How do thyroid hormones (T3 & T4) exert their action? Which receptors do thyroid hormones act on?

  • Thyroid hormones exert their actions via intranuclear receptors
  • Enter cells via membrane transporter proteins
  • Bind to intranuclear receptors causing activation and conformation changes
  • Allows binding of the complex to specific “thyroid responsive” sections of DNA, leading to DNA transcription and gene expression

There are to major subtypes of thyroid receptors (TR-α and TR-β) each with their own isoforms:

TR-α1
  • Widely expressed
  • Particularly high expression in cardiac and skeletal muscle
TR-α2
  • Widely expressed
  • Unable to bind hormone
  • Function unclear
TR-β1
  • Brain, liver and kidney
TR-β2
  • Hypothalamus and pituitary