Tubacin prevents neuronal migration defects and epileptic activity caused by rat Srpx2 silencing in utero

Pathogenic MTOR somatic variant causing focal cortical dysplasia drives hyperexcitability via overactivation of neuronal GluN2C N-methyl-D-aspartate receptors

OBJECTIVE

Genetic variations in proteins of the mechanistic target of rapamycin (mTOR) pathway cause a spectrum of neurodevelopmental disorders often associated with brain malformations and with intractable epilepsy. The mTORopathies are characterized by hyperactive mTOR pathway and comprise tuberous sclerosis complex (TSC) and focal cortical dysplasia (FCD) type II. How hyperactive mTOR translates into abnormal neuronal activity and hypersynchronous network remains to be better understood. Previously, the role of upregulated GluN2C-containing glutamate-gated N-methyl-D-aspartate receptors (NMDARs) has been demonstrated for germline defects in the TSC genes. Here, we questioned whether this mechanism would expand to other mTORopathies in the different context of a somatic genetic variation of the MTOR protein recurrently found in FCD type II.

METHODS

We used a rat model of FCD created by in utero electroporation of neural progenitors of dorsal telencephalon with expression vectors encoding either the wild-type or the pathogenic MTOR variant (p.S2215F). In this mosaic configuration, patch-clamp whole-cell recordings of the electroporated, spiny stellate neurons and extracellular recordings of the electroporated areas were performed in neocortical slices. Selective inhibitors were used to target mTOR activity and GluN2C-mediated currents.

RESULTS

Neurons expressing the mutant protein displayed an excessive activation of GluN2C NMDAR-mediated spontaneous excitatory postsynaptic currents. GluN2C-dependent increase in spontaneous spiking activity was detected in the area of electroporated neurons in the mutant condition and was restricted to a critical time window between postnatal days P9 and P20.

SIGNIFICANCE

Somatic MTOR pathogenic variant recurrently found in FCD type II resulted in overactivation of GluN2C-mediated neuronal NMDARs in neocortices of rat pups. The related and time-restricted local hyperexcitability was sensitive to subunit GluN2C-specific blockade. Our study suggests that GluN2C-related pathomechanisms might be shared in common by mTOR-related brain disorders.

Molecular mechanisms underlying microglial sensing and phagocytosis in synaptic pruning

Microglia are the main non-neuronal cells in the central nervous system that have important roles in brain development and functional connectivity of neural circuits. In brain physiology, highly dynamic microglial processes are facilitated to sense the surrounding environment and stimuli. Once the brain switches its functional states, microglia are recruited to specific sites to exert their immune functions, including the release of cytokines and phagocytosis of cellular debris. The crosstalk of microglia between neurons, neural stem cells, endothelial cells, oligodendrocytes, and astrocytes contributes to their functions in synapse pruning, neurogenesis, vascularization, myelination, and blood-brain barrier permeability. In this review, we highlight the neuron-derived "find-me," "eat-me," and "don't eat-me" molecular signals that drive microglia in response to changes in neuronal activity for synapse refinement during brain development. This review reveals the molecular mechanism of neuron-microglia interaction in synaptic pruning and presents novel ideas for the synaptic pruning of microglia in disease, thereby providing important clues for discovery of target drugs and development of nervous system disease treatment methods targeting synaptic dysfunction.

SRPX2 promotes cancer cell proliferation and migration of papillary thyroid cancer

Thyroid cancer is the endocrine tumor with the highest incidence at present. It originates from the thyroid follicular epithelium or follicular paraepithelial cells. There is an increasing incidence of thyroid cancer all over the world. We found that SRPX2 expression level was higher in papillary thyroid tumors than in normal thyroid tissues, and SRPX2 expression was closely related to tumor grade and clinical prognosis. Previous reports showed that SRPX2 could function by activating PI3K/AKT signaling pathway. In addition, in vitro experiments showed that SRPX2 promoted the proliferation and migration of papillary thyroid cancer (PTC). In conclusion, SRPX2 could promote the malignant development of PTC. This may be a potential treatment target for PTC.

X-linked neuronal migration disorders: Gender differences and insights for genetic screening

Cortical development depends on neuronal migration of both excitatory and inhibitory interneurons. Neuronal migration disorders (NMDs) are conditions characterised by anatomical cortical defects leading to varying degrees of neurocognitive impairment, developmental delay and seizures. Refractory epilepsy affects 15 million people worldwide, and it is thought that cortical developmental disorders are responsible for 25% of childhood cases. However, little is known about the epidemiology of these disorders, nor are their aetiologies fully understood, though many are associated with sporadic genetic mutations. In this review, we aim to highlight X-linked NMDs including lissencephaly, periventricular nodular heterotopia and polymicrogyria because of their mostly familial inheritance pattern. We focus on the most prominent genes responsible: including DCX, ARX, FLNA, FMR1, L1CAM, SRPX2, DDX3X, NSHDL, CUL4B and OFD1, outlining what is known about their prevalence among NMDs, and the underlying pathophysiology. X-linked disorders are important to recognise clinically, as females often have milder phenotypes. Consequently, there is a greater chance they survive to reproductive age and risk passing the mutations down. Effective genetic screening is important to prevent and treat these conditions, and for this, we need to know gene mutations and have a clear understanding of the function of the genes involved. This review summarises the knowledge base and provides clear direction for future work by both scientists and clinicians alike.

