Thyroid-stimulating Hormone Β-subunit Research Articles

Food and temperature change photoperiodic responses in two vole species.

Seasonal timing of reproduction in voles is driven by photoperiod. We hypothesized that a negative energy balance can modify spring-programmed photoperiodic responses in the hypothalamus, controlling reproductive organ development. We manipulated energy balance by the 'work-for-food' protocol, in which voles were exposed to increasing levels of food scarcity at different ambient temperatures under long photoperiod. We found that in common voles (Microtus arvalis) and tundra voles (Microtus oeconomus), photoperiod-induced pars tuberalis thyroid-stimulating hormone β-subunit (Tshβ) expression is reduced to potentially inhibit gonadal development when food is scarce. Reduction in gonadal size is more pronounced in tundra voles, in which anterior hypothalamic Kiss1 is additionally downregulated, especially in males. Low temperature additionally leads to decreased hypothalamic Rfrp expression, which potentially may facilitate further suppression of gonadal growth. Shutting off the photoperiodic axis when food is scarce in spring may be an adaptive response to save energy, leading to delayed reproductive organ development until food resources are sufficient for reproduction, lactation and offspring survival. Defining the mechanisms through which metabolic cues modify photoperiodic responses will be important for a better understanding of how environmental cues impact reproduction.

Thyrotropin, Hyperthyroidism, and Bone Mass.

Thyrotropin (TSH), traditionally seen as a pituitary hormone that regulates thyroid glands, has additional roles in physiology including skeletal remodeling. Population-based observations in people with euthyroidism or subclinical hyperthyroidism indicated a negative association between bone mass and low-normal TSH. The findings of correlative studies were supported by small intervention trials using recombinant human TSH (rhTSH) injection, and genetic and case-based evidence. Genetically modified mouse models, which disrupt the reciprocal relationship between TSH and thyroid hormone, have allowed us to examine an independent role of TSH. Since the first description of osteoporotic phenotype in haploinsufficient Tshr +/- mice with normal thyroid hormone levels, the antiosteoclastic effect of TSH has been documented in both in vitro and in vivo studies. Further studies showed that increased osteoclastogenesis in Tshr-deficient mice was mediated by tumor necrosis factor α. Low TSH not only increased osteoclastogenesis, but also decreased osteoblastogenesis in bone marrow-derived primary osteoblast cultures. However, later in vivo studies using small and intermittent doses of rhTSH showed a proanabolic effect, which suggests that its action might be dose and frequency dependent. TSHR was shown to interact with insulin-like growth factor 1 receptor, and vascular endothelial growth factor and Wnt pathway might play a role in TSH's effect on osteoblasts. The expression and direct skeletal effect of a biologically active splice variant of the TSHβ subunit (TSHβv) in bone marrow-derived macrophage and other immune cells suggest a local skeletal effect of TSHR. Further studies of how locally secreted TSHβv and systemic TSHβ interact in skeletal remodeling through the endocrine, immune, and skeletal systems will help us better understand the hyperthyroidism-induced bone disease.

Expression of lysophosphatidic acid receptor 1 in the adult female mouse pituitary gland

Lysophosphatidic acid receptor 1 (LPA1) is a receptor of lysophosphatidic acid (LPA). The present study investigated Lpar1 mRNA expression in the mouse pituitary gland by RT-PCR, in situ hybridization, and immunohistochemistry. Lpar1 mRNA was abundantly expressed in the pituitary gland. In situ hybridization and immunohistochemistry revealed over 90 % of a common glycoprotein α-subunit, luteinizing hormone β-subunit, and thyroid-stimulating hormone β-subunit immunoreactive cells co-expressed Lpar1 mRNA in the anterior pituitary gland, but few growth hormone, adrenocorticotropic hormone, and prolactin cells co-expressed Lpar1. Furthermore, Lpar1 mRNA levels in the pituitary gland were increased after ovariectomy and decreased after E2 administration. These results demonstrate that LPA1-mediated signaling may play physiological roles in gonadotropes and thyrotropes in the mouse pituitary gland.

