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Richard L. Huganir - One of the best experts on this subject based on the ideXlab platform.
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SynGAP isoforms differentially regulate synaptic plasticity and dendritic development
eLife, 2020Co-Authors: Yoichi Araki, Ingie Hong, Timothy R Gamache, Leonardo Collado-torres, Joo Heon Shin, Richard L. HuganirAbstract:SynGAP is a synaptic Ras GTPase-activating protein (GAP) with four C-terminal splice variants: α1, α2, β, and γ. Although studies have implicated SYNGAP1 in several cognitive disorders, it is not clear which SynGAP isoforms contribute to disease. Here, we demonstrate that SynGAP isoforms exhibit unique spatiotemporal expression patterns and play distinct roles in neuronal and synaptic development in mouse neurons. SynGAP-α1, which undergoes liquid-liquid phase separation with PSD-95, is highly enriched in synapses and is required for LTP. In contrast, SynGAP-β, which does not bind PSD-95 PDZ domains, is less synaptically targeted and promotes dendritic arborization. A mutation in SynGAP-α1 that disrupts phase separation and synaptic targeting abolishes its ability to regulate plasticity and instead causes it to drive dendritic development like SynGAP-β. These results demonstrate that distinct intrinsic biochemical properties of SynGAP isoforms determine their function, and individual isoforms may differentially contribute to the pathogenesis of SYNGAP1-related cognitive disorders.
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Twenty Years of SynGAP Research: From Synapses to Cognition
The Journal of Neuroscience, 2020Co-Authors: Timothy R Gamache, Yoichi Araki, Richard L. HuganirAbstract:SynGAP is a potent regulator of biochemical signaling in neurons and plays critical roles in neuronal function. It was first identified in 1998, and has since been extensively characterized as a mediator of synaptic plasticity. Because of its involvement in synaptic plasticity, SynGAP has emerged as a critical protein for normal cognitive function. In recent years, mutations in the SYNGAP1 gene have been shown to cause intellectual disability in humans and have been linked to other neurodevelopmental disorders, such as autism spectrum disorders and schizophrenia. While the structure and biochemical function of SynGAP have been well characterized, a unified understanding of the various roles of SynGAP at the synapse and its contributions to neuronal function remains to be achieved. In this review, we summarize and discuss the current understanding of the multifactorial role of SynGAP in regulating neuronal function gathered over the last two decades.
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syngap splice variants display heterogeneous spatio temporal expression and subcellular distribution in the developing mammalian brain
Journal of Neurochemistry, 2020Co-Authors: Gemma Gou, Murat Kilinc, Yoichi Araki, Richard L. Huganir, Adriana Rocafernandez, Elena Serrano, Rita Reigviader, Cristian De QuintanaschmidtAbstract:The SynGAP protein is a major regulator of synapse biology and neural circuit function. Genetic variants linked to epilepsy and intellectual disability disrupt synaptic function and neural excitability. SynGAP has been involved in multiple signaling pathways and can regulate small GTPases with very different roles. Yet, the molecular bases behind this pleiotropy are poorly understood. We hypothesize that different SynGAP isoforms will mediate different sets of functions and that deciphering their spatio-temporal expression and subcellular localization will accelerate understanding their multiple functions. Using isoform-specific antibodies recognizing SynGAP in mouse and human samples we found distinctive developmental expression patterns for all SynGAP isoforms in five mouse brain areas. Particularly noticeable was the delayed expression of SynGAP-α1 isoforms, which directly bind to postsynaptic density-95, in cortex and hippocampus during the first 2 weeks of postnatal development. Suggesting that during this period other isoforms would have a more prominent role. Furthermore, we observed subcellular localization differences between isoforms, particularly throughout postnatal development. Consistent with previous reports, SynGAP was enriched in the postsynaptic density in the mature forebrain. However, SynGAP was predominantly found in non-synaptic locations in a period of early postnatal development highly sensitive to SynGAP levels. While, α1 isoforms were always found enriched in the postsynaptic density, α2 isoforms changed from a non-synaptic to a mostly postsynaptic density localization with age and β isoforms were always found enriched in non-synaptic locations. The differential expression and subcellular distribution of SynGAP isoforms may contribute to isoform-specific regulation of small GTPases, explaining SynGAP pleiotropy.
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SynGAP splice isoforms differentially regulate synaptic plasticity and dendritic development
2020Co-Authors: Yoichi Araki, Ingie Hong, Timothy R Gamache, Leonardo Collado-torres, Joo Heon Shin, Richard L. HuganirAbstract:SynGAP is a synaptic Ras GTPase-activating protein (GAP) with four C-terminal splice variants: α1, α2, β, and γ. Although recent studies have implicated SYNGAP1 haploinsufficiency in ID/ASD pathogenesis, the degree to which each SynGAP isoform contributes to disease pathogenesis remains elusive. Here we demonstrate that individual SynGAP isoforms exhibit unique spatiotemporal expression and have distinct roles in neuronal and synaptic development. The SynGAP-α1 isoform, which undergoes robust liquid-liquid phase-separation with PSD-95 and is highly-enriched in synapses, is expressed late in development and disperses from synaptic spines in response to LTP-inducing synaptic activity to allow for AMPA receptor insertion and spine enlargement. In contrast, the SynGAP-β isoform, which undergoes less liquid-liquid phase-separation with PSD95 and is less synaptically targeted, is expressed early in development and promotes dendritic arborization. Interestingly, a SynGAP-α1 mutation that disrupts phase separation and synaptic targeting abolishes its function in plasticity and instead drives dendritic arbor development like the β isoform. These results demonstrate that distinct phase separation and synaptic targeting properties of SynGAP isoforms determine their function.
