Amplification efficiency: linking baseline and bias in the analysis of quantitative PCR data

Despite the central role of quantitative PCR (qPCR) in the quantification of mRNA transcripts, most analyses of qPCR data are still delegated to the software that comes with the qPCR apparatus. This is especially true for the handling of the fluorescence baseline. This article shows that baseline estimation errors are directly reflected in the observed PCR efficiency values and are thus propagated exponentially in the estimated starting concentrations as well as 'fold-difference' results. Because of the unknown origin and kinetics of the baseline fluorescence, the fluorescence values monitored in the initial cycles of the PCR reaction cannot be used to estimate a useful baseline value. An algorithm that estimates the baseline by reconstructing the log-linear phase downward from the early plateau phase of the PCR reaction was developed and shown to lead to very reproducible PCR efficiency values. PCR efficiency values were determined per sample by fitting a regression line to a subset of data points in the log-linear phase. The variability, as well as the bias, in qPCR results was significantly reduced when the mean of these PCR efficiencies per amplicon was used in the calculation of an estimate of the starting concentration per sample.

Effect of amiodarone and dronedarone administration in rats on thyroid hormone-dependent gene expression in different cardiac components

OBJECTIVE

In view of their different actions on thyroid hormone receptor (TR) isoforms we set out to investigate whether amiodarone (AM) and dronedarone (Dron) have different and/or component-specific effects on cardiac gene expression.

DESIGN

Rats were treated with AM or Dron and the expression of TRalpha 1, TRalpha 2, TRbeta 1 and several tri-iodothyronine (T3)-regulated genes was studied in different parts of the heart, namely the right atrium (RA), left ventricular wall (LVW) and apex.

METHODS

Rats were treated for 14 days with 100 mg/kg body weight AM or Dron. The expression of TRalpha 1, TRalpha 2, TRbeta 1 and T3-regulated genes was studied using real-time PCR and non-radioactive in situ hybridisation.

RESULTS

AM and Dron affected TR expression in the RA similarly by decreasing TRalpha 1 and beta 1 expression by about 50%. In the LVW, AM and Dron decreased TRbeta 1 and, interestingly, AM increased TRalpha 1. In the apex, AM also increased TRalpha 2. The changes seen in T3-dependent gene expression are reminiscent of foetal reprogramming.

CONCLUSION

Taken together, our results indicate that AM and Dron have similar effects on the expression of TR isoforms in the RA, which could partly contribute to their ability to decrease heart rate. On the other hand, the more profound effect of AM appears on TR- and T3-dependent gene expression in the left ventricle suggests foetal reprogramming.

Expression of thyroid hormone receptors A and B in developing rat tissues; evidence for extensive posttranscriptional regulation

The perinatal changes in the pattern of expression of the thyroid hormone receptor (TR) isoforms TRalpha (1) TRalpha (2), TRbeta (1), and TRbeta (2) were investigated using in situ hybridization and immunohistochemistry, and RT-PCR and western blotting as visualization and quantification techniques respectively. In liver, lung, and kidney, TRalpha mRNA was expressed in the stromal and TRbeta mRNA in the parenchymal component of the tissues. When compared with liver, TRalpha mRNA concentrations were tenfold higher in lung, kidney, and intestine, and 100-fold higher in brain, with TRalpha (2) mRNA concentrations exceeding those of TRalpha (1) 5-to 10-fold. Tissue TRbeta (1) mRNA concentrations were similar in liver, lung, and brain, and 3- to 5-fold higher in kidney and intestine. None of the TRbeta (2) mRNA could be detected outside the pituitary. Tissue TRalpha (2) and TRbeta (1) protein levels reached adult levels at 5 days before birth, whereas TRalpha (1) protein peaked after birth. Because of the distinct time-course of thyroid hormone-binding receptors TRalpha (1) and TRbeta (1), we speculate that an initiating, TRbeta (1)-mediated signaling from the parenchyma is followed by a TRalpha (1)-mediated response in the stroma. When compared with organs with a complementary parenchymal-stromal expression pattern, organs with extensive cellular co-expression of TRalpha and TRbeta (brain and intestinal epithelium) were characterized by a very low TRalpha protein: mRNA ratio, implying a low translational efficiency of TR mRNA or a high turnover of TR protein. The data indicate that the TR-dependent regulatory cascades are controlled differently in organs with a complementary tissue expression pattern and in those with cellular co-expression of the TRalpha and TRbeta genes.

Thyroid hormone receptor isoform expression in livers of critically ill patients

OBJECTIVE

The THRA gene encodes two isoforms of the thyroid hormone receptor (TR), TRalpha1 and TRalpha2. The ratio of these splice variants could have a marked influence on T3-regulated gene expression, especially during illness.

DESIGN

We studied the expression of the isoforms TRbeta1, TRalpha1, and TRalpha2 and 5'-deiodinase in postmortem liver biopsies of 58 patients who were critically ill and died in the intensive care unit (ICU). All mRNA levels were determined using real-time PCR.

MAIN OUTCOME

All ratios of the biopsies were higher than those found in three normal liver biopsies due to an increased TRalpha1 level. The TRalpha1/TRalpha2 ratio increased with age and severity of illness following the equation: TRalpha1/TRalpha2 ratio = - 1.854 + (0.0323 x age) + (0.0431 x Therapeutic Intervention Scoring System score) indicating that 28% of the changed TRalpha1/TRalpha2 ratio can be predicted by these clinical variables. There was no effect of randomization to intensive insulin therapy or glucocorticoid or thyroid hormone treatment on the TRalpha1/TRalpha2 ratio or TRbeta1. Furthermore, no relation was seen between the expression levels of the 5'-deiodinase mRNA and TR isoforms or the triiodothyronine T3 levels.

CONCLUSION

It appears that in critically ill patients the ratio of TRalpha1/TRalpha2 expression increases with age and severity of illness, possibly indicating a mechanism to enhance sensitivity to T3 in the oldest and sickest patients.

PGC-1alpha regulates the isoform mRNA ratio of the alternatively spliced thyroid hormone receptor alpha transcript

Transcripts derived from the thyroid hormone receptor alpha (TRalpha) gene are alternatively spliced resulting in a functional receptor TRalpha1 and a non-T3-binding variant TRalpha2 that can exert a dominant negative effect on the transactivation functions of other TRs. There is evidence that the ratio of TRalpha isoform transcripts can be modulated and here, we investigate whether the PPARgamma co-activator alpha (PGC-1alpha) has an effect on this splicing process. PGC-1alpha was discovered not only as a transcriptional co-activator, but also has certain motifs characteristic of splicing factors. We demonstrate that PGC-1alpha alters the ratio of endogenously expressed TRalpha isoform transcripts in HepG2 cells, by decreasing TRalpha1 mRNA levels twofold. This change in isoform ratio is accompanied by a decrease in 5'-deiodinase expression, whereas no differences were found in TRbeta1 expression. Deletion of the RNA-processing domain of PGC-1alpha abrogated the effect on the TRalpha splicing, whereas expression of only the RNA-processing domain favored TRalpha1 expression. PGC-1alpha showed a similar effect on the splicing of a TRalpha minigene containing only the last four exons and introns of the TRalpha gene. These data suggest that PGC-1alpha is involved in the RNA processing of TRalpha transcripts.

Expression pattern and ontogenesis of thyroid hormone receptor isoforms in the mouse heart

Nuclear thyroid hormone (T3) receptors (TR) play a critical role in mediating the effects of T3 on development, differentiation and normal physiology of many organs. The heart is a major target organ of T3, and recent studies in knockout mice demonstrated distinct effects of the different TR isoforms on cardiac function, but the specific actions of TR isoforms and their specific localization in the heart remain unclear. We therefore studied the expression of TRalpha1, TRalpha2 and TRbeta1 isoforms in the mouse heart at different stages of development, using monoclonal antibodies against TRalpha1, TRalpha2 and TRbeta1. In order to identify distinct components of the embryonic heart, in situ hybridization for cardiac-specific markers was used with the expression pattern of sarcoplasmic reticulum calcium-ATPase 2a as a marker of myocardial structures, while the pattern of expression of connexin40 was used to indicate the developing chamber myocardium and peripheral ventricular conduction system. Here we show that in the ventricles of the adult heart the TRbeta1 isoform is confined to the cells that form the peripheral ventricular conduction system. TRalpha1, on the other hand, is present in working myocardium as well as in the peripheral ventricular conduction system. In the atria and in the proximal conduction system (sinoatrial node, atrio-ventricular node), TRalpha1 and TRbeta1 isoforms are co-expressed. We also found the heterogeneous expression of the TRalpha1, TRalpha2 and TRbeta1 isoforms in the developing mouse heart, which, in the case of the TRbeta1 isoform, gradually revealed a dynamic expression pattern. It was present in all cardiomyocytes at the early stages of cardiogenesis, but from embryonic day 11.5 and into adulthood, TRbeta1 demonstrated a gradual confinement to the peripheral ventricular conduction system (PVCS), suggesting a specific role of this isoform in the formation of PVCS. Detailed knowledge of the distribution of TRalpha1 and TRbeta1 in the heart is of importance for understanding not only their mechanism of action in the heart but also the design and (clinical) use of TR isoform-specific agonists and antagonists.