Identification of Novel Missense Mutations of the TSH-β Subunit Gene in Pediatric Patients with Congenital Central Hypothyroidism

Background: Congenital central hypothyroidism (CCH) is a rare autosomal recessive disease caused by mutations in the thyroid-stimulating hormone β subunit (TSHβ) gene. Since patients with CCH do not experience increased serum levels of TSH, the diagnosis is usually delayed, which leads to negative consequences in the neonatal TSH screening. Genetic diagnostic studies enable us to identify affected relatives at high risk for rapid diagnosis and treatment of the disorder. Objectives: This study aimed to investigate genetic variations in the TSHβ gene for the first time in Iranian patients with CCH. Methods: Seven children affected by congenital TSH-deficient hypothyroidism were investigated for mutations in TSHβ. Variable TSH levels in these patients ranged from low values for diagnosis to significant values, so central hypothyroidism was assumed due to mutations in the TSHβ gene. Results: We identified two novel heterozygous (F11Y and G106R) and one homozygous (T14A) missense mutations in the coding sequence of exons 2 and 3. One of the new heterozygous mutations (F11Y) and a homozygous (T14A) missense mutation were found in exon 2 of the TSHß-subunit gene. The novel mutation G106R in exon 3 was found in three pediatric patients with congenital hypothyroidism. c.40A>G (T14A, rs10776792) appears to be the most common genetic variation associated with TSH deficiency. The others were c.32T>A in exon 2 and c.316G>C in exon 3, which resulted in a change from phenylalanine to tyrosine (p.F11Y) and glycine to arginine (G106R), respectively. Conclusions: The identification of these mutations for the first time in Iranian patients suggests that CCH is more common than previously recognized, and the TSHβ gene may be the mutational hot spot.

The Human TSHβ Subunit Proteins and Their Binding Sites on the TSH Receptor Using Molecular Dynamics Simulation.

To gain further insight into the binding of the normal and variant human TSHβ subunits (TSHβ and TSHβv), we modeled the 2 monomeric proteins and studied their interaction with the TSH receptor ectodomain (TSHR-ECD) using molecular dynamics simulation Furthermore, analyzed their bioactivity in vitro using recombinant proteins to confirm that such binding was physiologically relevant. Examining the interaction of TSHβ and TSHβv with the TSHR-ECD model using molecular dynamic simulation revealed strong binding of these proteins to the receptor ECD. The specificity of TSHβ and TSHβv binding to the TSHR-ECD was examined by analyzing the hydrogen-bonding residues of these subunits to the FSH receptor ECD, indicating the inability of these molecules to bind to the FSH receptors. Furthermore, the modelling suggests that TSHβ and TSHβv proteins clasped the concave surface of the leucine rich region of the TSHR ECD in a similar way to the native TSH using dynamic hydrogen bonding. These mutually exclusive stable interactions between the subunits and ECD residues included some high-affinity contact sites corresponding to binding models of native TSH. Furthermore, we cloned TSHβ and TSHβv proteins using the entire coding ORF and purified the flag-tagged proteins. The expressed TSHβ subunit proteins retained bioactivity both in a coculture system as well as with immune-purified proteins. In summary, we showed that such interactions can result in a functional outcome and may exert physiological or pathophysiological effects in immune cells.

Thyroid stimulating hormone β-subunit splice variant is expressed in all fractional subsets of bone marrow hematopoietic cells and peripheral blood leukocytes and is modulated during bacterial infection

Thyroid stimulating hormone (TSH), a hormone produced in the anterior pituitary, is used to regulate thyroid hormone secretion. It has been known for over three decades that TSH is made by the cells of the immune system; however, the functional role of immune system TSH is unclear. We previously demonstrated that an alternatively-spliced isoform of TSHβ, referred to as the TSHβ splice variant (TSHβv), is the primary form of TSHβ made by hematopoietic cells in mice and humans. Most studies have linked TSHβv expression to myeloid cells of the immune system; however, it has recently been demonstrated that plasma cells in patients with Hashimoto’s thyroiditis may be a source of immune system TSHβv. Here, we demonstrate that TSHβv is expressed in bone marrow precursors of lymphoid cells, monocytes, and granulocytes, as well as in mesenteric lymph node (MLN) cells. Plasma cells generated by in vitro culture with bacterial lipopolysaccharide (LPS), and MLN cells from mice infected with L. monocytogenes expressed TSHβv. There was an increase in the intensity of intracellular TSHβv expression in MLN cells following exposure to LPS, and in the proportion of TSHβv+ CD138+ MLN cells following L. monocytogenes infection. The number of TSHβv+ cells increased in MLN cells, particularly among CD138+ cells, following bacterial infection. This was confirmed by an increase in gene expression of BLIMP-1, the transcription factor for CD138, following infection. Levels of circulating thyroxine dropped significantly in mice 24 hrs post-infection. These findings suggest that immune system TSHβv may contribute to the host immune response during bacterial infection.