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Low-Dose Perampanel Rescues Cortical Gamma Dysregulation Associated With Parvalbumin Interneuron GluA2 Upregulation in Epileptic SYNGAP1+/- Mice.
Biological Psychiatry, 2020Co-Authors: Brennan J. Sullivan, Yoichi Araki, Richard L. Huganir, Simon Ammanuel, Pavel A. Kipnis, Shilpa D. KadamAbstract:Abstract Background Loss-of-function SYNGAP1 mutations cause a neurodevelopmental disorder characterized by intellectual disability and epilepsy. SYNGAP1 is a Ras GTPase-activating protein that underlies the formation and experience-dependent regulation of postsynaptic densities. The mechanisms that contribute to this proposed monogenic cause of intellectual disability and epilepsy remain unresolved. Methods We established the phenotype of the epileptogenesis in a SYNGAP1+/− mouse model using 24-hour video electroencephalography (vEEG)/electromyography recordings at advancing ages. We administered an acute low dose of perampanel, a Food and Drug Administration–approved AMPA receptor (AMPAR) antagonist, during a follow-on 24-hour vEEG to investigate the role of AMPARs in SYNGAP1 haploinsufficiency. Immunohistochemistry was performed to determine the region- and location-specific differences in the expression of the GluA2 AMPAR subunit. Results A progressive worsening of the epilepsy with emergence of multiple seizure phenotypes, interictal spike frequency, sleep dysfunction, and hyperactivity was identified in SYNGAP1+/− mice. Interictal spikes emerged predominantly during non–rapid eye movement sleep in 24-hour vEEG of SYNGAP1+/− mice. Myoclonic seizures occurred at behavioral-state transitions both in SYNGAP1+/− mice and during an overnight EEG from a child with SYNGAP1 haploinsufficiency. In SYNGAP1+/− mice, EEG spectral power analyses identified a significant loss of gamma power modulation during behavioral-state transitions. A significant region-specific increase of GluA2 AMPAR subunit expression in the somas of parvalbumin-positive interneurons was identified. Conclusions Acute dosing with perampanel significantly rescued behavioral state–dependent cortical gamma homeostasis, identifying a novel mechanism implicating Ca2+-impermeable AMPARs on parvalbumin-positive interneurons underlying circuit dysfunction in SYNGAP1 haploinsufficiency.
Mary B Kennedy - One of the best experts on this subject based on the ideXlab platform.
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A sex difference in the response of the rodent postsynaptic density to synGAP haploinsufficiency
eLife, 2020Co-Authors: Tara L Mastro, Anthony Preza, Shinjini Basu, Sumantra Chattarji, Sally M. Till, Peter C. Kind, Mary B KennedyAbstract:SynGAP is a postsynaptic density (PSD) protein that binds to PDZ domains of the scaffold protein PSD-95. We previously reported that heterozygous deletion of SYNGAP1 in mice is correlated with increased steady-state levels of other key PSD proteins that bind PSD-95, although the level of PSD-95 remains constant (Walkup et al., 2016). For example, the ratio to PSD-95 of Transmembrane AMPA-Receptor-associated Proteins (TARPs), which mediate binding of AMPA-type glutamate receptors to PSD-95, was increased in young SYNGAP1+/-mice. Here we show that only females and not males show a highly significant correlation between an increase in TARP and a decrease in synGAP in the PSDs of SYNGAP1+/-rodents. The data reveal a sex difference in the adaptation of the PSD scaffold to synGAP haploinsufficiency.
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phosphorylation of synaptic gtpase activating protein syngap by polo like kinase plk2 alters the ratio of its gap activity toward hras rap1 and rap2 gtpases
Biochemical and Biophysical Research Communications, 2018Co-Authors: Ward G Walkup, Michael J Sweredoski, Robert Graham, Sonja Hess, Mary B KennedyAbstract:SynGAP is a Ras and Rap GTPase-activating protein (GAP) found in high concentration in the postsynaptic density (PSD) fraction from mammalian forebrain where it binds to PDZ domains of PSD-95. Phosphorylation of pure recombinant synGAP by Ca^(2+)/calmodulin-dependent protein kinase II (CaMKII) shifts the balance of synGAP's GAP activity toward inactivation of Rap1; whereas phosphorylation by cyclin-dependent kinase 5 (CDK5) has the opposite effect, shifting the balance toward inactivation of HRas. These shifts in balance contribute to regulation of the numbers of surface AMPA receptors, which rise during synaptic potentiation (CaMKII) and fall during synaptic scaling (CDK5). Polo-like kinase 2 (Plk2/SNK), like CDK5, contributes to synaptic scaling. These two kinases act in concert to reduce the number of surface AMPA receptors following elevated neuronal activity by tagging spine-associated RapGAP protein (SPAR) for degradation, thus raising the level of activated Rap. Here we show that Plk2 also phosphorylates and regulates synGAP. Phosphorylation of synGAP by Plk2 stimulates its GAP activity toward HRas by 65%, and toward Rap1 by 16%. Simultaneous phosphorylation of synGAP by Plk2 and CDK5 at distinct sites produces an additive increase in GAP activity toward HRas (∼230%) and a smaller, non-additive increase in activity toward Rap1 (∼15%). Dual phosphorylation also produces an increase in GAP activity toward Rap2 (∼40–50%), an effect not produced by either kinase alone. As we previously observed for CDK5, addition of Ca^(2+)/CaM causes a substrate-directed doubling of the rate and stoichiometry of phosphorylation of synGAP by Plk2, targeting residues also phosphorylated by CaMKII. In summary, phosphorylation by Plk2, like CDK5, shifts the ratio of GAP activity of synGAP to produce a greater decrease in active Ras than in active Rap, which would produce a shift toward a decrease in the number of surface AMPA receptors in neuronal dendrites.
