Differential expression of sPLA₂ following spinal cord injury and a functional role for sPLA₂‐IIA in mediating oligodendrocyte death

Abstract

After the initial mechanical insult of spinal cord injury (SCI), secondary mediators propagate a massive loss of oligodendrocytes. We previously showed that following SCI both the total phospholipases activity and cytosolic PLA2-IVα protein expression increased. However, the expression of secreted isoforms of PLA2 (sPLA2) and their possible roles in oligodendrocyte death following SCI remains unclear. Here we report that mRNAs extracted 15 min, 4 hr, 1 day, or 1 month after cervical SCI show marked upregulation of sPLA2-IIA and IIE at 4 hr after injury. In contrast, SCI induced down regulation of sPLA2-X, and no change in sPLA2-IB, IIC, V, and XIIA expression. At the lesion site, sPLA2-IIA and IIE expression were localized to oligodendrocytes. Recombinant human sPLA2-IIA (0.01, 0.1, or 2 μM) induced a dose-dependent cytotoxicity in differentiated adult oligodendrocyte precursor cells but not primary astrocytes or Schwann cells in vitro. Most importantly, pretreatment with S3319, a sPLA2-IIA inhibitor, before a 30 min H2O2 injury (1 or 10 mM) significantly reduced oligodendrocyte cell death at 48 hr. Similarly, pretreatment with S3319 before injury with IL-1β and TNFα prevented cell death and loss of oligodendrocyte processes at 72 hr. Collectively, these findings suggest that sPLA2-IIA and IIE are increased following SCI, that increased sPLA2-IIA can be cytotoxic to oligodendrocytes, and that in vitro blockade of sPLA2 can create sparing of oligodendrocytes in two distinct injury models. Therefore sPLA2-IIA may be an important mediator of oligodendrocyte death and a novel target for therapeutic intervention following SCI.

Role of phospholipase A2s and lipid mediators in secondary damage after spinal cord injury

“…We have not detected sPLA 2 GIIA expression in the naive uninjured spinal cord , suggesting that the presence of sPLA 2 activity reported earlier is attributable to other forms of sPLA 2 expressed constitutively for normal physiological functions (Titsworth et al 2009). sPLA 2 activity has been shown to be increased after spinal cord trauma (Liu et al 2006), and we have reported that sPLA 2 GIIA expression is induced during the first week after SCI, peaking at day 3 and appearing mainly in oligodendrocytes and astrocytes and in a small proportion in neurons and microglia/macrophages ).…”

“…However, of 14 mammalian PLA 2 s analyzed, only cPLA 2 GIVA, iPLA 2 VIA, and sPLA 2 IIA are significantly up-regulated at the mRNA level after SCI (Table 2; Liu et al 2006;Titsworth et al 2009;López-Vales et al 2011). Emerging evidence indicates an important role for members of the PLA 2 superfamily in secondary tissue damage and in tissue protection after SCI.…”

“…sPLA 2 activity has been shown to be increased after spinal cord trauma (Liu et al 2006), and we have reported that sPLA 2 GIIA expression is induced during the first week after SCI, peaking at day 3 and appearing mainly in oligodendrocytes and astrocytes and in a small proportion in neurons and microglia/macrophages ). Unlike contusion injury in mice, protein levels of sPLA 2 GIIA and sPLA 2 GIIE are up-regulated in rats at 4 h after SCI but not at later time points, being expressed mainly in oligodendrocytes (Titsworth et al 2009). Using a highly selective small amide inhibitor of sPLA 2 GIIA (GK115; Antonopoulou et al 2008), we have reported that sPLA 2 contributes to secondary damage after SCI .…”

“…Expression and role of PLA 2 s in SCI Multiple forms of mammalian PLA 2 s that include sPLA 2 IB, IIA, IIC, and V, cPLA 2 GIVA, and iPLA 2 GVIA are constitutively detected in the normal rat spinal cord (Liu et al 2006;Titsworth et al 2009). However, of 14 mammalian PLA 2 s analyzed, only cPLA 2 GIVA, iPLA 2 VIA, and sPLA 2 IIA are significantly up-regulated at the mRNA level after SCI (Table 2; Liu et al 2006;Titsworth et al 2009;López-Vales et al 2011).…”

Kainate Receptors Mediate Regulated Exocytosis of Secretory Phospholipase A2 in SH-SY5Y Neuroblastoma Cells

“…sPLA 2 -IIA plays a role in nociception from the paw and orofacial region [20,21] and may contribute to neuronal injury in acute and chronic neurodegenerative diseases. sPLA 2 -IIA activity and expression are upregulated after cerebral ischemia [22,23] and spinal cord injury [24] . Enzyme expression is increased in Alzheimer's disease, especially in regions containing amyloid-␤ plaques [25] .…”