Thyroid: biological actions of 'nonclassical' thyroid hormones.

Area of Science:

• Endocrinology
• Molecular Biology
• Cell Biology

Background:

• Thyroid hormones (THs) regulate cellular functions via genomic and nongenomic pathways.
• Nongenomic actions of THs occur at various cellular locations, including the plasma membrane and organelles.
• Peripheral TH metabolism yields nonclassical THs, previously considered inactive.

Purpose of the Study:

• To review the current understanding of nonclassical thyroid hormone actions.
• To discuss the biological significance of endogenous TH metabolites.
• To explore the role of nonclassical THs in organisms from nonmammals to humans.

Main Methods:

• Literature review of current research on nonclassical THs.
• Analysis of studies detailing TH metabolite effects.
• Synthesis of findings on TH actions across different species.

Main Results:

• Nonclassical THs exhibit significant biological effects, challenging their prior classification as inactive.
• These metabolites modulate membrane receptors, mitochondrial functions, kinases, and deacetylases.
• Evidence suggests diverse roles for nonclassical THs in modulating thyroid-related effects.

Conclusions:

• Nonclassical THs are biologically active and play crucial roles in cellular regulation.
• Understanding these metabolites opens new avenues for research into thyroid hormone action.
• Nonclassical THs contribute to thyroid-related effects across a spectrum of biological complexity.