Biology subjects

Paoletti, P.

Publications and source records attributed to Paoletti, P..

5 recordsLinked to original sources

bioRxiv2026

Distribution, assembly and mechanism of GluN1/GluN3A excitatory glycine receptors

NMDA receptors play key roles in brain development, plasticity and diseases. While glutamate and glycine co-gated GluN2-containing NMDARs have been extensively characterized, little is known regarding GluN3A-containing NMDARs that form receptors gated by glycine only. Here, combining native purification, mass spectrometry, cryo-EM and electrophysiology, we provide key insights on the molecular logic of GluN3A-NMDARs. We demonstrate that native GluN3A receptors account for a sizeable fraction of total NMDARs, are enriched at extrasynaptic compartments in the adult brain, and assemble specifically as diheteromeric GluN1/GluN3A excitatory glycine receptors (eGlyRs) rather than as triheteromeric GluN1/GluN2/GluN3A receptors. The architecture of eGlyRs reveal splayed and loosely packed extracellular domains, strikingly different from conventional GluN1/GluN2 receptors. Through back-and- forth structural and functional validations, we demonstrate how the combined effects of a weak ligand-binding domain (LBD) dimer interface and high intrinsic mobility of the N-terminal domains (NTDs) shape the atypical gating of eGlyRs. These findings illuminate GluN3A-NMDAR physiology and mechanism, with implications for neuronal signaling and pharmacology.

neuroscience↗

bioRxiv2024

Optical profiling of NMDA receptor molecular diversity at synaptic and extrasynaptic sites

Neurotransmitter receptors are the linchpin of neuronal communication. These receptors often form large multimeric complexes that differ in their subunit composition, distribution and signaling properties. Studying individual subtypes in native tissues with subunit stoichiometry resolution remains challenging. This is the case of NMDA receptors (NMDARs), a class of glutamate-gated ion channels playing essential roles in brain development and plasticity. These receptors co-exist as multiple subtypes, with GluN1/GluN2A (GluN2A diheteromers), GluN1/GluN2B (GluN2B diheteromers) and GluN1/GluN2A/GluN2B (GluN2A/GluN2B triheteromers) receptors prevailing in the adult forebrain. Despite numerous investigations, the relative abundance and subcellular distribution of these subtypes remain contentious. Here, we designed a photochemical tool (Opto2B) enabling specific and reversible modulation of GluN2B diheteromers, while leaving other receptor subtypes unaffected (in particular GluN2A/GluN2B tri-heteromers). Using Opto2B, we established the differential contribution of GluN2B diheteromers to synaptic and extrasynaptic NMDAR pools during development. In particular, we show that in adult hippocampal CA1 pyramidal cells, GluN2A-receptors predominate in both pools, with no preferential contribution of GluN2B diheteromers to extrasynaptic currents. Our study clarifies decades of controversial research on extrasynaptic NMDARs and paves the way for interrogating NMDAR signaling diversity with unprecedented molecular and spatio-temporal resolution. Significance StatementPharmacological and genetic approaches, the gold standards for investigating receptor diversity, cannot easily distinguish between receptor populations containing one or more copies of the same subunit. For NMDARs, discriminating GluN2A/GluN2B triheteromers (containing one copy of GluN2A and one copy of GluN2B) from their diheteromeric counterparts (containing two copies of GluN2A or GluN2B) remains difficult. Here, we designed the first tool (Opto2B) allowing selective modulation of GluN2B diheteromers, leaving GluN2A/GluN2B triheteromers unaffected. Using Opto2B, we show that GluN2B diheteromers form a minor population in both synaptic and extrasynaptic compartments of the adult CA1 hippocampus, refuting the common belief of an enrichment of GluN2B diheteromers at extrasynaptic sites. This study should inform future drug discovery programs and studies on NMDAR molecular physiology.

