Teresa M. Reyes

Dissociable Deficits of Executive Function Caused by Gestational Adversity are Linked to Specific Transcriptional Changes in the Prefrontal Cortex

Poor-quality maternal diet during pregnancy, and subsequent gestational growth disturbances in the offspring, have been implicated in the etiology of multiple neurodevelopmental disorders, including ADHD, schizophrenia, and autism. These disorders are characterized, in part, by abnormalities in responses to reward and errors of executive function. Here, we demonstrate dissociable deficits in reward processing and executive function in male and female mice, solely due to maternal malnutrition via high-fat or low-protein diets. Gestational exposure to a high-fat diet delayed acquisition of a fixed ratio response, and decreased motivation as assessed by progressive ratio. In contrast, offspring of a low-protein diet displayed no deficits in operant learning, but were more prone to assign salience to a cue that predicts reward (sign-tracking) in a Pavlovian-conditioned approach task. In the 5-choice serial reaction time task (5-CSRTT), gestational exposure to a high-fat diet promoted impulsivity, whereas exposure to a low-protein diet led to marked inattention. These dissociable executive function deficits are known to be mediated by the medial prefrontal cortex (PFC), which displays markers of epigenetic dysregulation in neurodevelopmental disorders. Following behavioral characterization, we assayed PFC gene expression using a targeted PCR array and found that both maternal diets increased overall transcription in PFC. Cluster analysis of the relationships between individual transcripts and behavioral outcomes revealed a cluster of primarily epigenetic modulators, whose overexpression was linked to executive function deficits. The overexpression of four genes, DNA methyltransferase 1 (DNMT1), δ-opioid receptor (OPRD1), cannabinoid receptor 1 (CNR1), and catechol-o-methyltransferase (COMT), was strongly associated with overall poor performance. All 5-CSRTT deficits were associated with DNMT1 upregulation, whereas impulsive behavior could be dissociated from inattention by overexpression of OPRD1 or COMT, respectively, as well as a distinct cluster of epigenetic regulators. These data provide molecular support for dissociable domains of executive function.

Obesity at conception programs the opioid system in the offspring brain.

Maternal obesity during pregnancy increases the risk for offspring obesity, in part through effects on the developing brain. Previous research has shown that perinatal consumption of highly palatable foods by the mother can influence the development of offspring taste preferences and alter gene expression within the central nervous system (CNS) reward system. Opioids stimulate consumption of both fats and carbohydrates, and overconsumption of these energy dense foods increases the risk for obesity. What has remained unclear is whether this risk can be transmitted to the offspring before gestation or if it is wholly the gestational exposure that affects offspring brain development. Utilizing an embryo transfer experimental design, 2-cell embryos were obtained from obese or control dams, and transferred to obese or control gestational carriers. Expression of the mu-opioid receptor (MOR), preproenkephalin (PENK), and the dopamine transporter was evaluated in the hypothalamus and reward circuitry (ventral tegmental area, prefrontal cortex, and nucleus accumbens) in adult and late embryonic brains. Obesity before pregnancy altered expression levels of both MOR and PENK, with males relatively more affected than females. These data are the first to demonstrate that obesity at conception, in addition to during gestation, can program the brain reward system.

Diet, behavior and immunity across the lifespan

It is increasingly appreciated that perinatal events can set an organism on a life-long trajectory for either health or disease, resilience or risk. One early life variable that has proven critical for optimal development is the nutritional environment in which the organism develops. Extensive research has documented the effects of both undernutrition and overnutrition, with strong links evident for an increased risk for obesity and metabolic disorders, as well as adverse mental health outcomes. Recent work has highlighted a critical role of the immune system, in linking diet with long term health and behavioral outcomes. The present review will summarize the recent literature regarding the interactions of diet, immunity, and behavior.

Removal of high-fat diet after chronic exposure drives binge behavior and dopaminergic dysregulation in female mice

A significant contributor to the obesity epidemic is the overconsumption of highly palatable, energy dense foods. Chronic intake of palatable foods is associated with neuroadaptations within the mesocorticolimbic dopamine system adaptations which may lead to behavioral changes, such as overconsumption or bingeing. We examined behavioral and molecular outcomes in mice that were given chronic exposure to a high-fat diet (HFD; 12weeks), with the onset of the diet either in adolescence or adulthood. To examine whether observed effects could be reversed upon removal of the HFD, animals were also studied 4weeks after a return to chow feeding. Most notably, female mice, particularly those exposed to HFD starting in adolescence, demonstrated the emergence of binge-like behavior when given restricted access to a palatable food. Further, changes in dopamine-related gene expression and dopamine content in the prefrontal cortex were observed. Some of these HFD-driven phenotypes reversed upon removal of the diet, whereas others were initiated by removal of the diet. These findings have implications for obesity management and interventions, as both pharmacological and behavioral therapies are often combined with dietary interventions (e.g., reduction in calorie dense foods).

