PKD1 Promotes Functional Synapse Formation Coordinated with N-Cadherin in Hippocampus

Getting smart - Deciphering the neuronal functions of protein kinase D

Protein kinase D (PKD) is a family of serine/threonine kinases that play important roles in various signalling pathways in cells, including neuronal cells. In the nervous system, PKD has been shown to be involved in learning and memory formation by regulating neurotransmitter release, neurite outgrowth and dendrite development, synapse formation and synaptic plasticity. In addition, PKD has been implicated in pain perception or neuroprotection during oxidative stress. Dysregulation of PKD expression and activity has been linked to several neurological disorders, including autism and epilepsy. In this review, we summarize the current knowledge on the function of the PKD family members in neuronal cells, including the spatial regulation of their downstream signalling pathways. We will further discuss the potential role of PKD in the pathogenesis of neurological disorders.

Identification of a de novo mutation of the FOXG1 gene and comprehensive analysis for molecular factors in Chinese FOXG1-related encephalopathies

Background

FOXG1-related encephalopathy, also known as FOXG1 syndrome or FOXG1-related disorder, affects most aspects of development and causes microcephaly and brain malformations. This syndrome was previously considered to be the congenital variant of Rett syndrome. The abnormal function or expression of FOXG1, caused by intragenic mutations, microdeletions or microduplications, was considered to be crucial pathological factor for this disorder. Currently, most of the FOXG1-related encephalopathies have been identified in Europeans and North Americans, and relatively few Chinese cases were reported.

Methods

Array-Comparative Genomic Hybridization (Array-CGH) and whole-exome sequencing (WES) were carried out for the proband and her parent to detect pathogenic variants.

Results

A de novo nonsense mutation (c.385G>T, p.Glu129Ter) of FOXG1 was identified in a female child in a cohort of 73 Chinese children with neurodevelopmental disorders/intellectual disorders (NDDs/IDs). In order to have a comprehensive view of FOXG1-related encephalopathy in China, relevant published reports were browsed and twelve cases with mutations in FOXG1 or copy number variants (CNVs) involving FOXG1 gene were involved in the analysis eventually. Feeding difficulties, seizures, delayed speech, corpus callosum hypoplasia and underdevelopment of frontal and temporal lobes occurred in almost all cases. Out of the 12 cases, eight patients (66.67%) had single-nucleotide mutations of FOXG1 gene and four patients (33.33%) had CNVs involving FOXG1 (3 microdeletions and 1 microduplication). The expression of FOXG1 could also be potentially disturbed by deletions of several brain-active regulatory elements located in intergenic FOXG1-PRKD1 region. Further analysis indicated that PRKD1 might be a cooperating factor to regulate the expression of FOXG1, MECP2 and CDKL5 to contribute the RTT/RTT-like disorders.

Discussion

This re-analysis would broaden the existed knowledge about the molecular etiology and be helpful for diagnosis, treatment, and gene therapy of FOXG1-related disorders in the future.

Flying under the radar: CDH2 (N-cadherin), an important hub molecule in neurodevelopmental and neurodegenerative diseases

CDH2 belongs to the classic cadherin family of Ca2+-dependent cell adhesion molecules with a meticulously described dual role in cell adhesion and β-catenin signaling. During CNS development, CDH2 is involved in a wide range of processes including maintenance of neuroepithelial integrity, neural tube closure (neurulation), confinement of radial glia progenitor cells (RGPCs) to the ventricular zone and maintaining their proliferation-differentiation balance, postmitotic neural precursor migration, axon guidance, synaptic development and maintenance. In the past few years, direct and indirect evidence linked CDH2 to various neurological diseases, and in this review, we summarize recent developments regarding CDH2 function and its involvement in pathological alterations of the CNS.

