Altered expression of pro-inflammatory and developmental genes in the fetal brain in a mouse model of maternal infection

Maternal immune activation and role of placenta in the prenatal programming of neurodevelopmental disorders

Maternal infection during pregnancy, leading to maternal immune activation (mIA) and cytokine release, increases the offspring risk of developing a variety of neurodevelopmental disorders (NDDs), including schizophrenia. Animal models have provided evidence to support these mechanistic links, with placental inflammatory responses and dysregulation of placental function implicated. This leads to changes in fetal brain cytokine balance and altered epigenetic regulation of key neurodevelopmental pathways. The prenatal timing of such mIA-evoked changes, and the accompanying fetal developmental responses to an altered in utero environment, will determine the scope of the impacts on neurodevelopmental processes. Such dysregulation can impart enduring neuropathological changes, which manifest subsequently in the postnatal period as altered neurodevelopmental behaviours in the offspring. Hence, elucidation of the functional changes that occur at the molecular level in the placenta is vital in improving our understanding of the mechanisms that underlie the pathogenesis of NDDs. This has notable relevance to the recent COVID-19 pandemic, where inflammatory responses in the placenta to SARS-CoV-2 infection during pregnancy and NDDs in early childhood have been reported. This review presents an integrated overview of these collective topics and describes the possible contribution of prenatal programming through placental effects as an underlying mechanism that links to NDD risk, underpinned by altered epigenetic regulation of neurodevelopmental pathways.

Role of YB-1 Protein in Inflammation

This review discusses the role of the multifunctional DNA/RNA-binding protein YB-1 in inflammation. YB-1 performs multiple functions in the cell depending on its location: it acts as transcriptional factor for many genes in the nucleus, regulates translation and stability of mRNA in the cytoplasm, and becomes a paracrine factor when secreted from the cells. The review presents the data on the YB-1-mediated regulation of inflammation-associated genes, as well as results of studies on the YB-1 role in animal model of various inflammatory diseases, such as glomerulonephritis, tubulointerstitial fibrosis, and bacterial sepsis, and on the YB-1 expression in different human diseases associated with inflammatory processes in kidney, liver, and endometrium. The last section of the review presents several approaches to the regulation of YB-1 with small molecules in the treatment of inflammatory diseases.

Maternal immune activation in rodent models: A systematic review of neurodevelopmental changes in gene expression and epigenetic modulation in the offspring brain

Maternal immune activation (mIA) during pregnancy is hypothesised to disrupt offspring neurodevelopment and predispose offspring to neurodevelopmental disorders such as schizophrenia. Rodent models of mIA have explored possible mechanisms underlying this paradigm and provide a vital tool for preclinical research. However, a comprehensive analysis of the molecular changes that occur in mIA-models is lacking, hindering identification of robust clinical targets. This systematic review assesses mIA-driven transcriptomic and epigenomic alterations in specific offspring brain regions. Across 118 studies, we focus on 88 candidate genes and show replicated changes in expression in critical functional areas, including elevated inflammatory markers, and reduced myelin and GABAergic signalling proteins. Further, disturbed epigenetic markers at nine of these genes support mIA-driven epigenetic modulation of transcription. Overall, our results demonstrate that current outcome measures have direct relevance for the hypothesised pathology of schizophrenia and emphasise the importance of mIA-models in contributing to the understanding of biological pathways impacted by mIA and the discovery of new drug targets.

Perinatal Inflammation Reprograms Neuroendocrine, Immune, and Reproductive Functions: Profile of Cytokine Biomarkers

Viral and bacterial infections causing systemic inflammation are significant risk factors for developing body. Inflammatory processes can alter physiological levels of regulatory factors and interfere with developmental mechanisms. The brain is the main target for the negative impact of inflammatory products during critical ontogenetic periods. Subsequently, the risks of various neuropsychiatric diseases such as Alzheimer's and Parkinson's diseases, schizophrenia, and depression are increased in the offspring. Inflammation-induced physiological disturbances can cause immune and behavioral disorders, reproductive deficiencies, and infertility. The influence of maternal immune stress is mediated by the regulation of pro-inflammatory cytokines such as interleukin (IL)-1β, IL-6, monocyte chemotactic protein 1, leukemia-inhibiting factor, and tumor necrosis factor-alpha secretion in the maternal-fetal system. The increasing number of patients with neuronal and reproductive disorders substantiates the identification of biomarkers for these disorders targeted at their therapy.

Inflammation-induced alterations in maternal-fetal Heme Oxygenase (HO) are associated with sustained innate immune cell dysregulation in mouse offspring

Heme oxygenase-1 (HO-1) is an evolutionarily conserved stress response enzyme and important in pregnancy maintenance, fetal and neonatal outcomes, and a variety of pathologic conditions. Here, we investigated the effects of an exposure to systemic inflammation late in gestation [embryonic day (E)15.5] on wild-type (Wt) and HO-1 heterozygous (Het, HO-1^+/-) mothers, fetuses, and offspring. We show that alterations in fetal liver and spleen HO homeostasis during inflammation late in gestation can lead to a sustained dysregulation of innate immune cell populations and intracellular myeloid HO-1 expression in the spleen through young adolescence [postnatal day 25] in mice.

Mechanisms of Reciprocal Regulation of Gonadotropin-Releasing Hormone (GnRH)-Producing and Immune Systems: The Role of GnRH, Cytokines and Their Receptors in Early Ontogenesis in Normal and Pathological Conditions

Different aspects of the reciprocal regulatory influence on the development of gonadotropin-releasing hormone (GnRH)-producing- and immune systems in the perinatal ontogenesis and their functioning in adults in normal and pathological conditions are discussed. The influence of GnRH on the development of the immune system, on the one hand, and the influence of proinflammatory cytokines on the development of the hypothalamic-pituitary-gonadal system, on the other hand, and their functioning in adult offspring are analyzed. We have focused on the effects of GnRH on the formation and functional activity of the thymus, as the central organ of the immune system, in the perinatal period. The main mechanisms of reciprocal regulation of these systems are discussed. The reproductive health of an individual is programmed by the establishment and development of physiological systems during critical periods. Regulatory epigenetic mechanisms of development are not strictly genetically controlled. These processes are characterized by a high sensitivity to various regulatory factors, which provides possible corrections for disorders.

Impact of prenatal lipopolysaccharide exposure on the development of rats

The intrauterine environment is infl uenced by several factors, genetic or environmental, which are essential in understanding the pathophysiological mechanisms of some diseases. In this study, the aim was to investigate the impact of prenatal lipopolysaccharide exposure on the development of rats. Fifty pregnant rats received intraperitoneal administration of lipopolysaccharide (100 µg/kg), or saline at the same dose, on the 9.5th day of pregnancy. The offspring of these rats were analyzed for indicators of brain and somatic development and maturation of physical characteristics. Refl ex ontogenesis was also analyzed by vibrissae placement, negative geotaxis, palmar grasp, precipice aversion, decubitus recovery and acceleration reaction. Administration of lipopolysaccharide on the 9.5th gestational day caused delayed opening of the auditory pavilion, reduction in the length of the tail, body, cranial axes, and body weight. Thus, maternal infections can interfere in the intrauterine environment, impairing functional and structural aspects of the central nervous system, as well as the maturation of physical characteristics.

