Receptor for activated C kinase 1 mediates the chronic constriction injury-induced neuropathic pain in the rats' peripheral and central nervous system.

Peripheral and central sensitization has been reported as significant features in the course of the occurrence and development of neuropathic pain (NP). Receptor for activated C kinase 1 (RACK1), a scaffold protein, participated in fundamental cellular activities and various neuronal functions. Peripheral and central sensitization are a state that the morphology of neuronal cell bodies as well as the corresponding function change, whether this process can be regulated by RACK1 is still unknown. In this study, the biological effects and mechanisms of RACK1 contributes to the pathogenesis of chronic constriction injury (CCI)-induced neuropathic pain were investigated. By western blot and staining, we found that RACK1 protein changed in dorsal root ganglion (DRG) neurons and spinal cord (SC) neurons except glial cells after CCI. Especially, RACK1 was co-located with IB4-, CGRP-positive neurons, suggesting it was related to integrate nociceptive information from the primary aff ;erents in DRG. The successful establishment of CCI models also directly led to mechanical allodynia and heat hyperalgesia, which could be reversed by intrathecal injection of RACK1 siRNA. Furthermore, intrathecal injection of RACK1 siRNA reduced the expression of RACK1 and accompanying spinal c-fos, which is the transcription factor and marker of neuronal activation. These results suggested that targeting RACK1 be a sensible approach for treating NP.

Interleukin-1 Receptor Associated Kinase 1 Mediates the Maintenance of Neuropathic Pain after Chronic Constriction Injury in Rats.

Neuropathic pain (NP) has complicated pathogenesis as it mainly involves a lesion or dysfunction of the somatosensory nervous system and its clinical treatment remains challenging. Chronic constriction injury (CCI) model is a widely used neuropathic pain model and involved in mechanisms including both nerve inflammatory and injury. Cytokines and their receptors play essential roles in the occurrence and persistence of neuropathic pain, but the underlying mechanisms have not well been understood. Therefore, Interleukin-1 receptor-associated kinase 1 (IRAK1) is chosen to explore the possible mechanisms of NP. In the present study, IRAK1 was found to persistently increase in the dorsal root ganglion (DRG) and spinal cord (SC) during CCI detected by western blot. The staining further confirmed that IRAK1 was mainly co-located in the DRG astrocytes or SC neurons, but less in the DRG microglia or SC astrocytes. Moreover, the region of increased IRAK1 expression was observed in superficial laminae of the spinal dorsal horn, which was the nociceptive neuronal expression domain, suggesting that IRAK1 may mediated CCI-induced pain by nociceptive primary afferent. In addition, intrathecal injection of Toll-like receptor 4 (TLR4) inhibitor or IRAK1 siRNA decreased the expression of IRAK1 accompanied with the alleviation of CCI-induced neuropathic pain. The upregulation of p-NF-κB expression was reversed by IRAK1 siRNA in SC, and intrathecal injection of p-NF-κB inhibitor relieved neuropathic pain. Taking together, targeting IRAK1 may be a potential treatment for chronic neuropathic pain.

Chemokine CXCL10/CXCR3 signaling contributes to neuropathic pain in spinal cord and dorsal root ganglia after chronic constriction injury in rats.

Inflammatory cytokines and chemokines play essential roles in the occurrence and persistence of neuropathic pain (NP). Chronic constriction injury (CCI) enhances the activation of p-ERK, which is involved in neuropathic pain. Although the chemokine CXCL10 and its receptor CXCR3 are implicated in the pathophysiology of itch, it is largely unexplored for neuropathic pain. In this study, we determined the role of the CXCL10-CXCR3 axis in NP using a well-established CCI model. CCI significantly induced mechanical allodynia and thermal hyperalgesia. Following the pain course, a significant increase of CXCL10 and CXCR3 in both dorsal root ganglion (DRG) neurons and spinal cord (SC) neurons was detected in rats. Furthermore, intrathecal injection of CXCR3 inhibitor AMG487 was found to attenuate pain hypersensitivity in a dose-dependent manner in CCI. The expression of p-ERK was also depressed after intrathecal injection of AMG487 associated with a significant laxation of hyperalgesia, which demonstrated that the interaction of CXCL10/CXCR3 possibly took part in neuropathic pain by regulating p-ERK signaling in the SC. Overall, these findings demonstrate that the CXCL10/CXCR3 signaling pathway is critical in CCI.

