Developmental Dopaminergic Signaling Modulates Neural Circuit Formation and Contributes to Autism Spectrum Disorder-Related Phenotypes.

Autism spectrum disorder (ASD) is a prevalent neurodevelopmental disorder with a complex etiology. Recent evidence suggests that dopamine plays a crucial role in neural development. However, whether and how disrupted dopaminergic signaling during development contributes to ASD remains unknown. In this study, human brain RNA sequencing transcriptome analysis revealed a significant correlation between changes in dopaminergic signaling pathways and neural developmental signaling in ASD patients. In the zebrafish model, disrupted developmental dopaminergic signaling led to neural circuit abnormalities and behavior reminiscent of autism. Dopaminergic signaling may impact neuronal specification by potentially modulating integrins. These findings shed light on the mechanisms underlying the link between disrupted developmental dopamine signaling and ASD, and they point to the possibility of targeting dopaminergic signaling in early development for ASD treatment.

Single-cell RNA sequencing reveals dysregulation of spinal cord cell types in a severe spinal muscular atrophy mouse model.

Although spinal muscular atrophy (SMA) is a motor neuron disease caused by the loss of survival of motor neuron (SMN) proteins, there is growing evidence that non-neuronal cells play important roles in SMA pathogenesis. However, transcriptome alterations occurring at the single-cell level in SMA spinal cord remain unknown, preventing us from fully comprehending the role of specific cells. Here, we performed single-cell RNA sequencing of the spinal cord of a severe SMA mouse model, and identified ten cell types as well as their differentially expressed genes. Using CellChat, we found that cellular communication between different cell types in the spinal cord of SMA mice was significantly reduced. A dimensionality reduction analysis revealed 29 cell subtypes and their differentially expressed gene. A subpopulation of vascular fibroblasts showed the most significant change in the SMA spinal cord at the single-cell level. This subpopulation was drastically reduced, possibly causing vascular defects and resulting in widespread protein synthesis and energy metabolism reductions in SMA mice. This study reveals for the first time a single-cell atlas of the spinal cord of mice with severe SMA, and sheds new light on the pathogenesis of SMA.

The role of CELF family in neurodevelopment and neurodevelopmental disorders.

RNA-binding proteins (RBPs) bind to RNAs and are crucial for regulating RNA splicing, stability, translation, and transport. Among these proteins, the CUGBP Elav-like family (CELF) is a highly conserved group crucial for posttranscriptional regulation by binding to CUG repeats. Comprising CELF1-6, this family exhibits diverse expression patterns and functions. Dysregulation of CELF has been implicated in various neural disorders, encompassing both neurodegenerative and neurodevelopmental conditions, such as Alzheimer's disease and autism. This article aims to provide a comprehensive summary of the CELF family's role in neurodevelopment and neurodevelopmental disorders. Understanding CELF's mechanisms may offer clues for potential therapeutic strategies by regulating their targets in neurodevelopmental disorders.

Expression of myelin transcription factor 1 and lamin B receptor mediate neural progenitor fate transition in the zebrafish spinal cord pMN domain.

The pMN domain is a restricted domain in the ventral spinal cord, defined by the expression of the olig2 gene. Though it is known that the pMN progenitor cells can sequentially generate motor neurons and oligodendrocytes, the lineages of these progenitors are controversial and how their progeny are generated is not well understood. Using single-cell RNA sequencing, here, we identified a previously unknown heterogeneity among pMN progenitors with distinct fates and molecular signatures in zebrafish. Notably, we characterized two distinct motor neuron lineages using bioinformatic analysis. We then went on to investigate specific molecular programs that regulate neural progenitor fate transition. We validated experimentally that expression of the transcription factor myt1 (myelin transcription factor 1) and inner nuclear membrane integral proteins lbr (lamin B receptor) were critical for the development of motor neurons and neural progenitor maintenance, respectively. We anticipate that the transcriptome features and molecular programs identified in zebrafish pMN progenitors will not only provide an in-depth understanding of previous findings regarding the lineage analysis of oligodendrocyte progenitor cells and motor neurons but will also help in further understanding of the molecular programming involved in neural progenitor fate transition.

Heterogeneity and Molecular Markers for CNS Glial Cells Revealed by Single-Cell Transcriptomics.

