TSH Receptor mRNA Research Articles

Expression of thyrotropin receptors in rat thymus

Thymic hyperplasia is associated with Graves' disease. It has been demonstrated that thyrotropin receptors are expressed in human thymus, and thymic thyrotropin receptors are suggested to be involved in the pathophysiology of Graves' dIsease. We have studied whether thyrotropin receptors are expressed in rat thymic tissue. Thyrotropin receptor mRNA was demonstrated in 5-day-old, 10-day-old, 20-day-old and adult rat thymus by reverse transcription polymerase chain reaction. Thyrotropin receptor mRNA was also demonstrated in cultured rat thymic epithelial cells. Thyrotropin stimulated cyclic AMP production in cultured rat thymic epithelial cells, suggesting the expression of functional thyrotropin receptors. The present results indicate that thyrotropin receptors are expressed in rat thymus.

Extrathyroidal manifestations of Graves' disease: the thyrotropin receptor is expressed in extraocular, but not cardiac, muscle tissues.

The existence of an autoantigen common to Graves' disease and its associated extrathyroidal manifestations has been proposed. As the TSH receptor (TSHR) is the primary target for autoimmunity against the thyroid in Graves' disease, much effort has gone into investigating the role of TSHR messenger ribonucleic acid (mRNA) transcripts in extrathyroidal tissue, particularly in the orbit. A high stringency RT-PCR technique had previously been employed by our laboratory to demonstrate the presence of full-length and splice variant TSHR mRNA in extraocular muscle (EOM). This technique demonstrated selective amplification of TSHR mRNA transcripts in thyroid and EOM, but not in abdominal muscle, kidney, or brain tissue. We used this technique in the present study to investigate the reported presence of TSHR mRNA transcripts in cardiac tissue. After removal of all visible fat from muscle tissues, high stringency RT-PCR was performed, and we found no TSHR transcripts in the muscle of any chamber of the normal human heart. In addition, in situ hybridization on fresh-frozen and paraffin-embedded sections confirmed the presence of TSHR transcripts in thyroid and EOM, but not in abdominal or cardiac muscle. These findings support the hypothesis that the TSHR is a shared antigen in the thyroid and EOM, but not in cardiac muscle.

Thyrotropin Receptors in Brown Adipose Tissue: Thyrotropin Stimulates Type II Iodothyronine Deiodinase and Uncoupling Protein-1 in Brown Adipocytes

It has been demonstrated that TSH receptors are expressed not only in thyroid gland but also in extrathyroidal tissues. Brown adipose tissue of guinea pig has been reported to express TSH receptor messenger RNA (mRNA), but the physiological roles of TSH receptors in brown adipose tissue have not been understood. We studied the expression and function of TSH receptors in rat brown adipose tissue and cultured rat brown adipocytes. Northern analysis demonstrated the expression of TSH receptor mRNA in rat brown adipose tissue and cultured rat brown adipocytes. TSH receptor mRNA in rat brown adipose tissue was decreased by cold exposure of the rat, and its mRNA in cultured rat brown adipocytes was also decreased by incubation with TSH or (Bu)2cAMP. TSH increased the intracellular cAMP concentration in cultured rat brown adipocytes in a dosedependent manner. Type II iodothyronine deiodinase mRNA, its activity, and uncoupling protein-1 mRNA in cultured rat brown adipocytes were significantly increased by incubation with TSH in a dose-dependent manner. These results suggest the expression of functional TSH receptors in brown adipose tissue, which may be involved in regulation of the expression of type II iodothyronine deiodinase and uncoupling protein-1.

Thyrotropin receptors in brown adipose tissue: thyrotropin stimulates type II iodothyronine deiodinase and uncoupling protein-1 in brown adipocytes.