SRPX2 attenuated oxygen–glucose deprivation and reperfusion-induced injury in cardiomyocytes via alleviating endoplasmic reticulum stress-induced apoptosis through targeting PI3K/Akt/mTOR axis

Myocardial infraction (MI) is the leading cause of high morbidity and mortality worldwide. It was still urgently needed to find new and effective drugs for MI treatment by the use of myocardial ischemia/reperfusion (I/R) model. Sushi repeats contain the protein X-Linked 2 (SRPX2), which regulates a variety of important cell functions. However, its possible role in myocardial I/R and the progression of MI is still unclear. In this study, we investigated the role of SRPX2 in myocardial I/R. SRPX2 showed low expression in IR rats and H9C2 cells induced by oxygen–glucose deprivation/reperfusion (OGD/R). SRPX2 could increase OGD/R-induced H9C2 cell survival. In addition, SRPX2 suppressed the apoptosis of OGD/R-induced H9C2 cells. Furthermore, we found that SRPX2 could inhibit ER stress induced by OGD/R in H9C2 cells. Mechanically, we found that SRPX2 suppressed the PI3K/Akt/mTOR pathway, thus attenuating OGD/R -induced injury in H9C2 cells. Therefore, SRPX2 has the potential to serve as a target for MI treatment.

Synapse Formation and Function Across Species: Ancient Roles for CCP, CUB, and TSP-1 Structural Domains

The appearance of synapses was a crucial step in the creation of the variety of nervous systems that are found in the animal kingdom. With increased complexity of the organisms came a greater number of synaptic proteins. In this review we describe synaptic proteins that contain the structural domains CUB, CCP, or TSP-1. These domains are found in invertebrates and vertebrates, and CUB and CCP domains were initially described in proteins belonging to the complement system of innate immunity. Interestingly, they are found in synapses of the nematode C. elegans, which does not have a complement system, suggesting an ancient function. Comparison of the roles of CUB-, CCP-, and TSP-1 containing synaptic proteins in various species shows that in more complex nervous systems, these structural domains are combined with other domains and that there is partial conservation of their function. These three domains are thus basic building blocks of the synaptic architecture. Further studies of structural domains characteristic of synaptic proteins in invertebrates such as C. elegans and comparison of their role in mammals will help identify other conserved synaptic molecular building blocks. Furthermore, this type of functional comparison across species will also identify structural domains added during evolution in correlation with increased complexity, shedding light on mechanisms underlying cognition and brain diseases.

Local administration of liposomal-based Srpx2 gene therapy reverses pulmonary fibrosis by blockading fibroblast-to-myofibroblast transition

Idiopathic pulmonary fibrosis (IPF) is a chronic and progressive fatal interstitial lung disease characterized by abnormal transition and proliferation of fibroblasts. The uncontrolled transition of fibroblasts, commonly known as myofibroblasts, are the principal source of the enormous extracellular matrix (ECM) depositing in lung parenchyma, leading to gradual failure of gas exchange and mortality of the patients. However, up to now, rare effective therapeutic strategies have been developed to blockade fibroblast-to-myofibroblast transition (FMT) in IPF.

Method: We illustrated that the lungs originated from IPF patients and mice with pulmonary fibrosis are characterized by the overexpression of sushi-repeat-containing protein, X-linked 2 (SRPX2). Further functionality studies identified the pivotal role of SRPX2 in FMT. Mechanistically, SRPX2 was involved in a TGFβR1/SMAD3/SRPX2/AP1/SMAD7 positive feedback loop. Specifically, SRPX2 was upregulated by TGF-β1 in a TGFβR1/SMAD3-dependent manner, after which SRPX2 in turn repressed the expression of AP1, subsequently minimized SMAD7 expression, through which it reduced the formation of inhibitory complex with TGFβR1 and enhanced SMAD signaling pathway to promote FMT and exacerbate pulmonary fibrosis. Notably, intratracheal administration of siRNA-loaded liposomes could effectively suppress the expression of Srpx2 in the lung and remarkably protect mice against BLM-induced pulmonary fibrosis, concomitant with a significant reduction of FMT.

Results: Accordingly, these data indicate that Srpx2 plays an essential role in the pathogenesis of pulmonary fibrosis and suggests the strategy aiming at silencing Srpx2 could be a promising therapeutic approach against pulmonary fibrosis in clinical settings.

