Localization and Clinical Significance of Thyrotropin Receptor mRNA Expression in Orbital Fat and Eye Muscle Tissues from Patients with Thyroid-Associated Ophthalmopathy

We have studied the cellular localization of thyrotropin receptor (TSH—R) mRNA in orbital fat and extraocular muscle tissues from patients with thyroid-associated ophthalmopathy (TAO) using Northern blot, reverse transcriptase polymerase chain reaction (RT—PCR), and in situ hybridization, and we correlated the findings with clinical estimates of ophthalmopathy. Although we failed to detect TSH—R mRNA in orbital tissues by Northern blot, TSH—R cDNA was amplified in orbital fat tissue from 13 of 25 patients with TAO and from 2 of 4 control subjects, in eye muscle tissue from 2 out of 7 patients with TAO, and in cultured orbital fibroblasts and subcutaneous fibroblasts from TAO patients. In situ hybridization showed that TSH—R mRNA was detected in cultured orbital fibroblasts as well as skin fibroblasts obtained from the patient. Furthermore, the expression of TSH—R mRNA in orbital fat tissue from patients with TAO significantly correlated with the orbital fat volume and the severity of ophthalmopathy, especially the extent of eye muscle dysfunction. These results suggest that the expression of TSH—R in the orbit, especially fibroblasts, may play a role in the pathogenesis and clinical manifestations of the ophthalmopathy in patients with TAO, although a secondary effect, involving fibroblasts in TAO is also possible.