A novel role for CAMKIIβ in the regulation of cortical neuron migration: implications for neurodevelopmental disorders

Synaptic rearrangement of NMDA receptors controls memory engram formation and malleability in the cortex

Initially hippocampal dependent, memory representations rely on a broadly distributed cortical network as they mature over time. How these cortical engrams acquire stability during systems-level memory consolidation without compromising their dynamic nature remains unclear. We identified a highly responsive "consolidation switch" in the synaptic composition of N-methyl-d-aspartate receptors (NMDARs), which dictates the progressive embedding and persistence of enduring memories in the rat cortex. Cortical GluN2B subunit-containing NMDARs were preferentially recruited upon encoding of associative olfactory memory to support neuronal allocation of memory engrams. As consolidation proceeds, a learning-induced redistribution of GluN2B subunit-containing NMDARs outward synapses increased synaptic GluN2A subunit contribution and enabled stabilization of remote memories. In contrast, synaptic reincorporation of GluN2B subunits occurred during subsequent forgetting. By manipulating the surface distribution of GluN2A and GluN2B subunit-containing NMDARs at cortical synapses, we uncovered that the rearrangement of GluN2B-containing NMDARs constitutes an essential tuning mechanism that determines the fate of cortical memory engrams and controls their malleability.

Understanding the pathogenetic mechanisms underlying altered neuronal function associated with CAMK2B mutations

'Dominant mutations in CAMK2B, encoding a subunit of the calcium/calmodulin-dependent protein kinase II (CAMK2), a serine/threonine kinase playing a key role in synaptic plasticity, learning and memory, underlie a recently characterized neurodevelopmental disorder (MRD54) characterized by delayed psychomotor development, mild to severe intellectual disability, hypotonia, and behavioral abnormalities. Targeted therapies to treat MRD54 are currently unavailable. In this review, we revise current knowledge on the molecular and cellular mechanisms underlying the altered neuronal function associated with defective CAMKIIβ function. We also summarize the identified genotype-phenotype correlations and discuss the disease models that have been generated to profile the altered neuronal phenotype and understand the pathophysiology of this disease.

Infection of Mouse Neural Progenitor Cells by Toxoplasma gondii Reduces Proliferation, Migration, and Neuronal Differentiation in Vitro

Congenital toxoplasmosis constitutes a major cause of pre- and postnatal complications. Fetal infection with Toxoplasma gondii influences development and can lead to microcephaly, encephalitis, and neurologic abnormalities. Systematic studies concerning the effects of neural progenitor cell infection with T. gondii are unavailable. Cortical intermediate progenitor cells cultivated as neurospheres obtained from E16.5 Swiss Webster mice were infected with T. gondii (ME49 strain) tachyzoites to mimic the developing mouse cerebral cortex in vitro. Infection was associated with decreased cell proliferation, detected by Ki-67 staining at 48 and 72 hours after infection in floating neurospheres, and reduced cellularity at 96 hours. Transient decreases in the expression of the neurogenesis-related transcription factors T-box brain protein 1, mouse atonal homolog protein 1, and hairy and enhancer of split protein 1 were found in infected cultures, while the level of transcription factor SOX-2 remained unaltered. Neurogenic potential, assessed in plated neurospheres, was impaired in infected cultures, as indicated by decreased late neuronal marker neurofilament heavy chain immunoreactivity. Infected cultures exhibited decreased overall migration rates at 48 and 120 hours. These findings indicate that T. gondii infection of neural progenitor cells may lead to reduced neurogenesis due to an imbalance in cell proliferation alongside an altered migratory profile. If translated to the in vivo situation, these data could explain, in part, cortical malformations in congenitally infected individuals.

