Ward C.R., Achenbach S.E., Peterson M.E., et al.
Journal of Veterinary Internal Medicine, 2000. 14: p.342.
Feline hyperthyroidism is a common, spontaneously occurring endocrine disease seen in middle-older aged cats. It is similar both histologically and functionally to human toxic nodular goiter, seen in a comparable population of middle-older aged humans. Several etiologies for human toxic nodular goiter have been proposed including abnormalities in number or function of components of the cell surface TSH receptor G protein signal transduction system. In previous studies, our laboratory has shown that the alpha subunit of the inhibitory G protein Gi shows reduced expression at the protein level in thyroid tissue extracts from hyperthyroid cats as compared to euthyroid cats (Hammer, Holt, and Ward, AJVR, accepted for publication). In an effort to continue these studies at the cellular level, we have attempted to culture feline thyrocytes from euthyroid and hyperthyroid animals and examine functional activity with the hope of studying cellular signaling mechanisms in vitro. Thyroids were surgically removed from euthyroid or hyperthyroid cats, minced, and enzymatically digested in Hank’s buffered salt solution containing collagenase, dispase, trypsin, and calf serum (Duncan Ferguson, personal communication). They were plated on 100 mm dishes in DMEM/F12 medium supplemented with calf serum, pen-strep/fungicide, insulin, hydrocortisone, transferrin, somatostatin, glycyll-histydydl-L-lysine acetate, and TSH (6H), with medium changes every 24 hours. The cells were incubated in water-saturated atmosphere of 5% CO2 at 37 degrees C. After 8-10 days in culture intracellular thyroglobulin was detected using FITC-labelled anti-human thyroglobulin (Dako Corp) and visualization by epifluorescence microscopy. Parallel experiments were carried out using the rat WRT thyroid cell line as a positive control. Fluorescence was localized in the cytoplasm of the thyrocytes in a diffuse, lacy pattern similar to that observed in the WRT thyroid cell line as a positive control. Fluorescence was localized in the cytoplasm of the thyrocytes in a diffuse, lacy pattern similar to that observed in the WRT cells. Thyrocytes from hyperthyroid animals showed slightly increased cytoplasmic fluorescence. We conclude that thyrocytes from euthyroid and hyperthyroid cats can be isolated and cultured under similar conditions to an established thyroid cell line. The detection of basal levels of cytoplasmic thyroglobulin suggests that euthyroid and hyperthyroid thyrocytes retain functionality under these conditions. Hyperthyroid cells may sustain a higher basal level of thyroglobulin production than euthyroid cells. We plan to continue using this system to study TSH receptor G protein signaling in feline thyrocytes in vitro.