Upregulation of RCAN1.4 in spinal dorsal horn is involved in inflammatory pain hypersensitivity

The calcium/calmodulin-dependent protein phosphase calcineurin (CaN) regulates synaptic plasticity by controlling the phosphorylation of synaptic proteins including AMPA type glutamate receptors. The regulator of calcineurin 1 (RCAN1) is characterized as an endogenous inhibitor of CaN and its dysregulation is implicated in multiple neurological disorders. However, whether RCAN1 is engaged in nociceptive processing in the spinal dorsal horn remains unrevealed. In this study, we found that RCAN1 was predominately expressed in pain related neurons in the superficial dorsal horn of the spinal cord. Intraplantar injection of complete Freund's adjuvant (CFA) specifically increased the total and synaptic expression of the RCAN1.4 isoform in spinal dorsal horn. The CFA-induced inflammation also caused an increased binding of RCAN1.4 to CaN. Overexpression of RCAN1.4 in spinal dorsal horn of intact mice produced both mechanical allodynia and thermal hyperalgesia, which were accompanied by increased synaptic expression and phosphorylation of GluA1 subunit. Furthermore, the siRNA-mediated knockdown of RCAN1.4 significantly attenuated the development of pain hypersensitivity, meanwhile, decreased the synaptic expression of GluA1 in mice with peripheral inflammation. These data suggested that the increased expression of RCAN1.4 contributed to the development of inflammatory pain hypersensitivity, at least in part by promoting the synaptic recruitment of GluA1-containing AMPA receptor.

Automated summary

This study found that RCAN1 is predominantly expressed in pain-related neurons in the spinal dorsal horn. Inflammation caused by CFA increased the expression of RCAN1.4 and its binding to CaN. Overexpression of RCAN1.4 led to mechanical allodynia and thermal hyperalgesia, accompanied by increased synaptic expression and phosphorylation of GluA1 subunit. Knockdown of RCAN1.4 attenuated pain hypersensitivity and decreased synaptic expression of GluA1.