Exercise rescues obese mothers' insulin sensitivity, placental hypoxia and male offspring insulin sensitivity

Abstract

The prevalence of obesity during pregnancy continues to increase at alarming rates. This is concerning as in addition to immediate impacts on maternal wellbeing, obesity during pregnancy has detrimental effects on the long-term health of the offspring through non-genetic mechanisms. A major knowledge gap limiting our capacity to develop intervention strategies is the lack of understanding of the factors in the obese mother that mediate these epigenetic effects on the offspring. We used a mouse model of maternal-diet induced obesity to define predictive correlations between maternal factors and offspring insulin resistance. Maternal hyperinsulinemia (independent of maternal body weight and composition) strongly associated with offspring insulin resistance. To test causality, we implemented an exercise intervention that improved maternal insulin sensitivity without changing maternal body weight or composition. This maternal intervention prevented excess placental lipid deposition and hypoxia (independent of sex) and insulin resistance in male offspring. We conclude that hyperinsulinemia is a key programming factor and therefore an important interventional target during obese pregnancy, and propose moderate exercise as a promising strategy to improve metabolic outcome in both the obese mother and her offspring.

Figure 1

Male offspring insulin is correlated to (a) maternal fasting insulin, but not to (b) maternal leptin, (c) maternal body weight, (d) maternal fat mass, (e) maternal triglycerides or (f) maternal total cholesterol. Dams (n = 11 control and n = 11 obese) were mated, allowed to litter and litters from both groups standardised to 6 pups per litter (equal male to female ratio). At weaning, dams were weighed and body composition assessed by TD-NMR. Dams were then fasted overnight and killed the following morning, when blood was collected for serum analysis. Male offspring from the control and obese dam groups were maintained to 8 weeks of age, when they were killed and blood collected for serum analysis. Data was analysed by 2- tailed Spearman correlation (alpha = 0.05), and presented as filled circles for matched control dams and offspring and as open circles for matched obese dams and offspring.

Figure 2. Glucose tolerance test at D18 of pregnancy and fed insulin concentrations at D19.

On day 18 of gestation, control (white bars), obese (black bars) and obese-exercised (grey bars) dams were fasted for 4 hours, weighed and given an intraperitoneal dose of glucose (1 g/kg). Tail blood glucose was measured at time 0 (before the injection) and then again at timed intervals from the time of injection. Tail blood glucose measurements during the GTT were analyzed and presented as (a) area under the curve measurements calculated by summation of trapezoids and (b) fed serum insulin concentrations at E19 as measured by ELISA. Data are presented as means+/−SEM, n = 6 per group. The effects of obesity and exercise were analyzed by One-way ANOVA followed by Tukey’s multiple comparison test.

Figure 3

Lipid accumulation in the placenta (a) Total lipid content of placentae from control (white bars), obese (black bars) and obese-exercised (grey bars) dams were determined by Folch method and data presented as means+/−SEM, n = 6 per group. The effects of obesity and exercise were analyzed One-way ANOVA followed by Tukey’s multiple comparison test; (b) Oil red O-stained placentae sectioned from frozen tissue show increased lipid deposition within the decidual (Db)/junctional zone (Jz), but not in the labyrinthine zone (Lz) of obese placentae compared to controls, which is normalized by exercise, Scale bar = 100 μM.

Figure 4. Placental HIF1A is upregulated by maternal obesity but attenuated by exercise.

(a) HIF1A protein levels in placentae from control (white bars), obese (black bars) and obese-exercised (grey bars) dams, with representative blots shown above. Data are presented as means+/− SEM, n = 6 per group and the effects of obesity and exercise were analyzed by One-way ANOVA followed by Tukey’s multiple comparison test; (b) Pearson correlation between maternal insulin and placental HIF1A protein levels, 2-tailed p = 0.002 (alpha = 0.05) and r = 0.68, with data from matched groups displayed for controls as filled circles, obese as filled squares and obese-exercised as open triangles.

Figure 5. Insulin sensitivity in offspring of obese mothers is restored to control levels by maternal exercise.

(a) Fasting serum insulin in male offspring at 8 weeks of age (b), Fasted IRS1 protein levels in epididymal adipose tissue of 8-week old male offspring of control (white bars), obese (black bars) and obese-exercised (grey bars) dams with representative blots shown above. Data are presented as means+/−SEM, n = 8 per group. The effects of obesity and exercise were analyzed One-way ANOVA followed by Tukey’s multiple comparison test.