Introduction: Investigation of normal human thyroid function using in vitro culture systems is dependent on cells that recapitulate physiology of differentiated thyrocytes. Primary thyrocytes retain features of the native organ but have limited lifespan in culture. Immortalized thyrocytes offer an alternative if challenges maintaining phenotypic stability can be overcome to retain functional features of primary cells.
Materials and methods: CI-SCREEN immortalization technology was applied to normal human thyroid tissue to generate four cell line variants. The lines were characterized for transgene integration, biomarker expression, genomic stability, and proliferation rates. Thyroid Stimulating Hormone (TSH)-dependent morphology, thyroglobulin production, thyroxine hormone synthesis, and viability were assessed using conventional 2D monolayer and 3D microtissue culture formats in huThyrEC or h7H medium.
Results: Despite differential transgene profiles, the lines had similar biomarker expression patterns and proliferation rates. In 2D culture there was no thyroxine synthesis or changes in viability, but TSH-dependent thyroglobulin production was more significant for several lines in h7H than huThyrEC medium. Comparatively, in 3D microtissues, TSH-dependent thyroglobulin induction was greater for cell lines in h7H medium. Synthesis of thyroxine in one cell line was higher than background with TSH exposure, but not significantly different than control.
Discussion: Immortalization of primary human thyrocytes yielded transgenic lines of epithelial origin. When evaluated in 2D or 3D culture formats, h7H medium supported thyroglobulin production to a greater magnitude than huThyrEC medium. One cell line cultured in 3D microtissue format marginally recapitulated T4 synthesis under continuous TSH exposure.
Conclusion: Select human thyroid cell lines exhibited morphological and functional features of primary thyrocytes and are a novel resource for in vitro disease modeling and toxicity testing that will enable reproducible culture models more representative of normal human thyroid function.
Keywords: Endocrine Toxicology; In Vitro Toxicology; Organotypic Culture Models; Thyroid.