Rac1 and Rac3 GTPases and TPC2 are required for axonal outgrowth and migration of cortical interneurons

Rho GTPases, among them Rac1 and Rac3, are major transducers of extracellular signals and are involved in multiple cellular processes. In cortical interneurons, the neurons that control the balance between excitation and inhibition of cortical circuits, Rac1 and Rac3 are essential for their development. Ablation of both leads to a severe reduction in the numbers of mature interneurons found in the murine cortex, which is partially due to abnormal cell cycle progression of interneuron precursors and defective formation of growth cones in young neurons. Here, we present new evidence that upon Rac1 and Rac3 ablation, centrosome, Golgi complex and lysosome positioning is significantly perturbed, thus affecting both interneuron migration and axon growth. Moreover, for the first time, we provide evidence of altered expression and localization of the two-pore channel 2 (TPC2) voltage-gated ion channel that mediates Ca2+ release. Pharmacological inhibition of TPC2 negatively affected axonal growth and migration of interneurons. Our data, taken together, suggest that TPC2 contributes to the severe phenotype in axon growth initiation, extension and interneuron migration in the absence of Rac1 and Rac3.

LBL Noninvasively Peelable Biointerfacial Adhesives for Cutaneo-Inspired pH/Tactility Artificial Receptors

Besides barrier functions, skin possesses multiple sentiences to external stimuli (e.g., temperature, force, and humidity) for human-outside interaction. Thus, skincare should be taken very seriously, especially by patients with sensory disorders. However, currently available skin-mimicking devices are always limited by so much insufficient response functions and nontunable interface behaviors so as not to realize precise health monitoring and self-defense against injury. Herein, a bioinspired cutaneous receptor-perceptual system (CRPS) patch is presented, integrating hybrid pH indicators and triboelectric nanogenerators into biointerface film-adhesives that are fabricated through facile layer-by-layer (LBL) self-assembly of amide and Schiff-base linkages between alginate grafted with N-hydroxysuccinimide ester (AN), tannic acid (TA), and polyethylenimine (PEI). This CRPS patch is adhered robustly to the soft-curved skin surface without failure via "molecular suturing," and amino acid enables its benign peel-on-demand from tissue interfaces. Postdamage self-healing brings it without surgical reoperation, avoiding extra cost, pain, as well as infection risks. Significantly, CRPS patches as artificial chemo/mechanoreceptors can remotely visualize skin physiological status by pH-induced chromism using smartphones and prevent skin contact injury by tactility-driven self-powered electrical signals. Overall, the LBL-based strategy to create controllably biointerface-adhesive CRPS patches will usher in a new era of the mobihealth care platform supporting smart diagnosis and self-protection.

Biomolecular condensate assembly of nArgBP2 tunes its functionality to manifest the structural plasticity of dendritic spines

nArgBP2, a candidate gene for intellectual disability, is a postsynaptic protein critical for dendritic spine development and morphogenesis, and its knockdown (KD) in developing neurons severely impairs spine-bearing excitatory synapse formation. Surprisingly, nArgBP2 KD in mature neurons did not cause morphological defects in the existing spines at rest, raising questions of how it functions in mature neurons. We found that unlike its inaction at rest, nArgBP2 KD completely inhibited the enlargement of dendritic spines during chemically induced long-term potentiation (cLTP) in mature neurons. We further found that nArgBP2 forms condensates in dendritic spines and that these condensates are dispersed by cLTP, which spatiotemporally coincides with spine head enlargement. Condensates with CaMKII phosphorylation-deficient mutant or CaMKII inhibition are neither dispersed nor accompanied by spine enlargement during cLTP. We found that nArgBP2 condensates in spines exhibited liquid-like properties, and in heterologous and in vitro expression systems, nArgBP2 undergoes liquid-liquid phase separation via multivalent intermolecular interactions between SH3 domains and proline-rich domains. It also forms coacervates with CaMKIIα, which is rapidly dissembled by calcium/CaMKIIα-dependent phosphorylation. We further showed that the interaction between nArgBP2 and WAVE1 competes with nArgBP2 phase separation and that blocking the nArgBP2-WAVE1 interaction prevents spine enlargement during cLTP. Together, our results suggest that nArgBP2 at rest is confined to the condensates but is released by CaMKIIα-mediated phosphorylation during synaptic plasticity, which regulates its timely interaction with WAVE1 to induce spine head enlargement in mature neurons.

