Modulation of AMPA receptor surface diffusion restores hippocampal plasticity and memory in Huntington’s disease models

International audienc

Neurexin-1β Binding to Neuroligin-1 Triggers the Preferential Recruitment of PSD-95 versus Gephyrin through Tyrosine Phosphorylation of Neuroligin-1

Adhesion between neurexin-1β (Nrx1β) and neuroligin-1 (Nlg1) induces early recruitment of the postsynaptic density protein 95 (PSD-95) scaffold; however, the associated signaling mechanisms are unknown. To dissociate the effects of ligand binding and receptor multimerization, we compared conditions in which Nlg1 in neurons was bound to Nrx1β or nonactivating HA antibodies. Time-lapse imaging, fluorescence recovery after photobleaching, and single-particle tracking demonstrated that in addition to aggregating Nlg1, Nrx1β binding stimulates the interaction between Nlg1 and PSD-95. Phosphotyrosine immunoblots and pull-down of gephyrin by Nlg1 peptides in vitro showed that Nlg1 can be phosphorylated at a unique tyrosine (Y782), preventing gephyrin binding. Expression of Nlg1 point mutants in neurons indicated that Y782 phosphorylation controls the preferential binding of Nlg1 to PSD-95 versus gephyrin, and accordingly the formation of inhibitory and excitatory synapses. We propose that ligand-induced changes in the Nlg1 phosphotyrosine level control the balance between excitatory and inhibitory scaffold assembly during synapse formation and stabilization

Gold nanoparticles for selective and remote heating of β-amyloid protein aggregates

5 pages, 3 figures, 2 tables.-- Issue title: "EMRS 2006 Symposium A: Current Trends in Nanoscience - from Materials to Applications" (Nice, France, May 29-Jun 2, 2006)Nanoparticles can be made to respond resonantly to a time-varying electromagnetic field with advantageous results related to the transfer of energy from the exciting field to the nanoparticles. The surface of each particle can be heated up, this heat being transmitted into the immediately surrounding tissue. This enables their use as hyperthermia agents delivering toxic amounts of thermal energy to targeted bodies such as tumours. Heating of nanoparticles in a magnetic field is mainly due to inductive coupling (via eddy currents), and in the case of magnetic particles, loss processes during the reorientation of the magnetization (hysteresis losses) or frictional losses (relaxational losses) if the particle can rotate in an environment of sufficiently low viscosity. We use this method to apply heat locally and remotely, dissolving toxic protein deposits of Aβ1–42 (amyloid deposits) via the combined use of weak microwave fields and gold nanoparticles (AuNP) without any bulk heating. This method can be extended to a number of systems where it may be desirable to remove proteins and other aggregates involved in different pathologiesThis work was supported by Generalitat de Catalunya [CeRBa and Grups Consolidats 2001 SGR 00066 and 2001 SGR 00047)], Ministerio de Educación y Ciencia (MAT2003-01124, BIO 2002-02301 and EET2001-4813) and Direccion de Investigacion de la Universidad de ChilePeer reviewe

Pre-post synaptic alignment through neuroligin-1 tunes synaptic transmission efficiency

International audienc

Nanoparticle-mediated local and remote manipulation of protein aggregation

The local heat delivered by metallic nanoparticles selectively attached to their target can be used as a molecular surgery to safely remove toxic and clogging aggregates. We apply this principle to protein aggregates, in particular to the amyloid beta protein (A beta) involved in Alzheimer's disease (AD), a neurodegenerative disease where unnaturally folded A beta proteins self-assemble and deposit forming amyloid fibrils and plaques. We show the possibility to remotely redissolve these deposits and to interfere with their growth, using the local heat dissipated by gold nanoparticles (AuNP) selectively attached to the aggregates and irradiated with low gigahertz electromagnetic fields. Simultaneous tagging and manipulation by AuNP of A beta at different stages of aggregation allow both, noninvasive exploration and dissolution of molecular aggregates

Lengthening of the stargazin cytoplasmic tail increases synaptic transmission by promoting interaction to deeper domains of PSD-95

