The Circadian Clock Is Sustained in the Thyroid Gland of VIP Receptor 2 Deficient Mice.

VIP/VPAC2-receptor signaling is crucial for functioning of the circadian clock in the suprachiasmatic nucleus (SCN) since the lack results in disrupted synchrony between SCN cells and altered locomotor activity, body temperature, hormone secretion and heart rhythm. Endocrine glands, including the thyroid, show daily oscillations in clock gene expression and hormone secretion, and SCN projections target neurosecretory hypothalamic thyroid-stimulating hormone (TSH)-releasing hormone cells. The aim of the study was to gain knowledge of mechanisms important for regulation of the thyroid clock by evaluating the impact of VIP/VPAC2-receptor signaling. Quantifications of mRNAs of three clock genes (Per1, Per2 and Bmal1) in thyroids of wild type (WT) and VPAC2-receptor deficient mice were done by qPCR. Tissues were taken every 4th h during 24-h 12:12 light-dark (LD) and constant darkness (DD) periods, both genders were used. PER1 immunoreactivity was visualized on sections of both WT and VPAC2 lacking mice during a LD cycle. Finally, TSH and the thyroid hormone T4 levels were measured in the sera by commercial ELISAs. During LD, rhythmic expression of all three mRNA was found in both the WT and knockout animals. In VPAC2-receptor knockout animals, the amplitudes were approximately halved compared to the ones in the WT mice. In the WT, Per1 mRNA peaked around "sunset", Per2 mRNA followed with approximately 2 h, while Bmal1 mRNA was in antiphase with Per1. In the VPAC2 knockout mice, the phases of the mRNAs were advanced approximately 5 h compared to the WT. During DD, the phases of all the mRNAs were identical to the ones found during LD in both groups of mice. PER1 immunoreactivity was delayed compared to its mRNA and peaked during the night in follicular cells of both the thyroid and parathyroid glands in the WT animals. In WT animals, TSH was high around the transition to darkness compared to light-on, while T4 did not change during the 24 h cycle. In conclusion, sustained and identical rhythms (phases and amplitudes) of three clock genes were found in VPAC2 deficient mice during LD and DD suggesting high degree of independence of the thyroid clock from the master SCN clock.

Central Congenital Hypothyroidism Caused by a Novel Mutation, C47W, in the Cysteine Knot Region of TSHß.

BACKGROUND: Isolated central congenital hypothyroidism (ICCH) is a rare form (1:50,000 newborns) of congenital hypothyroidism, which can present with growth and neuropsychological retardation. Unlike the more common primary CH (1:1,500-1:4,000), which presents on newborn screening with elevated serum thyroid-stimulating hormone (TSH) and low thyroxine (T4) and triiodothyronine (T3), ICCH presents with low TSH and low thyroid hormone levels. ICCH, therefore, may be missed in most newborn screens that are based only on elevated TSH. Most cases of ICCH have been associated with mutations in the TSHß gene. PATIENT: We present a consanguineous Sudanese family where the proband was diagnosed with "atypical" CH (serum TSH was low, not high). INTERVENTION AND OUTCOME: The propositus underwent whole-exome sequencing, and the C47W TSHß mutation was identified. Sanger sequencing confirmed the proband to be homozygous for C47W, and both parents were heterozygous for the same mutation. The mutation was predicted by several in silico methods to have a deleterious effect (SIFT 0.0, Damaging; Polyphen2_HDIV 0.973, probably damaging; MutationTaster 1, disease causing; and CADD 3.17, 16.62). C47W affects the first cysteine of the cysteine knot of the TSHß subunit. The cysteine knot region of TSHß is highly conserved across species and is critical for binding to the TSH receptor. Only two other mutations were previously reported along the cysteine knot and showed consistently low or undetectable serum TSH and low T4 and T3 levels. Other TSHß gene mutations causing ICCH have been reported in the "seatbelt" region, necessary for TSHß dimerization with the alpha subunit. CONCLUSIONS: Identification of a mutation in the TSHß gene reinforces the importance of identifying ICCH that can occur in the absence of elevated serum TSH and demonstrates the functional significance of the TSHß cysteine knot.

