67 Does the impact of obesity on murine oocyte metabolic activity depend on the diet of the previous generation?

Obesity affects millions of families worldwide. Diet-induced obesity is associated with reduced insulin sensitivity and hyperlipidemia. This alters nutrient availability in ovarian follicles and perturbs oocyte mitochondrial (MT) functions and metabolic activity, leading to reduced oocyte quality. In addition, offspring born to obese mothers may carry aberrant MT and epigenetic alterations, leading to a higher sensitivity to an obesogenic diet (OB). Whether this also occurs in their oocytes is not known. In this study, we evaluated whether the effects of an obesogenic diet on offspring metabolic health, oocyte quality, and metabolism are dependent on maternal obesity. Female Swiss outbred mice were fed a control (C, 10% fat, 7% sugar) or OB diet (60% fat, 20% sugar) for 7 wk (n = 6–8/group) then mated with the same males. Female offspring were weaned on C or OB diets in a 2 × 2 factorial design: 4 groups: C»C, C»OB, OB»C and OB»OB. Serum was collected from adult female offspring (10 wk) to measure insulin, total cholesterol (TC), triglycerides (TG), and non-esterified fatty acids (FFA). Oocytes were collected after hormonal stimulation and stained (n = 5–8/offspring) to assess lipid droplet content (LDC, using BODIPY) and MT inner membrane potential (MMP, using JC1) with confocal microscopy. Six oocytes per offspring were incubated (4 h) in 7 µL droplets of L15 lactate-free medium containing 0.5 mM pyruvate under oil. Fluorometric assays on the spent media were used to analyse oocyte metabolic activity. Data are reported as mean ± s.e.M. Maternal OB diet tended to increase TC (P = 0.057) but did not affect other serum parameters. Offspring OB diet increased TC (when born to C mothers, C»OB vs C»C: 180 ± 5.4 vs 113 ± 6.7; or born to OB mothers, OB»OB vs OB»C: 193 ± 10 vs 130 ± 5.3, mg/dL; P = 0.000). Offspring OB diet also increased fasting blood insulin (0.4 ± 0.1 vs 0.2 ± 0.0 and 0.7 ± 0.2 vs 0.1 ± 0.0 respectively, ng/mL; P = 0.014) and tended to increase FFA (P = 0.067). TG were not affected by diet. In oocytes, offspring diet increased LDC (7.2 ± 0.3 vs 5.7 ± 0.3 and 6.8 ± 0.3 vs 5.5 ± 0.3, × 10³ µm³) and MMP (50 ± 1.4 vs 43 ± 1.1 and 50.7 ± 1.4 vs 46.3 ± 1.6, respectively; × 10³ pixel intensity; P < 0.05) with no maternal effects. In contrast, oocyte pyruvate consumption tended to be lower in offspring from OB mothers (P = 0.054) and was significantly lower in OB-fed offspring (64 ± 4.5 vs 73 ± 3.2 and 57 ± 3.5 vs 65 ± 3.0 respectively; pmol/oocyte/h, P = 0.018). Oocyte lactate production tended to be lower in offspring from OB mothers (P = 0.092) without any offspring diet effects. No interactions between maternal and offspring diet effects were detected. In conclusion, OB-diet-fed offspring had hyperlipidemia and hyperinsulinemia, suggesting reduced insulin sensitivity. Oocytes from offspring fed an OB diet had higher intracellular lipids and mitochondrial activity and appear to have a reduced pyruvate metabolic dependence. Despite a tendency toward a higher TC and lower oocyte carbohydrate metabolism in offspring born to OB mothers, the effect of OB diet on the offspring health and oocyte metabolism was not dependent on the maternal diet.