It has been demonstrated that TSH receptors are expressed not only in thyroid gland but also in extrathyroidal tissues. Brown adipose tissue of guinea pig has been reported to express TSH receptor messenger RNA (mRNA), but the physiological roles of TSH receptors in brown adipose tissue have not been understood. We studied the expression and function of TSH receptors in rat brown adipose tissue and cultured rat brown adipocytes. Northern analysis demonstrated the expression of TSH receptor mRNA in rat brown adipose tissue and cultured rat brown adipocytes. TSH receptor mRNA in rat brown adipose tissue was decreased by cold exposure of the rat, and its mRNA in cultured rat brown adipocytes was also decreased by incubation with TSH or (Bu)(2)cAMP. TSH increased the intracellular cAMP concentration in cultured rat brown adipocytes in a dose dependent manner. Type II iodothyronine deiodinase mRNA, its activity, and uncoupling protein-1 mRNA in cultured rat brown adipocytes were significantly increased by incubation with TSH in a dose-dependent manner. These results suggest the expression of functional TSH receptors in brown adipose tissue, which may be involved in regulation of the expression of type II iodothyronine deiodinase and uncoupling protein-1.

The expression of thyrotropin receptor in the brain.

The regulation of the thyroid gland by TSH is mediated by a heterotrimeric G protein-coupled receptor. Nonthyroid effects of TSH have been reported, and expression of its receptor has been described in adipocytes and lymphocytes. We have previously reported the existence of specific and saturable binding sites of TSH and specific TSH effects in primary cultured rat brain astroglial cells. We now report expression of the TSH receptor gene in these cells; the coding sequence of the corresponding complementary DNA is identical to that previously established in thyroid. Using specific antisense RNA probe, expression of this gene was detected in some isolated or clustered glial fibrillary acidic protein-positive primary cultured cells by in situ hybridization. With this technique, we further detected TSH receptor messenger RNA (mRNA) expression in rat brain cryoslices in both neuronal cells and astrocytes. Its presence predominated in neuron-rich areas (pyriform and postcingulate cortex, hippocampus, and hypothalamic nuclei) and was mostly colocalized with neuron-specific enolase. In astrocytes, this mRNA was detected in the ependymal cell layer and the subependymal zone, and several isolated cells were also found in the brain parenchyma. We also detected TSH receptor mRNA and protein in primary cultured human astrocytes. The protein was detected as well in both rat and human brain cryoslices. Together, these findings clearly demonstrate the expression of the TSH receptor gene in the brain in both neuronal cells and astrocytes.

Characterization of autonomous thyroid adenoma: metabolism, gene expression, and pathology.

Fifty-one in vivo characterized autonomous single adenomas have been studied for functional parameters in vitro, for gene and protein expression and for pathology, and have been systematically compared to the corresponding extratumoral quiescent tissue. The adenomas were characterized by a high level of iodide trapping that corresponds to a high level of Na+ /iodide symporter gene expression, a high thyroperoxidase mRNA and protein content, and a low H2O2 generation. This explains the iodide metabolism characteristics demonstrated before, ie, the main cause of the "hot" character of the adenomas is their increased iodide transport. The adenomas spontaneously secreted higher amounts of thyroid hormone than the quiescent tissue and in agreement with previous in vivo data, this secretion could be further enhanced by thyrotropin (TSH). Inositol uptake was also increased but there was no spontaneous increase of the generation of inositol phosphates and this metabolism could be further activated by TSH. These positive responses to TSH are in agreement with the properties of TSH-stimulated thyroid cells in vitro and in vivo. They are compatible with the characteristics of mutated TSH receptors whose constitutive activation accounts for the majority of autonomous thyroid adenomas in Europe. The number of cycling cells, as evaluated by MIB-1 immunolabeling was low but increased in comparison with the corresponding quiescent tissue or normal tissue. The cycling cells are observed mainly at the periphery; there was very little apoptosis. Both findings account for the slow growth of these established adenomas. On the other hand, by thyroperoxidase immunohistochemistry, the whole lesion appeared hyperfunctional, which demonstrates a dissociation of mitogenic and functional stimulations. Thyroglobulin, TSH receptor, and E-cadherin mRNA accumulations were not modified in a consistent way, which confirms the near-constitutive expression of the corresponding genes in normal differentiated tissue. On the contrary, early immediate genes expressions (c-myc, NGF1B, egr 1, genes of the fos and jun families) were decreased. This may be explained by the proliferative heterogeneity of the lesion and the previously described short, biphasic expression of these genes when induced by mitogenic agents. All the characteristics of the autonomous adenomas can therefore be explained by the effect of the known activating mutations of genes coding for proteins of the TSH cyclic adenosine monophosphate (cAMP) cascade, all cells being functionally activated while only those at the periphery multiply. The reason of this heterogeneity is unknown.

