Thyrotropin Receptor Transcripts in Human Adipose Tissue

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Abstract
Thyroid associated ophthalmopathy (TAO) is generally considered to have an autoimmune pathogenesis but the target antigen has yet to be identified. It is most frequently associated with Graves’ disease and there is some logic in assuming that the same antigen, the thyrotropin receptor (TSHR), is the common link. Previous studies, mostly PCR based, aimed at investigating TSHR transcripts in the orbit, have yielded conflicting results, although there is circumstantial evidence for their presence in orbital fat. In this study, we have examined adult human adipose 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, following two rounds of PCR amplification but only when reverse transcription used a TSHR specific primer. In northern blots, despite loading all of the RNA obtained from total normal orbital fat contents, TSHR transcripts were at the limit of detection and similarly for large samples of 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 in the thyroid. We conclude that normal adult adipose tissues contain low levels of TSHR transcripts. In TAO, TSHR transcripts are elevated probably due to an increased number of cells, in particular of preadipocytes in orbital adipose tissue.