The endogenous neuronal complement inhibitor SRPX2 protects against complement-mediated synapse elimination during development

Complement-mediated synapse elimination has emerged as an important process in both brain development and neurological diseases, but whether neurons express complement inhibitors that protect synapses against complement-mediated synapse elimination remains unknown. Here, we show that the sushi domain protein SRPX2 is a neuronally expressed complement inhibitor that regulates complement-dependent synapse elimination. SRPX2 directly binds to C1q and blocks its activity, and SRPX2-/Y mice show increased C3 deposition and microglial synapse engulfment. They also show a transient decrease in synapse numbers and increase in retinogeniculate axon segregation in the lateral geniculate nucleus. In the somatosensory cortex, SRPX2-/Y mice show decreased thalamocortical synapse numbers and increased spine pruning. C3-/-;SRPX2-/Y double-knockout mice exhibit phenotypes associated with C3-/- mice rather than SRPX2-/Y mice, which indicates that C3 is necessary for the effect of SRPX2 on synapse elimination. Together, these results show that SRPX2 protects synapses against complement-mediated elimination in both the thalamus and the cortex.

Cortactin deacetylation by HDAC6 and SIRT2 regulates neuronal migration and dendrite morphogenesis during cerebral cortex development

Proper dendrite morphogenesis and neuronal migration are crucial for cerebral cortex development and neural circuit formation. In this study, we sought to determine if the histone deacetylase HDAC6 plays a role in dendrite development and neuronal migration of pyramidal neurons during cerebral cortex development. It was observed that knockdown of HDAC6 leads to defective dendrite morphogenesis and abnormal Golgi polarization in vitro, and the expression of wild type cortactin or deacetyl-mimetic cortactin 9KR rescued the defective phenotypes of the HDAC6 knockdown neurons. This suggests that HDAC6 promotes dendritic growth and Golgi polarization through cortactin deacetylation in vitro. We also demonstrated that ectopic expression of SIRT2, a cytoplasmic NAD⁺ − dependent deacetylase, suppresses the defects of HDAC6 knockdown neurons. These results indicate that HDAC6 and SIRT2 may be functionally redundant during dendrite development. Neurons transfected with both HDAC6 and SIRT2 shRNA or acetyl-mimetic cortactin 9KQ showed slow radial migration compared to the control cells during cerebral cortex development. Furthermore, a large portion of cortactin 9KQ-expressing pyramidal neurons at layer II/III in the cerebral cortex failed to form an apical dendrite toward the pial surface and had an increased number of primary dendrites, and the percentage of neurons with dendritic Golgi decreased in cortactin 9KQ-expressing cells, compared to control neurons. Taken together, this study suggests that HDAC6 and SIRT2 regulate neuronal migration and dendrite development through cortactin deacetylation in vivo.

α-Tubulin Acetylation Restricts Axon Overbranching by Dampening Microtubule Plus-End Dynamics in Neurons

Axon growth is tightly controlled to establish functional neural circuits during brain development. Despite the belief that cytoskeletal dynamics is critical for cell morphology, how microtubule acetylation regulates axon development in the mammalian central nervous system remains unclear. Here, we report that loss of α-tubulin acetylation by ablation of MEC-17 in mice predisposes neurons to axon overbranching and overgrowth. Introduction of MEC-17F183A lacking α-tubulin acetyltransferase activity into MEC-17-deficient neurons failed to rescue axon defects. Moreover, loss of α-tubulin acetylation led to increases in microtubule debundling, microtubule invasion into filopodia and growth cones, and microtubule plus-end dynamics along the axon. Taxol application dampened microtubule hyperdynamics and suppressed axon overbranching and overgrowth in MEC-17-deficient neurons. Thus, our study reveals that α-tubulin acetylation acts as a brake for axon overbranching and overgrowth by dampening microtubule dynamics, providing insight into the role of microtubule post-translational modifications in regulating neural development.

Exploring the association between SRPX2 variants and neurodevelopment: How causal is it?

The SRPX2 gene (Sushi-repeat-containing protein, X-linked, 2, OMIM*300642), located on Xq22.1, encodes a secreted protein that is highly expressed in neurons of cerebral cortex. SRPX2 was first implicated in neurodevelopment, learning and rolandic seizure when two patients with potentially pathogenic variants, c.980A>G (p.Asn327Ser) and c.215A>C (p.Tyr72Ser), in SRPX2 gene were identified. Subsequent experimental studies demonstrated that SRPX2 is needed for vocalization and synapse formation in mice, and that both silencing SRPX2 and injecting (p.Asn327Ser) in mouse models results in alteration in neuronal migration in cerebral cortex and epilepsy. A number of studies demonstrated that SRPX2 interacts with FOXP2 (Foxhead box protein P2), a gene responsible for speech and language disorder, and that FoxP2 controls timing and level of expression of SRPX2. Despite the supportive evidence for the role of SRPX2 in speech and language development and disorders, there are questions over its definitive association with neurodevelopmental disorders and epilepsy. In this paper, the role of SRPX2 as one in a network of many genes involved in speech and language is discussed. The goal of this paper is to examine the role of SRPX2 variants through describing two patients with potentially pathogenic variants in SRPX2, c.751G>C (p.Ala251Pro) and c.762G>T (p.Lys254Asn) presenting with language and motor delay, intellectual disability as well as congenital anomalies. We explore the contribution of SRPX2 variants to clinical phenotype in our patients and conclude that these variants at least partially explain the phenotype. Further studies are necessary to establish and confirm the association between SRPX2 and neurodevelopment particularly speech and language development.

