GSK-3 signaling in developing cortical neurons is essential for radial migration and dendritic orientation

Lead exposure induces neurodysfunction through caspase-1-mediated neuronal pyroptosis

Chronic lead (Pb) exposure causes neurodysfunction and contributes to the development of neurodegenerative disease. However, the mechanism of Pb-induced neurological dysfunction have yet to be fully elucidated. This study determined the role pyroptosis plays in Pb-induced neurodysfunction in neurons. We used both in vitro and in vivo approaches to explore whether Pb exposure induces caspase-1-mediated pyroptosis in neurons and its relationship to Pb-induced neurological disorders. Our findings showed that caspase-1-mediated pyroptosis in Pb-exposed neurons activated glycogen synthase kinase 3 protease activity by disrupting Ca2+/calmodulin-dependent protein kinase II/cAMP-response element binding protein pathway, leading to neurological disorders. Moreover, the caspase-1 inhibition VX-765 or the non-steroidal anti-inflammatory drug sodium para-aminosalicylic acid (PAS-Na) attenuated the Pb-induced neurological disorders by alleviating caspase-1 mediated neuronal pyroptosis. Our novel studies suggest that caspase-1-mediated pyroptosis in neurons represents a potential mechanism for Pb-induced neurodysfunction, identifying a putative target for attenuating the neurodegenerative effects induced by this metal.

GSK3: A potential target and pending issues for treatment of Alzheimer's disease

Glycogen synthase kinase-3 (GSK3), consisting of GSK3α and GSK3β subtypes, is a complex protein kinase that regulates numerous substrates. Research has observed increased GSK3 expression in the brains of Alzheimer's disease (AD) patients and models. AD is a neurodegenerative disorder with diverse pathogenesis and notable cognitive impairments, characterized by Aβ aggregation and excessive tau phosphorylation. This article provides an overview of GSK3's structure and regulation, extensively analyzing its relationship with AD factors. GSK3 overactivation disrupts neural growth, development, and function. It directly promotes tau phosphorylation, regulates amyloid precursor protein (APP) cleavage, leading to Aβ formation, and directly or indirectly triggers neuroinflammation and oxidative damage. We also summarize preclinical research highlighting the inhibition of GSK3 activity as a primary therapeutic approach for AD. Finally, pending issues like the lack of highly specific and affinity-driven GSK3 inhibitors, are raised and expected to be addressed in future research. In conclusion, GSK3 represents a target in AD treatment, filled with hope, challenges, opportunities, and obstacles.

Hirschsprung's disease: m6A methylase VIRMA suppresses cell migration and proliferation by regulating GSK3β

BACKGROUND

N6-methyladenosine (m6A) is the most abundant mRNA modification in mammals, participating in various biological processes. VIRMA is a key methyltransferase involved in m6A modification. However, the role of VIRMA in Hirschsprung's disease (HSCR) remains unclear. This study aims to investigate the function of VIRMA in HSCR and identify its corresponding regulatory mechanisms.

METHODS

The expression of VIRMA and GSK3β in colon tissues of HSCR was examined using RT-qPCR, Western blot, and Immunohistochemistry. Immunofluorescence detected localization of VIRMA and GSK3β. Cell proliferation was measured by CCK8 and EdU assays, and cell migration was evaluated via cell migration and wound healing assays. The stability of GSK3β mRNA was assessed using the actinomycin D assay and the overall level of m6A in cells was assessed by colorimetric assay.

RESULTS

VIRMA was significantly downregulated in narrow-segment colon tissue. Silencing of VIRMA inhibited cell proliferation and migration. VIRMA can inhibit the degradation of GSK3β mRNA and increase the expression of GSK3β. GSK3β was significantly upregulated in narrow-segment colon tissues. Accordingly, our findings showed that GSK3β mediated the VIRMA-driven cell migration and proliferation.

CONCLUSION

VIRMA can inhibit cell migration and proliferation by upregulating the expression of GSK3β, contributing to the onset of HSCR.

IMPACT

The expressions of VIRMA were significantly reduced in HSCR, while GSK3β expression was increased in HSCR, and can be used as a molecular marker. VIRMA overexpression promoted the proliferation and migration of SH-SY5Y and HEK-293T cells. VIRMA can inhibit the degradation of GSK3β mRNA and increase the expression of GSK3β.

Microtubule-binding protein MAP1B regulates interstitial axon branching of cortical neurons via the tubulin tyrosination cycle

Regulation of directed axon guidance and branching during development is essential for the generation of neuronal networks. However, the molecular mechanisms that underlie interstitial (or collateral) axon branching in the mammalian brain remain unresolved. Here, we investigate interstitial axon branching in vivo using an approach for precise labeling of layer 2/3 callosal projection neurons (CPNs). This method allows for quantitative analysis of axonal morphology at high acuity and also manipulation of gene expression in well-defined temporal windows. We find that the GSK3β serine/threonine kinase promotes interstitial axon branching in layer 2/3 CPNs by releasing MAP1B-mediated inhibition of axon branching. Further, we find that the tubulin tyrosination cycle is a key downstream component of GSK3β/MAP1B signaling. These data suggest a cell-autonomous molecular regulation of cortical neuron axon morphology, in which GSK3β can release a MAP1B-mediated brake on interstitial axon branching upstream of the posttranslational tubulin code.

Bright daylight produces negative effects on affective and cognitive outcomes in nocturnal rats

The daily light/dark cycle affects animals' learning, memory, and cognition. Exposure to insufficient daylight illumination negatively impacts emotion and cognition, leading to seasonal affective disorder characterized by depression, anxiety, low motivation, and cognitive impairment in diurnal animals. However, how this affects memory, learning, and cognition in nocturnal rodents is largely unknown. Here, we studied the effect of daytime light illuminance on memory, learning, cognition, and expression of mRNA levels in the hippocampus, thalamus, and cortex, the higher-order learning centers. Two experiments were performed. In experiment one, rats were exposed to 12 L:12D (12 h light and 12 h dark) with a 10, 100, or 1000 lx daytime light illuminance. After 30 days, various behavioral tests (novel object recognition test, hole board test, elevated plus maze test, radial arm maze, and passive avoidance test) were performed. In experiment 2, rats since birth were raised either under constant bright light (250 lx; LL) or a daily light-dark cycle (12 L:12D). After four months, behavioral tests (novel object recognition test, hole board test, elevated plus maze test, radial arm maze, passive avoidance test, Morris water maze, and Y-maze tests) were performed. At the end of experiments, rats were sampled, and mRNA expression of Brain-Derived Neurotrophic Factor (Bdnf), Tyrosine kinase (Trk), microRNA132 (miR132), Neurogranin (Ng), Growth Associated Protein 43 (Gap-43), cAMP Response Element-Binding Protein (Crebp), Glycogen synthase kinase-3β (Gsk3β), and Tumour necrosis factor-α (Tnf-α) were measured in the hippocampus, cortex, and thalamus of individual rats. Our results show that exposure to bright daylight (100 and 1000 lx; experiment 1) or constant light (experiment 2) compromises memory, learning, and cognition. Suppressed expression levels of these mRNA were also observed in the hypothalamus, cortex, and thalamus. These results suggest that light affects differently to different groups of animals.

