Altered neuronal physiology, development, and function associated with a common chromosome 15 duplication involving CHRNA7

Ion channels in neurodevelopment: lessons from the Integrin-KCNB1 channel complex

Ion channels modulate cellular excitability by regulating ionic fluxes across biological membranes. Pathogenic mutations in ion channel genes give rise to epileptic disorders that are among the most frequent neurological diseases affecting millions of individuals worldwide. Epilepsies are triggered by an imbalance between excitatory and inhibitory conductances. However, pathogenic mutations in the same allele can give rise to loss-of-function and/or gain-of-function variants, all able to trigger epilepsy. Furthermore, certain alleles are associated with brain malformations even in the absence of a clear electrical phenotype. This body of evidence argues that the underlying epileptogenic mechanisms of ion channels are more diverse than originally thought. Studies focusing on ion channels in prenatal cortical development have shed light on this apparent paradox. The picture that emerges is that ion channels play crucial roles in landmark neurodevelopmental processes, including neuronal migration, neurite outgrowth, and synapse formation. Thus, pathogenic channel mutants can not only cause epileptic disorders by altering excitability, but further, by inducing morphological and synaptic abnormalities that are initiated during neocortex formation and may persist into the adult brain.

Human pluripotent stem cell (hPSC) and organoid models of autism: opportunities and limitations

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder caused by genetic or environmental perturbations during early development. Diagnoses are dependent on the identification of behavioral abnormalities that likely emerge well after the disorder is established, leaving critical developmental windows uncharacterized. This is further complicated by the incredible clinical and genetic heterogeneity of the disorder that is not captured in most mammalian models. In recent years, advancements in stem cell technology have created the opportunity to model ASD in a human context through the use of pluripotent stem cells (hPSCs), which can be used to generate 2D cellular models as well as 3D unguided- and region-specific neural organoids. These models produce profoundly intricate systems, capable of modeling the developing brain spatiotemporally to reproduce key developmental milestones throughout early development. When complemented with multi-omics, genome editing, and electrophysiology analysis, they can be used as a powerful tool to profile the neurobiological mechanisms underlying this complex disorder. In this review, we will explore the recent advancements in hPSC-based modeling, discuss present and future applications of the model to ASD research, and finally consider the limitations and future directions within the field to make this system more robust and broadly applicable.

Negative and positive allosteric modulators of the α7 nicotinic acetylcholine receptor regulates the ability of adolescent binge alcohol exposure to enhance adult alcohol consumption

Rationale and Objectives: Ethanol acts directly on the α7 Nicotinic acetylcholine receptor (α7). Adolescent-binge alcohol exposure (ABAE) produces deleterious consequences during adulthood, and data indicate that the α7 receptor regulates these damaging events. Administration of an α7 Negative Allosteric Modulator (NAM) or the cholinesterase inhibitor galantamine can prophylactically prevent adult consequences of ABAE. The goals of the experiments were to determine the effects of co-administration of ethanol and a α7 agonist in the mesolimbic dopamine system and to determine if administration of an α7 NAM or positive allosteric modulator (PAM) modulates the enhancement of adult alcohol drinking produced by ABAE. Methods: In adult rats, ethanol and the α7 agonist AR-R17779 (AR) were microinjected into the posterior ventral tegmental area (VTA), and dopamine levels were measured in the nucleus accumbens shell (AcbSh). In adolescence, rats were treated with the α7 NAM SB-277011-A (SB) or PNU-120596 (PAM) 2 h before administration of EtOH (ABAE). Ethanol consumption (acquisition, maintenance, and relapse) during adulthood was characterized. Results: Ethanol and AR co-administered into the posterior VTA stimulated dopamine release in the AcbSh in a synergistic manner. The increase in alcohol consumption during the acquisition and relapse drinking during adulthood following ABAE was prevented by administration of SB, or enhanced by administration of PNU, prior to EtOH exposure during adolescence. Discussion: Ethanol acts on the α7 receptor, and the α7 receptor regulates the critical effects of ethanol in the brain. The data replicate the findings that cholinergic agents (α7 NAMs) can act prophylactically to reduce the alterations in adult alcohol consumption following ABAE.

Duplication Versus Deletion Through the Lens of 15q13.3: Clinical and Research Implications of Studying Copy Number Variants Associated with Neuropsychiatric Disorders in Induced Pluripotent Stem Cell-Derived Neurons

Copy number variants (CNVs), involving duplication or deletion of susceptible intervals of the human genome, underlie a range of neurodevelopmental and neuropsychiatric disorders. As accessible in vivo animal models of these disorders often cannot be generated, induced pluripotent stem cell (iPSC) models derived from patients carrying these CNVs can reveal alterations of brain development and neuronal function that contribute to these disorders. CNVs involving deletion versus duplication of a particular genomic interval often result both in distinct clinical phenotypes and in differential phenotypic penetrance. This review initially focuses on CNVs at 15q13.3, which contribute to autism spectrum disorder, attention deficit/hyperactivity disorder, and schizophrenia. Like most CNVs, deletions at 15q13.3 usually cause severe clinical phenotypes, while duplications instead result in highly variable penetrance, with some carriers exhibiting no clinical phenotype. Here, we describe cellular and molecular phenotypes seen in iPSC-derived neuronal models of 15q13.3 duplication and deletion, which may contribute both to the differential clinical consequences and phenotypic penetrance. We then relate this work to many other CNVs involving both duplication and deletion, summarizing findings from iPSC studies and their relationship to clinical phenotype. Together, this work highlights how CNVs involving duplication versus deletion can differentially alter neural development and function to contribute to neuropsychiatric disorders. iPSC-derived neuronal models of these disorders can be used both to understand the underlying neurodevelopmental alterations and to develop pharmacological or molecular approaches for phenotypic rescue that may suggest leads for patient intervention. Top: Deletion versus duplication of the same genomic interval results in different clinical phenotypes and degrees of phenotypic penetrance. Example findings schematized. Bottom: iPSC-derived neurons from individuals with these CNVs involving deletion versus duplication likewise often differential phenotypes (increases or decreases) in the categories shown. Figure created with BioRender.com.

