cAMP-dependent protein kinase activated Fyn in spinal dorsal horn to regulate NMDA receptor function during inflammatory pain

Abstract

J. Neurochem. (2011) 116, 93–104. Abstract Selective inhibition of GluN2B‐containing NMDA receptor (GluN2BR) in spinal dorsal horn effectively alleviates inflammatory pain, suggesting the up‐regulation of GluN2BR function involved in central sensitization. Previous studies have demonstrated that the increase in GluN2BR synaptic expression serves as a key step to enhance GluN2BR function after intradermal injection of Complete Freund’s Adjuvant (CFA). Here, we showed that cAMP‐dependent protein kinase (PKA) played an important role in redistributing GluN2BR at synapses, because inhibition of PKA activity impaired GluN2BR accumulation at post‐synaptic density (PSD)‐enriched fraction in CFA‐injected mice, and direct stimulation of PKA in naïve mice mimicked the effect of CFA by recruiting GluN2BR at PSD fraction to evoke pain sensitization. Analysis of PKA‐initiated signalings unraveled that PKA was able to activate Src‐family protein tyrosine kinases member Fyn, possibly by disrupting Fyn association with its inhibitory partner striatal‐enriched protein tyrosine phosphatase 61. The active Fyn then promoted GluN2B phosphorylation at Tyr1472, a molecular event known to prevent GluN2BR endocytosis. As a result, pharmacological or genetic manipulation of Fyn activity greatly depressed GluN2BR accumulation at PSD‐enriched fraction and ameliorated mechanical allodynia induced by PKA. Our data thus elucidated a critical role of PKA/Fyn/GluN2B signaling in triggering GluN2BR hyperfunction and pain hypersensitivity.

Therapeutic Implications for Striatal-Enriched Protein Tyrosine Phosphatase (STEP) in Neuropsychiatric Disorders

“…Accordingly, selective GluN2B receptor antagonists effectively alleviate inflammatory and neuropathic pain. The underlying mechanism seems to involve PKA, Fyn, and STEP (Yang et al, 2011). Intrathecal injections of the PKA agonist forskolin or complete Freund's adjuvant (CFA), an inducer of chronic pain, drive GluN2B-containing NMDARs into PSD fractions and increase Tyr 1472 phosphorylation.…”

“…The SFK inhibitor PP2 blocks the forskolinor CFA-induced increase in PSD-associated GluN2B, as well as Tyr 1472 phosphorylation, demonstrating that SFKs act downstream of PKA activation. It is noteworthy that the association of Fyn with STEP is decreased in mice after CFA injections, and this disruption leads to increased phosphorylation of Fyn at Tyr 420 (Yang et al, 2011). Given that PKA phosphorylates STEP and reduces STEP's affinity for its substrates (Paul et al, 2000(Paul et al, , 2003, it is certainly possible that the effects of forskolin and CFA on GluN2B phosphorylation and surface expression (Yang et al, 2011) are due to reduced STEP activity.…”

“…On the other hand, too little STEP protein and/or activity can also negatively affect neuronal function and has been recently implicated in Huntington's disease (HD), drug abuse, stroke/ischemia, and inflammatory pain (Valjent et al, 2005;Braithwaite et al, 2008;Tashev et al, 2009;Xu et al, 2009;Saavedra et al, 2011;Yang et al, 2011). Proof-of-concept studies using peptides that manipulate STEP's ability to interact with its substrates, as well as characterization of STEP KO mice, establish that manipulating STEP function may be beneficial for the treatment of these disorders.…”

Neural functions of calcineurin in synaptic plasticity and memory: Figure 1.

“…STEP binding and dephosphorylation of Fyn reduce its kinase activity , which decreases NMDA-R phosphorylation and activity (Yu et al 1997). PKA has been suggested to interfere with STEP association with Fyn (Yang et al 2011), suggesting an important balance between CaN and PKA activity for its regulation. Further to NMDA-R, STEP is involved in AMPA-R endocytosis after activation of mGluRs 1 and 5 (group 1) .…”

PKA is required for the modulation of spinal nociceptive information related to ephrinB–EphB signaling in mice

“…Given that spinal ephrinB-EphB signaling (Battaglia et al, 2003;Kobayashi et al, 2007;Dong et al, 2011) and PKA (Hu et al, 2001;Yang et al, 2011;Hang et al, 2013) play critical roles in the development and maintenance of inflammatory, neuropathic pain, and metastatic bone cancer pain, we want to determine whether spinal PKA activation contributes to the role of ephrinB-EphB signaling in inflammatory, neuropathic, and bone cancer pain. We first analyzed the effect of intrathecal injection of EphB2-Fc, which blocks ephrinB-EphB signaling , on the expression of spinal PKAca and p-CREB in formalin-induced inflammatory pain.…”