Inhibition of protein tyrosine phosphatases in spinal dorsal horn attenuated inflammatory pain by repressing Src signaling

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Tyrosine phosphorylation of N-methyl-D-aspartate (NMDA) subtype glutamate receptors by Src-family protein tyrosine kinases (SFKs) plays a critical role in spinal sensitization. Besides SFKs, the tyrosine phosphorylation levels of proteins are also determined by protein tyrosine phosphatases (PTPs). However, whether PTPs are involved in spinal nociceptive processing is largely unknown. The present study found that intrathecal application of broad-spectrum PTPs inhibitors orthovanadate or Bpv (phen) generated little effects on the paw withdrawal thresholds of intact rats to Von Frey filament stimuli. Although the basal nociceptive responses didn't require the involvement of PTPs, the mechanical allodynia evoked by intrathecal injection of NMDA was greatly attenuated by orthovanadate and Bpv (phen), suggesting that PTPs activity, once stimulated by NMDA receptors, became essential for spinal sensitization. Biochemical analysis demonstrated that PTPs functioned to activate SFKs member Src and promote Src interaction with NR2B subunit-containing NMDA receptors (NR2B receptors). As a result, PTPs inhibition largely suppressed Src-mediated NR2B phosphorylation at Tyr1472 and reduced the synaptic concentration of NR2B receptors in spinal dorsal horn of NMDA-treated rats. Importantly, intraplantar injection of Complete Freund's Adjuvant (CFA) naturally activated spinal PTPs to initiate Src signaling, because PTPs inhibition significantly repressed Src activity, reduced Src phosphorylation of NR2B, decreased NR2B synaptic accumulation and eventually ameliorated inflammatory pain. These data indicated an important role played by spinal PTPs in inducing Src-dependent NR2B receptor hyperfunction and suggested that PTPs inhibition might represent an effective strategy for the treatment of inflammatory pain.

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