Functional human TSHß splice variant produced by plasma cell may be involved in the immunologic injury of thyroid in the patient with Hashimoto's thyroiditis.

Hashimoto's Thyroiditis (HT) is the most common cause of hypothyroidism in areas of the world where iodine levels are sufficient. However, the pathogenesis of HT has not been completely elucidated. The first functional human TSHß splice variant was supposed to be involved in the pathology of Hashimoto's thyroiditis. The question remains as to which kind of intrathyroid cells expresses functional TSHß splice variant and whether there are expression variations of functional TSHß splice variant in the injured thyroid of patient with HT. For the answer to this question, immune-injured thyroids were obtained from 30 patients with HT. Localization study of functional TSHß splice variant in injured thyroid was done by immunofluorescence double staining. Transcription and translation level of functional TSHß splice variant were detected by using qRT-PCR and semi-quantitative immunohistochemistry method, respectively. The correlation between expression level of functional TSHß splice variant and degree of thyroid follicles damage was assessed. It was firstly identified that functional TSHß splice variant was predominately expressed by plasma cells infiltrated around follicles and germinal center in injured thyroid of patient with HT. Of particular interest, the TSHß splice variant was expressed at significantly higher levels in the thyroid tissues of patients with HT than that in the normal thyroid tissues, furthermore, expression level of TSHß splice variant was positive related with the degree of follicles damage in thyroid of patient with HT. These findings defined the immune-derived functional TSHß splice variant that resided in the thyroid of patient with HT, which exerted the unique effects on the pathogenesis of HT, meanwhile, we considered these findings to have significant implications for understanding immune-endocrine interactions in a number of ways.

Age- and gender-specific TSH reference intervals in people with no obvious thyroid disease in Tayside, Scotland: the Thyroid Epidemiology, Audit, and Research Study (TEARS).

OBJECTIVE: The aim of the study was to examine the association of tested TSH with age, gender, and diabetes in a large population-based cohort without evidence of thyroid disease. DESIGN: Record-linkage technology was used retrospectively to identify people without evidence of thyroid disease in the general population of Tayside, Scotland, from July 1, 2003, to December 31, 2009. COHORT: All Tayside residents who had thyroid function tests performed were identified. Using a unique patient identifier, data linkage enabled a cohort without thyroid disease to be identified by excluding anyone with thyroid or antithyroid prescription, thyroid-related admission or surgery, treatment with radioactive iodine and/or positive thyroid antibodies. Cases below 18 years of age were also excluded. OUTCOME MEASURES: We measured TSH distribution among different age groups and by gender. RESULTS: We identified the latest TSH measurements in 153127 people from the reference population after applying the exclusion criteria. There was a significant increase in median TSH (1.58 mU/L at 31-40 y to 1.86 mU/L at >90 y; P < .001) and 97.5th centile TSH (3.98 to 5.94 mU/L, respectively) with increasing age. The 2.5th centile decreased with age (0.51 to 0.31 mU/L). Patients with diabetes had marginally higher TSH concentration (1.80 vs 1.70 mU/L; P < .001). CONCLUSION: The use of these age-specific reference intervals for TSH, especially in those over 70 years old, would result in the reclassification of many TSH results from "abnormal" to "normal" (within the 95th centile reference interval) and avoid unnecessary treatment.

A newly identified TSHß splice variant is involved in the pathology of Hashimoto's thyroiditis.

