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Papers by Kevin Cua
Thyroid Official Journal of the American Thyroid Association, Dec 1, 1999
We report an improved heterologous radioimmunoassay (RIA) for the measurement of thyrotropin (TSH... more We report an improved heterologous radioimmunoassay (RIA) for the measurement of thyrotropin (TSH) in mouse serum. The assay components are: antirat thyrotropin (rTSH) serum from the National Hormone and Pituitary Program, a commercial [125I]-labeled rTSH and mouse thyrotropin (mTSH) serum standards produced by dilution of a serum pool from hypothyroid mice with high TSH with a serum pool from mice treated with excess levothyroxine (LT4) (mTSH-0). Sensitivity was increased by reducing the amount of antibody and tracer and by taking advantage of the disequilibrium technique. Accuracy was greatly improved by the preparation of mouse serum TSH standards. TSH in serial dilutions of individual mice with high TSH of different etiologies paralleled the mTSH standard curve but not that of rTSH or a crude mouse TSH/luteinizing hormone (LH) reference preparation. The high-mTSH-serum standard contained 20 mU TSH per milliliter, measured in a bioassay utilizing a cell line stably transfected with human TSH receptor cDNA, and a relative TSH concentration of 40 ng/mL. The sensitivity of the RIA is 0.01 to 0.02 ng/mL, depending on the quality of the tracer and the preparation of mTSH-0 serum. The intra-assay and interassay coefficients of variations were, respectively: 16% and 27% at 0.04 ng/mL; 6.3% and 8.2% at 0.4 ng/mL; 5.4% and 9.8% at 1.7 ng/mL; 10% and 24% at 4.0 ng/mL. The mean TSH concentration in serum of 60-80-day-old male mice was four-fold higher than that in females of the same age. The assay was able to distinguish differences in serum TSH concentrations in five different strains of mice. Baseline serum TSH concentrations (mean +/- SD) of 70-day-old male mice were: 0.143 +/- 0.065 ng/mL in the CD-1 strain; 0.229 +/- 0.042 ng/mL in C57BL/6 mice; 0.084 +/- 0.017 ng/mL in SWR/J mice; 0.133 +/- 0.057 ng/mL in NOD SCID mice, and 0.266 +/- 0.122 ng/mL in FVB mice. Mean serum thyroxine (T4) concentrations were also significantly different among the mouse strains but did not correlate with the serum TSH level. Administration of levotriiodothyronine (LT3) suppressed the serum TSH to a greater degree in mice with higher baseline TSH values. Suppression of the thyroidal radioiodide uptake with LT3 correlated with that of serum TSH.
American Journal of Physiology - Endocrinology And Metabolism, 2002
We investigated the effect of thyroid hormone (TH) receptor (TR)α and -β isoforms in TH action in... more We investigated the effect of thyroid hormone (TH) receptor (TR)α and -β isoforms in TH action in the heart. Noninvasive echocardiographic measurements were made in mice homozygous for disruption of TRα (TRα0/0) or TRβ (TRβ−/−). Mice were studied at baseline, 4 wk after TH deprivation (using a low-iodine diet containing propylthiouracil), and after 4-wk treatment with TH. Baseline heart rates (HR) were similar in wild-type (WT) and TRα0/0 mice but were greater in TRβ−/− mice. With TH deprivation, HR decreased 49% in WT and 37% in TRβ−/− mice and decreased only 5% in TRα0/0 mice from baseline, whereas HR increased in all genotypes with TH treatment. Cardiac output (CO) and cardiac index (CI) in WT mice decreased (−31 and −32%, respectively) with TH deprivation and increased (+69 and +35%, respectively) with TH treatment. The effects of CO and CI were blunted with TH withdrawal in both TRα0/0 (+8 and −2%, respectively) and TRβ−/− mice (−17 and −18%, respectively). Treatment with TH re...
