Uteroplacental insufficiency alters rat hippocampal cellular phenotype in conjunction with ErbB receptor expression

Effects of intrauterine growth restriction on embryonic hippocampal dentate gyrus neurogenesis and postnatal critical period of synaptic plasticity that govern learning and memory function

Intrauterine growth restriction (IUGR) complicates up to 10% of human pregnancies and is the second leading cause of perinatal morbidity and mortality after prematurity. The most common etiology of IUGR in developed countries is uteroplacental insufficiency (UPI). For survivors of IUGR pregnancies, long-term studies consistently show a fivefold increased risk for impaired cognition including learning and memory deficits. Among these, only a few human studies have highlighted sex differences with males and females having differing susceptibilities to different impairments. Moreover, it is well established from brain magnetic resonance imaging that IUGR affects both white and gray matter. The hippocampus, composed of the dentate gyrus (DG) and cornu ammonis (CA) subregions, is an important gray matter structure critical to learning and memory, and is particularly vulnerable to the chronic hypoxic-ischemic effects of UPI. Decreased hippocampal volume is a strong predictor for learning and memory deficits. Decreased neuron number and attenuated dendritic and axonal morphologies in both the DG and CA are additionally seen in animal models. What is largely unexplored is the prenatal changes that predispose an IUGR offspring to postnatal learning and memory deficits. This lack of knowledge will continue to hinder the design of future therapy to improve learning and memory. In this review, we will first present the clinical susceptibilities and human epidemiology data regarding the neurological sequelae after IUGR. We will follow with data generated using our laboratory’s mouse model of IUGR, that mimics the human IUGR phenotype, to dissect at the cellular and molecular alterations in embryonic hippocampal DG neurogenesis. We will lastly present a newer topic of postnatal neuron development, namely the critical period of synaptic plasticity that is crucial in achieving an excitatory/inhibitory balance in the developing brain. To our knowledge, these findings are the first to describe the prenatal changes that lead to an alteration in postnatal hippocampal excitatory/inhibitory imbalance, a mechanism that is now recognized to be a cause of neurocognitive/neuropsychiatric disorders in at-risk individuals. Studies are ongoing in our laboratory to elucidate additional mechanisms that underlie IUGR-induced learning and memory impairment and to design therapy aimed at ameliorating such impairment.

Taurine supplementation improves hippocampal metabolism in immature rats with intrauterine growth restriction (IUGR) through protecting neurons and reducing gliosis

Taurine as an essential amino acid in the brain could play an important role in protecting the fetal brain of intrauterine growth restriction (IUGR). The hippocampus with IUGR showed neural metabolic disorder and structure changed that affected memory and learning ability. This study was aimed to identify the effect of taurine supplementation on the metabolism alterations and cellular composition changes of the hippocampus in IUGR immature rats. Metabolite concentrations were determined by magnetic resonance spectroscopy (MRS) in the hippocampus of juvenile rats with IUGR following taurine supplementation with antenatal or postnatal supply. The composition of neural cells in the hippocampus was observed by immunohistochemical staining (IHC) and western blotting (WB). Antenatal taurine supplementation increased the ratios of N-acetylaspartate (NAA) /creatine (Cr) and glutamate (Glu) /Cr of the hippocampus in the IUGR immature rats, but reduced the ratios of choline (Cho) /Cr and myoinositol (mI) /Cr. At the same time, the protein expression of NeuN in the IUGR rats was increased through intrauterine taurine supplementation, and the GFAP expression was reduced. Especially the effect of antenatal taurine was better than postpartum. Furthermore, there existed a positive correlation between the NAA/Cr ratio and the NeuN protein expression (R = 0.496 p < 0.001 IHC; R = 0.568 p < 0.001 WB), the same results existed in the relationship between the mI/Cr ratio and the GFAP protein expression (R = 0.338 p = 0.019 IHC; R = 0.440 p = 0.002 WB). Prenatal taurine supplementation can better improve hippocampal neuronal metabolism by increasing NAA / Cr ratio related to the number of neurons and reducing Cho / Cr ratio related to the number of glial cells.

Hippocampal mTOR Dysregulation and Morphological Changes in Male Rats after Fetal Growth Restriction

Fetal growth restriction (FGR) has been linked to long-term neurocognitive impairment, especially in males. To determine possible underlying mechanisms, we examined hippocampal cellular composition and mTOR signaling of male rat FGR offspring during main brain growth and development (postnatal days (PND) 1 and 12). FGR was either induced by a low-protein diet throughout pregnancy, experimental placental insufficiency by bilateral uterine vessel ligation or intrauterine stress by “sham” operation. Offspring after unimpaired gestation served as common controls. Low-protein diet led to a reduced cell density in the molecular dentate gyrus subregion, while intrauterine surgical stress was associated with increased cell density in the cellular CA2 subregion. Experimental placental insufficiency caused increased mTOR activation on PND 1, whereas intrauterine stress led to mTOR activation on PND 1 and 12. To determine long-term effects, we additionally examined mTOR signaling and Tau phosphorylation, which is altered in neurodegenerative diseases, on PND 180, but did not find any changes among the experimental groups. Our findings suggest that hippocampal cellular proliferation and mTOR signaling are dysregulated in different ways depending on the cause of FGR. While a low-protein diet induced a decreased cell density, prenatal surgical stress caused hyperproliferation, possibly via increased mTOR signaling.

Intrauterine Growth Restriction Causes Abnormal Embryonic Dentate Gyrus Neurogenesis in Mouse Offspring That Leads to Adult Learning and Memory Deficits

Human infants who suffer from intrauterine growth restriction (IUGR), which is a failure to attain their genetically predetermined weight, are at increased risk for postnatal learning and memory deficits. Hippocampal dentate gyrus (DG) granule neurons play an important role in memory formation; however, it is unknown whether IUGR affects embryonic DG neurogenesis, which could provide a potential mechanism underlying abnormal postnatal learning and memory function. Using a mouse model of the most common cause of IUGR, induced by hypertensive disease of pregnancy, we first assessed adult learning and memory function. We quantified the percentages of embryonic hippocampal DG neural stem cells (NSCs) and progenitor cells and developing glutamatergic granule neurons, as well as hippocampal volumes and neuron cell count and morphology 18 and 40 d after delivery. We characterized the differential embryonic hippocampal transcriptomic pathways between appropriately grown and IUGR mouse offspring. We found that IUGR offspring of both sexes had short-term adult learning and memory deficits. Prenatally, we found that IUGR caused accelerated embryonic DG neurogenesis and Sox2⁺ neural stem cell depletion. IUGR mice were marked by decreased hippocampal volumes and decreased doublecortin⁺ neuronal progenitors with increased mean dendritic lengths at postnatal day 18. Consistent with its known molecular role in embryonic DG neurogenesis, we also found evidence for decreased Wnt pathway activity during IUGR. In conclusion, we have discovered that postnatal memory deficits are associated with accelerated NSC differentiation and maturation into glutamatergic granule neurons following IUGR, a phenotype that could be explained by decreased embryonic Wnt signaling.

