The Role of Vesicular Glutamate Transporter 2 in Neuropathic Pain and Its Regulation Mechanism

Abstract

BACKGROUNDUp‐regulation of glutamate neurotransmission has been proposed as a crucial mechanism of neuropathic pain. Vesicular glutamate transporters (VGLUTs), which transport glutamate into presynaptic vesicles, are fundamental in glutamate storage and release. Several lines of evidence from genetically modified mice suggest a possible association of VGLUT2 with neuropathic pain.OBJECTIVEThe purpose of this study is to investigate the changes of VGLUT2 expression and function in neuropathic pain and to elucidate its regulatory mechanism, in a mouse spared nerve injury (SNI) model.METHODSThe changes in VGLUT2 expression were determined by western blot and immunohistochemistry in the spinal cord and pain‐related brain regions at different time points after SNI surgery. The cell distribution characteristics of VGLUT2 in the pathological condition were observed by immunofluorescent staining. RNA interference and VGLUT inhibitors were used to regulate the expression and function of VGLUT2 respectively, and the mechanical pain behavior was observed. The effects of VGLUT2 down‐regulation and inhibition on glutamate release were also investigated. The effects of Wnt/β‐catenin signaling on VGLUT2 expression and pain behavior were investigated by using the Wnt agonist, Wnt1, and Wnt/β‐catenin pathway inhibitor XAV939 in SNI mice.RESULTSVGLUT2 protein levels were significantly up‐regulated in the spinal cord, thalamus, periaqueductal gray and amygdala after SNI surgery. In SNI mice, VGLUT2 was mainly expressed in neurons (co‐locolized with NeuN and MAP2), but not glia cells (Iba‐1 and GFAP). Intrathecal or intracerebral administration of VGLUT2 shRNAs or the VGLUT inhibitor CSB6B significantly attenuated mechanical allodynia and decreased glutamate release. Meanwhile, Wnt1/β‐catenin signaling pathway was activated during the development of neuropathic pain. The Wnt agonist or Wnt1 significantly increased VGLUT2 expression, while Wnt/β‐catenin pathway inhibitor XAV939 decreased VGLUT2 expression. Moreover, administration of XAV939 7 days after SNI surgery significantly attenuated mechanical allodynia with a long duration of action, and this effect was in coincidence with VGLUT2 down‐regulation. In naïve mice, intrathecal administration of the Wnt agonist or Wnt1 produced mechanical allodynia, which was abolished by preventive VGLUT2 down‐regulation.CONCLUSIONNeuropathic pain are associated with the changes in VGLUT2 expression and function, and Wnt1/β‐catenin signaling up‐regulates VGLUT2 in the pathological condition.Support or Funding InformationThis work was supported by National Natural Science Foundation of China (81200850) and Beijing Natural Science Foundation (7123224).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.