Developmental regulation of thyrotropin receptor gene expression in the fetal and neonatal rat thyroid: relation to thyroid morphology and to thyroid-specific gene expression.

The TSH receptor plays a pivotal role in thyroid gland function, growth, and differentiation, but little is known about its role or regulation in the fetus and neonate. To explore these questions, we systematically evaluated TSH receptor gene expression at the level of messenger RNA (mRNA) in thyroid glands obtained from rat fetuses and neonates, from 14 days gestation to day 5 of postnatal life. Results were compared with histological evidence of differentiation and to thyroid-specific gene expression. Northern blot and RT-PCR analysis revealed that TSH mRNA was first detected at low levels on fetal day 15, but it increased 3- to 15-fold on fetal days 17-18. Up-regulation of TSH receptor mRNA on fetal day 17-18 was accompanied by the first appearance of colloid formation and of follicular development on morphological examination. It was also paralleled by increased expression of the thyroid-specific genes thyroglobulin (Tg) and thyroid peroxidase. Unexpectedly, TSH mRNA abundance was 2- to 3-fold higher in pregnant dams than in nonpregnant adult females or adult males. In view of the 8-day lapse between the first appearance of the thyroid diverticulum and up-regulation of TSH receptor gene expression, we conclude that pituitary TSH, acting through its receptor, plays an important role in terminal thyroid maturation, but it is not involved earlier in gestation. Similarly, these data support previous evidence that the weak thyrotropic activity of human CG could not be of significance in early fetal thyroid gland development. The increased TSH receptor mRNA on fetal day 17-18 may be attributable to up-regulation by TSH, which is first secreted into the fetal circulation at this time. The significance of the increased TSH receptor expression during pregnancy remains to be explored.

Demonstration of thyrotropin receptor mRNA in orbital fat and eye muscle tissues from patients with Graves' ophthalmopathy by in situ hybridization.

There is a controversy regarding whether there are thyrotropin (TSH) receptors in orbital fat and eye muscle tissues that may play a role in the pathogenesis of Graves' ophthalmopathy. To elucidate whether there are TSH receptors in orbital fat and eye muscle tissues in patients with Graves' ophthalmopathy, we applied the method of in situ hybridization in orbital fat and eye muscle tissues obtained during the operation for patients with Graves' ophthalmopathy, to directly detect TSH receptor mRNA. To identify whether the cells with positive TSH receptor mRNA are fibroblasts, we also did vimentin immunoreactivity study. To further prove the transcript does have a full length of TSH receptor, the samples of total RNA preparations, extracted from orbital fat and eye muscle tissues, were used as a template for reverse transcriptase polymerase chain reaction (RT-PCR) using three primer sets to generate cDNA fragments and cloned for sequencing. The results showed that the expression of TSH receptor mRNA was demonstrated in adipocytes and fibroblasts of orbital fat, and perimysial fibroblasts within eye muscle tissues by in situ hybridization and vimentin immunoreactivity study. Also, by using the RT-PCR, cloning and sequencing, we further proved that the transcript does have a full length of TSH receptor. The present study suggested that there are TSH receptors expressed in orbital fat and eye muscle tissues.

Expression of thyrotropin receptor on clonal osteoblast-like rat osteosarcoma cells.

The expression of thyrotropin receptor (TSH-R) on various cells derived from bone, including osteoblast-like rat osteosarcoma cells (UMR106 cells), was investigated. TSH receptor mRNA was detected in UMR106 cells by Northern blot analysis. 125I-labeled TSH binding analysis revealed specific high- and low-affinity binding sites (association constants of 5.6 x 10(9) M(-1) and 3.0 x 10(7) M(-1), respectively) on UMR106 cells. Recombinant TSH, but not recombinant human chorionic gonadotropin, increased cyclic adenosine monophosphate (cAMP) production in a concentration-dependent manner in these cells. Furthermore, immunoglobulin Gs from patients with Graves' disease induced cAMP response in UMR106 cells, and the cAMP response index in this cell line correlated with thyroid-stimulating antibody (TSAb) activity detected by Chinese hamster ovary (CHO)-K1 cells transfected with rat TSH-R. We have also demonstrated that recombinant TSH increased cAMP production in human osteoblast-like osteosarcoma (MG63) cells and mouse primary osteoblastic cells. These results suggest that osteoblasts possess functional TSH-R and that abnormal bone metabolism in Graves' disease may be partly explained by the interaction of TSAb with TSH-R in osteoblasts in some patients.

