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

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.

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-1β) levels were detected by ELISA kits.

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.

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.