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a model for regulation by syngap α1 of binding of synaptic proteins to pdz domain slots in the postsynaptic density
eLife, 2016Co-Authors: Ward G Walkup, Tara L Mastro, Leslie T Schenker, Jost Vielmetter, Rebecca Hu, Ariella Iancu, Meera Reghunathan, Barry Dylan Bannon, Mary B KennedyAbstract:The formation of memories is believed to depend on the strengthening of connections, called synapses, between neurons in the brain. When neurons are activated together, their synaptic connections become permanently strengthened to record the memory. This strengthening is called activity-dependent long-term potentiation. As long-term potentiation develops, more protein receptors are added to the receiving side of the synapse. This allows the receiving neuron to produce a larger electrical response to the signaling chemicals it receives from the neuron on the sending side of the synapse. The addition of receptors is regulated by a set of enzymes held near the membrane of the synapse by a protein scaffold known as the postsynaptic density. A major scaffold protein called PSD-95 contains binding sites, known as PDZ domains, that hold protein receptors and regulatory enzymes in place. One regulatory enzyme called synGAP is present in large numbers in the postsynaptic density and binds to the same PDZ domains as the receptors. Humans that have just one copy (instead of the usual two) of the gene that encodes synGAP have cognitive disabilities that are often accompanied by autism and epilepsy. By studying purified proteins, Walkup et al. found that adding phosphate groups to synGAP reduces the enzyme’s ability to bind to the PDZ domains. This reduced binding ability could make more PDZ domains available to bind to protein receptors and hold them at the synapse. To measure the effect of reduced synGAP levels on the proteins found at postsynaptic densities, Walkup et al. used mice that had just one copy of the synGAP gene in their neurons. These mice have less synGAP in their postsynaptic densities and more of three proteins that bind to PDZ domains. These proteins hold receptors in the synapse and help synapses to form. Thus, synGAP may restrict the binding of other proteins to the PDZ domains in order to regulate the strength of the synapse. Further experiments are now needed to investigate the importance of restriction by synGAP of binding to PDZ domains under a variety of circumstances in which the activity of neurons alters the strength of synapses.
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phosphorylation of synaptic gtpase activating protein syngap by ca2 calmodulin dependent protein kinase ii camkii and cyclin dependent kinase 5 cdk5 alters the ratio of its gap activity toward ras and rap gtpases
Journal of Biological Chemistry, 2015Co-Authors: Ward G Walkup, Lorraine R Washburn, Michael J Sweredoski, Holly J Carlisle, Robert Graham, Sonja Hess, Mary B KennedyAbstract:SynGAP is a neuron-specific Ras and Rap GTPase-activating protein (GAP) found in high concentration in the postsynaptic density (PSD) fraction from mammalian forebrain. We have previously shown that, in situ in the PSD fraction or in recombinant form in Sf9 cell membranes, synGAP is phosphorylated by Ca^(2+)/calmodulin-dependent protein kinase II (CaMKII), another prominent component of the PSD. Here we show that recombinant synGAP (r-synGAP), lacking 102 residues at the N-terminus, can be purified in soluble form and is phosphorylated by cyclin-dependent kinase 5 (CDK5) as well as by CaMKII. Phos-phorylation of r-synGAP by CaMKII increases its HRas GAP activity by 25% and its Rap1 GAP activity by 76%. Conversely, phosphorylation by CDK5 increases r-synGAPs HRas GAP activity by 98% and its Rap1 GAP activity by 20%. Thus, phosphorylation by both kinases increases synGAP activity, but CaMKII shifts the relative GAP activity toward inactivation of Rap1; whereas CDK5 shifts the relative activity toward inactivation of HRas. GAP activity toward Rap2 is not altered by phosphorylation by either kinase. CDK5 phosphorylates synGAP primarily at two sites, S773 and S802. Phosphorylation at S773 inhibits r-synGAP activity, whereas phosphorylation at S802 increases it. However, the net effect of concurrent phosphorylation of both sites, S773 and S802, is an increase in GAP activity. SynGAP is phosphorylated at S773 and S802 in the PSD fraction, and its phosphorylation by CDK5 and CaMKII is differentially regulated by activation of NMDA-type glutamate receptors in cultured neurons.