Glial cells, including astrocytes, oligodendrocytes, and microglia, are the major components in the central nervous system (CNS). Studies have revealed the heterogeneity of each glial cell type and that they each may play distinct roles in physiological processes and/or neurological diseases. Single-cell sequencing (scRNA-seq) technology developed in recent years has extended our understanding of glial cell heterogeneity from the perspective of transcriptome profiling. This review summarizes the marker genes of major glial cells in the CNS and reveals their heterogeneity in different species, CNS regions, developmental stages, and pathological states (Alzheimer's disease and spinal cord injury), expanding our knowledge of glial cell heterogeneity on both molecular and functional levels.

Neurotoxicity of nanoparticles: Insight from studies in zebrafish.

Nanoparticles are widely used in industry and personal care, and they inevitably end up in people's bodies and the environment. The widespread use of nanoparticles has raised new concerns about their neurotoxicity, as nanoparticles can enter the nervous system by blood-brain barrier. In neurotoxicity testing, the zebrafish provides powerful tools to overcome the limitations of other models. This paper will provide a comprehensive review of the power of zebrafish in neurotoxicity tests and the neurotoxic effects of nanoparticles, including inorganic, organic, and metal-based nanoparticles, on zebrafish from different perspectives. Such information can be used to predict not only the effects of nanoparticles on other species exposed to the aquatic environment but also the neurotoxicity of nanoparticles in humans.

Epitranscriptomic m6A regulation following spinal cord injury.

RNA methylation is involved in multiple physiological and pathological processes. However, the role of RNA methylation in spinal cord regeneration has not been reported. In this study, we find an altered m6A (N6-methyladenosine) RNA methylation profiling following zebrafish spinal cord injury (SCI), in line with an altered transcription level of the m6A methylase Mettl3. Interestingly, many of the differential m6A-tagged genes associated with neural regeneration are hypomethylated, but their transcription levels are upregulated in SCI. Moreover, we find that METTL3 may be important for spinal cord regeneration. We also show a conserved feature of METTL3 changes in mouse SCI model, in which the expression of METTL3 is increased in both astrocytes and neural stem cells. Together, our results indicate that m6A RNA methylation is dynamic and conserved following SCI and may contribute to spinal cord regeneration.

Astrocytic reprogramming combined with rehabilitation strategy improves recovery from spinal cord injury.

After spinal cord injury (SCI), the irreversible loss of neurons and the dense glial scar are two of the leading causes of axon regeneration failure. The adult mammalian spinal cord lacks the ability to spontaneously produce new neurons, making it a key challenge to provide new neurons for spinal cord regeneration. Additionally, the dual role of the glial scar (both inhibitory and protective) makes it difficult to manipulate it for therapeutic purposes. In this study, using a single transcription factor Sry-related HMG-box 2 (Sox2) delivered by adeno-associated virus (AAV), we reprogrammed some of the astrocytes targeted by the viral vectors in the glial scar into neurons in a severe SCI model. We show that this astrocytic reprogramming alone can propel axon regeneration by not only replenishing the lost neurons, but also moderately reducing the density of the glial scar without interrupting its integrity. Beyond that, astrocytic reprogramming can significantly improve functional recovery when combined with running wheel rehabilitation, which provides use-dependent plasticity. These findings may provide us with a new idea for how to manipulate the glial scar and a promising therapeutic strategy that combines biological intervention with a rehabilitation strategy.

Integrative systems and functional analyses reveal a role of dopaminergic signaling in myelin pathogenesis.

BACKGROUND: Myelin sheaths surrounding axons are critical for electrical signal transmission in the central nervous system (CNS). Diseases with myelin defects such as multiple sclerosis (MS) are devastating neurological conditions for which few effective treatments are available. Dysfunction of the dopaminergic system has been observed in multiple neurological disorders. Its role in myelin pathogenesis, however, is unclear. METHODS: This work used a combination of literature curation, bioinformatics, pharmacological and genetic manipulation, as well as confocal imaging techniques. Literature search was used to establish a complete set of genes which is associated with MS in humans. Bioinformatics analyses include pathway enrichment and crosstalk analyses with human genetic association studies as well as gene set enrichment and causal relationship analyses with transcriptome data. Pharmacological and CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9) genetic manipulation were applied to inhibit the dopaminergic signaling in zebrafish. Imaging techniques were used to visualize myelin formation in vivo. RESULTS: Systematic analysis of human genetic association studies revealed that the dopaminergic synapse signaling pathway is enriched in candidate gene sets. Transcriptome analysis confirmed that expression of multiple dopaminergic gene sets was significantly altered in patients with MS. Pathway crosstalk analysis and gene set causal relationship analysis reveal that the dopaminergic synapse signaling pathway interacts with or is associated with other critical pathways involved in MS. We also found that disruption of the dopaminergic system leads to myelin deficiency in zebrafish. CONCLUSIONS: Dopaminergic signaling may be involved in myelin pathogenesis. This study may offer a novel molecular mechanism of demyelination in the nervous system.