Thyroid, 1999
We report an improved heterologous radioimmunoassay (RIA) for the measurement of thyrotropin (TSH... more We report an improved heterologous radioimmunoassay (RIA) for the measurement of thyrotropin (TSH) in mouse serum. The assay components are: antirat thyrotropin (rTSH) serum from the National Hormone and Pituitary Program, a commercial [125I]-labeled rTSH and mouse thyrotropin (mTSH) serum standards produced by dilution of a serum pool from hypothyroid mice with high TSH with a serum pool from mice treated with excess levothyroxine (LT4) (mTSH-0). Sensitivity was increased by reducing the amount of antibody and tracer and by taking advantage of the disequilibrium technique. Accuracy was greatly improved by the preparation of mouse serum TSH standards. TSH in serial dilutions of individual mice with high TSH of different etiologies paralleled the mTSH standard curve but not that of rTSH or a crude mouse TSH/luteinizing hormone (LH) reference preparation. The high-mTSH-serum standard contained 20 mU TSH per milliliter, measured in a bioassay utilizing a cell line stably transfected with human TSH receptor cDNA, and a relative TSH concentration of 40 ng/mL. The sensitivity of the RIA is 0.01 to 0.02 ng/mL, depending on the quality of the tracer and the preparation of mTSH-0 serum. The intra-assay and interassay coefficients of variations were, respectively: 16% and 27% at 0.04 ng/mL; 6.3% and 8.2% at 0.4 ng/mL; 5.4% and 9.8% at 1.7 ng/mL; 10% and 24% at 4.0 ng/mL. The mean TSH concentration in serum of 60-80-day-old male mice was four-fold higher than that in females of the same age. The assay was able to distinguish differences in serum TSH concentrations in five different strains of mice. Baseline serum TSH concentrations (mean +/- SD) of 70-day-old male mice were: 0.143 +/- 0.065 ng/mL in the CD-1 strain; 0.229 +/- 0.042 ng/mL in C57BL/6 mice; 0.084 +/- 0.017 ng/mL in SWR/J mice; 0.133 +/- 0.057 ng/mL in NOD SCID mice, and 0.266 +/- 0.122 ng/mL in FVB mice. Mean serum thyroxine (T4) concentrations were also significantly different among the mouse strains but did not correlate with the serum TSH level. Administration of levotriiodothyronine (LT3) suppressed the serum TSH to a greater degree in mice with higher baseline TSH values. Suppression of the thyroidal radioiodide uptake with LT3 correlated with that of serum TSH.
Proceedings of the National Academy of Sciences, 2001
Only three of the four thyroid hormone receptor (TR) isoforms, ␣1, 1, and 2, bind thyroid hormo... more Only three of the four thyroid hormone receptor (TR) isoforms, ␣1, 1, and 2, bind thyroid hormone (TH) and are considered to be true TRs. TR␣2 binds to TH response elements on DNA, but its role in vivo is still unknown. We produced mice completely deficient in TR␣ (TR␣ o/o) that maintain normal serum thyroid-stimulating hormone (TSH) concentration despite low serum thyroxine (T4), suggesting increased sensitivity to TH. We therefore examined the effects of TH (L-3,3,5triiodothyronine, L-T3) given to TH-deprived and to intact TR␣ o/o mice. Controls were wild-type (WT) mice of the same strain and mice resistant to TH due to deficiency in TR (TR ؊/؊). In liver, T3 produced significantly greater responses in TR␣ o/o and smaller responses in TR ؊/؊ as compared with WT mice. In contrast, cardiac responses to L-T3 were absent or reduced in TR␣ o/o , whereas they were similar in WT and TR ؊/؊ mice, supporting the notion that TR␣1 is the dominant TH-dependent TR isoform in heart. 5-Triiodothyronine (L-T3) given to intact mice produced a greater suppression of serum T4 in TR␣ o/o than it did in WT mice and reduced by a greater amount the TSH response to TSH-releasing hormone. This is an in vivo demonstration that a TR deficiency can enhance sensitivity to TH. This effect is likely due to the abrogation of the constitutive ''silencing'' effect of TR␣2 in tissues expressing the TR isoforms.
Journal of Endocrinology, 2002
The maintenance of thyroid hormone (TH) homeostasis is dependent on the synthesis and secretion o... more The maintenance of thyroid hormone (TH) homeostasis is dependent on the synthesis and secretion of TH regulated by TSH. This is achieved, in turn, by the negative feedback of TH on TSH secretion and synthesis, which requires the interaction with TH receptors (TRs). Derived by alternative splicing of two gene transcription products, three TRs (TRbeta1, TRbeta2 and TRalpha1) interact with TH while another, TRalpha2, binds to DNA but not to TH. In this study we compare the results of thyroid function tests in mice with deletions of the TRalpha and TRbeta genes alone and present novel data on mice that are double homozygous and combined heterozygous. Homozygous deletions of both the TRalpha and TRbeta in the same mouse (TRalphao/o; TRbeta-/-) resulted in serum TSH values only slightly lower than those in athyreotic, Pax8 knockout mice. Whereas the absence of TRalpha alone does not cause resistance to TH, the absence of TRbeta in the presence of TRalpha results in a 205, 169, 544% increa...