The holistic approach to the CHRNA7 gene, hsa-miR-3158-5p, and 15q13.3 hotspot CNVs in migraineurs

Migraine is a neurological disease characterized by severe headache attacks. Combinations of different genetic variations such as copy number variation (CNV) in a gene and microRNA (miRNA) expression can provide a holistic approach to the disease as a pathophysiological, diagnostic, and therapeutic target. CNVs, the Cholinergic Receptor Nicotinic Alpha 7 Subunit (CHRNA7) gene, and expression of gene-targeting miRNAs (hsa-miR-548e-5p and hsa-miR-3158-5p) in migraineurs (n = 102; with aura, n = 43; without aura, n = 59) and non-migraines (n = 120) aged 15-60 years, comparative, case-control study was conducted. Genetic markers were compared with biochemical parameters (BMI, WBC, Urea, GFR, ESR, CRP, HBG). All analyzes were performed by quantitative Real-Time PCR (q-PCR) and fold change was calculated with the 2^-ΔΔCT method. The diagnostic power of the CHRNA7 gene, CNV, and miRNAs were analyzed with the receiver operating curve (ROC). CHRNA7 gene and hsa-miR-3158-5p are down-regulated in migraineurs and the gene is controlled by this miRNA via CNVs (p < .05). Both deletion and duplication were detected in patients with migraine for CVN numbers (p = .05). The number of CNV deletions was higher than duplications. When CHRNA7-CNV-hsa-miR-3158-5p was modeled together in the ROC analysis, the area under the curve (AUC) was 0.805, and the diagnostic power was "good". In migraineurs, the CHRNA7 gene can be controlled by hsa-miR-3158-5p via CNVs to modulate the mechanism of pain. These three genetic markers have diagnostic potential and may be used in antimigraine treatments.

Deepening the understanding of CNVs on chromosome 15q11-13 by using hiPSCs: An overview

The human α7 neuronal nicotinic acetylcholine receptor gene (CHRNA7) is widely expressed in the central and peripheral nervous systems. This receptor is implicated in both brain development and adult neurogenesis thanks to its ability to mediate acetylcholine stimulus (Ach). Copy number variations (CNVs) of CHRNA7 gene have been identified in humans and are genetically linked to cognitive impairments associated with multiple disorders, including schizophrenia, bipolar disorder, epilepsy, Alzheimer's disease, and others. Currently, α7 receptor analysis has been commonly performed in animal models due to the impossibility of direct investigation of the living human brain. But the use of model systems has shown that there are very large differences between humans and mice when researchers must study the CNVs and, in particular, the CNV of chromosome 15q13.3 where the CHRNA7 gene is present. In fact, human beings present genomic alterations as well as the presence of genes of recent origin that are not present in other model systems as well as they show a very heterogeneous symptomatology that is associated with both their genetic background and the environment where they live. To date, the induced pluripotent stem cells, obtained from patients carrying CNV in CHRNA7 gene, are a good in vitro model for studying the association of the α7 receptor to human diseases. In this review, we will outline the current state of hiPSCs technology applications in neurological diseases caused by CNVs in CHRNA7 gene. Furthermore, we will discuss some weaknesses that emerge from the overall analysis of the published articles.

Signalling pathways in autism spectrum disorder: mechanisms and therapeutic implications

Autism spectrum disorder (ASD) is a prevalent and complex neurodevelopmental disorder which has strong genetic basis. Despite the rapidly rising incidence of autism, little is known about its aetiology, risk factors, and disease progression. There are currently neither validated biomarkers for diagnostic screening nor specific medication for autism. Over the last two decades, there have been remarkable advances in genetics, with hundreds of genes identified and validated as being associated with a high risk for autism. The convergence of neuroscience methods is becoming more widely recognized for its significance in elucidating the pathological mechanisms of autism. Efforts have been devoted to exploring the behavioural functions, key pathological mechanisms and potential treatments of autism. Here, as we highlight in this review, emerging evidence shows that signal transduction molecular events are involved in pathological processes such as transcription, translation, synaptic transmission, epigenetics and immunoinflammatory responses. This involvement has important implications for the discovery of precise molecular targets for autism. Moreover, we review recent insights into the mechanisms and clinical implications of signal transduction in autism from molecular, cellular, neural circuit, and neurobehavioural aspects. Finally, the challenges and future perspectives are discussed with regard to novel strategies predicated on the biological features of autism.