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Neuronal Release of Cytokine IL-3 Triggered by Mechanosensitive Autostimulation of the P2X7 Receptor Is Neuroprotective

View Article: PubMed Central - PubMed

ABSTRACT

Mechanical strain due to increased pressure or swelling activates inflammatory responses in many neural systems. As cytokines and chemokine messengers lead to both pro-inflammatory and neuroprotective actions, understanding the signaling patterns triggered by mechanical stress may help improve overall outcomes. While cytokine signaling in neural systems is often associated with glial cells like astrocytes and microglia, the contribution of neurons themselves to the cytokine response is underappreciated and has bearing on any balanced response. Mechanical stretch of isolated neurons was previously shown to trigger ATP release through pannexin hemichannels and autostimulation of P2X7 receptors (P2X7Rs) on the neural membrane. Given that P2X7Rs are linked to cytokine activation in other cells, this study investigates the link between neuronal stretch and cytokine release through a P2X7-dependent pathway. Cytokine assays showed application of a 4% strain to isolated rat retinal ganglion cells (RGCs) released multiple cytokines. The P2X7R agonist BzATP also released multiple cytokines; Interleukin 3 (IL-3), TNF-α, CXCL9, VEGF, L-selectin, IL-4, GM-CSF, IL-10, IL-1Rα, MIP and CCL20 were released by both stimuli, with the release of IL-3 greatest with either stimuli. Stretch-dependent IL-3 release was confirmed with ELISA and blocked by P2X7R antagonists A438079 and Brilliant Blue G (BBG), implicating autostimulation of the P2X7R in stretch-dependent IL-3 release. Neuronal IL-3 release triggered by BzATP required extracellular calcium. The IL-3Rα receptor was expressed on RGCs but not astrocytes, and both IL-3Rα and IL-3 itself were predominantly expressed in the retinal ganglion cell layer of adult retinal sections, implying autostimulation of receptors by released IL-3. While the number of surviving ganglion cells decreased with time in culture, the addition of IL-3 protected against this loss of neurons. Expression of mRNA for IL-3 and IL-3Rα increased in rat retinas stretched with moderate intraocular pressure (IOP) elevation; BBG blocked the rise in IL-3, implicating a role for the P2X7R in transcriptional regulation in vivo. In summary, mechanical stretch triggers release of cytokines from neurons that can convey neuroprotection. The enhancement of these signals in vivo implicates P2X7R-mediated IL-3 signaling as an endogenous pathway that could minimize damage following neuronal exposure to chronic mechanical strain.

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Related in: MedlinePlus

Model for mechanosensitive P2X7/IL-3 signaling in neurons. Mechanical strain of the neurons leads to ATP release through pannexin hemichannels; this released ATP autostimulates P2X7Rs, leading to an influx of Ca2+. P2X7R activation leads to the release of multiple cytokines, including IL-3, dependent upon this Ca2+ influx. The released IL-3 autostimulates IL-3Rα/IL-3Rβ receptors on the neurons, providing neuroprotection via JAK2 signaling pathways. Together, this provides a signaling pathway to protect neurons from moderate mechanical strain and stretch.
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Figure 5: Model for mechanosensitive P2X7/IL-3 signaling in neurons. Mechanical strain of the neurons leads to ATP release through pannexin hemichannels; this released ATP autostimulates P2X7Rs, leading to an influx of Ca2+. P2X7R activation leads to the release of multiple cytokines, including IL-3, dependent upon this Ca2+ influx. The released IL-3 autostimulates IL-3Rα/IL-3Rβ receptors on the neurons, providing neuroprotection via JAK2 signaling pathways. Together, this provides a signaling pathway to protect neurons from moderate mechanical strain and stretch.

Mentions: This study demonstrates that moderate stretch triggers the release of multiple cytokines from isolated neurons. A parallel cytokine release is produced by exposing the cells to P2X7R agonist BzATP. The correlation between the release profiles triggered by stretch and P2X7R stimulation suggested that the cytokine release pathways were linked. IL-3 showed the largest proportional release by either stimuli, and the ability of two different P2X7R antagonists to inhibit the stretch-dependent IL-3 release strongly suggested the release required P2X7R stimulation. We have previously demonstrated that stretch initiates a release of ATP through pannexin hemichannels from these neurons capable of autostimulating their P2X7R; the ability of apyrase to prevent swelling activated currents through the P2X7R, to reduce the regulatory volume decrease accompanying swelling, and to block the rise in intracellular calcium that followed swelling confirmed the central role of released extracellular ATP in the stimulation of this P2X7 receptor (Xia et al., 2012). The stretch-dependent release of IL-3 is consistent with this release of ATP and autostimulation of the P2X7R (Figure 5).


