Disruption of δ-opioid receptor phosphorylation at Threonine 161 attenuates morphine tolerance in rats with CFA-induced inflammatory hypersensitivity

Abstract

Objective Our previous study identified Threonine , located in the second intracellular loop of the δ-opioid receptor (DOR), as the only consensus phosphorylation site for cyclin-dependent kinase 5 (Cdk5). The aim of this study was to assess the function of DOR phosphorylation by Cdk5 in complete Freund's adjuvant (CFA)-induced inflammatory pain and morphine tolerance. Methods Dorsal root ganglion (DRG) neurons of rats with CFA-induced inflammatory pain were acutely dissociated and the biotinylation method was used to explore the membrane localization of phosphorylated DOR at Thr-161 (pThr-161-DOR), and paw withdrawal latency was measured after intrathecal delivery of drugs or Tat-peptide, using a radiant heat stimulator in rats with CFA-induced inflammatory pain. Results Both the total amount and the surface localization of pThr-161-DOR were significantly enhanced in the ipsilateral DRG following CFA injection.Intrathecal delivery of the engineered Tat fusion-interefering peptide corresponding to the second intracellular loop of DOR (Tat-DOR-2L) increased inflammatory hypersensitivity, and inhibited DOR-but not µ-opioid receptor-mediated spinal analgesia in CFA-treated rats. However, intrathecal delivery of Tat-DOR-2L postponed morphine antinociceptive tolerance in rats with CFA-induced inflammatory pain. Conclusion Phosphorylation of DOR at Thr-161 by Cdk5 attenuates hypersensitivity and potentiates morphine tolerance in rats with CFA-induced inflammatory pain, while disruption of the phosphorylation of DOR at Thr-161 attenuates morphine tolerance.

Molecular Pharmacology ofδ-Opioid Receptors

“…Its substitution by Ala or the inhibition of Cdk5 reduces basal DOPr phosphorylation status both in immortalized cell lines and in DRG neurons . As detailed in section V.A, in its phosphorylated state, Thr161 promoted DOPr expression at the membrane and its heterodimerization with MOPrs Chen et al, 2012).…”

“…Finally, DOPrs are also substrates for Cdk5 Chen et al, 2012). Cdk5 is a prolinedirected serine/threonine kinase that requires proline in the +1 position and displays a preference for substrates bearing a basic residue in the +3 position relative to the substrate residue (Songyang et al, 1996).…”

Recent progress in understanding the mechanisms of pain and itch

“…They also discuss the controversy in the field [14] . The functional interactions of the µ-and δ-opioid receptors are further supported in the paper from Chen et al, reporting that the disruption of phosphorylation of the δ-opioid receptor at a specific site (Threonine 161) can attenuate morphine tolerance in the context of inflammatory pain [15] .…”

“…Ten laboratories from China and the USA have contributed 11 papers to this special issue: 5 reviews and 6 full research articles [5][6][7][8][9][10][11][12][13][14][15] . This special issue aims to cover several areas of research in pain and itch, from peripheral to central mechanisms, and also from neuronal to glial mechanisms.…”

Opioid receptor trafficking and interaction in nociceptors

“…Early studies showed that blockage of δ‐opioid receptors enhanced morphine analgesia, and reduced analgesic tolerance (Abdelhamid et al ., ; Schiller et al ., 1999a,b; Schiller, ). Further studies revealed that morphine tolerance can be reduced by intrathecal application of the antisense oligodeoxynucleotide of the δ‐opioid receptor gene ( Oprd1 ), deleting either Oprd1 or the preproenkephalin gene ( Penk1 ), preventing δ‐opioid receptor phosphorylation or deleting Tac1 , which reduces the transport of δ‐opioid receptors to the spinal dorsal horn via LDCVs (Standifer et al ., ; Zhu et al ., ; Nitsche et al ., ; Guan et al ., ; Xie et al ., ; Chen et al ., ).…”