Memory function and serotonin transporter promoter gene polymorphism in ecstasy (MDMA) users

Although 3,4-methylenedioxymethamphetamine (MDMA or ecstasy) has been shown to damage brain serotonin (5-HT) neurons in animals and possibly humans, little is known about the long-term consequences of MDMA-induced 5-HT neurotoxic lesions on functions in which 5-HT is involved, such as cognitive function. Because 5-HT transporters play a key element in the regulation of synaptic 5-HT transmission it may be important to control for the potential covariance effect of a polymorphism in the 5-HT transporter promoter gene region (5-HTTLPR) when studying the effects of MDMA as well as cognitive functioning. The aim of the study was to investigate the effects of moderate and heavy MDMA use on cognitive function, as well as the effects of long-term abstention from MDMA, in subjects genotyped for 5-HTTLPR. A second aim of the study was to determine whether these effects differ for females and males. Fifteen moderate MDMA users (<55 lifetime tablets), 22 heavy MDMA+ users (>55 lifetime tablets), 16 ex-MDMA+ users (last tablet > 1 year ago) and 13 controls were compared on a battery of neuropsychological tests. DNA from peripheral nuclear blood cells was genotyped for 5-HTTLPR using standard polymerase chain reaction methods.A significant group effect was observed only on memory function tasks (p = 0.04) but not on reaction times (p = 0.61) or attention/executive functioning (p = 0.59). Heavy and ex-MDMA+ users performed significantly poorer on memory tasks than controls. In contrast, no evidence of memory impairment was observed in moderate MDMA users. No significant effect of 5-HTTLPR or gender was observed. While the use of MDMA in quantities that may be considered "moderate" is not associated with impaired memory functioning, heavy use of MDMA use may lead to long lasting memory impairments. No effect of 5-HTTLPR or gender on memory function or MDMA use was observed.

Functional thyrotropin receptor expression in the pituitary folliculo-stellate cell line TtT/GF

Thyrotropin secretion from the anterior pituitary is regulated mainly through TRH and thyroid hormones. Recent findings of a TSH receptor (TSHR) on folliculo-stellate (FS) cells in the human anterior pituitary indicate that TSH secretion might, in addition, be regulated in a paracrine manner via FS cells. In order to elucidate the physiological relevance of TSHR expression in FS cells we evaluated the effects of TSH on a murine FS cell line, TtT/GF. First, Western blot analysis confirmed the expression of TSHR protein in these cells. Second, three potential second messenger pathways were studied. Last, cDNA array hybridization was used to evaluate the effect of TSH on gene expression levels. TSH failed to induce either the adenylate cyclase/cAMP pathway, the phosphatidylinositol/calcium pathway, or the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) 3 pathway. Most of the genes regulated by TSH were related to cell proliferation, cell differentiation, and apoptosis. Moreover, TSH induced STAT5a and TGFbeta2 expression. We report that TtT/GF cells express a functional TSHR that is not coupled to cAMP nor IP (3) but probably signals through the JAK/STAT5a pathway. Functional TSHR expression in this cell line offers an in vitro model to study the role of TSHR in FS cells.

Thyroid hormone receptor expression in the human hypothalamus and anterior pituitary

In the present study, we describe for the first time the distribution of thyroid hormone receptor (TR) isoforms in the human postmortem hypothalamus and anterior pituitary using immunocytochemistry. We used a set of polyclonal antisera raised against the specific isoforms of the human TR. The distribution of TR alpha 1, alpha 2, beta 1, and beta 2 was studied in consecutive sections of six hypothalami and pituitaries. Staining intensity showed strong interindividual variation but was consistently present in the infundibular nucleus, paraventricular nucleus, and supraoptic nucleus. In addition, strong TR immunoreactivity was observed in the anterior pituitary. Neuropeptide Y and proopiomelanocortin mRNA-positive cells in the infundibular nucleus, which were studied in three other hypothalami, appeared not to express TRs, and thus, the neurons expressing TRs in the human mediobasal hypothalamus remain to be characterized.

Expression of adenohypophyseal-hormone receptors in a murine folliculo-stellate cell line

Adenohypophyseal-hormone production is regulated by hypothalamic peptides and target-gland hormones. Additionally, paracrine regulation by folliculo-stellate cells within the pituitary has been suggested. We recently showed TSH receptor expression in human folliculo-stellate cells and speculated that receptors for other adenohypophyseal hormones might also be expressed by folliculo-stellate cells. Using RT-PCR, we evaluated the expression of receptors for TSH, GH, ACTH, LH, FSH and PRL in a murine folliculo-stellate cell line, TtT/GF. Transcripts of TSH receptor, GH receptor and ACTH receptor were detected in this cell line. LH receptor, FSH receptor and PRL receptor expression, however, could not be demonstrated. We conclude that the TtT/GF cells express some, but not all, receptors for anterior pituitary hormones. This indicates that folliculo-stellate cells might act as mediators in the paracrine regulation of at least some of the hormones secreted by the anterior pituitary.

Hyper and hypothyroidism change the expression and diurnal variation of thyroid hormone receptor isoforms in rat liver without major changes in their zonal distribution

We investigated the effect of hypothyroidism or hyperthyroidism on mRNA and protein expression, diurnal variation and zonal distribution of thyroid hormone receptor (TR) isoforms TRalpha1, TRalpha2 and TRbeta1 in rat liver. Hypothyroidism results in increased isoform mRNA and protein expression whereas hyperthyroidism shows a decreased TRalpha1 and TRalpha2 mRNA and protein expression. During hyperthyroidism no change is seen in TRbeta1 mRNA, but TRbeta1 protein is upregulated in the light period and downregulated in the dark period. Diurnal changes (measured at 13:30 and 19:30 h) in the TR isoform proteins are abolished in hypothyroidism and hyperthyroidism, with the exception of a reversal in diurnal changes of TRbeta1 in hyperthyroidism. Zonal distribution of the isoforms is not affected by hypo- or hyperthyroidism. We therefore conclude that thyroid hormone influences both the levels and the diurnal expression of its receptor isoforms but not the zonal distribution.

Diurnal variation in rat liver thyroid hormone receptor (TR)-alpha messenger ribonucleic acid (mRNA) is dependent on the biological clock in the suprachiasmatic nucleus, whereas diurnal variation of TR beta 1 mRNA is modified by food intake

Previous studies have shown a diurnal variation of certain isoforms of thyroid hormone receptors (TR) in rat liver. The genesis of these diurnal changes is still unknown. To clarify whether the biological clock, located in the hypothalamic suprachiasmatic nucleus (SCN), is involved, we made selective SCN lesions. Rats with an SCN lesion lost their circadian rhythm of plasma corticosterone and TSH when compared with intact animals. TR alpha 1 and TR alpha 2 mRNA expression of control rats was higher in the light period than in the dark period; changes that were abolished in the rats with SCN lesions. In contrast, liver TR beta 1 mRNA of intact rats showed a diurnal variation that failed to reach statistical significance. To evaluate whether these effects could be explained indirectly by the disappearance of rhythmic feeding behavior in rats with SCN lesions, we performed a second experiment in which otherwise intact animals were subjected to a regular feeding (RF) schedule, with one meal every 4 h. When compared with rats with free access to food, RF only affected TR beta 1 mRNA expression and had no effect on the diurnal changes in TR alpha 1 and TR alpha 2. We conclude that liver TR beta 1 expression is most clearly affected by food intake. Diurnal changes in liver TR alpha 1 and TR alpha 2 are controlled by the biological clock in the SCN but not via changes in the daily rhythm of food intake. The findings may have physiological relevance for diurnal variation of T(3)-dependent gene expression, which is supported by a diurnal variation in the expression of the 5'-deiodinase gene.

Zonal expression of the thyroid hormone receptor alpha isoforms in rodent liver

Many metabolic processes occur simultaneously in the liver in different locations along the porto-central axis of the liver units. These processes are often regulated by hormones, one of which is thyroid hormone which for its action depends on the presence of the different isoforms of the thyroid hormone receptor (TR). These are encoded by two genes: c-erbA-alpha encoding TRalpha1 and TRalpha2 and their respective Delta isoforms, and c-erbA-beta which encodes TRbeta1, TRbeta2 and TRbeta3. We recently found a zonal (pericentral) expression of and a diurnal variation in the TRbeta1 isoform in rat liver. We were therefore also interested to see whether TRalpha1 and TRalpha2 expression showed similar characteristics. For this reason we raised both polyclonal and monoclonal antibodies against TRalpha1 and TRalpha2 isoforms and characterised these. Antibody specificity was tested using Western blots and immunohistochemistry in liver of TR isoform-specific knockout animals. Using these antibodies we found that the TRalpha1 and TRalpha2 isoforms are zonally expressed around the central vein in rat liver. The experiments show that the portal to central gradient of TRalpha1 is broader than that of TRbeta1. Moreover, the expression of the TRalpha2 protein showed a diurnal variation with a peak in the afternoon when the animals are least active whereas no such variation was found for the TRalpha1 protein. From our data it appears that both the TRalpha1 and TRalpha2 isoforms show a zonal distribution in liver. This finding, together with the observed diurnal rhythm, has major implications for interpreting and timing experiments concerning the TR and its downstream actions in liver.