General and Comparative Endocrinology, 2002
The house musk shrew Suncus murinus (Insectivora: Soricidae) has been reported as having low thyr... more The house musk shrew Suncus murinus (Insectivora: Soricidae) has been reported as having low thyroxine to 3,3'5-triiodothyronine (T(3)) converting activity in liver and kidney homogenates and was assumed to be type 1 iodothyronine deiodinase (D1)-deficient. To study whether this is due to structural abnormality of shrew D1, we cloned the cDNA and characterized the enzyme. The deduced amino acid sequence of shrew D1 was found to be highly homologous to other known D1s and the enzyme itself to have similar catalytic activity. However, unlike in other species, the D1 activity was detected only in liver. Moreover, the D1 activity in liver of the shrew was less than half of that in rat liver and its expression was not up-regulated by T(3). In contrast, a very high activity of D2 was demonstrated in brain and brown adipose tissue. The present study also revealed that the serum level of T(3) in the shrew was in the same range as these in other mammals. These results suggest that D2 contributes to the production and maintenance of T(3) levels in the house musk shrew.
Endocrinology, 1998
Thyroid hormone (TH) responsive genes can be both positively and negatively regulated by TH throu... more Thyroid hormone (TH) responsive genes can be both positively and negatively regulated by TH through receptors (TR) ␣ and  expressed in most body tissues. However, their relative roles in the regulation of specific gene expression remain unknown. The TR knockout mouse, which lacks both TR1 and TR2 isoforms, provides a model to examine the role of these receptors in mediating TH action. TR deficient (TRϪ/Ϫ) mice that show no compensatory increase in TR␣, and wild-type (TRϩ/ϩ) mice of the same strain were deprived of TH by feeding them a low iodine diet containing propylthiouracil, and were then treated with supraphysiological doses of L-T 3 (0.5, 5.5, and 25 g/day/mouse). TH deprivation alone increased the serum cholesterol concentration by 25% in TRϩ/ϩ mice and reduced it paradoxically by 23% in TRϪ/Ϫ mice. TH deprivation reduced the serum alkaline phosphatase (AP) concentration by 31% in TRϩ/ϩ mice but showed no change in the TRϪ/Ϫ mice. Treatment with L-T 3 (0.5 to 25 g/ mouse/day) caused a 57% decrease in serum cholesterol and a 231% increase in serum AP in the TRϩ/ϩ mice. The TRϪ/Ϫ mice were resistant to the L-T 3 induced changes in serum cholesterol and showed increase in AP only with the highest L-T 3 dose. Basal heart rate (HR) in TRϪ/Ϫ mice was higher than that of TRϩ/ϩ mice by 11%. HR and energy expenditure (EE) in both TRϩ/ϩ and TRϪ/Ϫ mice showed similar decreases (49 and 46%)and increases (49 and 41%) in response to TH deprivation and L-T 3 treatment, respectively. The effect of TH on the accumulation of messenger RNA (mRNA) of TH regulated liver genes was also examined. TH deprivation down regulated spot 14 (S14) mRNA and showed no change in malic enzyme (ME) mRNA in both TRϩ/ϩ and TRϪ/Ϫ mice. In contrast treatment with L-T 3 produced an increase in S14 and ME but no change in TRϪ/Ϫ mice. From these results, it can be concluded that regulation of HR and EE are independent of TR. With the exception of serum cholesterol concentration and liver ME mRNA accumulation, all other markers of TH action examined during TH deprivation exhibited the expected responses in the absence of TR. Thus, as previously shown for serum TSH, TR is not absolutely necessary for some changes typical of hypothyroidism to occur. In contrast, except for HR and EE, the full manifestation of TH-mediated action required the presence of TR.
