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 T3, T4 and the T3 analog, 3,3′,5-triiodothyroacetic acid TRIAC in human umbilical vein endothelial cells (HUVECs). We also analyzed the role of αvβ3 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, αvβ3 integrin was pharmacologically inhibited by tetraiodothyroacetic acid (TETRAC) or genetically blocked by silencing αv mRNA and PI3K, MAPKs and intracellular calcium by selective inhibitors. The following results were obtained. Thyroid hormones and the T3 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 b0,+L-arginine transporters, eNOS mRNA and NO production. These effects were suppressed by αvβ3 integrin inhibition with TETRAC or αv 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 αvβ3 integrin receptor and subsequent PI3K, MAPK and intracellular Ca2+ signaling pathways.
Marta Toral, Rosario Jimenez, Sebastián Montoro-Molina, Miguel Romero, Rosemary Wangensteen, Juan Duarte and Félix Vargas
Isabel Rodríguez-Gómez, Inmaculada Banegas, Rosemary Wangensteen, Andrés Quesada, Rosario Jiménez, Mercedes Gómez-Morales, Francisco O'Valle, Juan Duarte and Félix Vargas
The purpose was to analyse the cardiac and renal capillary density and glomerular morphology resulting from a chronic excess or deficiency of thyroid hormones (THs) in rats. We performed histopathological, morphometrical and immunohistochemical analyses in hypothyroid and hyperthyroid rats to evaluate the density of mesenteric, renal and cardiac vessels at 4 weeks after induction of thyroid disorders. The main angiogenic factors in plasma, heart and kidney were measured as possible mediators of vascular changes. Mesenteric vessel branching was augmented and decreased in hyper- and hypothyroid rats respectively. The numerical density of CD31-positive capillaries was higher in left and right ventricles and in cortical and medullary kidney from both hyper- and hypothyroid rats vs controls. Numbers of podocytes and glomeruli per square millimetre were similar among groups. Glomerular area and percentage mesangium were greater in the hyperthyroid vs control or hypothyroid groups. No morphological renal lesions were observed in any group. Vascularisation of the mesenteric bed is related to TH levels, but an increased capillarity was observed in heart and kidney in both thyroid disorders. This increase may be produced by higher tissue levels of angiogenic factors in hypothyroid rats, whereas haemodynamic factors would predominate in hyperthyroid rats. Our results also indicate that the renal dysfunctions of thyroid disorders are not related to cortical or medullary microvascular rarefaction and that the proteinuria of hyperthyroidism is not secondary to a podocyte deficit. Finally, TH or its analogues may be useful to increase capillarity in renal diseases associated with microvascular rarefaction.