Koolen-de Vries Syndrome (KdVS) is a neurodevelopmental disorder (NDD) caused by KANSL1 haploinsufficiency with no treatment options. To investigate neuronal network activity in KdVS, human induced pluripotent stem cell (hiPSC)-derived neurons from KdVS patients and controls were cultured on microelectrode arrays (MEAs). KdVS networks exhibited reduced burst rates and increased variability in burst rhythmicity. To bridge molecular and functional aspects of the syndrome, we applied MEA-seq, integrating electrophysiological recordings with high-throughput transcriptome profiling. This analysis revealed a negative correlation between the NDD-associated gene CLCN4 and network burst rate. Knockdown of CLCN4 in KdVS neurons restored network bursting toward control levels, highlighting how transcriptome profiling can identify mediators linking genetic defects to relevant physiological phenotypes. We also identified significant correlations between mitochondrial gene expression and network activity and consequently confirmed impaired mitochondrial function in KdVS hiPSC-derived neurons. Using the KdVS transcriptomic signature for computational screening against the LINCS drug perturbation database, we predicted compounds capable of reversing dysregulated gene expression. Ten candidates were prioritized for experimental validation, focusing on mitochondrial function. Among these, the antioxidant phloretin improved multiple aspects of the KdVS-related network activity phenotype, reduced reactive oxygen species, and rescued synaptic density across patient lines, revealing its potential as a therapeutic candidate. Together, these findings demonstrate that integrative MEA-seq profiling can connect molecular and electrophysiological alterations in KdVS, providing a robust framework for identifying novel drugs and druggable pathways for KdVS and potentially other neurodevelopmental disorders.

Dysfunctional GABAergic and dopaminergic neurons are thought to exist in the ventral midbrain of patients with schizophrenia, yet transcriptional changes underpinning these abnormalities have not yet been localized to specific neuronal subsets. In the ventral midbrain, control over dopaminergic activity is maintained by both excitatory (glutamate) and inhibitory (GABA) input neurons. To elucidate neuron pathology at the single-cell level, we characterized the transcriptional diversity of distinct NEUN+ populations in the human ventral midbrain and then tested for schizophrenia-associated changes in neuronal subset proportions and gene activity changes within neuronal subsets. Combining single nucleus RNA-sequencing with fluorescence-activated sorting of NEUN+ nuclei, we analysed 31 669 nuclei. Initially, we detected 18 transcriptionally distinct neuronal populations in the human ventral midbrain, including two 'mixed' populations. The presence of neuronal populations in the midbrain was orthogonally validated with immunohistochemical stainings. 'Mixed' populations contained nuclei expressing transcripts for vesicular glutamate transporter 2 (SLC17A6) and glutamate decarboxylase 2 (GAD2), but these transcripts were not typically co-expressed by the same nucleus. Upon more fine-grained subclustering of the two 'mixed' populations, 16 additional subpopulations were identified that were transcriptionally classified as excitatory or inhibitory. In the midbrains of individuals with schizophrenia, we observed potential differences in the proportions of two (sub)populations of excitatory neurons, two subpopulations of inhibitory neurons, one 'mixed' subpopulation, and one subpopulation of TH-expressing neurons. This may suggest that transcriptional changes associated with schizophrenia broadly affect excitatory, inhibitory, and dopamine neurons. We detected 99 genes differentially expressed in schizophrenia compared to controls within neuronal subpopulations identified from the two 'mixed' populations, with most (67) changes within small GABAergic neuronal subpopulations. Overall, single-nucleus transcriptomic analyses profiled a high diversity of GABAergic neurons in the human ventral midbrain, identified putative shifts in the proportion of neuronal subpopulations, and suggested dysfunction of specific GABAergic subpopulations in schizophrenia, providing directions for future research.

