Lysophosphatidylcholine Stimulates IL-1β Release from Microglia via a P2X7 Receptor-Independent Mechanism

Abstract

IL-1β released from activated macrophages contributes significantly to tissue damage in inflammatory, degenerative, and autoimmune diseases. In the present study, we identified a novel mechanism of IL-1β release from activated microglia (brain macrophages) that occurred independently of P2X7 ATP receptor activation. Stimulation of LPS-preactivated microglia with lysophosphatidylcholine (LPC) caused rapid processing and secretion of mature 17-kDa IL-1β. Neither LPC-induced IL-1β release nor LPC-stimulated intracellular Ca2+ increases were affected by inhibition of P2X7 ATP receptors with oxidized ATP. Microglial LPC-induced IL-1β release was suppressed in Ca2+-free medium or during inhibition of nonselective cation channels with Gd3+ or La3+. It was also attenuated when Ca2+-activated K+ channels were blocked with charybdotoxin (CTX). The electroneutral K+ ionophore nigericin did not reverse the suppressive effects of CTX on LPC-stimulated IL-1β release, demonstrating the importance of membrane hyperpolarization. Furthermore, LPC-stimulated caspase activity was unaffected by Ca2+-free medium or CTX, suggesting that secretion but not processing of IL-1β is Ca2+- and voltage-dependent. In summary, these data indicate that the activity of nonselective cation channels and Ca2+-activated K+ channels is required for optimal IL-1β release from LPC-stimulated microglia.

Lysophospholipids and ATP Mutually Suppress Maturation and Release of IL-1β in Mouse Microglial Cells Using a Rho-Dependent Pathway

“…LPC was recently reported to be a potent endogenous inducer of mIL-1␤ release in microglial cells (21). In agreement with this report, we demonstrated that LPC alone triggered the release of mIL-1␤ in mouse microglial cells.…”

“…In agreement with this report, we demonstrated that LPC alone triggered the release of mIL-1␤ in mouse microglial cells. In primary microglia, the lower concentrations of LPC (20 -40 M) were able to generate a significant amount of mIL-1␤, suggesting that this event physiologically occurs during inflammation as described in a previous report (21). In contrast, we demonstrated the anti-inflammatory function of LPC by showing the inhibition of P2X7R-dependent mIL-1␤ release.…”

“…Additionally, LPC is shown to activate nonselective cation channels and to induce the K ϩ efflux through the activation of Ca 2ϩ -dependent K ϩ channels, and this ultimately leads to the release of mIL-1␤ in microglia (21). Similarly, sphingosylphosphorylcholine (SPC), another bioactive lysophospholipid, as well as LPC are reported to enhance P2X7R-mediated IL-1␤ release in THP-1 cells by increasing the binding affinity of agonists to P2X7R (22).…”

Microvesicles shed from microglia activated by the P2X7-p38 pathway are involved in neuropathic pain induced by spinal nerve ligation in rats

“…7c). The change in IL-1β was consistent with previous studies, in which IL-1β was packaged in the bleb of MVs and secreted through the activation of P2X7 receptors [11,44]. However, the other two cytokines, TNF-α and IL-6, displayed no distinct changes.…”

Significance of Brain Tissue Oxygenation and the Arachidonic Acid Cascade in Stroke

“…In addition to AA, glycerophospholipid metabolism by PLA 2 s following stroke also elevate LPC levels in blood, cerebrospinal fluid, and brain tissue following ischemic and hemorrhagic stroke (61,62,79,164). LPCs act as potent mediators of inflammation in the brain following stroke via stimulated release of interleukin 1b (162) and subsequent activation of microglia (122,143).…”