Analysis of differentiation-induced expression mechanisms of thyrotropin receptor gene in adipocytes.

Rat adipose tissue, as well as differentiated 3T3-L1 cells, has been shown to express TSH receptor (TSHR) mRNA in amounts approaching those in the thyroid. We investigated the molecular mechanisms of TSHR gene expression in adipose cells. Primer extension and cloned cDNA sequences showed that transcription of the TSHR gene in rat adipose tissue was from multiple start sites clustered between -89 to -68 bp and almost identical to those in FRTL-5 thyroid cells. By transient expression analysis, we localized, between -146 and -90 bp, a positive regulatory element, the activity of which was markedly increased after the differentiation of 3T3-L1 cells. Deoxyribonuclease I protection showed that nuclear extracts from differentiated 3T3-L1 cells strongly protected two sequences, from -146 to -127 bp, including a cAMP response element-like sequence and from -112 to -106 bp containing a putative Ets-binding sequence. In differentiated 3T3-L1 cells, disruption or deletion of either sequence was found to result in the loss of enhancer activity, suggesting both elements may synergistically activate the TSHR promoter. Electrophoretic mobility shift analysis revealed the induction of new protein/DNA complexes formed either with the cAMP response element-like site or with putative Ets elements after the differentiation into adipocytes. In contrast, nuclear proteins, whose binding to DNA was diminished after the differentiation of 3T3-L1 cells, were found to interact with the site contiguous to the 5'-end of the putative Ets-binding sequence. Mutations of this binding site, which reduced the protein/DNA complex formation, increased TSHR promoter activity in undifferentiated cells. These observations suggested that differentiation-induced diminution of suppressor interactions may allow the enhancers to synergistically activate the transcription of TSHR gene in adipocytes.

Analysis of Differentiation-Induced Expression Mechanisms of Thyrotropin Receptor Gene in Adipocytes

Rat adipose tissue, as well as differentiated 3T3-L1 cells, has been shown to express TSH receptor (TSHR) mRNA in amounts approaching those in the thyroid. We investigated the molecular mechanisms of TSHR gene expression in adipose cells. Primer extension and cloned cDNA sequences showed that transcription of the TSHR gene in rat adipose tissue was from multiple start sites clustered between −89 to −68 bp and almost identical to those in FRTL-5 thyroid cells. By transient expression analysis, we localized, between −146 and −90 bp, a positive regulatory element, the activity of which was markedly increased after the differentiation of 3T3-L1 cells. Deoxyribonuclease I protection showed that nuclear extracts from differentiated 3T3-L1 cells strongly protected two sequences, from− 146 to −127 bp, including a cAMP response element-like sequence and from −112 to −106 bp containing a putative Ets-binding sequence. In differentiated 3T3-L1 cells, disruption or deletion of either sequence was found to result in the loss of enhancer activity, suggesting both elements may synergistically activate the TSHR promoter. Electrophoretic mobility shift analysis revealed the induction of new protein/DNA complexes formed either with the cAMP response element-like site or with putative Ets elements after the differentiation into adipocytes. In contrast, nuclear proteins, whose binding to DNA was diminished after the differentiation of 3T3-L1 cells, were found to interact with the site contiguous to the 5′-end of the putative Ets-binding sequence. Mutations of this binding site, which reduced the protein/DNA complex formation, increased TSHR promoter activity in undifferentiated cells. These observations suggested that differentiation-induced diminution of suppressor interactions may allow the enhancers to synergistically activate the transcription of TSHR gene in adipocytes.

Effects of cytokines on expression of thyrotropin receptor mRNA in rat preadipocytes.