Endocrinology, 1997
Thyroid hormone responsive genes can be both positively and negatively regulated by thyroid hormo... more Thyroid hormone responsive genes can be both positively and negatively regulated by thyroid hormone. TSH is down-regulated by thyroid hormone and rises during thyroid hormone deprivation. Because both thyroid hormone receptor (TR) ␣ and  genes are expressed in the pituitary gland, it is unclear what the relative roles of TR␣ and TR are in TSH regulation. Experiments using over expression of artificial genes have yielded conflicting results. The TR knockout mouse that lacks both TR1 and TR2 isoforms provides a model to examine the role of these receptors in TSH regulation. TR deficient (TRϪ/Ϫ) and wild-type (TRϩ/ϩ) mice of the same strain were deprived of thyroid hormone by feeding them a low iodine diet containing propylthiouracil and were then treated with different doses of L-T 3 and L-T 4. Thyroid hormone deprivation rapidly increased the serum TSH level in both TRϩ/ϩ and TRϪ/Ϫ mice, reaching a similar level in the absence of thyroid hormone. In contrast, the decline of serum TSH by treatment with both L-T 3 and L-T 4 was severely blunted in TRϪ/Ϫ mice, and full suppression was not achieved with the maximal L-T 3 dose of 25 g/day⅐mouse. These data indicate that TR is not required for the up-regulation of TSH in thyroid hormone deficiency. However, although TR␣ alone can mediate thyroid hormone induced TSH suppression, TR enhances the sensitivity of TSH down-regulation and may be essential for the complete suppression of TSH.
Endocrinology, 1997
Thyroid hormone responsive genes can be both positively and negatively regulated by thyroid hormo... more Thyroid hormone responsive genes can be both positively and negatively regulated by thyroid hormone. TSH is down-regulated by thyroid hormone and rises during thyroid hormone deprivation. Because both thyroid hormone receptor (TR) alpha and beta genes are expressed in the pituitary gland, it is unclear what the relative roles of TR alpha and TR beta are in TSH regulation. Experiments using over expression of artificial genes have yielded conflicting results. The TR beta knock-out mouse that lacks both TR beta1 and TR beta2 isoforms provides a model to examine the role of these receptors in TSH regulation. TR beta deficient (TR beta-/-) and wild-type (TR beta+/+) mice of the same strain were deprived of thyroid hormone by feeding them a low iodine diet containing propylthiouracil and were then treated with different doses of L-T3 and L-T4. Thyroid hormone deprivation rapidly increased the serum TSH level in both TR beta+/+ and TR beta-/- mice, reaching a similar level in the absence ...
Thyroid Official Journal of the American Thyroid Association, Dec 1, 1999
We report an improved heterologous radioimmunoassay (RIA) for the measurement of thyrotropin (TSH... more We report an improved heterologous radioimmunoassay (RIA) for the measurement of thyrotropin (TSH) in mouse serum. The assay components are: antirat thyrotropin (rTSH) serum from the National Hormone and Pituitary Program, a commercial [125I]-labeled rTSH and mouse thyrotropin (mTSH) serum standards produced by dilution of a serum pool from hypothyroid mice with high TSH with a serum pool from mice treated with excess levothyroxine (LT4) (mTSH-0). Sensitivity was increased by reducing the amount of antibody and tracer and by taking advantage of the disequilibrium technique. Accuracy was greatly improved by the preparation of mouse serum TSH standards. TSH in serial dilutions of individual mice with high TSH of different etiologies paralleled the mTSH standard curve but not that of rTSH or a crude mouse TSH/luteinizing hormone (LH) reference preparation. The high-mTSH-serum standard contained 20 mU TSH per milliliter, measured in a bioassay utilizing a cell line stably transfected with human TSH receptor cDNA, and a relative TSH concentration of 40 ng/mL. The sensitivity of the RIA is 0.01 to 0.02 ng/mL, depending on the quality of the tracer and the preparation of mTSH-0 serum. The intra-assay and interassay coefficients of variations were, respectively: 16% and 27% at 0.04 ng/mL; 6.3% and 8.2% at 0.4 ng/mL; 5.4% and 9.8% at 1.7 ng/mL; 10% and 24% at 4.0 ng/mL. The mean TSH concentration in serum of 60-80-day-old male mice was four-fold higher than that in females of the same age. The assay was able to distinguish differences in serum TSH concentrations in five different strains of mice. Baseline serum TSH concentrations (mean +/- SD) of 70-day-old male mice were: 0.143 +/- 0.065 ng/mL in the CD-1 strain; 0.229 +/- 0.042 ng/mL in C57BL/6 mice; 0.084 +/- 0.017 ng/mL in SWR/J mice; 0.133 +/- 0.057 ng/mL in NOD SCID mice, and 0.266 +/- 0.122 ng/mL in FVB mice. Mean serum thyroxine (T4) concentrations were also significantly different among the mouse strains but did not correlate with the serum TSH level. Administration of levotriiodothyronine (LT3) suppressed the serum TSH to a greater degree in mice with higher baseline TSH values. Suppression of the thyroidal radioiodide uptake with LT3 correlated with that of serum TSH.