Gonads or body? Differences in gonadal and somatic photoperiodic growth response in two vole species.

To optimally time reproduction, seasonal mammals use a photoperiodic neuroendocrine system (PNES) that measures photoperiod and subsequently drives reproduction. To adapt to late spring arrival at northern latitudes, a lower photoperiodic sensitivity and therefore a higher critical photoperiod for reproductive onset is necessary in northern species to arrest reproductive development until spring onset. Temperature-photoperiod relationships, and hence food availability-photoperiod relationships, are highly latitude dependent. Therefore, we predict PNES sensitivity characteristics to be latitude dependent. Here, we investigated photoperiodic responses at different times during development in northern (tundra or root vole, Microtus oeconomus) and southern vole species (common vole, Microtus arvalis) exposed to constant short (SP) or long photoperiod (LP). Although the tundra vole grows faster under LP, no photoperiodic effect on somatic growth is observed in the common vole. In contrast, gonadal growth is more sensitive to photoperiod in the common vole, suggesting that photoperiodic responses in somatic and gonadal growth can be plastic, and might be regulated through different mechanisms. In both species, thyroid-stimulating hormone β-subunit (Tshβ) and iodothyronine deiodinase2 (Dio2) expression is highly increased under LP, whereas Tshr and Dio3 decrease under LP. High Tshr levels in voles raised under SP may lead to increased sensitivity to increasing photoperiods later in life. The higher photoperiodic-induced Tshr response in tundra voles suggests that the northern vole species might be more sensitive to thyroid-stimulating hormone when raised under SP. In conclusion, species differences in developmental programming of the PNES, which is dependent on photoperiod early in development, may form different breeding strategies as part of latitudinal adaptation.

The Pathogenic TSH β-subunit Variant C105Vfs114X Causes a Modified Signaling Profile at TSHR.

(1) Background: Central congenital hypothyroidism (CCH) is a rare endocrine disorder that can be caused by mutations in the β-subunit of thyrotropin (TSHB). The TSHB mutation C105Vfs114X leads to isolated thyroid-stimulating-hormone-(TSH)-deficiency and results in a severe phenotype. The aim of this study was to gain more insight into the underlying molecular mechanism and the functional effects of this mutation based on two assumptions: a) the three-dimensional (3D) structure of TSH should be modified with the C105V substitution, and/or b) whether the C-terminal modifications lead to signaling differences. (2) Methods: wild-type (WT) and different mutants of hTSH were generated in human embryonic kidney 293 cells (HEK293 cells) and TSH preparations were used to stimulate thyrotropin receptor (TSHR) stably transfected into follicular thyroid cancer cells (FTC133-TSHR cells) and transiently transfected into HEK293 cells. Functional characterization was performed by determination of Gs, mitogen activated protein kinase (MAPK) and Gq/11 activation. (3) Results: The patient mutation C105Vfs114X and further designed TSH mutants diminished cyclic adenosine monophosphate (cAMP) signaling activity. Surprisingly, MAPK signaling for all mutants was comparable to WT, while none of the mutants induced PLC activation. (4) Conclusion: We characterized the patient mutation C105Vfs114X concerning different signaling pathways. We identified a strong decrease of cAMP signaling induction and speculate that this could, in combination with diverse signaling regarding the other pathways, accounting for the patient’s severe phenotype.

