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Quantitation of beta 1 triiodothyronine receptor mRNA in human tissues by competitive reverse transcription
S Meier-Heusler1, A Pernin, H Liang
1Thyroid Unit, University Hospital Geneva, Switzerland.
Abstract:
Thyroid hormones act by binding to nuclear receptor proteins, the thyroid hormone receptors (TR) alpha and beta. Data from cell culture and animal studies indicate that TR expression may be regulated to modulate target organ responsiveness to thyroid hormone. To investigate whether such adaptive changes in TR expression occur in humans, we determined the mRNA levels of the hTR beta 1 in various thyroid states. Patients with overt hypo- or hyperthyroidism were enrolled in the study. Total RNA was isolated from peripheral blood mononuclear cells and hTR beta 1 mRNA levels determined by quantitative competitive reverse transcription PCR. For comparison, hTR beta 1 mRNA levels were determined in lymphocytes and normal thyroid tissue of euthyroid patients. Human TR beta 1 mRNA levels in lymphocytes were 1.8 +/- 0.4, 1.9 +/- 0.5, 1.1 +/- 0.4 10(-18) mol/microgram RNA in hypo-, eu- and hyperthyroid patients, respectively, corresponding to an estimated 0.5 - 2 molecules per cell. Although the mean hTR beta 1 mRNA levels were 40% lower in hyperthyroid than in euthyroid subjects, this difference did not reach statistical significance. Similar levels of hTR beta 1 mRNA levels were detected in thyroid gland from euthyroid patients. In summary, we developed an assay for the quantitative determination of hTR beta 1 mRNA levels in small human tissue samples, containing as little as 50 ng of total RNA. Absolute hTR beta 1 mRNA levels are very low with an estimated one molecule of mRNA being present in a mononuclear blood cell or thyrocyte. No up-regulation of hTR beta 1 was seen in hypothyroid relative to euthyroid patients. However, there is a non-significant trend towards a down-regulation of hTR beta 1 mRNA levels in hyperthyroid patients.
Insights
Thyroid hormone receptor beta 1 (hTR beta 1) mRNA levels were measured in human blood cells across different thyroid states. Results showed very low hTR beta 1 levels, with no significant changes in hypothyroidism or hyperthyroidism.
Area of Science:
- Endocrinology
- Molecular Biology
- Genetics
Background:
- Thyroid hormones regulate cellular functions via nuclear thyroid hormone receptors (TR) alpha and beta.
- TR expression modulation is a potential mechanism for adapting target organ responsiveness to thyroid hormones.
- Investigating human TR expression changes in thyroid dysfunction is crucial.
Purpose of the Study:
- To determine human thyroid hormone receptor beta 1 (hTR beta 1) mRNA levels in various thyroid states.
- To assess if hTR beta 1 expression is adaptively regulated in human hypo- and hyperthyroidism.
- To establish a method for quantifying hTR beta 1 mRNA in limited human tissue samples.
Main Methods:
- Quantitative competitive reverse transcription PCR was used to measure hTR beta 1 mRNA levels.
- Total RNA was isolated from peripheral blood mononuclear cells (PBMCs) of hypo-, eu-, and hyperthyroid patients.
- hTR beta 1 mRNA levels were also assessed in lymphocytes and thyroid tissue from euthyroid individuals.
Main Results:
- Absolute hTR beta 1 mRNA levels were found to be very low, approximately one molecule per cell in PBMCs and thyrocytes.
- No significant up-regulation of hTR beta 1 mRNA was observed in hypothyroid patients compared to euthyroid controls.
- A non-significant trend towards down-regulation of hTR beta 1 mRNA was noted in hyperthyroid patients.
Conclusions:
- A sensitive assay for quantifying hTR beta 1 mRNA in small human samples was developed.
- Human TR beta 1 mRNA levels are inherently low in mononuclear blood cells and thyroid cells.
- Adaptive regulation of hTR beta 1 mRNA levels in response to altered thyroid states in humans was not significantly demonstrated in this study.