Triiodothyronine affects the alternative splicing of thyroid hormone receptor alpha mRNA

The c-erbAalpha gene encodes two thyroid hormone receptors, TRalpha1 and TRalpha2, that arise from alternative splicing of the TRalpha pre-mRNA. TRalpha2 is not able to bind triiodothyronine (T(3)) and acts as a weak antagonist of TRs. It has been suggested that the balance of TRalpha1 to TRalpha2 is important in maintaining homeostasis. Here, we study the effect of thyroid hormone on the splicing of TRalpha under various conditions in HepG2 cells. First, T(3) was added to HepG2 cells that endogenously express TRalpha. This resulted in a decrease in the TRalpha1:TRalpha2 mRNA ratio after the addition of 10(-)(8 )M or 10(-)(7 )M T(3). Then, HepG2 cells were incubated with sera from hypothyroid or hyperthyroid patients. Sera from hyperthyroid patients (n=6) decreased the TRalpha1:TRalpha2 ratio compared with HepG2 cells incubated with sera from euthyroid patients (n=8). Sera from hypothyroid patients (n=6) had no effect on the TRalpha1:TRalpha2 ratio but supplementation with T(3) caused a decrease in the ratio. Finally, we tested sera from patients with nonthyroidal illness (NTI; n=17) which showed no effect on TRalpha splicing when compared with controls. Free thyroxine levels in sera from hypo-, eu-, and hyperthyroid patients, but not that of NTI patients, were negatively correlated (P<0.01) to the TRalpha1:TRalpha2 ratio. We next studied the expression of the splicing factors hnRNP A1 and ASF/SF2 (SF2) in relation to the splicing of the TRalpha gene. In HepG2 cells incubated with NTI sera a negative relationship was found between the ratio of hnRNP A1:SF2 and the TRalpha1:TRalpha2 ratio. A high hnRNP A1:SF2 ratio is associated with the use of the distal 5'-splice site. The splicing direction should then change towards TRalpha2, which is indeed the case. Rev-ErbA, which is partly complementary to TRalpha2 and could therefore interfere in the splicing process, did not relate to the TRalpha1:TRalpha2 ratio. In conclusion, high T(3) levels induce a low TRalpha1:TRalpha2 ratio which could protect the cell from excessive T(3)-induced gene expression. In vivo, this might be a mechanism to keep tIssues relatively euthyroid during high serum T(3) levels.

TSH-R expression and cytokine profile in orbital tissue of active vs. inactive Graves' ophthalmopathy patients

OBJECTIVE

From in vitro studies using cultures of orbital fibroblasts, it has become clear that cytokines play an important role in the orbital inflammation in Graves' ophthalmopathy (GO). Orbital fibroblasts seem to be the key target cells of the autoimmune attack, and they are able to express the TSH receptor (TSH-R). In vivo data on the presence of cytokines in orbital tissues are sparse, and mostly limited to samples obtained from patients with endstage, inactive GO; the same holds true for the presence of the TSH-R. The aim of the present study was to determine whether the cytokine profile and TSH-R expression differ in the active vs. the inactive stage of GO.

DESIGN AND MEASUREMENTS

Orbital fat/connective tissue was obtained from six patients with active, untreated GO undergoing emergency orbital decompression, and from 11 patients with inactive GO subjected to rehabilitative decompressive surgery. The mRNA levels of various cytokines and the TSH-R were assessed by real-time polymerase chain reaction (PCR) using the LightCycler. Data are expressed as ratios (unknown mRNA/beta-actin mRNA).

RESULTS

Active GO patients had much higher TSH-R expression than inactive patients: 4/0-24 (median value/range) vs. 0/0-9, P = 0.01. TSH-R expression was related to the Clinical Activity Score (r = 0.595, P = 0.015). Patients with active GO compared to those with inactive GO had higher mRNA levels of the proinflammatory cytokines interleukin-1beta (IL-1beta) (445/153-877 vs. 0/0-455, P = 0.001), IL-6 (1583/968-18825 vs. 559/0-7181, P = 0.01), IL-8 (1422/38-7579 vs. 32/0-1081, P = 0.046) and IL-10 (145/58-318 vs. 27/0-189, P = 0.002). In active GO there also existed a trend towards a predominance of T helper 1 (Th1)-derived cytokines as evident from higher IL-2 (37/0-158 vs. 0/0-68, P = 0.043), interferon-gamma (IFN-gamma) (20/0-79 vs. 0/0-16, P = 0.12) and IL-12 (2.3/0-14.8 vs. 0/0-1.6, P = 0.10) mRNAs. IL-1 receptor agonist (IL-1RA), IL-2 receptor (IL-2R), IL-3, IL-4, IL-5, IL-13, IL-18 and tumour necrosis factor-alpha (TNF-alpha) mRNAs were similar in both groups.

CONCLUSIONS

These data show that at the mRNA level, TSH-R expression is largely present only during the active stages of GO. The active phase is characterized by the presence of proinflammatory and Th1-derived cytokines, whereas other cytokines, among them Th2-derived cytokines, do not seem to be linked to a specific stage of GO.

Dronerarone acts as a selective inhibitor of 3,5,3'-triiodothyronine binding to thyroid hormone receptor-alpha1: in vitro and in vivo evidence

Dronedarone (Dron), without iodine, was developed as an alternative to the iodine-containing antiarrhythmic drug amiodarone (AM). AM acts, via its major metabolite desethylamiodarone, in vitro and in vivo as a thyroid hormone receptor alpha(1) (TRalpha(1)) and TRbeta(1) antagonist. Here we investigate whether Dron and/or its metabolite debutyldronedarone inhibit T(3) binding to TRalpha(1) and TRbeta(1) in vitro and whether dronedarone behaves similarly to amiodarone in vivo. In vitro, Dron had a inhibitory effect of 14% on the binding of T(3) to TRalpha(1), but not on TRbeta(1). Desethylamiodarone inhibited T(3) binding to TRalpha(1) and TRbeta(1) equally. Debutyldronedarone inhibited T(3) binding to TRalpha(1) by 77%, but to TRbeta(1) by only 25%. In vivo, AM increased plasma TSH and rT(3), and decreased T(3). Dron decreased T(4) and T(3), rT(3) did not change, and TSH fell slightly. Plasma total cholesterol was increased by AM, but remained unchanged in Dron-treated animals. TRbeta(1)-dependent liver low density lipoprotein receptor protein and type 1 deiodinase activities decreased in AM-treated, but not in Dron-treated, animals. TRalpha(1)-mediated lengthening of the QTc interval was present in both AM- and Dron-treated animals. The in vitro and in vivo findings suggest that dronedarone via its metabolite debutyldronedarone acts as a TRalpha(1)-selective inhibitor.

Induction of thyroid hormone-degrading deiodinase in cardiac hypertrophy and failure

The similarities between the changes in cardiac gene expression in pathological ventricular hypertrophy and hypothyroidism suggest a role of impaired cardiac thyroid hormone (TH) action in the development of contractile dysfunction during chronic cardiac pressure overload. Here we studied the possible involvement of altered cardiac TH metabolism using a rat model of right-ventricular (RV) hypertrophy induced by pressure-overload. Pathological RV hypertrophy was indicated by decreased mRNA levels of sarcoplasmic reticulum(SR) Ca2-ATPase type 2a (SERCA2a) and myosin heavy chain a (MHCalpha), and increased levels of MHCbeta mRNA. Enzyme activity of type HI deiodinase (D3), which converts T4 and T3 to the inactive compounds rT3 and 3,3'-T2, respectively, was identified in ventricular tissue. This activity was stimulated up to five fold in hypertrophic RV, but remained unaltered in the non-hypertrophic left ventricle (LV). A low level of type Ideiodinase activity was also detected, which decreased significantly in both RV and LV. Stimulation of RV D3 activity was significantly higher in those animals in which hypertrophy progressed to heart failure, compared to animals that developed compensatory hypertrophy. The induction of a cardiac TR-degrading deiodinase maybe expected to result in reduced cellular levels of T3 and thereby contribute to a local hypothyroid state in the hypertrophic and, particularly, in the failing ventricle.