Transcriptional regulation of the chicken CRHR2 gene by pituitary transcription factors

Corticotropin-releasing hormone (CRH) is known to act as a potent thyrotropin-releasing factor in non-mammalian species such as chicken and bullfrog. This interaction is mediated by type 2 CRH receptors (CRHR2) expressed by the thyrotropes in the pituitary gland. However, the response elements (REs) and their corresponding transcription factors (TFs) that control CRHR2 expression in thyrotropes are not known. Since thyrotrope-specific expression of the β-subunit of thyrotropin is synergistically stimulated by the co-expression of POU1F1 and GATA2, we hypothesised that in non-mammalian vertebrates like chicken, CRHR2 expression is controlled by the same TFs and that their REs are present in the chicken CRHR2 gene promoter. In situ hybridisation and immunohistochemistry suggest that chicken thyrotropes, like those of mammals, express the mRNAs for the TFs GATA2, POU1F1 and PITX1, but not NR5A1. Using luciferase reporter assays, we show that both GATA2 and PITX1 can activate the promoter of CRHR2, but PITX1 requires a functional GATA2 RE to be present. POU1F1 alone did not affect promoter activity, but synergistically increased the effect of GATA2. Promoter deletion analysis and mutagenesis showed that essential GATA2 and PITX1 REs are located between 116 and 198 bp upstream of the start codon. These REs are highly conserved in non-mammalian species. Additionally, NR5A1 (steroidogenic factor 1) suppressed both GATA2- and PITX1-induced promoter activity and may therefore play a role in restricting CRHR2 expression in gonadotropes. We conclude that the expression of CRHR2 in chicken thyrotropes is stimulated by GATA2 with interactions with POU1F1 and PITX1, in the absence of NR5A1.

Functional divergence of thyrotropin beta-subunit paralogs gives new insights into salmon smoltification metamorphosis

Smoltification is a metamorphic event in salmon life history, which initiates downstream migration and pre-adapts juvenile salmon for seawater entry. While a number of reports concern thyroid hormones and smoltification, few and inconclusive studies have addressed the potential role of thyrotropin (TSH). TSH is composed of a α-subunit common to gonadotropins, and a β-subunit conferring hormone specificity. We report the presence and functional divergence of duplicated TSH β-subunit paralogs (tshβa and tshβb) in Atlantic salmon. Phylogeny and synteny analyses allowed us to infer that they originated from teleost-specific whole genome duplication. Expression profiles of both paralogs in the pituitary were measured by qPCR throughout smoltification in Atlantic salmon from the endangered Loire-Allier population raised in a conservation hatchery. This revealed a striking peak of tshβb expression in April, concomitant with downstream migration initiation, while tshβa expression remained relatively constant. In situ hybridization showed two distinct pituitary cell populations, tshβa cells in the anterior adenohypophysis, and tshβb cells near to the pituitary stalk, a location comparable to the pars tuberalis TSH cells involved in seasonal physiology and behaviour in birds and mammals. Functional divergence of tshβ paralogs in Atlantic salmon supports a specific role of tshβb in smoltification.

Effects of environmentally relevant concentrations of tris (2-butoxyethyl) phosphate on growth and transcription of genes involved in the GH/IGF and HPT axes in zebrafish (Danio rerio)

Tris (2-butoxyethyl) phosphate (TBOEP), as one of the most widely used organophosphate flame retardants (OPFRs), is applied in nearly all manufactured items and materials. It has been reported that TBOEP could cause developmental impairments and disrupt the endocrine regulation of fish growth during acute toxic experiments. However, concentrations to which fish were exposed in these studies were greater than environmentally relevant concentrations ever reported. This study examined effects on growth associated with exposure of zebrafish to 0, 0.1, 1 and 10 μg/L TBOEP during 20–90 days post fertilization (dpf). The changes in growth indicators and bioaccumulation of TBOEP were examined along with the transcription of related genes in the growth hormone/insulin-like growth factor (GH/IGF) axis and the hypothalamic-pituitary-thyroid (HPT) axis. The average body contents of TBOEP were higher in females than in males in all the exposure groups. Exposure to environmentally relevant concentrations of TBOEP significantly decreased body length and body mass and down-regulated expression of several genes involved in the GH/IGF and HPT axes. Exposure to TBOEP decreased plasma thyroxine (T4) content accompanied by decreased mRNA level of thyrotropin β-subunit (tshβ) in females at 60 dpf, but no effects were observed at 90 dpf. These results suggested that bioaccumulation of TBOEP and down-regulation of genes involved in the GH/IGF axis might be responsible for the observed growth inhibition in zebrafish exposed to TBOEP.

