Gene-environment interactions in cortical interneuron development and dysfunction: A review of preclinical studies

Group 2 innate lymphoid cells promote inhibitory synapse development and social behavior

The innate immune system shapes brain development and is implicated in neurodevelopmental diseases. It is critical to define the relevant immune cells and signals and their impact on brain circuits. In this work, we found that group 2 innate lymphoid cells (ILC2s) and their cytokine interleukin-13 (IL-13) signaled directly to inhibitory interneurons to increase inhibitory synapse density in the developing mouse brain. ILC2s expanded and produced IL-13 in the developing brain meninges. Loss of ILC2s or IL-13 signaling to interneurons decreased inhibitory, but not excitatory, cortical synapses. Conversely, ILC2s and IL-13 were sufficient to increase inhibitory synapses. Loss of this signaling pathway led to selective impairments in social interaction. These data define a type 2 neuroimmune circuit in early life that shapes inhibitory synapse development and behavior.

Brain health equity and the influence of social determinants across the life cycle

Social determinants of health are social, economic and environmental factors known to influence health and development of infants, children and adults. Advancing equity in brain health relies upon interdisciplinary collaboration and recognition of the impact of social determinants on brain health through the lifespan and across generations. Critical periods of fetal, infant and early childhood development encompass intrinsic genetic and extrinsic environmental influences with complex gene-environment interactions. This review discusses the influence of social determinants on the continuum of brain health from preconception and pregnancy health, through fetal, infant and childhood neurodevelopment into adulthood. Opportunities for intervention to address the social determinants of brain health across the life cycle are highlighted.

Genetic approaches to elucidating cortical and hippocampal GABAergic interneuron diversity

GABAergic interneurons (INs) in the mammalian forebrain represent a diverse population of cells that provide specialized forms of local inhibition to regulate neural circuit activity. Over the last few decades, the development of a palette of genetic tools along with the generation of single-cell transcriptomic data has begun to reveal the molecular basis of IN diversity, thereby providing deep insights into how different IN subtypes function in the forebrain. In this review, we outline the emerging picture of cortical and hippocampal IN speciation as defined by transcriptomics and developmental origin and summarize the genetic strategies that have been utilized to target specific IN subtypes, along with the technical considerations inherent to each approach. Collectively, these methods have greatly facilitated our understanding of how IN subtypes regulate forebrain circuitry via cell type and compartment-specific inhibition and thus have illuminated a path toward potential therapeutic interventions for a variety of neurocognitive disorders.

Maternal Prenatal Use of Alcohol, Tobacco, and Illicit Drugs and Associations with Childhood Cancer Subtypes

BACKGROUND

The association between childhood cancer risk and maternal prenatal substance use/abuse remains uncertain due to modest sample sizes and heterogeneous study designs.

METHODS

We surveyed parents of children with cancer regarding maternal gestational use of tobacco, alcohol, and illicit drugs, using a Likert-type scale, and demographic, perinatal, and clinical variables. Multivariable log-Poisson regression assessed differences in frequency of prenatal substance use across fifteen childhood cancer subtypes, adjusting for birthweight, gestational age, and demographic factors.

RESULTS

Respondents from 3,145 unique families completed the survey (92% biological mothers). A minority reported gestational use of tobacco products (14%), illicit drugs including marijuana or cocaine (4%), or more than a moderate amount of alcohol (2%). Prenatal illicit drug use was associated with increased prevalence of intracranial embryonal tumors [prevalence ratio (PR) = 1.94; confidence interval [CI], 1.05-3.58], including medulloblastoma (PR = 1.82) and supratentorial primitive neuroectodermal tumors (PNET; PR = 2.66), and was also associated with retinoblastoma (PR = 3.11; CI, 1.20-8.08). Moderate to heavy alcohol consumption was strongly associated with elevated prevalence of non-Hodgkin lymphoma (PR = 5.94; CI, 1.84-19.21). Prenatal smoking was not associated with elevated prevalence of any childhood cancer subtype.

CONCLUSIONS

We identify novel associations between illicit drug use during pregnancy and increased prevalence of nonglioma central nervous system tumors, including medulloblastoma, supratentorial PNETs, and retinoblastoma. Gestational exposure to alcohol was positively associated with non-Hodgkin lymphoma.

IMPACT

Although alcohol and tobacco use during pregnancy has declined, gestational cannabis use has risen. Investigating its impact on neurodevelopment and brain tumorigenesis is vital, with important implications for childhood cancer research and public health education.

Maternal sevoflurane exposure increases the epilepsy susceptibility of adolescent offspring by interrupting interneuron development

BACKGROUND

Exposure to general anesthesia influences neuronal functions during brain development. Recently, interneurons were found to be involved in developmental neurotoxicity by anesthetic exposure. But the underlying mechanism and long-term consequences remain elusive.

