Study on the Pathogenesis of Graves' Ophthalmopathy using 3T3-L1 Cells Which Express Thyrotropin Receptor

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It has been speculated that thyrotripin Receptor (TSHR) elicites the autoimmune reaction in retroorbital tissues in Graves' patlents and causes the ophthalmopathy. We investigated the molecular mechanisms of expression in rat adipocytes and 3T3-L1 cells.Results : TSHR is expressed in the presence of insulin, dexamethazone, and IBMX.Primer extension and cloned cDNA sequences showed that transcription of TSHR gene in rat adipose tissue was from multiple stasites between -89 to -68. TSH-dependent down regulation of TSHR was observed 1 hr after TSH addition a dis not need protein synthesis. Down regulation was cAMP-dependent. DNase Iprotection assay showed 1 nuclear extracts from differentiated 3T3-L1 cells protected sesquence-146 to -127 which contained cAMP-responsive element. Furthermore, we found another protection site downstream of-127. Gel shift analysis with antibodies against many known transcription factors revealed that the transcription factor (s) which bound to the downstream elements is (were) secific to the adipocytes. We are now identifying the molecule which binds to the downstream element. Finally, we evaluated the effects of various PPAR_<gamma> activators and recombinant adenovirus which expresses PPAR_<gamma>2, and we found that PPAR_<gamma> activators and recombinant adenovirus stimulated the differentiation and the expression of TSHR in 3T3-L1 cells. Express of TSHR was accompanied by the TSH-stimulated cAMP prodction.Summary : Differentiation of adipocytes are closely related to the expression of TSHR mRNA.There is a complicated mechanism which allow the a enormous amount of expression of TSHR in adipocytes.