Haploinsufficiency of CACNA1A, encoding the pore-forming α1 subunit of P/Q-type voltage-gated calcium channels, is associated with a clinically variable phenotype ranging from cerebellar ataxia to neurodevelopmental syndromes with epilepsy and intellectual disability. To understand the pathological mechanisms of CACNA1A loss-of-function variants, we characterized a human neuronal model for CACNA1A haploinsufficiency by differentiating isogenic induced pluripotent stem cell lines into glutamatergic neurons and investigated the effect of CACNA1A haploinsufficiency on mature neuronal networks through a combination of electrophysiology, gene expression analysis and in silico modelling. We observed an altered network synchronization in CACNA1A+/- networks alongside synaptic deficits, notably marked by an augmented contribution of GluA2 subunit-lacking α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. Intriguingly, these synaptic perturbations coexisted with increased non-synaptically driven activity, as characterized by inhibition of N-methyl-D-aspartate and AMPA receptors on micro-electrode arrays. Single-cell electrophysiology and gene expression analysis corroborated this increased intrinsic excitability through reduced potassium channel function and expression. Moreover, we observed partial mitigation of the CACNA1A+/- network phenotype by 4-aminopyridine, a therapeutic intervention for episodic ataxia type 2. Positive modulation of small conductance calcium-activated potassium channels could reverse the CACNA1A+/- network electrophysiological phenotype. In summary, our study pioneers the characterization of a human induced pluripotent stem cell-derived neuronal model for CACNA1A haploinsufficiency and has unveiled new mechanistic insights. Beyond showcasing synaptic deficits, this neuronal model exhibited increased intrinsic excitability mediated by diminished potassium channel function, underscoring its potential as a therapeutic discovery platform with predictive validity.

The relatively slow pace of cortical development in humans has long been a topic of investigation. Studies seeking to understand the underlying mechanisms have mostly focused on neurogenetic comparisons with extant species. Here we ask if developmental tempo differences may have also existed between us and our extinct relatives for whom genomes are available. To do so, we nominate a sapiens-specific derived allele, virtually fixed in contemporary populations, which resides in an enhancer region active during early cortical development. The single nucleotide variant is predicted to significantly affect CHD2 expression, a chromatin remodeler known to play an important role in neural development and for which haploinsufficiency is associated with epilepsy and autism. We leverage patient induced pluripotent stem lines (iPSC) and engineered iPSCs in which we reintroduced the ancestral allele and generated heterozygous loss-of-function mutations. We reveal that CHD2 deficiency impairs lysosomal acidification and autophagosome flux. In contrast, ancestralized lines, which we find express higher levels of CHD2, exhibit enhanced lysosomal function and consequently accelerated autophagosome flux, consistent with our observations in chimpanzee and bonobo lines. This set of findings demonstrates that CHD2 dosage critically regulates the autolysosomal pathway. Through deep phenotyping of cortical organoid and neuron cultures, we show that the CHD2-modulated autolysosomal pathway impacts the timing of developmental programs, acquisition of neuronal functional properties and circuit maturation. Finally, we validate an estrogen-dependent rewiring of CHD2 regulation in the evolution of our lineage, providing a mechanistic understanding of how a single nucleotide variant in a regulatory region contributed to the modern pace of neuronal development and maturation. Together, our findings establish CHD2 as a regulator in setting neurodevelopmental tempo via the autolysosomal pathway. ### Competing Interest Statement The authors have declared no competing interest.

Astrocytes play a pivotal role in neuronal network development. Despite the well-known role of astrocytes in the pathophysiology of neurologic disorders, the utilization of human induced pluripotent stem cell (hiPSC)-derived astrocytes in neuronal networks remains limited. Here, we present a streamlined one-step protocol for the differentiation of hiPSCs directly into functional astrocytes without the need for ectopic gene expression or neural progenitor cell generation. We found that culturing hiPSCs directly in commercial astrocyte medium, was sufficient to differentiate hiPSCs into functional astrocytes within five weeks. Validation to varying extents across thirty hiPSC-lines demonstrated consistent astrocyte differentiation with minimal batch-to-batch variability. We confirmed astrocyte identity and functionality of the hiPSC-astrocyte monocultures by immunofluorescence, flowcytometry, RNA sequencing, glutamate uptake assays and calcium signaling recordings. Optimization of the protocol enabled co-culture of hiPSC-astrocytes with Ngn2 hiPSC-derived neurons (iNeurons), promoting neuronal differentiation and synapse formation. Lastly, we used single-cell electrophysiology and multi-electrode arrays to confirm robust neuronal network development in 5-week-old hiPSC-astrocyte and iNeuron co-cultures. This protocol offers a rapid and efficient method to establish all-human astrocyte-neuron co-cultures, facilitating the investigation of cell-type-specific contributions to disease pathogenesis. While validated across multiple hiPSC lines, we actively encourage researchers to test and provide feedback on this protocol to enhance its validation for future iterations.### Competing Interest StatementThe authors have declared no competing interest.