Overexpression of P2X4 receptor in Schwann cells promotes motor and sensory functional recovery and remyelination via BDNF secretion after nerve injury.

Of the seven P2X receptor subtypes, P2X4 receptor (P2X4R) is widely distributed in the central nervous system, including in neurons, astrocytes, and microglia. Accumulating evidence supports roles for P2X4R in the central nervous system, including regulating cell excitability, synaptic transmission, and neuropathic pain. However, little information is available about the distribution and function of P2X4R in the peripheral nervous system. In this study, we find that P2X4R is mainly localized in the lysosomes of Schwann cells in the peripheral nervous system. In cultured Schwann cells, TNF-a not only enhances the synthesis of P2X4R protein but also promotes P2X4R trafficking to the surface of Schwann cells. TNF-a-induced BDNF secretion in Schwann cells is P2X4R dependent. in vivo experiments reveal that expression of P2X4R in Schwann cells of injured nerves is strikingly upregulated following nerve crush injury. Moreover, overexpression of P2X4R in Schwann cells by genetic manipulation promotes motor and sensory functional recovery and accelerates nerve remyelination via BDNF release following nerve injury. Our results suggest that enhancement of P2X4R expression in Schwann cells after nerve injury may be an effective approach to facilitate the regrowth and remyelination of injured nerves.

Transcriptional Profiling at High Temporal Resolution Reveals Robust Immune/Inflammatory Responses during Rat Sciatic Nerve Recovery.

After peripheral nerve injury, immune/inflammatory responses are triggered, which are critical for nerve regeneration. Despite their importance, the underlying molecular changes in immune/inflammatory responses remain largely unknown. In this study, we systematically analyzed differentially expressed genes in immune/inflammatory-related pathways at high temporal resolution and experimentally validated gene expression changes with RT-PCR following sciatic nerve crush in rats. We found that immune/inflammatory reactions not only occur in the acute injury but also remained activated over two weeks after injury. Detailed bioinformatic studies suggested that multiple immune/inflammatory pathways, including agranulocyte adhesion and diapedesis, granulocyte adhesion and diapedesis, IL-6 signaling, and IL-10 signaling, were sustained activated during nerve degeneration and regeneration. Our current study expands our understanding of the molecular basis of altered immune/inflammatory-related pathways following injury and thus might offer the possibility of targeting related molecules as therapeutic intervention for peripheral nerve regeneration.

A Serotonin Circuit Acts as an Environmental Sensor to Mediate Midline Axon Crossing through EphrinB2.

Modulation of connectivity formation in the developing brain in response to external stimuli is poorly understood. Here, we show that the raphe nucleus and its serotonergic projections regulate pathfinding of commissural axons in zebrafish. We found that the raphe neurons extend projections toward midline-crossing axons and that when serotonergic signaling is blocked by pharmacological inhibition or by raphe neuron ablation, commissural pathfinding is disrupted. We demonstrate that the serotonin receptor htr2a is expressed on these commissural axons and that genetic knock-down of htr2a disrupts crossing. We further show that knock-down of htr2a or ablation of the raphe neurons increases ephrinB2a protein levels in commissural axons. An ephrinB2a mutant can rescue midline crossing when serotonergic signaling is blocked. Furthermore, we found that regulation of serotonin expression in the raphe neurons is modulated in response to the developmental environment. Hypoxia causes the raphe to decrease serotonin levels, leading to a reduction in midline crossing. Increasing serotonin in the setting of hypoxia restored midline crossing. Our findings demonstrate an instructive role for serotonin in axon guidance acting through ephrinB2a and reveal a novel mechanism for developmental interpretation of the environmental milieu in the generation of mature neural circuitry. SIGNIFICANCE STATEMENT: We show here that serotonin has a novel role in regulating connectivity in response to the developmental environment. We demonstrate that serotonergic projections from raphe neurons regulate pathfinding of crossing axons. The neurons modulate their serotonin levels, and thus alter crossing, in response to the developmental environment including hypoxia. The findings suggest that modification of the serotonergic system by early exposures may contribute to permanent CNS connectivity alterations. This has important ramifications because of the association between premature birth and accompanying hypoxia, and increased risk of autism and evidence associating in utero exposure to some antidepressants and neurodevelopmental disorders. Finally, this work demonstrates that the vertebrate CNS can modulate its connectivity in response to the external environment.

