High-fat diet before and during pregnancy causes marked up-regulation of placental nutrient transport and fetal overgrowth in C57/BL6 mice

Abstract

Maternal overweight and obesity in pregnancy often result in fetal overgrowth, which increases the risk for the baby to develop metabolic syndrome later in life. However, the mechanisms underlying fetal overgrowth are not established. We developed a mouse model and hypothesized that a maternal high-fat (HF) diet causes up-regulation of placental nutrient transport, resulting in fetal overgrowth. C57BL/6J female mice were fed a control (11% energy from fat) or HF (32% energy from fat) diet for 8 wk before mating and throughout gestation and were studied at embryonic day 18.5. The HF diet increased maternal adiposity, as assessed by fat pad weight, and circulating maternal leptin, decreased serum adiponectin concentrations, and caused a marked increase in fetal growth (+43%). The HF diet also increased transplacental transport of glucose (5-fold) and neutral amino acids (10-fold) in vivo. In microvillous plasma membranes (MVMs) isolated from placentas of HF-fed animals, protein expression of glucose transporter 1 (GLUT1) was increased 5-fold, and protein expression of sodium-coupled neutral amino acid transporter (SNAT) 2 was elevated 9-fold. In contrast, MVM protein expression of GLUT 3 or SNAT4 was unaltered. These data suggest that up-regulation of specific placental nutrient transporter isoforms constitute a mechanism linking maternal high-fat diet and obesity to fetal overgrowth.

Figure 1.

Maternal glucose tolerance test at E18.5 after a 6-hour fast. Values are means ± se; n = 5/diet. C (○) and HF diets (▪) were given to female mice 8 wk before and throughout gestation. An i.p. injection of 2 g/kg of a 30% glucose solution was given, and blood glucose measurements from the tail vein at time points are shown. No significant difference was seen between the two diet groups.

Figure 2.

Fetal, placental, and total litter weights at E18.5. Values are means ± se. C and HF diets were given to female mice 8 wk before and throughout gestation. P < 0.05 was considered significant; unpaired Student’s t test; n ≥ 18 litters/diet.

Figure 3.

Placental nutrient transport capacity in vivo at E18.5. Unidirectional maternal-fetal clearances (K_mf) for methylglucose and MeAIB were measured in anesthetized dams (n=5/diet). Values are means± sem. C and HF diets were fed to female mice 8 wk before and throughout gestation. *P < 0.05, **P < 0.001; unpaired Student’s t test.

Figure 4.

Protein expression of placental nutrient transporters at E18.5. C and HF diets were given to female mice 8 wk before and throughout gestation. Representative Western blots are shown for GLUT1, SNAT2, SNAT4, and β-actin in isolated MVM and GLUT3 and β-actin in homogenates of pooled placentas from animals fed either the C or HF diet.

Figure 5.

Protein expression of placental nutrient transporters at E18.5. Summary of densitometry of SNAT 2 and GLUT 1 band (normalized for β-actin). Values are means ± sem; n = 7 (pooled placentas from 7 litters for each diet). No difference was seen in SNAT4 or GLUT3 expression. *P < 0.05, **P < 0.001; unpaired Student’s t test.