CNS Macrophages and Infant Infections

The central nervous system (CNS) harbors its own immune system composed of microglia in the parenchyma and CNS-associated macrophages (CAMs) in the perivascular space, leptomeninges, dura mater, and choroid plexus. Recent advances in understanding the CNS resident immune cells gave new insights into development, maturation and function of its immune guard. Microglia and CAMs undergo essential steps of differentiation and maturation triggered by environmental factors as well as intrinsic transcriptional programs throughout embryonic and postnatal development. These shaping steps allow the macrophages to adapt to their specific physiological function as first line of defense of the CNS and its interfaces. During infancy, the CNS might be targeted by a plethora of different pathogens which can cause severe tissue damage with potentially long reaching defects. Therefore, an efficient immune response of infant CNS macrophages is required even at these early stages to clear the infections but may also lead to detrimental consequences for the developing CNS. Here, we highlight the recent knowledge of the infant CNS immune system during embryonic and postnatal infections and the consequences for the developing CNS.

Maternal Immune Activation Induces Neuroinflammation and Cortical Synaptic Deficits in the Adolescent Rat Offspring

Maternal immune activation (MIA), induced by infection during pregnancy, is an important risk factor for neuro-developmental disorders, such as autism. Abnormal maternal cytokine signaling may affect fetal brain development and contribute to neurobiological and behavioral changes in the offspring. Here, we examined the effect of lipopolysaccharide-induced MIA on neuro-inflammatory changes, as well as synaptic morphology and key synaptic protein level in cerebral cortex of adolescent male rat offspring. Adolescent MIA offspring showed elevated blood cytokine levels, microglial activation, increased pro-inflammatory cytokines expression and increased oxidative stress in the cerebral cortex. Moreover, pathological changes in synaptic ultrastructure of MIA offspring was detected, along with presynaptic protein deficits and down-regulation of postsynaptic scaffolding proteins. Consequently, ability to unveil MIA-induced long-term alterations in synapses structure and protein level may have consequences on postnatal behavioral changes, associated with, and predisposed to, the development of neuropsychiatric disorders.

The fetal origins of mental illness

The impact of infections and inflammation during pregnancy on the developing fetal brain remains incompletely defined, with important clinical and research gaps. Although the classic infectious TORCH pathogens (ie, Toxoplasma gondii, rubella virus, cytomegalovirus [CMV], herpes simplex virus) are known to be directly teratogenic, emerging evidence suggests that these infections represent the most extreme end of a much larger spectrum of injury. We present the accumulating evidence that prenatal exposure to a wide variety of viral and bacterial infections-or simply inflammation-may subtly alter fetal brain development, leading to neuropsychiatric consequences for the child later in life. The link between influenza infections in pregnant women and an increased risk for development of schizophrenia in their children was first described more than 30 years ago. Since then, evidence suggests that a range of infections during pregnancy may also increase risk for autism spectrum disorder and depression in the child. Subsequent studies in animal models demonstrated that both pregnancy infections and inflammation can result in direct injury to neurons and neural progenitor cells or indirect injury through activation of microglia and astrocytes, which can trigger cytokine production and oxidative stress. Infectious exposures can also alter placental serotonin production, which can perturb neurotransmitter signaling in the developing brain. Clinically, detection of these subtle injuries to the fetal brain is difficult. As the neuropsychiatric impact of perinatal infections or inflammation may not be known for decades after birth, our construct for defining teratogenic infections in pregnancy (eg, TORCH) based on congenital anomalies is insufficient to capture the full adverse impact on the child. We discuss the clinical implications of this body of evidence and how we might place greater emphasis on prevention of prenatal infections. For example, increasing uptake of the seasonal influenza vaccine is a key strategy to reduce perinatal infections and the risk for fetal brain injury. An important research gap exists in understanding how antibiotic therapy during pregnancy affects the fetal inflammatory load and how to avoid inflammation-mediated injury to the fetal brain. In summary, we discuss the current evidence and mechanisms linking infections and inflammation with the increased lifelong risk of neuropsychiatric disorders in the child, and how we might improve prenatal care to protect the fetal brain.

Antigenic Targets of Patient and Maternal Autoantibodies in Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a neurodevelopmental disorder whose behavioral symptoms become apparent in early childhood. The underlying pathophysiological mechanisms are only partially understood and the clinical manifestations are heterogeneous in nature, which poses a major challenge for diagnosis, prognosis and intervention. In the last years, an important role of a dysregulated immune system in ASD has emerged, but the mechanisms connecting this to a disruption of brain development are still largely unknown. Although ASD is not considered as a typical autoimmune disease, self-reactive antibodies or autoantibodies against a wide variety of targets have been found in a subset of ASD patients. In addition, autoantibodies reactive to fetal brain proteins have also been described in the prenatal stage of neurodevelopment, where they can be transferred from the mother to the fetus by transplacental transport. In this review, we give an extensive overview of the antibodies described in ASD according to their target antigens, their different origins, and timing of exposure during neurodevelopment.

A Critical Evaluation of Current Concepts in Cerebral Palsy

Spastic cerebral palsy (CP), despite the name, is not consistently identifiable by specific brain lesions. CP animal models focus on risk factors for development of CP, yet few reproduce the diagnostic symptoms. Animal models of CP must advance beyond risk factors to etiologies, including both the brain and spinal cord.

Neonatal infection leads to increased susceptibility to Aβ oligomer-induced brain inflammation, synapse loss and cognitive impairment in mice

Harmful environmental stimuli during critical stages of development can profoundly affect behavior and susceptibility to diseases. Alzheimer disease (AD) is the most frequent neurodegenerative disease, and evidence suggest that inflammatory conditions act cumulatively, contributing to disease onset. Here we investigated whether infection early in life can contribute to synapse damage and cognitive impairment induced by amyloid-β oligomers (AβOs), neurotoxins found in AD brains. To this end, wild-type mice were subjected to neonatal (post-natal day 4) infection by Escherichia coli (1 × 10⁴ CFU/g), the main cause of infection in low-birth-weight premature infants in the US. E. coli infection caused a transient inflammatory response in the mouse brain starting shortly after infection. Although infected mice performed normally in behavioral tasks in adulthood, they showed increased susceptibility to synapse damage and memory impairment induced by low doses of AβOs (1 pmol; intracerebroventricular) in the novel object recognition paradigm. Using in vitro and in vivo approaches, we show that microglial cells from E. coli-infected mice undergo exacerbated activation when exposed to low doses of AβOs. In addition, treatment of infected pups with minocycline, an antibiotic that inhibits microglial pro-inflammatory polarization, normalized microglial response to AβOs and restored normal susceptibility of mice to oligomer-induced cognitive impairment. Interestingly, mice infected with by E. coli (1 × 10⁴ CFU/g) during adolescence (post-natal day 21) or adulthood (post-natal day 60) showed normal cognitive performance even in the presence of AβOs (1 pmol), suggesting that only infections at critical stages of development may lead to increased susceptibility to amyloid-β-induced toxicity. Altogether, our findings suggest that neonatal infections can modulate microglial response to AβOs into adulthood, thus contributing to amyloid-β-induced synapse damage and cognitive impairment.

