Profiling parvalbumin interneurons using iPSC: challenges and perspectives for Autism Spectrum Disorder (ASD)

Neuroanatomical changes of ionotropic glutamatergic and GABAergic receptor densities in male mice modeling idiopathic and syndromic autism spectrum disorder

Autism spectrum disorder (ASD) comprises a wide range of neurodevelopment conditions primarily characterized by impaired social interaction and repetitive behavior, accompanied by a variable degree of neuropsychiatric characteristics. Synaptic dysfunction is undertaken as one of the key underlying mechanisms in understanding the pathophysiology of ASD. The excitatory/inhibitory (E/I) hypothesis is one of the most widely held theories for its pathogenesis. Shifts in E/I balance have been proven in several ASD models. In this study, we investigated three mouse lines recapitulating both idiopathic (the BTBR strain) and genetic (Fmr1 and Shank3 mutants) forms of ASD at late infancy and early adulthood. Using receptor autoradiography for ionotropic excitatory (AMPA and NMDA) and inhibitory (GABAA) receptors, we mapped the receptor binding densities in brain regions known to be associated with ASD such as prefrontal cortex, dorsal and ventral striatum, dorsal hippocampus, and cerebellum. The individual mouse lines investigated show specific alterations in excitatory ionotropic receptor density, which might be accounted as specific hallmark of each individual line. Across all the models investigated, we found an increased binding density to GABAA receptors at adulthood in the dorsal hippocampus. Interestingly, reduction in the GABAA receptor binding density was observed in the cerebellum. Altogether, our findings suggest that E/I disbalance individually affects several brain regions in ASD mouse models and that alterations in GABAergic transmission might be accounted as unifying factor.

Association between resting-state functional brain connectivity and gene expression is altered in autism spectrum disorder

Gene expression covaries with brain activity as measured by resting state functional magnetic resonance imaging (MRI). However, it is unclear how genomic differences driven by disease state can affect this relationship. Here, we integrate from the ABIDE I and II imaging cohorts with datasets of gene expression in brains of neurotypical individuals and individuals with autism spectrum disorder (ASD) with regionally matched brain activity measurements from fMRI datasets. We identify genes linked with brain activity whose association is disrupted in ASD. We identified a subset of genes that showed a differential developmental trajectory in individuals with ASD compared with controls. These genes are enriched in voltage-gated ion channels and inhibitory neurons, pointing to excitation-inhibition imbalance in ASD. We further assessed differences at the regional level showing that the primary visual cortex is the most affected region in ASD. Our results link disrupted brain expression patterns of individuals with ASD to brain activity and show developmental, cell type, and regional enrichment of activity linked genes.

Gene expression patterns have been associated with functional activity patterns in the brain. Here the authors determine how gene expression patterns in the human brain supports brain phenotypes obtained from resting state fMRI imaging, identifying brain regions and genes relevant to autism.

Cadherin-13 is a critical regulator of GABAergic modulation in human stem-cell-derived neuronal networks

Activity in the healthy brain relies on a concerted interplay of excitation (E) and inhibition (I) via balanced synaptic communication between glutamatergic and GABAergic neurons. A growing number of studies imply that disruption of this E/I balance is a commonality in many brain disorders; however, obtaining mechanistic insight into these disruptions, with translational value for the patient, has typically been hampered by methodological limitations. Cadherin-13 (CDH13) has been associated with autism and attention-deficit/hyperactivity disorder. CDH13 localizes at inhibitory presynapses, specifically of parvalbumin (PV) and somatostatin (SST) expressing GABAergic neurons. However, the mechanism by which CDH13 regulates the function of inhibitory synapses in human neurons remains unknown. Starting from human-induced pluripotent stem cells, we established a robust method to generate a homogenous population of SST and MEF2C (PV-precursor marker protein) expressing GABAergic neurons (iGABA) in vitro, and co-cultured these with glutamatergic neurons at defined E/I ratios on micro-electrode arrays. We identified functional network parameters that are most reliably affected by GABAergic modulation as such, and through alterations of E/I balance by reduced expression of CDH13 in iGABAs. We found that CDH13 deficiency in iGABAs decreased E/I balance by means of increased inhibition. Moreover, CDH13 interacts with Integrin-β1 and Integrin-β3, which play opposite roles in the regulation of inhibitory synaptic strength via this interaction. Taken together, this model allows for standardized investigation of the E/I balance in a human neuronal background and can be deployed to dissect the cell-type-specific contribution of disease genes to the E/I balance.

Effects of perinatal dioxin exposure on mirror neuron activity in 9-year-old children living in a hot spot of dioxin contamination in Vietnam

BACKGROUND

For 8 years, we have followed up a birth cohort comprising 241 mother-and-infant pairs living around the Da Nang airbase, a hot spot of dioxin contamination in Vietnam, and have reported the impacts of perinatal dioxin exposure on the neurodevelopment of children at various ages. In the present study, 9 years after birth, we investigated the effects of perinatal dioxin exposure on mu and theta rhythms by analyzing EEG power during the execution and observation of hand movements, which indicate mirror neuron system activity.

METHODS

One hundred fifty-five 9-year-old children (86 boys and 69 girls) from the Da Nang birth cohort participated in the EEG examination with free viewing of hand movements. The dioxin levels in their mothers' breast milk, measured 1 month after birth, were used as perinatal dioxin exposure markers. A log transform of the ratio of EEG power during execution or observation of the hand movements relative to the power during observation of a bouncing ball for theta and mu rhythms was used to evaluate mirror neuron activity.