Altered synaptic protein expression, aberrant spine morphology, and impaired spatial memory in Dlgap2 mutant mice, a genetic model of autism spectrum disorder

A microdeletion of approximately 2.4 Mb at the 8p23 terminal region has been identified in a Taiwanese autistic boy. Among the products transcribed/translated from genes mapped in this region, the reduction of DLGAP2, a postsynaptic scaffold protein, might be involved in the pathogenesis of autism spectrum disorder (ASD). DLGAP2 protein was detected in the hippocampus yet abolished in homozygous Dlgap2 knockout (Dlgap2 KO) mice. In this study, we characterized the hippocampal phenotypes in Dlgap2 mutant mice. Dlgap2 KO mice exhibited impaired spatial memory, indicating poor hippocampal function in the absence of DLGAP2. Aberrant expressions of postsynaptic proteins, including PSD95, SHANK3, HOMER1, GluN2A, GluR2, mGluR1, mGluR5, βCAMKII, ERK1/2, ARC, BDNF, were noticed in Dlgap2 mutant mice. Further, the spine density was increased in Dlgap2 KO mice, while the ratio of mushroom-type spines was decreased. We also observed a thinner postsynaptic density thickness in Dlgap2 KO mice at the ultrastructural level. These structural changes found in the hippocampus of Dlgap2 KO mice might be linked to impaired hippocampus-related cognitive functions such as spatial memory. Mice with Dlgap2 deficiency, showing signs of intellectual disability, a common co-occurring condition in patients with ASD, could be a promising animal model which may advance our understanding of ASD.

Elucidation of pathological mechanism caused by human disease mutation in CaMKIIβ

Recently, we have identified CaMKIIα and CaMKIIβ mutations in patients with neurodevelopmental disorders by whole exome sequencing study. Most CaMKII mutants have increased phosphorylation of Thr286/287, which induces autonomous activity of CaMKII, using cell culture experiments. In this study, we explored the pathological mechanism of motor dysfunction observed exclusively in a patient with Pro213Leu mutation in CaMKIIβ using a mouse model of the human disease. The homozygous CaMKIIβ Pro213Leu knockin mice showed age-dependent motor dysfunction and growth failure from 2 weeks after birth. In the cerebellum, the mutation did not alter the mRNA transcript level, but the CaMKIIβ protein level was dramatically decreased. Furthermore, in contrast to previous result from cell culture, Thr287 phosphorylation of CaMKIIβ was also reduced. CaMKIIβ Pro213Leu knockin mice showed similar motor dysfunction as CaMKIIβ knockout mice, newly providing evidence for a loss of function rather than a gain of function. Our disease model mouse showed similar phenotypes of the patient, except for epileptic seizures. We clearly demonstrated that the pathological mechanism is a reduction of mutant CaMKIIβ in the brain, and the physiological aspects of mutation were greatly different between in vivo and cell culture.

The Calcium/Calmodulin-Dependent Kinases II and IV as Therapeutic Targets in Neurodegenerative and Neuropsychiatric Disorders

CaMKII and CaMKIV are calcium/calmodulin-dependent kinases playing a rudimentary role in many regulatory processes in the organism. These kinases attract increasing interest due to their involvement primarily in memory and plasticity and various cellular functions. Although CaMKII and CaMKIV are mostly recognized as the important cogs in a memory machine, little is known about their effect on mood and role in neuropsychiatric diseases etiology. Here, we aimed to review the structure and functions of CaMKII and CaMKIV, as well as how these kinases modulate the animals’ behavior to promote antidepressant-like, anxiolytic-like, and procognitive effects. The review will help in the understanding of the roles of the above kinases in the selected neurodegenerative and neuropsychiatric disorders, and this knowledge can be used in future drug design.

Role of calcium/calmodulin-dependent kinase 2 in neurodevelopmental disorders

Neurodevelopmental disorders are a complex and heterogeneous group of neurological disorders characterized by their early-onset and estimated to affect more than 3% of children worldwide. The rapid advancement of sequencing technologies in the past years allowed the identification of hundreds of variants in several different genes causing neurodevelopmental disorders. Between those, new variants in the Calcium/calmodulin dependent protein kinase II (CAMK2) genes were recently linked to intellectual disability. Despite many years of research on CAMK2, this proves for the first time that this well-known and highly conserved molecule plays an important role in the human brain. In this review, we give an overview of the identified CAMK2 variants, and we speculate on potential mechanisms through which dysfunctions in CAMK2 result in neurodevelopmental disorders. Additionally, we discuss how the identification of CAMK2 variants might result in new exciting discoveries regarding the function of CAMK2 in the human brain.

