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The synaptic removal of AMPA-type glutamate receptors (AMPARs) is a core mechanism for hippocampal long-term depression (LTD). In this study, we address the role of microtubule-dependent transport of AMPARs as a driver for vesicular trafficking and sorting during LTD. Here, we show that the kinesin-1 motor KIF5A/C is strictly required for LTD expression in CA3-to-CA1 hippocampal synapses. Specifically, we find that KIF5 is required for an efficient internalization of AMPARs after NMDA receptor activation. We show that the KIF5/AMPAR complex is assembled in an activity-dependent manner and associates with microsomal membranes upon LTD induction. This interaction is facilitated by the vesicular adaptor protrudin, which is also required for LTD expression. We propose that protrudin links KIF5-dependent transport to endosomal sorting, preventing AMPAR recycling to synapses after LTD induction. Therefore, this work identifies an activity-dependent molecular motor and the vesicular adaptor protein that executes AMPAR synaptic removal during LTD., Spanish Ministry of Science (SAF2017-86983-R, PID2020-117651RB) to J.A.E. A.L., Y.G., and A.F.-R. were recipients of predoctoral contracts from the Spanish Ministry of Science. A.B. was funded by the European Union (Marie Curie Intra-European Fellowship program). F.F.H. was funded by the Deutsche Forschungsgemeinschaft (DFG) project 416580360 and HE8413/1-1 and by the Ritz-Stiftung. M.K. was funded by the DFG grants FOR2419 project KN556/11-1 and KN556/11-2

The deregulation of brain cholesterol metabolism is typical in acute neuronal injury (such as stroke, brain trauma and epileptic seizures) and chronic neurodegenerative diseases (Alzheimer's disease). Since both conditions are characterized by excessive stimulation of glutamate receptors, we have here investigated to which extent excitatory neurotransmission plays a role in brain cholesterol homeostasis. We show that a short (30 min) stimulation of glutamatergic neurotransmission induces a small but significant loss of membrane cholesterol, which is paralleled by release to the extracellular milieu of the metabolite 24S-hydroxycholesterol. Consistent with a cause–effect relationship, knockdown of the enzyme cholesterol 24-hydroxylase (CYP46A1) prevented glutamate-mediated cholesterol loss. Functionally, the loss of cholesterol modulates the magnitude of the depolarization-evoked calcium response. Mechanistically, glutamate-induced cholesterol loss requires high levels of intracellular Ca2+, a functional stromal interaction molecule 2 (STIM2) and mobilization of CYP46A1 towards the plasma membrane. This study underscores the key role of excitatory neurotransmission in the control of membrane lipid composition, and consequently in neuronal membrane organization and function.

International audience; In mammalian neurons, the generation and propagation of the action potential result from the presence of dense clusters of voltage-gated sodium channels (Nav) at the axonal initial segment (AIS) and nodes of Ranvier. In these two structures, the assembly of specific supra-molecular complexes composed of numerous partners, such as cytoskeletal scaffold proteins and signaling proteins ensures the high concentration of Nav channels. Understanding how neurons regulate the expression and discrete localization of Nav channels is critical to understanding the diversity of normal neuronal function as well as neuronal dysfunction caused by defects in these processes. Here, we review the mechanisms establishing the clustering of Nav channels at the AIS and in the node and discuss how the alterations of Nav channel clustering can lead to certain pathophysiologies.

Disseminated herpes simplex virus type 1 (HSV-1) infection during pregnancy is poorly described even though it is associated with high maternal and fetal morbidity and neonatal mortality in humans. In a previous paper using mice as a model, the authors demonstrated that HSV-1 is transmitted hematogenously from mother to offspring, the virus colonizing the central nervous system and provoking high mortality. In the present study, viral DNA levels in latently infected mothers were investigated during pregnancy and after delivery in mice. Samples from different organs were obtained before gestation (latency), three times during pregnancy (17, 4.5, and 1 day before delivery), and four times after delivery (1 day, 1 week, 1 and 2 months). A dramatic decrease in viral DNA concentration was observed during pregnancy, especially in the nervous system, with postnatal recovery to latent levels. All the brain regions studied showed similar trends. The viral copy numbers detected in mothers at delivery +1 day were independent of viral inoculum size. The spread of the virus to the above organs was examined immunohistochemically and, in general, more intense viral staining was observed after delivery in each. Because immunoglobulin levels can be modified by infections during pregnancy, the authors examined the levels of specific HSV-1 antibodies. Variation in HSV-1 DNA concentration was found to be associated with changes in the full spectrum of immunoglobulins (but especially immunoglobulin M [IgM]) over pregnancy, whereas at delivery -1 day a significant inverse relationship between immunoglobulins and HSV-1 DNA was observed. IgGs provided protection during the postnatal phase.

