Iodide uptake and organification, tri-iodothyronine secretion, cyclic AMP accumulation and cell proliferation in an optimized system of human thyroid follicles cultured in collagen gel suspended in serum-free medium.

An experimental system was established for measuring cell function and proliferation of human thyroid follicles cultured in collagen gel suspended in serum-free medium. Optimal culture conditions were defined and the system was characterized. The human thyrocytes were functional as indicated by their ability to respond to a TSH stimulus (as low as 1-10 microU/ml), in a time- and dose-dependent fashion, with at least a 15-fold increase in iodide uptake and organification, tri-iodothyronine (T3) secretion (demonstrated to derive from de-novo T3 biosynthesis) and cyclic AMP accumulation. Moreover, the same system allowed the measurement of cell proliferation (as indicated by thymidine incorporation and DNA content) following epidermal growth factor (EGF) and phorbol ester challenge under conditions of cell density and medium identical to those for the differentiated functions. The functional responses and cell proliferation were markedly higher compared with those of the same cells in the presence of serum or maintained in monolayer culture. Normal cell polarity, which critically determines functional capacity of thyroid follicles was maintained (as demonstrated by electron microscopy) by the use of collagen gel and serum-free medium. The use of thyroid cells of human origin assumes great importance in view of the wide species differences reported. Cryopreservation of cells rather than the necessity of using freshly derived cells confers greater convenience. The present model system provides a powerful tool for studying human thyroid physiology and pathophysiology.