New insights into the role of GSK-3β in the brain: from neurodegenerative disease to tumorigenesis

Glycogen synthase kinase 3 (GSK-3) is a serine/threonine kinase widely expressed in various tissues and organs. Unlike other kinases, GSK-3 is active under resting conditions and is inactivated upon stimulation. In mammals, GSK-3 includes GSK-3 α and GSK-3β isoforms encoded by two homologous genes, namely, GSK3A and GSK3B. GSK-3β is essential for the control of glucose metabolism, signal transduction, and tissue homeostasis. As more than 100 known proteins have been identified as GSK-3β substrates, it is sometimes referred to as a moonlighting kinase. Previous studies have elucidated the regulation modes of GSK-3β. GSK-3β is involved in almost all aspects of brain functions, such as neuronal morphology, synapse formation, neuroinflammation, and neurological disorders. Recently, several comparatively specific small molecules have facilitated the chemical manipulation of this enzyme within cellular systems, leading to the discovery of novel inhibitors for GSK-3β. Despite these advancements, the therapeutic significance of GSK-3β as a drug target is still complicated by uncertainties surrounding the potential of inhibitors to stimulate tumorigenesis. This review provides a comprehensive overview of the intricate mechanisms of this enzyme and evaluates the existing evidence regarding the therapeutic potential of GSK-3β in brain diseases, including Alzheimer's disease, Parkinson's disease, mood disorders, and glioblastoma.

New insights into glycogen synthase kinase-3: A common target for neurodegenerative diseases

Glycogen synthase kinase 3 (GSK-3) is a highly conserved protein serine/threonine kinase that plays a central role in a wide variety of cellular processes to coordinate catabolic and anabolic pathways and regulate cell growth and fate. There is increasing evidence showing that abnormal glycogen synthase kinase 3 (GSK-3) is associated with the pathogenesis and progression of many disorders, such as cancer, diabetes, psychiatric diseases, and neurodegenerative diseases. In this review, we summarize recent findings about the regulatory role of GSK-3 in the occurrence and development of multiple neurodegenerative diseases, mainly focusing on Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. The aim of this study is to provide new insight into the shared working mechanism of GSK-3 as a therapeutic target of multiple neurodegenerative diseases.

Borjeson-Forssman-Lehmann Syndrome: Clinical Features and Diagnostic Challenges

Borjeson-Forssman-Lehmann syndrome (BFLS) is an X-linked recessive disorder resulting from mutations in the PHF6 gene. The syndrome is characterized by short stature, obesity, hypogonadism, hypotonia, intellectual disability, distinctive facial features, fleshy ears, and finger and toe abnormalities. However, the diagnostic challenge in identifying BFLS remains a topic of interest. In this case report, we present the clinical characteristics of a proband with BFLS, highlighting the additional features of hypotonia, intellectual disability, and distinctive facial features. While no definitive treatment exists for BFLS, patients benefit from specialized education and ongoing supervision from early childhood through adulthood. Symptomatic treatment, including close follow-up, may be necessary for complications such as seizures and hearing problems. Mastectomy or testosterone replacement therapy may be considered on a case-by-case basis. Genetic counseling for X-linkage should be offered to affected families.

MAP1B Regulates Cortical Neuron Interstitial Axon Branching Through the Tubulin Tyrosination Cycle

Regulation of directed axon guidance and branching during development is essential for the generation of neuronal networks. However, the molecular mechanisms that underlie interstitial axon branching in the mammalian brain remain unresolved. Here, we investigate interstitial axon branching in vivo using an approach for precise labeling of layer 2/3 callosal projection neurons (CPNs), allowing for quantitative analysis of axonal morphology at high acuity and also manipulation of gene expression in well-defined temporal windows. We find that the GSK3β serine/threonine kinase promotes interstitial axon branching in layer 2/3 CPNs by releasing MAP1B-mediated inhibition of axon branching. Further, we find that the tubulin tyrosination cycle is a key downstream component of GSK3β/MAP1B signaling. We propose that MAP1B functions as a brake on axon branching that can be released by GSK3β activation, regulating the tubulin code and thereby playing an integral role in sculpting cortical neuron axon morphology.

Neuronal Histone Methyltransferase EZH2 Regulates Neuronal Morphogenesis, Synaptic Plasticity, and Cognitive Behavior in Mice

The histone methyltransferase enhancer of zeste 2 polycomb repressive complex 2 subunit (EZH2)-mediated trimethylation of histone H3 lysine 27 (H3K27me3) regulates neural stem cell proliferation and fate specificity through silencing different gene sets in the central nervous system. Here, we explored the function of EZH2 in early post-mitotic neurons by generating a neuron-specific Ezh2 conditional knockout mouse line. The results showed that a lack of neuronal EZH2 led to delayed neuronal migration, more complex dendritic arborization, and increased dendritic spine density. Transcriptome analysis revealed that neuronal EZH2-regulated genes are related to neuronal morphogenesis. In particular, the gene encoding p21-activated kinase 3 (Pak3) was identified as a target gene suppressed by EZH2 and H3K27me3, and expression of the dominant negative Pak3 reversed Ezh2 knockout-induced higher dendritic spine density. Finally, the lack of neuronal EZH2 resulted in impaired memory behaviors in adult mice. Our results demonstrated that neuronal EZH2 acts to control multiple steps of neuronal morphogenesis during development, and has long-lasting effects on cognitive function in adult mice.

Light at night: effect on the daily clock, learning, memory, cognition, and expression of transcripts in different brain regions of rat

The rapid increase in urbanization is altering the natural composition of the day-night light ratio. The light/dark cycle regulates animal learning, memory, and mood swings. A study was conducted to examine the effect of different quantity and quality of light at night on the daily clock, learning, memory, cognition, and expression of transcripts in key learning centers. Treatment was similar for experiments one to three. Rats were exposed for 30 days to 12 h light and 12 h dark with a night light of 2 lx (dLAN group), 250 lx (LL), or without night light (LD). In experiment one, after 28 days, blood samples were collected and 2 days later, animals were exposed to constant darkness. In experiment two, after 30 days of treatment, animals were subjected to various tests involving learning, memory, and cognition. In experiment three, after 30 days of treatment, animals were sampled, and transcript levels of brain-derived neurotrophic factor, tyrosine kinase, Growth-Associated Protein 43, Neurogranin, microRNA-132, cAMP Response Element-Binding Protein, Glycogen synthase kinase-3β, and Tumor necrosis factor α were measured in hippocampus, thalamus, and cortex tissues. In experiment four, animals were exposed to night light of 0.019 W/m2 but of either red (640 nm), green (540 nm), or blue (450 nm) wavelength for 30 days, and similar tests were performed as mentioned in experiment 2. While in experiment five, after 30 days of respective wavelength treatments, all animals were sampled for gene expression studies. Our results show that exposure to dLAN and LL affects the daily clock as reflected by altered melatonin secretion and locomotor activity, compromises the learning, memory, and cognitive ability, and alterations in the expression levels of transcripts in the hypothalamus, cortex, and thalamus. The effect is night light intensity dependent. Further, blue light at night has less drastic effects than green and red light. These results could be of the potential use of framing the policies for the use of light at night.

The immunomodulatory effect of lithium as a mechanism of action in bipolar disorder

Bipolar disorder (BD) is a chronic mental disorder characterized by recurrent episodes of mania and depression alternating with periods of euthymia. Although environmental and genetic factors have been described, their pathogenesis is not fully understood. Much evidence suggests a role for inflammatory mediators and immune dysregulation in the development of BD. The first-line treatment in BD are mood-stabilizing agents, one of which is lithium (Li) salts. The Li mechanism of action is not fully understood, but it has been proposed that its robust immunomodulatory properties might be one of the mechanisms responsible for its effectiveness. In this article, the authors present the current knowledge about immune system changes accompanying BD, as well as the immunomodulatory effect of lithium. The results of studies describing connections between immune system changes and lithium effectiveness are often incoherent. Further research is needed to understand the connection between immune system modulation and the therapeutic action of lithium in BD.

Neurogenesis redirects β-catenin from adherens junctions to the nucleus to promote axonal growth

Here, we show that, in the developing spinal cord, after the early Wnt-mediated Tcf transcription activation that confers dorsal identity to neural stem cells, neurogenesis redirects β-catenin from the adherens junctions to the nucleus to stimulate Tcf-dependent transcription in a Wnt-independent manner. This new β-catenin activity regulates genes implicated in several aspects of contralateral axon growth, including axon guidance and adhesion. Using live imaging of ex-vivo chick neural tube, we showed that the nuclear accumulation of β-catenin and the rise in Tcf-dependent transcription both initiate before the dismantling of the adherens junctions and remain during the axon elongation process. Notably, we demonstrated that β-catenin activity in post-mitotic cells depends on TCF7L2 and is central to spinal commissural axon growth. Together, our results reveal Wnt-independent Tcf/β-catenin regulation of genes that control the growth and guidance of commissural axons in chick spinal cord.