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Molecular and behavioral changes associated with adult hippocampus-specific SYNGAP1 knockout
Learning & Memory, 2012Co-Authors: Mary Muhia, Mary B Kennedy, Silvia Willadt, Benjamin K. Yee, Joram Feldon, Jean-charles Paterna, Severin Schwendener, Kaspar E. Vogt, Irene KnueselAbstract:The synaptic Ras/Rap-GTPase-activating protein (SYNGAP1) plays a unique role in regulating specific downstream intracellular events in response to N-methyl-D-aspartate receptor (NMDAR) activation. Constitutive heterozygous loss of SYNGAP1 disrupts NMDAR-mediated physiological and behavioral processes, but the disruptions might be of developmental origin. Therefore, the precise role of SYNGAP1 in the adult brain, including its relative functional significance within specific brain regions, remains unexplored. The present study constitutes the first attempt in achieving adult hippocampal-specific SYNGAP1 knockout using the Cre/loxP approach. Here, we report that this manipulation led to a significant numerical increase in both small and large GluA1 and NR1 immunoreactive clusters, many of which were non-opposed to presynaptic terminals. In parallel, the observed marked decline in the amplitude of spontaneous excitatory currents (sEPSCs) and inter-event intervals supported the impression that SYNGAP1 loss might facilitate the accumulation of extrasynaptic glutamatergic receptors. In addition, SYNGAP1-mediated signaling appears to be critical for the proper integration and survival of newborn neurons. The manipulation impaired reversal learning in the probe test of the water maze and induced a delay-dependent impairment in spatial recognition memory. It did not significantly affect anxiety or reference memory acquisition but induced a substantial elevation in spontaneous locomotor activity in the open field test. Thus, the present study demonstrates the functional significance of SYNGAP1 signaling in the adult brain by capturing several changes that are dependent on NMDAR and hippocampal integrity.
Yoichi Araki - One of the best experts on this subject based on the ideXlab platform.
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SynGAP isoforms differentially regulate synaptic plasticity and dendritic development
eLife, 2020Co-Authors: Yoichi Araki, Ingie Hong, Timothy R Gamache, Leonardo Collado-torres, Joo Heon Shin, Richard L. HuganirAbstract:SynGAP is a synaptic Ras GTPase-activating protein (GAP) with four C-terminal splice variants: α1, α2, β, and γ. Although studies have implicated SYNGAP1 in several cognitive disorders, it is not clear which SynGAP isoforms contribute to disease. Here, we demonstrate that SynGAP isoforms exhibit unique spatiotemporal expression patterns and play distinct roles in neuronal and synaptic development in mouse neurons. SynGAP-α1, which undergoes liquid-liquid phase separation with PSD-95, is highly enriched in synapses and is required for LTP. In contrast, SynGAP-β, which does not bind PSD-95 PDZ domains, is less synaptically targeted and promotes dendritic arborization. A mutation in SynGAP-α1 that disrupts phase separation and synaptic targeting abolishes its ability to regulate plasticity and instead causes it to drive dendritic development like SynGAP-β. These results demonstrate that distinct intrinsic biochemical properties of SynGAP isoforms determine their function, and individual isoforms may differentially contribute to the pathogenesis of SYNGAP1-related cognitive disorders.
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Twenty Years of SynGAP Research: From Synapses to Cognition
The Journal of Neuroscience, 2020Co-Authors: Timothy R Gamache, Yoichi Araki, Richard L. HuganirAbstract:SynGAP is a potent regulator of biochemical signaling in neurons and plays critical roles in neuronal function. It was first identified in 1998, and has since been extensively characterized as a mediator of synaptic plasticity. Because of its involvement in synaptic plasticity, SynGAP has emerged as a critical protein for normal cognitive function. In recent years, mutations in the SYNGAP1 gene have been shown to cause intellectual disability in humans and have been linked to other neurodevelopmental disorders, such as autism spectrum disorders and schizophrenia. While the structure and biochemical function of SynGAP have been well characterized, a unified understanding of the various roles of SynGAP at the synapse and its contributions to neuronal function remains to be achieved. In this review, we summarize and discuss the current understanding of the multifactorial role of SynGAP in regulating neuronal function gathered over the last two decades.
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syngap splice variants display heterogeneous spatio temporal expression and subcellular distribution in the developing mammalian brain
Journal of Neurochemistry, 2020Co-Authors: Gemma Gou, Murat Kilinc, Yoichi Araki, Richard L. Huganir, Adriana Rocafernandez, Elena Serrano, Rita Reigviader, Cristian De QuintanaschmidtAbstract:The SynGAP protein is a major regulator of synapse biology and neural circuit function. Genetic variants linked to epilepsy and intellectual disability disrupt synaptic function and neural excitability. SynGAP has been involved in multiple signaling pathways and can regulate small GTPases with very different roles. Yet, the molecular bases behind this pleiotropy are poorly understood. We hypothesize that different SynGAP isoforms will mediate different sets of functions and that deciphering their spatio-temporal expression and subcellular localization will accelerate understanding their multiple functions. Using isoform-specific antibodies recognizing SynGAP in mouse and human samples we found distinctive developmental expression patterns for all SynGAP isoforms in five mouse brain areas. Particularly noticeable was the delayed expression of SynGAP-α1 isoforms, which directly bind to postsynaptic density-95, in cortex and hippocampus during the first 2 weeks of postnatal development. Suggesting that during this period other isoforms would have a more prominent role. Furthermore, we observed subcellular localization differences between isoforms, particularly throughout postnatal development. Consistent with previous reports, SynGAP was enriched in the postsynaptic density in the mature forebrain. However, SynGAP was predominantly found in non-synaptic locations in a period of early postnatal development highly sensitive to SynGAP levels. While, α1 isoforms were always found enriched in the postsynaptic density, α2 isoforms changed from a non-synaptic to a mostly postsynaptic density localization with age and β isoforms were always found enriched in non-synaptic locations. The differential expression and subcellular distribution of SynGAP isoforms may contribute to isoform-specific regulation of small GTPases, explaining SynGAP pleiotropy.