Can Neonatal Systemic Inflammation and Hypoxia Yield a Cerebral Palsy-Like Phenotype in Periadolescent Mice?

Cerebral palsy (CP) is one of the most common childhood-onset motor disabilities, attributed to injuries of the immature brain in the foetal or early postnatal period. The underlying mechanisms are poorly understood, rendering prevention and treatment strategies challenging. The aim of the present study was to establish a mouse model of CP for preclinical assessment of new interventions. For this purpose, we explored the impact of a double neonatal insult (i.e. systemic inflammation combined with hypoxia) on behavioural and cellular outcomes relevant to CP during the prepubertal to adolescent period of mice. Pups were subjected to intraperitoneal lipopolysaccharide (LPS) injections from postnatal day (P) 3 to P6 followed by hypoxia at P7. Gene expression analysis at P6 revealed a strong inflammatory response in a brain region-dependent manner. A comprehensive battery of behavioural assessments performed between P24 and P47 showed impaired limb placement and coordination when walking on a horizontal ladder in both males and females. Exposed males also displayed impaired performance on a forelimb skilled reaching task, altered gait pattern and increased exploratory activity. Exposed females showed a reduction in grip strength and traits of anxiety-like behaviour. These behavioural alterations were not associated with gross morphological changes, white matter lesions or chronic inflammation in the brain. Our results indicate that the neonatal double-hit with LPS and hypoxia can induce subtle long-lasting deficits in motor learning and fine motor skills, which partly reflect the symptoms of children with CP who have mild gross and fine motor impairments.

Maternal immune activation with staphylococcal enterotoxin A produces unique behavioral changes in C57BL/6 mouse offspring

Stimulation of the immune system during pregnancy, known as maternal immune activation (MIA), can cause long-lasting neurobiological and behavioral changes in the offspring. This phenomenon has been implicated in the etiology of developmental psychiatric disorders, such as autism and schizophrenia. Much of this evidence is predicated on animal models using bacterial agents such as LPS and/or viral mimics such as Poly I:C, both of which act through toll-like receptors. However, fewer studies have examined the role of direct activation of maternal T-cells during pregnancy using microbial agents. Bacterial superantigens, such as Staphylococcal Enterotoxin A and B (SEA; SEB), are microbial proteins that activate CD4+ T-cells and cause prominent T-cell proliferation and cytokine production. We injected pregnant and non-pregnant adult female C57BL/6 mice with 200 μg/Kg of SEA, SEB, or 0.9% saline, and measured splenic T-cell-derived cytokine concentrations (viz., IL-2, IFN-γ, IL-6, and IL-4) 2 h later; animals injected with SEA were also measured for splenic concentrations of TNF-α and IL-17A. Half of the injected pregnant animals were brought to term, and their offspring were tested on a series of behavioral tasks starting at six weeks of age (postnatal day 42 [P42]). These tasks included social interaction, the elevated plus maze (EPM), an open field and object recognition (OR) task, prepulse inhibition (PPI) of sensorimotor gating, and the Morris water maze (MWM). Results showed that SEA and SEB induced significant concentrations of all measured cytokines, and in particular IFN-γ, although cytokine responses were greater following SEA exposure. In addition, pregnancy induced an inhibitory effect on cytokine production. Behavioral results showed distinct phenotypes among offspring from SEA- or SEB-injected mothers, very likely due to differences in the magnitude of cytokines generated in response to each toxin. Offspring from SEA-injected mothers displayed modest decreases in social behavior, but increased anxiety, locomotion, interest in a novel object, and short-term spatial memory, while offspring of SEB-injected mothers only exhibited increased anxiety and locomotion. There were no deficits in PPI, which was actually pronounced in SEA and SEB offspring. Overall, the novel use of SEA and SEB as prenatal immune challenges elicited distinct behavioral profiles in the offspring that both mirrors and diverges from previous models of maternal immune activation in important ways. We conclude that superantigen-induced T-cell-mediated maternal immune activation is a valid and valuable model for studying and expanding our understanding of the effects of prenatal immune challenge on neurodevelopmental and behavioral alterations in offspring.

Prenatal Programming of Neuroendocrine System Development by Lipopolysaccharide: Long-Term Effects

Various stress factors during critical periods of fetal development modulate the epigenetic mechanisms controlling specific genes, which can affect the structure and function of physiological systems. Maternal immune stress by bacterial infection simulated by lipopolysaccharide (LPS) in an experiment is considered to be a powerful programming factor of fetal development. Studies of the molecular mechanisms controlling the formation and functioning of physiological systems are in the pilot stage. LPSs are the most potent natural inflammation factors. LPS-induced increases in fetal levels of pro- and anti-inflammatory cytokines can affect brain development and have long-term effects on behavior and neuroendocrine functions. The degradation of serotonergic neurons induced by LPS in the fetus is attributed to the increased levels of interleukin (IL)-6 and tumor necrosis factor (TNFα) as well as to anxiety and depression in children. Dopamine deficiency causes dysthymia, learning disability, and Parkinson’s disease. According to our data, an LPS-induced increase in the levels of IL-6, leukemia inhibitory factor (LIF), and monocyte chemotactic protein (MCP-1) in maternal and fetal rats during early pregnancy disturbs the development and functioning of gonadotropin-releasing hormone production and reproductive systems. It is important to note the high responsiveness of epigenetic developmental mechanisms to many regulatory factors, which offers opportunities to correct the defects.

Maternal prenatal depression predicts infant negative affect via maternal inflammatory cytokine levels

Maternal depressive symptoms during pregnancy are associated with risk for offspring emotional and behavioral problems, but the mechanisms by which this association occurs are not known. Infant elevated negative affect (increased crying, irritability, fearfulness, etc.) is a key risk factor for future psychopathology, so understanding its determinants has prevention and early intervention potential. An understudied yet promising hypothesis is that maternal mood affects infant mood via maternal prenatal inflammatory mechanisms, but this has not been prospectively examined in humans. Using data from a pilot study of women followed from the second trimester of pregnancy through six months postpartum (N = 68) our goal was to initiate a prospective study as to whether maternal inflammatory cytokines mediate the association between maternal depressive symptoms and infant offspring negative affect. The study sample was designed to examine a broad range of likely self-regulation and mood-regulation problems in offspring; to that end we over-selected women with a family history or their own history of elevated symptoms of attention-deficit/hyperactivity disorder. Results supported the hypothesis: maternal pro-inflammatory cytokines during the third trimester (indexed using a latent variable that included plasma interleukin-6, tumor necrosis factor-alpha and monocyte chemoattractant protein-1 concentrations as indicators) mediated the effect, such that higher maternal depressive symptoms were associated with higher maternal inflammation, and this mediated the effect on maternal report of infant negative affect (controlling for maternal affect during the infant period). This is the first human study to demonstrate that maternal inflammatory cytokines mediate the association between prenatal depression and infant outcomes, and the first to demonstrate a biological mechanism through which depressive symptoms impact infant temperament.

