Truncating neurotrypsin mutation in autosomal recessive nonsyndromic mental retardation

Overexpression of Motopsin, an Extracellular Serine Protease Related to Intellectual Disability, Promotes Adult Neurogenesis and Neuronal Responsiveness in the Dentate Gyrus

Motopsin, a serine protease encoded by PRSS12, is secreted by neuronal cells into the synaptic clefts in an activity-dependent manner, where it induces synaptogenesis by modulating Na+/K+-ATPase activity. In humans, motopsin deficiency leads to severe intellectual disability and, in mice, it disturbs spatial memory and social behavior. In this study, we investigated mice that overexpressed motopsin in the forebrain using the Tet-Off system (DTG-OE mice). The elevated agrin cleavage or the reduced Na+/K+-ATPase activity was not detected. However, motopsin overexpression led to a reduction in spine density in hippocampal CA1 basal dendrites. While motopsin overexpression decreased the ratio of mature mushroom spines in the DG, it increased the ratio of immature thin spines in CA1 apical dendrites. Female DTG-OE mice showed elevated locomotor activity in their home cages. DTG-OE mice showed aberrant behaviors, such as delayed latency to the target hole in the Barnes maze test and prolonged duration of sniffing objects in the novel object recognition test (NOR), although they retained memory comparable to that of TRE-motopsin littermates, which normally express motopsin. After NOR, c-Fos-positive cells increased in the dentate gyrus (DG) of DTG-OE mice compared with that of DTG-SO littermates, in which motopsin overexpression was suppressed by the administration of doxycycline, and TRE-motopsin littermates. Notably, the numbers of doublecortin- and 5-bromo-2'-deoxyuridine-labeled cells significantly increased in the DG of DTG-OE mice, suggesting increased adult neurogenesis. Importantly, our results revealed a new function in addition to modulating neuronal responsiveness and spine morphology in the DG: the regulation of neurogenesis.

Description of novel variants in consanguineous Pakistani families affected with intellectual disability

BACKGROUND

Intellectual disability (ID) is a neurodevelopmental condition, affecting 1-3% of the population. Genetic factors play a key role causing the limitation in intellectual functioning and adaptive behavior. The heterogeneity of ID makes it more difficult for genetic and clinical diagnosis. Mapping of variants through next generation DNA sequencing in consanguineous families would help to understand the molecular parthenogenesis of ID.

OBJECTIVE

The aim of this study was to describe the genetic variants of ID in consanguineous Pakistani families.

METHODS

We analyzed four unrelated consanguineous Pakistani families having an intellectual disability through whole exome sequencing (WES). Data was analyzed using different bioinformatics tools and software.

RESULTS

We mapped four novel variants in different ID genes. Each variant is found in different family, co-segregating with a recessive pattern of inheritance. The variants found are; c.1437delG:p.Asn480Thrfs*10, mapped in FKRP, c.2041 C>A:p.Leu681Met in HIRA, c.382 C>T:p.Arg128Cys in BDH1 and c.267+1G>A:p.? identified in TRAPPC6B.

CONCLUSIONS

These variants help in demonstration of status and molecular basis of intellectual disability in Pakistani population leading to provision of genetic counseling services and a contribution in disease variant database.

Mice deficient in synaptic protease neurotrypsin show impaired spaced long-term potentiation and blunted learning-induced modulation of dendritic spines

Neurotrypsin (NT) is a neuronal trypsin-like serine protease whose mutations cause severe mental retardation in humans. NT is activated in vitro by Hebbian-like conjunction of pre- and postsynaptic activities, which promotes the formation of dendritic filopodia via proteolytic cleavage of the proteoglycan agrin. Here, we investigated the functional importance of this mechanism for synaptic plasticity, learning, and extinction of memory. We report that juvenile neurotrypsin-deficient (NT^-/-) mice exhibit impaired long-term potentiation induced by a spaced stimulation protocol designed to probe the generation of new filopodia and their conversion into functional synapses. Behaviorally, juvenile NT^-/- mice show impaired contextual fear memory and have a sociability deficit. The latter persists in aged NT^-/- mice, which, unlike juvenile mice, show normal recall but impaired extinction of contextual fear memories. Structurally, juvenile mutants exhibit reduced spine density in the CA1 region, fewer thin spines, and no modulation in the density of dendritic spines following fear conditioning and extinction in contrast to wild-type littermates. The head width of thin spines is reduced in both juvenile and aged NT^-/- mice. In vivo delivery of adeno-associated virus expressing an NT-generated fragment of agrin, agrin-22, but not a shorter agrin-15, elevates the spine density in NT^-/- mice. Moreover, agrin-22 co-aggregates with pre- and postsynaptic markers and increases the density and size of presynaptic boutons and presynaptic puncta, corroborating the view that agrin-22 supports the synaptic growth.

Deconstruction of Neurotrypsin Reveals a Multi-factorially Regulated Activity Affecting Myotube Formation and Neuronal Excitability

Neurotrypsin (NT) is a highly specific nervous system multi-domain serine protease best known for its selective processing of the potent synaptic organizer agrin. Its enzymatic activity is thought to influence processes of synaptic plasticity, with its deregulation causing accelerated neuromuscular junction (NMJ) degeneration or contributing to forms of mental retardation. These biological effects are likely to stem from NT-based regulation of agrin signaling. However, dissecting the exact biological implications of NT-agrin interplay is difficult, due to the scarce molecular detail regarding NT activity and NT-agrin interactions. We developed a strategy to reliably produce and purify a catalytically competent engineered variant of NT called "NT-mini" and a library of C-terminal agrin fragments, with which we performed a thorough biochemical and biophysical characterization of NT enzyme functionality. We studied the regulatory effects of calcium ions and heparin, identified NT's heparin-binding domain, and discovered how zinc ions induce modulation of enzymatic activity. Additionally, we investigated myotube differentiation and hippocampal neuron excitability, evidencing a dose-dependent increase in neuronal activity alongside a negative impact on myoblast fusion when using the active NT enzyme. Collectively, our results provide in vitro and cellular foundations to unravel the molecular underpinnings and biological significance of NT-agrin interactions.

The Role of the Extracellular Matrix in Neural Progenitor Cell Proliferation and Cortical Folding During Human Neocortex Development

Extracellular matrix (ECM) has long been known to regulate many aspects of neural development in many different species. However, the role of the ECM in the development of the human neocortex is not yet fully understood. In this review we discuss the role of the ECM in human neocortex development and the different model systems that can be used to investigate this. In particular, we will focus on how the ECM regulates human neural stem and progenitor cell proliferation and differentiation, how the ECM regulates the architecture of the developing human neocortex and the effect of mutations in ECM and ECM-associated genes in neurodevelopmental disorders.

Motopsin deficiency imparts partial insensitivity to doxorubicin-induced hippocampal impairments in adult mice

Motopsin is a serine protease that plays a crucial role in synaptic functions. Loss of motopsin function causes severe intellectual disability in humans. In this study, we evaluated the role of motopsin in the neuropathological development of cognitive impairments following chemotherapy, also known as chemobrain. Motopsin knockout (KO) and wild-type (WT) mice were intravenously injected with doxorubicin (Dox) or saline four times every 8 days and were evaluated for open field, novel object recognition, and passive avoidance tests. Parvalbumin-positive neurons in the hippocampus were immunohistochemically analyzed. Dox administration significantly decreased the total distance in the open field test in both WT and motopsin KO mice without affecting the duration spent in the center square. A significant interaction between the genotype and drug treatment was detected in the recognition index (the rate to investigate a novel object) in the novel object recognition test, although Dox treatment did not affect the total investigation time. Additionally, Dox treatment significantly decreased the recognition index in WT mice, whereas it tended to increase the recognition index in motopsin KO mice. Dox treatment did not affect the latency to enter a dark compartment in either WT or motopsin KO mice in the passive avoidance test. Interestingly, Dox treatment increased the parvalbumin-positive neurons in the stratum oriens of the hippocampus CA1 region of only WT mice, not motopsin KO mice. Our data suggest that motopsin deficiency imparted partial insensitivity to Dox-induced hippocampal impairments. Alternatively, motopsin may contribute to the neuropathology of chemobrain.

Two Sisters From Qatar With TUSC3 Genetic Mutation: Psychiatric Considerations

Defects in the tumor suppressor candidate 3 (TUSC3) gene have been identified in individuals with autosomal recessive intellectual disability (ARID). Our report on two sisters from Qatar with a mutation in the TUSC3 gene focuses on the behavioral manifestations and management provided to them. The sisters, daughters of consanguineous parents, exhibited aggressive and impulsive behavior, along with hyperactivity and emotional dysregulation. They also exhibited abnormal sleep and eating patterns. Behavioral therapy and psychotropic medications including aripiprazole 3.75mg, clonidine 0.025mg, and guanfacine 1mg were used for the management of aggressive and agitated behavior. The two girls showed a reduction in aggressive behavior, hyperactivity, impulsivity, and insomnia in response to 2mg daily of guanfacine. Few families around the world were reported to have mutations in the TUSC3 gene resulting in intellectual disability. We describe the first two reported cases of TUSC3 gene mutation in Qatar. We encourage further research to study the effects of TUSC3 gene mutation, its manifestations, and treatment.

Novel Peptide NT/K-CRS Derived from Kringle Structure of Neurotrypsin Inhibits Neovascularization In Vitro and In Vivo

Purpose: To assess the anti-neovascularization effect of a novel peptide NT/K-CRS derived from the kringle domain of neurotrypsin in vitro and in vivo. Methods: Primary human umbilical vein endothelial cells (HUVECs) were treated with vascular endothelial growth factor (VEGF) in advance. Cell migration, lumen formation, and cell proliferation assays were performed to determine the anti-neovascularization effect of NT/K-CRS in HUVECs. TUNEL and 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium tests were conducted to evaluate cell viability. Chick chorioallantoic membrane and oxygen-induced retinopathy model were established to assess the anti-angiogenic role of NT/K-CRS in vivo. Results: The in vitro results showed that NT/K-CRS effectively decreased VEGF-induced cell migration and endothelial tube formation, with no significant effect on cell proliferation and cell viability. In addition, NT/K-CRS showed great efficacy in angiogenesis inhibition in chicken embryos. The cytokine release syndrome (CRS) peptide also inhibited retinal neovascularization and improved retinal blood perfusion in oxygen-treated mouse pups through intravitreal injection. Conclusions: NT/K-CRS peptide derived from the kringle domain of neurotrypsin can strongly inhibit neovascularization in vitro and vivo. This novel peptide may become a promising therapeutic agent for neovascular-related ocular diseases.

Identification of CDKL3 as a critical regulator in development of glioma through regulating RRM2 and the JNK signaling pathway

Glioma is one of the most commonly diagnosed intracranial malignancies. The molecular mechanism underlying the development of glioma is still largely unknown. In this study, we present the first report concerning the function and mechanism of cyclin‐dependent kinase‐like 3 (CDKL3) in the development and prognosis of glioma. It is shown that CDKL3 was upregulated in glioma tissues and could independently predict poor prognosis of patients. Silencing CDKL3 in glioma cells could inhibit cell proliferation and migration and induce cell apoptosis and cell cycle arrest, whereas the overexpression of CDKL3 promoted cell proliferation. The in vivo experiments also indicated that knockdown of CDKL3 significantly suppressed tumor growth of glioma. Gene expression profiling of CDKL3 knockdown U87 cells identified RRM2 as a potential target of CDKL3, which was proved to have direct interaction with CDKL3. Given similar effects on glioma development with CDKL3, knockdown of RRM2 could rescue the effects of CDKL3 overexpression on glioma cells. Moreover, knockdown of CDKL3 or RRM2 suppressed the activity of JNK signaling, whereas CDKL3 overexpression produced the opposite effect. In conclusion, our results identified CDKL3 as a promotor for glioma, probably through the regulation of RRM2 and activation of the JNK signalling pathway, highlighting the significance of CDKL3 as a promising therapeutic target of glioma.

Novel Peptide NT/K-CFY Derived from Kringle Structure of Neurotrypsin Inhibits Neovascularization

Purpose: To assess the anti-neovascularization effect of a novel peptide NT/K-CFY derived from the kringle domain of neurotrypsin.Materials and Methods: Cell migration, lumen formation and cell proliferation assays were performed to determine the anti-neovascularization effect of NT/K-CFY in primary human umbilical vein endothelial cells (HUVECs). Chick chorioallantoic membrane (CAM) and oxygen-induced retinopathy (OIR) models were established to assess the anti-angiogenic role of NT/K-CFY in vivo. The retinal expression of vascular endothelial growth factor (VEGF) and pigment epithelium-derived factor (PEDF) was examined by western blot and real-time PCR in OIR model.Results: The in vitro results showed that NT/K-CFY effectively and safely decreased VEGF-induced cell migration, cell proliferation and tube formation in HUVECs. In addition, NT/K-CFY showed certain efficacy in angiogenesis inhibition in chicken embryos and oxygen-treated mouse pups. Moreover, the CFY peptide also improved retinal blood perfusion and reversed the abnormal expression of VEGF and PEDF in OIR mouse model.Conclusion: NT/K-CFY peptide strongly inhibits neovascularization in vitro and vivo. This novel peptide may become a promising therapeutic agent for ocular angiogenesis-related diseases.

Whole exome sequencing revealed novel variants in consanguineous Pakistani families with intellectual disability

BACKGROUND

Intellectual disability (ID) is a heterogeneous disorder affecting 1-3% of the population. Elucidation of monogenic variants for ID is a current challenge. These variants can be better demonstrated in consanguineous affected families.

OBJECTIVE

The study was designed to find the genetic variants of ID in consanguineous families.

METHODS

We analyzed five unrelated consanguineous Pakistani families affected with ID using whole exome sequencing (WES). Data was analyzed using different bioinformatics tools and software.

RESULTS

We mapped four variants including three novels in four different ID known genes. Each variant is found in a different family, co-segregating with a recessive pattern of inheritance. The novel variants found are; c. 2_4del (p.?) mapped in ROS1 and c. 718G>A (p.Gly240Arg) in GRM1. Another novel causative variant, c.2673del (p.Gly892Aspfs*17) identified in COL18A1 in a recessive form, a gene reported for Knobloch syndrome that manifests ID along with typical retinal abnormalities, and this phenotype was confirmed on reverse phenotyping. A mutation c.2134C>T (p.Arg712*) in TRAPPC9 has been found first time in the homozygous recessive form in our enrolled three affected siblings while it was previously reported in compound heterozygous form in a Caucasian descent. While fifth family remained unsolved.

CONCLUSION

These mutations in four different genes with a recessive inheritance would be a contribution to the disease variant database of this devastating disorder.

Dissecting the Extracellular Complexity of Neuromuscular Junction Organizers

Synapse formation is a very elaborate process dependent upon accurate coordination of pre and post-synaptic specialization, requiring multiple steps and a variety of receptors and signaling molecules. Due to its relative structural simplicity and the ease in manipulation and observation, the neuromuscular synapse or neuromuscular junction (NMJ)-the connection between motor neurons and skeletal muscle-represents the archetype junction system for studying synapse formation and conservation. This junction is essential for survival, as it controls our ability to move and breath. NMJ formation requires coordinated interactions between motor neurons and muscle fibers, which ultimately result in the formation of a highly specialized post-synaptic architecture and a highly differentiated nerve terminal. Furthermore, to ensure a fast and reliable synaptic transmission following neurotransmitter release, ligand-gated channels (acetylcholine receptors, AChRs) are clustered on the post-synaptic muscle cell at high concentrations in sites opposite the presynaptic active zone, supporting a direct role for nerves in the organization of the post-synaptic membrane architecture. This organized clustering process, essential for NMJ formation and for life, relies on key signaling molecules and receptors and is regulated by soluble extracellular molecules localized within the synaptic cleft. Notably, several mutations as well as auto-antibodies against components of these signaling complexes have been related to neuromuscular disorders. The recent years have witnessed strong progress in the understanding of molecular identities, architectures, and functions of NMJ macromolecules. Among these, prominent roles have been proposed for neural variants of the proteoglycan agrin, its receptor at NMJs composed of the lipoprotein receptor-related protein 4 (LRP4) and the muscle-specific kinase (MuSK), as well as the regulatory soluble synapse-specific protease Neurotrypsin. In this review we summarize the current state of the art regarding molecular structures and (agrin-dependent) canonical, as well as (agrin-independent) non-canonical, MuSK signaling mechanisms that underscore the formation of neuromuscular junctions, with the aim of providing a broad perspective to further stimulate molecular, cellular and tissue biology investigations on this fundamental intercellular contact.

Structural characterization of the third scavenger receptor cysteine-rich domain of murine neurotrypsin

Neurotrypsin (NT) is a multi-domain serine protease of the nervous system with only one known substrate: the large proteoglycan Agrin. NT has seen to be involved in the maintenance/turnover of neuromuscular junctions and in processes of synaptic plasticity in the central nervous system. Roles which have been tied to its enzymatic activity, localized in the C-terminal serine-protease (SP) domain. However the purpose of NT's remaining 3-4 scavenger receptor cysteine-rich (SRCR) domains is still unclear. We have determined the crystal structure of the third SRCR domain of murine NT (mmNT-SRCR3), immediately preceding the SP domain and performed a comparative structural analysis using homologous SRCR structures. Our data and the elevated degree of structural conservation with homologous domains highlight possible functional roles for NT SRCRs. Computational and experimental analyses suggest the identification of a putative binding region for Ca²⁺ ions, known to regulate NT enzymatic activity. Furthermore, sequence and structure comparisons allow to single out regions of interest that, in future studies, might be implicated in Agrin recognition/binding or in interactions with as of yet undiscovered NT partners.

Transcriptomic and morphophysiological evidence for a specialized human cortical GABAergic cell type

We describe convergent evidence from transcriptomics, morphology, and physiology for a specialized GABAergic neuron subtype in human cortex. Using unbiased single-nucleus RNA sequencing, we identify ten GABAergic interneuron subtypes with combinatorial gene signatures in human cortical layer 1 and characterize a group of human interneurons with anatomical features never described in rodents, having large 'rosehip'-like axonal boutons and compact arborization. These rosehip cells show an immunohistochemical profile (GAD1+CCK+, CNR1-SST-CALB2-PVALB-) matching a single transcriptomically defined cell type whose specific molecular marker signature is not seen in mouse cortex. Rosehip cells in layer 1 make homotypic gap junctions, predominantly target apical dendritic shafts of layer 3 pyramidal neurons, and inhibit backpropagating pyramidal action potentials in microdomains of the dendritic tuft. These cells are therefore positioned for potent local control of distal dendritic computation in cortical pyramidal neurons.

Shaping Synapses by the Neural Extracellular Matrix

Accumulating data support the importance of interactions between pre- and postsynaptic neuronal elements with astroglial processes and extracellular matrix (ECM) for formation and plasticity of chemical synapses, and thus validate the concept of a tetrapartite synapse. Here we outline the major mechanisms driving: (i) synaptogenesis by secreted extracellular scaffolding molecules, like thrombospondins (TSPs), neuronal pentraxins (NPs) and cerebellins, which respectively promote presynaptic, postsynaptic differentiation or both; (ii) maturation of synapses via reelin and integrin ligands-mediated signaling; and (iii) regulation of synaptic plasticity by ECM-dependent control of induction and consolidation of new synaptic configurations. Particularly, we focused on potential importance of activity-dependent concerted activation of multiple extracellular proteases, such as ADAMTS4/5/15, MMP9 and neurotrypsin, for permissive and instructive events in synaptic remodeling through localized degradation of perisynaptic ECM and generation of proteolytic fragments as inducers of synaptic plasticity.

Involvement of Nuclear Receptor REV-ERBβ in Formation of Neurites and Proliferation of Cultured Adult Neural Stem Cells

Neural stem cells (NSCs) serve as the source of both neurons and support cells, and neurogenesis is reportedly linked to the circadian clock. This study aimed to clarify the functional role of the circadian rhythm-related nuclear receptor, REV-ERBβ, in neurogenesis of NSCs from adult brain. Accordingly, Rev-erbβ expression and the effect of Rev-erbβ gene-specific knockdown on neurogenesis in vitro was examined in adult rodent NSCs. Initial experiments confirmed REV-ERBβ expression in cultured adult NSCs, while subsequent gene expression and gene ontogeny analyses identified functional genes upregulated or downregulated by REV-ERBβ. In particular, expression levels of factors associated with proliferation, stemness, and neural differentiation were affected. Knockdown of Rev-erbβ showed involvement of REV-ERBβ in regulation of cellular proliferation and self-renewal of cultured adult NSCs. Moreover, Rev-erbβ-knockdown cells formed neurons with a slightly shrunken morphology, fewer new primary neurites, and reduced length and branch formation of neurites. Altogether, this suggests that REV-ERBβ is involved in neurite formation during neuronal differentiation of cultured adult NSCs. In summary, REV-ERBβ is a known circadian regulatory protein that appears to be involved in neurogenesis via regulation of networks for cell proliferation and neural differentiation/maturation in adult NSCs.

Vulnerability or resilience of motopsin knockout mice to maternal separation stress depending on adulthood behaviors

BACKGROUND

Both environmental and genetic conditions contribute to the robust development of neuronal circuits and adulthood behaviors. Loss of motopsin gene function causes severe intellectual disability in humans and enhanced social behavior in mice. Furthermore, childhood maltreatment is a risk factor for some psychiatric disorders, and children with disabilities have a higher risk of abuse than healthy children.

MATERIALS AND METHODS

In this study, we investigated the effects of maternal separation (MS) on adulthood behaviors of motopsin knockout (KO) and wild-type (WT) mice.

RESULTS

The MS paradigm decreased the duration that WT mice stayed in the center area of an open field, but not for motopsin KO mice; however, it decreased the novel object recognition index in both genotypes. In the marble burying test, motopsin KO mice buried fewer marbles than WT mice, regardless of the rearing conditions. The MS paradigm slightly increased and reduced open arm entry in the elevated plus maze by WT and motopsin KO mice, respectively. In the three-chamber test, the rate of sniffing the animal cage was increased by the MS paradigm only for motopsin KO mice. After the three-chamber test, motopsin KO mice had fewer cFos-positive cells in the prelimbic cortex, which is involved in emotional response, than WT mice. In the infralimbic cortex, the MS paradigm decreased the number of cFos-positive cells in motopsin KO mice.

CONCLUSION

Our results suggest that motopsin deficiency and childhood adversity independently affect some behaviors, but they may interfere with each other for other behaviors. Defective neuronal circuits in the prefrontal cortex may add to this complexity.

The Molecular Genetics of Autosomal Recessive Nonsyndromic Intellectual Disability: a Mutational Continuum and Future Recommendations

Intellectual disability (ID) is a clinical manifestation of the central nervous system without any major dysmorphologies of the brain. Biologically it affects learning capabilities, memory, and cognitive functioning. The basic defining features of ID are characterized by IQ<70, age of onset before 18 years, and impairment of at least two of the adaptive skills. Clinically it is classified in a syndromic (with additional abnormalities) and a nonsyndromic form (with only cognitive impairment). The study of nonsyndromic intellectual disability (NSID) can best explain the pathophysiology of cognition, intelligence and memory. Genetic analysis in autosomal recessive nonsyndrmic ID (ARNSID) has mapped 51 disease loci, 34 of which have revealed their defective genes. These genes play diverse physiological roles in various molecular processes, including methylation, proteolysis, glycosylation, signal transduction, transcription regulation, lipid metabolism, ion homeostasis, tRNA modification, ubiquitination and neuromorphogenesis. High-density SNP array and whole exome sequencing has increased the pace of gene discoveries and many new mutations are being published every month. The lack of uniform criteria has assigned multiple identifiers (or accession numbers) to the same MRT locus (e.g. MRT7 and MRT22). Here in this review we describe the molecular genetics of ARNSID, prioritize the candidate genes in uncharacterized loci, and propose a new nomenclature to reorganize the mutation data that will avoid the confusion of assigning duplicate accession numbers to the same ID locus and to make the data manageable in the future as well.

Genetic Defects Underlie the Non-syndromic Autosomal Recessive Intellectual Disability (NS-ARID)

Intellectual disability (ID) is a neurodevelopmental disorder which appears frequently as the result of genetic mutations and may be syndromic (S-ID) or non-syndromic (NS-ID). ID causes an important economic burden, for patient's family, health systems, and society. Identifying genes that cause S-ID can easily be evaluated due to the clinical symptoms or physical anomalies. However, in the case of NS-ID due to the absence of co-morbid features, the latest molecular genetic techniques can be used to understand the genetic defects that underlie it. Recent studies have shown that non-syndromic autosomal recessive (NS-ARID) is extremely heterogeneous and contributes much more than X-linked ID. However, very little is known about the genes and loci involved in NS-ARID relative to X-linked ID, and whose complete genetic etiology remains obscure. In this review article, the known genetic etiology of NS-ARID and possible relationships between genes and the associated molecular pathways of their encoded proteins has been reviewed which will enhance our understanding about the underlying genes and mechanisms in NS-ARID.

Exome sequencing of Pakistani consanguineous families identifies 30 novel candidate genes for recessive intellectual disability

Intellectual disability (ID) is a clinically and genetically heterogeneous disorder, affecting 1-3% of the general population. Although research into the genetic causes of ID has recently gained momentum, identification of pathogenic mutations that cause autosomal recessive ID (ARID) has lagged behind, predominantly due to non-availability of sizeable families. Here we present the results of exome sequencing in 121 large consanguineous Pakistani ID families. In 60 families, we identified homozygous or compound heterozygous DNA variants in a single gene, 30 affecting reported ID genes and 30 affecting novel candidate ID genes. Potential pathogenicity of these alleles was supported by co-segregation with the phenotype, low frequency in control populations and the application of stringent bioinformatics analyses. In another eight families segregation of multiple pathogenic variants was observed, affecting 19 genes that were either known or are novel candidates for ID. Transcriptome profiles of normal human brain tissues showed that the novel candidate ID genes formed a network significantly enriched for transcriptional co-expression (P<0.0001) in the frontal cortex during fetal development and in the temporal-parietal and sub-cortex during infancy through adulthood. In addition, proteins encoded by 12 novel ID genes directly interact with previously reported ID proteins in six known pathways essential for cognitive function (P<0.0001). These results suggest that disruptions of temporal parietal and sub-cortical neurogenesis during infancy are critical to the pathophysiology of ID. These findings further expand the existing repertoire of genes involved in ARID, and provide new insights into the molecular mechanisms and the transcriptome map of ID.

Dependence receptor involvement in subtilisin-induced long-term depression and in long-term potentiation

The serine protease subtilisin induces a form of long-term depression (LTD) which is accompanied by a reduced expression of the axo-dendritic guidance molecule Unco-ordinated-5C (Unc-5C). One objective of the present work was to determine whether a loss of Unc-5C function contributed to subtilisin-induced LTD by using Unc-5C antibodies in combination with the pore-forming agents Triton X-100 (0.005%) or streptolysin O in rat hippocampal slices. In addition we have assessed the effect of subtilisin on the related dependence receptor Deleted in Colorectal Cancer (DCC) and used antibodies to this protein for functional studies. Field excitatory postsynaptic potentials (fEPSPs) were analyzed in rat hippocampal slices and protein extracts were used for Western blotting. Subtilisin produced a greater loss of DCC than of Unc-5C, but the antibodies had no effect on resting excitability or fEPSPs and did not modify subtilisin-induced LTD. However, antibodies to DCC but not Unc-5C did reduce the amplitude of theta-burst long-term potentiation (LTP). In addition, two inhibitors of endocytosis - dynasore and tat-gluR2(3Y) - were tested and, although the former compound had no effect on neurophysiological responses, tat-gluR2(3Y) did reduce the amplitude of subtilisin-induced LTD without affecting the expression of DCC or Unc-5C but with some loss of PostSynaptic Density Protein-95. The results support the view that the dependence receptor DCC may be involved in LTP and suggest that the endocytotic removal of a membrane protein or proteins may contribute to subtilisin-induced LTD, although it appears that neither Unc-5C nor DCC are involved in this process.

Suppression of agrin-22 production and synaptic dysfunction in Cln1 (-/-) mice

OBJECTIVE

Oxidative stress in the brain is highly prevalent in many neurodegenerative disorders including lysosomal storage disorders, in which neurodegeneration is a devastating manifestation. Despite intense studies, a precise mechanism linking oxidative stress to neuropathology in specific neurodegenerative diseases remains largely unclear.

METHODS

Infantile neuronal ceroid lipofuscinosis (INCL) is a devastating neurodegenerative lysosomal storage disease caused by mutations in the ceroid lipofuscinosis neuronal-1 (CLN1) gene encoding palmitoyl-protein thioesterase-1. Previously, we reported that in the brain of Cln1 (-/-) mice, which mimic INCL, and in postmortem brain tissues from INCL patients, increased oxidative stress is readily detectable. We used molecular, biochemical, immunohistological, and electrophysiological analyses of brain tissues of Cln1 (-/-) mice to study the role(s) of oxidative stress in mediating neuropathology.

RESULTS

Our results show that in Cln1 (-/-) mice oxidative stress in the brain via upregulation of the transcription factor, CCAAT/enhancer-binding protein-δ, stimulated expression of serpina1, which is an inhibitor of a serine protease, neurotrypsin. Moreover, in the Cln1 (-/-) mice, suppression of neurotrypsin activity by serpina1 inhibited the cleavage of agrin (a large proteoglycan), which substantially reduced the production of agrin-22, essential for synaptic homeostasis. Direct whole-cell recordings at the nerve terminals of Cln1 (-/-) mice showed inhibition of Ca(2+) currents attesting to synaptic dysfunction. Treatment of these mice with a thioesterase-mimetic small molecule, N-tert (Butyl) hydroxylamine (NtBuHA), increased agrin-22 levels.

INTERPRETATION

Our findings provide insight into a novel pathway linking oxidative stress with synaptic pathology in Cln1 (-/-) mice and suggest that NtBuHA, which increased agrin-22 levels, may ameliorate synaptic dysfunction in this devastating neurodegenerative disease.

N-Glycosylation modulates filopodia-like protrusions induced by sez-6 through regulating the distribution of this protein on the cell surface

Seizure-related gene 6 (sez-6) is a trans-membrane protein expressed by neuronal cells that modulates dendritic branching. It has three clusters of eleven possible N-glycosylation sites in the extracellular domain region: sugar chain (SC)1-3, SC4-7, and SC8-11. Recent reports suggest that N-glycosylation modulates the membrane trafficking and function of trans-membrane proteins. Here, we studied the role of N-glycosylation in sez-6 function. We transfected mutants lacking one, two, or all N-glycosylation clusters into neuro2a cells. A mutant lacking all N-glycosylation was transported to the cell membrane. Mutants lacking one cluster (sez-6 ΔSC1-3, ΔSC4-7, ΔSC8-11) were evenly distributed on the cell membrane and secreted into the conditioned medium, as in wild-type sez-6; in contrast, the unglycosylated mutant, sez-6 ΔSC1-11, and mutants having only one cluster (sez-6 SC1-3, SC8-11) were localized in some portions on the cell membrane. Despite sez-6 SC4-7 having only one cluster, it was transported like the wild type. Among mutants behaving like the wild type, sez-6 ΔSC1-3 and ΔSC4-7 reduced neurite formation. Interestingly, mutants lacking SC4-7 (sez-6 ΔSC4-7) did not affect the formation of filopodia-like protrusions. In contrast, other mutants as well as the wild type induced it, suggesting that SC4-7 is crucial for filopodia-like protrusions. Our results indicate that N-glycosylation regulates cell morphology through modulating the cell surface distribution of sez-6 protein.

Extracellular matrix control of dendritic spine and synapse structure and plasticity in adulthood

Dendritic spines are the receptive contacts at most excitatory synapses in the central nervous system. Spines are dynamic in the developing brain, changing shape as they mature as well as appearing and disappearing as they make and break connections. Spines become much more stable in adulthood, and spine structure must be actively maintained to support established circuit function. At the same time, adult spines must retain some plasticity so their structure can be modified by activity and experience. As such, the regulation of spine stability and remodeling in the adult animal is critical for normal function, and disruption of these processes is associated with a variety of late onset diseases including schizophrenia and Alzheimer's disease. The extracellular matrix (ECM), composed of a meshwork of proteins and proteoglycans, is a critical regulator of spine and synapse stability and plasticity. While the role of ECM receptors in spine regulation has been extensively studied, considerably less research has focused directly on the role of specific ECM ligands. Here, we review the evidence for a role of several brain ECM ligands and remodeling proteases in the regulation of dendritic spine and synapse formation, plasticity, and stability in adults.

Inactivition of CDKL3 mildly inhibits proliferation of cells at VZ/SVZ in brain

CDKL3 has an important role in regulating cell growth and/or differentiation, and its inactivation is recently reported to be related to non-syndromic mild mental retardation (MR). MR is a common neurological disorder, predominantly characterized by impaired cognitive function. Though genetic factors play a very important role in the pathogenesis of MR, to date, only few genes linked to MR have been characterized and understood very well. Here, we investigated the role of the CDKL3 in the proliferation of cells surrounding the brain ventricle, and the results showed down-regulating CDKL3 by the method of RNAi in the cells surrounding the brain ventricle of the mouse embryo at E15 may inhibit their proliferation. As our previous study had shown that Cdkl3 mRNA expression is developmentally regulated in the central nervous system, peaking during late embryonic and early postnatal stages which are the key stages of neurite formation and maturation, furtherly, the present findings indicated that CDKL3 may be involved in proliferation of cells surrounding the brain ventricle where neuronal progenitor cells are enriched during the late embryo stage, supporting the notion that CDKL3 inactivation contributes to non-syndromic mild MR.

Effects of different tissue microenvironments on gene expression in breast cancer cells

In metastasis, circulating tumor cells penetrate the walls of blood vessels and enter the metastatic target tissue, thereby becoming exposed to novel and relatively unsupportive microenvironments. In the new microenvironments, the tumor cells often remain in a dormant state indefinitely and must adapt before they are able to successfully colonize the tissue. Very little is known about this adaptive process. We studied temporal changes in gene expression when breast cancer cells adapt to survive and grow on brain, bone marrow, and lung tissue maintained in an in vivo culture system, as models of the metastatic colonization of these tissues. We observed the transient activation of genes typically associated with homeostasis and stress during the initial stages of adaptation, followed by the activation of genes that mediate more advanced functions, such as elaboration of cell morphology and cell division, as the cells adapted to thrive in the host tissue microenvironment. We also observed the temporary induction of genes characteristic of the host tissue, which was particularly evident when tumor cells were grown on brain tissue. These early transient gene expression events suggest potential points of therapeutic intervention that are not evident in data from well-established tumors.

Activity-controlled proteolytic cleavage at the synapse

Activity-controlled enzymatic cleavage of proteins on the surface of synaptic membranes or in the synaptic or perisynaptic interstitial compartment represents a direct way to regulate synaptic structure, function, and number. Extracellular proteolysis at synapses was initially understood to be plasticity enabling by freeing synapses from the constraints provided by the extracellular matrix. However, recent observations indicate that at least part of the extracellular protein cleavage results in activation of previously cryptic functions that regulate adaptive changes of synapses and neuronal circuits. Here, we focus on peptidases with distinct localization and function at synapses combined with regulation by neuronal and synaptic activity, and evaluate their function in the context of developmental and/or adult synaptic plasticity.

Axenfeld-Rieger syndrome: further clinical and array delineation of four unrelated patients with a 4q25 microdeletion

Axenfeld-Rieger syndrome (ARS) is an autosomal dominant disorder with variable expressivity. It is characterized by dysgenesis of the anterior segment of the eye together with dental, cardiac, and umbilical anomalies. There is a high incidence of secondary high tension glaucoma. It is a genetically heterogeneous condition due to deletion or mutations of FOXC1 (6p25) or PITX2 (4q25). We report on four unrelated patients with overlapping microdeletions encompassing PITX2 at 4q25. We compare the genotypes and phenotypes of these newly described ARS patients and discuss the involvement of contiguous genes. Patients 1, 2, and 3 had mild learning difficulties, not typically seen in patients with ARS. We implicate the adjacent neuronally expressed genes; NEUROG2, UGT8, NDST3, and PRSS12 as potentially causal. Our findings support the use of microarray analysis in ARS patients for full prognostic information in infants presenting with ARS-like phenotypes.

Neural ECM proteases in learning and synaptic plasticity

Recent studies implicate extracellular proteases in synaptic plasticity, learning, and memory. The data are especially strong for such serine proteases as thrombin, tissue plasminogen activator, neurotrypsin, and neuropsin as well as matrix metalloproteinases, MMP-9 in particular. The role of those enzymes in the aforementioned phenomena is supported by the experimental results on the expression patterns (at the gene expression and protein and enzymatic activity levels) and functional studies, including knockout mice, specific inhibitors, etc. Counterintuitively, the studies have shown that the extracellular proteolysis is not responsible mainly for an overall degradation of the extracellular matrix (ECM) and loosening perisynaptic structures, but rather allows for releasing signaling molecules from the ECM, transsynaptic proteins, and latent form of growth factors. Notably, there are also indications implying those enzymes in the major neuropsychiatric disorders, probably by contributing to synaptic aberrations underlying such diseases as schizophrenia, bipolar, autism spectrum disorders, and drug addiction.

Genetics of recessive cognitive disorders

Most severe forms of intellectual disability (ID) have specific genetic causes. Numerous X chromosome gene defects and disease-causing copy-number variants have been linked to ID and related disorders, and recent studies have revealed that sporadic cases are often due to dominant de novo mutations with low recurrence risk. For autosomal recessive ID (ARID) the recurrence risk is high and, in populations with frequent parental consanguinity, ARID is the most common form of ID. Even so, its elucidation has lagged behind. Here we review recent progress in this field, show that ARID is not rare even in outbred Western populations, and discuss the prospects for improving its diagnosis and prevention.

Presenilins regulate neurotrypsin gene expression and neurotrypsin-dependent agrin cleavage via cyclic AMP response element-binding protein (CREB) modulation

Presenilins, the catalytic components of the γ-secretase complex, are upstream regulators of multiple cellular pathways via regulation of gene transcription. However, the underlying mechanisms and the genes regulated by these pathways are poorly characterized. In this study, we identify Tequila and its mammalian ortholog Prss12 as genes negatively regulated by presenilins in Drosophila larval brains and mouse embryonic fibroblasts, respectively. Prss12 encodes the serine protease neurotrypsin, which cleaves the heparan sulfate proteoglycan agrin. Altered neurotrypsin activity causes serious synaptic and cognitive defects; despite this, the molecular processes regulating neurotrypsin expression and activity are poorly understood. Using γ-secretase drug inhibitors and presenilin mutants in mouse embryonic fibroblasts, we found that a mature γ-secretase complex was required to repress neurotrypsin expression and agrin cleavage. We also determined that PSEN1 endoproteolysis or processing of well known γ-secretase substrates was not essential for this process. At the transcriptional level, PSEN1/2 removal induced cyclic AMP response element-binding protein (CREB)/CREB-binding protein binding, accumulation of activating histone marks at the neurotrypsin promoter, and neurotrypsin transcriptional and functional up-regulation that was dependent on GSK3 activity. Upon PSEN1/2 reintroduction, this active epigenetic state was replaced by a methyl CpG-binding protein 2 (MeCP2)-containing repressive state and reduced neurotrypsin expression. Genome-wide analysis revealed hundreds of other mouse promoters in which CREB binding is similarly modulated by the presence/absence of presenilins. Our study thus identifies Tequila and neurotrypsin as new genes repressed by presenilins and reveals a novel mechanism used by presenilins to modulate CREB signaling based on controlling CREB recruitment.

Mental retardation-related protease, motopsin (prss12), binds to the BRICHOS domain of the integral membrane protein 2a

Motopsin (prss12), a mosaic serine protease secreted by neuronal cells, is believed to be important for cognitive function, as the loss of its function causes severe nonsyndromic mental retardation. To understand the molecular role of motopsin, we identified the integral membrane protein 2a (Itm2a) as a motopsin-interacting protein using a yeast two-hybrid system. A pull-down assay showed that the BRICHOS domain of Itm2a was essential for this interaction. Motopsin and Itm2a co-localized in COS cells and in cultured neurons when transiently expressed in these cells. Both proteins were co-immunoprecipitated from lysates of these transfected COS cells. Itm2a was strongly detected in a brain lysate prepared between postnatal day 0 and 10, during which period motopsin protein was also enriched in the brain. Immunohistochemistry detected Itm2a as patchy spots along endothelial cells of brain capillaries (which also expressed myosin II regulatory light chain [RLC]), and on glial fibrillary acidic protein (GFAP)-positive processes in the developing cerebral cortex. The data raise the possibility that secreted motopsin interacts with endothelial cells in the developing brain.

Zymogen activation of neurotrypsin and neurotrypsin-dependent agrin cleavage on the cell surface are enhanced by glycosaminoglycans

The serine peptidase neurotrypsin is stored in presynaptic nerve endings and secreted in an inactive zymogenic form by synaptic activity. After activation, which requires activity of postsynaptic NMDA (N-methyl-D-aspartate) receptors, neurotrypsin cleaves the heparan sulfate proteoglycan agrin at active synapses. The resulting C-terminal 22-kDa fragment of agrin induces dendritic filopodia, which are considered to be precursors of new synapses. In the present study, we investigated the role of GAGs (glycosaminoglycans) in the activation of neurotrypsin and neurotrypsin-dependent agrin cleavage. We found binding of neurotrypsin to the GAG side chains of agrin, which in turn enhanced the activation of neurotrypsin by proprotein convertases and resulted in enhanced agrin cleavage. A similar enhancement of neurotrypsin binding to agrin, neurotrypsin activation and agrin cleavage was induced by the four-amino-acid insert at the y splice site of agrin, which is crucial for the formation of a heparin-binding site. Non-agrin GAGs also contributed to binding and activation of neurotrypsin and, thereby, to agrin cleavage, albeit to a lesser extent. Binding of neurotrypsin to cell-surface glycans locally restricts its conversion from zymogen into active peptidase. This provides the molecular foundation for the local action of neurotrypsin at or in the vicinity of its site of synaptic secretion. By its local action at synapses with correlated pre- and post-synaptic activity, the neurotrypsin-agrin system fulfils the requirements for a mechanism serving experience-dependent modification of activated synapses, which is essential for adaptive structural reorganizations of neuronal circuits in the developing and/or adult brain.

A mutation in the serine protease TMPRSS4 in a novel pediatric neurodegenerative disorder

Background

To elucidate the genetic basis of a novel neurodegenerative disorder in an Old Order Amish pedigree by combining homozygosity mapping with exome sequencing.

Methods and results

We identified four individuals with an autosomal recessive condition affecting the central nervous system (CNS). Neuroimaging studies identified progressive global CNS tissue loss presenting early in life, associated with microcephaly, seizures, and psychomotor retardation; based on this, we named the condition Autosomal Recessive Cerebral Atrophy (ARCA). Using two unbiased genetic approaches, homozygosity mapping and exome sequencing, we narrowed the candidate region to chromosome 11q and identified the c.995C > T (p.Thr332Met) mutation in the TMPRSS4 gene. Sanger sequencing of additional relatives confirmed that the c.995C > T genotype segregates with the ARCA phenotype. Residue Thr332 is conserved across species and among various ethnic groups. The mutation is predicted to be deleterious, most likely due to a protein structure alteration as demonstrated with protein modelling.

Conclusions

This novel disease is the first to demonstrate a neurological role for a transmembrane serine proteases family member. This study demonstrates a proof-of-concept whereby combining exome sequencing with homozygosity mapping can find the genetic cause of a rare disease and acquire better understanding of a poorly described protein in human development.

Extracellular matrix molecules, their receptors, and secreted proteases in synaptic plasticity

Neural cells secrete diverse molecules, which accumulate in the extracellular space and form the extracellular matrix (ECM). Interactions between cells and the ECM are well recognized to play the crucial role in cell migration and guidance of growing axons, whereas formation of mature neural ECM in the form of perineuronal nets is believed to restrict certain forms of developmental plasticity. On the other hand, major components of perineuronal nets and other ECM molecules support induction of functional plasticity, the most studied form of which is long-term potentiation. Here, we review the underlying mechanisms by which ECM molecules, their receptors and remodeling proteases regulate the induction and maintenance of synaptic modifications. In particular, we highlight that activity-dependent secretion and activation of proteases leads to a local cleavage of the ECM and release of signaling proteolytic fragments. These molecules regulate transmitter receptor trafficking, actin cytoskeleton, growth of dendritic spines, and formation of dendritic filopodia.

Genotype-phenotype analysis of 4q deletion syndrome: proposal of a critical region

Chromosome 4q deletion syndrome (4q- syndrome) is a rare condition, with an estimated incidence of 1 in 100,000. Although variable, the clinical spectrum commonly includes craniofacial, developmental, digital, skeletal, and cardiac involvement. Data on the genotype-phenotype correlation within the 4q arm are limited. We present detailed clinical and genetic information by array CGH on 20 patients with 4q deletions. We identified a patient who has a ∼465 kb deletion (186,770,069-187,234,800, hg18 coordinates) in 4q35.1 with all clinical features for 4q deletion syndrome except for developmental delay, suggesting that this is a critical region for this condition and a specific gene responsible for orofacial clefts and congenital heart defects resides in this region. Since the patients with terminal deletions all had cleft palate, our results provide further evidence that a gene associated with clefts is located on the terminal segment of 4q. By comparing and contrasting our patients' genetic information and clinical features, we found significant genotype-phenotype correlations at a single gene level linking specific phenotypes to individual genes. Based on these data, we constructed a hypothetical partial phenotype-genotype map for chromosome 4q which includes BMP3, SEC31A, MAPK10, SPARCL1, DMP1, IBSP, PKD2, GRID2, PITX2, NEUROG2, ANK2, FGF2, HAND2, and DUX4 genes.

The brain's extracellular matrix and its role in synaptic plasticity

The extracellular matrix (ECM) of the brain has important roles in regulating synaptic function and plasticity. A juvenile ECM supports the wiring of neuronal networks, synaptogenesis, and synaptic maturation. The closure of critical periods for experience-dependent shaping of neuronal circuits coincides with the implementation of a mature form of ECM that is characterized by highly elaborate hyaluronan-based structures, the perineuronal nets (PNN), and PNN-like perisynaptic ECM specializations. In this chapter, we will focus on some recently reported aspects of ECM functions in brain plasticity. These include (a) the discovery that the ECM can act as a passive diffusion barrier for cell surface molecules including neurotransmitter receptors and in this way compartmentalize cell surfaces, (b) the specific functions of ECM components in actively regulating synaptic plasticity and homeostasis, and (c) the shaping processes of the ECM by extracellular proteases and in turn the activation particular signaling pathways.

Genetic suppression of agrin reduces mania-like behavior in Na+ , K+ -ATPase α3 mutant mice

Myshkin mice heterozygous for an inactivating mutation in the neuron-specific Na(+) ,K(+) -ATPase α3 isoform show behavior analogous to mania, including an abnormal endogenous circadian period. Agrin is a proteoglycan implicated as a regulator of synapses that has been proposed to inhibit activity of Na(+) ,K(+) -ATPase α3. We examined whether the mania-related behavior of Myshkin mice could be rescued by a reduction in the expression of agrin through genetic knockout. The suppression of agrin reduced hyperambulation and holeboard exploration, restored anxiety-like behavior (or reduced risk-taking behavior), improved prepulse inhibition and shortened the circadian period. Hence, agrin is important for regulating mania-like behavior and circadian rhythms. In Myshkin mice, the suppression of agrin increased brain Na(+) ,K(+) -ATPase activity by 11 ± 4%, whereas no effect on Na(+) ,K(+) -ATPase activity was detected when agrin was suppressed in mice without the Myshkin mutation. These results introduce agrin as a potential therapeutic target for the treatment of mania and other neurological disorders associated with reduced Na(+) ,K(+) -ATPase activity and neuronal hyperexcitability.