Liver phosphatidylinosital 3-kinase/protein kinase B pathway is involved in the decrease of insulin sensitivity in rats with fetal growth restriction

Abstract

Objective To investigate the effect of liver phosphatidylinosital 3-kinase/protein kinase B (PI3-K/AKT) pathway on the decrease of insulin sensitivity in fetal growth restriction (FGR) rats.Methods Twenty pregnant female rats were randomly divided into two groups one day after conception:normal-protein group and low protein group (n=10,respectively).Rats in low-protein group was given low protein diet (8.00％ protein) during pregnancy to build FGR model,while normal-protein group was given normal protein diet (20.00％ protein).On day 3,7,14,30,60 and 90 after birth,fasting blood samples of 8 male FGR offsprings from low-protein group and 8 normal offsprings from normal-protein group were collected to measure fasting plasma glucose and insulin level.Then insulin resistance index and insulin sensitivity index were calculated to determine insulin sensitivity.On day 7,14,30,60 and 90 after birth,liver tissue of 8 male FGR and normal offsprings were collected,insulin receptor substrate 1,2 (IRS1/IRS2)and glucose transporter 4 (GLUT4) mRNA expression were measured by real-time fluorescence polymerase chain reaction and the protein expressions of IRS1,PI3-K (subunit p110β),and AKT and phosphorylated AKT (pAKT) were measured by Western blot.The relationships between the expression changes of key molecules of PI3-K/AKT pathway and insulin sensitivity were analyzed by correlation and multiple linear regression method.Results (1) Mean birth weight of baby rats in low-protein group was significantly lower than that of normal-protein group [(4.92±0.36) g vs (6.43±0.59) g,t=14.73,P＜0.05].The incidence of FGR in low-protein group was 88.2％ (97/110); and for male offsprings,it was 94.1 ％ (48/51).(2) Compared to normal offsprings,fasting plasma glucose levels of male FGR offsprings were significantly higher from the age of 60 days to 90 days.Insulin levels and insulin resistance index were significantly higher and insulin sensitivity index was lower from the age of 30 days to 90 days,P＜0.05 respectively.(3) Compared to normal offsprings,IRS1 (0.45 ± 0.02 vs 0.68± 0.03,t=16.633,P＜0.05) and IRS2 mRNA (0.34±0.10 vs 0.70±0.19,t=4.864,P＜0.05) expressions in FGR offsprings were lower from day 7 after birth to day 90 (0.48±0.03 vs 0.59±0.05,t=5.237,P＜0.05; 0.49±0.20 vs 0.70±0.11,t=2.253,P＜0.05).There were no differences in expressions of GIUT4 mRNA and AKT protein between two groups (P＞ 0.05).IRS1,PI3-K and pAKT protein expressions of FGR offsprings decreased significantly from day 14 (0.22±0.05 vs 0.52±0.11,t=7.024,P＜0.05; 0.46±0.03 vs 0.97±0.08,t=17.508,P＜0.05; 0.62±0.10 vs 0.89±0.08,t=6.100,P＜0.05) to day 90 (1.11±0.08 vs 1.32±0.14,t=3.714,P＜0.05; 0.63±0.07 vs 1.00±0.19,t=5.206,P＜0.05;0.28±0.03 vs 0.45±0.10,t=4.880,P＜0.05).(4) The pAKT protein expression level of FGR rats was positively correlated with insulin sensitivity index (r=0.704,P＜0.05) ; while negatively correlated to the level of fasting plasma glucose (r=-0.609,P＜0.05),fasting insulin (r=-0.561,P＜0.05) and insulin resistance index (r =0.577,P＜ 0.05).Conclusions The changes of some key molecules' expressions of PI3-K/AKT pathway in liver might be involved in the insulin resistance in FGR rats. Key words: Fetal growth retardation; Insulin resistance; 1-Phosphatidylinositol 3-kinase; Protooncogene proteins c-akt; Liver; Disease models,animal