Mouse Modeling of Small for Gestational Age with Obese Metabolic Phenotypes in Adult Stage

Abstract

Background Small for gestational age (SGA) in human is defined as the newborns with birth weight below the 10th percentile, whose prevalence continues to increase due to advanced maternal age. SGA children have a higher risk of developing metabolic disorders including obesity and diabetes later in adult life. Reliable SGA mouse models are needed to study their pathophysiology. Previous reports have suggested various SGA mouse models through dietary restriction of pregnant dams, but their low reproducibility is no small limitation. Therefore, we attempted to improve SGA mouse models with high reproducibility by modifying the dietary restriction. We aimed to model SGA with a smaller height and weight at birth followed by phenotypes of metabolic disorders including glucose tolerance and fatness in adult stages. Methods The 8-week-old C57BL6/J mice were given a normal Chow diet and protein-restricted diet (PRD, 6% protein by kcal) during pregnancy or pregnancy plus lactation. In the PRD group, frequent cannibalism and neglect occurred, so the foster mother system was introduced to minimize the mortality rate. Body weight and nasal-anal length were measured to define SGA. Intraperitoneal glucose tolerance test and body composition (fatness) were measured as metabolic variables. Results By PRD during pregnancy (~3 week), significantly smaller height (30.1±0.2 vs 22.4±0.4 mm, p<0.0001) and weight [1.42±0.02 vs 0.83±0.02 g, p<0.0001 (n=19~37)] and weight at birth were achieved. However, the survival rate in PRD group after postnatal day (PND) 1 was very low (38.1%) due to cannibalism and neglect from dams. We supposed that a golden time exists to rescue newborns to the foster mother to increase the survival, and the survival rate of PND 1 was increased up to 70% by rigorous care before 9am on e19.5 day (plus 1pm and 5pm if needed): fast delivery to the foster mother immediately after birth was most important for the survival. Most PRD group caught up with the height and weight of control group in the first week (PND 7), and there was no difference in body fat mass or glucose tolerance tests in 32 weeks of age. To induce metabolic phenotypes and failure of catch-up growth, PRD period was extended from pregnancy to even lactation period (~6 week). With this extended protocol, the differences in height were maintained until 12 weeks of age and there was a significant difference in body mass index (BMI) [male 0.30±0.01 vs 0.36±0.01 g/cm2, p<0.0001 (n=6~10); female 0.25±0.01 vs 0.31±0.01 g/cm2, p<0.0001 (n=7 for each)] in 12 weeks of age. Conclusion Sufficient duration of protein restriction (pregnancy ~ lactation) yields better phenotype of SGA with high adult BMI with improved survival rate of SGA pups by the rigorous care. Various metabolic parameters are regularly being measured further to confirm metabolic derangement, and if appropriate, this method can be effectively used in future studies.