Activation of placental insulin and mTOR signaling in a mouse model of maternal obesity associated with fetal overgrowth

Abstract

Fetal overgrowth is common in obese women and is associated with perinatal complications and increased risk for the child to develop metabolic syndrome later in life. Placental nutrient transport capacity has been reported to be increased in obese women giving birth to large infants; however, the underlying mechanisms are not well established. Obesity in pregnancy is characterized by elevated maternal serum insulin and leptin, hormones that stimulate placental amino acid transporters in vitro. We hypothesized that maternal obesity activates placental insulin/IGF-I/mTOR and leptin signaling pathways. We tested this hypothesis in a mouse model of obesity in pregnancy that is associated with fetal overgrowth. C57BL/6J female mice were fed a control (C) or a high-fat/high-sugar (HF/HS) pelleted diet supplemented by ad libitum access to sucrose (20%) solution. Placentas were collected at embryonic day 18.5. Using Western blot analysis, placental mTOR activity was determined along with energy, inflammatory, leptin, and insulin signaling pathways (upstream modulators of mTOR). Phosphorylation of S6 ribosomal protein (S-235/236), 4E-BP1 (T-37/46), Insulin receptor substrate 1 (Y-608), Akt (T-308), and STAT-3 (Y-705) was increased in obese dams. In contrast, expression of placental caspase-1, IкBα, IL-1β, and phosphorylated-JNK(p46/54-T183/Y185) was unaltered. Fetal amino acid availability is a key determinant of fetal growth. We propose that activation of placental insulin/IGF-I/mTOR and leptin signaling pathways in obese mice stimulates placental amino acid transport and contributes to increased fetal growth.

Keywords: fetal growth; fetal programming; intracellular signaling proteins; maternal-fetal exchange; pregnancy.

Copyright © 2016 the American Physiological Society.

Figures

Fig. 1.

Placental S6 phosphorylation in mice fed a control (C) or high-fat/high-sugar (HF/HS) diet. A: representative Western blots of S6 (S-235/236) and total S6 in homogenates of mice placenta at E18.5. B: summary of the Western blot data. After normalization to β-actin, the mean density of control samples was assigned an arbitrary value of 1. Subsequently, individual control and HF/HS density values were expressed relative to this mean. Values are given as means ± SE; n = 12/each group, *P < 0.05 vs. control, using unpaired Student's t-test.

Fig. 2.

Placental 4E-BP1 phosphorylation in mice fed a control (C) or HF/HS diet. A: representative A: Western blots of 4E-BP1 (T-37/46) and total 4E-BP1 in homogenates of mice placenta at E18.5. B: summary of the Western blot data. After normalization to β-actin, the mean density of control samples was assigned an arbitrary value of 1. Subsequently, individual control and HF/HS density values were expressed relative to this mean. Values are given as means ± SE; n = 12/each group, *P < 0.05 vs. control, using unpaired Student's t-test.

Fig. 3.

Placental AMPK phosphorylation in mice fed a control (C) or HF/HS diet. A: representative Western blots of AMPK (T-172) and total AMPK in homogenates of mice placenta at E18.5. B: summary of the Western blot data. After normalization to β-actin, the mean density of control samples was assigned an arbitrary value of 1. Subsequently, individual control and HF/HS density values were expressed relative to this mean. Values are given as means ± SE; n = 12/each group, *P < 0.05 vs. control, using unpaired Student's t-test.

Fig. 4.

Placental IRS-1 and Akt phosphorylation in mice fed a control (C) or HF/HS diet. A: representative Western blots of IRS-1 (Y-608), Akt (T-308), and total IRS-1/Akt in homogenates of mice placenta at E18.5. B: summary of the Western blot data. After normalization to β-actin, the mean density of control samples was assigned an arbitrary value of 1. Subsequently, individual control and HF/HS density values were expressed relative to this mean. Values are given as means ± SE; n = 12/each group, *P < 0.05 vs. control, using unpaired Student's t-test.

Fig. 5.

Placental of caspase-1, IκBα, JNKp46/54-T183/Y185 and IL-1β expression mice fed a control (C) or HF/HS diet. A: representative Western blots of caspase-1, IκBα, JNKp46/54-T183/Y185, and IL-1β in homogenates of mice placenta at E18.5. B: summary of the Western blot data. After normalization to β-actin, the mean density of control samples was assigned an arbitrary value of 1. Subsequently, individual control and HF/HS density values were expressed relative to this mean. Values are given as means ± SE; n = 12/each group.

Fig. 6.

Placental phosphorylated STAT-3 expression in mice fed a control (C) or HF/HS diet. A: representative Western blots of STAT-3 (Y-705) and total STAT-3 in homogenates of mice placenta at E18.5. B: summary of the Western blot data. After normalization to β-actin, the mean density of control samples was assigned an arbitrary value of 1. Subsequently, individual control and HF/HS density values were expressed relative to this mean. Values are given as means ± SE; n = 12/each group. *P < 0.05 vs. control, using unpaired Student's t-test.