Progranulin Protects against Hyperglycemia-Induced Neuronal Dysfunction through GSK3β Signaling

Type II diabetes affects over 530 million individuals worldwide and contributes to a host of neurological pathologies. Uncontrolled high blood glucose (hyperglycemia) is a major factor in diabetic pathology, and glucose regulation is a common goal for maintenance in patients. We have found that the neuronal growth factor progranulin protects against hyperglycemic stress in neurons, and although its mechanism of action is uncertain, our findings identified Glycogen Synthase Kinase 3β (GSK3β) as being potentially involved in its effects. In this study, we treated mouse primary cortical neurons exposed to high-glucose conditions with progranulin and a selective pharmacological inhibitor of GSK3β before assessing neuronal health and function. Whole-cell and mitochondrial viability were both improved by progranulin under high-glucose stress in a GSK3β-dependent manner. This extended to autophagy flux, indicated by the expressions of autophagosome marker Light Chain 3B (LC3B) and lysosome marker Lysosome-Associated Membrane Protein 2A (LAMP2A), which were affected by progranulin and showed heterogeneous changes from GSK3β inhibition. Lastly, GSK3β inhibition attenuated downstream calcium signaling and neuronal firing effects due to acute progranulin treatment. These data indicate that GSK3β plays an important role in progranulin's neuroprotective effects under hyperglycemic stress and serves as a jumping-off point to explore progranulin's protective capabilities in other neurodegenerative models.

Elucidation of the GSK3α Structure Informs the Design of Novel, Paralog-Selective Inhibitors

Glycogen synthase kinase 3 (GSK3) remains a therapeutic target of interest for diverse clinical indications. However, one hurdle in the development of small molecule GSK3 inhibitors has been safety concerns related to pan-inhibition of both GSK3 paralogs, leading to activation of the Wnt/β-catenin pathway and potential for aberrant cell proliferation. Development of GSK3α or GSK3β paralog-selective inhibitors that could offer an improved safety profile has been reported but further advancement has been hampered by the lack of structural information for GSK3α. Here we report for the first time the crystal structure for GSK3α, both in apo form and bound to a paralog-selective inhibitor. Taking advantage of this new structural information, we describe the design and in vitro testing of novel compounds with up to ∼37-fold selectivity for GSK3α over GSK3β with favorable drug-like properties. Furthermore, using chemoproteomics, we confirm that acute inhibition of GSK3α can lower tau phosphorylation at disease-relevant sites in vivo, with a high degree of selectivity over GSK3β and other kinases. Altogether, our studies advance prior efforts to develop GSK3 inhibitors by describing GSK3α structure and novel GSK3α inhibitors with improved selectivity, potency, and activity in disease-relevant systems.

Ketamine impairs growth cone and synaptogenesis in human GABAergic projection neurons via GSK-3β and HDAC6 signaling

The growth cone guides the axon or dendrite of striatal GABAergic projection neurons that protrude into the midbrain and cortex and form complex neuronal circuits and synaptic networks in a developing brain, aberrant projections and synaptic connections in the striatum related to multiple brain disorders. Previously, we showed that ketamine, an anesthetic, reduced dendritic growth, dendritic branches, and spine density in human striatal GABAergic neurons. However, whether ketamine affects the growth cone, the synaptic connection of growing striatal GABAergic neurons has not been tested. Using human GABAergic projection neurons derived from human inducible pluripotent stem cells (hiPSCs) and embryonic stem cells (ES) in vitro, we tested ketamine effects on the growth cones and synapses in developing GABAergic neurons by assessing the morphometry and the glycogen synthase kinase-3 (GSK-3) and histone deacetylase 6 (HDAC6) pathway. Ketamine exposure impairs growth cone formation, synaptogenesis, dendritic development, and maturation via ketamine-mediated activation of GSK-3 pathways and inhibiting HDAC6, an essential stabilizing protein for dendritic morphogenesis and synapse maturation. Our findings identified a novel ketamine neurotoxic pathway that depends on GSK-3β and HDAC6 signaling, suggesting that microtubule acetylation is a potential target for reducing ketamine's toxic effect on GABAergic projection neuronal development.

Dynamic proteomic and phosphoproteomic atlas of corticostriatal axons in neurodevelopment

Mammalian axonal development begins in embryonic stages and continues postnatally. After birth, axonal proteomic landscape changes rapidly, coordinated by transcription, protein turnover, and post-translational modifications. Comprehensive profiling of axonal proteomes across neurodevelopment is limited, with most studies lacking cell-type and neural circuit specificity, resulting in substantial information loss. We create a Cre-dependent APEX2 reporter mouse line and map cell-type-specific proteome of corticostriatal projections across postnatal development. We synthesize analysis frameworks to define temporal patterns of axonal proteome and phosphoproteome, identifying co-regulated proteins and phosphorylations associated with genetic risk for human brain disorders. We discover proline-directed kinases as major developmental regulators. APEX2 transgenic reporter proximity labeling offers flexible strategies for subcellular proteomics with cell type specificity in early neurodevelopment, a critical period for neuropsychiatric disease.

GSK3 Is a Central Player in Retinal Degenerative Diseases but a Challenging Therapeutic Target

Glycogen synthase kinase 3 (GSK3) is a key regulator of many cellular signaling processes and performs a wide range of biological functions in the nervous system. Due to its central role in numerous cellular processes involved in cell degeneration, a rising number of studies have highlighted the interest in developing therapeutics targeting GSK3 to treat neurodegenerative diseases. Although recent works strongly suggest that inhibiting GSK3 might also be a promising therapeutic approach for retinal degenerative diseases, its full potential is still under-evaluated. In this review, we summarize the literature on the role of GSK3 on the main cellular functions reported as deregulated during retinal degeneration, such as glucose homeostasis which is critical for photoreceptor survival, or oxidative stress, a major component of retinal degeneration. We also discuss the interest in targeting GSK3 for its beneficial effects on inflammation, for reducing neovascularization that occurs in some retinal dystrophies, or for cell-based therapy by enhancing Müller glia cell proliferation in diseased retina. Together, although GSK3 inhibitors hold promise as therapeutic agents, we highlight the complexity of targeting such a multitasked kinase and the need to increase our knowledge of the impact of reducing GSK3 activity on these multiple cellular pathways and biological processes.

Cell Type-Specific Transcriptional Control of Gsk3β in the Developing Mammalian Neocortex

Temporal control of neurogenesis is central for the development and evolution of species-specific brain architectures. The balance between progenitor expansion and neuronal differentiation is tightly coordinated by cell-intrinsic and cell-extrinsic cues. Wnt signaling plays pivotal roles in the proliferation and differentiation of neural progenitors in a temporal manner. However, regulatory mechanisms that adjust intracellular signaling amplitudes according to cell fate progression remain to be elucidated. Here, we report the transcriptional controls of Gsk3β, a critical regulator of Wnt signaling, in the developing mouse neocortex. Gsk3β expression was higher in ventricular neural progenitors, while it gradually declined in differentiated neurons. We identified active cis-regulatory module (CRM) of Gsk3β that responded to cell type-specific transcription factors, such as Sox2, Sox9, and Neurogenin2. Furthermore, we found extensive conservation of the CRM among mammals but not in non-mammalian amniotes. Our data suggest that a mammalian-specific CRM drives the cell type-specific activity of Gsk3β to fine tune Wnt signaling, which contributes to the tight control of neurogenesis during neocortical development.

