Association of NaV1.8 with lipid rafts in DRG sensory neurons

Abstract

Voltage gated sodium channels (VGSCs) play a key role in the initiation and propagation of action potentials in neuronal cells. NaV1.8 is a Tetrodotoxin resistant VGSC expressed in nociceptors and underlies the majority of sodium currents during action potentials. Many studies have highlighted a key role of NaV1.8 in different pain pathways. Lipid rafts are microdomains of the plasma membrane highly enriched in cholesterol and sphingolipids characterised by unique physical features: a liquid ordered phase and the resistance to nonionic detergent at 4°C. Lipid rafts are thought to act as platforms on the membrane where proteins and lipids can be compartmentalised and functionally clustered. In the present study we investigated NaV1.8 sub-cellular localisation and explored the idea that it is associated with lipid rafts in nociceptors. We hypothesised that lipid rafts on primary sensory neurons act as a platform on the membrane where NaV1.8 can be trafficked and underlie action potentials generation. We demonstrated that NaV1.8 is associated with lipid rafts along the sciatic nerve ex vivo and in DRG neurons in vitro. We also found that NaV1.8 is distributed in clusters along the axons of DRG neurons in vitro and ex vivo. We investigated the functional meaning of NaV1.8-raft association by studying action potential propagation in sensory neurons, in response to mechanical and chemical stimulation, by calcium imaging. Disruption of the association between NaV1.8 and lipid rafts in cultured sensory neurons, by methyl-betacyclodextrin and 7-ketocholesterol, caused a reduction in the number of cells able to propagate action potentials. In addition, lipid raft depletion caused a remarkable reduction in the conduction velocity upon mechanical stimulation. These findings highlight the importance of the association between NaV1.8 and lipid rafts in the conduction of action potentials and could lead to new perspectives in the study of NaV1.8 trafficking and nociceptor excitability.