[Speech and language neurodevelopmental disorders in epilepsy: pathophysiologic mechanisms and therapeutic approaches]

Speech and language development may be impaired in all forms of epilepsy involving specialized functional areas in the dominant cerebral hemisphere and their connections. The concept of epilepsy-aphasia clinical spectrum was recently proposed, but the notion of aphasia is quite conditional here as many of these patients demonstrate disorders of speech and language development from their infancy. Those forms of epilepsy are considered as continuum from the most severe Landau-Kleffner syndrome (LKS) and epilepsy with continuous spike-and-wave during sleep (CSWS) (also indicating as electrical status epilepticus during sleep - ESES) to intermediate epilepsy-aphasia disorders (with incomplete correspondence to diagnostic criteria of LKS and epilepsy with CSWS). The mild end of the spectrum is represented by benign childhood epilepsy with centrotemporal spikes (rolandic), which is often associated with speech and language disorders. The importance of genetic factors is discussed, including mutations in SRPX2, GRIN2A and other genes. The perspectives of individualized pharmacotherapy in epilepsy, co-morbid with neurodevelopmental disorders or impairments of speech and language development, are depending on the progress in genetic studies. In the new generation of antiepileptic drugs the positive influence on neuroplasticity mechanisms and higher cerebral functions are supposed for levetiracetam.

Sociability and synapse subtype-specific defects in mice lacking SRPX2, a language-associated gene

The FoxP2 transcription factor and its target genes have been implicated in developmental brain diseases with a prominent language component, such as developmental verbal dyspraxia and specific language impairment. How FoxP2 affects neural circuitry development remains poorly understood. The sushi domain protein SRPX2 is a target of FoxP2, and mutations in SRPX2 are associated with language defects in humans. We have previously shown that SRPX2 is a synaptogenic protein that increases excitatory synapse density. Here we provide the first characterization of mice lacking the SRPX2 gene, and show that these mice exhibit defects in both neural circuitry and communication and social behaviors. Specifically, we show that mice lacking SRPX2 show a specific reduction in excitatory VGlut2 synapses in the cerebral cortex, while VGlut1 and inhibitory synapses were largely unaffected. SRPX2 KO mice also exhibit an abnormal ultrasonic vocalization ontogenetic profile in neonatal pups, and reduced preference for social novelty. These data demonstrate a functional role for SRPX2 during brain development, and further implicate FoxP2 and its targets in regulating the development of vocalization and social circuits.

Sushi repeat-containing protein X-linked 2: A novel phylogenetically conserved hypothalamo-pituitary protein

Sushi repeat-containing protein X-linked 2 (SRPX2) is a novel protein associated with language development, synaptic plasticity, tissue remodeling, and angiogenesis. We investigated the expression and spatial localization of SRPX2 in normal mouse, rat, monkey, and human brain using in situ hybridization and immunohistochemistry. Antibody specificity was determined using in vitro siRNA based silencing of SRPX2. Cell type-specific expression was verified by double-labeling with oxytocin or vasopressin. Western blot was used to detect SRPX2 protein in rat and human plasma and cerebrospinal fluid. Unexpectedly, SRPX2 mRNA expression levels were strikingly higher in the hypothalamus as compared to the cortex. All SRPX2 immunoreactive (ir) neurons were localized in the hypothalamic paraventricular, periventricular, and supraoptic nuclei in mouse, rat, monkey, and human brain. SRPX2 colocalized with vasopressin or oxytocin in paraventricular and supraoptic neurons. Hypothalamic SRPX2-ir positive neurons gave origin to dense projections traveling ventrally and caudally toward the hypophysis. Intense axonal varicosities and terminal arborizations were identified in the rat and human neurohypophysis. SRPX2-ir cells were also found in the adenohypophysis. Light SRPX2-ir projections were observed in the dorsal and ventral raphe, locus coeruleus, and the nucleus of the solitary tract in mouse, rat and monkey. SRPX2 protein was also detected in plasma and CSF. Our data revealed intense phylogenetically conserved expression of SRPX2 protein in distinct hypothalamic nuclei and the hypophysis, suggesting its active role in the hypothalamo-pituitary axis. The presence of SRPX2 protein in the plasma and CSF suggests that some of its functions depend on secretion into body fluids.

In Utero Administration of Drugs Targeting Microglia Improves the Neurodevelopmental Outcome Following Cytomegalovirus Infection of the Rat Fetal Brain

Congenital cytomegalovirus (CMV) infections represent one leading cause of neurodevelopmental disorders. Recently, we reported on a rat model of CMV infection of the developing brain in utero, characterized by early and prominent infection and alteration of microglia-the brain-resident mononuclear phagocytes. Besides their canonical function against pathogens, microglia are also pivotal to brain development. Here we show that CMV infection of the rat fetal brain recapitulated key postnatal phenotypes of human congenital CMV including increased mortality, sensorimotor impairment reminiscent of cerebral palsy, hearing defects, and epileptic seizures. The possible influence of early microglia alteration on those phenotypes was then questioned by pharmacological targeting of microglia during pregnancy. One single administration of clodronate liposomes in the embryonic brains at the time of CMV injection to deplete microglia, and maternal feeding with doxycyxline throughout pregnancy to modify microglia in the litters' brains, were both associated with dramatic improvements of survival, body weight gain, sensorimotor development and with decreased risk of epileptic seizures. Improvement of microglia activation status did not persist postnatally after doxycycline discontinuation; also, active brain infection remained unchanged by doxycycline. Altogether our data indicate that early microglia alteration, rather than brain CMV load per se, is instrumental in influencing survival and the neurological outcomes of CMV-infected rats, and suggest that microglia might participate in the neurological outcome of congenital CMV in humans. Furthermore this study represents a first proof-of-principle for the design of microglia-targeted preventive strategies in the context of congenital CMV infection of the brain.