Translocation Associated Membrane Protein 1 Contributes to Chronic Constriction Injury-Induced Neuropathic Pain in the Dorsal Root Ganglion and Spinal Cord in Rats.

Neuropathic pain is a severe debilitating state caused by injury or dysfunction of somatosensory nervous system, and the clinical treatment is still challenging. Translocation associated membrane protein 1 (TRAM1), an adapter protein, participates in a variety of transduction pathways and mediates the biological functions such as cell proliferation, activation, and differentiation. However, whether TRAM1 is involved in the pathogenesis of neuropathic pain is still unclear. In our study, we reported the role of TRAM1 in the maintenance of neuropathic pain induced by chronic constriction injury (CCI) on rats. By western blot and staining, we found that TRAM1 increased in the dorsal root ganglion (DRG) neurons and spinal cord (SC) neurons after CCI. Being similar to IB4-, CGRP-positive expressed area, TRAM1 also expressed in the superficial laminae of the spinal cord dorsal horn (SCDH), suggesting it was related to the innervations of the primary afferents. Moreover, intrathecal injection of TRAM1 siRNA or Toll-like receptor 4 (TLR4) inhibitor induced low expression of TRAM1 in SC, which alleviated the pain response induced by CCI. The upregulation of p-NF-κB expression was reversed by TRAM1 siRNA in SC and DRG, and intrathecal injection of p-NF-κB inhibitor relieved neuropathic pain. All the data indicated that TRAM1 could take part in CCI-induced pain and might be a potential treatment for chronic neuropathic pain.

PKM2 is involved in neuropathic pain by regulating ERK and STAT3 activation in rat spinal cord.

BACKGROUND: Pyruvate kinase isozymes M2 (PKM2), as a member of pyruvate kinase family, plays a role of glycolytic enzyme in glucose metabolism. It also functions as protein kinase in cell proliferation, signaling, immunity, and gene transcription. In this study, the role of PKM2 in neuropathic pain induced by chronic constriction injury (CCI) was investigated. METHODS: Rats were randomly grouped to establish CCI models. PKM2, extracellular regulated protein kinases (EKR), p-ERK, signal transducers and activators of transcription (STAT3), p-STAT3, phosphoinositide 3-kinase/protein kinase B (PI3K/AKT) and p-PI3K/AKT proteins expression in spinal cord was examined by Western blot analysis. Cellular location of PKM2 was examined by immunofluorescence. Knockdown of PKM2 was achieved by intrathecal injection of specific small interfering RNA (siRNA). Von Frey filaments and radiant heat tests were performed to determine mechanical allodynia and thermal hyperalgesia respectively. Lactate and adenosine triphosphate (ATP) contents were measured by specific kits. Tumor necrosis factor alpha (TNF-α) and interleukin-1 beta (IL-1ß) levels were detected by ELISA kits. RESULTS: CCI markedly increased PKM2 level in rat spinal cord. Double immunofluorescent staining showed that PKM2 co-localized with neuron, astrocyte, and microglia. Intrathecal injection of PKM2 siRNA not only attenuated CCI-induced ERK and STAT3 activation, but also attenuated mechanical allodynia and thermal hyperalgesia induced by CCI. However, PKM2 siRNA failed to inhibit the activation of AKT. In addition, PKM2 siRNA significantly suppressed the production of lactate and pro-inflammatory mediators. CONCLUSION: Our findings demonstrate that inhibiting PKM2 expression effectively attenuates CCI-induced neuropathic pain and inflammatory responses in rats, possibly through regulating ERK and STAT3 signaling pathway.