Deiodinases: keeping the thyroid hormone supply in balance
- Department of Molecular and Clinical Endocrinology and Oncology, University of Naples ‘Federico II’, Naples 80131, Italy
- (Correspondence should be addressed to D Salvatore; Email: domsalva{at}unina.it)
Thyroid hormones (TH) are iodinated compounds that are required for the normal growth, development and function of nearly all vertebrate tissues. They do this by modulating the expression of many genes that are tightly regulated in a specific tissue- and time-dependent fashion. The primary mechanism of TH action involves the binding of 3,5,3′-triiodothyronine (T3) to its nuclear receptors in the context of regulatory TH response elements in target genes.
In humans, the thyroid produces the pro-hormone thyroxine (T4), and only about 20% of the active hormone, T3. T4 is largely inactive until it is deiodinated to T3 by the type 1 (D1) or 2 (D2) deiodinase. This reaction produces about 80% of the T3 present in the circulation in healthy subjects. A third deiodinase, D3, exerts an opposing function, i.e. it catalyzes inner ring deiodination, thereby inactivating T4 and T3. Given these functions, D3 is considered the major physiological inactivator and terminator of TH action at peripheral level.
Why should we care about deiodinases and why they are so important? The role of …