Genetics of human epilepsies: Continuing progress

Numerous epilepsy genes have been identified in the last years, mostly in the (rare) monogenic forms and thanks to the increased availability and the decreased cost of next-generation sequencing approaches. Besides the somehow expected group of epilepsy genes encoding various ion channel subunits (e.g. sodium or potassium channel subunits, or GABA receptors, or glutamate-gated NMDA receptors), more diversity has emerged recently, with novel epilepsy genes encoding proteins playing a wide range of physiological roles at the cellular and molecular levels, such as synaptic proteins, members of the mTOR pathway, or proteins involved in chromatin remodeling. The overall picture is somehow complicated: one given epilepsy gene can be associated with more than one epileptic phenotype, and with variable degrees of severity, from the benign to the severe forms (e.g. epileptic encephalopathies), and with various comorbid conditions such as migraine or autism spectrum of disorders. Conversely, one given epileptic syndrome may be associated with different genes, some of which have obvious links with each other (e.g. encoding different subunits of the same receptor) while other ones have no clear relationships. Also genomic copy number variations have been detected, some of which, albeit rare, may confer high risk to epilepsy. Whereas translation from gene identification to targeted medicine still remains challenging, progress in epilepsy genetics is currently revolutionizing genetic-based diagnosis and genetic counseling. Epilepsy gene identification also represents a key entry point to start in deciphering the underlying pathophysiological mechanisms via the design and the study of the most pertinent cellular and animal models - which may in turn provide proofs-of-principle for future applications in human epilepsies.

Functional Properties of Human NMDA Receptors Associated with Epilepsy-Related Mutations of GluN2A Subunit

Genetic variants of the glutamate activated N-methyl-D-aspartate (NMDA) receptor (NMDAR) subunit GluN2A are associated with the hyperexcitable states manifested by epileptic seizures and interictal discharges in patients with disorders of the epilepsy-aphasia spectrum (EAS). The variants found in sporadic cases and families are of different types and include microdeletions encompassing the corresponding GRIN2A gene as well as nonsense, splice-site and missense GRIN2A defects. They are located at different functional domains of GluN2A and no clear genotype-phenotype correlation has emerged yet. Moreover, GluN2A variants may be associated with phenotypic pleiotropy. Deciphering the consequences of pathogenic GRIN2A variants would surely help in better understanding of the underlying mechanisms. This emphasizes the need for functional studies to unravel the basic functional properties of each specific NMDAR variant. In the present study, we have used patch-clamp recordings to evaluate kinetic changes of mutant NMDARs reconstituted after co-transfection of cultured cells with the appropriate expression vectors. Three previously identified missense variants found in patients or families with disorders of the EAS and situated in the N-terminal domain (p.Ile184Ser) or in the ligand-binding domain (p.Arg518His and p.Ala716Thr) of GluN2A were studied in both the homozygous and heterozygous conditions. Relative surface expression and current amplitude were significantly reduced for NMDARs composed of mutant p.Ile184Ser and p.Arg518His, but not p.Ala716His, as compared with wild-type (WT) NMDARs. Amplitude of whole-cell currents was still drastically decreased when WT and mutant p.Arg518His-GluN2A subunits were co-expressed, suggesting a dominant-negative mechanism. Activation times were significantly decreased in both homozygous and heterozygous conditions for the two p.Ile184Ser and p.Arg518His variants, but not for p.Ala716His. Deactivation also significantly increased for p.Ile184Ser variant in the homozygous but not the heterozygous state while it was increased for p.Arg518His in both states. Our data indicate that p.Ile184Ser and p.Arg518His GluN2A variants both impacted on NMDAR function, albeit differently, whereas p.Ala716His did not significantly influence NMDAR kinetics, hence partly questioning its direct and strong pathogenic role. This study brings new insights into the functional impact that GRIN2A variants might have on NMDAR kinetics, and provides a mechanistic explanation for the neurological manifestations seen in the corresponding human spectrum of disorders.

