HOW IS THYROGLOBULIN  PROCESSED  IN THE THYROID?   8/7/2017

HOW IS THYROGLOBULIN  PROCESSED  IN THE THYROID?   8/7/2017

QUESTION- I am a second year medical student and I just had a question about thyroglobulin.After T3 and T4 are cleaved off by lysosomes, what happens to the remaining structure? Does it get recycled through the RER to become thyroglobulin again or ? Thank you so much for your time.   Stephanie Tan=

RESPONSE--Hi StephaniE.   Iodinated   thyroglobulin undergoes intralysosomal degradation that may involve two main steps: an early  and selective  proteolytic cleavage leading to the release of T3 and  T4, and a delayed  nonselective proteolysis  for extensive degradation of the remaining peptides of Tg.

Tg molecules with no or low hormone content present in early apical endosomes are recycled back to the follicular lumen. Some Tg molecules are also transported to the basolateral membrane via transcytotic vesicles (this process accounts for the presence of non-iodinated Tg in the plasma).

This is a very simplified answer to your question.  You can find more explanation and related publications on the mechanisms of Tg  endocytosis in the chapter Thyroid hormone synthesis and secretion  in www.Thyroidmanager.org. Hoping this will help you.

Françoise Miot PhD, IRIBHM, Université Libre de Bruxelles