Transporter-Mediated Uptake of Microcystin-LR in Human Trophoblasts: Regulation By Oxygen Concentration and Cell Fusion

Background Rising global temperatures and eutrophication are increasing the intensity and frequency of cyanobacterial harmful algal blooms that release toxins including microcystin-LR (MC-LR). MC-LR inhibits protein phosphatases in the human liver and brain, but its accumulation in the placenta is unclear. Placental transporter expression varies across pregnancy and is influenced by physiological cues, such as low oxygen concentrations which activate HIF1A, and trophoblast cell fusion forming syncytiotrophoblasts that engage CREB-driven transcription. This study examined whether MC-LR accumulates in placental cells, which transporters mediate uptake, and how these transporters are regulated by HIF1A and CREB.

Intracellular accumulation of MC-LR (0.1–10 µM, 3 hour) was measured in human cytotrophoblasts (JAR, BeWo) and extravillous trophoblasts (HTR-8/SVneo) by western blotting for MC-LR–adducted proteins. Organic anion transporting polypeptide (OATP) involvement was tested using cyclosporin A (10 µM), an OATP inhibitor, before exposure to the OATP substrate or MC-LR. Cells were also cultured under 3%, 8%, or 20% O₂ to induce hypoxic responses or treated with forskolin (a potent intracellular cAMP inducer) to stimulate cell fusion before MC-LR exposure.

MC-LR accumulated in all three placenta cell lines in a concentration-dependent manner. Cyclosporin A reduced MC-LR uptake by 57% in JAR cells, confirming OATP-mediated transport. Low O2 increased OATP4A1 expression and function but reduced protein phosphatase expression, decreasing MC-LR–bound proteins by 52–72%. Forskolin increased OATP4A1 expression and enhanced MC-LR uptake >2.5-fold.

MC-LR enters placental trophoblasts via active OATP transport, likely OATP4A1, and uptake increases under hypoxia and trophoblast fusion. Competing Interest Statement The authors have declared no competing interest. Footnotes Conflicts of Interest: The authors do not have conflicts of interest to disclose. Availability of Data: The data that support the findings of this study are available from the corresponding author upon reasonable request. Abbreviations - (B2M) - beta-2-microglobulin - (cAMP) - cyclic AMP - (cyc A) - cyclosporin A - (CTBs) - cytotrophoblasts - (EVTs) - extravillous trophoblasts - (GLUT) - glucose transporter - (GSH) - glutathione - (HABs) - harmful algal blooms - (HBSS) - Hanks Balanced Salt Solution - (HIF) - hypoxia-inducible factor - (MC-LR) - microcystin-LR - (OATP) - organic anion transporting polypeptide - (PP1/2A) - protein phosphatase 1/2A - (SLCO) - Solute Carrier superfamily - (STB) - syncytiotrophoblast - (CT) - threshold cycle