Specific detection of type III iodothyronine deiodinase protein in chicken cerebellar purkinje cells

Because iodothyronine deiodinases play a crucial role in the regulation of the available intracellular T(3) concentration, it is important to determine their cellular localization. In brain, the presence of type III iodothyronine deiodinase (D3) seems to be important to maintain homeostasis of T(3) levels. Until now, no cellular localization pattern of the D3 protein was reported in chicken brain. In this study polyclonal antisera were produced against specific peptides corresponding to the D3 amino acid sequence. Their use in immunocytochemistry led to the localization of D3 in the Purkinje cells of the chicken cerebellum. Both preimmune serum as well as the primary antiserum exhausted with the peptide itself were used as negative controls. Extracts of chick cerebellum and liver were made in the presence of Triton X-100 to solubilize the membrane-bound deiodinases. Using these extracts in Western blot analysis, a band of the expected molecular weight ( approximately 30 kDa) could be detected in both tissues. Using a full-length (32)P-labeled type III deiodinase cRNA probe, we identified a single mRNA species in the cerebellum that was of the exact same size as the hepatic control mRNA (+/-2.4 kb). RT-PCR, followed by subcloning and sequence analysis, confirmed the expression of D3 mRNA in the chicken cerebellum. In this study we provide the first evidence of the presence of the D3 protein in a neuronal cell type, namely Purkinje cells, by means of immunocytochemical staining. We were able to detect a protein fragment corresponding to the expected molecular mass (30 kDa) for type III deiodinase by means of Western blot analysis. RT-PCR as well as Northern blot analysis confirmed the presence of D3 mRNA in the cerebellum.

TR(beta)1 protein is preferentially expressed in the pericentral zone of rat liver and exhibits marked diurnal variation

We investigated the distribution and diurnal variation of TR(beta)1 protein expression in liver with specific antibodies against TR(beta)1. Immunohistochemistry showed a zonal distribution of TR(beta)1 with maximum expression in the pericentral zone matching some known T(3)-responsive enzyme activities in the liver, such as glutamine synthetase, cholesterol 7alpha- hydroxylase, and spot 14. Combining immunohistochemistry and image analysis we found and quantified the same zonal distribution for 5'-deiodinase type 1 as for TR(beta)1. Western blot analysis revealed a profound diurnal variation for TR(beta)1 protein expression, with highest levels at the beginning of the dark period. TR(beta)1 diurnal variation partly overlaps with the T(3)-responsive genes, cholesterol 7alpha-hydroxylase and spot 14. Furthermore, TR(beta)1 distribution along the porto-central axis does not change during the day, indicating that the zonal expression of TR(beta)1 is stable. This is the first time that zonal distribution in liver has been demonstrated for a member of the nuclear receptor family. This finding together with the observed diurnal rhythm has major implications for interpreting and timing experiments concerning the TR and its downstream actions in liver.

Peri-ischemic aminoguanidine fails to ameliorate neurologic and histopathologic outcome after transient spinal cord ischemia

Inhibition of neurotoxic events that lead to delayed cellular damage may prevent motor function loss after transient spinal cord ischemia. An important effect of the neuroprotective substance aminoguanidine (AG) is the inhibition of inducible nitric oxide synthase (iNOS), a perpetrator of focal ischemic damage. The authors studied the protective effects of AG on hind limb motor function and histopathologic outcome in an experimental model for spinal cord ischemia, and related these findings to the protein content of iNOS in the spinal cord. Temporary spinal cord ischemia was induced by 28 minutes of infrarenal balloon occlusion of the aorta in 40 anesthetized New Zealand White rabbits. Animals were assigned randomly to two treatments: saline (n = 20) or AG (n = 20; 100 mg/kg intravenously before occlusion). Postoperatively, treatment was continued with subcutaneous injections twice daily (saline or 100 mg/kg AG). Normothermia (38 degrees C) was maintained during ischemia, and rectal temperature was assessed before and after subcutaneous injections. Animals were observed for 96 hours for neurologic evaluation (Tarlov score), and the lumbosacral spinal cord was examined for ischemic damage after perfusion and fixation. Lastly, iNOS protein content was determined using Western blot analysis 48 hours after ischemia in five animals from each group. Neurologic outcome at 96 hours after reperfusion was the same in both groups. The incidence of paraplegia was 67% in the saline-treated group versus 53% in the AG-treated group. No differences in infarction volume, total number of viable motoneurons, or total number of eosinophilic neurons were present between the groups. At 48 hours after reperfusion, iNOS protein content in the spinal cord was increased in one animal in the AG-treated group and in three animals in the control group. The data indicate that peri-ischemic treatment with high-dose AG in rabbits offers no protection against a period of normothermic spinal cord ischemia. There was no conclusive evidence of spinal cord iNOS inhibition after treatment with AG.

The suprachiasmatic nucleus generates the diurnal changes in plasma leptin levels

At present it is not clear which factors are responsible for the diurnal pattern of plasma leptin levels, although the timing of food intake and circulating hormones such as glucocorticoids and insulin have both been proposed as independent determinants. In this study we show that ablation of the biological clock by thermal lesions of the hypothalamic suprachiasmatic nucleus (SCN) completely eliminates the diurnal pattern of plasma leptin levels. By contrast, removal of the diurnal corticosterone signal by adrenalectomy and corticosterone replacement did not affect diurnal plasma leptin levels. More importantly, removal of the nocturnal feeding signal by submitting the animals to a regular feeding schedule of six meals per day did not abolish the diurnal plasma leptin levels. However, both SCN lesions and the regular feeding schedule did cause an increase in the 24-h mean plasma leptin levels. As neither rhythmic feeding, insulin, or corticosterone signals can completely explain the diurnal plasma leptin rhythm, we conclude that biological clock control of the sympathetic input to the adipocyte is essential for regulation of the daily rhythm in leptin release.

The biological relevance of thyroid hormone receptors in immortalized human umbilical vein endothelial cells

The gene expression of thyroid hormone receptors (TR) in ECRF24 immortalized human umbilical vein endothelial cells (HUVECs) was investigated at both the mRNA and the protein level. Endothelin-1 (ET-1) and von Willebrand factor (vWF) production were measured in response to triiodothyronine (T(3)) administration. A real-time PCR technique was used to quantify the presence of mRNAs encoding for the different isoforms of the TR. The binding of T(3) to nuclear TRs was studied in isolated endothelial cell nuclei by Scatchard analysis. Expression of TR at the protein level was investigated by immunocytochemistry and Western blotting using TR-isoform-specific polyclonal rabbit antisera. ET-1 and vWF were measured in cell supernatants with a two-site immunoenzymatic assay. Scatchard analysis yielded a maximum binding capacity of 55 fmol T(3)/mg DNA (+/-200 sites/cell) with a K(d) of 125 pmol/l. Messenger RNAs encoding for the TRalpha1 and the TRalpha2 and the TRbeta1 were observed. The approximate number of mRNA molecules per cell was at least 50 molecules per cell for TRalpha1, five for TRalpha2 and two for TRbeta1. Immunocytochemistry revealed (peri)nuclear staining for TRbeta1, TRalpha1 and TRalpha2. ET-1 and vWF secretion did not increase upon addition of T(3) (10(-10)-10(-6) M). Immortalized ECRF24 HUVECs express TR, but at low levels. The number of TRs per endothelial cell is probably too low to be functional and no change in ET-1 or vWF production was found after addition of T(3). Therefore we conclude that the genomic effects of T(3) are unlikely to occur in these immortalized HUVECs.

Expression of the thyroid-stimulating hormone receptor in the folliculo-stellate cells of the human anterior pituitary

TSH secretion from the anterior pituitary is mainly regulated by TRH and thyroid hormones. We hypothesized that in addition the pituitary itself could modulate TSH production by sensing its own TSH release, enabling fine-tuning of TSH secretion. For such an ultra-short loop control, the pituitary should contain a TSH receptor (TSH-R). To find evidence for this we screened a human pituitary complementary DNA library with a digoxigenin-labeled TSH-R probe and found 2 positive clones of 32,000 plaques. One clone was sequenced and found to be completely identical to the thyroid TSH-R. Further proof was obtained by RT-PCR on a human anterior pituitary obtained at autopsy. In situ hybridization and immunohistochemistry confirmed the presence of TSH-R in the anterior pituitary at the messenger ribonucleic acid level as well as the protein level. Moreover, double labeling experiments revealed that TSH-R messenger ribonucleic acid as well as TSH-R protein colocalize with major histocompatibility complex class II expression of folliculo-stellate cells. We conclude that TSH-R is expressed in a subpopulation of folliculo-stellate cells in the human anterior pituitary. This finding suggests ultra-short loop regulation of TSH secretion. Putative recognition of the pituitary TSH-R by TSH-R antibodies might have clinical relevance in Graves' disease.