Role of inflammation in neurological damage and regeneration following spinal cord injury and its therapeutic implications.

Spinal cord injury (SCI) is an incurable trauma that frequently results in partial or complete loss of motor and sensory function. Massive neurons are damaged after the initial mechanical insult. Secondary injuries, which are triggered by immunological and inflammatory responses, also result in neuronal loss and axon retraction. This results in defects in the neural circuit and a deficiency in the processing of information. Although inflammatory responses are necessary for spinal cord recovery, conflicting evidence of their contributions to specific biological processes have made it difficult to define the specific role of inflammation in SCI. This review summarizes our understanding of the complex role of inflammation in neural circuit events following SCI, such as cell death, axon regeneration and neural remodeling. We also review the drugs that regulate immune responses and inflammation in the treatment of SCI and discuss the roles of these drugs in the modulation of neural circuits. Finally, we provide evidence about the critical role of inflammation in facilitating spinal cord neural circuit regeneration in zebrafish, an animal model with robust regenerative capacity, to provide insights into the regeneration of the mammalian central nervous system.

Tail nerve electrical stimulation promoted the efficiency of transplanted spinal cord-like tissue as a neuronal relay to repair the motor function of rats with transected spinal cord injury.

Following transected spinal cord injury (SCI), there is a critical need to restore nerve conduction at the injury site and activate the silent neural circuits caudal to the injury to promote the recovery of voluntary movement. In this study, we generated a rat model of SCI, constructed neural stem cell (NSC)-derived spinal cord-like tissue (SCLT), and evaluated its ability to replace injured spinal cord and repair nerve conduction in the spinal cord as a neuronal relay. The lumbosacral spinal cord was further activated with tail nerve electrical stimulation (TNES) as a synergistic electrical stimulation to better receive the neural information transmitted by the SCLT. Next, we investigated the neuromodulatory mechanism underlying the action of TNES and its synergism with SCLT in SCI repair. TNES promoted the regeneration and remyelination of axons and increased the proportion of glutamatergic neurons in SCLT to transmit brain-derived neural information more efficiently to the caudal spinal cord. TNES also increased the innervation of motor neurons to hindlimb muscle and improved the microenvironment of muscle tissue, resulting in effective prevention of hindlimb muscle atrophy and enhanced muscle mitochondrial energy metabolism. Tracing of the neural circuits of the sciatic nerve and tail nerve identified the mechanisms responsible for the synergistic effects of SCLT transplantation and TNES in activating central pattern generator (CPG) neural circuits and promoting voluntary motor function recovery in rats. The combination of SCLT and TNES is expected to provide a new breakthrough for patients with SCI to restore voluntary movement and control their muscles.

Construction of a niche-specific spinal white matter-like tissue to promote directional axon regeneration and myelination for rat spinal cord injury repair.

Directional axon regeneration and remyelination are crucial for repair of spinal cord injury (SCI), but existing treatments do not effectively promote those processes. Here, we propose a strategy for construction of niche-specific spinal white matter-like tissue (WMLT) using decellularized optic nerve (DON) loaded with neurotrophin-3 (NT-3)-overexpressing oligodendrocyte precursor cells. A rat model with a white matter defect in the dorsal spinal cord of the T10 segment was used. The WMLT transplantation group showed significant improvement in coordinated motor functions compared with the control groups. WMLT transplants integrated well with host spinal cord white matter, effectively addressing several barriers to directional axonal regeneration and myelination during SCI repair. In WMLT, laminin was found to promote development of oligodendroglial lineage (OL) cells by binding to laminin receptors. Interestingly, laminin could also guide linear axon regeneration via interactions with specific integrins on the axon surface. The WMLT developed here utilizes the unique microstructure and bioactive matrix of DON to create a niche rich in laminin, NT-3 and OL cells to achieve significant structural repair of SCI. Our protocol can help to promote research on repair of nerve injury and construction of neural tissues and organoids that form specific cell niches.