Molecular mechanisms regulating the spatial configuration of neurites

Precise neural networks, composed of axons and dendrites, are the structural basis for information processing in the brain. Therefore, the correct formation of neurites is critical for accurate neural function. In particular, the three-dimensional structures of dendrites vary greatly among neuron types, and the unique shape of each dendrite is tightly linked to specific synaptic connections with innervating axons and is correlated with its information processing. Although many systems are involved in neurite formation, the developmental mechanisms that control the orientation, size, and arborization pattern of neurites definitively defines their three-dimensional structure in tissues. In this review, we summarize these regulatory mechanisms that establish proper spatial configurations of neurites, especially dendrites, in invertebrates and vertebrates.

Amygdala DCX and blood Cdk14 are implicated as cross-species indicators of individual differences in fear, extinction, and resilience to trauma exposure

Doublecortin (DCX) has long been implicated in, and employed as a marker for, neurogenesis, yet little is known about its function in non-neurogenic brain regions, including the amygdala. This study sought first to explore, in rodents, whether fear learning and extinction modulate amygdala DCX expression and, second, to assess the utility of peripheral DCX correlates as predictive biomarkers of trauma response in rodents and humans. Pavlovian conditioning was found to alter DCX protein levels in mice 24 h later, resulting in higher DCX expression associated with enhanced learning in paradigms examining both the acquisition and extinction of fear (p < 0.001). This, in turn, is associated with differences in freezing on subsequent fear expression tests, and the same relationship between DCX and fear extinction was replicated in rats (p < 0.001), with higher amygdala DCX levels associated with more rapid extinction of fear. RNAseq of amygdala and blood from mice identified 388 amygdala genes that correlated with DCX (q < 0.001) and which gene ontology analyses revealed were significantly over-represented for neurodevelopmental processes. In blood, DCX-correlated genes included the Wnt signaling molecule Cdk14 which was found to predict freezing during both fear acquisition (p < 0.05) and brief extinction protocols (p < 0.001). High Cdk14 measured in blood immediately after testing was also associated with less freezing during fear expression testing (p < 0.01). Finally, in humans, Cdk14 expression in blood taken shortly after trauma was found to predict resilience in males for up to a year post-trauma (p < 0.0001). These data implicate amygdala DCX in fear learning and suggest that Cdk14 may serve as a predictive biomarker of trauma response.

Regulation of Autophagy by the Glycogen Synthase Kinase-3 (GSK-3) Signaling Pathway

Autophagy is a vital cellular mechanism that benefits cellular maintenance and survival during cell stress. It can eliminate damaged or long-lived organelles and improperly folded proteins to maintain cellular homeostasis, development, and differentiation. Impaired autophagy is associated with several diseases such as cancer, neurodegenerative diseases, and age-related macular degeneration (AMD). Several signaling pathways are associated with the regulation of the autophagy pathway. The glycogen synthase kinase-3 signaling pathway was reported to regulate the autophagy pathway. In this review, we will discuss the mechanisms by which the GSK-3 signaling pathway regulates autophagy. Autophagy and lysosomal function are regulated by transcription factor EB (TFEB). GSK-3 was shown to be involved in the regulation of TFEB nuclear expression in an mTORC1-dependent manner. In addition to mTORC1, GSK-3β also regulates TFEB via the protein kinase C (PKC) and the eukaryotic translation initiation factor 4A-3 (eIF4A3) signaling pathways. In addition to TFEB, we will also discuss the mechanisms by which the GSK-3 signaling pathway regulates autophagy by modulating other signaling molecules and autophagy inducers including, mTORC1, AKT and ULK1. In summary, this review provides a comprehensive understanding of the role of the GSK-3 signaling pathway in the regulation of autophagy.

Non-Canonical Wnt Signaling Regulates Cochlear Outgrowth and Planar Cell Polarity via Gsk3β Inhibition

During development, sensory hair cells (HCs) in the cochlea assemble a stereociliary hair bundle on their apical surface with planar polarized structure and orientation. We have recently identified a non-canonical, Wnt/G-protein/PI3K signaling pathway that promotes cochlear outgrowth and coordinates planar polarization of the HC apical cytoskeleton and alignment of HC orientation across the cochlear epithelium. Here, we determined the involvement of the kinase Gsk3β and the small GTPase Rac1 in non-canonical Wnt signaling and its regulation of the planar cell polarity (PCP) pathway in the cochlea. We provided the first in vivo evidence for Wnt regulation of Gsk3β activity via inhibitory Ser9 phosphorylation. Furthermore, we carried out genetic rescue experiments of cochlear defects caused by blocking Wnt secretion. We showed that cochlear outgrowth was partially rescued by genetic ablation of Gsk3β but not by expression of stabilized β-catenin; while PCP defects, including hair bundle polarity and junctional localization of the core PCP proteins Fzd6 and Dvl2, were partially rescued by either Gsk3β ablation or constitutive activation of Rac1. Our results identify Gsk3β and likely Rac1 as downstream components of non-canonical Wnt signaling and mediators of cochlear outgrowth, HC planar polarity, and localization of a subset of core PCP proteins in the cochlea.

GSK-3 and Tau: A Key Duet in Alzheimer's Disease

Glycogen synthase kinase-3 (GSK-3) is a ubiquitously expressed serine/threonine kinase with a plethora of substrates. As a modulator of several cellular processes, GSK-3 has a central position in cell metabolism and signaling, with important roles both in physiological and pathological conditions. GSK-3 has been associated with a number of human disorders, such as neurodegenerative diseases including Alzheimer’s disease (AD). GSK-3 contributes to the hyperphosphorylation of tau protein, the main component of neurofibrillary tangles (NFTs), one of the hallmarks of AD. GSK-3 is further involved in the regulation of different neuronal processes that are dysregulated during AD pathogenesis, such as the generation of amyloid-β (Aβ) peptide or Aβ-induced cell death, axonal transport, cholinergic function, and adult neurogenesis or synaptic function. In this review, we will summarize recent data about GSK-3 involvement in these processes contributing to AD pathology, mostly focusing on the crucial interplay between GSK-3 and tau protein. We further discuss the current development of potential AD therapies targeting GSK-3 or GSK-3-phosphorylated tau.

Deciphering the roles of glycogen synthase kinase 3 (GSK3) in the treatment of autism spectrum disorder and related syndromes

Autism spectrum disorder (ASD) is a complex and multifactorial neurodevelopmental disorder characterized by the presence of restricted interests and repetitive behaviors besides deficits in social communication. Syndromic ASD is a subset of ASD caused by underlying genetic disorders, most commonly Fragile X Syndrome (FXS) and Rett Syndrome (RTT). Various mutations and consequent malfunctions in core signaling pathways have been identified in ASD, including glycogen synthase kinase 3 (GSK3). A growing body of evidence suggests a key role of GSK3 dysregulation in the pathogenesis of ASD and its related disorders. Here, we provide a synopsis of the implication of GSK3 in ASD, FXS, and RTT as a promising therapeutic target for the treatment of ASD.

Regulation of GSK3β by Ser389 Phosphorylation During Neural Development

GSK3β is a constitutively active kinase that promotes cell death, which requires strict regulatory mechanisms. Although Akt-mediated phosphorylation at Ser9 is the default mechanism to inactivate GSK3β, phosphorylation of GSK3β at Ser389 by p38 MAPK has emerged as an alternative inhibitory pathway that provides cell protection and repair in response to DNA damage. Phosphorylation of Ser389 GSK3β has been detected in adult brain, where it has been related to neuronal survival and behavior. However, the use of this pathway to regulate GSK3β in the neonatal developing brain is unknown. In this study, we show that phosphorylation of GSK3β at Ser389 in the brain is developmentally regulated, with the highest levels corresponding to the first 2 weeks of age. Moreover, we found that the phosphorylation of GSK3β at Ser389 is the preferential mechanism for inactivating brain GSK3β in 2-week-old mice. Importantly, we show that phospho-Ser389 GSK3β expression is predominant in neuronal cell cultures from neonatal brain relative to other cell populations. However, phospho-Ser389 GSK3β is triggered by DNA double-strand breaks in all developing neural cell types examined. Thus, the phosphorylation of GSK3β on Ser389 could be a central regulatory mechanism to restrain GSK3β during neurogenesis early in life.