A mechanistic base for alternative splicing of human immune system-derived thyroid stimulating hormone (TSH) β-subunit.

Abstract Thyroid stimulating hormone (TSH) is a glycoprotein hormone consisting of an α and a β chain. Within the hypothalamus-pituitary-thyroid axis, TSH is produced by thyrotropic cells in the anterior pituitary. Upon release into the circulation, TSH binds to receptors in the thyroid, resulting in the release of triiodothyronine (T3) and thyroxine (T4). T3 and T4 regulate nearly every aspect of mammalian physiology, including basal metabolism, growth and development, mood, and cognition. Although TSHβ has been known for years to be produced by cells of the immune system, the functional significance of that has remained unclear. My laboratory identified a splice variant of human TSHβ (TSHβv) that consists of a truncated but biologically active portion of TSHβ made from exon 3 with the deletion of exon 2. The signal peptide of TSHβv is coded for by a portion of the 3′ end of intron 2. TSHβv is primarily produced by bone marrow cells and peripheral blood leukocytes, particularly though not exclusively by cells of the myeloid/monocyte lineage. An unresolved question pertains to the molecular mechanisms that account for TSHβv alternative splicing, Here, a model is presented whereby TSHβv is made through a series of unique genetic reorganization steps. These findings have implications not only for understanding how the TSHβv isoform is made, but also for gaining insights into the involvement of immune system TSHβ in health and disease.

Regulatory effects of immune system thyroid stimulating hormone β-subunit splice variant (TSHβv) on thyroid hormone secretion in mice.

Abstract It has been known for over three decades that thyroid stimulating hormone (TSH) is made by cells of the immune system, yet little is known about the biological significance of that. Studies in my laboratory identified a novel splice variant of the TSH β-subunit (TSHβv) that is produced by bone marrow (BM) hematopoietic cells and peripheral leukocytes in humans and mice. As shown here, recombinant mouse TSHβ (rTSHβ) binds in a dose-dependent manner to the TSH receptor (TSHR) on the mouse AM macrophage cell line, and circulating T4 levels are suppressed 38% in mice 24 hrs after injection of rTSHβv. Moreover, TSHβ-producing leukocytes traffic to the thyroid during systemic L. monocytogenes infection. TSHβv is suppressed in mouse macrophages following transfection with short-hairpin RNA TSHβv (shRNA-TSHβv) expression plasmids, and is suppressed in BM cells transduced with shRNA-TSHβv lentivirus pseudoparticles. These findings collectively suggest that binding of immune system TSHβv to the TSHR on thyroid follicular cells may serve to modulate thyroid hormone output, thus providing a novel mechanism for regulating host metabolism during times of immune stress. Experiments are underway in mice to understand the in vivo involvement of immune system TSHβv in healthy conditions, and during chronic inflammation such as in autoimmune thyroiditis.

Total chemical synthesis of human thyroid-stimulating hormone (hTSH) β-subunit: Application of arginine-tagged acetamidomethyl (AcmR) protecting groups

The β-subunit of human thyroid stimulating hormone (hTSH) has been synthesized as a single glycoform bearing a chitobiose disaccharide at the native glycosylation site. Key to the successful completion of this synthesis was the introduction of an arginine-tagged acetamidomethyl group, which served to greatly facilitate handling of a glycopeptide fragment with poor aqueous solubility. This general solution to the challenge of working with intractable peptides is expected to find wide use in protein synthesis.