Short- and Long-Term Implications of Small for Gestational Age

Fetal growth restriction (FGR) describes a fetus' inability to attain adequate weight gain based on genetic potential and gestational age and is the second most common cause of perinatal morbidity and mortality after prematurity. Infants who have suffered fetal growth restriction are at the greatest risks for short- and long-term complications. This article specifically details the neurologic and cardiometabolic sequalae associated with fetal growth restriction, as well as the purported mechanisms that underlie their pathogenesis. We end with a brief discussion about further work that is needed to gain a more complete understanding of fetal growth restriction.

Mechanisms Underlying Neurologic Injury in Intrauterine Growth Restriction

Intrauterine growth restriction is a condition that prevents normal fetal development, and previous studies have reported that intrauterine growth restriction is caused by adverse intrauterine factors. This condition affects both short- and long-term neurodevelopmental disorders. Studies have revealed that neurodevelopmental disorders can contribute to gray and white matter damage and decrease the brain volume of affected individuals. Further, these disorders are associated with increased risks of mental retardation, cognitive impairment, and cerebral palsy, which seriously affect the quality of life. Although the mechanisms underlying the neurologic injury associated with intrauterine growth restriction are not completely clear, studies have revealed that neuronal apoptosis, neuroinflammation, oxidative stress, excitatory toxicity, disruption of blood-brain barrier, and epigenetics may be involved in this process. This article reviews the manifestations and possible mechanisms underlying neurologic injury in intrauterine growth restriction and provides a theoretical basis for the effective prevention and treatment of this condition.

The Effects of Hesperidin on BDNF/TrkB Signaling Pathway and Oxidative Stress Parameters in the Cerebral Cortex of the Utero-placental Insufficiency Fetal Rat Model

Introduction:

Uteroplacental Insufficiency (UPI) produces critical neurodevelopmental problems affecting the Intrauterine Growth Restricted (IUGR) in offspring. This study aimed to investigate the possible neuroprotective roles of Hesperidin (Hes) on the fetal cerebral cortex of the UPI rat model.

Methods:

In this experimental study, 40 pregnant Wistar rats (age: ∼40 days, Mean±SD weight: 180±10 g) were randomly divided into 5 groups (n= 8/group). The study groups included control (normal saline, orally), UPI+NS (uterine vessel ligation+normal saline, orally), UPI+HES25, UPI+HES50, and UPI+HES100 (uterine vessel ligation+25, 50 and 100 mg/kg Hes, orally). After being anesthetized by ketamine and xylazine, UPI was induced by permanent bilateral closure of the uterine vessels on Gestation Day (GD) 18. From GD15, the Hes/NS-treated groups received Hes/normal saline until GD21. On GD21, the uterus, placenta, and fetus were dissected out and weighed. The oxidative stress parameters, including Catalase (CAT) activity, Malondialdehyde (MDA), and Total Antioxidant Capacity (TAC) were measured in the fetal cerebral cortex. The expression of Brain-Derived Neurotrophic Factor (BDNF) and Tropomyosin Receptor Kinase B (TrkB) was assessed by RT qPCR methods. The obtained data were analyzed by Analysis of Variance (ANOVA) and Tukey’s post hoc test.

Results:

The present study findings identified a significant difference in the uterine and fetus weight in Hes-treated mothers (P< 0.05). In the fetus, Hes reduced MDA, and increased CAT activity and TAC (P<0.001 in the UPI+Hes100 group, compared to the UPI+NS group). UPI reduced BDNF and TrkB mRNA expression, compared to the control group (P<0.05). Also, Significant increases in BDNF and TrkB mRNA expression were observed after administrating Hes in the fetal cerebral cortex of the UPI rat model, in a dose-dependent manner (P<0.05).

Conclusion:

Hes, as a neuroprotective and antioxidant agent, accelerates BDNF-TrkB signaling pathway and suppresses oxidative stress parameters in the cerebral cortex of the UPI rat model.

Intrauterine growth restriction followed by oxygen support uniquely interferes with genetic regulators of myelination

Intrauterine growth restriction (IUGR) and oxygen exposure in isolation and combination adversely affect the developing brain, putting infants at risk for neurodevelopmental disability including cerebral palsy. Rodent models of IUGR and postnatal hyperoxia have demonstrated oligodendroglial injury with subsequent white matter injury (WMI) and motor dysfunction. Here we investigate transcriptomic dysregulation in IUGR with and without hyperoxia exposure to account for the abnormal brain structure and function previously documented. We performed RNA sequencing and analysis using a mouse model of IUGR and found that IUGR, hyperoxia, and the combination of IUGR with hyperoxia (IUGR/hyperoxia) produced distinct changes in gene expression. IUGR in isolation demonstrated the fewest differentially expressed genes compared to control. In contrast, we detected several gene alterations in IUGR/hyperoxia; genes involved in myelination were strikingly downregulated. We also identified changes to specific regulators including TCF7L2, BDNF, SOX2, and DGCR8, through Ingenuity Pathway Analysis, that may contribute to impaired myelination in IUGR/hyperoxia. Our findings show that IUGR with hyperoxia induces unique transcriptional changes in the developing brain. These indicate mechanisms for increased risk for WMI in IUGR infants exposed to oxygen and suggest potential therapeutic targets to improve motor outcomes.Significance StatementThis study demonstrates that perinatal exposures of IUGR and/or postnatal hyperoxia result in distinct transcriptomic changes in the developing brain. In particular, we found that genes involved in normal developmental myelination, myelin maintenance, and remyelination were most dysregulated when IUGR was combined with hyperoxia. Understanding how multiple risk factors lead to WMI is the first step in developing future therapeutic interventions. Additionally, because oxygen exposure is often unavoidable after birth, an understanding of gene perturbations in this setting will increase our awareness of the need for tight control of oxygen use to minimize future motor disability.

