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Expression of the alpha 1, alpha 2, and beta 1 T3-receptor mRNAs in the fasted rat measured using competitive PCR
O Bakker1, H Razaki, J de Jong
1Department of Endocrinology, Academic Medical Centre, Amsterdam, The Netherlands.
Abstract:
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.
Insights
Fasting increases alpha 2 thyroid hormone receptor (TR) mRNA in rat liver, but not alpha 1 or beta 1 isoforms. Heart TR isoform mRNA levels remained unchanged during fasting.
Area of Science:
- Endocrinology
- Molecular Biology
- Gene Expression Regulation
Background:
- Fasting impacts thyroid hormone receptor (TR) binding capacity and gene responsiveness.
- Changes in TR isoform mRNA expression may explain altered thyroid hormone sensitivity during fasting.
Purpose of the Study:
- To quantify alpha 1, alpha 2, and beta 1 TR isoform mRNA levels in the liver and heart of fasted rats.
- To investigate the role of TR isoform mRNA changes in mediating fasting-induced alterations in thyroid hormone action.
Main Methods:
- Utilized a competitive PCR method for precise mRNA quantification.
- Designed isoform-specific competitors to ensure similar amplification efficiencies.
- Analyzed mRNA levels in liver and heart tissues from rats subjected to a 48-hour fasting period.
Main Results:
- Fasting led to a threefold increase in alpha 2 TR mRNA levels in rat liver (P < 0.002).
- No significant changes were observed in alpha 1 or beta 1 TR mRNA levels in the liver.
- No alterations in any TR isoform mRNA levels were detected in the heart.
Conclusions:
- Fasting specifically upregulates alpha 2 TR mRNA in the liver, suggesting a potential role in adaptive responses.
- The lack of change in other TR isoforms and in the heart indicates tissue-specific regulation of TR expression during fasting.
- These findings contribute to understanding the molecular mechanisms underlying thyroid hormone adaptation to nutrient deprivation.