Evolution of the POU1F1 transcription factor in mammals: Rapid change of the alternatively-spliced β-domain

The POU1F1 (Pit-1) transcription factor is important in regulating expression of growth hormone, prolactin and TSH β-subunit, and controlling development of the anterior pituitary cells in which these hormones are produced. POU1F1 is a conserved protein comprising three main domains, an N-terminal transcription activation domain (TAD), a POU-specific domain and a C-terminal homeodomain. Within the TAD, a β-domain can be inserted by alternative splicing, giving an extended ‘β-variant’ with altered properties. Here sequence data from over 100 species were used to assess the variability of POU1F1 in mammals. This showed that the POU-specific domain and homeodomain are very strongly conserved, and that the TAD is somewhat less conserved, as are linker and hinge regions between these main domains. On the other hand, the β-domain is very variable, apparently evolving at a rate not significantly different from that expected for unconstrained, neutral evolution. In several species stop and/or frameshift mutations within the β-domain would prevent expression of the β-variant as a functional protein. In most species expression of the β-variant is low (<5% of total POU1F1 expression). The rate of evolution of POU1F1 in mammals shows little variation, though the lineage leading to dog does show an episode of accelerated change. This comparative genomics study suggests that in most mammalian species POU1F1 variants produced by alternative splicing may have little physiological significance.

Expanding the Role of Thyroid-Stimulating Hormone in Skeletal Physiology.

The dogma that thyroid-stimulating hormone (TSH) solely regulates the production of thyroid hormone from the thyroid gland has hampered research on its wider physiological roles. The action of pituitary TSH on the skeleton has now been well described; in particular, its action on osteoblasts and osteoclasts. It has also been recently discovered that the bone marrow microenvironment acts as an endocrine circuit with bone marrow-resident macrophages capable of producing a novel TSH-β subunit variant (TSH-βv), which may modulate skeletal physiology. Interestingly, the production of this TSH-βv is positively regulated by T3 accentuating such modulation in the presence of thyroid overactivity. Furthermore, a number of small molecule ligands acting as TSH agonists, which allosterically modulate the TSH receptor have been identified and may have similar modulatory influences on bone cells suggesting therapeutic potential. This review summarizes our current understanding of the role of TSH, TSH-β, TSH-βv, and small molecule agonists in bone physiology.

Pituitary-thyroid axis development during the larval-juvenile transition in the pejerrey Odontesthes bonariensis.

The morphological development of the thyroid gland of pejerrey Odontesthes bonariensis during larval-juvenile transition was studied and related to whole-body concentrations of thyroxine (T4 ) and tri-iodothyronine (T3 ). A complementary (c)DNA fragment of the thyroid-stimulating hormone β-subunit (tshb) was sequenced and transcript levels quantified during this period. Follicles with eosinophilic and T4 -immunoreactive colloids were detected at hatching together with tshb transcript levels and whole-body concentrations of T4 and T3 hormones. Thyroid follicles were located in the subpharyngeal region associated with the ventral aorta below the hyoid bone. Follicle structure switched from the rounded form at hatching to oval in juveniles. Significant increase of follicle number per larva, mean colloidal area and total colloidal area was observed throughout development with maximum values at the end of the larval-juvenile transition. A significant decrease of tshb expression together with a significant increase in T4 and T3 whole-body concentrations was observed prior to achieving the juvenile phenotype. These results are in accordance with a negative feedback regulation of tshb expression by thyroid hormones and a possible association between thyroid hormone levels and the acceleration of metabolic processes necessary to complete metamorphosis.

Semicarbazide-induced thyroid disruption in Japanese flounder (Paralichthys olivaceus) and its potential mechanisms