Dietary omega-3 deficiency exacerbates inflammation and reveals spatial memory deficits in mice exposed to lipopolysaccharide during gestation

Maternal immune activation (MIA) is a common environmental insult on the developing brain and represents a risk factor for neurodevelopmental disorders. Animal models of in utero inflammation further revealed a causal link between maternal inflammatory activation during pregnancy and behavioural impairment relevant to neurodevelopmental disorders in the offspring. Accumulating evidence point out that proinflammatory cytokines produced both in the maternal and fetal compartments are responsible for social, cognitive and emotional behavioral deficits in the offspring. Polyunsaturated fatty acids (PUFAs) are essential fatty acids with potent immunomodulatory activities. PUFAs and their bioactive derivatives can promote or inhibit many aspects of the immune and inflammatory response. PUFAs of the n-3 series ('n-3 PUFAs', also known as omega-3) exhibit anti-inflammatory/pro-resolution properties and promote immune functions, while PUFAs of the n-6 series ('n-6 PUFAs' or omega-6) favor pro-inflammatory responses. The present study aimed at providing insight into the effects of n-3 PUFAs on the consequences of MIA on brain development. We hypothesized that a reduction in n-3 PUFAs exacerbates both maternal and fetal inflammatory responses to MIA and later-life defects in memory in the offspring. Based on a lipopolysaccharide (LPS) model of MIA (LPS injection at embryonic day 17), we showed that n-3 PUFA deficiency 1) alters fatty acid composition of the fetal and adult offspring brain; 2) exacerbates maternal and fetal inflammatory processes with no significant alteration of microglia phenotype, and 3) induces spatial memory deficits in the adult offspring. We also showed a strong negative correlation between brain content in n-3 PUFA and cytokine production in MIA-exposed fetuses. Overall, our study is the first to address the deleterious effects of n-3 PUFA deficiency on brain lipid composition, inflammation and memory performances in MIA-exposed animals and indicates that it should be considered as a potent environmental risk factor for the apparition of neurodevelopmental disorders.

The intestinal microbiome and Alzheimer's disease: A review

Alzheimer's disease (AD) is an increasingly common neurodegenerative disease. Since the intestinal microbiome is closely related to nervous system diseases, alterations in the composition of intestinal microbiota could potentially contribute to the pathophysiology of AD. However, how the initial interactions with intestinal microbes alter events later in life, such as during neurodegenerative diseases, is still unclear. This review summarizes what is known about the relationship between the intestinal microbiome and AD.

Prenatal inflammation exposure-programmed cardiovascular diseases and potential prevention

In recent years, the rapid development of medical and pharmacological interventions has led to a steady decline in certain noncommunicable chronic diseases (NCDs), such as cancer. However, the overall incidence of cardiovascular diseases (CVDs) has not seemed to decline. CVDs have become even more prevalent in many countries and represent a global health threat and financial burden. An increasing number of epidemiological and experimental studies have demonstrated that maternal insults not only can result in birth defects but also can cause developmental functional defects that contribute to adult NCDs. In the current review, we provide an overview of evidence from both epidemiological investigations and experimental animal studies supporting the concept of developmental reprogramming of adult CVDs in offspring that have experienced prenatal inflammation exposure (PIE) during fetal development (PIE-programmed CVDs), a disease-causing event that has not been effectively controlled. This review describes the epidemiological observations, data from animal models, and related mechanisms for the pathogenesis of PIE-programmed CVDs. In addition, the potential therapeutic interventions of PIE-programmed CVDs are discussed. Finally, we also deliberate the need for future mechanistic studies and biomarker screenings in this important field, which creates a great opportunity to combat the global increase in CVDs by managing the adverse effects of inflammation for prepregnant and pregnant individuals who are at risk for PIE-programmed CVDs.

Maternal inflammation induces immune activation of fetal microglia and leads to disrupted microglia immune responses, behavior, and learning performance in adulthood

Maternal inflammation during pregnancy can have detrimental effects on embryonic development that persist during adulthood. However, the underlying mechanisms and insights in the responsible cell types are still largely unknown. Here we report the effect of maternal inflammation on fetal microglia, the innate immune cells of the central nervous system (CNS). In mice, a challenge with LPS during late gestation stages (days 15-16-17) induced a pro-inflammatory response in fetal microglia. Adult whole brain microglia of mice that were exposed to LPS during embryonic development displayed a persistent reduction in pro-inflammatory activation in response to a re-challenge with LPS. In contrast, hippocampal microglia of these mice displayed an increased inflammatory response to an LPS re-challenge. In addition, a reduced expression of brain-derived neurotrophic factor (BDNF) was observed in hippocampal microglia of LPS-offspring. Microglia-derived BDNF has been shown to be important for learning and memory processes. In line with these observations, behavioral- and learning tasks with mice that were exposed to maternal inflammation revealed reduced home cage activity, reduced anxiety and reduced learning performance in a T-maze. These data show that exposure to maternal inflammation during late gestation results in long term changes in microglia responsiveness during adulthood, which is different in nature in hippocampus compared to total brain microglia.

Microglial Priming and Alzheimer's Disease: A Possible Role for (Early) Immune Challenges and Epigenetics?

Neuroinflammation is thought to contribute to Alzheimer's disease (AD) pathogenesis that is, to a large extent, mediated by microglia. Given the tight interaction between the immune system and the brain, peripheral immune challenges can profoundly affect brain function. Indeed, both preclinical and clinical studies have indicated that an aberrant inflammatory response can elicit behavioral impairments and cognitive deficits, especially when the brain is in a vulnerable state, e.g., during early development, as a result of aging, or under disease conditions like AD. However, how exactly peripheral immune challenges affect brain function and whether this is mediated by aberrant microglial functioning remains largely elusive. In this review, we hypothesize that: (1) systemic immune challenges occurring during vulnerable periods of life can increase the propensity to induce later cognitive dysfunction and accelerate AD pathology; and (2) that "priming" of microglial cells is instrumental in mediating this vulnerability. We highlight how microglia can be primed by both neonatal infections as well as by aging, two periods of life during which microglial activity is known to be specifically upregulated. Lasting changes in (the ratios of) specific microglial phenotypes can result in an exaggerated pro-inflammatory cytokine response to subsequent inflammatory challenges. While the resulting changes in brain function are initially transient, a continued and/or excess release of such pro-inflammatory cytokines can activate various downstream cellular cascades known to be relevant for AD. Finally, we discuss microglial priming and the aberrant microglial response as potential target for treatment strategies for AD.

Novel NTRK1 Frameshift Mutation in Congenital Insensitivity to Pain With Anhidrosis

Congenital insensitivity to pain with anhidrosis is a rare autosomal recessive disorder. It has been reported that the defect in the NTRK1 gene encoding tropomyosin-related kinase A (TrkA) can cause congenital insensitivity to pain with anhidrosis. Nerve growth factor (NGF), the product of NGFB, mediates biological effects by binding to and activating tropomyosin-related kinase A. In addition, necdin (encoded by NDN) is also essential in nerve growth factor-tropomyosin-related kinase A pathway. We performed mutation analysis in NTRK1, NGFB, and NDN genes in a Chinese Han 17-year-old female patient with congenital insensitivity to pain with anhidrosis and her healthy family members. As a result, the patient was found to have a novel insertion in exon 7 (c.727insT) of NTRK1, which causes premature termination, and a single nucleotide polymorphism (rs2192206 G>A) in NDN. Our findings imply that the genetic variations of the nerve growth factor-tropomyosin-related kinase A pathway play an important role in congenital insensitivity to pain with anhidrosis.