Desethylamiodarone interferes with the binding of co-activator GRIP-1 to the beta 1-thyroid hormone receptor

Ligand binding to the thyroid hormone nuclear receptor beta1 (TRbeta(1)) is inhibited by desethylamiodarone (DEA), the major metabolite of the widely used anti-arrhythmic drug amiodarone. Gene expression of thyroid hormone (triiodothyronine, T(3))-regulated genes can therefore be affected by amiodarone due to less ligand binding to the receptor. Previous studies have indicated the possibility of still other explanations for the inhibitory effects of amiodarone on T(3)-dependent gene expression, probably via interference with receptor/co-activator and co-repressor complex. The binding site of DEA is postulated to be on the outside surface of the receptor protein overlapping the regions where co-activator and co-repressor bind. Here we show the effect of a drug metabolite on the interaction of TRbeta(1) with the co-activator GRIP-1 (glucocorticoid receptor interacting protein-1). The T(3)-dependent binding of GRIP-1 to the TRbeta(1) is disrupted by DEA. A DEA dose experiment showed that the drug metabolite acts like an antagonist under 'normal' conditions (at 10(-7) M T(3) and 5x10(-6)-->10(-3) M DEA), but as an agonist under extreme conditions (at 0 and 10(-9) M T(3) and >10(-4) M DEA). To our knowledge, these results show for the first time that a metabolite of a drug which was not devised for this purpose can interfere with nuclear receptor/co-activator interaction.

Effect of ischemic pretreatment on heat shock protein 72, neurologic outcome, and histopathologic outcome in a rabbit model of spinal cord ischemia

OBJECTIVE

In the present study, we investigated the effect of ischemic pretreatment on heat shock protein 72 concentration and neurologic and histopathologic outcome after transient spinal cord ischemia.

METHODS

In 28 New Zealand White rabbits, an aortic occlusion device was placed infrarenally. The animals were randomly assigned to 2 groups: ischemic pretreatment (n = 14 animals) and control (n = 14 animals). The duration of ischemic pretreatment was 6 minutes. After 24 hours, the aorta was occluded for 26 minutes in both groups of animals. Neurologic function was assessed 24 and 48 hours after the definite ischemic insult. At 48 hours, the animals were killed for histopathologic evaluation of the spinal cord. In a separate set of animals, heat shock protein 72 levels were determined in the lumbar spinal cord after both a 6- and 10-minute ischemic period, with the use of a Western blot analysis.

RESULTS

No significant difference in neurologic outcome between the groups was observed at 24 and 48 hours. The incidence of paraplegia and severe paresis at 48 hours was 79% in the control group and 92% in the ischemic pretreatment group. There was no difference in histopathologic scores between the groups. Heat shock protein 72 could be clearly detected 1 and 2 days after 6- or 10-minute periods of spinal cord ischemia.

CONCLUSIONS

In the present rabbit study, ischemic pretreatment could not induce tolerance against a moderately severe spinal cord ischemic insult, despite increased heat shock protein 72 levels after the preconditioning stimulus.

Changes in plasma low-density lipoprotein (LDL)- and high-density lipoprotein cholesterol in hypo- and hyperthyroid patients are related to changes in free thyroxine, not to polymorphisms in LDL receptor or cholesterol ester transfer protein genes

Thyroid function disorders lead to changes in lipoprotein metabolism. Both plasma low-density lipoprotein cholesterol (LDL-C) and high-density lipoprotein cholesterol (HDL-C) increase in hypothyroidism and decrease in hyperthyroidism. Changes in LDL-C relate to altered clearance of LDL particles caused by changes in expression of LDL receptors on liver cell surfaces. Changes in cholesterol ester transfer activity partly explain changes in HDL-C. It has been suggested that the magnitude of these changes is related to polymorphisms of involved genes. The aim of the present study is to investigate whether the polymorphic AvaII restriction site in exon 13 of the LDL receptor gene and the polymorphic TaqIB site in intron 1 of the cholesterol ester transfer protein are associated with the magnitude of the changes in plasma LDL-C and HDL-C, respectively, in the transition from the hypo- or hyperthyroid to the euthyroid state. From a consecutive group of 66 untreated hypothyroid and 60 hyperthyroid patients, 47 Caucasians in each group were analyzed. Fasting LDL-C and HDL-C were measured at baseline and 3 months after restoration of the euthyroid state. Genotype was determined by means of PCR techniques. The homozygous presence of a restriction site was designated as +/+, heterozygous as +/-, and absence as -/-. Trend analysis was done with ANOVA. Among hypo- or hyperthyroid patients, subgroups with different genotypes did not differ in thyroid function pre- or post treatment. The mean decrease in LDL-C (mmol/L +/- SD) in hypothyroid patients with different AvaII genotypes did not differ: - 1.07 +/- 1.44 (-/-, N = 15), -1.25 +/- 1.53 (+/-, N = 19), and -1.18 +/- 1.01 (+/+, N = 13) mmol/L [not significant (NS)]; neither did the mean increase in hyperthyroid patients: 1.07 +/- 0.90 (-/-, N = 18), 0.92 +/- 1.00 (+/-, N = 21), and 1.20 +/- 0.45 (+/+, N = 6) (NS). The mean decrease in HDL-C (mmol/L +/- SD) in hypothyroid patients with different TaqIB genotypes did not differ: -0.22 +/- 0.26 (-/-, N = 13), -0.15 +/- 0.23 (+/-, N = 21), and -0.12 +/- 0.22 (+/+, N = 9) (NS); neither did the mean increase in hyperthyroid patients: 0.29 +/- 0.39 (-/-, N = 7), 0.26 +/- 0.23 (+/-, N = 22), and 0.19 +/- 0.31 (+/+, N = 18) (NS). Changes in LDL-C and HDL-C correlated with the logarithm of the change in free T4 (fT4), expressed as the fT4 posttreatment/fT4 pretreatment ratio (r = -0.81, P < 0.001; and r = -0.62, P < 0.001, respectively). In conclusion, in the transition from hypo- or hyperthyroidism to euthyroidism, no association is found between AvaII genotype and changes in plasma LDL-C nor between TaqIB genotype and changes in HDL-C. Changes in LDL-C and HDL-C correlate with changes in fT4.

Altered gene expression in Staphylococcus aureus upon interaction with human endothelial cells

Staphylococcus aureus is isolated from a substantial number of patients with infective endocarditis who are not known to have predisposing heart abnormalities. It has been suggested that the infection is initiated by the direct binding of S. aureus to human vascular endothelium. To determine the mutual response of the endothelial cells and the bacteria, we studied the interaction between S. aureus and human vascular endothelium. Scanning electron microscopic analyses showed that binding of S. aureus to human umbilical vein endothelial cells (HUVEC) mainly occurred via thread-like protrusions extending from the cell surface. Bound bacteria appeared to be internalized via retraction of the protrusions into newly formed invaginations of the endothelial cell surface. The growth phase of S. aureus had a major impact on the interaction with HUVEC. Logarithmically growing bacteria showed increased binding to, and were more readily internalized by, HUVEC compared to stationary-phase bacteria. To assess the bacterial response to the cellular environment, an expression library of S. aureus was used to identify genes whose expression was induced after 4 h of exposure to HUVEC. The identified genes could be divided into different categories based on the functions of the encoded proteins (transport, catabolism, biosynthesis, and DNA repair). Further analyses of five of the S. aureus transposon clones showed that HUVEC as well as human serum are stimuli for triggering gene expression in S. aureus.

Association of thyrotrophin receptor antibodies with the clinical features of Graves' ophthalmopathy

OBJECTIVE

Graves' ophthalmopathy (GO) and Graves' hyperthyroidism are closely associated diseases and thought to be caused by the same autoimmune process. An obvious explanation for this would be the presence of autoantibodies reacting with an autoantigen present in the orbit and the thyroid gland. The TSH-Receptor (TSH-R) antibodies are a likely candidate, because they cause Graves' hyperthyroidism and the TSH-R appears to be present also in orbital tissues. If TSH-R antibodies are responsible for the ophthalmopathy one would expect their titres to correlate with clinical characteristics of the eye disease. The aim of the present study is to see whether TSH-R antibodies are related to the activity and severity of the thyroid-associated ophthalmopathy.

DESIGN AND PATIENTS

TSH-R antibody levels were measured as TBII (TRAK assay), and TSI (cAMP response of a TSH-R transfected cell line) in serum of 63 patients with untreated moderately severe GO, accompanying Graves' thyroid disease; all patients had been euthyroid for > 2 months.

RESULTS

TBII and TSI titres were strongly related to each other. TBII or TSI titres did not correlate with thyroidal or orbital disease duration, nor with TPO antibody levels. In contrast, we found a striking and highly significant correlation between the Clinical Activity Score (CAS) of the eye disease, and both TBII (r = 0.54; P < 0.0001) and TSI (r = 0.50; P < 0.0001). In addition, a weaker but significant relation was found between proptosis (in mm) and TBII (r = 0.36; P = 0.004) and TSI (r = 0.49; P = 0.0001). No correlation was found with eye muscle motility.