RESULTS

In both brain hemispheres, the log power ratio in the theta band was significantly higher (i.e., less reduction of power) during observation of hand movements in girls exposed to high levels of TCDD. In boys, however, dioxin congeners other than TCDD, including HxCDDs and several PCDF congeners, contributed to increased log power ratios in the theta band. Particularly for PCDF congeners, the log power ratios in the lowest group among 4 exposure groups were lowest and significantly increased (i.e., decreasing reduction of power) with increasing dose.

CONCLUSION

Perinatal TCDD exposure may influence the mirror neuron system of the brain, which plays an important role for social-emotional behavior in children, particularly in girls living in a hot spot of dioxin contamination in Vietnam.

The Role of Parvalbumin Interneurons in Neurotransmitter Balance and Neurological Disease

While great progress has been made in the understanding of neurological illnesses, the pathologies, and etiologies that give rise to these diseases still remain an enigma, thus, also making treatments for them more challenging. For effective and individualized treatment, it is beneficial to identify the underlying mechanisms that govern the associated cognitive and behavioral processes that go awry in neurological disorders. Parvalbumin fast-spiking interneurons (Pv-FSI) are GABAergic cells that are only a small fraction of the brain's neuronal network, but manifest unique cellular and molecular properties that drastically influence the downstream effects on signaling and ultimately change cognitive behaviors. Proper brain functioning relies heavily on neuronal communication which Pv-FSI regulates, excitatory-inhibitory balances and GABAergic disinhibition between circuitries. This review highlights the depth of Pv-FSI involvement in the cortex, hippocampus, and striatum, as it pertains to expression, neurotransmission, role in neurological disorders, and dysfunction, as well as cognitive behavior and reward-seeking. Recent research has indicated that Pv-FSI play pivotal roles in the molecular pathophysiology and cognitive-behavioral deficits that are core features of many psychiatric disorders, such as schizophrenia, autism spectrum disorders, Alzheimer's disease, and drug addiction. This suggests that Pv-FSI could be viable targets for treatment of these disorders and thus calls for further examination of the undeniable impact Pv-FSI have on the brain and cognitive behavior.

Comprehensive Analysis of RNA-Seq Gene Expression Profiling of Brain Transcriptomes Reveals Novel Genes, Regulators, and Pathways in Autism Spectrum Disorder

BACKGROUND

Autism spectrum disorder (ASD) is a neurodevelopmental disorder with deficits in social communication ability and repetitive behavior. The pathophysiological events involved in the brain of this complex disease are still unclear.

METHODS

In this study, we aimed to profile the gene expression signatures of brain cortex of ASD patients, by using two publicly available RNA-seq studies, in order to discover new ASD-related genes.

RESULTS

We detected 1567 differentially expressed genes (DEGs) by meta-analysis, where 1194 were upregulated and 373 were downregulated genes. Several ASD-related genes previously reported were also identified. Our meta-analysis identified 235 new DEGs that were not detected using the individual RNA-seq studies used. Some of those genes, including seven DEGs (PAK1, DNAH17, DOCK8, DAPP1, PCDHAC2, and ERBIN, SLC7A7), have been confirmed in previous reports to be associated with ASD. Gene Ontology (GO) and pathways analysis showed several molecular pathways enriched by the DEGs, namely, osteoclast differentiation, TNF signaling pathway, complement and coagulation cascade. Topological analysis of protein-protein interaction of the ASD brain cortex revealed proteomics hub gene signatures: MYC, TP53, HDAC1, CDK2, BAG3, CDKN1A, GABARAPL1, EZH2, VIM, and TRAF1. We also identified the transcriptional factors (TFs) regulating DEGs, namely, FOXC1, GATA2, YY1, FOXL1, USF2, NFIC, NFKB1, E2F1, TFAP2A, HINFP.

CONCLUSION

Novel core genes and molecular signatures involved with ASD were identified by our meta-analysis.

Generation of cerebral cortical GABAergic interneurons from pluripotent stem cells

The cerebral cortex functions by the complex interactions of intrinsic and extrinsic neuronal activities, glial actions, and the effects of humoral factors. The intrinsic neuronal influences are mediated by two major subclasses: excitatory glutamatergic neurons that generally have axonal projections extending beyond the neuron's locality and inhibitory GABAergic neurons that generally project locally. These interneurons can be grouped based on morphological, neurochemical, electrophysiological, axonal targeting, and circuit influence characteristics. Cortical interneurons (CIns) can also be grouped based on their origins within the subcortical telencephalon. Interneuron subtypes, of which a dozen or more are thought to exist, are characterized by combinations of these subgrouping features. Due to their well-documented relevance to the causes of and treatments for neuropsychiatric disorders, and to their remarkable capacity to migrate extensively following transplantation, there has been tremendous interest in generating cortical GABAergic interneurons from human pluripotent stem cells. In this concise review, we discuss recent progress in understanding how interneuron subtypes are generated in vivo, and how that progress is being applied to the generation of rodent and human CIns in vitro. In addition, we will discuss approaches for the rigorous designation of interneuron subgroups or subtypes in transplantation studies, and challenges to this field, including the protracted maturation of human interneurons.

In vitro models for ASD-patient-derived iPSCs and cerebral organoids

Autism spectrum disorder (ASD) is a set of pervasive neurodevelopmental disorders. The causation is multigenic in most cases, which makes it difficult to model the condition in vitro. Advances in pluripotent stem cell technology has made it possible to generate in vitro models of human brain development. Induced pluripotent stem cells (iPSCs) can be generated from somatic cells and have the ability to differentiate to all of the body's cells. This chapter aims to give an overview of the iPSC technology for generating neural cells and cerebral organoids as models for neurodevelopment and how these models are utilized in the study of ASD. The combination of iPSC technology and the genetic modification tool CRISPR/Cas9 is described, and current limitations and future perspectives of iPSC technology is discussed.