The neurite growth inhibitory effects of soluble TNFα on developing sympathetic neurons are dependent on developmental age

During development, the growth of neural processes is regulated by an array of cellular and molecular mechanisms which influence growth rate, direction and branching. Recently, many members of the TNF superfamily have been shown to be key regulators of neurite growth during development. The founder member of this family, TNFα can both promote and inhibit neurite growth depending on the cellular context. Specifically, transmembrane TNFα promotes neurite growth, while soluble TNFα inhibits it. While the growth promoting effects of TNFα are restricted to a defined developmental window of early postnatal development, whether the growth inhibitory effects of soluble TNFα occur throughout development is unknown. In this study we used the extensively studied, well characterised neurons of the superior cervical ganglion to show that the growth inhibitory effects of soluble TNFα are restricted to a specific period of late embryonic and early postnatal development. Furthermore, we show that this growth inhibitory effect of soluble TNFα requires NF-κB signalling at all developmental stages at which soluble TNFα inhibits neurite growth. These findings raise the possibility that increases in the amount of soluble TNFα in vivo, for example as a result of maternal inflammation, could negatively affect neurite growth in developing neurons at specific stages of development.

Lipopolysaccharide-induced maternal inflammation affects the gonadotropin-releasing hormone neuron development in fetal mice

Recent studies provide evidence that prenatal immunological stress may affect the programming of reproductive health and sexual behavior in adult animals. The aim of this study was to investigate the influence of maternal inflammation, induced by an intraperitoneal (i.p.) injection of lipopolysaccharide (LPS, 45 µg/kg) on embryonic day 11.5 (E 11.5), on the development of the gonadotropin-releasing hormone (GnRH) system in mouse fetuses as well as on the proinflammatory cytokine level in pregnant mice and their fetuses. In the fetuses, the GnRH neuron migration from the olfactory pit to the forebrain was estimated on embryonic days 14.5 and 18.5. The levels of the proinflammatory cytokines interleukin (IL)-6, monocyte chemotactic protein (MCP)-1, tumor necrosis factor (TNF)-α and leukemia inhibitory factor (LIF) were measured with the cytometric bead and ELISA array method in the maternal and fetal blood, amniotic fluid and fetal cerebrospinal fluid (CSF). According to our data, activation of the immune system by LPS treatment on embryonic day 11.5 leads to an increased quantity of neurons in the nasal and olfactory bulb areas and a decreased quantity in the forebrain area on embryonic day 14.5. There was a slight decrease in the total number of neurons in the forebrain area on embryonic day 18.5. The levels of proinflammatory cytokines were significantly increased within 3 h after LPS treatment in the maternal and fetal blood, amniotic fluid and fetal CSF. IL-6-receptor immunoreactivity was detected on olfactory/vomeronasal axons. Thus, prenatal immunological stress delays the GnRH neuron migration in the nasal compartment of mouse fetuses, which may be mediated by the regulation of IL-6, MCP-1 and LIF secretion in the maternal-fetal system.

Neonatal systemic inflammation in rats alters retinal vessel development and simulates pathologic features of retinopathy of prematurity

Background

Alteration of retinal angiogenesis during development leads to retinopathy of prematurity (ROP) in preterm infants, which is a leading cause of visual impairment in children. A number of clinical studies have reported higher rates of ROP in infants who had perinatal infections or inflammation, suggesting that exposure of the developing retina to inflammation may disturb retinal vessel development. Thus, we investigated the effects of systemic inflammation on retinal vessel development and retinal inflammation in neonatal rats.

Methods

To induce systemic inflammation, we intraperitoneally injected 100 μl lipopolysaccharide (LPS, 0.25 mg/ml) or the same volume of normal saline in rat pups on postnatal days 1, 3, and 5. The retinas were extracted on postnatal days 7 and 14, and subjected to assays for retinal vessels, inflammatory cells and molecules, and apoptosis.

Results

We found that intraperitoneal injection of LPS impaired retinal vessel development by decreasing vessel extension, reducing capillary density, and inducing localized overgrowth of abnormal retinal vessels and dilated peripheral vascular ridge, all of which are characteristic findings of ROP. Also, a large number of CD11c⁺ inflammatory cells and astrocytes were localized in the lesion of abnormal vessels. Further analysis revealed that the number of major histocompatibility complex (MHC) class II^loCD68^loCD11b^loCD11c^hi cells in the retina was higher in LPS-treated rats compared to controls. Similarly, the levels of TNF-α, IL-1β, and IL-12a were increased in LPS-treated retina. Also, apoptosis was increased in the inner retinal layer where retinal vessels are located.

Conclusions

Our data demonstrate that systemic LPS-induced inflammation elicits retinal inflammation and impairs retinal angiogenesis in neonatal rats, implicating perinatal inflammation in the pathogenesis of ROP.

Differential distribution of Y-box-binding protein 1 and cold shock domain protein A in developing and adult human brain

The two cold shock domain containing proteins, Y-box-binding protein-1 and cold shock domain protein A were immunolocalized in developing and adult human brain. With the exception of a small population of hypothalamic astrocytes, brain Y-box-binding protein-1 was predominantly found in multiple neurons in the mature human CNS, which might be related to its involvement in neurotransmission and other neuron-associated functions. Cold shock domain protein A was typically observed in astrocytes, oligodendrocytes, choroid plexus epithelia and nerve fibers. However, in circumscribed brain regions as hypothalamus, habenula, and cerebellum, this protein was also expressed in neurons. In the prenatal brain, both proteins were found to be abundantly expressed in radial glial cells, neuroblasts and neurons, which might be an anatomical correlate of the proposed roles of both proteins in cell proliferation and differentiation. In addition, Y-box-binding protein-1 was identified in cultured, lipopolysaccharide-stimulated microglial cells, which underscores its putative role as a mediator in immune and inflammatory processes.

Maternal inflammation promotes fetal microglial activation and increased cholinergic expression in the fetal basal forebrain: role of interleukin-6

BACKGROUND

Perinatal exposure to infectious agents with associated maternal immune activation (MIA) leads to neuroanatomical and behavioral dysregulation reminiscent of autism spectrum disorders. Persistent microglial activation as well as increased choline acetyltransferase (ChAT) activity in the basal forebrain (BF) are characteristic of autistic subjects. Previous studies have shown that medium from activated microglia promotes cholinergic differentiation of precursors in the BF. We sought to determine whether MIA in vivo would lead to a similar effect on developing BF neurons.

METHODS

Pregnant mice were treated with the viral mimic polyinosinic-polycytidylic acid (poly(I:C)) or saline.