CONCLUSION

TSH-R antibody levels correlate directly with clinical features of Graves' ophthalmopathy. The results support the hypothesis of a pathogenetic role of TSH-R antibodies and the TSH-R in the orbit of Graves' ophthalmopathy patients.

Effect of mutations in the beta1-thyroid hormone receptor on the inhibition of T3 binding by desethylamiodarone

Desethylamiodarone (DEA) acts as a competitive inhibitor of triiodothyronine (T3) binding to the alpha1-thyroid hormone receptor (TR alpha1) but as a non-competitive inhibitor with respect to TR beta1. To gain insight into the position of the binding site of desethylamiodarone on TR beta1 we investigated the naturally occurring mutants Y321C, R429Q, P453A, P453T and the artificial mutants L421R and E457A in the ligand binding domain of human TR beta1. The IC50 values (in microM) of DEA for P453A (50 +/- 11) and P453T (55 +/- 16) mutant TR beta1 are not different from that for the wild type TR beta1 (56 +/- 15), but the IC50 values of R429Q (32 +/- 7; P<0.001) and E457A (17 +/- 3; P<0.001) are significantly lower than of the wild type. Scatchard plots and Langmuir analyses indicate a non-competitive nature of the inhibition by DEA of T3 binding to all four mutant TR beta1s tested. Mutants P453A and P453T do not influence overall electrostatic potential, and also do not influence the affinity for DEA compared to wild type. Mutant E457A causes a change from a negatively charged amino acid to a hydrophobic amino acid, enhancing the affinity for DEA. Mutant R429Q, located in helix 11, causes an electrostatic potential change from positive to uncharged, also resulting in greater affinity for DEA. We therefore postulate that amino acids R429 and E457 are at or close to the binding site for DEA, and that DEA does not bind in the T3 binding pocket itself, in line with the non-competitive nature of the inhibition of T3 binding to TR beta1 by DEA.

Amiodarone decreases gene expression of low-density lipoprotein receptor at both the mRNA and the protein level

Amiodarone, a potent antiarrhythmic drug, decreases plasma and tissue triiodothyronine (T3) and increases plasma cholesterol levels, resembling changes seen during hypothyroidism. The increase of serum cholesterol during amiodarone medication is associated with a decreased expression of the hepatic low-density lipoprotein (LDL) receptor mRNA. To further elucidate the mechanism of amiodarone-induced hypercholesterolemia, we investigated whether the decreased mRNA levels are the result of decreased transcription or increased degradation or both, and whether protein expression is decreased accordingly. Relative to pair-fed controls, amiodarone treatment increased plasma cholesterol by 69% and decreased expression of the mRNA encoding for the hepatic LDL receptor by 45%. To study this decrease in mRNA, we performed a run-on assay, from which it appears that amiodarone acts by decreasing LDL receptor mRNA expression 2.5-fold at the transcriptional level. The decay rate of liver LDL receptor mRNA, measured at different time points after injecting actinomycin D, was not different between amiodarone-treated and control animals (116+/-32 minutes and 84+/-10 minutes, P=.44). Hepatocytes in primary culture isolated from amiodarone-treated and control animals were used to determine specific binding of [125I]-LDL to hepatic LDL receptors. Amiodarone decreased specific LDL binding and Scatchard analysis demonstrated that amiodarone treatment reduced the number of LDL receptors by 69%, without affecting the dissociation constant (Kd). In conclusion, amiodarone-induced hypercholesterolemia can be explained by decreased transcription of the LDL receptor gene, resulting in lower mRNA and protein levels.

Effects of triiodothyronine and amiodarone on the promoter of the human LDL receptor gene

Treatment of patients with amiodarone, a potent anti arrhythmic drug, increases plasma LDL cholesterol levels, similar to that seen during hypothyroidism. This increase is the result of a decreased expression of the hepatic LDL receptor gene. We investigated the effects of thyroid hormone, amiodarone and desethylamiodarone on the first 687 bp upstream of the first ATG of the human LDL receptor gene by co-transfection with TRbeta1 into HepG2 cells. Promoter activity showed a dose-dependent increase upon addition of thyroid hormone up to a maximum of 600% at 10(-6) M T3. Using 5'-deletions it was found that a functional TRE(s) is present between -687 bp and -160 bp upstream of the ATG of the LDL receptor gene. Amiodarone and desethylamiodarone at 10(-6) M reduced basal LDL receptor promoter activity further then with the TRbeta1 alone (to 30% vs. 50% respectively, p<0.01) but interestingly in combination with T3 these compunds show a synergistic effect on promoter activity (to 225% T3 alone vs. 380% respectively, p<0.01).

The decrease of liver LDL receptor mRNA during fasting is related to the decrease in serum T3

Fasting is associated with a reduction in serum T3 and T4 and a rise of plasma LDL cholesterol. We hypothesized that an hypothyroid-like condition induced by fasting is responsible for the rise in LDL cholesterol. We therefore examined the relation between changes in thyroid hormone and cholesterol metabolism in rats fasted for 0, 8, 12, 24 or 48 h. Fasting resulted in a decrease of liver 5'-deiodinase mRNA from 8 h (to 50%, p < 0.05, n = 6), of serum T3 from 12 h and of serum T4 at 48 h; serum TSH remained unchanged. Furthermore, plasma LDL cholesterol increased from 24 h onwards preceded by a decrease of liver LDL receptor mRNA which in turn is related to serum T3 (r = 0.55, p < 0.05, n = 19). Adding T3 at a concentration such that normal T3 levels are maintained during 48 h fasting, prevents the decrease in the LDL receptor mRNA. Fasting did not change hepatic HMG CoA reductase mRNA but decreased cholesterol 7 alpha-hydroxylase mRNA, which however was not related to the decrease of serum T3.

IN CONCLUSION

(1) Fasting induces a hypothyroid-like condition in which inhibition of hepatic conversion of T4 into T3 may be responsible for the decrease of serum T3. (2) Fasting induces an increase of plasma LDL cholesterol, apparently caused by a decrease of hepatic LDL receptor gene expression which is (partly) related to the fall in serum T3.

Expression of the alpha 1, alpha 2, and beta 1 T3-receptor mRNAs in the fasted rat measured using competitive PCR

Fasting is associated with a decrease in the maximal binding capacity of the T3-receptor in different tissues and the responsiveness of some genes to exogenous T3 is not as pronounced as normal. One possible explanation for these observations is a change in the expression of one or all of the isoform mRNAs. We set out to measure the levels of the alpha 1, alpha 2, and beta 1 isoform mRNAs in liver and heart of fasted rats using a competitive PCR method. We constructed competitors based on the isoforms themselves so the amplification efficiencies of the target and the competitor are similar. Using this method we found that during fasting levels of alpha 2 mRNA in the liver of rats increased threefold (P < 0.002) over a 48-h period, whereas alpha 1 and beta 1 did not show any change. In the heart, no change in any of the TR isoform mRNAs was found.

Anti-heat shock protein (hsp)72 antibodies are present in patients with Graves' disease (GD) and in smoking control subjects

Hsp72 is expressed in thyroidal tissue and on retroocular fibroblasts from patients with GD. In this study we investigated whether GD patients have hsp72 antibodies, and if they correlate with disease characteristics. Because smoking is associated with GD and might up-regulate hsp72 expression, we also studied the effect of smoking on hsp antibody levels. Hsp72 IgG antibodies were determined by dot-blotting, using recombinant human stress-inducible hsp72. Dot-blot densities were measured using a videoimaging system in 38 healthy controls, 45 patients with GD, including 34 with varying degrees of ophthalmopathy, and in 13 GD patients before and after treatment of thyrotoxicosis with methimazole. Hsp72 antibodies were detectable more frequently in GD patients (26/45, 58%), than in controls (12/38, 32%; P < 0.02). GD patients had higher antibody levels than controls; mean +/- s.e.m. optical densities: 26.8 +/- 2.6 versus 18.8 +/- 2.4 (P = 0.018). Levels did not correlate with any parameter of disease severity or activity. Hsp72 antibody levels did not change upon reaching euthyroidism. In controls, but not in patients, hsp72 antibodies could be detected more frequently in smokers (6/10, 60%) versus nonsmokers (6/28, 21%; P = 0.024). Patients with GD have higher hsp72 IgG antibody levels than controls, without correlation with any disease characteristic. Among healthy controls, smoking is associated with elevated hsp72 antibodies. This suggests that these antibodies might be a marker for autoimmune susceptibility.