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SynGAP splice isoforms differentially regulate synaptic plasticity and dendritic development
2020Co-Authors: Yoichi Araki, Ingie Hong, Timothy R Gamache, Leonardo Collado-torres, Joo Heon Shin, Richard L. HuganirAbstract:SynGAP is a synaptic Ras GTPase-activating protein (GAP) with four C-terminal splice variants: α1, α2, β, and γ. Although recent studies have implicated SYNGAP1 haploinsufficiency in ID/ASD pathogenesis, the degree to which each SynGAP isoform contributes to disease pathogenesis remains elusive. Here we demonstrate that individual SynGAP isoforms exhibit unique spatiotemporal expression and have distinct roles in neuronal and synaptic development. The SynGAP-α1 isoform, which undergoes robust liquid-liquid phase-separation with PSD-95 and is highly-enriched in synapses, is expressed late in development and disperses from synaptic spines in response to LTP-inducing synaptic activity to allow for AMPA receptor insertion and spine enlargement. In contrast, the SynGAP-β isoform, which undergoes less liquid-liquid phase-separation with PSD95 and is less synaptically targeted, is expressed early in development and promotes dendritic arborization. Interestingly, a SynGAP-α1 mutation that disrupts phase separation and synaptic targeting abolishes its function in plasticity and instead drives dendritic arbor development like the β isoform. These results demonstrate that distinct phase separation and synaptic targeting properties of SynGAP isoforms determine their function.
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Low-Dose Perampanel Rescues Cortical Gamma Dysregulation Associated With Parvalbumin Interneuron GluA2 Upregulation in Epileptic SYNGAP1+/- Mice.
Biological Psychiatry, 2020Co-Authors: Brennan J. Sullivan, Yoichi Araki, Richard L. Huganir, Simon Ammanuel, Pavel A. Kipnis, Shilpa D. KadamAbstract:Abstract Background Loss-of-function SYNGAP1 mutations cause a neurodevelopmental disorder characterized by intellectual disability and epilepsy. SYNGAP1 is a Ras GTPase-activating protein that underlies the formation and experience-dependent regulation of postsynaptic densities. The mechanisms that contribute to this proposed monogenic cause of intellectual disability and epilepsy remain unresolved. Methods We established the phenotype of the epileptogenesis in a SYNGAP1+/− mouse model using 24-hour video electroencephalography (vEEG)/electromyography recordings at advancing ages. We administered an acute low dose of perampanel, a Food and Drug Administration–approved AMPA receptor (AMPAR) antagonist, during a follow-on 24-hour vEEG to investigate the role of AMPARs in SYNGAP1 haploinsufficiency. Immunohistochemistry was performed to determine the region- and location-specific differences in the expression of the GluA2 AMPAR subunit. Results A progressive worsening of the epilepsy with emergence of multiple seizure phenotypes, interictal spike frequency, sleep dysfunction, and hyperactivity was identified in SYNGAP1+/− mice. Interictal spikes emerged predominantly during non–rapid eye movement sleep in 24-hour vEEG of SYNGAP1+/− mice. Myoclonic seizures occurred at behavioral-state transitions both in SYNGAP1+/− mice and during an overnight EEG from a child with SYNGAP1 haploinsufficiency. In SYNGAP1+/− mice, EEG spectral power analyses identified a significant loss of gamma power modulation during behavioral-state transitions. A significant region-specific increase of GluA2 AMPAR subunit expression in the somas of parvalbumin-positive interneurons was identified. Conclusions Acute dosing with perampanel significantly rescued behavioral state–dependent cortical gamma homeostasis, identifying a novel mechanism implicating Ca2+-impermeable AMPARs on parvalbumin-positive interneurons underlying circuit dysfunction in SYNGAP1 haploinsufficiency.
Gavin Rumbaugh - One of the best experts on this subject based on the ideXlab platform.
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SynGAP is expressed in the murine suprachiasmatic nucleus and regulates circadian-gated locomotor activity and light-entrainment capacity.
The European journal of neuroscience, 2020Co-Authors: Sydney Aten, Gavin Rumbaugh, Anisha Kalidindi, Hyojung Yoon, Kari R. Hoyt, Karl ObrietanAbstract:The suprachiasmatic nucleus (SCN) of the hypothalamus functions as the master circadian clock. The phasing of the SCN oscillator is locked to the daily solar cycle, and an intracellular signaling cassette from the small GTPase Ras to the p44/42 mitogen-activated protein kinase (ERK/MAPK) pathway is central to this entrainment process. Here, we analyzed the expression and function of SynGAP-a GTPase-activating protein that serves as a negative regulator of Ras signaling-within the murine SCN. Using a combination of immunohistochemical and Western blotting approaches, we show that SynGAP is broadly expressed throughout the SCN. In addition, temporal profiling assays revealed that SynGAP expression is regulated over the circadian cycle, with peak expression occurring during the circadian night. Further, time-of-day-gated expression of SynGAP was not observed in clock arrhythmic BMAL1 null mice, indicating that the daily oscillation in SynGAP is driven by the inherent circadian timing mechanism. We also show that SynGAP phosphorylation at serine 1138-an event that has been found to modulate its functional efficacy-is regulated by clock time and is responsive to photic input. Finally, circadian phenotypic analysis of SYNGAP1 heterozygous mice revealed enhanced locomotor activity, increased sensitivity to light-evoked clock entrainment, and elevated levels of light-evoked MAPK activity, which is consistent with the role of SynGAP as a negative regulator of MAPK signaling. These findings reveal that SynGAP functions as a modulator of SCN clock entrainment, an effect that may contribute to sleep and circadian abnormalities observed in patients with SYNGAP1 gene mutations.
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SYNGAP1 Dynamically Regulates the Fine-Scale Reorganization of Cortical Circuits in Response to Sensory Experience
2020Co-Authors: Nerea Llamosas, Thomas Vaissiere, Camilo Rojas, Courtney A Miller, Sheldon D. Michaelson, Gavin RumbaughAbstract:Experience induces complex, neuron-specific changes in population activity within sensory cortex circuits. However, the mechanisms that enable neuron-specific changes within cortical populations remain unclear. To explore the idea that synapse strengthening is involved, we studied fine-scale cortical plasticity in SYNGAP1 mice, a neurodevelopmental disorder model useful for linking synapse biology to circuit functions. Repeated functional imaging of the same L2/3 somatosensory cortex neurons during single whisker experience revealed that SYNGAP1 selectively regulated the plasticity of a low-active, or silent, neuronal subpopulation. SYNGAP1 also regulated spike-timing-dependent synaptic potentiation and experience-mediated in vivo synapse bouton formation, but not synaptic depression or bouton elimination in L2/3. Adult re-expression of SYNGAP1 restored plasticity of silent neurons, demonstrating that this gene controls dynamic cellular processes required for population-specific changes to cortical circuits during experience. These findings suggest that abnormal experience-dependent redistribution of cortical population activity may contribute to the etiology of neurodevelopmental disorders.
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syngap splice variants display heterogeneous spatio temporal expression and subcellular distribution in the developing mammalian brain
bioRxiv, 2019Co-Authors: Gemma Gou, Gavin Rumbaugh, Murat Kilinc, Yoichi Araki, Richard L. Huganir, Adriana Rocafernandez, Elena Serrano, Rita Reigviader, Cristian De Quintanaschmidt, Àlex BayésAbstract:Abstract The SYNGAP1 gene is a major regulator of synapse biology and neural circuit function. Genetic variants linked to epilepsy and intellectual disability disrupt synaptic function and neural excitability. The SynGAP protein has been involved in multiple signaling pathways and can regulate small GTPases with very different functions. Yet, the molecular bases behind this pleiotropy are poorly understood. We hypothesize that different SynGAP isoforms will mediate different sets of functions and that deciphering their spatio-temporal expression and subcellular localization will accelerate our understanding of the multiple functions performed by SynGAP. Using antibodies that detect all isoforms of SynGAP, we found that its subcellular localization changed throughout postnatal development. Consistent with previous reports, SynGAP was enriched in the postsynaptic density in the mature forebrain. However, this was age-dependent and SynGAP was predominantly found in non-synaptic locations in a period of postnatal development highly sensitive to SynGAP levels. Furthermore, we identified different expression patterns in the spatial and temporal axes for different SynGAP isoforms. Particularly noticeable was the delayed expression of SynGAP α1 isoforms, which bind to PSD-95 at the postsynaptic density, in cortex and hippocampus during the first two weeks of postnatal development. The subcellular localization of SynGAP was also isoform-dependent. While, α1 isoforms were highly enriched in the postsynaptic density, other C-terminal isoforms were less enriched or even more abundant in non-synaptic locations, particularly during the postnatal period. Thus, the regulation of expression and subcellular distribution of SynGAP isoforms may contribute to isoform-specific regulation of small GTPases, explaining SynGAP pleiotropy.
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Re-expression of SynGAP Protein in Adulthood Improves Translatable Measures of Brain Function and Behavior in a Model of Neurodevelopmental Disorders
2018Co-Authors: Thomas K Creson, Thomas Vaissiere, Camilo Rojas, Courtney A Miller, Ernie Hwaun, Murat Kilinc, J. Lloyd Holder, Jianrong Tang, Laura Lee Colgin, Gavin RumbaughAbstract:Background: Neurodevelopmental disorder (NDD) risk genes have pleiotropic biological functions, such as control over both developmental and non-developmental processes that influence disease-related phenotypes. Currently, it remains unclear how developmental versus non-developmental processes influence the duration and/or effectiveness of permissive treatment windows for NDDs. SYNGAP1 haploinsufficiency causes an NDD defined by autistic traits, cognitive impairment, and epilepsy. SYNGAP1 heterozygosity in mice disrupts a developmental critical period, and, consistent with this, certain behavioral abnormalities are resistant to gene therapy initiated in adulthood. However, the SYNGAP1 endophenotype is extensive and this protein has diverse cell biological functions. Therefore, SynGAP pleiotropy may influence the permissive treatment window for previously untested disease-relevant phenotypes. Methods: A whole-body gene restoration technique was used to determine how restoration of SynGAP protein in adult heterozygous mice impacted previously untested phenotypes, such as memory, seizure susceptibility, systems-level cortical hyperexcitability, and hippocampal oscillations linked to mnemonic processes. Results: Adult restoration of SynGAP protein in haploinsufficient mice reversed long-term contextual memory deficits and behavioral measures of seizure susceptibility. Moreover, SynGAP re-expression in adult mice eliminated brain state-dependent, patient-linked paroxysmal interictal spiking and increased the amplitude of hippocampal theta oscillations. Conclusions: SynGAP protein in the mature brain dynamically regulates neural circuit function and influences disease-relevant phenotypes. The impact of these findings is that treatments targeting certain debilitating aspects of SYNGAP1-related disorders may be effective throughout life. Moreover, the efficacy of experimental treatments for SYNGAP1 patients may be quantifiable through changes in species-conserved, state-dependent pathological electroencephalogram signals.
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The first international conference on SYNGAP1-related brain disorders: a stakeholder meeting of families, researchers, clinicians, and regulators
Journal of Neurodevelopmental Disorders, 2018Co-Authors: Monica Weldon, Murat Kilinc, J. Lloyd Holder, Gavin RumbaughAbstract:Background Pathologic mutations in SYNGAP1 cause a genetically defined form of intellectual disability (ID) with comorbid epilepsy and autistic features. While only recently discovered, pathogenicity of this gene is a relatively frequent genetic cause of classically undefined developmental delay that progresses to ID with commonly occurring comorbidities. Main body A meeting of 150 people was held that included affected individuals and their caregivers, clinicians that treat this and related brain disorders, neuroscientists that study SYNGAP1 biology or the function of related genes, and representatives from government agencies that fund science and approve new medical treatments. The meeting focused on developing a consensus among all stakeholders as to how best to achieve a more fundamental and profound understanding of SYNGAP1 biology and its role in human disease. Short conclusion From all of these proceedings, several areas of consensus emerged. The clinicians and geneticists agreed that the prevalence of epilepsy and sensory processing impairments in SYNGAP1 -related brain disorders approached 100%. The neurobiologists agreed that more basic research is needed to better understand the molecular and cellular functions of the SYNGAP1 gene, which will lead to targets for therapeutic intervention. Finally, everyone agreed that there is a pressing need to form a robust patient registry as an initial step toward a prospective natural history study of patients with pathogenic SYNGAP1 variants.
Fadi F. Hamdan - One of the best experts on this subject based on the ideXlab platform.
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Decrease of SYNGAP1 in GABAergic cells impairs inhibitory synapse connectivity, synaptic inhibition and cognitive function.
Nature Communications, 2016Co-Authors: Martin H. Berryer, Bidisha Chattopadhyaya, Paul Xing, Ilse Riebe, Ciprian M. Bosoi, Nathalie T. Sanon, Judith Antoine-bertrand, Maxime Lévesque, Massimo Avoli, Fadi F. HamdanAbstract:Haploinsufficiency of the SYNGAP1 gene, which codes for a Ras GTPase-activating protein, impairs cognition both in humans and in mice. Decrease of SYNGAP1 in mice has been previously shown to cause cognitive deficits at least in part by inducing alterations in glutamatergic neurotransmission and premature maturation of excitatory connections. Whether SYNGAP1 plays a role in the development of cortical GABAergic connectivity and function remains unclear. Here, we show that SYNGAP1 haploinsufficiency significantly reduces the formation of perisomatic innervations by parvalbumin-positive basket cells, a major population of GABAergic neurons, in a cell-autonomous manner. We further show that SYNGAP1 haploinsufficiency in GABAergic cells derived from the medial ganglionic eminence impairs their connectivity, reduces inhibitory synaptic activity and cortical gamma oscillation power, and causes cognitive deficits. Our results indicate that SYNGAP1 plays a critical role in GABAergic circuit function and further suggest that SYNGAP1 haploinsufficiency in GABAergic circuits may contribute to cognitive deficits.
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Mutations in SYNGAP1 Cause Intellectual Disability, Autism, and a Specific Form of Epilepsy by Inducing Haploinsufficiency
Human Mutation, 2012Co-Authors: Martin H. Berryer, Fadi F. Hamdan, Rikke S. Møller, Laura L. Klitten, Lionel Carmant, Jeremy Schwartzentruber, Lysanne Patry, Sylvia Dobrzeniecka, Daniel Rochefort, Mathilde Neugnot-cerioliAbstract:De novo mutations in SYNGAP1, which codes for a RAS/RAP GTP-activating protein, cause nonsyndromic intellectual disability (NSID). All disease-causing point mutations identified until now in SYNGAP1 are truncating, raising the possibility of an association between this type of mutations and NSID. Here, we report the identification of the first pathogenic missense mutations (c.1084T>C [p.W362R], c.1685C>T [p.P562L]) and three novel truncating mutations (c.283dupC [p.H95PfsX5], c.2212_2213del [p.S738X], and (c.2184del [p.N729TfsX31]) in SYNGAP1 in patients with NSID. A subset of these patients also showed ataxia, autism, and a specific form of generalized epilepsy that can be refractory to treatment. All of these mutations occurred de novo, except c.283dupC, which was inherited from a father who is a mosaic. Biolistic transfection of wild-type SYNGAP1 in pyramidal cells from cortical organotypic cultures significantly reduced activity-dependent phosphorylated extracellular signal-regulated kinase (pERK) levels. In contrast, constructs expressing p.W362R, p.P562L, or the previously described p.R579X had no significant effect on pERK levels. These experiments suggest that the de novo missense mutations, p.R579X, and possibly all the other truncating mutations in SYNGAP1 result in a loss of its function. Moreover, our study confirms the involvement of SYNGAP1 in autism while providing novel insight into the epileptic manifestations associated with its disruption.
