The effects of maternal diets, varying in fat content, on proximal hepatic and skeletal muscle insulin signalling in neonatal wistar rat offspring
The incidence of type 2 diabetes (T2D) is persistently increasing globally. T2D is associated with pancreatic β cell dysfunction and insulin resistance in peripheral tissues such as the liver and skeletal muscle. Skeletal muscle is the major site for insulin stimulated glucose uptake. Maintenance on a gestational high fat diet may programme insulin resistance. Programming is induced by the exposure of organisms to either a stimulus or insult during foetal and/or early neonatal life and alters offspring physiology and metabolism. The aim of the present study was therefore to investigate the effects of maternal diets, varying in fat content, on neonatal hepatic and skeletal muscle gene (mRNA) and protein (immunoreactivity) expression of proximal insulin signalling factors: insulin receptor alpha (IRα), insulin receptor substrate 2 (IRS2) and phosphoinositide 3-kinase-p110 alpha (PI3K-p110α), and to assess the therapeutic potential of Aspalathus linearis extract after high fat programming. Pregnant rats were randomised into groups maintained on diets with varying fat proportions: 10% (control), 20% (20F), 30% (30F) and 40% (40F) fat as energy throughout gestation. Neonatal liver and skeletal muscle were collected to determine the proximal insulin signalling expression profiles of the target factors: IRα, IRS2 and PI3K-p110α. Quantitative polymerase chain reaction (qPCR) was applied to determine mRNA expression of these target insulin signalling factors. Immunostaining of the target proteins in the liver and skeletal muscle was performed followed by relative quantification with image analysis software. Further, Aspalathus linearis (Al) extract was orally administered to mothers during gestation in the 10% (Control-Al) and 40% (HFD-Al) diets at a dose of 150 mg/kg. Body weight, food intake and blood glucose concentrations were monitored throughout gestation in mothers. Maternal diets, varying in the percentage of fat content, showed no significant effect on neonatal hepatic IR and IRS2 mRNA expression. However, hepatic PI3K mRNA expression was elevated in 30F neonates compared to 20F neonates. Skeletal muscle IR and PI3K mRNA expression were reduced in the 30F and 40F neonates compared to 20F neonates. There was reduced hepatic IRα immunoreactivity in 40F neonates compared to control and 20F neonates. Further, skeletal muscle IRα immunoreactivity was significantly reduced in 30F and 40F neonates compared to control neonates. Therefore foetal high fat programming reduced IRα in both the liver and skeletal muscle which may impair proximal insulin signalling in these glucose recipient organs. Aspalathus linearis had no effect on maternal serum insulin and glucagon concentrations. In addition, maternal caloric intake, body weight and organ weights (liver, brain and pancreas) were not altered amongst the groups. Further, HFD-Al neonates were heavier than control neonates. In conclusion, Aspalathus linearis, at a dose of 150 mg/kg, had neither harmful nor ameliorative effects in pregnant mothers fed high fat diet during gestation. In addition, Aspalathus linearis treatment had no ameliorative effects on neonates from mothers fed high fat diet throughout gestation.