Biology subjects

LEVI, S.

Publications and source records attributed to LEVI, S..

3 recordsLinked to original sources

bioRxiv2022

Lateral diffusion of NKCC1 contributes to neuronal chloride homeostasis and is rapidly regulated by the WNK signaling pathway

An upregulation of the Na+-K+-2Cl- co-transporter NKCC1, the main chloride importer in mature neurons, can lead to depolarizing/excitatory responses mediated by GABAA receptors and thus to hyperactivity. Understanding the regulatory mechanisms of NKCC1 would help prevent intra-neuronal chloride accumulation that occurs in pathologies with defective inhibition. The cellular and molecular regulatory mechanisms of NKCC1 are poorly understood. Here, we report in mature hippocampal neurons that GABAergic activity controls the membrane diffusion and clustering of NKCC1 via the chloride-sensitive WNK1 kinase and the downstream SPAK kinase that directly phosphorylates NKCC1 on key threonine residues. At rest, this signaling pathway has little effect on intracellular Cl- concentration but it participates to the elevation of intraneuronal Cl- concentration in hyperactivity condition associated with an up-regulation of NKCC1. The fact that the chloride exporter KCC2 is also regulated in mature neurons by the WNK1 pathway indicates that this pathway will be a target of choice in the pathology.

neuroscience↗

bioRxiv2022

The fast diffusion of NKCC1 along the axon is driven by glutamatergic activity

NKCC1 and KCC2 transporters regulate neuronal chloride homeostasis and thus synaptic inhibition. KCC2 activity is tuned by diffusion-capture in an activity-dependent manner. The mechanisms controlling NKCC1 in neurons are unknown. We found using super-resolution imaging that NKCC1 like KCC2 form nanodomains in the somato-dendritic membrane at extrasynaptic sites and at the periphery of excitatory and inhibitory synapses. NKCC1 nanoclusters are half the size and density in molecules than KCC2 clusters. This is accompanied by a higher mobility of NKCC1 compared to KCC2 in the dendritic membrane, suggesting a weaker NKCC1 anchoring to the cytoskeleton. In contrast, NKCC1, but not KCC2, is confined to endocytic zones, which would explain its controlled surface expression and the fact that endocytic zones would provide a reservoir from which NKCC1 could be released into the membrane. Finally, we show an increased confinement of NKCC1 in axons but not in dendrites upon glutamatergic activity blockade, indicating a selective mechanism of regulation in the axon. We propose that a rapid regulation of NKCC1 by lateral diffusion in the axon would control presynaptic glutamate release and the firing of action potentials.

neuroscience↗

bioRxiv2017

A simple and powerful analysis of lateral subdiffusion using single particle tracking

In biological membranes many factors such as cytoskeleton, lipid composition, crowding and molecular interactions deviate lateral diffusion from the expected random walks. These factors have different effects on diffusion but act simultaneously so the observed diffusion is a complex mixture of diffusive behaviors (directed, >Brownian, anomalous or confined). Therefore commonly used approaches to quantify diffusion based on averaging of the displacements, such as the mean square displacement, are not adapted to the analysis of this heterogeneity. We introduce a new parameter, the packing coefficient Pc, which gives an estimate of the degree of free movement that a molecule displays in a period of time independently of its global diffusivity. Applying this approach to two different situations (diffusion of a lipid probe and trapping of receptors at synapses), we show that Pc detected and localized temporary changes of diffusive behavior both in time and in space. More importantly, it allowed the detection of periods with very high confinement (~immobility), their frequency and duration, and thus it can be used to calculate the effective kon and koff of scaffolding interactions such those that immobilize receptors at synapses.

biophysics↗