12 research outputs found
Elevated synaptic vesicle release probability in synaptophysin/gyrin family quadruple knockouts
Synaptophysins 1 and 2 and synaptogyrins 1 and 3 constitute a major family of
synaptic vesicle membrane proteins. Unlike other widely expressed synaptic vesicle proteins such
as vSNAREs and synaptotagmins, the primary function has not been resolved. Here, we report
robust elevation in the probability of release of readily releasable vesicles with both high and low
release probabilities at a variety of synapse types from knockout mice missing all four family
members. Neither the number of readily releasable vesicles, nor the timing of recruitment to the
readily releasable pool was affected. The results suggest that family members serve as negative
regulators of neurotransmission, acting directly at the level of exocytosis to dampen connection
strength selectively when presynaptic action potentials fire at low frequency. The widespread
expression suggests that chemical synapses may play a frequency filtering role in biological
computation that is more elemental than presently envisioned
Control of protein synthesis and memory by GluN3A-NMDA receptors through inhibition of GIT1/mTORC1 assembly
De novo protein synthesis is required for synapse modifications underlying stable memory encoding. Yet neurons are highly compartmentalized cells and how protein synthesis can be regulated at the synapse level is unknown. Here, we characterize neuronal signaling complexes formed by the postsynaptic scaffold GIT1, the mechanistic target of rapamycin (mTOR) kinase, and Raptor that couple synaptic stimuli to mTOR-dependent protein synthesis; and identify NMDA receptors containing GluN3A subunits as key negative regulators of GIT1 binding to mTOR. Disruption of GIT1/mTOR complexes by enhancing GluN3A expression or silencing GIT1 inhibits synaptic mTOR activation and restricts the mTOR-dependent translation of specific activity-regulated mRNAs. Conversely, GluN3A removal enables complex formation, potentiates mTOR-dependent protein synthesis, and facilitates the consolidation of associative and spatial memories in mice. The memory enhancement becomes evident with light or spaced training, can be achieved by selectively deleting GluN3A from excitatory neurons during adulthood, and does not compromise other aspects of cognition such as memory flexibility or extinction. Our findings provide mechanistic insight into synaptic translational control and reveal a potentially selective target for cognitive enhancement
RNAi-Based GIuN3A Silencing Prevents and Reverses Disease Phenotypes Induced by Mutant huntingtin
Huntington’s disease (HD) is a dominantly inherited neurodegenerative disease caused by expansion of a polyglutamine tract
in the huntingtin protein. HD symptoms include severe motor,
cognitive, and psychiatric impairments that result from
dysfunction and later degeneration of medium-sized spiny
neurons (MSNs) in the striatum. A key early pathogenic mechanism is dysregulated synaptic transmission due to enhanced
surface expression of juvenile NMDA-type glutamate receptors
containing GluN3A subunits, which trigger the aberrant pruning of synapses formed by cortical afferents onto MSNs. Here,
we tested the therapeutic potential of silencing GluN3A expression in YAC128 mice, a well-established HD model. Recombinant adeno-associated viruses encoding a short-hairpin RNA
against GluN3A (rAAV-shGluN3A) were generated, and the
ability of different serotypes to transduce MSNs was compared.
A single injection of rAAV9-shGluN3A into the striatum of
1-month-old mice drove potent (>90%) and long-lasting reductions of GluN3A expression in MSNs, prevented dendritic
spine loss and improved motor performance in YAC128
mice. Later delivery, when spine pathology is already apparent,
was also effective. Our data provide proof-of-concept for
GluN3A silencing as a beneficial strategy to prevent or reverse
corticostriatal disconnectivity and motor impairment in HD
and support the use of RNAi-based or small-molecule approaches for harnessing this therapeutic potential
Phenylbutyrate rescues dendritic spine loss associated with memory déficits in a Mouse modelo f Alzheimer´s disease
Alzheimer’s disease (AD) and ageing are associated with
impaired learning and memory, and recent findings point toward modulating
chromatin remodeling through histone acetylation as a promising
therapeutic strategy. Here we report that systemic administration of the
HDAC inhibitor 4-phenylbutyrate (PBA) reinstated fear learning in the
Tg2576 mouse model of AD. Tg2576 mice develop age-dependent amyloid
pathology and cognitive decline that closely mimics disease progression
in humans. Memory reinstatement by PBA was observed independently
of the disease stage: both in 6-month-old Tg2576 mice, at the
onset of the first symptoms, but also in aged, 12- to 16-month-old mice,
when amyloid plaque deposition and major synaptic loss has occurred.
Reversal of learning deficits was associated to a PBA-induced clearance
of intraneuronal Ab accumulation, which was accompanied by mitigation
of endoplasmic reticulum (ER) stress, and to restoration of dendritic
spine densities of hippocampal CA1 pyramidal neurons to control levels.