Taurine improves the differentiation of neural stem cells in fetal rats with intrauterine growth restriction via activation of the PKA-CREB-BDNF signaling pathway

Intrauterine growth restriction (IUGR) affects brain neural stem cell (NSC) differentiation. In the present study, we investigated whether taurine supplementation may improve NSC differentiation in IUGR fetal rats via the protein kinase A-cyclic adenosine monophosphate (cAMP) response element protein-brain derived neurotrophic factor (PKA-CREB-BDNF) signaling pathway. The IUGR fetal rat model was established with a low-protein diet. Fresh subventricular zone (SVZ) tissue from the fetuses on the 14th day of pregnancy was microdissected and dissociated into single-cell suspensions, then was cultured to form neurospheres. The neurospheres were divided into the control group, the IUGR group, the IUGR+taurine (taurine) group, the IUGR+H89 (H89) group and the IUGR+taurine+H89 (taurine+H89) group. The mRNA and protein expression levels of PKA, CREB and BDNF were measured by reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting (WB). Tuj-1-positive neurons and GFAP-positive glial cells were detected by immunofluorescence. The total number of proliferating NSCs and the percentage of Tuj-1-positive neurons in the IUGR group were lower than those in the control group, but the percentage of GFAP-positive cells was higher in the IUGR group than in the control group. Taurine supplementation increased the total number of neural cells and the percentage of Tuj-1-positive neurons, and reduced the percentage of GFAP-positive cells among differentiated NSCs after IUGR. H89 reduced the total number and percentage of Tuj-1-positive neurons and increased the percentage of GFAP-positive cells. The mRNA and protein levels of PKA, CREB, and BDNF were lower in the IUGR group. The mRNA and protein expression levels of these factors were increased by taurine supplementation but reduced by the addition of H89. Taurine supplementation increased the ratio of neurons to glial cells and prevented gliosis in the differentiation of NSCs in IUGR fetal rats by activating the PKA-CREB-BDNF signaling pathway.

The Effect of Prenatal Food Restriction on Brain Proteome in Appropriately Grown and Growth Restricted Male Wistar Rats

Background

Fetal growth restriction (FGR) has been associated with a higher risk of developing adverse perinatal outcomes and distinct neurodevelopmental and neurobehavioral disorders. The aim of the present study was to investigate the impact of prenatal food restriction on the brain proteome in both FGR and appropriately grown rats and to identify potential pathways connecting maternal malnutrition with altered brain development.

Methods

Ten time-dated pregnant Wistar rats were housed individually at their 12th day of gestation. On the 15th day of gestation, the rats were randomly divided into two groups, namely the food restricted one (n = 6) and the control group (n = 4). From days 15 to 21 the control group had unlimited access to food and the food restricted group was given half the amount of food that was on average consumed by the control group, based on measurements taken place the day before. On the 21st day of gestation, all rats delivered spontaneously and after birth all newborn pups of the food restricted group were weighed and matched as appropriately grown (non-FGR) or growth restricted (FGR) and brain tissues were immediately collected. A multiplex experiment was performed analyzing brain tissues from 4 FGR, 4 non-FGR, and 3 control male offspring. Differentially expressed proteins (DEPs) were subjected to bioinformatics analysis in order to identify over-represented processes.

Results

Proteomic analysis resulted in the profiling of 3,964 proteins. Gene ontology analysis of the common DEPs using DAVID (https://david.ncifcrf.gov/) showed significant enrichment for terms related to cellular morphology, learning, memory and positive regulation of NF-kappaB signaling. Ingenuity Pathway Analysis showed significant induction of inflammation in FGR pups, whereas significant induction of cell migration and cell spreading were observed in non-FGR pups.

Conclusion

This study demonstrated that in both FGR and non-FGR neonates, a range of adaptive neurodevelopmental processes takes place, which may result in altered cellular morphology, chronic stress, poor memory and learning outcomes. Furthermore, this study highlighted that not only FGR, but also appropriately grown pups, which have been exposed to prenatal food deprivation may be at increased risk for impaired cognitive and developmental outcomes.

Hippocampal neurogenesis and memory in adolescence following intrauterine growth restriction

Intrauterine growth restriction (IUGR) is associated with hippocampal alterations that can increase the risk of short-term memory impairments later in life. Despite the role of hippocampal neurogenesis in learning and memory, research into the long-lasting impact of IUGR on these processes is limited. We aimed to determine the effects of IUGR on neuronal proliferation, differentiation and morphology, and on memory function at adolescent equivalent age. At embryonic day (E) 18 (term ∼E22), placental insufficiency was induced in pregnant Wistar rats via bilateral uterine vessel ligation to generate IUGR offspring (n = 10); control offspring (n = 11) were generated via sham surgery. From postnatal day (P) 36-44, spontaneous location recognition (SLR), novel object location and recognition (NOL, NOR), and open field tests were performed. Brains were collected at P45 to assess neurogenesis (immunohistochemistry), dendritic morphology (Golgi staining), and brain-derived neurotrophic factor expression (BDNF; Western blot analysis). In IUGR versus control rats there was no difference in object preference in the NOL or NOR, the similar and dissimilar condition of the SLR task, or in locomotion and anxiety-like behavior in the open field. There was a significant increase in the linear density of immature neurons (DCX+) in the subgranular zone (SGZ) of the dentate gyrus (DG), but no difference in the linear density of proliferating cells (Ki67+) in the SGZ, nor in areal density of mature neurons (NeuN+) or microglia (Iba-1+) in the DG in IUGR rats compared to controls. Dendritic morphology of dentate granule cells did not differ between groups. Protein expression of the BDNF precursor (pro-BDNF), but not mature BDNF, was increased in the hippocampus of IUGR compared with control rats. These findings highlight that while the long-lasting prenatal hypoxic environment may impact brain development, it may not impact hippocampal-dependent learning and memory in adolescence.

Immunoreactivity of MAPK Signaling in a Rat Model of Intrauterine Growth Retardation Induced by Uterine Artery Ligation

BACKGROUND/AIM

Intrauterine growth retardation (IUGR) causes very low birth weight and is related to the morbidity and mortality of the newborn. In our previous study, expression of brain-derived neurotrophic factor (BDNF) was found reduced in the cerebral cortex and dentate gyrus of fetuses with IUGR. BDNF protected cortical neurons against hypoxic injury via activation of the extracellular signal-related kinase (ERK) pathway. The aim of the current study was to observe the immunoreactivity of ERK in mature neurons and proliferating cells.