Mechanisms and Therapeutic Implications of GSK-3 in Treating Neurodegeneration

Neurodegenerative disorders are spreading worldwide and are one of the greatest threats to public health. There is currently no adequate therapy for these disorders, and therefore there is an urgent need to accelerate the discovery and development of effective treatments. Although neurodegenerative disorders are broad ranging and highly complex, they may share overlapping mechanisms, and thus potentially manifest common targets for therapeutic interventions. Glycogen synthase kinase-3 (GSK-3) is now acknowledged to be a central player in regulating mood behavior, cognitive functions, and neuron viability. Indeed, many targets controlled by GSK-3 are critically involved in progressing neuron deterioration and disease pathogenesis. In this review, we focus on three pathways that represent prominent mechanisms linking GSK-3 with neurodegenerative disorders: cytoskeleton organization, the mammalian target of rapamycin (mTOR)/autophagy axis, and mitochondria. We also consider the challenges and opportunities in the development of GSK-3 inhibitors for treating neurodegeneration.

Glycogen synthase kinase-3β inhibitor SB216763 promotes DNA repair in ischemic retinal neurons

Glycogen synthase kinase-3β (GSK-3β) has been shown to attenuate DNA damage in nerve cells, thereby enhancing neuronal survival under pathological conditions; however, the underlying mechanism remains unclear. An in vitro serum-starvation retinal neuron model and in vivo ischemia/reperfusion retina injury rat model were established and treated with SB216763, a GSK-3β inhibitor. SB21673 decreased the formation of γ-H2A histone family member X foci and enhanced the viability of ischemic retinal neurons. In addition, SB216763 upregulated expression of phosphorylated-CREB1, a ligase IV transcription factor, and significantly increased the transcriptional activity of ligase IV in ischemic retinal neurons. These results were confirmed in rat retinas following ischemia/reperfusion injury. Furthermore, we found that unlike lithium chlorine (a well-known direct inhibitor of GSK-3β), SB216763 inhibited GSK-3β activity by suppressing its phosphorylation. Taken together, our results suggest that GSK-3β inhibition enhances repair of DNA double-strand breaks by upregulating ligase IV expression in ischemic retinal neurons. This study was approved by the Institutional Animal Care and Use Committee of Zhongshan Ophthalmic Center on February 18, 2018.

Evaluation of the effects of the T-type calcium channel enhancer SAK3 in a rat model of TAF1 deficiency

The TATA-box binding protein associated factor 1 (TAF1) is part of the TFIID complex that plays a key role during the initiation of transcription. Variants of TAF1 are associated with neurodevelopmental disorders. Previously, we found that CRISPR/Cas9 based editing of the TAF1 gene disrupts the morphology of the cerebral cortex and blunts the expression as well as the function of the CaV3.1 (T-type) voltage gated calcium channel. Here, we tested the efficacy of SAK3 (ethyl 8′-methyl-2′, 4-dioxo-2-(piperidin-1-yl)-2′H-spiro [cyclopentane-1, 3′-imidazo [1, 2-a] pyridine]-2-ene-3-carboxylate), a T-type calcium channel enhancer, in an animal model of TAF1 intellectual disability (ID) syndrome. At post-natal day 3, rat pups were subjected to intracerebroventricular (ICV) injection of either gRNA-control or gRNA-TAF1 CRISPR/Cas9 viruses. At post-natal day 21, the rat pups were given SAK3 (0.25 mg/kg, p.o.) or vehicle for 14 days (i.e. till post-natal day 35) and then subjected to behavioral, morphological, and molecular studies. Oral administration of SAK3 (0.25 mg/kg, p.o.) significantly rescued locomotion abnormalities associated with TAF1 gene editing. SAK3 treatment prevented the loss of cortical neurons and GFAP-positive astrocytes observed after TAF1 gene editing. In addition, SAK3 protected cells from apoptosis. SAK3 also restored the Brain-derived neurotrophic factor/protein kinase B/Glycogen Synthase Kinase 3 Beta (BDNF/AKT/GSK3β) signaling axis in TAF1 edited animals. Finally, SAK3 normalized the levels of three GSK3β substrates - CaV3.1, FOXP2, and CRMP2. We conclude that the T-type calcium channel enhancer SAK3 is beneficial against the deleterious effects of TAF1 gene-editing, in part, by stimulating the BDNF/AKT/GSK3β signaling pathway.

Enhanced FGFR3 activity in postmitotic principal neurons during brain development results in cortical dysplasia and axonal tract abnormality

Abnormal levels of fibroblast growth factors (FGFs) and FGF receptors (FGFRs) have been detected in various neurological disorders. The potent impact of FGF-FGFR in multiple embryonic developmental processes makes it challenging to elucidate their roles in postmitotic neurons. Taking an alternative approach to examine the impact of aberrant FGFR function on glutamatergic neurons, we generated a FGFR gain-of-function (GOF) transgenic mouse, which expresses constitutively activated FGFR3 (FGFR3K650E) in postmitotic glutamatergic neurons. We found that GOF disrupts mitosis of radial-glia neural progenitors (RGCs), inside-out radial migration of post-mitotic glutamatergic neurons, and axonal tract projections. In particular, late-born CUX1-positive neurons are widely dispersed throughout the GOF cortex. Such a cortical migration deficit is likely caused, at least in part, by a significant reduction of the radial processes projecting from RGCs. RNA-sequencing analysis of the GOF embryonic cortex reveals significant alterations in several pathways involved in cell cycle regulation and axonal pathfinding. Collectively, our data suggest that FGFR3 GOF in postmitotic neurons not only alters axonal growth of postmitotic neurons but also impairs RGC neurogenesis and radial glia processes.

Isozyme-Specific Role of SAD-A in Neuronal Migration During Development of Cerebral Cortex

SAD kinases regulate presynaptic vesicle clustering and neuronal polarization. A previous report demonstrated that Sada-/- and Sadb-/- double-mutant mice showed perinatal lethality with a severe defect in axon/dendrite differentiation, but their single mutants did not. These results indicated that they were functionally redundant. Surprisingly, we show that on a C57BL/6N background, SAD-A is essential for cortical development whereas SAD-B is dispensable. Sada-/- mice died within a few days after birth. Their cortical lamination pattern was disorganized and radial migration of cortical neurons was perturbed. Birth date analyses with BrdU and in utero electroporation using pCAG-EGFP vector showed a delayed migration of cortical neurons to the pial surface in Sada-/- mice. Time-lapse imaging of these mice confirmed slow migration velocity in the cortical plate. While the neurites of hippocampal neurons in Sada-/- mice could ultimately differentiate in culture to form axons and dendrites, the average length of their axons was shorter than that of the wild type. Thus, analysis on a different genetic background than that used initially revealed a nonredundant role for SAD-A in neuronal migration and differentiation.

Reelin Functions, Mechanisms of Action and Signaling Pathways During Brain Development and Maturation

During embryonic development and adulthood, Reelin exerts several important functions in the brain including the regulation of neuronal migration, dendritic growth and branching, dendritic spine formation, synaptogenesis and synaptic plasticity. As a consequence, the Reelin signaling pathway has been associated with several human brain disorders such as lissencephaly, autism, schizophrenia, bipolar disorder, depression, mental retardation, Alzheimer’s disease and epilepsy. Several elements of the signaling pathway are known. Core components, such as the Reelin receptors very low-density lipoprotein receptor (VLDLR) and Apolipoprotein E receptor 2 (ApoER2), Src family kinases Src and Fyn, and the intracellular adaptor Disabled-1 (Dab1), are common to most but not all Reelin functions. Other downstream effectors are, on the other hand, more specific to defined tasks. Reelin is a large extracellular protein, and some aspects of the signal are regulated by its processing into smaller fragments. Rather than being inhibitory, the processing at two major sites seems to be fulfilling important physiological functions. In this review, I describe the various cellular events regulated by Reelin and attempt to explain the current knowledge on the mechanisms of action. After discussing the shared and distinct elements of the Reelin signaling pathway involved in neuronal migration, dendritic growth, spine development and synaptic plasticity, I briefly outline the data revealing the importance of Reelin in human brain disorders.

