title: Connexin-43 induces chemokine release from spinal cord astrocytes to maintain late-phase neuropathic pain in mice.
abstract: Accumulating evidence suggests that spinal cord astrocytes play an important role in neuropathic pain sensitization by releasing astrocytic mediators (e.g. cytokines, chemokines and growth factors). However, it remains unclear how astrocytes control the release of astrocytic mediators and sustain late-phase neuropathic pain. Astrocytic connexin-43 (now known as GJ1) has been implicated in gap junction and hemichannel communication of cytosolic contents through the glial syncytia and to the extracellular space, respectively. Connexin-43 also plays an essential role in facilitating the development of neuropathic pain, yet the mechanism for this contribution remains unknown. In this study, we investigated whether nerve injury could upregulate connexin-43 to sustain late-phase neuropathic pain by releasing chemokine from spinal astrocytes. Chronic constriction injury elicited a persistent upregulation of connexin-43 in spinal astrocytes for >3 weeks. Spinal (intrathecal) injection of carbenoxolone (a non-selective hemichannel blocker) and selective connexin-43 blockers (connexin-43 mimetic peptides (43)Gap26 and (37,43)Gap27), as well as astroglial toxin but not microglial inhibitors, given 3 weeks after nerve injury, effectively reduced mechanical allodynia, a cardinal feature of late-phase neuropathic pain. In cultured astrocytes, TNF-α elicited marked release of the chemokine CXCL1, and the release was blocked by carbenoxolone, Gap26/Gap27, and connexin-43 small interfering RNA. TNF-α also increased connexin-43 expression and hemichannel activity, but not gap junction communication in astrocyte cultures prepared from cortices and spinal cords. Spinal injection of TNF-α-activated astrocytes was sufficient to induce persistent mechanical allodynia, and this allodynia was suppressed by CXCL1 neutralization, CXCL1 receptor (CXCR2) antagonist, and pretreatment of astrocytes with connexin-43 small interfering RNA. Furthermore, nerve injury persistently increased excitatory synaptic transmission (spontaneous excitatory postsynaptic currents) in spinal lamina IIo nociceptive synapses in the late phase, and this increase was suppressed by carbenoxolone and Gap27, and recapitulated by CXCL1. Together, our findings demonstrate a novel mechanism of astrocytic connexin-43 to enhance spinal cord synaptic transmission and maintain neuropathic pain in the late-phase via releasing chemokines.
authors.affiliation: 1 Departments of Anaesthesiology and Neurobiology, Duke University Medical Centre, Durham, NC, 27710, USA.
authors.forename: Gang
authors.initials: G
authors.lastname: Chen
authors.affiliation: 1 Departments of Anaesthesiology and Neurobiology, Duke University Medical Centre, Durham, NC, 27710, USA.
authors.forename: Chul-Kyu
authors.initials: CK
authors.lastname: Park
authors.affiliation: 1 Departments of Anaesthesiology and Neurobiology, Duke University Medical Centre, Durham, NC, 27710, USA.
authors.forename: Rou-Gang
authors.initials: RG
authors.lastname: Xie
authors.affiliation: 1 Departments of Anaesthesiology and Neurobiology, Duke University Medical Centre, Durham, NC, 27710, USA.
authors.forename: Temugin
authors.initials: T
authors.lastname: Berta
authors.affiliation: 2 Centre for Translational Neuromedicine, University of Rochester Medical Centre, Rochester, NY, 14642, USA.
authors.forename: Maiken
authors.initials: M
authors.lastname: Nedergaard
authors.affiliation: 1 Departments of Anaesthesiology and Neurobiology, Duke University Medical Centre, Durham, NC, 27710, USA ru-rong.ji@duke.edu.
authors.forename: Ru-Rong
authors.initials: RR
authors.lastname: Ji
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000378:metabolism*; D001522:Behavior, Animal / Q000502:physiology; D002478:Cells, Cultured; D054360:Chemokine CXCL1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D018925:Chemokines / Q000096:biosynthesis / Q000378:metabolism*; D018031:Connexin 43 / Q000378:metabolism* / Q000502:physiology; D004195:Disease Models, Animal; D006930:Hyperalgesia / Q000209:etiology / Q000378:metabolism* / Q000628:therapy; D007278:Injections, Spinal; D051379:Mice; D008822:Mice, Transgenic; D009437:Neuralgia / Q000209:etiology / Q000378:metabolism* / Q000628:therapy; D010455:Peptides / Q000008:administration & dosage / Q000502:physiology; D023063:Receptors, Interleukin-8B / Q000037:antagonists & inhibitors / Q000378:metabolism; D013116:Spinal Cord / Q000166:cytology / Q000378:metabolism* / Q000473:pathology; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism / Q000502:physiology*; D015854:Up-Regulation
chemical_list: D054360:Chemokine CXCL1; D018925:Chemokines; D018031:Connexin 43; C514423:Gap 26 peptide; D010455:Peptides; D023063:Receptors, Interleukin-8B; D014409:Tumor Necrosis Factor-alpha
keywords: CXCL1; CXCR2; carbenoxolone (CBX); hemichannels; neuro-glial interaction