MATERIALS AND METHODS

Uterine artery ligation was performed at 17 days of gestation (dg). Rat fetuses were obtained at 21 dg using cesarean section. Fetuses were designated either to the growth retardation (GR) group when removed from the horn with uterine artery ligation, or to the control group when removed from the other horn with the untied artery. Immunohistochemistry was performed with primary antibodies on paraffin-embedded forebrain sections.

RESULTS

The density and proportion of cells expressing PCNA, ERK, and phosphate ERK in the subventricular zone (SVZ) was not different between the control and GR group. The density and proportion of NeuN- and phosphate ERK-positive cells in the cerebral parietal cortex was lower in the GR group, compared to the control group.

CONCLUSION

Although IUGR had no effect on the proliferation of cells in the SVZ, it reduced neuronal survival in the cerebral parietal cortex, which was associated with the decrease of pERK-positive cell density and proportion in the cerebral cortex.

Animal models for neonatal brain injury induced by hypoxic ischemic conditions in rodents

Neonatal hypoxia-ischemia and resulting encephalopathies are of significant concern. Intrapartum asphyxia is a leading cause of neonatal death globally. Among surviving infants, there remains a high incidence of hypoxic-ischemic encephalopathy due to neonatal hypoxic-ischemic brain injury, manifesting as mild conditions including attention deficit hyperactivity disorder, and debilitating disorders such as cerebral palsy. Various animal models of neonatal hypoxic brain injury have been implemented to explore cellular and molecular mechanisms, assess the potential of novel therapeutic strategies, and characterize the functional and behavioural correlates of injury. Each of the animal models has individual advantages and limitations. The present review looks at several widely-used and alternative rodent models of neonatal hypoxia and hypoxia-ischemia; it highlights their strengths and limitations, and their potential for continued and improved use.

Maternal Undernourishment in Guinea Pigs Leads to Fetal Growth Restriction with Increased Hypoxic Cells and Oxidative Stress in the Brain

BACKGROUND

We determined whether maternal nutrient restriction (MNR) in guinea pigs leading to fetal growth restriction (FGR) impacts markers for brain hypoxia and oxidative stress.

METHODS

Guinea pigs were fed ad libitum (control) or 70% of the control diet before pregnancy, switching to 90% at mid-pregnancy (MNR). Near term, hypoxyprobe-1 (HP-1) was injected into pregnant sows. Fetuses were then necropsied and brain tissues were processed for HP-1 (hypoxia marker) and 4HNE, 8-OHdG, and 3-nitrotyrosine (oxidative stress markers) immunoreactivity (IR).

RESULTS

FGR-MNR fetal and brain weights were decreased 38 and 12%, respectively, with brain/fetal weights thereby increased 45% as a measure of brain sparing, and more so in males than females. FGR-MNR HP-1 IR was increased in most of the brain regions studied, and more so in males than females, while 4HNE and 8-OHdG IR were increased in select brain regions, but with no sex differences.

CONCLUSIONS

Chronic hypoxia is likely to be an important signaling mechanism in the FGR brain, but with males showing more hypoxia than females. This may involve sex differences in adaptive decreases in growth and normalizing of oxygen, with implications for sex-specific alterations in brain development and risk for later neuropsychiatric disorder.

Why considering sexual differences is necessary when studying encephalopathy of prematurity through rodent models

Preterm birth is a high-risk factor for the development of gray and white matter abnormalities, referred to as "encephalopathy of prematurity," that may lead to life-long motor, cognitive, and behavioral impairments. The prevalence and clinical outcomes of encephalopathy of prematurity differ between sexes, and elucidating the underlying biological basis has become a high-priority challenge. Human studies are often limited to assessment of brain region volumes by MRI, which does not provide much information about the underlying mechanisms of lesions related to very preterm birth. However, models using KO mice or pharmacological manipulations in rodents allow relevant observations to help clarify the mechanisms of injury sustaining sex-differential vulnerability. This review focuses on data obtained from mice aged P1-P5 or rats aged P3 when submitted to cerebral damage such as hypoxia-ischemia, as their brain lesions share similarities with lesion patterns occurring in very preterm human brain, before 32 gestational weeks. We first report data on the mechanisms underlying the development of sexual brain dimorphism in rodent, focusing on the hippocampus. In the second part, we describe sex specificities of rodent models of encephalopathy of prematurity (RMEP), focusing on mechanisms underlying differences in hippocampal vulnerability. Finally, we discuss the relevance of these RMEP. Together, this review highlights the need to systematically search for potential effects of sex when studying the mechanisms underlying deficits in RMEP in order to design effective sex-specific medical interventions in human preterms.

Development of the cerebral cortex and the effect of the intrauterine environment

The human brain is one of the most complex structures currently under study. Its external shape is highly convoluted, with folds and valleys over the entire surface of the cortex. Disruption of the normal pattern of folding is associated with a number of abnormal neurological outcomes, some serious for the individual. Most of our knowledge of the normal development and folding of the cerebral cortex (gyrification) focuses on the internal, biological (i.e. genetically driven) mechanisms of the brain that drive gyrification. However, the impact of an adverse intrauterine and maternal physiological environment on cortical folding during fetal development has been understudied. Accumulating evidence suggests that the state of the intrauterine and maternal environment can have a significant impact on gyrification of the fetal cerebral cortex. This review summarises our current knowledge of how development in a suboptimal intrauterine and maternal environment can affect the normal development of the folded cerebral cortex.

Intrauterine growth restriction and development of the hippocampus: implications for learning and memory in children and adolescents

Intrauterine growth restriction (IUGR) is often the result of compromised placental function and suboptimal uteroplacental blood flow. Children born with IUGR have impaired cognitive functioning and specific memory deficits, indicating long-lasting impairments in hippocampal functioning; indeed, hippocampal volume is reduced in infants with IUGR. Animal studies have provided valuable insight into the nature of deficits in hippocampal-dependent functions observed in children born with IUGR; outcomes of experimental IUGR reveal reduced neuron numbers and morphological alterations in the cornu ammonis fields 1 and 3 and dentate gyrus subregions of the hippocampus. However, whether such early and ongoing structural changes in the hippocampus could account for deficits in spatial memory reported in adolescent rats with IUGR is yet to be established. Understanding the association between hippocampal structural and functional alterations in IUGR will aid in the development of interventions to minimise the effect of IUGR on the hippocampus and long-term cognitive outcomes.