The hypothalamic transcriptional response to stress is severely impaired in offspring exposed to adverse nutrition during gestation

Gestation is a time of profound vulnerability, as insults during pregnancy increase the lifelong risk of morbidity for the offspring. Increasingly, maternal diet is recognized as a key factor influencing the developing fetus. Poor-quality maternal diets, whether they provide an excess or an insufficiency of nutrients, lead to overt gestational growth disturbances in the offspring, and elevated risk for a common cluster of metabolic and mental disorders. Metabolic disturbances, particularly a substantially increased risk of obesity, have been linked in both maternal overnutrition and maternal undernutrition with abnormal development of the offspring hypothalamus, which serves a vital role in the central regulation of feeding. Additionally, the hypothalamus also coordinates physiological responses to stressors, and may thus play a role in vulnerability to psychiatric disease in these offspring. We examined hypothalamic molecular and endocrine responses to a psychological stressor (restraint) and a physiological stressor (lipopolysaccharide; LPS) in adult offspring from dams fed a high-fat diet or a low-protein diet during gestation and lactation. Targeted gene expression in the hypothalamus for 26 genes of interest sorted via hierarchical clustering revealed that the vast majority of these transcripts were substantially upregulated by both stressors. In contrast, offspring of maternal high-fat and low-protein diets mounted essentially no gene expression response to either stressor. However, male and female offspring of all conditions showed elevated hypothalamic-pituitary-adrenal glucocorticoid responses to both stressors, though the recovery of corticosterone responses after stress termination was significantly impaired in offspring of poor-quality maternal diets. Overall, it appears that the ability of the hypothalamus to respond in the immediate aftermath of stressful experiences is severely impaired in offspring of poor-quality maternal diets, regardless of whether the diet provided insufficient nutrients or excessive nutrients.

Methyl donor supplementation alters cognitive performance and motivation in female offspring from high-fat diet–fed dams

During gestation, fetal nutrition is entirely dependent on maternal diet. Maternal consumption of excess fat during pregnancy has been linked to an increased risk of neurologic disorders in offspring, including attention deficit/hyperactivity disorder, autism, and schizophrenia. In a mouse model, high‐fat diet (HFD)–fed offspring have cognitive and executive function deficits as well as whole‐genome DNA and promoter‐specific hypomethylation in multiple brain regions. Dietary methyl donor supplementation during pregnancy or adulthood has been used to alter DNA methylation and behavior. Given that extensive brain development occurs during early postnatal life—particularly within the prefrontal cortex (PFC), a brain region critical for executive function—we examined whether early life methyl donor supplementation (e.g., during adolescence) could ameliorate executive function deficits observed in offspring that were exposed to maternal HFD. By using operant testing, progressive ratio, and the PFC‐dependent 5‐choice serial reaction timed task (5‐CSRTT), we determined that F1 female offspring (B6D2F1/J) from HFD‐fed dams have decreased motivation (decreased progressive ratio breakpoint) and require a longer stimulus length to complete the 5‐CSRTT task successfully, whereas early life methyl donor supplementation increased motivation and shortened the minimum stimulus length required for a correct response in the 5‐CSRTT. Of interest, we found that expression of 2 chemokines, CCL2 and CXCL10, correlated with the median stimulus length in the 5‐CSRTT. Furthermore, we found that acute adult supplementation of methyl donors increased motivation in HFD‐fed offspring and those who previously received supplementation with methyl donors. These data point to early life as a sensitive time during which dietary methyl donor supplementation can alter PFC‐dependent cognitive behaviors.—McKee, S. E., Grissom, N. M., Herdt, C. T., Reyes, T. M. Methyl donor supplementation alters cognitive performance and motivation in female offspring from high‐fat diet–fed dams. FASEB J. 31, 2352–2363 (2017). www.fasebj.org

Intrauterine inflammation induces sex-specific effects on neuroinflammation, white matter, and behavior

Exposure to inflammation during pregnancy has been linked to adverse neurodevelopmental consequences for the offspring. One common route through which a developing fetus is exposed to inflammation is with intrauterine inflammation. To that end, we utilized an animal model of intrauterine inflammation (IUI; intrauterine lipopolysaccharide (LPS) administration, 50µg, E15) to assess placental and fetal brain inflammatory responses, white matter integrity, anxiety-related behaviors (elevated zero maze, light dark box, open field), microglial counts, and the CNS cytokine response to an acute injection of LPS in both males and females. These studies revealed that for multiple endpoints (fetal brain cytokine levels, cytokine response to adult LPS challenge) male IUI offspring were uniquely affected by intrauterine inflammation, while for other endpoints (behavior, microglial number) both sexes were similarly affected. These data advance our understanding of sex-specific effects of early life exposure to inflammation in a translationally- relevant model.

