IL-6 stimulates system A amino acid transporter activity in trophoblast cells through STAT3 and increased expression of SNAT2

Abstract

Changes in placental nutrient transport are closely associated with abnormal fetal growth. However, the molecular mechanisms underlying the regulation of placental amino acid transporters are unknown. We demonstrate that physiological concentrations of the proinflammatory cytokines interleukin (IL)-6 and tumor necrosis factor (TNF)-alpha stimulate the activity of amino acid transporter system A, but not system L, in cultured human primary trophoblast cells. Both cytokines increased the gene and protein expression of the Na(+)-coupled neutral amino acid transporter (SNAT)2 isoform and upregulated SNAT1 protein expression. IL-6 increased Tyr705 phosphorylation of signal transducer and activator of transcription 3 (STAT3). In cells transfected with small interfering RNA (siRNA) targeting STAT3, the RNA and protein expression of SNAT2, but not SNAT1, was reduced and the stimulating effect of IL-6 on system A activity was abolished. Despite eliciting similar responses in amino acid transport activity and transporter expression, TNF-alpha effects on system A activity were not mediated through the JAK/STAT pathway. In conclusion, we have identified a novel regulatory pathway involving increased gene expression of the SNAT2 isoform mediated by a STAT-dependent pathway, which links IL-6 to increased activity of system A, a ubiquitously expressed transporter of neutral amino acids. From these new findings, we propose that upregulation of amino acid transporters by cytokines may contribute to increased placental nutrient transport and fetal overgrowth, which are commonly found in pregnancies complicated by maternal diabetes and obesity.

Oleic acid stimulates system A amino acid transport in primary human trophoblast cells mediated by toll-like receptor 4

“…This protocol has been widely used and validated, and results in the isolation of cells that are expressing cytokeratin 7, a syncytial marker, that do not express vimentin, and that undergo biochemical differentiation as measured by hCG release ( 21,27,32,33 ). The cells were plated on 6-well plates at a density of 1.5 × 10 6 per well (for and p38 mitogen-activated protein kinase (MAPK).…”

“…For instance, interleukin 6 (IL-6), leptin, and tumor necrosis factor ɑ (TNF-ɑ) increases the activity of the system A amino acid transporter ( 27,28 ). The effects of IL-6 and leptin, but not TNF-ɑ, are mediated through activation of signal transducer and activator of transcription 3 (STAT3) ( 27,28 ). In a hepatocarcinoma cell line (HepG2), exposure to oleic acid increases phosphorylation of STAT3 ( 29 ) and activates mTOR signaling ( 26 ).…”

“…Transfection of primary trophoblast cell cultures was carried out as previously described ( 27,35 ). Twenty hours after plating, the trophoblast cells were transfected with cell culture media containing 0.1 µM TLR4 siRNA (Validated MISSION siRNA, SASI_Hs01_00122250, NM_138554; Sigma-Aldrich) and 0.3% Dharmafect transfection reagent (Thermo Scientifi c, Rockford, IL) for 24 h. Mock transfected trophoblast cells were given an equal amount of Dharmafect transfection reagent.…”

Folic acid uptake by the human syncytiotrophoblast is affected by gestational diabetes, hyperleptinemia, and TNF-α

“…High levels of this cytokine have been shown to decrease l-methionine uptake (data not shown) or to increase arachidonic and docosahexaenoic acid uptake (data not shown) or system A activity (36) in human trophoblasts. Altogether, these observations reinforce the idea that TNF-α may well act as a regulator of placental nutrient transport.…”

Impact de l’obésité et du diabète maternels sur la fonction placentaire

“…Dans le modèle de souris obèses, l'inflammation placentaire et l'activation des macrophages [11] sont plus importantes chez les foetus mâles que chez les foetus femelles [11]. Les cytokines pro-inflammatoires (IL-6 et TNF-) stimulent l'activité du système A des transporteurs des acides aminés (transporteurs des acides aminés neutres comme l'alanine, la sérine et la glutamine) dans les cellules trophoblastiques humaines en culture [24]. De plus, l'IL-6 induit l'accumulation des acides gras dans le trophoblaste.…”