Antenatal taurine supplementation in fetal rats with growth restriction improves neural stem cell proliferation by inhibiting the activities of Rho family factors

OBJECTIVE

To investigate whether antenatal taurine supplementation improves neural stem cell proliferation in rats with fetal growth restriction (FGR) through regulating the activity of Rho family factors.

METHODS

FGR models were established via food restriction throughout pregnancy. Pregnant rats were randomly divided into the control group, the FGR group (given 40% of the normal daily feeding in the control group), and the Taurine group (FGR model treated with 300 mg/kg·d taurine from gestational day seven). Expression of fatty acid binding protein-7 (FABP-7), Rho-associated coiled coil-forming protein kinase (ROCK2), Ras homolog gene family member A (RhoA), and rac in the brains of newborn rats was detected by reverse transcription-polymerase chain reaction (RT-PCR), immunohistochemistry (IHC), and Western blotting (WB).

RESULTS

Relative FABP7 mRNA levels, the optical density (OD) values of FABP7-positive cells and the expression levels of the tested proteins all demonstrated that the number of neural stem cells (NSCs) in brain tissue was lower in the FGR group than in the control group but was significantly increased after antenatal taurine supplementation (p < .05). Compared with the control group, the mRNA and protein levels of RhoA and ROCK2 were higher in the FGR group but lower in the Taurine group (p < .05). In contrast, the rac mRNA level was lower in the FGR group than in the control group but was higher in the Taurine group (p < .05).

CONCLUSIONS

Taurine prenatal supplementation improved neural stem cell proliferation in rats with FGR by inhibiting the activity of Rho family factors.

Neonatal and Long-Term Consequences of Fetal Growth Restriction

BACKGROUND

Fetal Growth Restriction (FGR) is one of the most common noxious antenatal conditions in humans, inducing a substantial proportion of preterm delivery and leading to a significant increase in perinatal mortality, neurological handicaps and chronic diseases in adulthood. This review summarizes the current knowledge about the postnatal consequences of FGR, with a particular emphasis on the long-term consequences on respiratory, cardiovascular and neurological structures and functions.

RESULT AND CONCLUSION

FGR represents a global health challenge, and efforts are urgently needed to improve our understanding of the critical factors leading to FGR and subsequent insults to the developing organs.

The extent of intrauterine growth restriction determines the severity of cerebral injury and neurobehavioural deficits in rodents

Background

Cerebral Palsy (CP) is the most common physical pediatric neurodevelopmental disorder and spastic diplegic injury is its most frequent subtype. CP results in substantial neuromotor and cognitive impairments that have significant socioeconomic impact. Despite this, its underlying pathophysiological mechanisms and etiology remain incompletely understood. Furthermore, there is a need for clinically relevant injury models, which a) reflect the heterogeneity of the condition and b) can be used to evaluate new translational therapies. To address these key knowledge gaps, we characterized a chronic placental insufficiency (PI) model, using bilateral uterine artery ligation (BUAL) of dams. This injury model results in intrauterine growth restriction (IUGR) in pups, and animals recapitulate the human phenotype both in terms of neurobehavioural and anatomical deficits.

Methods

Effects of BUAL were studied using luxol fast blue (LFB)/hematoxylin & eosin (H&E) staining, immunohistochemistry, quantitative Magnetic Resonance Imaging (MRI), and Catwalk neurobehavioural tests.

Results

Neuroanatomical analysis revealed regional ventricular enlargement and corpus callosum thinning in IUGR animals, which was correlated with the extent of growth restriction. Olig2 staining revealed reductions in oligodendrocyte density in white and grey matter structures, including the corpus callosum, optic chiasm, and nucleus accumbens. The caudate nucleus, along with other brain structures such as the optic chiasm, internal capsule, septofimbrial and lateral septal nuclei, exhibited reduced size in animals with IUGR. The size of the pretectal nucleus was reduced only in moderately injured animals. MAG/NF200 staining demonstrated reduced myelination and axonal counts in the corpus callosum of IUGR animals. NeuN staining revealed changes in neuronal density in the hippocampus and in the thickness of hippocampal CA2 and CA3 regions. Diffusion weighted imaging (DWI) revealed regional white and grey matter changes at 3 weeks of age. Furthermore, neurobehavioural testing demonstrated neuromotor impairments in animals with IUGR in paw intensities, swing speed, relative print positions, and phase dispersions.

Conclusions

We have characterized a rodent model of IUGR and have demonstrated that the neuroanatomical and neurobehavioural deficits mirror the severity of the IUGR injury. This model has the potential to be applied to examine the pathobiology of and potential therapeutic strategies for IUGR-related brain injury. Thus, this work has potential translational relevance for the study of CP.

Early-Life Nutritional Programming of Cognition-The Fundamental Role of Epigenetic Mechanisms in Mediating the Relation between Early-Life Environment and Learning and Memory Process

The perinatal period is a window of heightened plasticity that lays the groundwork for future anatomic, physiologic, and behavioral outcomes. During this time, maternal diet plays a pivotal role in the maturation of vital organs and the establishment of neuronal connections. However, when perinatal nutrition is either lacking in specific micro- and macronutrients or overloaded with excess calories, the consequences can be devastating and long lasting. The brain is particularly sensitive to perinatal insults, with several neurologic and psychiatric disorders having been linked to a poor in utero environment. Diseases characterized by learning and memory impairments, such as autism, schizophrenia, and Alzheimer disease, are hypothesized to be attributed in part to environmental factors, and evidence suggests that the etiology of these conditions may date back to very early life. In this review, we discuss the role of the early-life diet in shaping cognitive outcomes in offspring. We explore the endocrine and immune mechanisms responsible for these phenotypes and discuss how these systemic factors converge to change the brain's epigenetic landscape and regulate learning and memory across the lifespan. Through understanding the maternal programming of cognition, critical steps may be taken toward preventing and treating diseases that compromise learning and memory.