Disruption of NEUROD2 causes a neurodevelopmental syndrome with autistic features via cell-autonomous defects in forebrain glutamatergic neurons

While the transcription factor NEUROD2 has recently been associated with epilepsy, its precise role during nervous system development remains unclear. Using a multi-scale approach, we set out to understand how Neurod2 deletion affects the development of the cerebral cortex in mice. In Neurod2 KO embryos, cortical projection neurons over-migrated, thereby altering the final size and position of layers. In juvenile and adults, spine density and turnover were dysregulated in apical but not basal compartments in layer 5 neurons. Patch-clamp recordings in layer 5 neurons of juvenile mice revealed increased intrinsic excitability. Bulk RNA sequencing showed dysregulated expression of many genes associated with neuronal excitability and synaptic function, whose human orthologs were strongly associated with autism spectrum disorders (ASD). At the behavior level, Neurod2 KO mice displayed social interaction deficits, stereotypies, hyperactivity, and occasionally spontaneous seizures. Mice heterozygous for Neurod2 had similar defects, indicating that Neurod2 is haploinsufficient. Finally, specific deletion of Neurod2 in forebrain excitatory neurons recapitulated cellular and behavioral phenotypes found in constitutive KO mice, revealing the region-specific contribution of dysfunctional Neurod2 in symptoms. Informed by these neurobehavioral features in mouse mutants, we identified eleven patients from eight families with a neurodevelopmental disorder including intellectual disability and ASD associated with NEUROD2 pathogenic mutations. Our findings demonstrate crucial roles for Neurod2 in neocortical development, whose alterations can cause neurodevelopmental disorders including intellectual disability and ASD.

CaMKIIβ in Neuronal Development and Plasticity: An Emerging Candidate in Brain Diseases

The calcium/calmodulin-dependent protein kinase II (CaMKII) is a ubiquitous and central player in Ca²⁺ signaling that is best known for its functions in the brain. In particular, the α isoform of CaMKII has been the subject of intense research and it has been established as a central regulator of neuronal plasticity. In contrast, little attention has been paid to CaMKIIβ, the other predominant brain isoform that interacts directly with the actin cytoskeleton, and the functions of CaMKIIβ in this organ remain largely unexplored. However, recently, the perturbation of CaMKIIβ expression has been associated with multiple neuropsychiatric and neurodevelopmental diseases, highlighting CAMK2B as a gene of interest. Herein, after highlighting the main structural and expression differences between the α and β isoforms, we will review the specific functions of CaMKIIβ, as described so far, in neuronal development and plasticity, as well as its potential implication in brain diseases.

Development of an L-type Ca2+ channel-dependent Ca2+ transient during the radial migration of cortical excitatory neurons

Increasing evidence has shown that voltage-gated L-type Ca²⁺ channels (LTCCs) are crucial for neurodevelopmental events, including neuronal differentiation/migration and neurite morphogenesis/extension. However, the time course of their functional maturation during the development of excitatory neurons remains unknown. Using a combination of fluorescence in situ hybridization and in utero electroporation-based labeling, we found that the transcripts of Cacna1c and Cacna1d, which encode the LTCC pore-forming subunits, were upregulated in the intermediate zone (IZ) during radial migration. Ca²⁺ imaging using GCaMP6s in acute brain slices showed spontaneous Ca²⁺ transients in migrating neurons throughout the IZ. Neurons in the IZ upper layer, especially in the multipolar-to-bipolar transition layer (TL), exhibited more frequent Ca²⁺ transients than adjacent layers and responded to FPL64176, a potent activator of LTCC. Consistently, nimodipine, an LTCC blocker, inhibited spontaneous Ca²⁺ transients in neurons in the TL. Collectively, we showed a hitherto unknown increased prevalence of LTCC-dependent Ca²⁺ transients in the TL of the IZ upper layer during the radial migration of excitatory neurons, which could be essential for the regulation of Ca²⁺-dependent neurodevelopmental processes.