Molecular mechanisms of synaptogenesis

Synapses are the basic units for information processing and storage in the nervous system. It is only when the synaptic connection is established, that it becomes meaningful to discuss the structure and function of a circuit. In humans, our unparalleled cognitive abilities are correlated with an increase in the number of synapses. Additionally, genes involved in synaptogenesis are also frequently associated with neurological or psychiatric disorders, suggesting a relationship between synaptogenesis and brain physiology and pathology. Thus, understanding the molecular mechanisms of synaptogenesis is the key to the mystery of circuit assembly and neural computation. Furthermore, it would provide therapeutic insights for the treatment of neurological and psychiatric disorders. Multiple molecular events must be precisely coordinated to generate a synapse. To understand the molecular mechanisms underlying synaptogenesis, we need to know the molecular components of synapses, how these molecular components are held together, and how the molecular networks are refined in response to neural activity to generate new synapses. Thanks to the intensive investigations in this field, our understanding of the process of synaptogenesis has progressed significantly. Here, we will review the molecular mechanisms of synaptogenesis by going over the studies on the identification of molecular components in synapses and their functions in synaptogenesis, how cell adhesion molecules connect these synaptic molecules together, and how neural activity mobilizes these molecules to generate new synapses. Finally, we will summarize the human-specific regulatory mechanisms in synaptogenesis and results from human genetics studies on synaptogenesis and brain disorders.

Soft substrates promote direct chemical reprogramming of fibroblasts into neurons

Fibroblasts can be directly reprogrammed via a combination of small molecules to generate induced neurons (iNs), bypassing intermediate stages. This method holds great promise for regenerative medicine; however, it remains inefficient. Recently, studies have suggested that physical cues may improve the direct reprogramming of fibroblasts into neurons, but the underlying mechanisms remain to be further explored, and the physical factors reported to date do not exhibit the full properties of the extracellular matrix (ECM). Previous in vitro studies mainly used rigid polystyrene dishes, while one of the characteristics of the native in-vivo environment of neurons is the soft nature of brain ECM. The reported stiffness of brain tissue is very soft ranging between 100 Pa and 3 kPa, and the effect of substrate stiffness on direct neuronal reprogramming has not been explored. Here, we show for the first time that soft substrates substantially improved the production efficiency and quality of iNs, without needing to co-culture with glial cells during reprogramming, producing more glutamatergic neurons with electrophysiological functions in a shorter time. Transcriptome sequencing indicated that soft substrates might promote glutamatergic neuron reprogramming through integrins, actin cytoskeleton, Hippo signalling pathway, and regulation of mesenchymal-to-epithelial transition, and competing endogenous RNA network analysis provided new targets for neuronal reprogramming. We demonstrated that soft substrates may promote neuronal reprogramming by inhibiting microRNA-615-3p-targeting integrin subunit beta 4. Our findings can aid the development of regenerative therapies and help improve our understanding of neuronal reprogramming. STATEMENT OF SIGNIFICANCE: : First, we have shown that low stiffness promotes direct reprogramming on the basis of small molecule combinations. To the best of our knowledge, this is the first report on this type of method, which may greatly promote the progress of neural reprogramming. Second, we found that miR-615-3p may interact with ITGB4, and the soft substrates may promote neural reprogramming by inhibiting microRNA (miR)-615-3p targeting integrin subunit beta 4 (ITGB4). We are the first to report on this mechanism. Our findings will provide more functional neurons for subsequent basic and clinical research in neurological regenerative medicine, and will help to improve the overall understanding of neural reprogramming. This work also provides new ideas for the design of medical biomaterials for nerve regeneration.

A Glance at the Molecules That Regulate Oligodendrocyte Myelination

Oligodendrocyte (OL) myelination is a critical process for the neuronal axon function in the central nervous system. After demyelination occurs because of pathophysiology, remyelination makes repairs similar to myelination. Proliferation and differentiation are the two main stages in OL myelination, and most factors commonly play converse roles in these two stages, except for a few factors and signaling pathways, such as OLIG2 (Oligodendrocyte transcription factor 2). Moreover, some OL maturation gene mutations induce hypomyelination or hypermyelination without an obvious function in proliferation and differentiation. Herein, three types of factors regulating myelination are reviewed in sequence.