Learning and memory disabilities in IUGR babies: Functional and molecular analysis in a rat model

INTRODUCTION

1Intrauterine growth restriction (IUGR) is the failure of the fetus to achieve its inherent growth potential, and it has frequently been associated with neurodevelopmental problems in childhood. Neurological disorders are mostly associated with IUGR babies with an abnormally high cephalization index (CI) and a brain sparing effect. However, a similar correlation has never been demonstrated in an animal model. The aim of this study was to determine the correlations between CI, functional deficits in learning and memory and alterations in synaptic proteins in a rat model of IUGR.

METHODS

2Utero-placental insufficiency was induced by meso-ovarian vessel cauterization (CMO) in pregnant rats at embryonic day 17 (E17). Learning performance in an aquatic learning test was evaluated 25 days after birth and during 10 days. Some synaptic proteins were analyzed (PSD95, Synaptophysin) by Western blot and immunohistochemistry.

RESULTS

3Placental insufficiency in CMO pups was associated with spatial memory deficits, which are correlated with a CI above the normal range. CMO pups presented altered levels of synaptic proteins PSD95 and synaptophysin in the hippocampus.

CONCLUSIONS

4The results of this study suggest that learning disabilities may be associated with altered development of excitatory neurotransmission and synaptic plasticity. Although interspecific differences in fetal response to placental insufficiency should be taken into account, the translation of these data to humans suggest that both IUGR babies and babies with a normal birth weight but with intrauterine Doppler alterations and abnormal CI should be closely followed to detect neurodevelopmental alterations during the postnatal period.

Mild intrauterine hypoperfusion reproduces neurodevelopmental disorders observed in prematurity

Severe intrauterine ischemia is detrimental to the developing brain. The impact of mild intrauterine hypoperfusion on neurological development, however, is still unclear. We induced mild intrauterine hypoperfusion in rats on embryonic day 17 via arterial stenosis with metal microcoils wrapped around the uterine and ovarian arteries. All pups were born with significantly decreased birth weights. Decreased gray and white matter areas were observed without obvious tissue damage. Pups presented delayed newborn reflexes, muscle weakness, and altered spontaneous activity. The levels of proteins indicative of inflammation and stress in the vasculature, i.e., RANTES, vWF, VEGF, and adiponectin, were upregulated in the placenta. The levels of mRNA for proteins associated with axon and astrocyte development were downregulated in fetal brains. The present study demonstrates that even mild intrauterine hypoperfusion can alter neurological development, which mimics the clinical signs and symptoms of children with neurodevelopmental disorders born prematurely or with intrauterine growth restriction.

Review: Neuroinflammation in intrauterine growth restriction

Disruption to the maternal environment during pregnancy from events such as hypoxia, stress, toxins, inflammation, and reduced placental blood flow can affect fetal development. Intrauterine growth restriction (IUGR) is commonly caused by chronic placental insufficiency, interrupting supply of oxygen and nutrients to the fetus resulting in abnormal fetal growth. IUGR is a major cause of perinatal morbidity and mortality, occurring in approximately 5-10% of pregnancies. The fetal brain is particularly vulnerable in IUGR and there is an increased risk of long-term neurological disorders including cerebral palsy, epilepsy, learning difficulties, behavioural difficulties and psychiatric diagnoses. Few studies have focused on how growth restriction interferes with normal brain development in the IUGR neonate but recent studies in growth restricted animal models demonstrate increased neuroinflammation. This review describes the role of neuroinflammation in the progression of brain injury in growth restricted neonates. Identifying the mediators responsible for alterations in brain development in the IUGR infant is key to prevention and treatment of brain injury in these infants.

[Effect of antepartum taurine supplementation in regulating the activity of Rho family factors and promoting the proliferation of neural stem cells in neonatal rats with fetal growth restriction]

OBJECTIVE

To study the possible effect of antepartum taurine supplementation in regulating the activity of Rho family factors and promoting the proliferation of neural stem cells in neonatal rats with fetal growth restriction (FGR), and to provide a basis for antepartum taurine supplementation to promote brain development in children with FGR.

METHODS

A total of 24 pregnant Sprague-Dawley rats were randomly divided into three groups: control, FGR, and taurine (n=8 each ). A rat model of FGR was established by food restriction throughout pregnancy. RT-PCR, immunohistochemistry, and Western blot were used to measure the expression of the specific intracellular markers for neural stem cells fatty acid binding protein 7 (FABP7), Rho-associated coiled-coil containing protein kinase 2 (ROCK2), ras homolog gene family, member A (RhoA), and Ras-related C3 botulinum toxin substrate (Rac).

RESULTS

The FGR group had significantly lower OD value of FABP7-positive cells and mRNA and protein expression of FABP7 than the control group, and the taurine group had significantly higher OD value of FABP7-positive cells and mRNA and protein expression of FABP7 than the FGR group (P<0.05). The FGR group had significantly higher mRNA expression of RhoA and ROCK2 than the control group. The taurine group had significantly higher mRNA expression of RhoA and ROCK2 than the control group and significantly lower expression than the FGR group (P<0.05). The FGR group had significantly lower mRNA expression of Rac than the control group. The taurine group had significantly higher mRNA expression of Rac than the FGR and control groups (P<0.05). The FGR group had significantly higher protein expression of RhoA and ROCK2 than the control group. The taurine group had significantly lower protein expression of RhoA and ROCK2 than the FGR group (P<0.05).

CONCLUSIONS

Antepartum taurine supplementation can promote the proliferation of neural stem cells in rats with FGR, and its mechanism may be related to the regulation of the activity of Rho family factors.

Maternal Calorie Restriction Causing Uteroplacental Insufficiency Differentially Affects Mammalian Placental Glucose and Leucine Transport Molecular Mechanisms

We examined the effect of mild (Mi; ∼25%) and moderate (Mo; ∼50%) maternal calorie restriction (MCR) vs ad libitum-fed controls on placental glucose and leucine transport impacting fetal growth potential. We observed in MiMCR a compensatory increase in transplacental (TP) glucose transport due to increased placental glucose transporter isoform (GLUT)-3 but no change in GLUT1 protein concentrations. This change was paralleled by increased glut3 mRNA and 5-hydroxymethylated cytosines with enhanced recruitment of histone 3 lysine demethylase to the glut3 gene locus. To assess the biologic relevance of placental GLUT1, we also examined glut1 heterozygous null vs wild-type mice and observed no difference in placental GLUT3 and TP or intraplacental glucose and leucine transport. Both MCR states led to a graded decrease in TP and intraplacental leucine transport, with a decline in placental L amino acid transporter isoform 2 (LAT2) concentrations and increased microRNA-149 (targets LAT2) and microRNA-122 (targets GLUT3) expression in MoMCR alone. These changes were accompanied by a step-wise reduction in uterine and umbilical artery Doppler blood flow with decreased fetal left ventricular ejection fraction and fractional shortening. We conclude that MiMCR transactivates placental GLUT3 toward preserving TP glucose transport in the face of reduced leucine transport. This contrasts MoMCR in which a reduction in placental GLUT3 mediated glucose transport with a reciprocal increase in miR-122 expression was encountered. A posttranscriptional reduction in LAT2-mediated leucine transport also occurred with enhanced miR-149 expression. Both MCR states, although not affecting placental GLUT1, resulted in uteroplacental insufficiency and fetal growth restriction with compromised cardiovascular health.