Next-generation DNA sequencing identifies novel gene variants and pathways involved in specific language impairment

A significant proportion of children have unexplained problems acquiring proficient linguistic skills despite adequate intelligence and opportunity. Developmental language disorders are highly heritable with substantial societal impact. Molecular studies have begun to identify candidate loci, but much of the underlying genetic architecture remains undetermined. We performed whole-exome sequencing of 43 unrelated probands affected by severe specific language impairment, followed by independent validations with Sanger sequencing, and analyses of segregation patterns in parents and siblings, to shed new light on aetiology. By first focusing on a pre-defined set of known candidates from the literature, we identified potentially pathogenic variants in genes already implicated in diverse language-related syndromes, including ERC1, GRIN2A, and SRPX2. Complementary analyses suggested novel putative candidates carrying validated variants which were predicted to have functional effects, such as OXR1, SCN9A and KMT2D. We also searched for potential "multiple-hit" cases; one proband carried a rare AUTS2 variant in combination with a rare inherited haplotype affecting STARD9, while another carried a novel nonsynonymous variant in SEMA6D together with a rare stop-gain in SYNPR. On broadening scope to all rare and novel variants throughout the exomes, we identified biological themes that were enriched for such variants, including microtubule transport and cytoskeletal regulation.

SRPX2 Enhances the Epithelial-Mesenchymal Transition and Temozolomide Resistance in Glioblastoma Cells

Glioblastoma (GBM) is the most common and most aggressive central nervous system tumor in adults. Due to GBM cell invasiveness and resistance to chemotherapy, current medical interventions are not satisfactory, and the prognosis for GBM is poor. It is necessary to investigate the underlying mechanism of GBM metastasis and drug resistance so that more effective treatments can be developed for GBM patients. sushi repeat-containing protein, X-linked 2 (SRPX2) is a prognostic biomarker in many different cancer cell lines and is associated with poor prognosis in cancer patients. SRPX2 overexpression promotes interactions between tumor and endothelial cells, leading to tumor progression and metastasis. We hypothesize that SRPX2 also contributes to GBM chemotherapy resistance and metastasis. Our results revealed that GBM tumor samples from 42 patients expressed higher levels of SRPX2 than the control normal brain tissue samples. High-SRPX2 expression levels are correlated with poor prognosis in those patients, as well as resistance to temozolomide in cultured GBM cells. Up-regulating SRPX2 expression in cultured GBM cell lines facilitated invasiveness and migration of GBM cells, while down-regulating SRPX2 through RNA interference was inhibitory. These results suggest that SRPX2 plays an important role in GBM metastasis. Epithelial to mesenchymal transition (EMT) is one of the processes that facilitate GBM metastasis and resistance to chemotherapy. EMT marker expression was decreased in SRPX2 down-regulated GBM cells, and MAPK signaling pathway marker expression was also decreased when SRPX2 is knocked down in GBM-cultured cells. Blocking the MAPK signaling pathway inhibited GBM metastasis but did not inhibit cell invasion and migration in SRPX2 down-regulated cells. Our results indicate that SRPX2 facilitates GBM metastasis by enhancing the EMT process via the MAPK signaling pathway.

Cytomegalovirus Infection of the Rat Developing Brain In Utero Prominently Targets Immune Cells and Promotes Early Microglial Activation

Background

Congenital cytomegalovirus infections are a leading cause of neurodevelopmental disorders in human and represent a major health care and socio-economical burden. In contrast with this medical importance, the pathophysiological events remain poorly known. Murine models of brain cytomegalovirus infection, mostly neonatal, have brought recent insights into the possible pathogenesis, with convergent evidence for the alteration and possible involvement of brain immune cells.

Objectives and Methods

In order to confirm and expand those findings, particularly concerning the early developmental stages following infection of the fetal brain, we have created a model of in utero cytomegalovirus infection in the developing rat brain. Rat cytomegalovirus was injected intraventricularly at embryonic day 15 (E15) and the brains analyzed at various stages until the first postnatal day, using a combination of gene expression analysis, immunohistochemistry and multicolor flow cytometry experiments.

Results

Rat cytomegalovirus infection was increasingly seen in various brain areas including the choroid plexi and the ventricular and subventricular areas and was prominently detected in CD45^low/int, CD11b⁺ microglial cells, in CD45^high, CD11b⁺ cells of the myeloid lineage including macrophages, and in CD45⁺, CD11b^– lymphocytes and non-B non-T cells. In parallel, rat cytomegalovirus infection of the developing rat brain rapidly triggered a cascade of pathophysiological events comprising: chemokines upregulation, including CCL2-4, 7 and 12; infiltration by peripheral cells including B-cells and monocytes at E17 and P1, and T-cells at P1; and microglia activation at E17 and P1.

Conclusion

In line with previous findings in neonatal murine models and in human specimen, our study further suggests that neuroimmune alterations might play critical roles in the early stages following cytomegalovirus infection of the brain in utero. Further studies are now needed to determine which role, whether favorable or detrimental, those putative double-edge swords events actually play.