PSD-95 is a prominent organizer of the postsynaptic density (PSD) that can present a filamentous orientation perpendicular to the plasma membrane. Interactions between PSD-95 and transmembrane proteins might be particularly sensitive to this orientation, as "long" cytoplasmic tails might be required to reach deeper PSD-95 domains. Extension/retraction of transmembrane protein C-tails offer a new way of regulating binding to PSD-95. Using stargazin as a model, we found that enhancing the apparent length of stargazin C-tail through phosphorylation or by an artificial linker was sufficient to potentiate binding to PSD-95, AMPAR anchoring, and synaptic transmission. A linear extension of stargazin C-tail facilitates binding to PSD-95 by preferentially engaging interaction with the farthest located PDZ domains regarding to the plasma membrane, which present a greater affinity for the stargazin PDZ-domain-binding motif. Our study reveals that the concerted orientation of the stargazin C-tail and PSD-95 is a major determinant of synaptic strength

Functional recruitment of dynamin requires multimeric interactions for efficient endocytosis

International audienc

CaMKII Metaplasticity Drives Aβ Oligomer-Mediated Synaptotoxicity

Summary: Alzheimer’s disease (AD) is emerging as a synaptopathology driven by metaplasticity. Indeed, reminiscent of metaplasticity, oligomeric forms of the amyloid-β peptide (oAβ) prevent induction of long-term potentiation (LTP) via the prior activation of GluN2B-containing NMDA receptors (NMDARs). However, the downstream Ca2+-dependent signaling molecules that mediate aberrant metaplasticity are unknown. In this study, we show that oAβ promotes the activation of Ca2+/calmodulin-dependent kinase II (CaMKII) via GluN2B-containing NMDARs. Importantly, we find that CaMKII inhibition rescues both the LTP impairment and the dendritic spine loss mediated by oAβ. Mechanistically resembling metaplasticity, oAβ prevents subsequent rounds of plasticity from inducing CaMKII T286 autophosphorylation, as well as the associated anchoring and accumulation of synaptic AMPA receptors (AMPARs). Finally, prolonged oAβ treatment-induced CaMKII misactivation leads to dendritic spine loss via the destabilization of surface AMPARs. Thus, our study demonstrates that oAβ engages synaptic metaplasticity via aberrant CaMKII activation. : Opazo et al. show that oligomeric and synaptotoxic forms of the Aβ peptide trigger the rapid activation of CaMKII throughout the neuron. They find that aberrant CaMKII activation leads to deficits in long-term potentiation and ultimately synaptic loss via the destabilization of AMPA receptors. Keywords: CaMKII, oligomeric Aβ, NMDAR, GluN2B, AMPAR, Alzheimer’s disease, APP, dendritic spines, metaplasticity, long-term potentiation, LT

Differential Nanoscale Topography and Functional Role of GluN2-NMDA Receptor Subtypes at Glutamatergic Synapses

NMDA receptors (NMDARs) play key roles in the use-dependent adaptation of glutamatergic synapses underpinning memory formation. In the forebrain, these plastic processes involve the varied contributions of GluN2A- and GluN2B-containing NMDARs that have different signaling properties. Although the molecular machinery of synaptic NMDAR trafficking has been under scrutiny, the postsynaptic spatial organization of these two receptor subtypes has remained elusive. Here, we used super-resolution imaging of NMDARs in rat hippocampal synapses to unveil the nanoscale topography of native GluN2A- and GluN2B-NMDARs. Both subtypes were found to be organized in separate nanodomains that vary over the course of development. Furthermore, GluN2A- and GluN2B-NMDAR nanoscale organizations relied on distinct regulatory mechanisms. Strikingly, the selective rearrangement of GluN2A- and GluN2B-NMDARs, with no overall change in NMDAR current amplitude, allowed bi-directional tuning of synaptic LTP. Thus, GluN2A- and GluN2B-NMDAR nanoscale organizations are differentially regulated and seem to involve distinct signaling complexes during synaptic adaptation

Engineering selective competitors for the discrimination of highly conserved protein-protein interaction modules

International audienceDesigning highly specific modulators of protein-protein interactions (PPIs) is especially challenging in the context of multiple paralogs and conserved interaction surfaces. In this case, direct generation of selective and competitive inhibitors is hindered by high similarity within the evolutionary-related protein interfaces. We report here a strategy that uses a semi-rational approach to separate the modulator design into two functional parts. We first achieve specificity toward a region outside of the interface by using phage display selection coupled with molecular and cellular validation. Highly selective competition is then generated by appending the more degenerate interaction peptide to contact the target interface. We apply this approach to specifically bind a single PDZ domain within the postsynaptic protein PSD-95 over highly similar PDZ domains in PSD-93, SAP-97 and SAP-102. Our work provides a paralog-selective and domain specific inhibitor of PSD-95, and describes a method to efficiently target other conserved PPI modules