No abstract

Rat somatosensory neurons express a junctional protein, junctophilin-4 (JPH4) r JPH4 is necessary for the formation of store operated Ca 2+ entry (SOCE) complex at the junctions between plasma membrane and endoplasmic reticulum in these neurons. r Knockdown of JPH4 impairs endoplasmic reticulum Ca 2+ store refill and junctional Ca 2+ signalling in sensory neurons. r In vivo knockdown of JPH4 in the dorsal root ganglion (DRG) sensory neurons significantly attenuated experimentally induced inflammatory pain in rats. r Junctional nanodomain Ca 2+ signalling maintained by JPH4 is an important contributor to the inflammatory pain mechanisms.

Accumulating observations suggest that peripheral somatosensory ganglia may regulate nociceptive transmission, yet direct evidence is sparse. Here, in experiments on rats and mice, we show that the peripheral afferent nociceptive information in mice undergoes dynamic filtering within the dorsal root ganglion (DRG) and suggest that this filtering occurs at the axonal bifurcations (t-junctions). Using synchronous in vivo electrophysiological recordings from the peripheral and central processes of sensory neurons (in the spinal nerve and dorsal root), ganglionic transplantation of GABAergic progenitor cells, and optogenetics, we demonstrate existence of tonic and dynamic filtering of action potentials traveling through the DRG. Filtering induced by focal application of GABA or optogenetic GABA release from the DRG-transplanted GABAergic progenitor cells was specific to nociceptive fibers. Light-sheet imaging and computer modeling demonstrated that, compared to other somatosensory fiber types, nociceptors have shorter stem axons, making somatic control over t-junctional filtering more efficient. Optogenetically induced GABA release within DRG from the transplanted GABAergic cells enhanced filtering and alleviated hypersensitivity to noxious stimulation produced by chronic inflammation and neuropathic injury in vivo. These findings support “gating” of pain information by DRGs and suggest new therapeutic approaches for pain relief.

Junctions of endoplasmic reticulum and plasma membrane (ER-PM junctions) serve as signaling hubs in prokaryotic cells. ER-PM junctions are present in peripheral sensory neurons and are necessary for pro-inflammatory G protein coupled receptor signalling and for inflammatory pain generation. Yet, the principles of ER-PM junctions assembly and maintenance, as well as their role in inflammatory signaling in sensory neurons are only beginning to emerge. Here we discovered that a member of the junctophilin family of proteins, JPH4, is abundantly expressed in rat dorsal root ganglion (DRG) neurons and is necessary for the formation of store operated Ca 2+ entry (SOCE) complex at the ER-PM junctions in response to the G-protein induced ER Ca 2+ store depletion. Furthermore, we demonstrate a key role of the JPH4 and ER Ca 2+ stores in the maintenance of inflammatory pain. Indeed, knockdown of JPH4 expression in DRG in vivo significantly reduced the duration of pain produced by inflammatory mediator bradykinin. Since the ER supplies Ca 2+ for the excitatory action of multiple inflammatory mediators, we suggest that junctional Ca 2+ signalling maintained by JPH4 is an important contributor to the inflammatory pain mechanisms.

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