Cultured rat preadipocytes express thyrotropin receptor (TSHR) during their differentiation. To evaluate the effects of inflammatory cytokines on the expression of TSHR in cultured rat preadipocytes, we cultured those cells in the presence of recombinant human tumor necrosis factor (rhTNF)-alpha, recombinant human interferon (rhIFN)-gamma, and human transforming growth factor (hTGF)-beta1. The effects on the level of TSHR mRNA and signal transduction were evaluated. Addition to the medium of 1 ng/mL TNF-alpha, 1 ng/mL rhIFN-gamma, and 1 ng/mL hTGF-beta1 during the differentiation of rat preadipocytes inhibited the expression of TSHR mRNA. The decrease in TSHR mRNA was accompanied by a decrease in TSH-stimulated cyclic adenosine monophosphate (cAMP) production. Histochemical analysis showed that these cytokines inhibited the morphological differentiation of the cells. These cytokines also decreased the expression of mRNA for such fat-specific proteins as lipoprotein lipase and aP2. Results indicate that the loss of expression and function of the TSHR is closely related to the inhibition of differentiation. This confirms the close relation between the expression of the TSHR and the differentiation of the rat preadipocytes.

Thyrotropin receptor expression in Graves' orbital adipose/connective tissues: potential autoantigen in Graves' ophthalmopathy.

It is acknowledged that the TSH receptor (TSHr) on thyroid follicular cells is the autoantigen involved in the hyperthyroidism of Graves' disease. However, whether this receptor is expressed in extrathyroidal tissues, and whether it participates directly in the pathogenesis of Graves' ophthalmopathy (GO) are unclear. We sought to detect the expression of TSHr messenger ribonucleic acid (mRNA) and protein in orbital adipose/connective tissue specimens and in human orbital preadipocyte fibroblast cultures using liquid hybridization analysis and immunohistochemical methods. We demonstrated intact and variant TSHr mRNA transcripts and TSHr-like immunoreactivity in orbital adipose/connective tissue specimens from patients with GO. In addition, TSHr-like immunoreactivity was detected in early passage GO preadipocyte fibroblast cultures that were shown to include some adipose cells. In contrast, neither TSHr mRNA nor protein was detected in normal orbital adipose/connective tissue specimens or in late passage GO orbital fibroblast cultures containing no lipid-laden adipose cells. In conclusion, we showed that TSHr is expressed in the adipose/connective tissue of the diseased orbit in GO. In addition, TSHr is demonstrable in early passage GO preadipocyte orbital fibroblast cultures that contain a subpopulation of adipocytes. Subsequent passaging of these cells results in the loss of both TSHr expression and adipocyte-specific staining. These results suggest that both the expression of this receptor and the accumulation of adipose tissue in the orbit in GO may be induced in vivo by a humoral factor(s) not present in the cell culture environment.

Defective thyrotropin receptor G-protein cyclic adenosine monophosphate signaling mechanism in the FTC human follicular thyroid cancer cell line

Background. Several studies report the effect of thyrotropin (thyroid-stimulating hormone [TSH]) on weakly (FTC-133) and aggressively invasive (FTC-238) clones of a human follicular thyroid cancer cell line. Specifically, TSH induces fibronectin secretion by FTC-133, possibly as a result of increased cyclic adenosine monophosphate (cAMP), yet induces in vitro invasion through a protein kinase C-dependent mechanism. In normal thyrocytes, TSH activates cAMP through a stimulatory G-protein (Gs)-linked pathway. In the FTC model we studied the effect of TSH on adenylate cyclase activation. Methods. TSH receptor (TSH-R) mRNA was studied by reverse transciptase polymerase chain reaction. Fibronectin transcription was analyzed by Northern blot and densitometry. cAMP levels were determined by an enzyme immunoassay. Gs α. expression was determined by Western blot and a possible activating mutation at position 201 in Gs α sought by direct sequencing. Results. Reverse transcriptase polymerase chain reaction confirmed the presence of TSH-R mRNA in FTC-133 and FTC-238. TSH did not increase transcription of fibronectin mRNA. FTC-133 cells exhibited higher cAMP levels than did FTC-238 cells: 30.4 ± 8.0 versus 13.0 ± 3.5 femtomoles/10 4 cells (mean ± SD; p < 0.001, Mann-Whitney rank-sum test). TSH did not raise cAMP levels in either clone. Gs α expression is equal in both cell lines and is not increased by TSH; sequencing showed no position 201 mutations in Gs α. Conclusions. Prototypical TSH-Gs-cAMP signal transduction is not functional in FTC-133 or FTC-238. Our findings implicate perturbation in TSH-R.