Neuronal Release of Cytokine IL-3 Triggered by Mechanosensitive Autostimulation of the P2X7 Receptor Is Neuroprotective
Model for mechanosensitive P2X7/IL-3 signaling in neurons. Mechanical strain of the neurons leads to ATP release through pannexin hemichannels; this released ATP autostimulates P2X7Rs, leading to an influx of Ca2+. P2X7R activation leads to the release of multiple cytokines, including IL-3, dependent upon this Ca2+ influx. The released IL-3 autostimulates IL-3Rα/IL-3Rβ receptors on the neurons, providing neuroprotection via JAK2 signaling pathways. Together, this provides a signaling pathway to protect neurons from moderate mechanical strain and stretch.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5120082&req=5

Figure 5: Model for mechanosensitive P2X7/IL-3 signaling in neurons. Mechanical strain of the neurons leads to ATP release through pannexin hemichannels; this released ATP autostimulates P2X7Rs, leading to an influx of Ca2+. P2X7R activation leads to the release of multiple cytokines, including IL-3, dependent upon this Ca2+ influx. The released IL-3 autostimulates IL-3Rα/IL-3Rβ receptors on the neurons, providing neuroprotection via JAK2 signaling pathways. Together, this provides a signaling pathway to protect neurons from moderate mechanical strain and stretch.
Mentions: This study demonstrates that moderate stretch triggers the release of multiple cytokines from isolated neurons. A parallel cytokine release is produced by exposing the cells to P2X7R agonist BzATP. The correlation between the release profiles triggered by stretch and P2X7R stimulation suggested that the cytokine release pathways were linked. IL-3 showed the largest proportional release by either stimuli, and the ability of two different P2X7R antagonists to inhibit the stretch-dependent IL-3 release strongly suggested the release required P2X7R stimulation. We have previously demonstrated that stretch initiates a release of ATP through pannexin hemichannels from these neurons capable of autostimulating their P2X7R; the ability of apyrase to prevent swelling activated currents through the P2X7R, to reduce the regulatory volume decrease accompanying swelling, and to block the rise in intracellular calcium that followed swelling confirmed the central role of released extracellular ATP in the stimulation of this P2X7 receptor (Xia et al., 2012). The stretch-dependent release of IL-3 is consistent with this release of ATP and autostimulation of the P2X7R (Figure 5).

View Article: PubMed Central - PubMed

ABSTRACT

Mechanical strain due to increased pressure or swelling activates inflammatory responses in many neural systems. As cytokines and chemokine messengers lead to both pro-inflammatory and neuroprotective actions, understanding the signaling patterns triggered by mechanical stress may help improve overall outcomes. While cytokine signaling in neural systems is often associated with glial cells like astrocytes and microglia, the contribution of neurons themselves to the cytokine response is underappreciated and has bearing on any balanced response. Mechanical stretch of isolated neurons was previously shown to trigger ATP release through pannexin hemichannels and autostimulation of P2X7 receptors (P2X7Rs) on the neural membrane. Given that P2X7Rs are linked to cytokine activation in other cells, this study investigates the link between neuronal stretch and cytokine release through a P2X7-dependent pathway. Cytokine assays showed application of a 4% strain to isolated rat retinal ganglion cells (RGCs) released multiple cytokines. The P2X7R agonist BzATP also released multiple cytokines; Interleukin 3 (IL-3), TNF-α, CXCL9, VEGF, L-selectin, IL-4, GM-CSF, IL-10, IL-1Rα, MIP and CCL20 were released by both stimuli, with the release of IL-3 greatest with either stimuli. Stretch-dependent IL-3 release was confirmed with ELISA and blocked by P2X7R antagonists A438079 and Brilliant Blue G (BBG), implicating autostimulation of the P2X7R in stretch-dependent IL-3 release. Neuronal IL-3 release triggered by BzATP required extracellular calcium. The IL-3Rα receptor was expressed on RGCs but not astrocytes, and both IL-3Rα and IL-3 itself were predominantly expressed in the retinal ganglion cell layer of adult retinal sections, implying autostimulation of receptors by released IL-3. While the number of surviving ganglion cells decreased with time in culture, the addition of IL-3 protected against this loss of neurons. Expression of mRNA for IL-3 and IL-3Rα increased in rat retinas stretched with moderate intraocular pressure (IOP) elevation; BBG blocked the rise in IL-3, implicating a role for the P2X7R in transcriptional regulation in vivo. In summary, mechanical stretch triggers release of cytokines from neurons that can convey neuroprotection. The enhancement of these signals in vivo implicates P2X7R-mediated IL-3 signaling as an endogenous pathway that could minimize damage following neuronal exposure to chronic mechanical strain.

No MeSH data available.


Related in: MedlinePlus