Thyrotropin (TSH) is a protein that plays a key role in the control of thyroid function. TSH consists of a common α-subunit and a unique ß-subunit; the latter is responsible for hormone specificity. A novel splice variant of human TSHß was identified in 2009. To date, only the tissue distribution of the human TSHß splice variant mRNA has been studied. Therefore, we aimed to characterize the protein translated from this splice variant. Salting-out, dialysis and concentration of serum proteins were followed by immunoprecipitation to identify the hTSHß splice variant in serum. Stable CHO cell lines expressing the hTSHß splice variant and V5-hTSHα were generated. After co-culture, co-immunoprecipitation was used to determine if the hTSHß splice variant can dimerise with TSHα. We showed for the first time that the hTSHß splice variant exists in human serum and dimerises with TSHα. To explore the relationship between the TSHß splice variant and the pathogenesis of autoimmune thyroiditis, we assessed variations in the mRNA expression of the TSHß splice variant in the peripheral blood leukocytes (PBLs) of Hashimoto's thyroiditis (HT) patients using quantitative RT-PCR. We found that the mRNA expression levels of the TSHß splice variant were higher in the PBLs of HT patients who were not undergoing prednisone therapy (n = 10, P < 0.0001) and in the PBLs of HT patients with a longer duration of illness (>18 months) who were undergoing prednisone therapy (n = 5, P = 0.023) than in those of the control group. This pattern was reversed in the PBLs of HT patients with a shorter duration of illness (<9 months) who were undergoing prednisone therapy (n = 8, P < 0.0001). Dexamethasone inhibition of the TSHß splice variant mRNA expression occurred in a dose- and time-dependent manner. These results demonstrated that the TSHß splice variant may participate in the pathogenesis of HT.

NR4A1 (Nur77) mediates thyrotropin-releasing hormone-induced stimulation of transcription of the thyrotropin ß gene: analysis of TRH knockout mice.

Thyrotropin-releasing hormone (TRH) is a major stimulator of thyrotropin-stimulating hormone (TSH) synthesis in the anterior pituitary, though precisely how TRH stimulates the TSHß gene remains unclear. Analysis of TRH-deficient mice differing in thyroid hormone status demonstrated that TRH was critical for the basal activity and responsiveness to thyroid hormone of the TSHß gene. cDNA microarray and K-means cluster analyses with pituitaries from wild-type mice, TRH-deficient mice and TRH-deficient mice with thyroid hormone replacement revealed that the largest and most consistent decrease in expression in the absence of TRH and on supplementation with thyroid hormone was shown by the TSHß gene, and the NR4A1 gene belonged to the same cluster as and showed a similar expression profile to the TSHß gene. Immunohistochemical analysis demonstrated that NR4A1 was expressed not only in ACTH- and FSH- producing cells but also in thyrotrophs and the expression was remarkably reduced in TRH-deficient pituitary. Furthermore, experiments in vitro demonstrated that incubation with TRH in GH4C1 cells increased the endogenous NR4A1 mRNA level by approximately 50-fold within one hour, and this stimulation was inhibited by inhibitors for PKC and ERK1/2. Western blot analysis confirmed that TRH increased NR4A1 expression within 2 h. A series of deletions of the promoter demonstrated that the region between bp -138 and +37 of the TSHß gene was responsible for the TRH-induced stimulation, and Chip analysis revealed that NR4A1 was recruited to this region. Conversely, knockdown of NR4A1 by siRNA led to a significant reduction in TRH-induced TSHß promoter activity. Furthermore, TRH stimulated NR4A1 promoter activity through the TRH receptor. These findings demonstrated that 1) TRH is a highly specific regulator of the TSHß gene, and 2) TRH mediated induction of the TSHß gene, at least in part by sequential stimulation of the NR4A1-TSHß genes through a PKC and ERK1/2 pathway.

Conversion of TSH heterodimer to a single polypeptide chain increases bioactivity and longevity.