GSK-3β Contributes to Parkinsonian Dopaminergic Neuron Death: Evidence From Conditional Knockout Mice and Tideglusib

Glycogen synthase kinase-3 (GSK-3) dysregulation has been implicated in nigral dopaminergic neurodegeneration, one of the main pathological features of Parkinson’s disease (PD). The two isoforms, GSK-3α and GSK-3β, have both been suggested to play a detrimental role in neuronal death. To date, several studies have focused on the role of GSK-3β on PD pathogenesis, while the role of GSK-3α has been largely overlooked. Here, we report in situ observations that both GSK-3α and GSK-3β are dephosphorylated at a negatively acting regulatory serine, indicating kinase activation, selectively in nigral dopaminergic neurons following exposure of mice to 1-methyl-4-pheny-1,2,3,6-tetrahydropyridine (MPTP). To identify whether GSK-3α and GSK-3β display functional redundancy in regulating parkinsonian dopaminergic cell death, we analysed dopaminergic neuron-specific Gsk3a null (Gsk3a^ΔDat) and Gsk3b null (Gsk3b^ΔDat) mice, respectively. We found that Gsk3b^ΔDat, but not Gsk3a^ΔDat, showed significant resistance to MPTP insult, revealing non-redundancy of GSK-3α and GSK-3β in PD pathogenesis. In addition, we tested the neuroprotective effect of tideglusib, the most clinically advanced inhibitor of GSK-3, in the MPTP model of PD. Administration of higher doses (200 mg/kg and 500 mg/kg) of tideglusib exhibited significant neuroprotection, whereas 50 mg/kg tideglusib failed to prevent dopaminergic neurodegeneration from MPTP toxicity. Administration of 200 mg/kg tideglusib improved motor symptoms of MPTP-treated mice. Together, these data demonstrate GSK-3β and not GSK-3α is critical for parkinsonian neurodegeneration. Our data support the view that GSK-3β acts as a potential therapeutic target in PD and tideglusib would be a candidate drug for PD neuroprotective therapy.

Phosphorylation of CRMP2 is required for migration and positioning of Purkinje cells: Redundant roles of CRMP1 and CRMP4

Proper migration and positioning of Purkinje cells are important for formation of the developing cerebellum. Although several cyclin-dependent kinase 5 (Cdk5) substrates are known to be critical for ordered neuronal migration, there are no reports of mutant mouse-based, in vivo studies on the function of Cdk5-phosphorylation substrates in migration of Purkinje cells. We focused on the analysis of collapsin response mediator protein 2 (CRMP2), one of the Cdk5 substrates, because a previous study reported migration defects of cortical neurons with shRNA-mediated knockdown of CRMP2. However, CRMP2 KI/KI mice, in which Cdk5-phosphorylation is inhibited, showed little defects in Purkinje cell migration and positioning. We hypothesized compensatory redundant functions of the other CRMPs, and analyzed the migration and positioning of Purkinje cells in the cerebellum in every combination of CRMP1 knockout (KO), CRMP2 KI/KI, and CRMP4 KO mice. Severe disturbance of migration and positioning of Purkinje cells were observed in the triple mutant mice. We also found motor coordination defects in the triple CRMPs mutant mice. These results suggest the importance of both, phosphorylation of CRMP2 by Cdk5 and the redundant functions of CRMP1 and CRMP4 in proper migration and positioning of Purkinje cells in developing cerebellum.

Molecular mechanisms of cell polarity in a range of model systems and in migrating neurons

Cell polarity is defined as the asymmetric distribution of cellular components along an axis. Most cells, from the simplest single-cell organisms to highly specialized mammalian cells, are polarized and use similar mechanisms to generate and maintain polarity. Cell polarity is important for cells to migrate, form tissues, and coordinate activities. During development of the mammalian cerebral cortex, cell polarity is essential for neurogenesis and for the migration of newborn but as-yet undifferentiated neurons. These oriented migrations include both the radial migration of excitatory projection neurons and the tangential migration of inhibitory interneurons. In this review, I will first describe the development of the cerebral cortex, as revealed at the cellular level. I will then define the core molecular mechanisms - the Par/Crb/Scrib polarity complexes, small GTPases, the actin and microtubule cytoskeletons, and phosphoinositides/PI3K signaling - that are required for asymmetric cell division, apico-basal and front-rear polarity in model systems, including C elegans zygote, Drosophila embryos and cultured mammalian cells. As I go through each core mechanism I will explain what is known about its importance in radial and tangential migration in the developing mammalian cerebral cortex.

PDK1 regulates the survival of the developing cortical interneurons

Inhibitory interneurons are critical for maintaining the excitatory/inhibitory balance. During the development cortical interneurons originate from the ganglionic eminence and arrive at the dorsal cortex through two tangential migration routes. However, the mechanisms underlying the development of cortical interneurons remain unclear. 3-Phosphoinositide-dependent protein kinase-1 (PDK1) has been shown to be involved in a variety of biological processes, including cell proliferation and migration, and plays an important role in the neurogenesis of cortical excitatory neurons. However, the function of PDK1 in interneurons is still unclear. Here, we reported that the disruption of Pdk1 in the subpallium achieved by crossing the Dlx5/6-Cre-IRES-EGFP line with Pdk1^fl/fl mice led to the severely increased apoptosis of immature interneurons, subsequently resulting in a remarkable reduction in cortical interneurons. However, the tangential migration, progenitor pools and cell proliferation were not affected by the disruption of Pdk1. We further found the activity of AKT-GSK3β signaling pathway was decreased after Pdk1 deletion, suggesting it might be involved in the regulation of the survival of cortical interneurons. These results provide new insights into the function of PDK1 in the development of the telencephalon.

Neurogenesis, neuronal migration, and axon guidance

Development of the central nervous system (CNS) is a complex, dynamic process that involves a precisely orchestrated sequence of genetic, environmental, biochemical, and physical factors from early embryonic stages to postnatal life. Duringthe past decade, great strides have been made to unravel mechanisms underlying human CNS development through the employment of modern genetic techniques and experimental approaches. In this chapter, we review the current knowledge regarding the main developmental processes and signaling mechanisms of (i) neurogenesis, (ii) neuronal migration, and (iii) axon guidance. We discuss mechanisms related to neural stem cells proliferation, migration, terminal translocation of neuronal progenitors, and axon guidance and pathfinding. For each section, we also provide a comprehensive overview of the underlying regulatory processes, including transcriptional, posttranscriptional, and epigenetic factors, and a myriad of signaling pathways that are pivotal to determine the fate of neuronal progenitors and newly formed migrating neurons. We further highlight how impairment of this complex regulating system, such as mutations in its core components, may cause cortical malformation, epilepsy, intellectual disability, and autism in humans. A thorough understanding of normal human CNS development is thus crucial to decipher mechanisms responsible for neurodevelopmental disorders and in turn guide the development of effective and targeted therapeutic strategies.