Increased expression of the Na+/I- symporter in cultured human thyroid cells exposed to thyrotropin and in Graves' thyroid tissue.

The Na+/I- symporter (NIS) is important in hormone synthesis in the thyroid gland. NIS activity, as reflected by I- uptake, was increased by TSH (1 mU/mL) or forskolin (10 mumol/L) in primary cultured human thyroid cells. Northern blot analysis revealed that incubation of these cells with TSH or forskolin for 24 h increased the abundance of NIS messenger ribonucleic acid (mRNA) 2.3- and 2.5-fold, respectively. Immunoblot analysis revealed 2.7- and 2.4-fold increases, respectively, in the amount of NIS protein after 48 h, suggesting that elevated levels of intracellular cAMP induced the expression of NIS in human thyrocytes. We then studied the levels of NIS mRNA and protein in Graves' thyroid tissue and found that the amount of NIS mRNA in thyroid tissue from individuals with Graves' disease (n = 5) was 3.8 times that in normal thyroid tissue (n = 5). The abundance of NIS mRNA was significantly correlated with that of thyroid peroxidase or thyroglobulin mRNAs, but not with that of TSH receptor mRNA, in the Graves' and normal thyroid tissue specimens. The amount of NIS protein was also increased 3.1-fold in Graves' thyroid tissue compared with that in normal thyroid tissue. The increased expression of NIS may thus contribute to the development of Graves' disease.

Cloning and Expression of a Brain-Derived TSH Receptor

Several hormones not only regulate the activity of endocrine cells and non-endocrine tissues but also serve as neuronal transmitters or modulators of neuronal activity. Accordingly, the expression and physiological significance of hormonal receptors in the central nervous system (CNS) could be demonstrated for a whole set of hormones (e. g. hCG/LH, GH, T3, CRF, TRH). The G-protein coupled TSH receptor is densely expressed in the thyroid gland and mediates the production and secretion of thyroid hormones. Not all TSH effects, especially in neurological and psychiatric disease states, can readily be explained by the action of the hormone on the thyroid gland and/or TRH levels. Therefore, it has been suggested that TSH might exert its effects directly in the CNS, although no direct proof for a TSH receptor in the human brain has been provided yet. Here we describe the cloning of a TSH receptor from an ovine hypothalamic cDNA library that is similar to thyroid derived cDNA clones. The comparison of amino acid sequences indicates that several protein domains important for the function and activity of the receptor are highly conserved. RT-PCR and RNA protection assay demonstrated that the TSH receptor mRNA is widely expressed throughout the ovine brain. The expression of a TSH receptor in the CNS indicates that TSH is not only a hormonal messenger for the thyroid gland but can also act directly in the brain. Further studies should focus on the physiological role of TSH in the CNS and the regulation of TSH receptor expression in the mammalian brain.

Differential expression of thyrotropin receptor mRNA in the porcine heart.

Thyrotropin receptor (TSHR) mRNA expression has previously been detected in human heart, suggesting a possible role for the receptor in cardiac function and pathophysiology. In the present study we examined the regional distribution of TSHR mRNA in pig heart to map potential cardiac sites of TSH action. Polyadenylated mRNA extracted from thyroid, atria, ventricles, aorta, coronary arteries, epicardial fat, and purified preparations of atrial and ventricular cardiomyocytes was subjected to reverse-transcriptase polymerase chain reaction (RT-PCR) using primers designed to amplify a 311 base pair (bp) DNA segment of the human TSHR. After reverse transcription of 100 ng mRNA, cDNA was amplified by PCR using TSHR primers and compared by electrophoresis on 2% agarose gels. Relative levels of TSHR cDNA (normalized to glyceraldehyde 3-phosphate dehydrogenase [GAPDH]) were as follows: Coronary arteries, epicardial fat > right atrium > left atrium > right ventricle, aorta > left ventricle, ventricular cardiocytes. In contrast to ventricular cardiocytes, purified atrial cardiocytes expressed levels of TSHR mRNA readily detectable with RT-PCR. These findings demonstrate that TSHR mRNA expression in porcine heart varies regionally, and furthermore suggest that areas of highest expression (coronary arteries, adipose tissue, right atrium) are potential sites for a functional or pathologic role of the TSHR.