Male-specific deficits in natural reward learning in a mouse model of neurodevelopmental disorders

Neurodevelopmental disorders, including autism spectrum disorders, are highly male biased, but the underpinnings of this are unknown. Striatal dysfunction has been strongly implicated in the pathophysiology of neurodevelopmental disorders, raising the question of whether there are sex differences in how the striatum is impacted by genetic risk factors linked to neurodevelopmental disorders. Here we report male-specific deficits in striatal function important to reward learning in a mouse model of 16p11.2 hemideletion, a genetic mutation that is strongly associated with the risk of neurodevelopmental disorders, particularly autism and attention-deficit hyperactivity disorder. We find that male, but not female, 16p11.2 deletion animals show impairments in reward-directed learning and maintaining motivation to work for rewards. Male, but not female, deletion animals overexpress mRNA for dopamine receptor 2 and adenosine receptor 2a in the striatum, markers of medium spiny neurons signaling via the indirect pathway, associated with behavioral inhibition. Both sexes show a 50% reduction of mRNA levels of the genes located within the 16p11.2 region in the striatum, including the kinase extracellular-signal related kinase 1 (ERK1). However, hemideletion males show increased activation in the striatum for ERK1, both at baseline and in response to sucrose, a signaling change associated with decreased striatal plasticity. This increase in ERK1 phosphorylation is coupled with a decrease in the abundance of the ERK phosphatase striatum-enriched protein-tyrosine phosphatase in hemideletion males. In contrast, females do not show activation of ERK1 in response to sucrose, but notably hemideletion females show elevated protein levels for ERK1 as well as the related kinase ERK2 over what would be predicted by mRNA levels. These data indicate profound sex differences in the impact of a genetic lesion linked with neurodevelopmental disorders, including mechanisms of male-specific vulnerability and female-specific resilience impacting intracellular signaling in the brain.

Suboptimal nutrition in early life affects the inflammatory gene expression profile and behavioral responses to stressors

Nutritional conditions in early life can have a lasting impact on health and disease risk, though the underlying mechanisms are incompletely understood. In the healthy individual, physiological and behavioral responses to stress are coordinated in such a way as to mobilize resources necessary to respond to the stressor and to terminate the stress response at the appropriate time. Induction of proinflammatory gene expression within the brain is one such example that is initiated in response to both physiological and psychological stressors, and is the focus of the current study. We tested the hypothesis that early life nutrition would impact the proinflammatory transcriptional response to a stressor. Pregnant and lactating dams were fed one of three diets; a low-protein diet, a high fat diet, or the control diet through pregnancy and lactation. Adult male offspring were then challenged with either a physiological stressor (acute lipopolysaccharide injection, IP) or a psychological stressor (15 min restraint). Expression of 20 proinflammatory and stress-related genes was evaluated in hypothalamus, prefrontal cortex, amygdala and ventral tegmental area. In a second cohort, behavioral responses (food intake, locomotor activity, metabolic rate) were evaluated. Offspring from low protein fed dams showed a generally reduced transcriptional response, particularly to LPS, and resistance to behavioral changes associated with restraint, while HF offspring showed an exacerbated transcriptional response within the PFC, a reduced transcriptional response in hypothalamus and amygdala, and an exacerbation of the LPS-induced reduction of locomotor activity. The present data identify differential proinflammatory transcriptional responses throughout the brain driven by perinatal diet as an important variable that may affect risk or resilience to stressors.

Voluntary exercise blocks Western diet-induced gene expression of the chemokines CXCL10 and CCL2 in the prefrontal cortex

Obesity increases inflammation, both peripherally and centrally, and exercise can ameliorate some of the negative health outcomes associated with obesity. Within the brain, the effect of obesity on inflammation has been well characterized in the hypothalamus and hippocampus, but has been relatively understudied in other brain regions. The current study was designed to address two primary questions; (1) whether western diet (high fat/high sucrose) consumption would increase markers of inflammation in the prefrontal cortex and (2) whether concurrent voluntary wheel running would ameliorate any inflammation. Adult male mice were exposed to a western diet or a control diet for 8weeks. Concurrently, half the animals were given running wheels in their home cages, while half did not have access to wheels. At the conclusion of the study, prefrontal cortex was removed and expression of 18 proinflammatory genes was assayed. Expression of a number of proinflammatory molecules was upregulated by consumption of the western diet. For two chemokines, chemokine (C-C motif) ligand 2 (CCL2) and C-X-C motif chemokine 10 (CXCL10), voluntary exercise blocked the increase in the expression of these genes. Cluster analysis confirmed that the majority of the tested genes were upregulated by western diet, and identified another small cluster of genes that were downregulated by either diet or exercise. These data identify a proinflammatory phenotype within the prefrontal cortex of mice fed a western diet, and indicate that chemokine induction can be blocked by voluntary exercise.