Semicarbazide (SMC) is a carcinogenic and genotoxic substance that has been found in aquatic systems. SMC may also cause thyroid follicular epithelial cell injury in rats, but the thyroid-disrupting properties of SMC and its potential mechanisms remain unclear. In this study, we exposed fertilized eggs of Japanese flounder (Paralichthys olivaceus) to 1, 10, 100, and 1000μg/L SMC for 55 d to assess the impact of SMC exposure on the thyroid system. The number of larvae in each metamorphic stage was counted, the concentrations of whole-body thyroid hormones (THs) 3,5,3′-triiodothyronine (T3) and thyroxine (T4) were measured, and the transcription levels of genes involved in the hypothalamic-pituitary-thyroid (HPT) axis and gamma-aminobutyric acid (GABA) synthesis were quantified. The results showed that 10μg/L SMC significantly increased whole-body T3 levels, and 100 and 1000μg/L SMC markedly enhanced whole-body T4 and T3 levels. Furthermore, 100μg/L SMC exposure shortened the time it took for flounder larvae to complete metamorphosis by 2 d as compared to the control group. Thus, this study demonstrated that SMC exerted thyroid-disrupting effects on Japanese flounder. SMC-mediated stimulation of TH levels was primarily related to transcriptional alterations of pituitary-derived thyroid stimulating hormone β-subunit (tshβ) and hepatic deiodinase (id). In the 10 and 100μg/L SMC exposure groups, the increased TH levels may have resulted from inhibition of TH metabolism caused by down-regulation of id3 mRNA expression, while at 1000μg/L SMC-exposed group, up-regulation of tshβ and id1 transcripts was expected to enhance the synthesis of T4 and the conversion of T4 to T3 and, consequently, result in higher T4 and T3 levels. In addition, 1000μg/L SMC-induced down-regulation in glutamic acid decarboxylase gad65 and gad67 transcription may have also contributed to the increased TH levels. The thyroid-disrupting effects of 10 and 100μg/L SMC indicated that environmentally relevant concentrations of SMC posed potential environmental risks to aquatic organisms. Overall, our results demonstrated for the first time that SMC exhibited thyroid-disrupting properties by affecting the HPT axis and GABA synthesis, providing theoretical support for environmental risk assessment.

Cinnamon intake reduces serum T3 level and modulates tissue-specific expression of thyroid hormone receptor and target genes in rats.

Cinnamon has several effects on energy metabolism. However, no data exist on the impact of cinnamon intake on thyroid hormone serum concentrations and action, since thyroid hormones (THs) play a major role in metabolism. Male rats were treated with cinnamon water extract (400 mg kg(-1) body weight, 25 days). Cinnamon supplementation resulted in a lower serum total T3 level accompanied by normal serum T4 and TSH levels. The cinnamon-treated rats did not exhibit significant differences in TSHβ subunit, TRβ or deiodinase type 2 mRNA expression in the pituitary. In the liver, cinnamon did not change the TRβ protein expression or the deiodinase type 1 mRNA expression, suggesting that there were no changes in T3 signaling or metabolism in this organ. However, mitochondrial GPDH, a target gene for T3 in the liver, exhibited no changes in mRNA expression, although its activity level was reduced by cinnamon. In the cardiac ventricle, T3 action was markedly reduced by cinnamon, as demonstrated by the lower TRα mRNA and protein levels, reduced SERCA2a and RyR2 and increased phospholamban mRNA expression. This study has revealed that TH action is a novel target of cinnamon, demonstrating impairment of T3 signaling in the cardiac ventricles. © 2015 Society of Chemical Industry.

Ontogeny of the Saccus Vasculosus, a Seasonal Sensor in Fish.

TSH secreted from the pars distalis (PD) of the pituitary gland stimulates the thyroid gland. In contrast, TSH secreted from the pars tuberalis (PT) of the pituitary gland regulates seasonal reproduction. The ontogeny of thyrotrophs and the regulatory mechanisms of TSH are apparently different between the PD and the PT. Interestingly, fish do not have an anatomically distinct PT, and the saccus vasculosus (SV) of fish is suggested to act as a seasonal sensor. Thus, it is possible that the SV is analogous to the PT. Here we examined the ontogeny of the pituitary gland and SV using rainbow trout. A histological analysis demonstrated the development of the pituitary anlage followed by that of the SV. Lhx3 and Pit-1, which are required for the development of PD thyrotrophs, clearly labeled the pituitary anlage. The common glycoprotein α-subunit (CGA) and TSH β-subunit (TSHB) genes were also detected in the pituitary anlage. In contrast, none of these genes were detected in the SV anlage. We then performed a microarray analysis and identified parvalbumin (Pvalb) as a marker for SV development. Because Pvalb expression was not detected in the pituitary anlage, no relationship was observed between the development of the SV and the pituitary gland. In contrast to embryos, Lhx3, Pit-1, CGA, and TSHB were all expressed in the adult SV. These results suggest that the morphological differentiation of SV occurs during the embryonic stage but that the functional differentiation into a seasonal sensor occurs in a later developmental stage.