Lipocalin-2 (Lcn2) expression is mediated by maternal nutrition during the development of the fetal liver

Abstract

The mechanisms by which maternal protein deficiency programs insulin action in the offspring are poorly understood. The interpretation of transcriptomics is complicated by homeostatic adaptations, for example, changes in amino acid metabolism, which are potentially unrelated to the programming mechanism. The fatty acid composition of the maternal diet modulates the programming of insulin action, offering a possible strategy to circumvent these complications. Fetal livers harvested on d21 of gestation from pregnant rats fed high-protein (18 % w/w) and low-protein (9 % w/w) diets prepared with either corn or soya oil were screened with rat genome microarrays. Although a low-protein maternal diet altered the abundance of more than one hundred mRNAs in the fetal liver, only 40 were changed by the fatty acid composition of the diet (P < 0.05). One of these mRNAs was identified as lipocalin-2 (Lcn2). This pattern of differential expression was confirmed by qRT-PCR. The expression of Lcn2 was decreased by low-protein diets when the diet contained soya oil, whereas the effect of protein was much smaller in the group fed diets prepared with corn oil. The decrease in Lcn2 expression produced by soya oil persisted into adult life. Levels of the Lcn2 protein were closely correlated to the mRNA abundance. The results suggest a possible involvement of Lcn2 in the programming of hepatic function.

Fig. 1

Expression of lipocalin-2 (Lcn2) determined by qRT-PCR. Expression is relative to the 18S ribosomal RNA in arbitrary units. Data are mean ± SEM. Columns sharing a superscript letter are not significantly different (P > 0.05). a Expression in fetal liver of female fetuses on d21 of gestation 18S n = 8, 9S n = 10, 18C n = 8, 9C n = 7. Data were analyzed by REML Protein P = 0.007 Oil P = 0.008 Protein·Oil P = 0.273. b Expression in fetal liver of male fetuses on d21 of gestation (n = 6 for all groups). c Expression in liver of female offspring at 6 weeks of age (n = 6 for all groups). Data were analyzed by two-way ANOVA Protein P = 0.167, Oil P = 0.035, Protein·Oil P = 0.94

Fig. 2

Lipocalin-2 protein levels in protein extracted from the liver of female fetuses at d21 of gestation. a The pixel density of replicate 100 μg samples ± SEM (n = 6). Data were analyzed by one-way ANOVA P = 0.017, and columns sharing a superscript letter are not significantly different (P > 0.05). A typical blot is shown in the lower panel Sal = 25 μg protein extracted from the liver of an adult rat infected with Salmonella enterica (Robertson et al. 2003). b Correlation between Lcn2 protein expression (pixel density on Western blots) and mRNA (relative expression by RT-PCR) of a subset of samples, n = 6 per treatment. Line fitted by linear regression (P < 0.001, R ² = 0.32)