American Journal of Physiology - Endocrinology And Metabolism, 2002
We investigated the effect of thyroid hormone (TH) receptor (TR)α and -β isoforms in TH action in... more We investigated the effect of thyroid hormone (TH) receptor (TR)α and -β isoforms in TH action in the heart. Noninvasive echocardiographic measurements were made in mice homozygous for disruption of TRα (TRα0/0) or TRβ (TRβ−/−). Mice were studied at baseline, 4 wk after TH deprivation (using a low-iodine diet containing propylthiouracil), and after 4-wk treatment with TH. Baseline heart rates (HR) were similar in wild-type (WT) and TRα0/0 mice but were greater in TRβ−/− mice. With TH deprivation, HR decreased 49% in WT and 37% in TRβ−/− mice and decreased only 5% in TRα0/0 mice from baseline, whereas HR increased in all genotypes with TH treatment. Cardiac output (CO) and cardiac index (CI) in WT mice decreased (−31 and −32%, respectively) with TH deprivation and increased (+69 and +35%, respectively) with TH treatment. The effects of CO and CI were blunted with TH withdrawal in both TRα0/0 (+8 and −2%, respectively) and TRβ−/− mice (−17 and −18%, respectively). Treatment with TH re...
Thyroid, 1999
We report an improved heterologous radioimmunoassay (RIA) for the measurement of thyrotropin (TSH... more We report an improved heterologous radioimmunoassay (RIA) for the measurement of thyrotropin (TSH) in mouse serum. The assay components are: antirat thyrotropin (rTSH) serum from the National Hormone and Pituitary Program, a commercial [125I]-labeled rTSH and mouse thyrotropin (mTSH) serum standards produced by dilution of a serum pool from hypothyroid mice with high TSH with a serum pool from mice treated with excess levothyroxine (LT4) (mTSH-0). Sensitivity was increased by reducing the amount of antibody and tracer and by taking advantage of the disequilibrium technique. Accuracy was greatly improved by the preparation of mouse serum TSH standards. TSH in serial dilutions of individual mice with high TSH of different etiologies paralleled the mTSH standard curve but not that of rTSH or a crude mouse TSH/luteinizing hormone (LH) reference preparation. The high-mTSH-serum standard contained 20 mU TSH per milliliter, measured in a bioassay utilizing a cell line stably transfected with human TSH receptor cDNA, and a relative TSH concentration of 40 ng/mL. The sensitivity of the RIA is 0.01 to 0.02 ng/mL, depending on the quality of the tracer and the preparation of mTSH-0 serum. The intra-assay and interassay coefficients of variations were, respectively: 16% and 27% at 0.04 ng/mL; 6.3% and 8.2% at 0.4 ng/mL; 5.4% and 9.8% at 1.7 ng/mL; 10% and 24% at 4.0 ng/mL. The mean TSH concentration in serum of 60-80-day-old male mice was four-fold higher than that in females of the same age. The assay was able to distinguish differences in serum TSH concentrations in five different strains of mice. Baseline serum TSH concentrations (mean +/- SD) of 70-day-old male mice were: 0.143 +/- 0.065 ng/mL in the CD-1 strain; 0.229 +/- 0.042 ng/mL in C57BL/6 mice; 0.084 +/- 0.017 ng/mL in SWR/J mice; 0.133 +/- 0.057 ng/mL in NOD SCID mice, and 0.266 +/- 0.122 ng/mL in FVB mice. Mean serum thyroxine (T4) concentrations were also significantly different among the mouse strains but did not correlate with the serum TSH level. Administration of levotriiodothyronine (LT3) suppressed the serum TSH to a greater degree in mice with higher baseline TSH values. Suppression of the thyroidal radioiodide uptake with LT3 correlated with that of serum TSH.