GSK-3 modulates SHH-driven proliferation in postnatal cerebellar neurogenesis and medulloblastoma

Cerebellar development requires regulated proliferation of cerebellar granule neuron progenitors (CGNPs). Inadequate CGNP proliferation causes cerebellar hypoplasia whereas excessive CGNP proliferation can cause medulloblastoma, the most common malignant pediatric brain tumor. Although sonic hedgehog (SHH) signaling is known to activate CGNP proliferation, the mechanisms downregulating proliferation are less defined. We investigated CGNP regulation by GSK-3, which downregulates proliferation in the forebrain, gut and breast by suppressing mitogenic WNT signaling in mouse. In striking contrast to these systems, we found that co-deleting Gsk3a and Gsk3b blocked CGNP proliferation, causing severe cerebellar hypoplasia. The GSK-3 inhibitor CHIR-98014 similarly downregulated SHH-driven proliferation. Transcriptomic analysis showed activated WNT signaling and upregulated Cdkn1a in Gsk3a/b -deleted CGNPs. Ctnnb co-deletion increased CGNP proliferation and rescued cerebellar hypoproliferation in Gsk3a/b mutants, demonstrating physiological control of CGNPs by GSK-3, mediated through WNT. SHH-driven medulloblastomas similarly required GSK-3, as co-deleting Gsk3a/b blocked tumor growth in medulloblastoma-prone SmoM2 mice. These data show that a GSK-3/WNT axis modulates the developmental proliferation of CGNPs and the pathological growth of SHH-driven medulloblastoma. The requirement for GSK-3 in SHH-driven proliferation suggests that GSK-3 may be targeted for SHH-driven medulloblastoma therapy.

GSK-3β at the Intersection of Neuronal Plasticity and Neurodegeneration

In neurons, Glycogen Synthase Kinase-3β (GSK-3β) has been shown to regulate various critical processes underlying structural and functional synaptic plasticity. Mouse models with neuron-selective expression or deletion of GSK-3β present behavioral and cognitive abnormalities, positioning this protein kinase as a key signaling molecule in normal brain functioning. Furthermore, mouse models with defective GSK-3β activity display distinct structural and behavioral abnormalities, which model some aspects of different neurological and neuropsychiatric disorders. Equalizing GSK-3β activity in these mouse models by genetic or pharmacological interventions is able to rescue some of these abnormalities. Thus, GSK-3β is a relevant therapeutic target for the treatment of many brain disorders. Here, we provide an overview of how GSK-3β is regulated in physiological synaptic plasticity and how aberrant GSK-3β activity contributes to the development of dysfunctional synaptic plasticity in neuropsychiatric and neurodegenerative disorders.

The ASD Living Biology: from cell proliferation to clinical phenotype

Autism spectrum disorder (ASD) has captured the attention of scientists, clinicians and the lay public because of its uncertain origins and striking and unexplained clinical heterogeneity. Here we review genetic, genomic, cellular, postmortem, animal model, and cell model evidence that shows ASD begins in the womb. This evidence leads to a new theory that ASD is a multistage, progressive disorder of brain development, spanning nearly all of prenatal life. ASD can begin as early as the 1st and 2nd trimester with disruption of cell proliferation and differentiation. It continues with disruption of neural migration, laminar disorganization, altered neuron maturation and neurite outgrowth, disruption of synaptogenesis and reduced neural network functioning. Among the most commonly reported high-confidence ASD (hcASD) genes, 94% express during prenatal life and affect these fetal processes in neocortex, amygdala, hippocampus, striatum and cerebellum. A majority of hcASD genes are pleiotropic, and affect proliferation/differentiation and/or synapse development. Proliferation and subsequent fetal stages can also be disrupted by maternal immune activation in the 1st trimester. Commonly implicated pathways, PI3K/AKT and RAS/ERK, are also pleiotropic and affect multiple fetal processes from proliferation through synapse and neural functional development. In different ASD individuals, variation in how and when these pleiotropic pathways are dysregulated, will lead to different, even opposing effects, producing prenatal as well as later neural and clinical heterogeneity. Thus, the pathogenesis of ASD is not set at one point in time and does not reside in one process, but rather is a cascade of prenatal pathogenic processes in the vast majority of ASD toddlers. Despite this new knowledge and theory that ASD biology begins in the womb, current research methods have not provided individualized information: What are the fetal processes and early-age molecular and cellular differences that underlie ASD in each individual child? Without such individualized knowledge, rapid advances in biological-based diagnostic, prognostic, and precision medicine treatments cannot occur. Missing, therefore, is what we call ASD Living Biology. This is a conceptual and paradigm shift towards a focus on the abnormal prenatal processes underlying ASD within each living individual. The concept emphasizes the specific need for foundational knowledge of a living child's development from abnormal prenatal beginnings to early clinical stages. The ASD Living Biology paradigm seeks this knowledge by linking genetic and in vitro prenatal molecular, cellular and neural measurements with in vivo post-natal molecular, neural and clinical presentation and progression in each ASD child. We review the first such study, which confirms the multistage fetal nature of ASD and provides the first in vitro fetal-stage explanation for in vivo early brain overgrowth. Within-child ASD Living Biology is a novel research concept we coin here that advocates the integration of in vitro prenatal and in vivo early post-natal information to generate individualized and group-level explanations, clinically useful prognoses, and precision medicine approaches that are truly beneficial for the individual infant and toddler with ASD.

High-throughput three-dimensional chemotactic assays reveal steepness-dependent complexity in neuronal sensation to molecular gradients

Many cellular programs of neural development are under combinatorial regulation by different chemoattractive or chemorepulsive factors. Here, we describe a microfluidic platform that utilizes well-controlled three-dimensional (3D) diffusion to generate molecular gradients of varied steepness in a large array of hydrogel cylinders, allowing high-throughput 3D chemotactic assays for mechanistic dissection of steepness-dependent neuronal chemotaxis. Using this platform, we examine neuronal sensitivity to the steepness of gradient composed of netrin-1, nerve growth factor, or semaphorin3A (Sema3A) proteins, and reveal dramatic diversity and complexity in the associated chemotactic regulation of neuronal development. Particularly for Sema3A, we find that serine/threonine kinase-11 and glycogen synthase kinase-3 signaling pathways are differentially involved in steepness-dependent chemotactic regulation of coordinated neurite repellence and neuronal migration. These results provide insights to the critical role of gradient steepness in neuronal chemotaxis, and also prove the technique as an expandable platform for studying other chemoresponsive cellular systems.

Differential Roles of Glycogen Synthase Kinase 3 Subtypes Alpha and Beta in Cortical Development

Glycogen synthase kinases 3 (GSK3) α and β are expressed in the nervous system, and disruption of GSK3 signaling has been implicated in a wide range of neurodevelopmental and psychiatric disorders. Although several studies have established a role of GSK3 signaling in the nervous system, much less is known about isoform-specific functions. Here, we have examined the role of GSK3α and GSK3β in the developing neocortex by performing in utero electroporation with specific small interfering RNAs targeting each isoform. We found that depletion of either GSK3α or GSK3β commonly promoted the proliferation of neural progenitor cells in the ventricular zone, but at later stages, knocking down of each isoform resulted in distinct outcomes. In particular, the transformation of radial progenitors to intermediate progenitor cells was promoted in GSK3α-depleted cells, but markedly prevented in GSK3β-depleted cells. Moreover, knocking down of GSK3β but not GSK3α prevented the generation of upper-layer Cux1⁺ neurons. Consistent with the distinct outcomes, protein levels of c-Myc and β-catenin, well-known substrates of GSK3, were differentially affected by depletion of GSK3α and GSK3β. Together, these results suggest that GSK3α and GSK3β might play distinct roles in the genesis and differentiation of neuronal lineage cells during neocortex development by differential regulation of downstream signaling pathways.