Epileptogenesis after traumatic brain injury in Plaur-deficient mice

Binding of the extracellular matrix proteinase urokinase-type plasminogen activator (uPA) to its receptor, uPAR, regulates tissue remodeling during development and after injury in different organs, including the brain. Accordingly, mutations in the Plaur gene, which encodes uPAR, have been linked to language deficits, autism, and epilepsy, both in mouse and human. Whether uPAR deficiency modulates epileptogenesis and comorbidogenesis after brain injury, however, is unknown. To address this question, we induced traumatic brain injury (TBI) by controlled cortical impact (CCI) in 10 wild-type (Wt-CCI) and 16 Plaur-deficient (uPAR-CCI) mice. Sham-operated mice served as controls (10 Wt-sham, 10 uPAR-sham). During the 4-month follow-up, the mice were neurophenotyped by assessing the somatomotor performance with the composite neuroscore test, emotional learning and memory with fear conditioning to tone and context, and epileptogenesis with videoelectroencephalography monitoring and the pentylenetetrazol (PTZ) seizure susceptibility test. At the end of the testing, the mice were perfused for histology to analyze cortical and hippocampal neurodegeneration and mossy fiber sprouting. Fourteen percent (1/7) of the mice in the Wt-CCI and 0% in the uPAR-CCI groups developed spontaneous seizures (p>0.05; chi-square). Both the Wt-CCI and uPAR-CCI groups showed increased seizure susceptibility in the PTZ test (p<0.05), impaired recovery of motor function (p<0.001), and neurodegeneration in the hippocampus and cortex (p<0.05) compared with the corresponding sham-operated controls. Motor recovery and emotional learning showed a genotype effect, being more impaired in uPAR-CCI than in Wt-CCI mice (p<0.05). The findings of the present study indicate that uPAR deficiency does not increase susceptibility to epileptogenesis after CCI injury but has an unfavorable comorbidity-modifying effect after TBI.

Inhibiting histone deacetylase 6 partly protects cultured rat cortical neurons from oxygen‑glucose deprivation‑induced necroptosis

Necroptosis has an important role in ischemia-reperfusion damage. The expression of histone deacetylase 6 (HDAC6) is upregulated in neurons following ischemia-reperfusion, however, whether HDAC6 is closely involved in the necroptosis, which occurs during ischemia-reperfusion damage remains to be elucidated. In the present study, the roles of HDAC6 in the necroptosis of cultured rat cortical neurons were investigated in a oxygen-glucose deprivation (OGD) model. The results demonstrated that OGD induced marked necroptosis of cultured rat cortical neurons and upregulated the expression of HDAC6 in the cultured neurons, compared with the control (P<0.05). The necroptosis inhibitor, necrostatin-1 (Nec-1), decreased The expression of HDAC6 in the OGD-treated cultured neurons, accompanied by the inhibition of necroptosis. Further investigation revealed that, compared with OGD treatment alone, inhibiting the activity of HDAC6 with tubacin, a specific HDAC6 inhibitor, reduced the OGD-induced necroptosis of the cultured rat cortical neurons (P<0.05), which was similar to the change following treatment with Nec-1 (P>0.05). In addition, inhibiting the activity of HDAC6 reversed the OGD-induced increase of reactive oxygen species (ROS) and the OGD-induced decrease of acetylated tubulin in the cultured rat cortical neurons (P<0.05), compared with the neurons treated with OGD alone). The levels of acetylated tubulin in the cultured neurons following treatment with OGD and tubacin were significantly higher than those in the control (P<0.05). These results suggested that HDAC6 was involved in the necroptosis of neurons during ischemia-reperfusion by modulating the levels of ROS and acetylated tubulin.

Insights into the genetic foundations of human communication

The human capacity to acquire sophisticated language is unmatched in the animal kingdom. Despite the discontinuity in communicative abilities between humans and other primates, language is built on ancient genetic foundations, which are being illuminated by comparative genomics. The genetic architecture of the language faculty is also being uncovered by research into neurodevelopmental disorders that disrupt the normally effortless process of language acquisition. In this article, we discuss the strategies that researchers are using to reveal genetic factors contributing to communicative abilities, and review progress in identifying the relevant genes and genetic variants. The first gene directly implicated in a speech and language disorder was FOXP2. Using this gene as a case study, we illustrate how evidence from genetics, molecular cell biology, animal models and human neuroimaging has converged to build a picture of the role of FOXP2 in neurodevelopment, providing a framework for future endeavors to bridge the gaps between genes, brains and behavior.

Efficient strategy for the molecular diagnosis of intellectual disability using targeted high-throughput sequencing

Background

Intellectual disability (ID) is characterised by an extreme genetic heterogeneity. Several hundred genes have been associated to monogenic forms of ID, considerably complicating molecular diagnostics. Trio-exome sequencing was recently proposed as a diagnostic approach, yet remains costly for a general implementation.

Methods

We report the alternative strategy of targeted high-throughput sequencing of 217 genes in which mutations had been reported in patients with ID or autism as the major clinical concern. We analysed 106 patients with ID of unknown aetiology following array-CGH analysis and other genetic investigations. Ninety per cent of these patients were males, and 75% sporadic cases.

