Deiodinases and the Metabolic Code for Thyroid Hormone Action.
Level 5 - mechanism / opinion, no new human data
Narrative review synthesizing physiological and mechanistic data without primary clinical trial or cohort data.
PubMed 33720335 · doi:10.1210/endocr/bqab059
What was done
This narrative review synthesizes evidence from cell, animal, and human models regarding the role of iodothyronine deiodinases in regulating thyroid hormone signaling. It outlines the distinct roles of type 2 deiodinase (D2) and type 3 deiodinase (D3) in metabolically relevant tissues such as brown adipose tissue, skeletal muscle, and liver during development and in adulthood.
What was found
The abstract reports mechanistic pathways and directions of effect without quantitative metrics. D2 converts thyroxine (T4) to 3,5,3'-triiodothyronine (T3), is induced by cyclic AMP, and is associated with PGC-1 expression and increased energy expenditure. D3 inactivates T3 to 3,3'-diiodothyronine (T2) and T4 to reverse T3 (rT3), is induced by hypoxia-inducible factor 1α, and dampens T3 signaling and metabolic rate.
Why it matters
It details how local, tissue-specific enzymatic activation and inactivation of thyroid hormones regulate cellular metabolism beyond simple circulating hormone concentrations. This paradigm explains how intracellular thyroid signaling dynamically modulates metabolic pathways in health and disease.
Limits
The abstract describes a narrative review without systematic search criteria, meta-analytic pooling, or primary experimental data. No sample sizes, patient populations, or quantitative effect sizes are provided.
Cited by
- context Reverse T3 is produced by the body and acts as a physiological brake when active T3 levels are elevated.