The tetrodotoxin-resistant (TTX-R) voltage-gated sodium channel Nav1.8 is predominantly expressed in peripheral afferent neurons, but in case of neuronal injury an ectopic and detrimental expression of Nav1.8 occurs in neurons of the CNS. In CNS neurons, Nav1.2 and Nav1.6 channels accumulate at the axon initial segment, the site of the generation of the action potential, through a direct interaction with the scaffolding protein ankyrin G (ankG). This interaction is regulated by protein kinase CK2 phosphorylation. In this study, we quantitatively analyzed the interaction between Nav1.8 and ankG. GST pull-down assay and surface plasmon resonance technology revealed that Nav1.8 strongly and constitutively interacts with ankG, in comparison to what observed for Nav1.2. An ion channel bearing the ankyrin-binding motif of Nav1.8 displaced the endogenous Nav1 accumulation at the axon initial segment of hippocampal neurons. Finally, Nav1.8 and ankG co-localized in skin nerves fibers. Altogether, these results indicate that Nav1.8 carries all the information required for its localization at ankG micro-domains. The constitutive binding of Nav1.8 with ankG could contribute to the pathological aspects of illnesses where Nav1.8 is ectopically expressed in CNS neurons. The peripheral voltage-gated sodium channel Nav1.8 can be abnormally expressed in central nervous system (CNS) neurons in cases of neuronal injury. We here demonstrated that Nav1.8 binds strongly and constitutively to the scaffolding protein ankyrin G. This indicates that Nav1.8 concentrates at the ankyrin G micro-domains and could disturb the electrophysiological signature of CNS neurons where it is ectopicaly expressed.

International audience; In neurons, voltage-gated sodium (Nav) channels underlie the generation and propagation of the action potential. The proper targeting and concentration of Nav channels at the axon initial segment (AIS) and at the nodes of Ranvier are therefore vital for neuronal function. In AIS and nodes, Nav channels are part of specific supra-molecular complexes that include accessory proteins, adhesion proteins and cytoskele-tal adaptors. Multiple approaches, from biochemical characterization of protein–protein interactions to functional studies using mutant mice, have addressed the mechanisms of Nav channel targeting to AIS and nodes. This review summarizes our current knowledge of both the intrinsic determinants and the role of partner proteins in Nav targeting. A few fundamental trafficking mechanisms, such as selective endocytosis and diffusion/retention, have been characterized. However, a lot of exciting questions are still open, such as the mechanism of differentiated Nav subtype localization and targeting, and the possible interplay between electrogenesis properties and Nav concentration at the AIS and the nodes.

Ion channel immobilization by ankyrin G is regulated by casein kinase 2 in immature hippocampal neurons., In mammalian neurons, the precise accumulation of sodium channels at the axonal initial segment (AIS) ensures action potential initiation. This accumulation precedes the immobilization of membrane proteins and lipids by a diffusion barrier at the AIS. Using single-particle tracking, we measured the mobility of a chimeric ion channel bearing the ankyrin-binding motif of the Nav1.2 sodium channel. We found that ankyrin G (ankG) limits membrane diffusion of ion channels when coexpressed in neuroblastoma cells. Site-directed mutants with decreased affinity for ankG exhibit increased diffusion speeds. In immature hippocampal neurons, we demonstrated that ion channel immobilization by ankG is regulated by protein kinase CK2 and occurs as soon as ankG accumulates at the AIS of elongating axons. Once the diffusion barrier is formed, ankG is still required to stabilize ion channels. In conclusion, our findings indicate that specific binding to ankG constitutes the initial step for Nav channel immobilization at the AIS membrane and precedes the establishment of the diffusion barrier.

In neurons, generation and propagation of action potentials requires the precise accumulation of sodium channels at the axonal initial segment (AIS) and in the nodes of Ranvier through ankyrin G scaffolding. We found that the ankyrin-binding motif of Nav1.2 that determines channel concentration at the AIS depends on a glutamate residue (E1111), but also on several serine residues (S1112, S1124, and S1126). We showed that phosphorylation of these residues by protein kinase CK2 (CK2) regulates Nav channel interaction with ankyrins. Furthermore, we observed that CK2 is highly enriched at the AIS and the nodes of Ranvier in vivo. An ion channel chimera containing the Nav1.2 ankyrin-binding motif perturbed endogenous sodium channel accumulation at the AIS, whereas phosphorylation-deficient chimeras did not. Finally, inhibition of CK2 activity reduced sodium channel accumulation at the AIS of neurons. In conclusion, CK2 contributes to sodium channel organization by regulating their interaction with ankyrin G.

Background Excitotoxicity, a common hallmark of different neurological disorders including Alzheimer’s disease (AD), is the consequence of exacerbated neuronal stimulation and leads to a high influx of calcium trough membrane glutamate receptors [1]. On the other hand, high levels of the cholesterol metabolite 24S-hydroxycholesterol (24-HC) have been found in cerebral spinal fluid (CSF) from AD patients [2,3]. Brain cholesterol homeostasis is an essential, tightly-regulated process that ensures neuronal integrity, viability, and function. One of the mechanisms that neurons put to work to regulate the amount of cellular cholesterol is its conversion into the metabolite 24-HC by the 24-cholesterol hydroxylase CYP46A1 [4]. In this work, we explored the possibility that excitotoxicity, a common process that precedes neurodegeneration, could be a direct modulator of the 24-HC production via a CYP46A1-mediated hydroxylation of cholesterol.