Expression of the TRPM6 in mouse placental trophoblasts; potential role in maternal-fetal calcium transport.

The placenta is required to transport calcium (Ca²⁺) from mother to fetus during fetal bone mineralization. In an attempt to clarify the molecular basis of Ca²⁺ entry for this transport, we identified TRPM6 as a candidate for apical Ca²⁺ entry pathway. TRPM6 mRNA increased during the last 4 days of pregnancy, coinciding with fetal bone mineralization in mice. TRPM6 mRNA and protein was localized in the trophoblasts in labyrinth where the maternal-fetal Ca²⁺ transport occurs. In patch-clamp recordings, we observed TRPM6/TRPM7-like currents in mouse trophoblasts after starting fetal bone mineralization but not before mineralization. Plasma membrane Ca²⁺ permeability was significantly increased in TRPM6/TRPM7 expressed HEK293 cells under physiological Mg²⁺ and ATP concentration but not in TRPM6 or TRPM7 homomer-expressing cells. These results suggest that TRPM6 is functionally expressed in mouse placental trophoblasts, implicating in maternal-fetal Ca²⁺ transport likely with TRPM7, which might enable to sustain fetal bone mineralization.

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