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Action of thyroid hormone in brain.
1Instituto de Investigaciones Biomedicas Alberto Sols, Consejo Superior de Investigaciones Cientfficas, Universidad Autónoma de Madrid, Spain. jbernal@iib.uam.es
Journal of Endocrinological Investigation
|April 9, 2002
Summary
Thyroid hormone is crucial for brain development, impacting gene expression and neuronal function. Paradoxically, T3 receptor knockout mice show minimal central nervous system effects despite severe hypothyroidism impacts.
Area of Science:
- Neuroscience
- Endocrinology
- Developmental Biology
Background:
- Thyroid hormone is essential for mammalian brain development, with severe neonatal hypothyroidism causing irreversible structural and functional deficits.
- Brain thyroid hormone levels are tightly regulated by deiodinase enzymes (types II and III) and mediated by nuclear receptors, primarily in neurons.
Purpose of the Study:
- To investigate the role of thyroid hormone and its nuclear receptors in brain development.
- To resolve the paradox between the severe effects of hypothyroidism and the minimal CNS phenotype in T3 receptor knockout mice.
Main Methods:
- Analysis of thyroid hormone metabolism in the brain, focusing on deiodinase activity and localization.
- Investigation of thyroid hormone receptor expression and function in neuronal and glial cells.
- Phenotypic analysis of T3 receptor null-mutant mice to assess central nervous system development and function.
Main Results:
- Thyroid hormone accelerates developmental gene expression changes in the brain.
- Type II deiodinase converts T4 to T3 in glial cells, while Type III deiodinase degrades T3 in neurons.
- T3 receptors regulate genes involved in myelination, mitochondrial function, neurotrophins, and intracellular signaling.
Conclusions:
- Despite the critical role of thyroid hormone in brain development, T3 receptor knockout mice exhibit a surprisingly mild CNS phenotype.
- Understanding the discrepancy between hypothyroidism effects and receptor knockout phenotypes is key to elucidating thyroid hormone's precise role in brain development and function.