Our laboratory is currently characterizing in vitro and ex vivo the functional activity of common polymorphisms of type-2 deiodinase gene. In order to achieve this goal, we have established a cell culture-based type-2 deiodinase expression system. Standard biochemistry methods are utilized for the enzymatic activity assay;protein/protein and nucleic acids/protein interactions are tested by immunoprecipitation and mobility shift assay. A common polymorphism in the 5UTR region of the DIO2 gene (258 A/G DIO2) has been associated with a shift in the ratio of circulating T3/T4, suggesting an increased in the activity of the enzyme in vivo leading to a shift of the reaction equilibrium. Our in vitro and ex vivo data, consistent with others genotype/phenotype association studies, indicate that the 258 A/G DIO2 variant induces an increase in the transcription of the gene by displacing a putative repressor. Current efforts are aimed to characterize the putative repressor factor interacting with the polymorphism. Preliminary analysis of the data has indicated multiple candidate transcription factors. Our current efforts are aimed to the characterization of the repressor. Pre-adipocyte differentiation and culture. During the past two FYs we have focused our effort in developing a system of re-differentiation of human adipocytes from stromal cells obtained during adipose tissue biopsy. This system will become the platform to test in a controlled fashion the effects of specific genotypes on adipose tissue function independently of the metabolic status of the subject at the time of the sampling. We are currently using this experimental model to characterize the role of thyroid hormones in the differentiation of the adipocytes and in the modulation of their transcriptosome. Further effort is directed toward characterizing the transcriptional pattern of this system throughout the differentiation process with a particular focus on the expression of brown-fat specific genes. Type-2 deiodinase assay in primary culture of follicular thyroid cells. Collaborative work carried out with Dr. Gershengorns group (NIDDK-CEB) has led to the development of a reliable assay for the measurement of type-2 deiodinase activity in primary cultures of thyroid cells as a read-out of TSH-cAMP pathway. This system has been successfully utilized to test the activity of agonists of the TSH receptor. Development of a cell-based system to characterize the effects of substances modulating the type-2 deiodinase activity. We are currently developing cell line stably expressing type-2 deiodinase and a Thyroid Hormone Responsive Element (TRE)-driven reporter construct in order to evaluate the activity of small substances modulating the type-2 deiodinase activity. Effects of common polymorphisms in the modulation of the clinical presentation of the Resistance to Thyroid Hormone syndrome (RTH). In collaboration with Dr. Forreset we have characterized the role of common SNPs in the intron control region of the beta-2 thyroid hormone receptor gene. We have demonstrated that a common SNP causes a pituitary, tissue-specific, increase in transcription of the gene. This SNP is in cis with a pathogenic R338W mutation of the beta-receptor in the index case of pituitary selective RTH. Thus this combination causes a tissue selective over expression of the mutant gene ultimately generating a pituitary-selective dominant-negative state, recapitulating the peculiar phenotype of the index case. The results of this study have been recently published in the Journal of Translational Medicine.
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