RESULTS

Poly(I:C) treatment resulted in increased production of cytokines and chemokines in fetal microglia and increased ChAT activity and cholinergic cell number in the perinatal BF. Whether microglial activation causes these changes is unclear. Examination of fetal brains from mice lacking interleukin-6 (IL-6 KOs) revealed an elevation in non-microglial-derived cytokines and chemokines over wild-type controls. Moreover, IL-6 KO offspring showed an elevation of ChAT activity even in the absence of poly(I:C) administration.

CONCLUSION

These data suggest that elevations in cytokines and/or chemokines caused either by maternal poly(I:C) administration or by the absence of IL-6 are associated with alterations in cholinergic development in the BF.

YB-1 is an early and central mediator of bacterial and sterile inflammation in vivo

In vitro studies identified Y-box-binding protein (YB)-1 as a key regulator of inflammatory mediators. In this study, we observed increased levels of secreted YB-1 in sera from sepsis patients. This led us to investigate the in vivo role of YB-1 in murine models of acute peritonitis following LPS injection, in sterile renal inflammation following unilateral ureteral obstruction, and in experimental pyelonephritis. LPS injection enhanced de novo secretion of YB-1 into the urine and the peritoneal fluid of LPS-treated mice. Furthermore, we could demonstrate a significant, transient upregulation and posttranslational modification (phosphorylation at serine 102) of YB-1 in renal and inflammatory cells. Increased renal cytoplasmic YB-1 amounts conferred enhanced expression of proinflammatory chemokines CCL2 and CCL5. Along these lines, heterozygous YB-1 knockout mice (YB-1(+/d)) that display 50% reduced YB-1 levels developed significantly lower responses to both LPS and sterile inflammation induced by unilateral ureteral obstruction. This included diminished immune cell numbers due to impaired migration propensities and reduced chemokine expression. YB-1(+/d) mice were protected from LPS-associated mortality (20% mortality on day 3 versus 80% in wild-type controls); however, immunosuppression in YB-1(+/d) animals resulted in 50% mortality. In conclusion, our findings identify YB-1 as a major, nonredundant mediator in both systemic and local inflammatory responses.

N-acetyl-cysteine prevents pyramidal cell disarray and reelin-immunoreactive neuron deficiency in CA3 after prenatal immune challenge in rats

BACKGROUND

Prenatal infection is a major risk factor for the occurrence of neuropsychiatric disorders. These have been associated with hippocampal neuroanatomical and functional abnormalities. In the present study, we evaluated the occurrence of pyramidal cell disarray and reelin neuronal deficit in the hippocampus, and the protective role of N-acetyl-cysteine (NAC) in a rodent experimental model of prenatal immune challenge.

METHODS

Sprague-Dawley rats received either 500 μg/kg of endotoxin (lipopolysaccharide, LPS) or 2 ml/kg of isotonic saline by i.p. injection on day 19 of gestation. After LPS injection, rats were or were not maintained on a preventive treatment of NAC (5 g/l in tap water), up to delivery. The pyramidal cell orientation and the number and type of reelin-expressing neurons were determined in male offspring.

RESULTS

Prenatal LPS challenge led to permanent pyramidal cell disarray and to an early and transient decreased density of reelin-immunoreactive neurons. These disorders, more pronounced in the CA3 area, were prevented by NAC.

CONCLUSION

Hippocampal cytoarchitectural alterations and reelin deficiency may be involved in the development of remote cognitive impairments in this model. The antioxidant NAC is an efficient neuroprotective drug that underlines the role of oxidative stress in prenatal infection and associated neurodevelopmental damage.

Innate immune regulation by toll-like receptors in the brain

The innate immune system plays an important role in cerebral health and disease. In recent years the role of innate immune regulation by toll-like receptors in the brain has been highlighted. In this paper the expression of toll-like receptors and endogenous toll-like receptor ligands in the brain and their role in cerebral ischemia will be discussed. Further, the ability of systemic toll-like receptor ligands to induce cerebral inflammation will be reviewed. Finally, the capacity of toll-like receptors to both increase (sensitization) and decrease (preconditioning/tolerance) the vulnerability of the brain to damage will be disclosed. Studies investigating the role of toll-like receptors in the developing brain will be emphasized.

The immune theory of psychiatric diseases: a key role for activated microglia and circulating monocytes

This review describes a key role for mononuclear phagocytes in the pathogenesis of major psychiatric disorders. There is accumulating evidence for activation of microglia (histopathology and PET scans) and circulating monocytes (enhanced gene expression of immune genes, an overproduction of monocyte/macrophage-related cytokines) in patients with bipolar disorder, major depressive disorder, and schizophrenia. These data are strengthened by observations in animal models, such as the MIA models, the chronic stress models, and the NOD mouse model. In these animal models of depressive-, anxiety-, and schizophrenia-like behavior, similar activations of microglia and circulating monocytes can be found. These animal models also make in-depth pathogenic studies possible and show that microglia activation impacts neuronal development and function in brain areas congruent with the altered depressive and schizophrenia-like behaviors.

Prenatal activation of Toll-like receptors-3 by administration of the viral mimetic poly(I:C) changes synaptic proteins, N-methyl-D-aspartate receptors and neurogenesis markers in offspring

Background

There is mounting evidence for a neurodevelopmental basis for disorders such as autism and schizophrenia, in which prenatal or early postnatal events may influence brain development and predispose the young to develop these and related disorders. We have now investigated the effect of a prenatal immune challenge on brain development in the offspring. Pregnant rats were treated with the double-stranded RNA polyinosinic:polycytidylic acid (poly(I:C); 10 mg/kg) which mimics immune activation occurring after activation of Toll-like receptors-3 (TLR3) by viral infection. Injections were made in late gestation (embryonic days E14, E16 and E18), after which parturition proceeded naturally and the young were allowed to develop up to the time of weaning at postnatal day 21 (P21). The brains of these animals were then removed to assess the expression of 13 different neurodevelopmental molecules by immunoblotting.

Results

Measurement of cytokine levels in the maternal blood 5 hours after an injection of poly(I:C) showed significantly increased levels of monocyte chemoattractant protein-1 (MCP-1), confirming immune activation. In the P21 offspring, significant changes were detected in the expression of GluN1 subunits of NMDA receptors, with no difference in GluN2A or GluN2B subunits or the postsynaptic density protein PSD-95 and no change in the levels of the related small GTPases RhoA or RhoB, or the NMDA receptor modulator EphA4. Among presynaptic molecules, a significant increase in Vesicle Associated Membrane Protein-1 (VAMP-1; synaptobrevin) was seen, with no change in synaptophysin or synaptotagmin. Proliferating Cell Nuclear Antigen (PCNA), as well as the neurogenesis marker doublecortin were unchanged, although Sox-2 levels were increased, suggesting possible changes in the rate of new cell differentiation.

Conclusions

The results reveal the induction by prenatal poly(I:C) of selective molecular changes in the brains of P21 offspring, affecting primarily molecules associated with neuronal development and synaptic transmission. These changes may contribute to the behavioural abnormalities that have been reported in adult animals after exposure to poly(I:C) and which resemble symptoms seen in schizophrenia and related disorders.