The Full Length and Splice Variant Thyrotropin Receptor Is Expressed Exclusively in Skeletal Muscle of Extraocular Origin: A Link to the Pathogenesis of Graves’ Ophthalmopathy

Graves’ ophthalmopathy occurs in up to 90% of patients with Graves’ disease, supporting the notion of a common denominator in the development of these two disorders. The thyrotropin receptor has been proposed as the link for this clinical association. In the present study we have investigated whether thyrotropin receptor mRNA species exist in extraocular muscle and non-ocular skeletal muscle by reverse transcription-polymerase chain reaction (RT-PCR). We have, with high stringency RT-PCR, Southern analysis, and direct sequencing of PCR products, identified for the first time the presence of both full length and splice variant thyrotropin receptor mRNA in extraocular but not non-ocular skeletal muscle. This extraocular muscle thyrotropin receptor expression was shared, as expected, with normal thyroid but not other control tissues including brain and kidney. These data demonstrate that the thyrotropin receptor, the autoimmune target of Graves’ disease, is exclusively expressed in extraocular muscle as well as the thyroid and lend support to the notion that it is a likely candidate autoantigen in Graves’ ophthalmopathy.

Transplantable rat thyroid cancer cell line FRTC transformed with muramyl dipeptide.

A rat thyroid cancer cell line, FRTC, was established from the normal rat thyroid cell line, FRTL-5. FRTL-5 cells were cultured in vitro with N-acetylmuramyl-L-alanyl-D-isoglutamine (MDP) for 4 days and were transplanted intraperitoneally into Fisher rats. Disseminated tumour formation in the peritoneum was found in ten out of ten rats in which MDP-treated FRTL-5 cells were transplanted. Colloid-like structures stained with anti-thyroglobulin (Tg) antibodies were observed in the tumours. On the other hand, no tumour was found in any of the rats in which untreated FRTL-5 cells were transplanted. No morphological changes were observed in FRTL-5 cells after long-term in vitro culture in the presence of MDP. MDP had no effect on thymidine incorporation, the production of cAMP or the expression of c-myc in FRTL-5 cells in vitro. Cells from the tumour (FRTC) secreted Tg in vitro and expressed Tg, thyroid peroxidase (TPO) and thyrotropin (TSH) receptor mRNA. The expression of TSH receptor mRNA increased in FRTC cells after TSH stimulation. FRTC cells produced cAMP in response to TSH stimulation in a dose-dependent manner. However, the growth of FRTC cells was TSH independent. Expression of c-myc and c-fos was observed in FRTC cells in vivo as well as in vitro. FRTC cells formed tumours in Fisher rats when transplanted subcutaneously. FRTC cells have several characteristics of differentiated thyroid cancer cells and may provide a good model for the study of human differentiated thyroid cancers.

Localization and clinical significance of thyrotropin receptor mRNA expression in orbital fat and eye muscle tissues from patients with thyroid-associated ophthalmopathy.

We have studied the cellular localization of thyrotropin receptor (TSH-R) mRNA in orbital fat and extraocular muscle tissues from patients with thyroid-associated ophthalmopathy (TAO) using Northern blot, reverse transcriptase polymerase chain reaction (RT-PCR), and in situ hybridization, and we correlated the findings with clinical estimates of ophthalmopathy. Although we failed to detect TSH-R mRNA in orbital tissues by Northern blot, TSH-R cDNA was amplified in orbital fat tissue from 13 of 25 patients with TAO and from 2 of 4 control subjects, in eye muscle tissue from 2 out of 7 patients with TAO, and in cultured orbital fibroblasts and subcutaneous fibroblasts from TAO patients. In situ hybridization showed that TSH-R mRNA was detected in cultured orbital fibroblasts as well as skin fibroblasts obtained from the patient. Furthermore, the expression of TSH-R mRNA in orbital fat tissue from patients with TAO significantly correlated with the orbital fat volume and the severity of ophthalmopathy, especially the extent of eye muscle dysfunction. These results suggest that the expression of TSH-R in the orbit, especially fibroblasts, may play a role in the pathogenesis and clinical manifestations of the ophthalmopathy in patients with TAO, although a secondary effect, involving fibroblasts in TAO is also possible.