Tri-iodothyronine prevents the amiodarone-induced decrease in the expression of the liver low-density lipoprotein receptor gene

Treatment with amiodarone, a potent antiarrhythmic drug, is associated with a dose-dependent increase in plasma cholesterol resulting from a decreased number of liver low-density lipoprotein (LDL) receptors. Similar changes occur in hypothyroidism, and it has been suggested that amiodarone acts via induction of a local 'hypothyroid-like' state in extrathyroidal tissues. The present study was designed to evaluate whether exogenous tri-iodothyronine (T3) could prevent the effects of amiodarone on LDL cholesterol. Rats were treated for 14 days with water, amiodarone 10 mg/100 g body weight (BW), or amiodarone and 2.5, 5 or 10 micrograms T3/100 g BW respectively. Relative to controls, amiodarone increased plasma LDL cholesterol by 31% and decreased liver LDL receptor mRNA by 56% and protein by 45%; liver T3 content was reduced by 21%. Addition of T3 to the treatment with amiodarone dose-dependently reversed all these changes, with a return to control values of plasma cholesterol and the number of liver LDL receptors, although LDL receptor mRNA remained slightly lower. Treatment of rats for 14 days with T3 alone (5 micrograms/100 g BW) decreased plasma LDL cholesterol by 19% and increased liver LDL receptor mRNA by 41%. In conclusion, T3 prevents the amiodarone-induced changes in plasma LDL cholesterol and liver LDL receptor gene expression. These findings suggest that the inhibitory effect of amiodarone on LDL receptor gene expression is mediated by T3-dependent pathways.

Thyrotropin-releasing hormone gene expression in the human hypothalamus

We studied the distribution of mRNA coding for thyrotropin-releasing hormone (TRH) in the human hypothalamus by means of in situ hybridization. In 10% formalin-fixed paraffin-embedded tissue sections of five hypothalami, TRH mRNA-containing cells were found in several nuclei and areas. Numerous TRH mRNA-containing cells were detected in the medial region of the caudal part of the paraventricular nucleus. These neurons were heavily labeled and mainly small to medium-sized. Few, lightly- and medium-labeled, small cells were detected in the suprachiasmatic nucleus. In addition, heavily labeled single cells were found in the perifornical area and the anterior- and lateral hypothalamic regions. In the latter region, occasional heavily labeled cells were found just dorsal to the supraoptic nucleus. Neither in the supraoptic nucleus nor in the sexually dimorphic nucleus of the preoptic area were TRH mRNA-containing cells found. This is the first description of TRH mRNA containing cells in the human hypothalamus.

Structure-function relationship of the inhibition of the 3,5,3'-triiodothyronine binding to the alpha1- and beta1-thyroid hormone receptor by amiodarone analogs

Desethylamiodarone (DEA), the major metabolite of the potent antiarrhythmic drug amiodarone (A), acts as a competitive inhibitor of T3, binding to the alpha1-thyroid hormone receptor (alpha1-T3R), but as a noncompetitive inhibitor with respect to the beta1-T3R. To gain insight into the structure- function relationship of the interaction between A metabolites and T3Rs, we investigated the effects of several A analogs on T3 binding to the alpha1-T3R and beta1-T3R in vitro. The analogs tested were: 1) compounds obtained by deethylation of A, DEA, and desdiethylamiodarone (DDEA); 2) compounds obtained by deiodination of A, monoiodoamiodarone and desdiiodoamiodarone (DDIA); and 3) benzofuran derivatives with various iodination grades, 2-butyl-3-(4-hydroxy-3,5-diiodo-benzoyl)benzofuran (L3373, two iodine atoms), L6424 (L3373 with one iodine atom), and L3372 (L3373, no iodine atoms). IC50, values of inhibition of T3 binding to alpha1-T3R and beta1-T3R, respectively, were as follows (mean +/- SD, expressed x 10(-5) M): DEA, 4.7 +/- 0.9 and 2.7 +/- 1.4 (P < 0.001); DDEA, 3.7 +/- 0.9 and 1.9 +/- 0.3 (P < 0.001); monoiodoamiodarone, more than 20 and more than 20; DDIA, 16.2 +/- 5.6 and 9.1 +/- 2.1 (P < 0.01); L3373, 3.8 +/- 1.0 and 3.6 +/- 0.5 (P = NS); L6424, 11.3 +/- 5.7 and 10 +/- 2.0 (P = NS); and L3372, no inhibition. Scatchard analyses in the presence of DDEA, DDIA, and L3373 demonstrated a dose-dependent decrease in Ka, but no change in the maximum binding capacity (MBC) of T3 binding to alpha1-T3R. Langmuir plots clearly indicated competitive inhibition of T3 binding to alpha1-T3R by DDEA, DDIA, and L3373. In contrast, these three analogs acted differently with respect to the beta1-T3R. DDEA and DDIA decreased both Ka and MBC in Scatchard plots using beta1-T3R, demonstrating noncompetitive inhibition. L3373 decreased dose-dependently Ka, but not MBC, values of T3 binding to the beta1-T3R and clearly acted as a competitive inhibitor. Ki plots indicated that DDEA, DDIA, and L3373 do not interfere significantly with occupied T3Rs. KI (inhibition constant for the unoccupied receptor) plots demonstrated increasing inhibition of the T3 binding to unoccupied receptors with increasing analog concentrations. In summary, 1) removal of one or two ethyl groups of A results in compounds with strong but almost equal potency of inhibiting T3R binding, whereas removal of one or two iodine atoms of A has a lower potency in this respect. The strong inhibitory potency of the benzofuran derivative L3373 (equalling that of the deethylated compounds) is lost upon deiodination. 2) All tested A analogs acted as competitive inhibitors to the alpha1-T3R. The behavior to the beta1-T3R was different; deethylation or deiodination of A resulted in noncompetitive inhibition, whereas L3373 was a competitive inhibitor. The potency of deethylated and deiodinated compounds (but not of the benzofuran derivatives) for inhibiting T3 binding was twice as high for the beta1-T3R as for the alpha1-T3R. 3) All tested A analogs preferentially interfere with T3 binding to unoccupied receptors. The implications of these findings for the structure-activity relationship are the following: 1) the size of the diethyl-substituted nitrogen group and of the two bulky iodine atoms in the A molecule hamper the binding of A at the T3 binding site of T3Rs; and 2) differences in the hormone-binding domain of alpha1- and beta1-T3Rs are likely to account for the competitive or noncompetitive nature of inhibition of T3 binding by A analogs.

The role of cytokines in the lipopolysaccharide-induced sick euthyroid syndrome in mice

To evaluate the role of cytokines in the sick euthyroid syndrome, we tried to establish an animal model of non-thyroidal illness in mice by the administration of a sub-lethal dose of bacterial endotoxin (lipopolysaccharide; LPS) which induces a variety of cytokines, including tumour necrosis factor (TNF alpha), interleukin-1 (IL-1 alpha), interleukin-6 (IL-6) and interferon-gamma (IFN gamma). When compared with pair-fed controls, a single dose of LPS resulted in (a) systemic illness, (b) induction of TNF alpha and IL-6 and (c) a decrease of liver 5'-deiodinase mRNA from 4 h onwards followed by a decrease of serum tri-iodothyronine (T3) and thyroxine (T4) at 8 h and of serum free T3 (fT3) and free T4 (fT4) at 24 h; serum TSH remained unchanged. We then studied whether a single dose or a combination of IL-1 alpha, TNF alpha, IL-6 or IFN gamma could induce the sick euthyroid syndrome in mice, again using pair-fed controls. None of the cytokines except IL-1 alpha caused systemic illness, and IL-1 alpha was the only cytokine that decreased liver 5'-deiodinase mRNA transiently. IL-1 alpha, TNF alpha or IL-6 did not decrease serum T3, T4 and TSH, but administration of IFN gamma decreased serum T4, T3 and fT3 in a dose-dependent manner without changes in serum TSH. Administration of all four cytokines together had no synergistic effects; observed changes were of a smaller magnitude than after LPS. The following conclusions were reached.(ABSTRACT TRUNCATED AT 250 WORDS)

Desethylamiodarone is a competitive inhibitor of the binding of thyroid hormone to the thyroid hormone alpha 1-receptor protein

Desethylamiodarone (DEA), the major metabolite of the potent antiarrythmic drug amiodarone, is a non-competitive inhibitor of the binding of thyroid hormone (T3) to the beta 1-thyroid hormone receptor (T3R). In the present study, we investigated whether DEA acts in a similar way with respect to the alpha 1-T3R. The chicken alpha 1-T3R, expressed in an E. coli system, was incubated in the presence or absence of DEA with [125I]T3 in buffer containing 0.05% Triton X-100, 0.05% BSA and 1% ethanol (v/v) in order to solubilise DEA. DEA, but not amiodarone, inhibited T3 binding in a dose-dependent manner; the IC50 value was 3.5 x 10(-5) M. Scatchard analyses in the presence of DEA demonstrated a dose-dependent decrease in Ka values, but no change in MBC. Lineweaver-Burk plots clearly indicated competitive inhibition by DEA. Pre-incubation of the alpha 1-receptor with DEA decreased maximal [125I]T3 binding, which was independent of the duration of pre-incubation. In conclusion, in contrast to the beta 1-T3R, where DEA acts as a non-competitive inhibitor, we now report as a new finding the competitive action of DEA to the alpha 1-T3R.

