Gestational overgrowth and undergrowth affect neurodevelopment: similarities and differences from behavior to epigenetics

Abstract

The size of an infant at birth, a measure of gestational growth, has been recognized for many years as a biomarker of future risk of morbidity. Both being born small for gestational age (SGA) and being born large for gestational age (LGA), are associated with increased rates of obesity and metabolic disorder, as well as a number of mental disorders including attention deficit/hyperactivity disorder, autism, anxiety, and depression. The common risks raise the question of what neurobiological mechanisms are altered in SGA and LGA offspring. Here we review recent findings allowing for direct comparison of neurobiological outcomes of SGA and LGA in human and animal models. We also present new data highlighting similarities and differences in behavior and neurobiology in our mouse models of SGA and LGA. Overall, there is significant data to support aberrant epigenetic mechanisms, particularly related to DNA methylation, in the brains of SGA and LGA offspring, leading to disruptions in the cell cycle in development and gene expression in adulthood.

Keywords: ADHD; BDNF; CNS; DA; DAT; DNA methylation; Dopamine; GWG; HF; IUGR; Intrauterine growth restriction; LGA; LP; MOR; Macrosomia; Mesolimbic; NAc; Opioid; PENK; PFC; PI3K; SGA; TH; VTA; attention deficit/hyperactivity disorder; brain-derived neurotrophic factor; central nervous system; dopamine; dopamine transporter; gestational weight gain; high-fat; intrauterine growth restriction; large for gestational age; low-protein; mu-opioid receptor; nucleus accumbens; phosphoinositide 3-kinase; prefrontal cortex; preproenkephalin; small for gestational age; tyrosine hydroxylase; ventral tegmental area.

Figure 1

LGA offspring demonstrate an exaggerated locomotor response to cocaine. Male mice (n=8/group) were tested for their locomotor response to cocaine using the Comprehensive Lab Animal Monitoring System (Columbus Instruments). For detailed methods, see (Vucetic, Totoki, et al., 2010). Animals were previously acclimated to the cages and were housed in the cages for 3 days: day 1 (undisturbed); day 2 saline injection (11am); day 3, cocaine (11am, 20 mg/kg, IP). There were no differences in locomotor activity either at baseline or in response to saline injection. In response to cocaine, both control and experimental groups of animals had a significant increase in activity, however, LGA offspring had an exaggerated locomotor response. The peak response was nearly twice that of controls, and these animals also took significantly longer to return to baseline levels of activity. (One-way repeated measures ANOVA, significant interaction between group and time, F(6,84)=2.25, *p<.05)

Figure 2

Male (left) and female (right) SGA (gray bars) and LGA (black bars) offspring were tested in the light-dark apparatus (n=9–10/group). Data represent the number of transitions between the light and the dark side of the box during the 5-min test period. In both sexes, SGA and LGA offspring make significantly more transitions as compared to control offspring (Student’s t-test). *p<.05, **p<.01

Figure 3

Social interaction in SGA (A) and LGA (B) males, and both SGA and LGA females (C). In males, social interaction was evaluated by placing the target mouse in a novel cage with an unfamiliar male mouse. Behaviors were coded for 10 min. SGA animals showed significantly less time in social behaviors, with no difference in non-social behaviors (Student’s t-test) *p<.05, n=5–6/group. This was primarily accounted for by a decrease in sniffs. Similarly, LGA animals (B) showed a decrease in the total social time and the number of social interactions, with no difference in nonsocial interactions. (Student’s t-test) *p<.05, n=5–6/group). Females were evaluated using a 3-chambered social choice task (C). For detailed methods, see (Sankoorikal et al., 2006). The data show the difference score, which is the time spent on the social side of the assay (chamber with a mouse in a cylinder) versus time spent on the nonsocial side (chamber with paper in a cylinder). The SGA females show a clear decrease in time spent on the social side when compared to control animals (which show a positive difference score, indicating that they spend more time in the chamber that houses another mouse, Student’s t-test, p<.05). LGA animals show a similar pattern to the SGA animals, however, this difference is not statistically reliable. n=6/group

Figure 4

Expression of target genes in SGA mice was determined by quantitative RT-PCR using gene specific Taqman Probes with Taqman gene expression Master Mix (ABI). For detailed methods, see (Vucetic et al., 2012). Changes in gene expression were calculated against an unchanged GAPDH standard. PENK was significantly reduced in the PFC of SGA mice, while MOR was significantly decreased in the NAc of SGA mice. n=4/group, Student’s t-test, *p<.05, **p<.01.

Figure 5

Global DNA Methylation in SGA offspring. The amount of global, genome-wide DNA methylation was quantified using the Methylamp Global DNA Methylation Quantification Ultra Kit (Epigentek). For detailed methods, see (Vucetic, Kimmel, et al., 2010). SGA offspring showed significantly reduced global methylation in the VTA, NAc, PFC and HYP, as compared to controls. Student’s t-test, *p<.05, n=6/group.

Figure 6

Expression of target genes in SGA and LGA mice was determined by quantitative RT-PCR using gene specific Taqman Probes with Taqman gene expression Master Mix (ABI). For detailed methods, see (Vucetic et al., 2012). Changes in gene expression were calculated against an unchanged GAPDH standard. DNMT1 and MeCP2 were significantly increased in the NAc in both SGA (top) and LGA (bottom) male offspring. Student’s t-test, n=5/group, *p<.05.