Identification and prevention of heterotopias in mouse neocortical neural cell migration incurred by surgical damages during utero electroporation procedures

In utero electroporation (IUE) is a useful technique for gene delivery in embryonic mouse brain. IUE technique is used to investigate the mammalian brain development in vivo. However, according to recent studies, IUE methodology has some limitations like the formation of artificial ectopias and heterotopias at the micro-injection site. Thus far, the artificial heterotopias generated by physical trauma during IUE are rarely reported. Here, we reported the artificial heterotopias and ectopias generated from surgical damages of micropipette in detail, and moreover, we described the protocol to avoid these phenotypes. For the experimental purpose, we transferred empty plasmids (pCAGIG-GFP) with green fluorescent-labelled protein into the cortical cortex by IUE and then compared the structure of the cortex region between the injected and un-injected cerebral hemispheres. The coronary section showed that ectopias and heterotopias were appeared on imperfect-injected brains, and layer maker staining, which including Ctip2 and TBR1 and laminin, can differentiate the physical damage, revealing the neurons in artificial ectopic and heterotopic area were not properly arranged. Moreover, premature differentiation of neurons in ectopias and heterotopias were observed. To avoid heterotopias and ectopias, we carefully manipulated the method of IUE application. Thus, this study might be helpful for the in utero electroporator to distinguish the artificial ectopias and heterotopias that caused by the physical injury by microneedle and the ways to avoid those undesirable circumstances.

Regulation of Multifunctional Calcium/Calmodulin Stimulated Protein Kinases by Molecular Targeting

Multifunctional calcium/calmodulin-stimulated protein kinases control a broad range of cellular functions in a multitude of cell types. This family of kinases contain several structural similarities and all are regulated by phosphorylation, which either activates, inhibits or modulates their kinase activity. As these protein kinases are widely or ubiquitously expressed, and yet regulate a broad range of different cellular functions, additional levels of regulation exist that control these cell-specific functions. Of particular importance for this specificity of function for multifunctional kinases is the expression of specific binding proteins that mediate molecular targeting. These molecular targeting mechanisms allow pools of kinase in different cells, or parts of a cell, to respond differently to activation and produce different functional outcomes.

Calcium signalling: a key regulator of neuronal migration

Neuronal migration is a crucial event in neuronal development for the construction of brain architecture and neuronal networks. Newborn neurons proliferate in the germinal zone and start migration toward their final destination. Migrating neurons adopt different routes, cell shapes and migratory modes depending on extracellular factors and outer physical substrates. Intracellular Ca2+ is an essential second messenger that regulates diverse cellular functions by activating Ca2+-dependent signalling molecules that underlie Ca2+-responsive cellular functions. Neuronal migration during brain architecture construction is no exception. Spontaneous Ca2+ transients are observed in several types of migrating neurons, and a series of Ca2+-dependent signalling molecules governing neuronal migration has been identified. In this review, we first summarize the molecular mechanisms that trigger intracellular Ca2+ elevation in migrating neurons. In the latter half of this review, we provide an overview of the literature on Ca2+-dependent signalling molecules underlying neuronal migration.

Role of P2 receptors in normal brain development and in neurodevelopmental psychiatric disorders

The purinergic signaling system, including P2 receptors, plays an important role in various central nervous system (CNS) disorders. Over the last few decades, a substantial amount of accumulated data suggest that most P2 receptor subtypes (P2X1, 2, 3, 4, 6, and 7, and P2Y₁, ₂, ₆, ₁₂, and ₁₃) regulate neuronal/neuroglial developmental processes, such as proliferation, differentiation, migration of neuronal precursors, and neurite outgrowth. However, only a few of these subtypes (P2X2, P2X3, P2X4, P2X7, P2Y₁, and P2Y₂) have been investigated in the context of neurodevelopmental psychiatric disorders. The activation of these potential target receptors and their underlying mechanisms mainly influence the process of neuroinflammation. In particular, P2 receptor-mediated inflammatory cytokine release has been indicated to contribute to the complex mechanisms of a variety of CNS disorders. The released inflammatory cytokines could be utilized as biomarkers for neurodevelopmental and psychiatric disorders to improve the early diagnosis intervention, and prognosis. The population changes in gut microbiota after birth are closely linked to neurodevelopmental/neuropsychiatric disorders in later life; thus, the dynamic expression and function of P2 receptors on gut epithelial cells during disease processes indicate a novel avenue for the evaluation of disease progression and for the discovery of related therapeutic compounds.