TSH is a dimeric glycoprotein hormone composed of a common α-subunit noncovalently linked to a hormone-specific ß-subunit. Previously, the TSH heterodimer was successfully converted to an active single-chain hormone by genetically fusing α and ß genes with [TSHß- carboxyl-terminal peptide (CTP)-α] or without (TSHß-α) the CTP of human chorionic gonadotropin ß-subunit as a linker. In the present study, TSH variants were expressed in Chinese hamster ovarian cells. The results indicated that TSHß-α single chain has the highest binding affinity to TSH receptor and the highest in vitro bioactivity. With regard to the in vivo bioactivity, all TSH variants increased the levels of T(4) in circulation after 2 and 4 h of treatment. However, the level of T(4) after treatment with TSH-wild type was significantly decreased after 6 and 8 h, compared with the levels after treatment with the other TSH variants. TSHß-α and TSHß-CTP-α single chains exhibited almost the same bioactivity after 8 h of treatment. Evaluating the half-life of TSH variants, TSHß-CTP-α single chain revealed the longest half-life in circulation, whereas TSH-wild type exhibited the shortest serum half-life. These findings indicate that TSH single-chain variants with or without CTP as a linker may display conformational structures that increase binding affinity and serum half-life, thereby, suggesting novel attitudes for engineering and constructing superagonists of TSH, which may be used for treating different conditions of defected thyroid gland activity. Other prominent potential clinical use of these variants is in a diagnostic test for metastasis and recurrence of thyroid cancer.

The natural history of the normal/mild elevated TSH serum levels in children and adolescents with Hashimoto's thyroiditis and isolated hyperthyrotropinaemia: a 3-year follow-up.

OBJECTIVE: The natural history of Hashimoto's thyroiditis (HT) and isolated hyperthyrotropinaemia (IH) is not well defined. We therefore studied the natural course of patients with HT and IH and looked for possible prognostic factors. DESIGN: This is retrospective cross-sectional study. PATIENTS: Three hundred and twenty-three patients with HT (88 boys and 235 girls) and 59 with IH (30 boys and 29 girls), mean age 9·9 ± 3·8 years were included in the study. When first examined, 236 of the children with HT had a normal TSH (G0) and in 87, it was elevated but <100% of the upper limit (G1). All IH subjects had elevated TSH. Potential risk factors for thyroid failure were evaluated after 3 years and included the presence or familiarity for endocrine/autoimmune diseases, premature birth, signs and symptoms of hypothyroidism, TSH levels, antithyroid antibodies and thyroid volume. RESULTS: HT: Of those with HT, 170 G0 patients remained stable, 31 moved to G1 and 35 to G2 (hypothyroidism). Thirty-six G1 children moved to G0, 17 remained stable and 34 moved to G2. Of patients with IH: 23 normalized, 28 remained stable and eight became overtly hypothyroid. In patients with HT, the presence of coeliac disease, elevated TSH and thyroid peroxidase antibodies (TPOAb) increased the risk of developing hypothyroidism by 4·0-, 3·4- and 3·5-fold, respectively. The increase in TSH levels during follow-up was strongly predictive of the development of hypothyroidism. In patients with IH, no predictive factor could be identified. CONCLUSIONS: Coeliac disease, elevated TSH and TPOAb at presentation and a progressive increase in TSH are predictive factors for thyroid failure in HT patients.

A rexinoid antagonist increases the hypothalamic-pituitary-thyroid set point in mice and thyrotrope cells.

Retinoid X receptor (RXR) signaling influences thyrotrope function. Synthetic RXR agonists, rexinoids, can cause central hypothyroidism. To test the hypothesis that endogenous rexinoids contribute to the TSH 'set point', TαT1 mouse thyrotrope cells were treated with a rexinoid antagonist, LG101208. Increasing concentrations of LG101208 significantly increased TSHß mRNA levels, indicating that the rexinoid antagonist may interfere with RXR-signaling by an endogenous rexinoid in thyrotropes. When the same experiments were repeated in the presence of charcoal-stripped serum the effect of the rexinoid antagonist was lost. Pretreatment with the transcription inhibitor DRB blocked the increase of TSHß mRNA levels by rexinoid antagonist, indicating the primary effect is at the level of gene transcription. Mice treated with LG101208 had higher levels of serum T4, T4/TSH ratios as well as pituitary α-subunit and TSHß mRNA compared with vehicle treated mice. Hypothalamic TRH levels were unchanged. In summary, the rexinoid antagonist, LG101208, increases TSH subunit mRNA levels in thyrotrope cells and mouse pituitaries, primarily at the level of gene transcription. These data suggest that an "endogenous rexinoid" contributes to the TSH 'set point' in thyrotropes.

