligand-activated transcription factors and a variety of TR isotypes, generated by two genes, mediate distinct processes. In addition, deiodinase enzymes that regulate levels of the main active form of thyroid hormone, T3, are likely to cooperate closely with TRs in specifying a localized and timely response to thyroid hormones in target tissues. Some of the most sensitive processes controlled by these pathways are in the auditory and visual sensory systems.

The tubby-like proteins, a family with roles in neuronal development and function

The identification of a mutation at the tubby (Tub) locus, which causes obesity and neurosensory degeneration, led to the discovery of the tubby-like proteins (TULPs). Tub and the genes that encode three tubby-like proteins (TULP1- TULP3) form a novel, small gene family that plays an important role in maintenance and function of neuronal cells during development and post-differentiation. Although exploration of the molecular function of these genes is still in its infancy, recent biochemical studies have provided ‘entry points’ into pathways whose elucidation will further our understanding of TULP action. In addition, mRNA expression and translocation of the TUB protein have been shown to be regulated by thyroid hormone and by G-protein-coupled receptor signaling, respectively. These latter findings may help to link the cellular function of TUB to known mechanisms for energy homeostasis.

Molecular cloning, expression and regulation of the avian tubby-like protein 1 (tulp1) gene

The tubby-like protein 1 (tulp1) gene is a member of the tubby multigene family which includes tub, tulp1, tulp2 and tulp3. Human and mouse tulp1 genes were cloned and mutations in tulp1 have been implicated in retinitis pigmentosa in man. Here we report on the cDNA cloning of the chicken tulp1 homologue and its protein product deduced from the nucleotide sequence. The chicken Tulp1 protein comprises 358 amino acids with a calculated molecular mass of 40 kDa. The overall structure of Tub and Tulp proteins, exemplified by the highly conserved C-terminal domain of 255 amino acids and the signature motif KLACE, is also preserved in chicken Tulp1. Phylogenetic analysis demonstrates that chicken tulp1 cDNA and protein are closely related to human and mouse tulp1. In addition, chicken tulp1 mRNA is abundantly expressed in retina similar to tulp1 expression in human and mouse. Two tulp1-specific transcripts of 2 and 3 kb in size were identified that showed differential regulation during embryonic and postnatal development. Finally, tulp1 mRNA was found to be expressed in chicken erythroid cells and upregulated by ligand-activated thyroid hormone receptor (TR alpha/c-erbA).