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De novo SYNGAP1 mutations in nonsyndromic intellectual disability and autism.
Biological Psychiatry, 2011Co-Authors: Fadi F. Hamdan, Sylvia Dobrzeniecka, Julie Gauthier, Hussein Daoud, Amélie Piton, Marie-odile Krebs, Ridha Joober, Jean-claude Lacaille, Amélie Nadeau, Jeff M. MilunskyAbstract:Background Little is known about the genetics of nonsyndromic intellectual disability (NSID). Recently, we reported de novo truncating mutations in the SYNGAP1 gene of 3 of 94 NSID cases, suggesting that its disruption represents a common cause of autosomal dominant NSID. Methods To further explore the involvement of SYNGAP1 in NSID, we sequenced its exons and intronic boundaries in 60 additional sporadic cases of NSID, including 30 patients with autism spectrum disorders (ASD) and 9 with epilepsy, and in 380 control individuals. Results We identified de novo out-of-frame deletions in two patients with NSID and mild generalized epilepsy (c.2677delC/p.Q893RfsX184 and c.321_324delGAAG/p. K108VfsX25) and a de novo splicing mutation (c.2294 + 1G>A), which results in the creation of a premature stop codon, in a patient with NSID and autism. No splicing or truncating mutations were found in control subjects. Conclusions We provide evidence that truncating mutations in SYNGAP1 are common in NSID and can be also associated with autism.
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Mutations in SYNGAP1 in autosomal nonsyndromic mental retardation.
New England Journal of Medicine, 2009Co-Authors: Fadi F. Hamdan, Sylvia Dobrzeniecka, Julie Gauthier, Dan Spiegelman, Anne Noreau, Yan Yang, Stéphanie Pellerin, Mélanie Côté, Elizabeth Perreau-linck, Lionel CarmantAbstract:Although autosomal forms of nonsyndromic mental retardation account for the majority of cases of mental retardation, the genes that are involved remain largely unknown. We sequenced the autosomal gene SYNGAP1, which encodes a ras GTPase-activating protein that is critical for cognition and synapse function, in 94 patients with nonsyndromic mental retardation. We identified de novo truncating mutations (K138X, R579X, and L813RfsX22) in three of these patients. In contrast, we observed no de novo or truncating mutations in SYNGAP1 in samples from 142 subjects with autism spectrum disorders, 143 subjects with schizophrenia, and 190 control subjects. These results indicate that SYNGAP1 disruption is a cause of autosomal dominant nonsyndromic mental retardation.
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SYNGAP1-Related Intellectual Disability
1993Co-Authors: J. Lloyd Holder, Fadi F. Hamdan, Jacques L. MichaudAbstract:Clinical characteristics SYNGAP1-related intellectual disability (SYNGAP1-ID) is characterized by developmental delay (DD) or intellectual disability (ID) (100% of affected individuals), generalized epilepsy (~84%), and autism spectrum disorder (ASD) and other behavioral abnormalities (≤50%). To date more than 50 individuals with SYNGAP1-ID have been reported. In the majority DD/ID was moderate to severe; in some it was mild. The epilepsy is generalized; a subset of individuals with epilepsy have myoclonic astatic epilepsy (Doose syndrome) or epilepsy with myoclonic absences. Behavioral abnormalities can include stereotypic behaviors (e.g., hand flapping, obsessions with certain objects) as well as poor social development. Feeding difficulties can be significant in some. Diagnosis/testing The diagnosis of SYNGAP1-ID is established in a proband with developmental delay or intellectual disability in whom molecular genetic testing identifies either a heterozygous pathogenic variant in SYNGAP1 (~89%) or a deletion of 6p21.3 (~11%). Management Treatment of manifestations: DD/ID are managed as per standard practice. No guidelines are available regarding choice of specific antiepileptic drugs (AEDs). In about 50% of patients, the epilepsy responds to a single antiepileptic drug (AED); in the remainder it is pharmacoresistant. Children may qualify for and benefit from interventions used in treatment of ASD. Consultation with a developmental pediatrician may guide parents through appropriate behavioral management strategies and/or provide prescription medications when necessary. Nasogastric/gastrostomy feeding may be required for individuals with persistent feeding issues. Surveillance: Monitor seizure manifestations and control; behavioral issues; developmental progress and educational needs. Genetic counseling SYNGAP1-ID is inherited in an autosomal dominant manner. To date almost all probands with SYNGAP1-ID whose parents have undergone molecular genetic testing have had a de novo germline pathogenic variant; however, vertical transmission (from a mildly affected, mosaic parent to the proband) has been reported in one family. Thus, while the risk to sibs appears to be low, it is presumed to be greater than in the general population because of the possibility of germline mosaicism in a parent. Once the SYNGAP1 pathogenic variant has been identified in an affected family member, prenatal testing for a pregnancy at increased risk and preimplantation genetic diagnosis are possible.