Intrauterine growth restriction combined with a maternal high-fat diet increases hepatic cholesterol and low-density lipoprotein receptor activity in rats

Intrauterine growth restriction (IUGR) and maternal consumption of a high-saturated-fat diet (HFD) increase the risk of hypercholesterolemia, a leading cause of morbidity and mortality. Many pregnant women eat a HFD, thus exposing the fetus to a HFD in utero. The cumulative effect of in utero exposure to IUGR and a HFD on offspring cholesterol levels remains unknown. Furthermore, little is known about the mechanism through which IUGR and maternal HFD consumption increase cholesterol. We hypothesize that IUGR combined with a maternal HFD would increase offspring serum and hepatic cholesterol accumulation via alteration in levels of key proteins involved in cholesterol metabolism. To test our hypothesis we used a rat model of surgically induced IUGR and fed the dams a regular diet or a HFD HFD-fed dams consumed the same kilocalories as regular diet-fed dams, with no difference between surgical intervention groups. In the offspring, IUGR combined with a maternal HFD increased hepatic cholesterol levels, low-density lipoprotein (LDL) receptor protein levels, and Ldlr activity in female rat offspring at birth and both sexes at postnatal day 14 relative to non-IUGR offspring both from regular diet- and HFD-fed dams. These findings suggest that IUGR combined with a maternal HFD increases hepatic cholesterol accumulation via increased LDL cholesterol uptake into the liver with resulting persistent increases in hepatic cholesterol accumulation.

The consequences of fetal growth restriction on brain structure and neurodevelopmental outcome

Fetal growth restriction (FGR) is a significant complication of pregnancy describing a fetus that does not grow to full potential due to pathological compromise. FGR affects 3-9% of pregnancies in high-income countries, and is a leading cause of perinatal mortality and morbidity. Placental insufficiency is the principal cause of FGR, resulting in chronic fetal hypoxia. This hypoxia induces a fetal adaptive response of cardiac output redistribution to favour vital organs, including the brain, and is in consequence called brain sparing. Despite this, it is now apparent that brain sparing does not ensure normal brain development in growth-restricted fetuses. In this review we have brought together available evidence from human and experimental animal studies to describe the complex changes in brain structure and function that occur as a consequence of FGR. In both humans and animals, neurodevelopmental outcomes are influenced by the timing of the onset of FGR, the severity of FGR, and gestational age at delivery. FGR is broadly associated with reduced total brain volume and altered cortical volume and structure, decreased total number of cells and myelination deficits. Brain connectivity is also impaired, evidenced by neuronal migration deficits, reduced dendritic processes, and less efficient networks with decreased long-range connections. Subsequent to these structural alterations, short- and long-term functional consequences have been described in school children who had FGR, most commonly including problems in motor skills, cognition, memory and neuropsychological dysfunctions.

Assessment of in vivo fetal growth and placental vascular function in a novel intrauterine growth restriction model of progressive uterine artery occlusion in guinea pigs

Intra-uterine growth restriction (IUGR) is associated with short and long-term metabolic and cardiovascular alterations. Mice and rats have been extensively used to study the effects of IUGR, but there are notable differences in fetal and placental physiology relative to those of humans that argue for alternative animal models. This study proposes that gradual occlusion of uterine arteries from mid-gestation in pregnant guinea pigs produces a novel model to better assess human IUGR. Fetal biometry and in vivo placental vascular function were followed by sonography and Doppler of control pregnant guinea pigs and sows submitted to surgical placement of ameroid constrictors in both uterine arteries (IUGR) at mid-gestation (35 days). The ameroid constrictors induced a reduction in the fetal abdominal circumference growth rate (0.205 cm day(-1) ) compared to control (0.241 cm day(-1) , P < 0.001) without affecting biparietal diameter growth. Umbilical artery pulsatility and resistance indexes at 10 and 20 days after surgery were significantly higher in IUGR animals than controls (P < 0.01). These effects were associated with a decrease in the relative luminal area of placental chorionic arteries (21.3 ± 2.2% vs. 33.2 ± 2.7%, P < 0.01) in IUGR sows at near term. Uterine artery intervention reduced fetal (∼30%), placental (∼20%) and liver (∼50%) weights (P < 0.05), with an increased brain to liver ratio (P < 0.001) relative to the control group. These data demonstrate that the ameroid constrictor implantations in uterine arteries in pregnant guinea pigs lead to placental vascular dysfunction and altered fetal growth that induces asymmetric IUGR.

In utero Undernutrition Programs Skeletal and Cardiac Muscle Metabolism

In utero undernutrition is associated with increased risk for insulin resistance, obesity, and cardiovascular disease during adult life. A common phenotype associated with low birth weight is reduced skeletal muscle mass. Given the central role of skeletal muscle in whole body metabolism, alterations in its mass as well as its metabolic characteristics may contribute to disease risk. This review highlights the metabolic alterations in cardiac and skeletal muscle associated with in utero undernutrition and low birth weight. These tissues have high metabolic demands and are known to be sites of major metabolic dysfunction in obesity, type 2 diabetes, and cardiovascular disease. Recent research demonstrates that mitochondrial energetics are decreased in skeletal and cardiac muscles of adult offspring from undernourished mothers. These effects apparently lead to the development of a thrifty phenotype, which may represent overall a compensatory mechanism programmed in utero to handle times of limited nutrient availability. However, in an environment characterized by food abundance, the effects are maladaptive and increase adulthood risks of metabolic disease.

