INCREASE BY TRIIODOTHYRONINE OF ENDOTHELIN-1, FIBRONECTIN AND VON-WILLEBRAND-FACTOR IN CULTURED ENDOTHELIAL-CELLS

Hyperthyroidism is associated with elevated plasma levels of endotheli um-derived proteins such as von Willebrand factor (vWF), fibronectin ( FN) and endothelin-1 (ET-1). This study was designed to characterize t he mechanisms involved in this phenomenon at the cellular level. vWF, FN and ET-1 secretion and mRNA expression were measured in human umbil ical vein endothelial cells (HUVECs) exposed to tri-iodothyronine (T-3 ) for 13 +/- 1 days, using ELISA, Western blot, RIA and Northern blot analysis respectively. Exposure of HUVECs to T-3 significantly increas ed vWF secretion (50 ng T-3/ml: 117 +/- 5%, P<0.01; 100 ng T-3/ml: 127 +/- 26%, P<0.01) as well as vWF mRNA expression (50 ng/ml: 116 +/- 13 %, P<0.001; 100 ng/ml: 136 +/- 30%, P<0.002) (results are means +/- S. D. analysed by the Wilcoxon signed rank test). FN secretion was signif icantly affected by 50 (145 +/- 42% of control, P<O.05) and 100 (116.8 +/- 16% of control, P<0.05) ng T-3/ml, and FN mRNA expression by 50 n g T-3/ml (123 +/- 20%, P<O.05). Long-term incubation with T-3 increase d both ET-1 secretion (25 ng/ml: 124 +/- 25%, P<0.001; 50 ng/ml: 165 /- 53%, P<0.05; 100 ng/ml: 116 +/- 17%, P<0.05) and prepro-ET-1 mRNA e xpression (25 ng/ml: 112 +/- 16%, P<0.05; 50 ng/ml: 134 +/- 43%, P<0.0 2; 100 ng/ml: 120 +/- 20%, P<0.02). Protein kinase C (PKC) isoforms ep silon and beta II were not significantly affected by T-3, whereas PKC alpha was increased in whole cell lysates and in membrane fractions of cells incubated with 100 but not 50 ng T-3/ml. Prepro-ET-1 mRNA stabi lity, cell numbers and proliferation, measured by [H-3]thymidine assay s, remained unaffected in HUVECs after exposure to T-3. These data ind icate thyroid hormone-induced upregulation of mRNA expression and prot ein synthesis of vWF, FN and ET-1, by PKC alpha-, beta II- and epsilon -independent pathways, explaining, at least in part, increased plasma concentrations of endothelial proteins and peptides in the hyperthyroi d state.