Thyroid hormone stimulates NO production via activation of the PI3K/Akt pathway in vascular myocytes.
OBJECTIVE
Thyroid hormone (TH) rapidly relaxes vascular smooth muscle cells (VSMCs). However, the mechanisms involved in this effect remain unclear. We hypothesize that TH-induced rapid vascular relaxation is mediated by VSMC-derived nitric oxide (NO) production and is associated with the phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) signalling pathway.


RESULTS
NO levels were determined using a NO-specific fluorescent dye (DAF-2) and nitrite (NO2-) levels. Expression of NO synthase (NOS) isoforms and proteins of the PI3K/Akt pathway was determined by both western blotting and immunocytochemistry. Myosin light chain (MLC) phosphorylation levels were also investigated by western blotting. Exposure of cultured VSMCs from rat thoracic aortas to triiodothyronine (T3) resulted in a significant decrease of MLC phosphorylation levels. T3 also induced a rapid increase in Akt phosphorylation and increased NO production in a dose-dependent manner (0.001-1 microM). VSMCs stimulated with T3 for 30 min showed an increase in the expression of all three NOS isoforms and augmented NO production, effects that were prevented by inhibitors of PI3K. Vascular reactivity studies showed that vessels treated with T3 displayed a decreased response to phenylephrine, which was reversed by NOS inhibition. These data suggest that T3 treatment induces greater generation of NO both in aorta and VSMCs and that this phenomenon is endothelium independent. In addition, these findings show for the first time that the PI3K/Akt signalling pathway is involved in T3-induced NO production by VSMCs, which occurs with expressive participation of inducible and neuronal NOS.


CONCLUSIONS
Our data strongly indicate that T3 causes NO-dependent rapid relaxation of VSMC and that this effect is mediated by the PI3K/Akt signalling pathway.
Carrillo-Sepúlveda
Maria Alícia
MA
Laboratory of Cell Biology and Functional Anatomy, Department of Anatomy, Institute of Biomedical Sciences, University of Sao Paulo, Avenida Professor Lineu Prestes 2415, Sao Paulo 05508-900, Brazil.
Ceravolo
Graziela S
GS
Fortes
Zuleica Bruno
ZB
Carvalho
Maria Helena
MH
Tostes
Rita C
RC
Laurindo
Francisco R
FR
Webb
R Clinton
RC
Barreto-Chaves
Maria Luiza M
ML
D000818:Animals; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000502:physiology; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism; D032389:Myocytes, Smooth Muscle / Q000187:drug effects* / Q000378:metabolism; D018994:Myosin Light Chains / Q000378:metabolism; D009569:Nitric Oxide / Q000096:biosynthesis*; D019001:Nitric Oxide Synthase / Q000502:physiology; D010656:Phenylephrine / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction / Q000187:drug effects*; D013963:Thyroid Hormones / Q000494:pharmacology*; D014661:Vasoconstriction
D018994:Myosin Light Chains; D013963:Thyroid Hormones; D010656:Phenylephrine; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt