Inhibition of spinal cytosolic phospholipase A2 expression by an antisense oligonucleotide attenuates tissue injury-induced hyperalgesia

Abstract Activation of the spinal phospholipase A 2 (PLA 2 ) –cyclooxygenase (COX) –prostaglandin signaling pathway is widely implicated in nociceptive processing. Although the role of spinal COX isoforms in pain signal transmission has been extensively characterized, our knowledge of PLA 2 enzymes in this cascade is limited. Among all PLA 2 groups, cytosolic calcium-dependent PLA 2 group IVA (cPLA 2 IVA) appears to be the predominant PLA 2 enzyme in the spinal cord. In the present study we sought to (i) characterize anatomical and cellular distribution and localization of cPLA 2 IVA in dorsal horn of rat spinal cord, (ii) verify efficacy and selectivity of intrathecal (IT) delivery of an antisense oligonucleotide (AS) targeting rat cPLA 2 IVA mRNA on spinal expression of this enzyme, and (iii) examine the effect of down-regulation of spinal cPLA 2 IVA on peripheral tissue injury–induced pain behavior. Here we demonstrate that cPLA 2 IVA is constitutively expressed in rat spinal cord, predominantly in dorsal horn neurons and oligodendrocytes but not in astrocytes or microglia. Intrathecal injection of AS significantly down-regulated both protein and gene expression of cPLA 2 IVA in rat spinal cord, while control missense oligonucleotide (MS) had no effect. Immunocytochemistry confirmed that the reduction occurred in neurons and oligodendrocytes. cPLA 2 IVA AS did not alter expression of several other PLA 2 isoforms, such as secretory PLA 2 (groups IIA and V) and calcium-independent PLA 2 (group VI), indicating that the AS was specific for cPLA 2 IVA. This selective knockdown of spinal cPLA 2 IVA did not change acute nociception (i.e. paw withdrawal thresholds to acute thermal stimuli and intradermal formalin-induced first phase flinching), however, it significantly attenuated formalin-induced hyperalgesia (i.e. second phase flinching behavior), which reflects spinal sensitization. Thus the present findings suggest that cPLA 2 IVA may specifically participate in spinal nociceptive processing.