Rescue from dwarfism by thyroid function compensation in rdw rats.

The rdw rat was initially reported as having hereditary dwarfism caused by pituitary dysfunction. Subsequent studies on the rdw rat, however, have demonstrated that the primary cause of rdw dwarfism is present in the thyroid gland but not in the pituitary gland. The primary cause of rdw rat disorders is a missense mutation of the thyroglobulin (Tg) gene by a one-point mutation. In the present study, we attempted to rescue the dwarfism of the rdw rats using a diet supplemented with thyroid powder (T-powder) and a thyroid graft (T-graft). The infants of the rdw rat were successfully raised to a mature stage body weight, accompanied by elevation of serum growth hormone (GH) and prolactin (PRL), by the T-powder. Furthermore, the T-graft successfully increased the body weight with fertility. The serum GH and PRL levels in the T-graft rdw rat significantly increased. The serum thyroid-stimulating hormone (TSH) levels in the T-graft rdw rat were significantly decreased but were significantly higher than those in the control rat. The GH and PRL mRNA expression in the rdw rat with the T-graft was virtually the same as that of the control, but the TSH beta mRNA differed from that of the control rats. Thus, the dwarfism in the rdw rat is rescued by thyroid function compensation, such as that afforded by T-powder and T-graft.

Novel TSHbeta subunit gene mutation causing congenital central hypothyroidism in a newborn male.

Newborn screening programs that use only high TSH levels as a marker for hypothyroidism may overlook neonates with congenital hypothyroidism (CH) due to TSH deficiency. We sought the cause of TSH deficiency in a neonate with low levels of thyroxine and TSH. The coding region of the TSHbeta gene was amplified and its sequence examined for mutations. Two mutations in exon 3 were identified: 1) a nucleotide deletion of T410 in codon 105 resulting in a frameshift in one allele, and 2) a previously unreported nucleotide deletion of T266 in codon 57, causing a frameshift and a premature stop at codon 62 in the other allele. We describe a compound heterozygous patient with TSHbeta mutations at codons 57 and 105 that interfered with a critical disulfide bond in the TSH molecule and caused CH. State screening programs that measure both T4 and TSH levels have the potential to detect newborns with congenital central hypothyroidism.

Modulation by steroid receptor coactivator-1 of target-tissue responsiveness in resistance to thyroid hormone.

Mutations in the thyroid hormone receptor-beta gene (TR beta) cause resistance to thyroid hormone. How the action of mutant thyroid hormone nuclear receptors (TRs) is regulated in vivo is not clear. We examined the effect of a TR coactivator, steroid receptor coactivator-1 (SRC-1), on target-tissue responsiveness by using a mouse model of resistance to thyroid hormone, TR beta PV knockin mice, in the SRC-1 null background. Lack of SRC-1 intensified the dysfunction of the pituitary-thyroid axis and impaired growth in TR beta(PV/+) mice but not in TR beta(PV/PV) mice. In TR beta(PV/PV) mice, however, lack of SRC-1 intensified the pathological progression of thyroid follicular cells to papillary hyperplasia, reminiscent of papillary neoplasia. In contrast, lack of SRC-1 did not affect responsiveness in the liver in regulating serum cholesterol in either TR beta(PV/+) or TR beta(PV/PV) mice. Lack of SRC-1 led to changes in the abnormal expression patterns of several T(3) target genes in the pituitary and liver. Thus, the present studies show that a coactivator such as SRC-1 could modulate the in vivo action of TR beta mutants in a tissue-dependent manner.