The Effect Of Maternal Dietary Restriction On Growth And Metabolism In Offspring And The DNA Methylation In Their Oocytes

Background:With the popularity of “lose weight” recently,be on a diet become common in pregnant women too.Therefore,intrauterine malnutrition is no longer present in pregnant women of the poverty-stricken areas,also appear in the pregnant women who're dieting.Intrauterine malnutrition can cause the growth restriction of fetal in utero and increase the risk of metabolism disorders when they grow up.The term ‘‘epigenetic'' was pointed out to document the association between environment and phenotypically changes without any change in DNA sequence.Furthermore,it proffered an explanation of how intrauterine malnutrition influence the growth and metabolism of their offspring.More and more evidences showed that the epigenetic modification can be stably inherited to the offspring through germ cells.Gestational period is not only the important period of embryo development,but also an important period of the primordial germ cells(PGCs)form and differentiate to germ cells,accompany by the large scale DNA methylation reprogramming.DNA methyltransferase(DNMTs)?active methyl and demethylation enzymes are take part in the DNA methylation reprogramming.Adverse environmental factors may affectthe activity of DNA methyltransferase or the number of active methyl,and so that the DNA methylation reprogramming are interfered.Genes involved in the DNA methylation reprogramming include the imprinting genes that regulate the development of the embryo in utero and the metabolic genes that regulate the metabolism of glucose and lipid.In order to investigate the effect of adverse intrauterine environment on the development of fetal and the mechanisms of epigenetics,we established a mouse model of maternal food restriction to explore the impact of intrauterine malnutrition on the growth and development and the DNA methylation level of genes in their offspring.Objective:we established a mouse model of maternal food restriction to explore the impact of intrauterine malnutrition on the growth and development and the DNA methylation level of genes in their offspring.Methods:ICR mice were mated with the normal male mice(1:1)in the first day.Next day,the mice with vaginal plug were considered as pregnancy.The pregnancy mice were grouped into the intrauterine malnutrition group and the control group randomly.The day found vaginal plug was seen as the 0.5 day of pregnancy(E0.5),the food eaten by pregnant mice every day was monitored from E0.5 to E12.5.The mice in the intrauterine malnutrition group were given half food of the daily consumption during E0.5-E12.5.The mice in control group were given normal amount food.The pregnant mice of both groups were given normal food after delivery.The number,birth weight and sex ratio of the offspring were observed,and the weight at different growth stages too.Once the offspring was 8 weeks,the glucose tolerance test(GTT)and insulin tolerance test(ITT)were conducted to detect the carbohydrate and insulin metabolism.Finally,the oocytes of female offspring mice were obtained to detect the DNA methylation level of genes with bisulfite treatment.Results:(1)Compare to normal feeding pregnant mice,mice with food restricted were less active,some of them were died before delivery.The pregnant mice with food restricted were smaller than the control mice at the delivery day.And the incidence of premature delivery was significantly increased(P < 0.05).Abortion,stillbirth were common in pregnant mice with food restriction,but the difference was not statistically significant(P > 0.05).(2)The number of offspring between this two groups was similar(P > 0.05).As well as the number of male offspring between the two groups(P > 0.05).However,the offspring of food restricted pregnant mice showed significant low birth weight(P < 0.05).(3)At the age of 3 weeks,there was still a low weight in the offspring of the food restricted pregnant mice,but the difference had no significant difference between groups(P > 0.05).After weaning at3 weeks,the offspring of food restricted pregnant mice began the catch-up growth.At the age of 6 weeks,the average body weight of offspring of food restricted pregnant mice was higher than that of the normal offspring,but the difference was not statistically significant(P > 0.05).During the period of 6-8 weeks,the weight of offspring of normal pregnancy mice increased slowly.But the body weight of offspring of food restriction pregnancy mice increased rapidly.At the age of 8 weeks,the body weight of offspring of food restriction pregnancy mice was significantly higher than that in control group(P < 0.05).According to the growth curve of male and female offspring,the male offspring mice of food restriction pregnancy mice were overweight or obese,but the weight of the female mice was low.The difference was not statistically significant(P > 0.05).(4)The metabolic curve of GTT and GTT experiments were similar between offspring of both groups.(5)The methylation level of H19 and IGF2 r in oocyte from offspring of both groups were similar.The methylation level of leptin in oocyte from offspring of normal pregnancy mice was1.76%,with it was 1.18% in oocyte from offspring of food restriction pregnancy mice,but the difference was not statistically significant(P < 0.05).The methylation ratios of adiponectin gene in the offspring of food restriction pregnant mice and normal pregnant mice were 32.5% and 35%,respectively.The difference was not statistically significant(P > 0.05).(6)Compare to the control group,the whole number and themale mice number of F2-UC and F2-CU had no significat difference between groups.Though the difference was not statistically significant,the birth weight of F2-UC was lower.The birth weight of F2-CU was significantly higher than control group(P<0.05).Conclusion:Food restriction at pregnancy period not only affect the outcome of pregnancy,but also increased the rate of stillbirth and premature birth.It also cause the low birth weight of offspring.The male offspring demonstrated obesity at 8 weeks,but the body weight of female rats was low,they all have normal glucose and insulin metabolism.Although the methylation level of H19,IGF2 r and leptin,adiponectin were normal,the second generation offspring showed abnormal birth weight.There may be other mechanisms affect the growth and development of second generation offspring.