Maternal immune activation by LPS selectively alters specific gene expression profiles of interneuron migration and oxidative stress in the fetus without triggering a fetal immune response

Maternal immune activation (MIA) is a risk factor for the development of schizophrenia and autism. Infections during pregnancy activate the mother's immune system and alter the fetal environment, with consequential effects on CNS function and behavior in the offspring, but the cellular and molecular links between infection-induced altered fetal development and risk for neuropsychiatric disorders are unknown. We investigated the immunological, molecular, and behavioral effects of MIA in the offspring of pregnant Sprague-Dawley rats given an intraperitoneal (0.25 mg/kg) injection of lipopolysaccharide (LPS) on gestational day 15. LPS significantly elevated pro-inflammatory cytokine levels in maternal serum, amniotic fluid, and fetal brain at 4 h, and levels decreased but remained elevated at 24 h. Offspring born to LPS-treated dams exhibited reduced social preference and exploration behaviors as juveniles and young adults. Whole genome microarray analysis of the fetal brain at 4 h post maternal LPS was performed to elucidate the possible molecular mechanisms by which MIA affects the fetal brain. We observed dysregulation of 3285 genes in restricted functional categories, with increased mRNA expression of cellular stress and cell death genes and reduced expression of developmentally-regulated and brain-specific genes, specifically those that regulate neuronal migration of GABAergic interneurons, including the Distal-less (Dlx) family of transcription factors required for tangential migration from progenitor pools within the ganglionic eminences into the cerebral cortex. Our results provide a novel mechanism by which MIA induces the widespread down-regulation of critical neurodevelopmental genes, including those previously associated with autism.

Role of cold shock Y-box protein-1 in inflammation, atherosclerosis and organ transplant rejection

Chemokines (chemoattractant cytokines) are crucial regulators of immune cell extravasation from the bloodstream into inflamed tissue. Dysfunctional regulation and perpetuated chemokine gene expression are linked to progressive chronic inflammatory diseases and, in respect to transplanted organs, may trigger graft rejection. RANTES (regulated upon activation, normal T cell expressed and secreted (also known as CCL5)) is a model chemokine with relevance in numerous inflammatory diseases where the innate immune response predominates. Transcription factor Y-box binding protein-1 (YB-1) serves as a trans-regulator of CCL5 gene transcription in vascular smooth muscle cells and leucocytes. This review provides an update on YB-1 as a mediator of inflammatory processes and focuses on the role of YB-1 in CCL5 expression in diseases with monocytic cell infiltrates, albeit acute or chronic. Paradigms of such diseases encompass atherosclerosis and transplant rejection where cold shock protein YB-1 takes a dominant role in transcriptional regulation.

Prenatal stress: role in psychotic and depressive diseases

RATIONALE

The birth of neurons, their migration to appropriate positions in the brain, and their establishment of the proper synaptic contacts happen predominately during the prenatal period. Environmental stressors during gestation can exert a major impact on brain development and thereby contribute to the pathogenesis of neuropsychiatric illnesses, such as depression and psychotic disorders including schizophrenia.

OBJECTIVE

The objectives here are to present recent preclinical studies of the impact of prenatal exposure to gestational stressors on the developing fetal brain and discuss their relevance to the neurobiological basis of mental illness. The focus is on maternal immune activation, psychological stresses, and malnutrition, due to the abundant clinical literature supporting their role in the etiology of neuropsychiatric illnesses.

RESULTS

Prenatal maternal immune activation, viral infection, unpredictable psychological stress, and malnutrition all appear to foster the development of behavioral abnormalities in exposed offspring that may be relevant to the symptom domains of schizophrenia and psychosis, including sensorimotor gating, information processing, cognition, social function, and subcortical hyperdopaminergia. Depression-related phenotypes, such as learned helplessness or anxiety, are also observed in some model systems. These changes appear to be mediated by the presence of proinflammatory cytokines and/or corticosteroids in the fetal compartment that alter the development the neuroanatomical substrates involved in these behaviors.

CONCLUSION

Prenatal exposure to environmental stressors alters the trajectory of brain development and can be used to generate animal preparations that may be informative in understanding the pathophysiological processes involved in several human neuropsychiatric disorders.

Prenatal LPS increases inflammation in the substantia nigra of Gdnf heterozygous mice

Prenatal systemic inflammation has been implicated in neurological diseases, but optimal animal models have not been developed. We investigated whether a partial genetic deletion of glial cell line-derived neurotrophic factor (Gdnf(+/-)) increased vulnerability of dopamine (DA) neurons to prenatal lipopolysaccharide (LPS). LPS [0.01 mg/kg intraperitoneal (i.p.)] or saline was administered to wild-type (WT) or Gdnf(+/-) pregnant mice on gestational day 9.5. Male offspring were examined at 3 weeks, 3 and 12 months of age. There was a progressive degeneration of tyrosine hydroxylase (TH)-positive neurons in the substantia nigra (SN) with age in Gdnf(+/-) but not in WT mice, with no observed effects on locus coeruleus (LC) noradrenergic neurons or DA neurons of the ventral tegmental area. Inflammatory markers were elevated in SN of LPS treated offspring, with exacerbation in Gdnf(+/-) mice. Intracellular accumulation of α-synuclein (α-syn) immunoreactivity in DA neurons of SN was observed in all groups of Gdnf(+/-) and in WT mice with prenatal LPS, with altered distribution between pars reticulata (pr) and pars compacta (pc). The findings suggest that prenatal LPS leads to accelerated neuropathology in the SN with age, and that a partial loss of GDNF exacerbates these effects, providing a novel model for age-related neuropathology of the nigrostriatal DA system.

Maternal immune activation and autism spectrum disorder: interleukin-6 signaling as a key mechanistic pathway

An emerging area of research in autism spectrum disorder (ASD) is the role of prenatal exposure to inflammatory mediators during critical developmental periods. Epidemiological data has highlighted this relationship showing significant correlations between prenatal exposure to pathogens, including influenza, and the occurrence of ASD. Although there has not been a definitive molecular mechanism established, researchers have begun to investigate this relationship as animal models of maternal infection have support- ed epidemiological findings. Several groups utilizing these animal models have found that activation of the maternal immune system, termed maternal immune activation (MIA), and more specifically the exposure of the developing fetus to maternal cytokines precipitate the neurological, immunological and behavioral abnormalities observed in the offspring of these animals. These abnormalities have correlated with clinical findings of immune dysregulation, neurological and behavioral abnormalities in some autistic individuals. Additionally, researchers have observed genetic variations in these models in genes which regulate neurological and immunological development, similar to what is observed clinically in ASD. Altogether, the role of MIA and cytokine dysregulation, as a key mediator in the neuropathological, behavioral and possibly genetic irregularities observed clinically in autism are important factors that warrant further investigation.

Postnatal development of lipopolysaccharide-induced inflammatory response in the brain

OBJECTIVE

This study aimed to characterize postnatal development of lipopolysaccharide (LPS)-induced inflammatory response in the brain.