Proceedings of the National Academy of Sciences, 2001
Only three of the four thyroid hormone receptor (TR) isoforms, ␣1, 1, and 2, bind thyroid hormo... more Only three of the four thyroid hormone receptor (TR) isoforms, ␣1, 1, and 2, bind thyroid hormone (TH) and are considered to be true TRs. TR␣2 binds to TH response elements on DNA, but its role in vivo is still unknown. We produced mice completely deficient in TR␣ (TR␣ o/o) that maintain normal serum thyroid-stimulating hormone (TSH) concentration despite low serum thyroxine (T4), suggesting increased sensitivity to TH. We therefore examined the effects of TH (L-3,3,5triiodothyronine, L-T3) given to TH-deprived and to intact TR␣ o/o mice. Controls were wild-type (WT) mice of the same strain and mice resistant to TH due to deficiency in TR (TR ؊/؊). In liver, T3 produced significantly greater responses in TR␣ o/o and smaller responses in TR ؊/؊ as compared with WT mice. In contrast, cardiac responses to L-T3 were absent or reduced in TR␣ o/o , whereas they were similar in WT and TR ؊/؊ mice, supporting the notion that TR␣1 is the dominant TH-dependent TR isoform in heart. 5-Triiodothyronine (L-T3) given to intact mice produced a greater suppression of serum T4 in TR␣ o/o than it did in WT mice and reduced by a greater amount the TSH response to TSH-releasing hormone. This is an in vivo demonstration that a TR deficiency can enhance sensitivity to TH. This effect is likely due to the abrogation of the constitutive ''silencing'' effect of TR␣2 in tissues expressing the TR isoforms.
Journal of Endocrinology, 2002
The maintenance of thyroid hormone (TH) homeostasis is dependent on the synthesis and secretion o... more The maintenance of thyroid hormone (TH) homeostasis is dependent on the synthesis and secretion of TH regulated by TSH. This is achieved, in turn, by the negative feedback of TH on TSH secretion and synthesis, which requires the interaction with TH receptors (TRs). Derived by alternative splicing of two gene transcription products, three TRs (TRbeta1, TRbeta2 and TRalpha1) interact with TH while another, TRalpha2, binds to DNA but not to TH. In this study we compare the results of thyroid function tests in mice with deletions of the TRalpha and TRbeta genes alone and present novel data on mice that are double homozygous and combined heterozygous. Homozygous deletions of both the TRalpha and TRbeta in the same mouse (TRalphao/o; TRbeta-/-) resulted in serum TSH values only slightly lower than those in athyreotic, Pax8 knockout mice. Whereas the absence of TRalpha alone does not cause resistance to TH, the absence of TRbeta in the presence of TRalpha results in a 205, 169, 544% increa...
General and Comparative Endocrinology, 2002
The house musk shrew Suncus murinus (Insectivora: Soricidae) has been reported as having low thyr... more The house musk shrew Suncus murinus (Insectivora: Soricidae) has been reported as having low thyroxine to 3,3'5-triiodothyronine (T(3)) converting activity in liver and kidney homogenates and was assumed to be type 1 iodothyronine deiodinase (D1)-deficient. To study whether this is due to structural abnormality of shrew D1, we cloned the cDNA and characterized the enzyme. The deduced amino acid sequence of shrew D1 was found to be highly homologous to other known D1s and the enzyme itself to have similar catalytic activity. However, unlike in other species, the D1 activity was detected only in liver. Moreover, the D1 activity in liver of the shrew was less than half of that in rat liver and its expression was not up-regulated by T(3). In contrast, a very high activity of D2 was demonstrated in brain and brown adipose tissue. The present study also revealed that the serum level of T(3) in the shrew was in the same range as these in other mammals. These results suggest that D2 contributes to the production and maintenance of T(3) levels in the house musk shrew.