Results

We identified 26 causative mutations: 16 in X-linked genes (ATRX, CUL4B, DMD, FMR1, HCFC1, IL1RAPL1, IQSEC2, KDM5C, MAOA, MECP2, SLC9A6, SLC16A2, PHF8) and 10 de novo in autosomal-dominant genes (DYRK1A, GRIN1, MED13L, TCF4, RAI1, SHANK3, SLC2A1, SYNGAP1). We also detected four possibly causative mutations (eg, in NLGN3) requiring further investigations. We present detailed reasoning for assigning causality for each mutation, and associated patients’ clinical information. Some genes were hit more than once in our cohort, suggesting they correspond to more frequent ID-associated conditions (KDM5C, MECP2, DYRK1A, TCF4). We highlight some unexpected genotype to phenotype correlations, with causative mutations being identified in genes associated to defined syndromes in patients deviating from the classic phenotype (DMD, TCF4, MECP2). We also bring additional supportive (HCFC1, MED13L) or unsupportive (SHROOM4, SRPX2) evidences for the implication of previous candidate genes or mutations in cognitive disorders.

Conclusions

With a diagnostic yield of 25% targeted sequencing appears relevant as a first intention test for the diagnosis of ID, but importantly will also contribute to a better understanding regarding the specific contribution of the many genes implicated in ID and autism.

The GABA excitatory/inhibitory developmental sequence: a personal journey

The developing brain is talkative but its language is not that of the adult. Most if not all voltage and transmitter-gated ionic currents follow a developmental sequence and network-driven patterns differ in immature and adult brains. This is best illustrated in studies engaged almost three decades ago in which we observed elevated intracellular chloride (Cl(-))i levels and excitatory GABA early during development and a perinatal excitatory/inhibitory shift. This sequence is observed in a wide range of brain structures and animal species suggesting that it has been conserved throughout evolution. It is mediated primarily by a developmentally regulated expression of the NKCC1 and KCC2 chloride importer and exporter respectively. The GABAergic depolarization acts in synergy with N-methyl-d-aspartate (NMDA) receptor-mediated and voltage-gated calcium currents to enhance intracellular calcium exerting trophic effects on neuritic growth, migration and synapse formation. These sequences can be deviated in utero by genetic or environmental insults leading to a persistence of immature features in the adult brain. This "neuroarcheology" concept paves the way to novel therapeutic perspectives based on the use of drugs that block immature but not adult currents. This is illustrated notably with the return to immature high levels of chloride and excitatory actions of GABA observed in many pathological conditions. This is due to the fact that in the immature brain a down regulation of KCC2 and an up regulation of NKCC1 are seen. Here, I present a personal history of how an unexpected observation led to novel concepts in developmental neurobiology and putative treatments of autism and other developmental disorders. Being a personal account, this review is neither exhaustive nor provides an update of this topic with all the studies that have contributed to this evolution. We all rely on previous inventors to allow science to advance. Here, I present a personal summary of this topic primarily to illustrate why we often fail to comprehend the implications of our own observations. They remind us - and policy deciders - why Science cannot be programed, requiring time, and risky investigations that raise interesting questions before being translated from bench to bed. Discoveries are always on sideways, never on highways.

Analysis of ELP4, SRPX2, and interacting genes in typical and atypical rolandic epilepsy

Rolandic epilepsy (RE) and its atypical variants (atypical rolandic epilepsy, ARE) along the spectrum of epilepsy-aphasia disorders are characterized by a strong but largely unknown genetic basis. Two genes with a putative (ELP4) or a proven (SRPX2) function in neuronal migration were postulated to confer susceptibility to parts of the disease spectrum: the ELP4 gene to centrotemporal spikes and SRPX2 to ARE. To reexamine these findings, we investigated a cohort of 280 patients of European ancestry with RE/ARE for the etiological contribution of these genes and their close interaction partners. We performed next-generation sequencing and single-nucleotide polymorphism (SNP)-array based genotyping to screen for sequence and structural variants. In comparison to European controls we could not detect an enrichment of rare deleterious variants of ELP4, SRPX2, or their interaction partners in affected individuals. The previously described functional p.N327S variant in the X chromosomal SRPX2 gene was detected in two affected individuals (0.81%) and also in controls (0.26%), with some preponderance of male patients. We did not detect an association of SNPs in the ELP4 gene with centrotemporal spikes as previously reported. In conclusion our data do not support a major role of ELP4 and SRPX2 in the etiology of RE/ARE.

Malformations of cortical development: clinical features and genetic causes

Malformations of cortical development are common causes of developmental delay and epilepsy. Some patients have early, severe neurological impairment, but others have epilepsy or unexpected deficits that are detectable only by screening. The rapid evolution of molecular biology, genetics, and imaging has resulted in a substantial increase in knowledge about the development of the cerebral cortex and the number and types of malformations reported. Genetic studies have identified several genes that might disrupt each of the main stages of cell proliferation and specification, neuronal migration, and late cortical organisation. Many of these malformations are caused by de-novo dominant or X-linked mutations occurring in sporadic cases. Genetic testing needs accurate assessment of imaging features, and familial distribution, if any, and can be straightforward in some disorders but requires a complex diagnostic algorithm in others. Because of substantial genotypic and phenotypic heterogeneity for most of these genes, a comprehensive analysis of clinical, imaging, and genetic data is needed to properly define these disorders. Exome sequencing and high-field MRI are rapidly modifying the classification of these disorders.