The subependymal zone (SEZ), also known as the subventricular zone (SVZ), constitutes a neurogenic niche that persists during postnatal life. In humans, the neurogenic potential of the SEZ declines after the first year of life. However, studies discovering markers of stem and progenitor cells highlight the neurogenic capacity of progenitors in the adult human SEZ, with increased neurogenic activity occurring under pathological conditions. In the present study, the complete cellular niche of the adult human SEZ was characterized by single -nucleus RNA sequencing, and compared between four youth (age 16-22) and four middle-aged adults (age 44-53). We identified 11 cellular clusters including clusters expressing marker genes for neural stem cells (NSCs), neuroblasts, immature neurons, and oligodendrocyte progenitor cells. The relative abundance of NSC and neuroblast clusters did not differ between the two age groups, indicating that the pool of SEZ NSCs does not decline in this age range. The relative abundance of oligodendrocyte progenitors and microglia decreased in middle -age, indicating that the cellular composition of human SEZ is remodeled between youth and adulthood. The expression of genes related to nervous system development was higher across different cell types, including NSCs, in youth as compared with middle -age. These transcriptional changes suggest ongoing central nervous system plasticity in the SEZ in youth, which declined in middle -age.

Dravet syndrome is a severe epileptic encephalopathy, characterized by (febrile) seizures, behavioural problems and developmental delay. Eighty per cent of patients with Dravet syndrome have a mutation in SCN1A, encoding Nav1.1. Milder clinical phenotypes, such as GEFS+ (generalized epilepsy with febrile seizures plus), can also arise from SCN1A mutations. Predicting the clinical phenotypic outcome based on the type of mutation remains challenging, even when the same mutation is inherited within one family. This clinical and genetic heterogeneity adds to the difficulties of predicting disease progression and tailoring the prescription of anti-seizure medication. Understanding the neuropathology of different SCN1A mutations may help to predict the expected clinical phenotypes and inform the selection of best-fit treatments. Initially, the loss of Na+-current in inhibitory neurons was recognized specifically to result in disinhibition and consequently seizure generation. However, the extent to which excitatory neurons contribute to the pathophysiology is currently debated and might depend on the patient clinical phenotype or the specific SCN1A mutation.To examine the genotype-phenotype correlations of SCN1A mutations in relation to excitatory neurons, we investigated a panel of patient-derived excitatory neuronal networks differentiated on multi-electrode arrays. We included patients with different clinical phenotypes, harbouring various SCN1A mutations, along with a family in which the same mutation led to febrile seizures, GEFS+ or Dravet syndrome.We hitherto describe a previously unidentified functional excitatory neuronal network phenotype in the context of epilepsy, which corresponds to seizurogenic network prediction patterns elicited by proconvulsive compounds. We found that excitatory neuronal networks were affected differently, depending on the type of SCN1A mutation, but did not segregate according to clinical severity. Specifically, loss-of-function mutations could be distinguished from missense mutations, and mutations in the pore domain could be distinguished from mutations in the voltage sensing domain. Furthermore, all patients showed aggravated neuronal network responses at febrile temperatures compared with controls. Finally, retrospective drug screening revealed that anti-seizure medication affected GEFS+ patient- but not Dravet patient-derived neuronal networks in a patient-specific and clinically relevant manner.In conclusion, our results indicate a mutation-specific excitatory neuronal network phenotype, which recapitulates the foremost clinically relevant features, providing future opportunities for precision therapies.