METHODS

Postnatal day (P)1, P21 and P70 Sprague-Dawley(®) rats were treated with saline or 0.25 mg/kg LPS for 2 h, and the mRNA expression of neuroinflammatory mediators in the brain was determined using reverse transcriptase-polymerase chain reaction (RT-PCR). The kinetics of LPS-induced neuroinflammatory mediators in the brain of P1 and P21 animals was determined using RT-PCR, and the kinetics of LPS-induced cytokines in the serum were determined using ELISA. The basal levels of Toll-like receptor (TLR)-4, CD14, and myeloid differentiation factor 88 (Myd88) were measured at the mRNA and protein levels using RT-PCR and Western blot assay respectively.

RESULTS

The mRNA expression levels of cytokines and chemokines were considerably increased in P21 and P70 brains but not significantly altered in P1 brain at 2 h following LPS stimulation. Instead, the induction of cytokines and chemokines was significantly delayed in the brain of P1 animals following LPS stimulation, which was associated with diminished Myd88 production in P1 brain. In parallel, the cytokine response in the serum of P1 animals after LPS stimulation was also delayed compared to P21 animals.

CONCLUSIONS

TLR-4-mediated innate immunity in the brain was significantly delayed in P1 animals, and underwent significant development during the early postnatal period.

Effects of prenatal infection on brain development and behavior: a review of findings from animal models

Epidemiological studies with human populations indicate associations between maternal infection during pregnancy and increased risk in offspring for central nervous system (CNS) disorders including schizophrenia, autism and cerebral palsy. Since 2000, a large number of studies have used rodent models of systemic prenatal infection or prenatal immune activation to characterize changes in brain function and behavior caused by the prenatal insult. This review provides a comprehensive summary of these findings, and examines consistencies and trends across studies in an effort to provide a perspective on our current state of understanding from this body of work. Results from these animal modeling studies clearly indicate that prenatal immune activation can cause both acute and lasting changes in behavior and CNS structure and function in offspring. Across laboratories, studies vary with respect to the type, dose and timing of immunogen administration during gestation, species used, postnatal age examined and specific outcome measure quantified. This makes comparison across studies and assessment of replicability difficult. With regard to mechanisms, evidence for roles for several acute mediators of effects of prenatal immune activation has emerged, including circulating interleukin-6, increased placental cytokines and oxidative stress in the fetal brain. However, information required to describe the complete mechanistic pathway responsible for acute effects of prenatal immune activation on fetal brain is lacking, and no studies have yet addressed the issue of how acute prenatal exposure to an immunogen is transduced into a long-term CNS change in the postnatal animal. Directions for further research are discussed.

Prenatal inflammation-induced hypoferremia alters dopamine function in the adult offspring in rat: relevance for schizophrenia

Maternal infection during pregnancy has been associated with increased incidence of schizophrenia in the adult offspring. Mechanistically, this has been partially attributed to neurodevelopmental disruption of the dopamine neurons, as a consequence of exacerbated maternal immunity. In the present study we sought to target hypoferremia, a cytokine-induced reduction of serum non-heme iron, which is common to all types of infections. Adequate iron supply to the fetus is fundamental for the development of the mesencephalic dopamine neurons and disruption of this following maternal infection can affect the offspring's dopamine function. Using a rat model of localized injury induced by turpentine, which triggers the innate immune response and inflammation, we investigated the effects of maternal iron supplementation on the offspring's dopamine function by assessing behavioral responses to acute and repeated administration of the dopamine indirect agonist, amphetamine. In addition we measured protein levels of tyrosine hydroxylase, and tissue levels of dopamine and its metabolites, in ventral tegmental area, susbtantia nigra, nucleus accumbens, dorsal striatum and medial prefrontal cortex. Offspring of turpentine-treated mothers exhibited greater responses to a single amphetamine injection and enhanced behavioral sensitization following repeated exposure to this drug, when compared to control offspring. These behavioral changes were accompanied by increased baseline levels of tyrosine hydroxylase, dopamine and its metabolites, selectively in the nucleus accumbens. Both, the behavioral and neurochemical changes were prevented by maternal iron supplementation. Localized prenatal inflammation induced a deregulation in iron homeostasis, which resulted in fundamental alterations in dopamine function and behavioral alterations in the adult offspring. These changes are characteristic of schizophrenia symptoms in humans.

Cellular localization of Y-box binding protein 1 in brain tissue of rats, macaques, and humans

Background

The Y-box binding protein 1 (YB-1) is considered to be one of the key regulators of transcription and translation. However, so far only limited knowledge exists regarding its cellular distribution in the adult brain.

Results

Analysis of YB-1 immunolabelling as well as double-labelling with the neuronal marker NeuN in rat brain tissue revealed a predominant neuronal expression in the dentate gyrus, the cornu ammonis pyramidal cell layer, layer III of the piriform cortex as well as throughout all layers of the parahippocampal cortex. In the hilus of the hippocampus single neurons expressed YB-1. The neuronal expression pattern was comparable in the hippocampus and parahippocampal cortex of adult macaques and humans. Double-labelling of YB-1 with the endothelial cell marker Glut-1, the multidrug transporter P-glycoprotein, and the astrocytic marker GFAP did not indicate a co-localization. Following status epilepticus in rats, no induction of YB-1 occurred in brain capillary endothelial cells and neurons.

Conclusion

In conclusion, our study demonstrates that YB-1 is predominantly expressed in neurons in the adult brain of rats, macaques and humans. Lack of a co-localization with Glut-1 and P-glycoprotein argues against a direct role of YB-1 in the regulation of blood-brain barrier P-glycoprotein.

Absence of circulating aldosterone attenuates foreign body reaction around surgical sutures

BACKGROUND AND AIMS

Adrenal hormones influence inflammatory and fibrotic activity and thereby are involved in wound-healing process. Any excess as well as any shortage of glucocorticoids leads to a delayed wound healing. Mineralocorticoids like aldosterone have a pro-fibrotic and pro-inflammatory impact; thus, reduction of circulating aldosterone should result in an attenuated inflammatory response to implanted foreign bodies.

MATERIAL AND METHODS

Eighteen rats were bilaterally adrenalectomized and substituted with dexamethasone (12 microg/kg per day) and 1% salt in their drinking water; 22 rats were sham-operated. The surgical suture material was removed after 3 weeks and analyzed for size of granuloma, ratio of collagen type I/III, apoptotic cells (terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick end labeling), expression of matrix metalloproteinase (MMP)-2, cyclooxygenase 2, tumor necrosis factor receptor 2 (TNF-R2), cluster of differentiation 68 (CD68), Ki67, and cold shock protein Y box binding protein 1 (YB-1). Cell expression was scored according to Remmele.

RESULTS

All animals developed foreign body granulomas around the sutures. Absence of circulating aldosterone after adrenalectomy (ADX) was associated with smaller granuloma size and a reduced ratio of collagen type I/III. Ki67 and MMP-2 showed the strongest expression in cells of the infiltrate around suture. In adrenalectomized rats, we observed significantly less CD68-positive macrophages and less Ki67-positive cells but no significant differences in the expression of YB-1, TNF-R2, or MMP-2. Looking for correlations and co-expressions of proteins, the number of significant Spearman correlations was reduced in the ADX group compared to controls (one and four, respectively).

CONCLUSION

The absence of circulating aldosterone attenuates inflammatory intensity around suture material. Foreign body granuloma seems to be an appropriate model to study chronic inflammatory process.