Insulin restores glucose inhibition of adenosine transport by increasing the expression and activity of the equilibrative nucleoside transporter 2 in human umbilical vein endothelium.
L-Arginine transport and nitric oxide (NO) synthesis (L-arginine/NO pathway) are stimulated by insulin, adenosine or elevated extracellular D-glucose in human umbilical vein endothelial cells (HUVEC). Adenosine uptake via the human equilibrative nucleoside transporters 1 (hENT1) and 2 (hENT2) has been proposed as a mechanism regulating adenosine plasma concentration, and therefore its vascular effects in human umbilical veins. Thus, altered expression and/or activity of hENT1 or hENT2 could lead to abnormal physiological plasma adenosine level. We have characterized insulin effect on adenosine transport in HUVEC cultured in normal (5 mM) or high (25 mM) D-glucose. Insulin (1 nM) increased overall adenosine transport associated with higher hENT2-, but lower hENT1-mediated transport in normal D-glucose. Insulin increased hENT2 protein abundance in normal or high D-glucose, but reduced hENT1 protein abundance in normal D-glucose. Insulin did not alter the reduced hENT1 protein abundance, but blocked the reduced hENT1 and hENT2 mRNA expression induced by high D-glucose. Insulin effect on hENT1 mRNA expression in normal D-glucose was blocked by N(G)-nitro-L-arginine methyl ester (L-NAME, NO synthase inhibitor) and mimicked by S-nitroso-N-acetyl-L,D-penicillamine (SNAP, NO donor). L-NAME did not block insulin effect on hENT2 expression. In conclusion, insulin stimulation of overall adenosine transport results from increased hENT2 expression and activity via a NO-independent mechanism. These findings could be important in hyperglycemia-associated pathological pregnancies, such as gestational diabetes, where plasma adenosine removal by the endothelium is reduced, a condition that could alter the blood flow from the placenta to the fetus affecting fetus growth and development.
Muñoz
Gonzalo
G
Cellular and Molecular Physiology Laboratory (CMPL), Medical Research Centre (CIM), Department of Obstetrics and Gynaecology, Faculty of Medicine, Pontificia Universidad Católica de Chile, Santiago, Chile.
San Martín
Rody
R
Farías
Marcelo
M
Cea
Luis
L
Vecchiola
Andrea
A
Casanello
Paola
P
Sobrevia
Luis
L
D000241:Adenosine / Q000378:metabolism*; D000345:Affinity Labels / Q000378:metabolism; D001692:Biological Transport; D002478:Cells, Cultured; D002956:Citrulline / Q000378:metabolism; D042783:Endothelial Cells / Q000166:cytology / Q000378:metabolism*; D033721:Equilibrative Nucleoside Transporter 1 / Q000235:genetics / Q000378:metabolism*; D033722:Equilibrative-Nucleoside Transporter 2 / Q000235:genetics / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D052250:Nitric Oxide Synthase Type III / Q000235:genetics / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D013868:Thioinosine / Q000031:analogs & derivatives / Q000378:metabolism; D014471:Umbilical Veins / Q000033:anatomy & histology*
D000345:Affinity Labels; D033721:Equilibrative Nucleoside Transporter 1; D033722:Equilibrative-Nucleoside Transporter 2; D007328:Insulin; D020033:Protein Isoforms; C438649:SLC29A1 protein, human; D002956:Citrulline; D013868:Thioinosine; D052250:Nitric Oxide Synthase Type III; C001789:4-nitrobenzylthioinosine; D005947:Glucose; D000241:Adenosine