Background: The increased inflammatory state observed in schizophrenia post-mortem brain and midbrain tissue [1-5] may have detrimental consequences on the brain vasculature of patients with schizophrenia. On the other hand, intrinsic alterations in the brain vasculature of schizophrenia patients may impair toxin efflux and favour the ingression of toxic material and immune cells into the central nervous system, leading to neuroinflammation. Evidence derived from blood and cerebrospinal fluid measurements indicated increased levels of adhesion molecules, such as sP-selectin and sICAM, in schizophrenia [6-8], which may favour the ingression of immune cells into the brain, and higher levels of albumin in CSF as compared to controls, suggesting increased BBB permeability in schizophrenia patients [6, 7, 9]. However, the proper functioning of the BBB involves a variety of cell types, and it is not known which cell type(s) of the BBB may be particularly affected in schizophrenia. Methods: We combined a fluorescence activated sorting isolation strategy with single-nucleus RNA sequencing (snRNAseq) to characterize the cells of the BBB in the midbrain of 15 schizophrenia donors and 14 matched controls, from the well-characterized Stanley Brain Collection. The cases used for the present study were previously grouped into high and low inflammation cases, based on the expression of inflammatory cytokines in their cortical grey matter, and 4 out of the 15 schizophrenia cases were assigned to the cortical high-inflammation group [10]. The different cell types of the BBB were identified with unbiased cluster analysis of nuclear transcriptomic profiles and annotated based on the expression of cell type-specific marker genes. Subclustering analysis, gene set enrichment and comparisons with previously published datasets were carried out to identify sub-populations among the main BBB cell types. We compared the transcriptomic profiles of the major BBB cell types between schizophrenia and controls. In addition, the relative abundance of the main BBB cell types and sub-populations was compared between the diagnoses, using generalized linear modeling. Results: We did not identify changes in the relative abundance of the major BBB cell types, nor in the sub-populations, associated with schizophrenia. However, we identified 14 differentially expressed genes in the cells of the BBB in schizophrenia as compared to controls, including genes that have previously been related to schizophrenia, such as FOXP2 and PDE4D. These transcriptional changes associated with schizophrenia were limited to the ependymal cells and pericytes. Additionally, we detected a sub-population of protoplasmic astrocytes enriched in the high inflammation schizophrenia subgroup. Genes more abundantly expressed in these schizophrenia-related protoplasmic astrocytes were associated with glutamatergic synaptic function rather than with inflammation. Conclusion: Our overall diagnostic results suggest the relative abundance of the BBB cell types and cellular sub-populations remains unaltered in schizophrenia pathology. Nonetheless, transcriptional changes in the midbrain BBB cells associated with schizophrenia are found, but are limited and are specific to two cell types, the ependymal and pericytes. In addition, the high inflammatory status observed in a subgroup of the patients may be interfering with the normal activities of protoplasmic astrocytes, possibly associated with midbrain dopamine and glutamate neurons.

Summary Mechanisms that underlie homeostatic plasticity have been extensively investigated at single-cell levels in animal models, but are less well understood at the network level. Here, we used microelectrode arrays to characterize neuronal networks following induction of homeostatic plasticity in human induced pluripotent stem cell (hiPSC)-derived glutamatergic neurons co-cultured with rat astrocytes. Chronic suppression of neuronal activity through tetrodotoxin (TTX) elicited a time-dependent network re-arrangement. Increased expression of AMPA receptors and the elongation of axon initial segments were associated with increased network excitability following TTX treatment. Transcriptomic profiling of TTX-treated neurons revealed up-regulated genes related to extracellular matrix organization, while down-regulated genes related to cell communication; also astrocytic gene expression was found altered. Overall, our study shows that hiPSC-derived neuronal networks provide a reliable in vitro platform to measure and characterize homeostatic plasticity at network and single-cell level; this platform can be extended to investigate altered homeostatic plasticity in brain disorders.

Mechanisms that underlie homeostatic plasticity have been extensively investigated at single-cell levels in animal models, but are less well understood at the network level. Here, we used microelectrode arrays to characterize neuronal networks following induction of homeostatic plasticity in human induced pluripotent stem cell (hiPSC)-derived glutamatergic neurons co-cultured with rat astrocytes. Chronic suppression of neuronal activity through tetrodotoxin (TTX) elicited a time-dependent network re-arrangement. Increased expression of AMPA receptors and the elongation of axon initial segments were associated with increased network excitability following TTX treatment. Transcriptomic profiling of TTX-treated neurons revealed up-regulated genes related to extracellular matrix organization, while down-regulated genes related to cell communication; also astrocytic gene expression was found altered. Overall, our study shows that hiPSC-derived neuronal networks provide a reliable in vitro platform to measure and characterize homeostatic plasticity at network and single-cell levels; this platform can be extended to investigate altered homeostatic plasticity in brain disorders.

The midbrain is an extensively studied brain region in schizophrenia, in view of its reported dopamine pathophysiology and neuroimmune changes associated with this disease. Besides the dopaminergic system, the midbrain contains other cell types that may be involved in schizophrenia pathophysiology. The neurovascular hypothesis of schizophrenia postulates that both the neurovasculature structure and the functioning of the blood-brain barrier (BBB) are compromised in schizophrenia. In the present study, potential alteration in the BBB of patients with schizophrenia was investigated by single-nucleus RNA sequencing of post-mortem midbrain tissue (15 schizophrenia cases and 14 matched controls). We did not identify changes in the relative abundance of the major BBB cell types, nor in the sub-populations, associated with schizophrenia. However, we identified 14 differentially expressed genes in the cells of the BBB in schizophrenia as compared to controls, including genes that have previously been related to schizophrenia, such as FOXP2 and PDE4D . These transcriptional changes were limited to the ependymal cells and pericytes, suggesting that the cells of the BBB are not broadly affected in schizophrenia.