Importance of the content and localization of tyrosine residues for thyroxine formation within the N-terminal part of human thyroglobulin

Thyroxine (T4) is formed by coupling of iodinated tyrosine residues within thyroglobulin (TG). In mature TG, some iodinated tyrosine residues are involved preferentially in T4 formation. In order to investigate the specific role of various tyrosine residues in T4 formation, N-terminal TG fragments with mutated tyrosine residues were constructed. An N-terminal TG fragment 198 amino acids in size and containing seven tyrosine residues at amino acid positions 5, 29, 89, 97, 107, 130 and 192 was expressed in a baculovirus system. Using site-directed mutagenesis, eight mutant TG fragments were constructed in which different tyrosine residues were replaced by phenylalanine. In the first four TG mutants, one single tyrosine residue (5, 89, 97 or 130) was mutated. In the mutant Y(5,89,97,130)F all of these four tyrosine residues were replaced. The sixth mutant Y(29,89,107,130,192)F contained only tyrosine residues 5 and 97 and the seventh (Y(29,89,97,192)F) contained only tyrosine residues 5, 107 and 130. A TG fragment (Y(5,29,89,97,107,130,192)F) in which all tyrosine residues were replaced by phenylalanine was used as a negative control. After in vitro iodination with lactoperoxidase, specific T4 formation was established in the non-mutated wild-type N-terminal TG fragment. In general the T4 formation in the mutant TG constructs decreased when the total number of tyrosine residues in the 198 amino acid fragment decreased, except fragment Y(29,89,97,192) containing three tyrosine residues, two of them being 5 and 130. Although the rate of T4 formation in this mutated N-terminal TG fragment was lower, the ultimate T4 generation was the same as in the wild-type fragment.(ABSTRACT TRUNCATED AT 250 WORDS)

Desethylamiodarone is a noncompetitive inhibitor of the binding of thyroid hormone to the thyroid hormone beta 1-receptor protein

It has been hypothesized that amiodarone (A), a potent antiarrythmic and antianginal drug, induces a local hypothyroid-like condition in extrathyroidal tissues. This might be related to competitive antagonism of A for the thyroid hormone receptor reported in some studies but denied in others. These conflicting results are presumably due to the poor solubility of A in a hydrophilic environment. We, therefore, studied the effect of the drug and its major metabolite, desethylamiodarone (DEA), on the in vitro binding of thyroid hormone (T3) to its receptor protein using the rat beta 1-thyroid hormone receptor expressed in Escherichia coli. A and DEA stayed in solution up to 10(-4) M when 0.05% Triton X-100 was added to the incubation buffer, as evidenced by a recovery of 80-90% for both chemicals, as measured by HPLC. DEA, but not A, had a clear inhibitory effect on the binding of T3 to its receptor (IC50, 1-3 x 10(-5) M). Scatchard analysis in the presence of DEA demonstrated a dose-dependent decrease in the Ka as well as the maximum binding capacity. Lineweaver-Burke analysis indicated noncompetitive inhibition. Plots of the intercepts of Lineweaver-Burke plots vs. DEA concentration were linear (y = 0.334 + 0.098x), giving a Ki of 30 microM for the binding of DEA to the occupied receptor. Plots of the slopes vs. inhibitor concentration were parabolic (y = 3.01 + 0.06x + 0.16x2), indicating a progressively stronger effect of DEA on the unoccupied receptor as concentrations rise. This preference for the unoccupied receptor is reflected in experiments that show a progressive loss of T3 binding when the receptor was incubated for increasing periods with DEA before adding T3. We conclude that DEA is a noncompetitive inhibitor of the binding of T3 to the beta 1-thyroid hormone receptor protein, interacting preferably with the unoccupied T3 receptor.

Amiodarone-induced hypercholesterolemia is associated with a decrease in liver LDL receptor mRNA

Amiodarone decreases plasma and tissue triiodothyronine (T3) and increases plasma cholesterol levels resembling changes seen during hypothyroidism. To elucidate the mechanism of amiodarone-induced hypercholesterolemia we investigated gene expression of three key proteins in cholesterol metabolism (cholesterol 7 alpha-hydroxylase, LDL receptor, HMG-CoA reductase) in livers of rats. Animals were treated with amiodarone or propylthiouracil (to induce mild hypothyroidism). The LDL receptor mRNA was downregulated (approximately 50%) in both amiodarone-treated and hypothyroid animals, while the other mRNA remained unchanged after 14-day treatment. The results suggest that amiodarone-induced hypercholesterolemia is associated with decreased LDL receptor mRNA levels.

Expression of a functional thyroglobulin fragment in a baculovirus system

The synthesis is described of an N-terminal thyroglobulin (Tg) polypeptide of 27 kDa, which is capable of hormonogenesis, in a baculovirus system. This polypeptide was made using a 657 bp Tg cDNA cloned from human thyroid RNA by a polymerase chain reaction method. The cDNA contained the information for the Tg signal peptide, the N-terminally located site for thyroid hormone formation and, at the 3' end, a sequence coding for six histidine residues. The fragments produced were purified using a nickel-nitrilotriacetic acid column using these six histidine residues. The products were analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and showed two glycosylated fragments of 32 and 34 kDa, both of which started with asparagine. Iodination of the fragments with lactoperoxidase in vitro resulted in the formation of thyroxine (T4). The formation rate of T4 in the fragments was about five times lower than that of the mature Tg dimer of 660 kDa, but ten times more rapid than in bovine serum albumin under the same conditions.

CAAT/enhancer binding protein is able to bind to ATF/CRE elements

The transcription factor C/EBP is known to be able to bind to two different classes of sites, a CAAT-box and one present in a number of viral enhancers. In this paper we show using band-shift assays, methylation interference and footprinting that C/EBP is also able to bind with high affinity to ATF/CRE sites. Competition with mutant ATF sites and methylation interference indicate that C/EBP may be able to bind to the ATF/CRE sites by virtue of their homology to the enhancer core elements. Furthermore, we show that C/EBP is able to direct transcription from this site in transient transfection experiments and that mutations in the ATF binding site that impair DNA binding also effect the ability of C/EBP to stimulate transcription.

The progesterone receptor can regulate transcription in the absence of a functional TATA box element

We have investigated the importance of the TATA box element in the induction of transcription by the progesterone receptor. Transcription was analyzed from promoters containing a steroid response element upstream of a wild-type or mutated TATA box. Mutation of the TATA box resulted in a loss of correctly initiated transcripts and abolished binding of TATA factor to the TATA box in vitro but did not inhibit transcriptional activation by the progesterone receptor. Thus we conclude that the receptor is able to stimulate the rate of transcription in the absence of a functional TATA box.

Tissue-specific differences in the binding of nuclear proteins to a CCAAT motif in the promoter of the androgen-regulated C3 gene

The expression of the gene for the C3 polypeptide is confined to the ventral prostate of the male rat and is regulated by androgens. To study the mechanism of this tissue-specific and hormone-dependent regulation we have used DNase-I footprinting and band-shift assays to locate binding sites for nuclear proteins isolated from different tissues. In this paper we present evidence that there are tissue-specific differences in the nuclear proteins that are able to bind to a CCAAT motif and a nuclear factor-I consensus that are present in the promoter of the rat C3 gene. Using competition assays and heat denaturation we show that the CAAT box/enhancer binding protein itself may be one of the transcription factors involved.

Turnover products of the apo very low density lipoprotein II messenger RNA from chicken liver

The mature apo Very Low Density Lipoprotein II (apo VLDLII) mRNA appears in chicken liver within a few hours after estrogen administration. Apart from this mRNA species, shorter RNA molecules hybridizing to apo VLDLII sequences have been detected in rooster liver upon estrogen stimulation. These molecules are present in the non-polyadenylated fraction of the total cellular- and polysomal RNA. Northern blotting and electron microscopy of R-loops were employed to show that these shorter RNA molecules are truncated at their 3'-end. The 3'-termini were further characterized by nuclease S1 analyses, and are located predominantly in the 3' untranslated region of the mRNA. Using a secondary structure model (Shelness and Williams, J. Biol. Chem. 260, 8637-8646, 1985), we show that the 3' termini map mainly in unpaired regions of the structure.

Estrogen-inducible binding of a nuclear factor to the vitellogenin upstream region

The estrogen-dependent binding of a protein to the upstream region of the chicken vitellogenin gene was detected by using in vivo dimethyl sulfate, genomic DNase I, and in vitro exonuclease III footprinting. The site is located between base pairs -848 and -824, and its sequence resembles that of the nuclear factor I binding site. The results suggest that a nuclear factor binding to this site is involved in the regulation of the vitellogenin gene.