A Systematic Screening of ADHD-Susceptible Variants From 25 Chinese Parents-Offspring Trios

Attention-deficit/hyperactivity disorder (ADHD) is one of the most prevalent and heritable childhood behavioral disorders. Although a number of ADHD-susceptible regions had been identified, details about the variations of genes and their related patterns involved in ADHD are still lacking. In this study, we collected 25 Chinese parents-offspring trios, each of which consisted of a child diagnosed with ADHD and his/her unaffected parents, and analyzed the variations from whole-genome sequencing data. SNVs in reported ADHD-susceptible regions and on the genes whose functions were related to dopamine were screened, and we identified a set of variants with functional annotations which were specifically detected in ADHD children, including most SNVs in the gene coding region that might impair protein functions and a few SNVs in promoter or 3' untranslated region (3'-UTR) that might affect the regulation of relative gene expression in a transcriptional or posttranscriptional level. All the information may further contribute to the understanding, prediction, prevention, and treatment of ADHD in clinical.

Single-nucleus RNA sequencing identified cells with ependymal cell-like features enriched in neonatal mice after spinal cord injury

The adult mammalian central nervous system has limited regenerative ability, and spinal cord injury (SCI) often causes lifelong motor disability. While regeneration is limited in adults, injured spinal cord tissue can be regenerated and neural function can be almost completely restored in neonates. However, difference of cellular composition in lesion has not been well characterized. To gain insight into the age-dependent cellular reaction after SCI, we performed single-nucleus RNA sequencing, analyzing 4,076 nuclei from sham and injured spinal cords from adult and neonatal mice. Clustering analysis identified 18 cell populations. We identified previously undescribed cells with ependymal cell-like gene expression profile, the number of which was increased in neonates after SCI. Histological analysis revealed that these cells line the central canal under physiological conditions in both adults and neonates. We confirmed that they were enriched in the lesion only in neonates. We further showed that these cells were positive for the cellular markers of ependymal cells, astrocytes and radial glial cells. This study provides a deeper understanding of neonate-specific cellular responses after SCI, which may determine regenerative capacity.

Phosphorylation-dependent positive feedback on the oxytocin receptor through the kinase PKD1 contributes to long-term social memory

Social memory enables one to recognize and distinguish specific individuals. It is fundamental to social behaviors that can be mediated by the oxytocin receptor (OXTR), such as forming relationships. We investigated the molecular regulation and function of OXTR in animal behavior involving social memory. We found that Ser²⁶¹ in OXTR was phosphorylated by protein kinase D1 (PKD1). Neuronal Ca²⁺ signaling and behavior analyses revealed that rats expressing a mutated form of OXTR that cannot be phosphorylated at this residue (OXTR S261A) in the medial amygdala (MeA) exhibited impaired long-term social memory (LTSM). Blocking the phosphorylation of wild-type OXTR in the MeA using an interfering peptide in rats or through conditional knockout of Pkd1 in mice reduced social memory retention, whereas expression of a phosphomimetic mutant of OXTR rescued it. In HEK293A cells, the PKD1-mediated phosphorylation of OXTR promoted its binding to G_q protein and, in turn, OXTR-mediated phosphorylation of PKD1, indicating a positive feedback loop. In addition, OXTR with a single-nucleotide polymorphism found in humans (rs200362197), which has a mutation in the conserved recognition region in the PKD1 phosphorylation site, showed impaired activation and signaling in vitro and in HEK293A cells similar to that of the S216A mutant. Our findings describe a phosphoregulatory loop for OXTR and its critical role in social behavior that might be further explored in associated disorders.

