Trophoblast-specific overexpression of the LAT1 increases transplacental transport of essential amino acids and fetal growth in mice.

Placental System L amino acid transporter activity is decreased in pregnancies complicated by intrauterine growth restriction (IUGR) and increased in fetal overgrowth. However, it is unknown if changes in the expression/activity of placental Large Neutral Amino Acid Transporter Small Subunit 1 (Slc7a5/LAT1) are mechanistically linked to placental function and fetal growth. We hypothesized that trophoblast-specific Slc7a5 overexpression increases placental transport of essential amino acids, activates the placental mechanistic target of rapamycin (mTOR) signaling, and promotes fetal growth in mice. Using lentiviral transduction of blastocysts with a Slc7a5 transgene, we achieved trophoblast-specific overexpression of Slc7a5 (Slc7a5 OX) with increased fetal (+27%) and placental weights (+10%). Trophoblast-specific Slc7a5 overexpression increased trophoblast plasma membrane (TPM) LAT1 protein abundance and TPM System L transporter (+53%) and System A transporter activity (+ 21%). Slc7a5 overexpression also increased transplacental transport of leucine (+ 85%) but not of the System A tracer, 14C-methylamino isobutyric acid, in vivo. Trophoblast-specific overexpression of Slc7a5 activated placental mTORC1, as assessed by increased (+44%) phosphorylation of S6 ribosomal protein (Ser 235/236), and mTORC2 as indicated by phosphorylation of PKCα-Tyr-657 (+47%) and Akt-Ser 473 (+96%). This is the first demonstration that placental transport of essential amino acids is mechanistically linked to fetal growth. The decreased placental System L activity in human IUGR and the increased placental activity of this transporter in some cases of fetal overgrowth may directly contribute to the development of these pregnancy complications.

Knockdown of Placental Major Facilitator Superfamily Domain Containing 2a in Pregnant Mice Reduces Fetal Brain Growth and Phospholipid Docosahexaenoic Acid Content.

INTRODUCTION: Docosahexaenoic acid (DHA) is an n-3 long chain polyunsaturated fatty acid critical for fetal brain development that is transported to the fetus from the mother by the placenta. The lysophosphatidylcholine (LPC) transporter, Major Facilitator Superfamily Domain Containing 2a (MFSD2a), is localized in the basal plasma membrane of the syncytiotrophoblast of the human placenta, and MFSD2a expression correlates with umbilical cord blood LPC-DHA levels in human pregnancy. We hypothesized that placenta-specific knockdown of MFSD2a in pregnant mice reduces phospholipid DHA accumulation in the fetal brain. METHODS: Mouse blastocysts (E3.5) were transduced with an EGFP-expressing lentivirus containing either an shRNA targeting MFSD2a or a non-coding sequence (SCR), then transferred to pseudopregnant females. At E18.5, fetuses were weighed and their placenta, brain, liver and plasma were collected. MFSD2a mRNA expression was determined by qPCR in the brain, liver and placenta and phospholipid DHA was quantified by LC-MS/MS. RESULTS: MFSD2a-targeting shRNA reduced placental mRNA MFSD2a expression by 38% at E18.5 (n = 45, p < 0.008) compared with SCR controls. MFSD2a expression in the fetal brain and liver were unchanged. Fetal brain weight was reduced by 13% (p = 0.006). Body weight, placenta and liver weights were unaffected. Fetal brain phosphatidyl choline and phosphatidyl ethanolamine DHA content was lower in fetuses with placenta-specific MFSD2a knockdown. CONCLUSIONS: Placenta-specific reduction in expression of the LPC-DHA transporter MFSD2a resulted in reduced fetal brain weight and lower phospholipid DHA content in the fetal brain. These data provide mechanistic evidence that placental MFSD2a mediates maternal-fetal transfer of LPC-DHA, which is critical for brain growth.

Placenta-specific Slc38a2/SNAT2 knockdown causes fetal growth restriction in mice.

Fetal growth restriction (FGR) is a complication of pregnancy that reduces birth weight, markedly increases infant mortality and morbidity and is associated with later-life cardiometabolic disease. No specific treatment is available for FGR. Placentas of human FGR infants have low abundance of sodium-coupled neutral amino acid transporter 2 (Slc38a2/SNAT2), which supplies the fetus with amino acids required for growth. We determined the mechanistic role of placental Slc38a2/SNAT2 deficiency in the development of restricted fetal growth, hypothesizing that placenta-specific Slc38a2 knockdown causes FGR in mice. Using lentiviral transduction of blastocysts with a small hairpin RNA (shRNA), we achieved 59% knockdown of placental Slc38a2, without altering fetal Slc38a2 expression. Placenta-specific Slc38a2 knockdown reduced near-term fetal and placental weight, fetal viability, trophoblast plasma membrane (TPM) SNAT2 protein abundance, and both absolute and weight-specific placental uptake of the amino acid transport System A tracer, 14C-methylaminoisobutyric acid (MeAIB). We also measured human placental SLC38A2 gene expression in a well-defined term clinical cohort and found that SLC38A2 expression was decreased in late-onset, but not early-onset FGR, compared with appropriate for gestational age (AGA) control placentas. The results demonstrate that low placental Slc38a2/SNAT2 causes FGR and could be a target for clinical therapies for late-onset FGR.