Thyroid hormones stimulate L-arginine transport in human endothelial cells

Thyroid hormone activity is associated with L-arginine metabolism and nitric oxide (NO) production, which participate in the cardiovascular manifestations of thyroid disorders. L-arginine transporters play an important role in activating L-arginine uptake and NO production. However, the effects of thyroid hormones on L-arginine transporters in endothelial cells have not yet been evaluated. The following methods were used. We measured L-arginine uptake, mRNA expression of L-arginine transporters, endothelial nitric oxide synthase (eNOS) mRNA and NO generation after the administration of T-3, T-4 and the T-3 analog, 3,3', 5-triiodothyroacetic acid TRIAC in human umbilical vein endothelial cells (HUVECs). We also analyzed the role of alpha v beta 3 integrin and of phosphatidyl-inositol-3 kinase (PI3K), mitogen-activated protein kinases (MAPKs: ERK1/2, p38 and SAPK-JNK) and intracellular calcium signaling pathways as underlying mechanisms. To this end, alpha v beta 3 integrin was pharmacologically inhibited by tetraiodothyroacetic acid (TETRAC) or genetically blocked by silencing alpha v mRNA and PI3K, MAPKs and intracellular calcium by selective inhibitors. The following results were obtained. Thyroid hormones and the T-3 analog TRIAC increased L-arginine uptake in HUVECs, the sodium-independent y(+)/CAT isoforms, except CAT2b, sodium-dependent y(+)L system and sodium-independent system b(0,+) L-arginine transporters, eNOS mRNA and NO production. These effects were suppressed by alpha v beta 3 integrin inhibition with TETRAC or alpha v integrin downregulation or by PI3K, MAPK or intracellular Ca2+ signaling inhibitors. In conclusion, we report for the first time that activation of L-arginine uptake by thyroid hormones is related to an upregulation of L-arginine transporters. This effect seems to be mediated by activation of alpha v beta 3 integrin receptor and subsequent PI3K, MAPK and intracellular Ca2+ signaling pathways.