Identification of genes associated with sudden cardiac death: a network- and pathway-based approach.

BACKGROUND: Sudden cardiac death (SCD) accounts for a large proportion of the total deaths across different age groups. Although numerous candidate genes related to SCD have been identified by genetic association studies and genome wide association studies (GWAS), the molecular mechanisms underlying SCD are still unclear, and the biological functions and interactions of these genes remain obscure. To clarify this issue, we performed a comprehensive and systematic analysis of SCD-related genes by a network and pathway-based approach. METHODS: By screening the publications deposited in the PubMed and Gene-Cloud Biotechnology Information (GCBI) databases, we collected the genes genetically associated with SCD, which were referred to as the SCD-related gene set (SCDgset). To analyze the biological processes and biochemical pathways of the SCD-related genes, functional analysis was performed. To explore interlinks and interactions of the enriched pathways, pathway crosstalk analysis was implemented. To construct SCD-specific molecular networks, Markov cluster algorithm and Steiner minimal tree algorithm were employed. RESULTS: We collected 257 genes that were reported to be associated with SCD and summarized them in the SCDgset. Most of the biological processes and biochemical pathways were related to heart diseases, while some of the biological functions may be noncardiac causes of SCD. The enriched pathways could be roughly grouped into two modules. One module was related to calcium signaling pathway and the other was related to MAPK pathway. Moreover, two different SCD-specific molecular networks were inferred, and 23 novel genes potentially associated with SCD were also identified. CONCLUSIONS: In summary, by means of a network and pathway-based methodology, we explored the pathogenetic mechanism underlying SCD. Our results provide valuable information in understanding the pathogenesis of SCD and include novel biomarkers for diagnosing potential patients with heart diseases; these may help in reducing the corresponding risks and even aid in preventing SCD.

The neurodevelopmental role of dopaminergic signaling in neurological disorders.

Dopamine (DA), a critical neurotransmitter of both the central and peripheral nerve system, plays important roles in a series of biological processes. Dysfunction of dopaminergic signalling may lead to a series of developmental disorders, including attention deficit/hyperactivity disorder, autism and schizophrenia. However, the exact roles of dopaminergic signalling in these diseases are far from fully understood. We analyse the roles of dopaminergic signalling in multiple physiological and pathological processes, focusing on brain development and related disorders. By summarizing current research in this area, we provide guidance for future studies. This review seeks to deepen our understanding of dopaminergic signalling in developmental disorders, which may offer clues for developing more effective therapeutic drugs.

Connexin Hemichannels in Astrocytes: Role in CNS Disorders.

In the central nervous system (CNS), astrocytes form networks interconnected by gap junctions made from connexins of the subtypes Cx30 and Cx43. When unopposed by an adjoining hemichannel, astrocytic connexins can act as hemichannels to control the release of small molecules such as ATP and glutamate into the extracellular space. Accruing evidence indicates that astrocytic connexins are crucial for the coordination and maintenance of physiologic CNS activity. Here we provide an update on the role of astrocytic connexins in neurodegenerative disorders, glioma, and ischemia. In addition, we address the regulation of Cx43 in chronic pain.

Transcriptome analysis of adherens junction pathway-related genes after peripheral nerve injury.

The neural regeneration process is driven by a wide range of molecules and pathways. Adherens junctions are critical cellular junctions for the integrity of peripheral nerves. However, few studies have systematically characterized the transcript changes in the adherens junction pathway following injury. In this study, a rat model of sciatic nerve crush injury was established by forceps. Deep sequencing data were analyzed using comprehensive transcriptome analysis at 0, 1, 4, 7, and 14 days after injury. Results showed that most individual molecules in the adherens junctions were either upregulated or downregulated after nerve injury. The mRNA expression of ARPC1B, ARPC3, TUBA8, TUBA1C, CTNNA2, ACTN3, MET, HGF, NME1 and ARF6, which are involved in the adherens junction pathway and in remodeling of adherens junctions, was analyzed using quantitative real-time polymerase chain reaction. Most of these genes were upregulated in the sciatic nerve stump following peripheral nerve injury, except for CTNNA2, which was downregulated. Our findings reveal the dynamic changes of key molecules in adherens junctions and in remodeling of adherens junctions. These key genes provide a reference for the selection of clinical therapeutic targets for peripheral nerve injury.