Expression of anionic and cationic amino acid transport proteins in the placentas of wild-type versus growth hormone over-expressing and null IGF-II and IGF-1 receptor mice

The effect of GH, IGF-I and IGF-II on the in vivo expression of Na⁺-coupled anionic (GLAST1, GLT1, EAAC1, EAAT4) and Na⁺-independent cationic (CAT1) amino acid transport proteins was evaluated by comparing transporter expression in Day 17 wild-type mouse placentas to that in placentas of transgenic mice that over-express bovine growth hormone (GH+) or mice that have null gene mutations for IGF-II or IGF-1 receptor. Whole placental GLT1, EAAC1 and EAAT4 steady-state mRNA levels were not affected by GH+ or null IGF-II mice. In contrast, GLAST1 and CAT1 mRNA expression was increased in null IGF-II placentas. CAT1 expression also was greater in null GH+ placentas. By immunoblot analysis, the amount of whole placental GLT1, GLAST1 and EAAC1 protein was decreased in GH+ placentas, whereas EAAT4 protein was not detected in treatment nor wild-type placentas. Immunohistochemistry revealed diminished placental EAAC1 protein expression in null IGF-I receptor mice and GLT1 in null IGF-II mice but no difference for GLAST1 or CAT1. These data indicate that GH, IGF-I and IGF-II differentially affect the expression of amino acid transporters.