CDYL Deficiency Disrupts Neuronal Migration and Increases Susceptibility to Epilepsy

During brain development, the correct migration of newborn neurons is one of the determinants of circuit formation, and neuronal migration defects may lead to neurological and psychiatric disorders. The molecular mechanisms underlying neuronal migration and related disorders are poorly understood. Here, we report that Chromodomain Y-like (CDYL) is critical for neuronal migration in mice. Knocking down CDYL caused neuronal migration defects and disrupted both mobility and multipolar-to-bipolar transition of migrating neurons. We find that CDYL regulates neuronal migration by transcriptionally repressing RhoA. In addition, CDYL deficiency increased the excitability of cortical pyramidal neurons and the susceptibility of mice to convulsant-induced seizures. These results demonstrate that CDYL is a regulator of neuronal migration and shed light on the pathogenesis of seizure-related neurodevelopmental disorders.

Gene Manipulation Strategies to Identify Molecular Regulators of Axon Regeneration in the Central Nervous System

Limited axon regeneration in the injured adult mammalian central nervous system (CNS) usually results in irreversible functional deficits. Both the presence of extrinsic inhibitory molecules at the injury site and the intrinsically low capacity of adult neurons to grow axons are responsible for the diminished capacity of regeneration in the adult CNS. Conversely, in the embryonic CNS, neurons show a high regenerative capacity, mostly due to the expression of genes that positively control axon growth and downregulation of genes that inhibit axon growth. A better understanding of the role of these key genes controlling pro-regenerative mechanisms is pivotal to develop strategies to promote robust axon regeneration following adult CNS injury. Genetic manipulation techniques have been widely used to investigate the role of specific genes or a combination of different genes in axon regrowth. This review summarizes a myriad of studies that used genetic manipulations to promote axon growth in the injured CNS. We also review the roles of some of these genes during CNS development and suggest possible approaches to identify new candidate genes. Finally, we critically address the main advantages and pitfalls of gene-manipulation techniques, and discuss new strategies to promote robust axon regeneration in the mature CNS.

CLASP2 Links Reelin to the Cytoskeleton during Neocortical Development

The Reelin signaling pathway plays a crucial role in regulating neocortical development. However, little is known about how Reelin controls the cytoskeleton during neuronal migration. Here, we identify CLASP2 as a key cytoskeletal effector in the Reelin signaling pathway. We demonstrate that CLASP2 has distinct roles during neocortical development regulating neuron production and controlling neuron migration, polarity, and morphogenesis. We found downregulation of CLASP2 in migrating neurons leads to mislocalized cells in deeper cortical layers, abnormal positioning of the centrosome-Golgi complex, and aberrant length/orientation of the leading process. We discovered that Reelin regulates several phosphorylation sites within the positively charged serine/arginine-rich region that constitute consensus GSK3β phosphorylation motifs of CLASP2. Furthermore, phosphorylation of CLASP2 regulates its interaction with the Reelin adaptor Dab1 and this association is required for CLASP2 effects on neurite extension and motility. Together, our data reveal that CLASP2 is an essential Reelin effector orchestrating cytoskeleton dynamics during brain development.

Identifying and Analyzing Novel Epilepsy-Related Genes Using Random Walk with Restart Algorithm

As a pathological condition, epilepsy is caused by abnormal neuronal discharge in brain which will temporarily disrupt the cerebral functions. Epilepsy is a chronic disease which occurs in all ages and would seriously affect patients' personal lives. Thus, it is highly required to develop effective medicines or instruments to treat the disease. Identifying epilepsy-related genes is essential in order to understand and treat the disease because the corresponding proteins encoded by the epilepsy-related genes are candidates of the potential drug targets. In this study, a pioneering computational workflow was proposed to predict novel epilepsy-related genes using the random walk with restart (RWR) algorithm. As reported in the literature RWR algorithm often produces a number of false positive genes, and in this study a permutation test and functional association tests were implemented to filter the genes identified by RWR algorithm, which greatly reduce the number of suspected genes and result in only thirty-three novel epilepsy genes. Finally, these novel genes were analyzed based upon some recently published literatures. Our findings implicate that all novel genes were closely related to epilepsy. It is believed that the proposed workflow can also be applied to identify genes related to other diseases and deepen our understanding of the mechanisms of these diseases.

Role of APP Interactions with Heterotrimeric G Proteins: Physiological Functions and Pathological Consequences

Following the discovery that the amyloid precursor protein (APP) is the source of β-amyloid peptides (Aβ) that accumulate in Alzheimer’s disease (AD), structural analyses suggested that the holoprotein resembles a transmembrane receptor. Initial studies using reconstituted membranes demonstrated that APP can directly interact with the heterotrimeric G protein Gαo (but not other G proteins) via an evolutionarily G protein-binding motif in its cytoplasmic domain. Subsequent investigations in cell culture showed that antibodies against the extracellular domain of APP could stimulate Gαo activity, presumably mimicking endogenous APP ligands. In addition, chronically activating wild type APP or overexpressing mutant APP isoforms linked with familial AD could provoke Go-dependent neurotoxic responses, while biochemical assays using human brain samples suggested that the endogenous APP-Go interactions are perturbed in AD patients. More recently, several G protein-dependent pathways have been implicated in the physiological roles of APP, coupled with evidence that APP interacts both physically and functionally with Gαo in a variety of contexts. Work in insect models has demonstrated that the APP ortholog APPL directly interacts with Gαo in motile neurons, whereby APPL-Gαo signaling regulates the response of migratory neurons to ligands encountered in the developing nervous system. Concurrent studies using cultured mammalian neurons and organotypic hippocampal slice preparations have shown that APP signaling transduces the neuroprotective effects of soluble sAPPα fragments via modulation of the PI3K/Akt pathway, providing a mechanism for integrating the stress and survival responses regulated by APP. Notably, this effect was also inhibited by pertussis toxin, indicating an essential role for Gαo/i proteins. Unexpectedly, C-terminal fragments (CTFs) derived from APP have also been found to interact with Gαs, whereby CTF-Gαs signaling can promote neurite outgrowth via adenylyl cyclase/PKA-dependent pathways. These reports offer the intriguing perspective that G protein switching might modulate APP-dependent responses in a context-dependent manner. In this review, we provide an up-to-date perspective on the model that APP plays a variety of roles as an atypical G protein-coupled receptor in both the developing and adult nervous system, and we discuss the hypothesis that disruption of these normal functions might contribute to the progressive neuropathologies that typify AD.

Pathogenesis of Börjeson-Forssman-Lehmann syndrome: Insights from PHF6 function

Intellectual disability encompasses a large set of neurodevelopmental disorders of cognition that are more common in males than females. Although mutations in over 100 X-linked genes associated to intellectual disability have been identified, only a few X-linked intellectual disability proteins have been intensively studied. Hence, the molecular mechanisms underlying the majority of X-linked intellectual disability disorders remain poorly understood. A substantial fraction of X-linked intellectual disability genes encode nuclear proteins, suggesting that elucidating their functions in the regulation of transcription may provide novel insights into the pathogenesis of intellectual disability. Recent studies have uncovered mechanisms by which mutations of the gene encoding plant homeodomain (PHD)-like finger protein 6 (PHF6) contribute to the pathogenesis of the X-linked intellectual disability disorder Börjeson-Forssman-Lehmann syndrome (BFLS). PHF6 plays a critical role in the migration of neurons in the mouse cerebral cortex in vivo, and patient-specific mutations disrupt the ability of PHF6 to promote neuronal migration. Interestingly, PHF6 physically associates with the PAF1 transcriptional elongation complex and thereby drives neuronal migration in the cerebral cortex. PHF6 also interacts with the NuRD chromatin remodeling complex and with the nucleolar transcriptional regulator UBF, though the biological role of these interactions remains to be characterized. In other studies, PHF6 mRNA has been identified as the target of the microRNA miR-128 in the cerebral cortex, providing new insights into regulation of PHF6 function in neuronal migration. Importantly, deregulation of PHF6 function in neuronal migration triggers the formation of white matter heterotopias that harbor neuronal hyperexcitability, which may be relevant to the pathogenesis of intellectual disability and seizures in BFLS. Collectively, these studies are beginning to provide key insights into the molecular pathogenesis of BFLS.