METHODS

Pregnant mice received 2.5% sevoflurane for 6-h on gestational day 14.5. Pentylenetetrazole (PTZ)-induced seizure, anxiety- and depression-like behavior tests were performed in 30- and 60-day-old male offspring. Cortical interneurons were labeled using Rosa26-EYFP/-; Nkx2.1-Cre mice. Immunofluorescence and electrophysiology were performed to determine the cortical interneuron properties. Q-PCR and in situ hybridization (ISH) were performed for the potential mechanism, and the finding was further validated by in utero electroporation (IUE).

RESULTS

In this study, we found that maternal sevoflurane exposure increased epilepsy susceptibility by using pentylenetetrazole (PTZ) induced-kindling models and enhanced anxiety- and depression-like behaviors in adolescent offspring. After sevoflurane exposure, the highly ordered cortical interneuron migration was disrupted in the fetal cortex. In addition, the resting membrane potentials of fast-spiking interneurons in the sevoflurane-treated group were more hyperpolarized in adolescence accompanied by an increase in inhibitory synapses. Both q-PCR and ISH indicated that CXCL12/CXCR4 signaling pathway downregulation might be a potential mechanism under sevoflurane developmental neurotoxicity which was further confirmed by IUE and behavioral tests. Although the above effects were obvious in adolescence, they did not persist into adulthood.

CONCLUSIONS

Our findings demonstrate that maternal anesthesia impairs interneuron migration through the CXCL12/CXCR4 signaling pathway, and influences the interneuron properties, leading to the increased epilepsy susceptibility in adolescent offspring. Our study provides a novel perspective on the developmental neurotoxicity of the mechanistic link between maternal use of general anesthesia and increased susceptibility to epilepsy.

Acquired Brain Injuries Across the Perinatal Spectrum: Pathophysiology and Emerging Therapies

The development of the central nervous system can be directly disrupted by a variety of acquired factors, including infectious, inflammatory, hypoxic-ischemic, and toxic insults. Influences external to the fetus also impact neurodevelopment, including placental health, maternal comorbidities, adverse experiences, environmental exposures, and social determinants of health. Acquired perinatal brain insults tend to affect the developing brain in a stage-specific manner that reflects the susceptible cell types, developmental processes, and risk factors present at the time of the insult. In this review, we discuss the pathophysiology, neurodevelopmental outcomes, and management of common acquired perinatal brain conditions. In the fetal brain, we divide insults based on trimester, and in the postnatal brain, we focus on common pathologies that have a presentation dependent on gestational age at birth: white matter injury and germinal matrix hemorrhage/intraventricular hemorrhage in preterm infants and hypoxic-ischemic encephalopathy in term infants. Although specific treatments for fetal and newborn brain disorders are currently limited, we emphasize therapies in preclinical or early clinical phases of the development pipeline. The growing number of novel cell type- and stage-specific emerging therapies suggests that in the near future we may have a dramatically improved ability to treat acquired perinatal brain disorders and to mitigate the associated neurodevelopmental consequences.

miR-375 upregulates lipid metabolism and inhibits cell proliferation involved in chicken fatty liver formation and inheritance via targeting recombination signal binding protein for immunoglobulin kappa J region (RBPJ)

Poultry is susceptible to fatty liver which lead to decrease egg production and increase mortality. But the potential molecular mechanisms remain largely unclear. In the current study, in combination with transcriptome sequencing and miRNA sequencing data analysis from F1 generation of the normal liver and fatty liver tissues, the differentially expressed miR-375 and its target gene RBPJ were screened and verified. The expression levels of miR-375 and RBPJ gene in the liver between control and fatty liver groups of F0-F3 generation for Jingxing-Huang (JXH) chicken are different significantly (P < 0.05 or P < 0.01). And downregulated RBPJ expression can promote TG content and lipid droplets in primary hepatocytes cultured in vitro (P < 0.01). Cell proliferation-related genes, including PMP22, IGF-1, IGF-2, and IGFBP-5, increased or decreased significantly after overexpression or knock-down RBPJ (P < 0.05 or P < 0.01), respectively. This study uniquely revealed that miR-375 induced lipid synthesis and inhibited cell proliferation may partly due to regulation of RBPJ expression, thereby involving in fatty liver formation and inheritance in chicken. The results could be useful in identifying candidate genes and revealing the pathogenesis of fatty liver that may be used for disease-resistance selective breeding in chicken.