Purpose of review The vascular hypothesis of schizophrenia (SZ) postulates that brain endothelial dysfunction contributes to brain pathophysiology. This review discusses recent evidence for and against this hypothesis, including data related to blood–brain barrier (BBB), brain endothelium, and brain blood supply, to provide a critical weighed update. Recent findings Different studies report a consistent proportion of SZ patients showing increased BBB permeability, reflected by higher levels of albumin in the cerebral spinal fluid. Of note, this was not a result of antipsychotic medication. The high inflammatory profile observed in some SZ patients is strongly associated with increased BBB permeability to circulating immune cells, and with more severe cognitive deficiencies. Also, sex was found to interact with BBB integrity and permeability in SZ. The strongest independent genetic association with SZ has been identified in FZD1, a hypoxia-response gene that is 600-fold higher expressed in early development endothelium as compared to adult brain endothelium. Regarding brain blood supply, there is evidence to suggest alterations in proper brain perfusion in SZ. Nonetheless, ex-vivo experiments suggested that widely used antipsychotics favor vasoconstriction; thus, alterations in cerebral perfusion might be related to the patients′ medication. Summary In some patients with SZ, a vulnerable brain endothelium may be interacting with environmental stressors, such as inflammation or hypoxia, converging into a more severe SZ symptomatology. Gene expression and performance of human brain endothelium could vary along with development and the establishment of the BBB; therefore, we encourage to investigate its possible contribution to SZ considering this dynamic context.

Schizophrenia (SZ) is a severe mental disorder that arises from abnormal neurodevelopment, caused by genetic and environmental factors. SZ often involves distortions in reality perception and it is widely associated with alterations in brain connectivity. In the present work, we used Human Induced Pluripotent Stem Cells (hiPSCs)-derived neuronal cultures to study neural communicational dynamics during early development in SZ. We conducted gene and protein expression profiling, calcium imaging recordings, and applied a mathematical model to quantify the dynamism of functional connectivity (FC) in hiPSCs-derived neuronal networks. Along the neurodifferentiation process, SZ networks displayed altered gene expression of the glutamate receptor-related proteins HOMER1 and GRIN1 compared to healthy control (HC) networks, suggesting a possible tendency to develop hyperexcitability. Resting-state FC in neuronal networks derived from HC and SZ patients emerged as a dynamic phenomenon exhibiting connectivity configurations reoccurring in time (hub states). Compared to HC, SZ networks were less thorough in exploring different FC configurations, changed configurations less often, presented a reduced repertoire of hub states and spent longer uninterrupted time intervals in this less diverse universe of hubs. Our results suggest that alterations in the communicational dynamics of SZ emerging neuronal networks might contribute to the previously described brain FC anomalies in SZ patients, by compromising the ability of their neuronal networks for rapid and efficient reorganization through different activity patterns.

Neuroblastoma is a highly metastatic tumor that emerges from neural crest cell progenitors. Focal Adhesion Kinase (FAK) is a regulator of cell migration that binds to the receptor Neogenin-1 and is upregulated in neuroblastoma. Here, we show that Netrin-1 ligand binding to Neogenin-1 leads to FAK autophosphorylation and integrin β1 activation in a FAK dependent manner, thus promoting neuroblastoma cell migration. Moreover, Neogenin-1, which was detected in all tumor stages and was required for neuroblastoma cell migration, was found in a complex with integrin β1, FAK, and Netrin-1. Importantly, Neogenin-1 promoted neuroblastoma metastases in an immunodeficient mouse model. Taken together, these data show that Neogenin-1 is a metastasis-promoting protein that associates with FAK, activates integrin β1 and promotes neuroblastoma cell migration.

Neuroblastoma (NB) is the most common pediatric extracranial solid tumor. It arises during development of the sympathetic nervous system. Netrin-4 (NTN4), a laminin-related protein, has been proposed as a key factor to target NB metastasis, although there is controversy about its function. Here, we show that NTN4 is broadly expressed in tumor, stroma and blood vessels of NB patient samples. Furthermore, NTN4 was shown to act as a cell adhesion molecule required for the migration induced by Neogenin-1 (NEO1) in SK-N-SH neuroblastoma cells. Therefore, we propose that NTN4, by forming a ternary complex with Laminin γ1 (LMγ1) and NEO1, acts as an essential extracellular matrix component, which induces the migration of SK-N-SH cells.