THYROTROPIN RECEPTOR TRANSCRIPTS IN HUMAN ADIPOSE-TISSUE

Thyroid associated ophthalmopathy (TAO) is generally considered to hav e an autoimmune pathogenesis but the target antigen has yet to be iden tified. It is most frequently associated with Graves' disease and ther e is some logic in assuming that the same antigen, the thyrotropin rec eptor (TSHR), is the common link. Previous studies, mostly PCR based, aimed at investigating TSHR transcripts in the orbit, have yielded con flicting results, although there is circumstantial evidence for their presence in orbital fat. In this study, we have examined adult human a dipose and muscle tissues from various locations, initially by PCR and subsequently by northern blot. We obtained the expected 610bp product in normal intestinal and orbital fat but not skeletal muscle, followi ng two rounds of PCR amplification but only when reverse transcription used a TSHR specific primer. In northern blots, despite loading all o f the RNA obtained from total normal orbital fat contents, TSHR transc ripts were at the limit of detection and similarly for large samples o f intestinal fat. The exception was RNA obtained from TAO orbital fat, in which TSHR transcripts of 4.6 and 1.7kb were clearly visible, as i n the thyroid. We conclude that normal adult adipose tissues contain l ow levels of TSHR transcripts. In TAO, TSHR transcripts are elevated p robably due to an increased number of cells, in particular of preadipo cytes in orbital adipose tissue.