Der humane Natrium-Jodid-Symporter (hNIS) : Entwicklung einer Methode zur Quantifizierung der hNIS-mRNA-Expression und Analyse der Rolle als Antigen bei autoimmunen Schilddrüsenerkrankungen
The human sodium-iodide-symporter (hNIS) is the key molecule for iodide uptake into the thyroid gland. Iodide is essential for the biosynthesis of the thyroid hormones T3 and T4. The symporter is localized at the basolateral membrane of thyroid follicular cells and transports iodide against its electrochemical gradient into the thyrocytes. In regard of this important function the symporter plays a particular role in diagnosis and differential diagnosis of thyroid diseases. New therapy strategies may focus on the sodium-iodide-symporter as a target of intervention. Most of the available data were obtained by studies of the symporter regulation in cell lines of the rat and mouse. Until now it is unclear, if and to what extent these results can be transferred on human thyrocytes. In this work basic mechanisms concerning the regulation of hNIS have been successfully demonstrated in cultures of primary human thyrocytes, which were isolated from surgically removed normal thyroid gland tissue. For molecular analysis a Real-Time PCR approach has been established and optimized. By using this technology it could be demonstrated, that hNIS mRNA expression was significantly increased after the addition of bTSH and forskolin, respectively. Both substances showed a time- and dose-dependency. Data in animals could demonstrate that cytokines and growth factors may have an influence on the expression of the symporter. To verify the influence of cytokines on hNIS the expression of the symporter was investigated in the human system. An addition of TGF-ß1 or TNF-alpha on cultured human thyrocytes results in a significantly decreased hNIS mRNA expression. These data point out, that the human sodium-iodide-symporter is regulated similarly like the symporter of rats. As other thyroid proteins hNIS may have a role in autoimmunity against the thyroid gland. A new radioligand-assay was developed in order to proof the existence of hNIS–autoantibodies in sera of patients with Graves’ disease and Hashimoto’s thyroiditis. For that purpose the "full length"-hNIS was cloned from cDNA of thyrocytes and its functional activity was examined after transfection into CHO cells. After the synthesis of hNIS through an in vitro transcription/translation system, hNIS was radio-labeled and incubated with different sera and finally precipitated with protein A sepharose. Positive hNIS antibodies were found in only 10% of the patients with Graves disease and in 20% of the patients with Hashimoto’s thyroiditis, respectively. These results offer evidence, that hNIS may be a new antigen in autoimmune thyroid disorders.
info:eu-repo/classification/ddc/610, Medizin
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