BackgroundPyruvate 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.MethodsRats 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-1β) levels were detected by ELISA kits.ResultsCCI 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.ConclusionOur 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.

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Neuropathic pain is elicited after a serious disorder of the nervous system and is along with the neural damage. It is usually chronic and challenging to treat. Transcription factor 4 (TCF4) is a key transcription factor of Wnt signaling system. Recent studies have shown that TCF4 interacts with β-catenin in the Wnt signaling pathway and coactivates downstream target genes in diverse systems. However, it is not well elucidated in the pathogenesis of neuropathic pain. In the present study, we investigated the role of TCF4 in the maintenance of neuropathic pain after chronic constriction injury (CCI) in rats. CCI induced persistent TCF4 upregulation in the dorsal root ganglion and spinal cord. Interestingly, TCF4 was mainly colocalized with neurons in the injured dorsal root ganglion and spinal cord on CCI day 7. Moreover, the expression patterns of β-catenin and glycogen synthase kinase-3β (GSK-3β) were parallel with that of TCF4 in vivo studies. Intrathecal injection of Wnt/β-catenin pathway inhibitor IWR-1-endo and TCF4 small interfering RNA (siRNA) significantly attenuated CCI-induced mechanical allodynia and heat hyperalgesia. The results suggest that TCF4 in the dorsal root ganglion and spinal cord is involved in the maintenance of CCI-induced neuropathic pain. Targeting TCF4 or Wnt/β-catenin signaling may be a potential treatment for chronic neuropathic pain.

Neuropathic pain, caused by a lesion or dysfunction of the somatosensory nervous system, is a severe debilitating condition with which clinical treatment remains challenging. Jun activation domain-binding protein (JAB1) is a multifunctional protein that participates in several signaling pathways, controlling cell proliferation and apoptosis. However, the expression and possible function of JAB1 in the pathogenesis of neuropathic pain has not been elucidated. This study aimed to investigate the possible involvement of JAB1. Here, employing a neuropathic pain model induced by chronic constriction injury (CCI) on rats, we reported the role of JAB1 in the maintenance of neuropathic pain. By western blot, we found that CCI markedly up-regulated JAB1 expression in the dorsal root ganglion (DRG) and spinal cord. Immunofluorescent assay demonstrated that JAB1 was extensively localized in IB4-, CGRP- and NF200-positive neurons in the injured L5 DRG, and mainly co-localized with NeuN in spinal cord. In addition, we showed that CCI induced phosphorylation of p65 and JNK in vivo. Intrathecal injection of JAB1 siRNA significantly attenuated the CCI-induced JNK and p65 phosphorylation and alleviated both mechanical allodynia and heat hyperalgesia in rats. Taken together, these results suggested that JAB1 promotes neuropathic pain via positively regulating JNK and NF-κB activation.