Endothelial cells stimulate proliferation of human thyroid epithelial cells

The present study was undertaken to investigate cellular interactions between human thyroid epithelial cells (thyrocytes) and endothelial cells. Normal thyrocytes were cultured with either mitomycin C-treated endothelial cells or mitomycin C-treated human foreskin fibroblasts. The proliferative responses of thyrocytes were markedly stimulated by endothelial cells, but not by skin fibroblasts. The proliferative response of the thyrocytes obtained from patients with Graves' disease were similar to that of normal thyrocytes. Furthermore, the cell number of thyrocytes in endothelial cell-thyrocyte co-culture was markedly increased as compared with that in thyrocytes alone. The culture medium of endothelial cells only partly had any effect in the endothelial cell-thyrocyte co-culture experiment. Indomethacin, a cyclooxygenase inhibitor, did not increase the endothelial cells-induced thyrocyte proliferation. Furthermore, the increased proliferative response of thyrocytes stimulated by endothelial cells was not suppressed by heparin. These results suggest that endothelial cells increase thyrocyte proliferation, and that cell contact or extracellular matrix production by endothelial cells may play an important role in the proliferation of thyrocytes.