Endocrinology, 1998
Thyroid hormone (TH) responsive genes can be both positively and negatively regulated by TH throu... more Thyroid hormone (TH) responsive genes can be both positively and negatively regulated by TH through receptors (TR) ␣ and  expressed in most body tissues. However, their relative roles in the regulation of specific gene expression remain unknown. The TR knockout mouse, which lacks both TR1 and TR2 isoforms, provides a model to examine the role of these receptors in mediating TH action. TR deficient (TRϪ/Ϫ) mice that show no compensatory increase in TR␣, and wild-type (TRϩ/ϩ) mice of the same strain were deprived of TH by feeding them a low iodine diet containing propylthiouracil, and were then treated with supraphysiological doses of L-T 3 (0.5, 5.5, and 25 g/day/mouse). TH deprivation alone increased the serum cholesterol concentration by 25% in TRϩ/ϩ mice and reduced it paradoxically by 23% in TRϪ/Ϫ mice. TH deprivation reduced the serum alkaline phosphatase (AP) concentration by 31% in TRϩ/ϩ mice but showed no change in the TRϪ/Ϫ mice. Treatment with L-T 3 (0.5 to 25 g/ mouse/day) caused a 57% decrease in serum cholesterol and a 231% increase in serum AP in the TRϩ/ϩ mice. The TRϪ/Ϫ mice were resistant to the L-T 3 induced changes in serum cholesterol and showed increase in AP only with the highest L-T 3 dose. Basal heart rate (HR) in TRϪ/Ϫ mice was higher than that of TRϩ/ϩ mice by 11%. HR and energy expenditure (EE) in both TRϩ/ϩ and TRϪ/Ϫ mice showed similar decreases (49 and 46%)and increases (49 and 41%) in response to TH deprivation and L-T 3 treatment, respectively. The effect of TH on the accumulation of messenger RNA (mRNA) of TH regulated liver genes was also examined. TH deprivation down regulated spot 14 (S14) mRNA and showed no change in malic enzyme (ME) mRNA in both TRϩ/ϩ and TRϪ/Ϫ mice. In contrast treatment with L-T 3 produced an increase in S14 and ME but no change in TRϪ/Ϫ mice. From these results, it can be concluded that regulation of HR and EE are independent of TR. With the exception of serum cholesterol concentration and liver ME mRNA accumulation, all other markers of TH action examined during TH deprivation exhibited the expected responses in the absence of TR. Thus, as previously shown for serum TSH, TR is not absolutely necessary for some changes typical of hypothyroidism to occur. In contrast, except for HR and EE, the full manifestation of TH-mediated action required the presence of TR.
Endocrinology, 1997
Thyroid hormone responsive genes can be both positively and negatively regulated by thyroid hormo... more Thyroid hormone responsive genes can be both positively and negatively regulated by thyroid hormone. TSH is down-regulated by thyroid hormone and rises during thyroid hormone deprivation. Because both thyroid hormone receptor (TR) ␣ and  genes are expressed in the pituitary gland, it is unclear what the relative roles of TR␣ and TR are in TSH regulation. Experiments using over expression of artificial genes have yielded conflicting results. The TR knockout mouse that lacks both TR1 and TR2 isoforms provides a model to examine the role of these receptors in TSH regulation. TR deficient (TRϪ/Ϫ) and wild-type (TRϩ/ϩ) mice of the same strain were deprived of thyroid hormone by feeding them a low iodine diet containing propylthiouracil and were then treated with different doses of L-T 3 and L-T 4. Thyroid hormone deprivation rapidly increased the serum TSH level in both TRϩ/ϩ and TRϪ/Ϫ mice, reaching a similar level in the absence of thyroid hormone. In contrast, the decline of serum TSH by treatment with both L-T 3 and L-T 4 was severely blunted in TRϪ/Ϫ mice, and full suppression was not achieved with the maximal L-T 3 dose of 25 g/day⅐mouse. These data indicate that TR is not required for the up-regulation of TSH in thyroid hormone deficiency. However, although TR␣ alone can mediate thyroid hormone induced TSH suppression, TR enhances the sensitivity of TSH down-regulation and may be essential for the complete suppression of TSH.
Endocrinology, 1997
Thyroid hormone responsive genes can be both positively and negatively regulated by thyroid hormo... more Thyroid hormone responsive genes can be both positively and negatively regulated by thyroid hormone. TSH is down-regulated by thyroid hormone and rises during thyroid hormone deprivation. Because both thyroid hormone receptor (TR) alpha and beta genes are expressed in the pituitary gland, it is unclear what the relative roles of TR alpha and TR beta are in TSH regulation. Experiments using over expression of artificial genes have yielded conflicting results. The TR beta knock-out mouse that lacks both TR beta1 and TR beta2 isoforms provides a model to examine the role of these receptors in TSH regulation. TR beta deficient (TR beta-/-) and wild-type (TR beta+/+) mice of the same strain were deprived of thyroid hormone by feeding them a low iodine diet containing propylthiouracil and were then treated with different doses of L-T3 and L-T4. Thyroid hormone deprivation rapidly increased the serum TSH level in both TR beta+/+ and TR beta-/- mice, reaching a similar level in the absence ...