Inhibition of amino acid transport system a by interleukin-1β in trophoblasts

OBJECTIVE: The current study sought to investigate the influence of interleukin-1 beta (IL-1 beta) on the Junction of the amino acid transport system A in trophoblasts. METHODS: BeWo choriocarcinoma cells were exposed to recombinant human IL-1 beta in serum-free medium. Cells incubated with serum-free medium in the absence of IL-1 beta were used as control. System A activity was determined in control and treated cells by measuring the uptake of alpha-(methylamino)isobutric acid. The results obtained were confirmed by measuring system A activity in placental brush border membrane vesicles isolated from pregnant rats injected with IL-1 beta. RESULTS: Treatment of BeWo cells with IL-1 beta resulted in a tune- and dose- dependent inhibition of system A. Treatment with IL-1 beta also inhibited the uptake of arginine, and glutamate but had no significant effect on the uptake of leucine, tryptophan, and ascorbate. The inhibition of system A activity by IL-1 beta was abolished in the presence of IL-1 beta receptor antagonist. The inhibitory effect was associated with a decrease in the maximal velocity of the transport system with no effect on the substrate affinity. Steady-state levels of both SNAT1 and SNAT2 mRNA were reduced by IL-1 beta treatment as evidenced by semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. In rat placental brush border membrane vesicles isolated from IL-1 beta-treated pregnant rats, system A activity was found to be decreased by approximately 40% compared to activity in control membrane vesicles. CONCLUSIONS: IL-I beta decreases SNAT1 and SNAT2 mRNA levels in trophoblasts, which is associated with a decrease in system A-mediated transport activity at the functional level. These findings may have important consequences under both physiologic conditions and pathogic conditions during pregnancy that are associated with elevated levels of IL-1 beta.