IUGR increases chromatin-remodeling factor Brg1 expression and binding to GR exon 1.7 promoter in newborn male rat hippocampus

Intrauterine growth restriction (IUGR) increases the risk for neurodevelopment delay and neuroendocrine reprogramming in both humans and rats. Neuroendocrine reprogramming involves the glucocorticoid receptor (GR) gene that is epigenetically regulated in the hippocampus. Using a well-characterized rodent model, we have previously shown that IUGR increases GR exon 1.7 mRNA variant and total GR expressions in male rat pup hippocampus. Epigenetic regulation of GR transcription may involve chromatin remodeling of the GR gene. A key chromatin remodeler is Brahma-related gene-1(Brg1), a member of the ATP-dependent SWItch/Sucrose NonFermentable (SWI/SNF) chromatin remodeling complex. Brg1 regulates gene expression by affecting nucleosome repositioning and recruiting transcriptional components to target promoters. We hypothesized that IUGR would increase hippocampal Brg1 expression and binding to GR exon 1.7 promoter, as well as alter nucleosome positioning over GR promoters in newborn male pups. Further, we hypothesized that IUGR would lead to accumulation of specificity protein 1 (Sp1) and RNA pol II at GR exon 1.7 promoter. Indeed, we found that IUGR increased Brg1 expression and binding to GR exon 1.7 promoter. We also found that increased Brg1 binding to GR exon 1.7 promoter was associated with accumulation of Sp1 and RNA pol II carboxy terminal domain pSer-5 (a marker of active transcription). Furthermore, the transcription start site of GR exon 1.7 was located within a nucleosome-depleted region. We speculate that changes in hippocampal Brg1 expression mediate GR expression and subsequently trigger neuroendocrine reprogramming in male IUGR rats.

Neurological outcomes of animal models of uterine artery ligation and relevance to human intrauterine growth restriction: a systematic review

AIM

This review explores the molecular, neurological, and behavioural outcomes in animal models of uterine artery ligation. We analyse the relevance of this type of model to the pathological and functional phenotypes that are consistent with cerebral palsy and its developmental comorbidities in humans.

METHOD

A literature search of the PubMed database was conducted for research using the uterine artery ligation model published between 1990 and 2013. From the studies included, any relevant neuroanatomical and behavioural deficits were then summarized from each document and used for further analysis.

RESULTS

There were 25 papers that met the criteria included for review, and several outcomes were summarized from the results of these papers. Fetuses with growth restriction demonstrated a gradient of reduced body weight with a relative sparing of brain mass. There was a significant reduction in the size of the somatosensory cortex, hippocampus, and corpus callosum. The motor cortex appeared to be spared of identifiable deficits. Apoptotic proteins were upregulated, while those important to neuronal survival, growth, and differentiation were downregulated. Neuronal apoptosis and astrogliosis occurred diffusely throughout the brain regions. White matter injury involved oligodendrocyte precursor maturation arrest, hypomyelination, and an aberrant organization of existing myelin. Animals with growth restriction demonstrated deficits in gait, memory, object recognition, and spatial processing.

INTERPRETATION

This review concludes that neuronal death, white matter injury, motor abnormalities, and cognitive deficits are important outcomes of uterine artery ligation in animal models. Therefore, this is a clinically relevant type of model, as these findings resemble deficits in human cerebral palsy.

IUGR disrupts the PPARγ-Setd8-H4K20me(1) and Wnt signaling pathways in the juvenile rat hippocampus

Intrauterine growth restriction (IUGR) programs neurodevelopmental impairment and long-term neurological morbidities. Neurological morbidities in IUGR infants are correlated with changes hippocampal volume. We previously demonstrated that IUGR alters hippocampal cellular composition in both neonatal and juvenile rat pups in association with altered hippocampal gene expression and epigenetic determinants. PPARγ signaling is important for neurodevelopment as well as epigenetic integrity in the brain via the PPARγ-Setd8-H4K20me(1) axis and Wnt signaling. We hypothesized that IUGR would decrease expression of PPARγ, Setd8, and H4K20me(1) in juvenile rat hippocampus. We further hypothesized that reduced PPARγ-Setd8-H4K20me(1) would be associated with reduced Wnt signaling genes Wnt3a and β-catenin, and wnt target gene Axin2. To test our hypothesis we used a rat model of uteroplacental insufficiency-induced IUGR. We demonstrated that PPARγ localizes to oligodendrocytes, neurons and astrocytes within the juvenile rat hippocampus. We also demonstrated that IUGR reduces levels of PPARγ, Setd8 and H4K20me(1) in male and female juvenile rat hippocampus in conjunction with reduced Wnt signaling components in only male rats. We speculate that reduced PPARγ and Wnt signaling may contribute to altered hippocampal cellular composition which, in turn, may contribute to impaired neurodevelopment and subsequent neurocognitive impairment in IUGR offspring.

Fetal growth restriction alters hippocampal 17-beta estradiol and estrogen receptor alpha levels in the newborn male rat

Fetal growth restriction (FGR) is associated with impaired neurodevelopmental outcomes in affected newborns. The pathogenesis of FGR-associated neurodevelopmental impairment implicates abnormal hippocampal function. The steroid hormone estrogen and its receptor, estrogen receptor alpha (ERα), are involved in the normal programming of hippocampal development and structure. However, the impact of FGR on hippocampal estrogen and hippocampal ERα is not well characterized. We hypothesized that FGR will reduce hippocampal and serum levels of 17-beta estradiol and its receptor, ERα, in the newborn rat hippocampus. We further hypothesize that FGR will reduce hippocampal ERα levels in a region-specific manner. To test our hypotheses, we used the well characterized rat model of FGR induced by uteroplacental-insufficiency in the pregnant Sprague-Dawley rat. Hippocampi and serum were obtained from FGR and control day 0 rat pups and examined for hippocampal 17-beta estradiol, serum 17-beta estradiol, and ERα mRNA and protein levels. Immunohistochemistry was performed to examine region-specific ERα staining. FGR decreased hippocampal 17-beta estradiol levels in the hippocampi of male newborn rats but not females. Serum 17-beta estradiol levels were not affected by FGR in either gender. FGR decreased hippocampal ERα mRNA levels in males but not females. Hippocampal ERα protein levels by Western blotting were not affected by FGR. However, FGR decreased apparent ERα staining in the cornu ammonis (CA)1, CA3, and dentate gyrus regions in the hippocampi of male newborn rats but not females. We conclude that FGR affects the programming of hippocampal estrogen and hippocampal ERα levels in the newborn rat in a gender-specific manner.