Detecting local genetic correlations with scan statistics

Genetic correlation analysis has quickly gained popularity in the past few years and provided insights into the genetic etiology of numerous complex diseases. However, existing approaches oversimplify the shared genetic architecture between different phenotypes and cannot effectively identify precise genetic regions contributing to the genetic correlation. In this work, we introduce LOGODetect, a powerful and efficient statistical method to identify small genome segments harboring local genetic correlation signals. LOGODetect automatically identifies genetic regions showing consistent associations with multiple phenotypes through a scan statistic approach. It uses summary association statistics from genome-wide association studies (GWAS) as input and is robust to sample overlap between studies. Applied to seven phenotypically distinct but genetically correlated neuropsychiatric traits, we identify 227 non-overlapping genome regions associated with multiple traits, including multiple hub regions showing concordant effects on five or more traits. Our method addresses critical limitations in existing analytic strategies and may have wide applications in post-GWAS analysis.

Interaction of Tau, IL-6 and mitochondria on synapse and cognition following sevoflurane anesthesia in young mice

Tau phosphorylation is associated with cognitive impairment in young mice. However, the underlying mechanism and targeted interventions remain mostly unknown. We set out to determine the potential interactions of Tau, interleukin 6 (IL-6) and mitochondria following treatment of anesthetic sevoflurane and to assess their influences on synapse number and cognition in young mice. Sevoflurane (3% for 2 ​h) was given to wild-type, Tau knockout, IL-6 knockout, and cyclophilin D (CypD) knockout mice on postnatal (P) day 6, 7 and 8. We measured amounts of phosphorylated Tau, IL-6, reactive oxygen species (ROS), mitochondrial membrane potential (MMP), ATP, postsynaptic density 95 (PSD-95), synaptophysin, N-cadherin, synapse number, and cognitive function in the mice, employing Western blot, electron microscope and Morris water maze among others. Here we showed that sevoflurane increased Tau phosphorylation and caused IL-6 elevation, mitochondrial dysfunction, synaptic loss and cognitive impairment in young wild-type, but not Tau knockout, mice. In young IL-6 knockout mice, sevoflurane increased Tau phosphorylation but did not cause mitochondrial dysfunction, synaptic loss or cognitive impairment. Finally, sevoflurane increased Tau phosphorylation and IL-6 amount, but did not induce synaptic loss and cognitive impairment, in young CypD knockout mice or WT mice pretreated with idebenone, an analog of co-enzyme Q10. In conclusion, sevoflurane increased Tau phosphorylation, which caused IL-6 elevation, leading to mitochondrial dysfunction in young mice. Such interactions caused synaptic loss and cognitive impairment in the mice. Idebenone mitigated sevoflurane-induced cognitive impairment in young mice. These studies would promote more research to study Tau in young mice.

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Research in context.•

Evidence before this studya.

Tau, a microtubule-associated protein that is predominantly expressed inside neurons, is associated with microtubule assembly and function. Tau phosphorylation, aggregation and spread all serve as the pathogenesis of age-dependent neurodegeneration in the old brain, as well as the neuropathogenesis of Alzheimer’s disease. However, the effects of Tau on the cellular changes and the function of the young brain are undetermined. Our previous studies showed that anesthetic sevoflurane induced Tau phosphorylation, IL-6 elevation, mitochondrial dysfunction and synaptic loss in brain tissues of neonatal mice, as well as cognitive impairment in the mice. However, the potential interactions of the Tau phosphorylation, IL-6 elevation and mitochondrial dysfunction and the influences of these interactions on synapse number and cognitive function in neonatal mice remains largely unknown.

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Added value of studyb.

Employing sevoflurane as a clinically relevant tool, and using the approaches including wild-type, Tau, IL-6, and CypD knockout neonatal mice, the present studies showed that Tau phosphorylation caused IL-6 elevation, which induced mitochondrial dysfunction, leading to synaptic loss and cognitive impairment in the neonatal mice. Idebenone, a synthetic analog of coenzyme Q10, mitigated the sevoflurane-induced cognitive impairment in the neonatal mice.

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Implications of all the available evidencec.

