Roles of phosphatidylinositol 3-kinase/protein kinase B signaling pathway in skeletal muscle, peroxisome proliferator-activated receptor γ and phosphatase and tension homologue deleted on chromosome 10 in regulating insulin sensitivity of rats with fetal growth restriction / 中华围产医学杂志

ABSTRACT

Objective To investigate the roles of phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) signaling pathway and its regulatory protein peroxisome proliferator-activated receptor γ (PPAR γ) and phosphatase and tension homologue deleted on chromosome 10 (PTEN) in regulating insulin sensitivity in rats with fetal growth restriction (FGR).Methods Sixteen pregnant rats were randomly divided into two groups including FGR and control groups on the 12th day of pregnancy (eight in each group).The FGR group was given low protein diet (8％ of casein) and restriction diet to establish the neonatal rat model of FGR.All maternal rats after delivery and newborn rats after weaning on 21 days after born were fed with normal diet.Each time blood samples were collected from eight newborn rats of each group to measure levels of fasting plasma glucose (FPG) and fasting insulin(FINS) at the time points of 21 days,two and four months after birth.Then insulin resistance index (IRI) and insulin sensitivity index (ISI) were calculated to evaluate insulin sensitivity.Expression of PI3K,AKT,PPAR γγ,PTEN and glucose transporters 4 (GLUT4) in skeletal muscle at mRNA and protein levels were measured at 21 days,two and four months after birth with real time fluorescence polymerase chain reaction and Western blot,respectively.Relationships between the expression of key molecules of PI3K/AKT signaling pathway and insulin sensitivity were analyzed.T-test,and Pearson's correlation analysis were used for statistical analysis.Results (1) The average birth weight of newborn rats in the FGR group was lower than that of the control group [(4.37± 0.69) vs (7.03±0.55) g,t=-20.75,P＜0.05].The incidence of FGR in the FGR group was 93.33％ (70/75).(2) Compared with normal offspring,those in the FGR group showed significantly increased FPG [two months after birth(5.53± 0.58) vs (7.49 ± 0.38) mmol/L,t=8.08;four months afterbirth(6.35±0.66) vs (8.94±0.90) mmol/L,t=6.58],FINS [two months afterbirth(9.18±0.66) vs (14.67± 1.90) mU/L,t=7.71;four months after birth(33.08±2.76) vs (56.33±2.81) mU/L,t=16.71] and IR1 (two months after birth2.25±0.31 vs 4.90±0.81,t=8.63;four months after birth9.30±0.90 vs 22.44±3.10,t=1 1.51),but decreased ISI (two months after birth0.020 ± 0.002 vs 0.009± 0.001,t=-10.1 4;four months after birth0.005±0.000 vs 0.002 ±0.000,t=-14.91) at two and four months after birth (all P＜0.05).(3) Compared with normal offspring,those in the FGR group showed decreased expression of PI3K (21 days after birth0.082±0.028 vs 0.019±0.004,t=-6.29;two months after birth0.020±0.003 vs 0.010±0.005,t=-4.78;four months after birth0.014±0.004 vs 0.003±0.001,t=-7.87) and GLUT4 (21 days after birth0.132±0.057 vs 0.041 ±0.019,t=-4.32;two months after birth0.183±0.084 vs 0.069±0.017,t=-3.74;four months after birth0.248±0.069 vs 0.113±0.040,t=-4.74) at mRNA level at 21 days,two and four months after birth (all P＜0.05).Compared with normal offspring,decreased expression of PPAR γ (two months after birth0.028±0.002 vs 0.012±0.005,t=-3.70;four months after birth0.030±0.008 vs 0.012±0.005,t=-3.80) and increased expression of PTEN (two months after birth0.020±0.004 vs 0.045±0.014,t=5.09;four months after birth0.023±0.007 vs 0.034±0.009,t=2.57) at mRNA level were observed in offspring of the FGR group at two and four months after birth (all P＜0.05).(4) Compared with normal offspring,expression of PI3K protein (21 days after birth0.22±0.01 vs 0.17±0.02,t=-6.62;two months after birth0.27±0.03 vs 0.16±0.02,t=-7.25;four months after birth0.18±0.01 vs 0.09±0.02,t=-9.79) and GLUT4 protein (21 days after birth0.21 ±0.01 vs 0.03±0.01,t=-27.29;two months after birth0.10±0.01 vs 0.06t±0.01,t=-3.90;four months after birth0.13 ±0.01 vs 0.08± 0.02,t=-8.10) decreased in offspring in the FGR group at 21 days,two and four months after birth (all P＜0.05).Compared with normal offspring,those in the FGR group showed decreased expression of PPAR γ protein (two months after birth0.10 ± 0.01 vs 0.07± 0.01,t =-7.29;four months after birth0.09±0.01 vs 0.08±0.01,t=-2.83),but increased expression of PTEN at protein level (two months after birth0.10±0.01 vs 0.15±0.02,t=6.01;four months after birth0.09±±0.01 vs 0.13±0.02,t=5.51) at two and four months after birth (all P＜0.05).(5) The IRI levels in offsprings in the FGR group were negatively correlated with the expression of PI3K,GLUT4 and PPAR γ at protein level (two months after birthr=-0.90,-0.92 and-0.79;four months after birthr=-0.92,-0.75 and-0.73,all P＜0.05),but positively correlated with the expression of PTEN at protein level (r=0.87 and 0.86,both P＜0.05) at two and four months after birth.Conclusions The abnormal expression of the key molecules of PI3K/AKT signaling pathway precedes the decrease of insulin sensitivity in newborn rats with FGR and the expression regulatory protein PPAR γ and PTEN are also changed,suggesting that these molecules may induce the impairment of insulin sensitivity in rats with FGR and be involved in the development of insulin resistance.