neuroscience↗

bioRxiv2023

Reversible inhibition of GluN2B-containing NMDA receptors with an in situ red-shifted, photodependent antagonist

NMDA receptors (NMDARs) are glutamate-gated ion channels playing a central role in synaptic transmission and plasticity. Dysregulation of NMDARs is linked to various neuropsychiatric disorders, emphasizing the need to understand the functional roles of individual NMDAR subtypes in the brain. GluN2B-containing NMDARs (GluN2B-NMDARs) are particularly important due to both pro-cognitive and pro-excitotoxic roles, although these functions remain under debate. Traditional pharmacological and genetic approaches have important shortcomings in terms of specificity and spatio-temporal resolution, limiting their use in native tissues. We therefore turned to optopharmacology, a technique based on the use of photosensitive ligands, whose activity can be reversibly tuned via illumination with different wavelengths. We developed OptoNAM-3, an azobenzene-based, photoswitchable negative allosteric modulator selective for GluN2B-NMDARs. OptoNAM-3 is a potent inhibitor of GluN2B-NMDARs in its trans configuration and inactive in its cis configuration. When bound to GluN2B-NMDARs, OptoNAM-3 displays remarkable red-shifting of its photoswitching properties that we attributed to geometric constraints imposed by the binding site onto the ligand azobenzene moiety. OptoNAM-3 allowed fast and reversible photomodulation of GluN2B-NMDAR activity in vitro using either UV/green or blue/green light illumination cycles. OptoNAM-3 furthermore acted as a reversible, red-shifted in vivo photomodulator of Xenopus tadpole locomotion. By enabling fast and reversible photocontrol of endogenous GluN2B-NMDARs with in vivo compatible photochemical properties, OptoNAM-3 should advance our understanding of the role of this class of NMDARs in brain function and dysfunction. Significance statementThis article presents the development and characterization of a photoswitchable negative allosteric modulator (NAM) targeting GluN2B-containing NMDA receptors (GluN2B-NMDARs). Traditional GluN2B-selective NAMs suffer from slow kinetics and irreversible effects, limiting their use in native tissues. OptoNAM-3 emerged as a potent and selective inhibitor of GluN2B-NMDARs, exhibiting fast temporal resolution of action and reversibility both in vitro and in vivo. OptoNAM-3 furthermore exhibited different spectral properties when in solution or bound to its target, thus behaving as an in situ "red-shifted" photodependent antagonist with improved in vivo compatibility. This study therefore provides a valuable photoswitchable tool for precise control of NMDAR activity in native tissues. It furthermore reveals the importance of the protein environment on the spectral properties of photosensitive molecules.

neuroscience↗

bioRxiv2021

Activity-dependent modulation of NMDA receptors by endogenous zinc shapes dendritic function in cortical neurons.

Activation of NMDA receptors (NMDARs) has been proposed to be a key component of single neuron computations in vivo. However is unknown if specific mechanisms control the function of such receptors and modulate input-output transformations performed by cortical neurons under in vivo-like conditions. Here we found that in layer 2/3 pyramidal neurons (L2/3 PNs), repeated synaptic stimulation results in an activity-dependent decrease in NMDARs activity by vesicular zinc. Such a mechanism shifted the threshold for dendritic non-linearities and strongly reduced LTP induction. Modulation of NMDARs was cell- and pathway-specific, being present selectively in L2/3-L2/3 connections but absent in ascending bottom-up inputs originating from L4 neurons. Numerical simulations highlighted that activity-dependent modulation of NMDARs has an important influence in dendritic computations endowing L2/3 PN dendrites with the ability to sustain dendritic non-linear integrations constant across different regimes of synaptic activity like those found in vivo. The present results therefore provide a new perspective on the action of vesicular zinc in cortical circuits by highlighting the role of this endogenous ion in normalizing dendritic integration of PNs during a constantly changing synaptic input pattern.

neuroscience↗

bioRxiv2021

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 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.

neuroscience↗