These findings demonstrated the role of Tau phosphorylation in cognitive impairment in neonatal mice, revealed the effects of the interactions of Tau phosphorylation, IL-6 elevation and mitochondrial dysfunction on the synapse number and cognitive function in the mice, and identified potential targeted intervention of the cognitive impairment in the neonatal mice.

Scientific Hypothesis-Testing Strengthens Neuroscience Research

Science needs to understand the strength of its findings. This essay considers the evaluation of studies that test scientific (not statistical) hypotheses. A scientific hypothesis is a putative explanation for an observation or phenomenon; it makes (or "entails") testable predictions that must be true if the hypothesis is true and that lead to its rejection if they are false. The question is, "how should we judge the strength of a hypothesis that passes a series of experimental tests?" This question is especially relevant in view of the "reproducibility crisis" that is the cause of great unease. Reproducibility is said to be a dire problem because major neuroscience conclusions supposedly rest entirely on the outcomes of single, p valued statistical tests. To investigate this concern, I propose to (1) ask whether neuroscience typically does base major conclusions on single tests; (2) discuss the advantages of testing multiple predictions to evaluate a hypothesis; and (3) review ways in which multiple outcomes can be combined to assess the overall strength of a project that tests multiple predictions of one hypothesis. I argue that scientific hypothesis testing in general, and combining the results of several experiments in particular, may justify placing greater confidence in multiple-testing procedures than in other ways of conducting science.

High expression of keratin 6C is associated with poor prognosis and accelerates cancer proliferation and migration by modulating epithelial-mesenchymal transition in lung adenocarcinoma

BACKGROUND

Lung adenocarcinoma (LUAD) is a more frequent subtype of lung cancer and most cases are discovered in the late stages. The proliferation and metastasis of LUAD are pivotal for disease progression. Despite unremitting deeper understanding of LUAD biology, the mechanisms involved in the proliferation and metastasis of LUAD remain unclear. The objective of our article was to inquiry the expression and the function of keratin 6C (KRT6C) in LUAD cells.

METHODS

First, the expression level and prognostic value of KRT6C in LUAD tissues were analyzed on the basis of the data acquired from TCGA database. Through qRT-PCR, the expression level of KRT6C on LUAD cell lines (A549, H1299, PC-9) and human normal lung cell line MRC-5 was tested. After that, CCK8 and colony formation assays was utilized to detect cell proliferation. In addition, to explore the influence of KRT6C on LUAD migration and invasion ability, scratch wound healing and transwell assays were utilized. Through western blotting, the protein expression levels of KRT6C, PCNA, E-cadherin, N-cadherin, Snail and Vimentin were detected.

RESULTS

The outcomes revealed that KRT6C was highly expressed in LUAD tissues and cell lines. Besides, elevated level of KRT6C was related to worse prognosis in LUAD patients. Ablation of KRT6C restrained proliferation, migration and invasion of A549 cells. KRT6C deficiency augmented the expression of E-cadherin as well as reduced the expression of N-cadherin, Snail and Vimentin.

CONCLUSION

Above all, these consequences indicated that depletion of KRT6C suppressed A549 cell proliferation, migration and invasion, which might be achieved by regulating EMT. In general, KRT6C is identified as a potential therapeutic target for LUAD.

PLD1 promotes dendritic spine morphogenesis via activating PKD1

Dendritic spines on the dendrites of pyramidal neurons are one of the most important components for excitatory synapses, where excitatory information exchanges and integrates. The defects of dendritic spine development have been closely connected with many nervous system diseases including autism, intellectual disability and so forth. Based on our previous studies, we here report a new functional signaling link between phospholipase D1 (PLD1) and protein kinase D1 (PKD1) in dendritic spine morphogenesis. Coimmunoprecipitation assays showed that PLD1 associates with PKD1. A series of knocking down and rescuing experiments demonstrated that PLD1 acts upstream of PKD1 in positively regulating dendritic spine morphogenesis. Using PLD1 inhibitor, we found that PLD1 activates PKD1 to promote dendritic spine morphogenesis. Thus, we further reveal the roles of the two different enzymes in neuronal development.