The Structural E/I Balance Constrains the Early Development of Cortical Network Activity

Neocortical networks have a characteristic constant ratio in the number of glutamatergic projection neurons (PN) and GABAergic interneurons (IN), and deviations in this ratio are often associated with developmental neuropathologies. Cultured networks with defined cellular content allowed us to ask if initial PN/IN ratios change the developmental population dynamics, and how different ratios impact the physiological excitatory/inhibitory (E/I) balance and the network activity development. During the first week in vitro, the IN content modulated PN numbers, increasing their proliferation in networks with higher IN proportions. The proportion of INs in each network set remained similar to the initial plating ratio during the 4 weeks cultivation period. Results from additional networks generated with more diverse cellular composition, including early-born GABA neurons, suggest that a GABA-dependent mechanism may decrease the survival of additional INs. A large variation of the PN/IN ratio did not change the balance between isolated spontaneous glutamatergic and GABAergic postsynaptic currents charge transfer (E/I balance) measured in PNs or INs. In contrast, the E/I balance of multisynaptic bursts reflected differences in IN content. Additionally, the spontaneous activity recorded by calcium imaging showed that higher IN ratios were associated with increased frequency of network bursts combined with a decrease of participating neurons per event. In the 4th week in vitro, bursting activity was stereotypically synchronized in networks with very few INs but was more desynchronized in networks with higher IN proportions. These results suggest that the E/I balance of isolated postsynaptic currents in single cells may be regulated independently of PN/IN proportions, but the network bursts E/I balance and the maturation of spontaneous network activity critically depends upon the structural PN/IN ratio.

Examining the developmental toxicity of piperonyl butoxide as a Sonic hedgehog pathway inhibitor

Piperonyl butoxide (PBO) is a semisynthetic chemical present in hundreds of pesticide formulations used in agricultural, commercial, and residential settings. PBO acts as a pesticide synergist by inhibiting insect cytochrome P450 enzymes and is often present at much higher concentrations than active insecticidal ingredients. PBO was recently discovered to also inhibit Sonic hedgehog (Shh) signaling, a key molecular pathway in embryonic development and in brain and face morphogenesis. Recent animal model studies have shown that in utero PBO exposure can cause overt craniofacial malformations or more subtle neurodevelopmental abnormalities. Related adverse developmental outcomes in humans are etiologically heterogeneous, and, while studies are limited, PBO exposure during pregnancy has been linked to neurodevelopmental deficits. Contextualized in PBO's newly recognized mechanism as a Shh signaling inhibitor, these findings support more rigorous examination of the developmental toxicity of PBO and its potential contribution to etiologically complex human birth defects. In this review, we highlight environmental sources of human PBO exposure and summarize existing animal studies examining the developmental impact of prenatal PBO exposure. Also presented are critical knowledge gaps in our understanding of PBO's pharmacokinetics and potential role in gene-environment and environment-environment interactions that should be addressed to better understand the human health impact of environmental PBO exposure.

Prenatal sevoflurane exposure causes neuronal excitatory/inhibitory imbalance in the prefrontal cortex and neurofunctional abnormality in rats

The balance of excitatory and inhibitory neurons in the central nervous system is critical for maintaining brain function and sevoflurane, a general anesthetic and an GABA receptor modulator, may change the balance of excitatory and inhibitory neurons in the cortex during early brain development. Herein, we investigated whether prenatal sevoflurane exposure (PSE) disturbs cortical neuronal development and brain function. Pregnant rats at the gestational day 14.5 were subjected to sevoflurane exposure at 3.0% for 3 h and their offspring were studied thereafter. We found a significant increase of parvalbumin-positive neurons, vesicular GABA transporter (VGAT) and GAD67 expression, and GABA neurotransmitter, and a significant decrease of vesicular glutamate transporter 1 (VGLUT1) expression and glutamate in the medial prefrontal cortex (mPFC) of offspring. Pyramidal neurons showed atrophy with shorter dendrites, less branches and lower spine density visualized by Golgi stain and a decrease of excitability with the increased miniature inhibitory postsynaptic current (mIPSC) frequency and amplitude, the decreased miniature excitatory postsynaptic current (mEPSC) frequency and excitation/inhibition (E/I) ratio using whole-cell recording in offspring. There was a significant increase of inhibitory synapse in the mPFC detected by electron microscopy. Furthermore, PSE animals showed hypo-excitatory phenotype including depression-like behaviors and learning deficits. Thus, our studies provide novel evidence that PSE causes the persisted imbalance of excitatory and inhibitory neurons in the mPFC, and this is very likely the mechanisms of the sevoflurane-induced brain functional abnormalities.

