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

Activation of the spinal phospholipase A2 (PLA2) –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 PLA2 enzymes in this cascade is limited. Among all PLA2 groups, cytosolic calcium-dependent PLA2 group IVA (cPLA2IVA) appears to be the predominant PLA2 enzyme in the spinal cord. In the present study we sought to (i) characterize anatomical and cellular distribution and localization of cPLA2IVA in dorsal horn of rat spinal cord, (ii) verify efficacy and selectivity of intrathecal (IT) delivery of an antisense oligonucleotide (AS) targeting rat cPLA2IVA mRNA on spinal expression of this enzyme, and (iii) examine the effect of down-regulation of spinal cPLA2IVA on peripheral tissue injury–induced pain behavior. Here we demonstrate that cPLA2IVA 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 cPLA2IVA in rat spinal cord, while control missense oligonucleotide (MS) had no effect. Immunocytochemistry confirmed that the reduction occurred in neurons and oligodendrocytes. cPLA2IVA AS did not alter expression of several other PLA2 isoforms, such as secretory PLA2 (groups IIA and V) and calcium-independent PLA2 (group VI), indicating that the AS was specific for cPLA2IVA. This selective knockdown of spinal cPLA2IVA 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 cPLA2IVA may specifically participate in spinal nociceptive processing.