Furthermore, the expression of plasticity-related proteins such as the
NMDA receptor subunit NR2B and the synaptic scaffold SAP102 was
significantly increased by PBA. Our data suggest that the beneficial
effects of PBA in memory are mediated both via its chemical chaperone-
like activity and via the transcriptional activation of a cluster of
proteins required for the induction of synaptic plasticity and structural
remodeling
Phenylbutyrate rescues dendritic spine loss associated with memory déficits in a Mouse modelo f Alzheimer´s disease
Alzheimer’s disease (AD) and ageing are associated with
impaired learning and memory, and recent findings point toward modulating
chromatin remodeling through histone acetylation as a promising
therapeutic strategy. Here we report that systemic administration of the
HDAC inhibitor 4-phenylbutyrate (PBA) reinstated fear learning in the
Tg2576 mouse model of AD. Tg2576 mice develop age-dependent amyloid
pathology and cognitive decline that closely mimics disease progression
in humans. Memory reinstatement by PBA was observed independently
of the disease stage: both in 6-month-old Tg2576 mice, at the
onset of the first symptoms, but also in aged, 12- to 16-month-old mice,
when amyloid plaque deposition and major synaptic loss has occurred.
Reversal of learning deficits was associated to a PBA-induced clearance
of intraneuronal Ab accumulation, which was accompanied by mitigation
of endoplasmic reticulum (ER) stress, and to restoration of dendritic
spine densities of hippocampal CA1 pyramidal neurons to control levels.
Furthermore, the expression of plasticity-related proteins such as the
NMDA receptor subunit NR2B and the synaptic scaffold SAP102 was
significantly increased by PBA. Our data suggest that the beneficial
effects of PBA in memory are mediated both via its chemical chaperone-
like activity and via the transcriptional activation of a cluster of
proteins required for the induction of synaptic plasticity and structural
remodeling
GluN3A subunit tunes NMDA receptor synaptic trafficking and content during postnatal brain development
Summary: Signaling via N-methyl-d-aspartate receptors (NMDARs) is critical for the maturation of glutamatergic synapses, partly through a developmental switch from immature synapses expressing primarily GluN2B- and GluN3A-containing subtypes to GluN2A-rich mature ones. This subunit switch is thought to underlie the synaptic stabilization of NMDARs necessary for neural network consolidation. However, the cellular mechanisms controlling the NMDAR exchange remain unclear. Using a combination of single-molecule and confocal imaging and biochemical and electrophysiological approaches, we show that surface GluN3A-NMDARs form a highly diffusive receptor pool that is loosely anchored to synapses. Remarkably, changes in GluN3A subunit expression selectively alter the surface diffusion and synaptic anchoring of GluN2A- but not GluN2B-NMDARs, possibly through altered interactions with cell surface receptors. The effects of GluN3A on NMDAR surface diffusion are restricted to an early time window of postnatal development in rodents, allowing GluN3A subunits to control the timing of NMDAR signaling maturation and neuronal network refinements
Sparse force‑bearing bridges between neighboring synaptic vesicles
Most vesicles in the interior of synaptic terminals are clustered in clouds close to active zone regions of the plasma membrane
where exocytosis occurs. Electron-dense structures, termed bridges, have been reported between a small minority of pairs of
neighboring vesicles within the clouds. Synapsin proteins have been implicated previously, but the existence of the bridges
as stable structures in vivo has been questioned. Here we use electron tomography to show that the bridges are present but
less frequent in synapsin knockouts compared to wildtype. An analysis of distances between neighbors in wildtype tomograms indicated that the bridges are strong enough to resist centrifugal forces likely induced by fxation with aldehydes. The
results confrm that the bridges are stable structures and that synapsin proteins are involved in formation or stabilization
Elevated synaptic vesicle release probability in synaptophysin/gyrin family quadruple knockouts
Synaptophysins 1 and 2 and synaptogyrins 1 and 3 constitute a major family of
synaptic vesicle membrane proteins. Unlike other widely expressed synaptic vesicle proteins such
as vSNAREs and synaptotagmins, the primary function has not been resolved. Here, we report
robust elevation in the probability of release of readily releasable vesicles with both high and low
release probabilities at a variety of synapse types from knockout mice missing all four family
members. Neither the number of readily releasable vesicles, nor the timing of recruitment to the
readily releasable pool was affected. The results suggest that family members serve as negative
regulators of neurotransmission, acting directly at the level of exocytosis to dampen connection
strength selectively when presynaptic action potentials fire at low frequency. The widespread
expression suggests that chemical synapses may play a frequency filtering role in biological
computation that is more elemental than presently envisioned
GluN3A excitatory glycine receptors control adult cortical and amygdalar circuits
International audienceGluN3A is an atypical glycine-binding subunit of NMDA receptors (NMDARs) whose actions in the brain are mostly unknown. Here, we show that the expression of GluN3A subunits controls the excitability of mouse adult cortical and amygdalar circuits via an unusual signaling mechanism involving the formation of excitatory glycine GluN1/GluN3A receptors (eGlyRs) and their tonic activation by extracellular glycine. eGlyRs are mostly extrasy- naptic and reside in specific neuronal populations, including the principal cells of the basolateral amygdala (BLA) and SST-positive interneurons (SST-INs) of the neocortex. In the BLA, tonic eGlyR currents are sensitive to fear-conditioning protocols, are subject to neuromodulation by the dopaminergic system, and control the sta- bility of fear memories. In the neocortex, eGlyRs control the in vivo spiking of SST-INs and the behavior-depen- dent modulation of cortical activity. GluN3A-containing eGlyRs thus represent a novel and widespread signaling modality in the adult brain, with attributes that strikingly depart from those of conventional NMDARs