Deletion of Semaphorin 3F in Interneurons Is Associated with Decreased GABAergic Neurons, Autism-like Behavior, and Increased Oxidative Stress Cascades

Autism and epilepsy are diseases which have complex genetic inheritance. Genome-wide association and other genetic studies have implicated at least 500+ genes associated with the occurrence of autism spectrum disorders (ASD) including the human semaphorin 3F (Sema 3F) and neuropilin 2 (NRP2) genes. However, the genetic basis of the comorbid occurrence of autism and epilepsy is unknown. The aberrant development of GABAergic circuitry is a possible risk factor in autism and epilepsy. Molecular biological approaches were used to test the hypothesis that cell-specific genetic variation in mouse homologs affects the formation and function of GABAergic circuitry. The empirical analysis with mice homozygous null for one of these genes, Sema 3F, in GABAergic neurons substantiated these predictions. Notably, deletion of Sema 3F in interneurons but not excitatory neurons during early development decreased the number of interneurons/neurites and mRNAs for cell-specific GABAergic markers and increased epileptogenesis and autistic behaviors. Studies of interneuron cell-specific knockout of Sema 3F signaling suggest that deficient Sema 3F signaling may lead to neuroinflammation and oxidative stress. Further studies of mouse KO models of ASD genes such as Sema 3F or NRP2 may be informative to clinical phenotypes contributing to the pathogenesis in autism and epilepsy patients.

Cellular stress mechanisms of prenatal maternal stress: Heat shock factors and oxidative stress

Development of the brain prenatally is affected by maternal experience and exposure. Prenatal maternal psychological stress changes brain development and results in increased risk for neuropsychiatric disorders. In this review, multiple levels of prenatal stress mechanisms (offspring brain, placenta, and maternal physiology) are discussed and their intersection with cellular stress mechanisms explicated. Heat shock factors and oxidative stress are closely related to each other and converge with the inflammation, hormones, and cellular development that have been more deeply explored as the basis of prenatal stress risk. Increasing evidence implicates cellular stress mechanisms in neuropsychiatric disorders associated with prenatal stress including affective disorders, schizophrenia, and child-onset psychiatric disorders. Heat shock factors and oxidative stress also have links with the mechanisms involved in other kinds of prenatal stress including external exposures such as environmental toxicants and internal disruptions such as preeclampsia. Integrative understanding of developmental neurobiology with these cellular and physiological mechanisms is necessary to reduce risks and promote healthy brain development.

Alteration of Hepatic Gene Expression along with the Inherited Phenotype of Acquired Fatty Liver in Chicken

Fatty liver is a widespread disease in chickens that causes a decrease in egg production and even death. The characteristics of the inherited phenotype of acquired fatty liver and the molecular mechanisms underlying it, however, are largely unknown. In the current study, fatty liver was induced in 3 breeds by a high-fat (HF) diet and a methionine choline-deficient (MCD) diet. The results showed that the dwarf Jingxing-Huang (JXH) chicken was more susceptible to fatty liver compared with the layer White Leghorns (WL) and local Beijing-You (BJY) breeds. In addition, it was found that the paternal fatty livers induced by HF diet in JXH chickens were inherited. Compared to birds without fatty liver in the control group, both offsprings and their sires with fatty livers in the paternal group exhibited altered hepatic gene expression profiles, including upregulation of several key genes involved in fatty acid metabolism, lipid metabolism and glucose metabolism (ACACA, FASN, SCD, ACSL5, FADS2, FABP1, APOA4 and ME1). This study uniquely revealed that acquired fatty liver in cocks can be inherited. The hepatic gene expression profiles were altered in chickens with the inherited phenotype of acquired paternal fatty liver and several genes could be candidate biomarkers.

Common basis for orofacial clefting and cortical interneuronopathy

Orofacial clefts (OFCs) of the lip and/or palate are among the most common human birth defects. Current treatment strategies focus on functional and cosmetic repair but even when this care is available, individuals born with OFCs are at high risk for persistent neurobehavioral problems. In addition to learning disabilities and reduced academic achievement, recent evidence associates OFCs with elevated risk for a constellation of psychiatric outcomes including anxiety disorders, autism spectrum disorder, and schizophrenia. The relationship between these outcomes and OFCs is poorly understood and controversial. Recent neuroimaging studies in humans and mice demonstrate subtle morphological brain abnormalities that co-occur with OFCs but specific molecular and cellular mechanisms have not been investigated. Here, we provide the first evidence directly linking OFC pathogenesis to abnormal development of GABAergic cortical interneurons (cINs). Lineage tracing revealed that the structures that form the upper lip and palate develop in molecular synchrony and spatiotemporal proximity to cINs, suggesting these populations may have shared sensitivity to genetic and/or teratogenic insult. Examination of cIN development in a mouse model of nonsyndromic OFCs revealed significant disruptions in cIN proliferation and migration, culminating in misspecification of the somatostatin-expressing subgroup. These findings reveal a unified developmental basis for orofacial clefting and disrupted cIN development, and may explain the significant overlap in neurobehavioral and psychiatric outcomes associated with OFCs and cIN dysfunction. This emerging mechanistic understanding for increased prevalence of adverse neurobehavioral outcomes in OFC patients is the entry-point for developing evidence-based therapies to improve patient outcomes.