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Claire H Mitchell, Farraj Albalawi, Wennan Lu; Increased IOP primes the NLRP3 inflammasome and increases IL-1β levels. Invest. Ophthalmol. Vis. Sci. 2017;58(8):851.
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The NLRP3 inflammasome is a multiprotein complex involved in the maturation of cytokine IL-1β. As IL-1β in turn drives the expression of many other cytokines, regulation of the inflammasome is a key upstream target. IL-1β has been implicated in the inflammatory response associated with glaucomatous neuropathy, but the links connecting elevated IOP and increased IL-1β levels are unclear. Here we examine the consequences of IOP elevation and mechanical strain on expression of inflammasome components.
Transient IOP elevation was induced in rats and mice by cannulating the anterior segment to a non-ischemic 50-60 mmHg for 4 hrs. Optic nerve head astrocytes were cultured from rats and mice. Levels of mRNA were compared using qPCR, levels of protein quantified from immunoblots, and location of protein changes identified with immunohistochemistry.
Moderate elevation of IOP increased expression of message for inflammasome components IL-1β, NLRP3 and caspase 1 in rat retinas. Immunoblots showed transient IOP elevation increased IL-1β protein. The rise in IL-1β was inhibited by injection of P2X7 antagonist Brilliant Blue G, while intravitreal injection of P2X7 agonist BzATP induced a rise in IL-1β message. Expression of IL-1β, NLRP3 and caspase 1 were also increased in mouse retina after transient IOP elevations, while IL-1β was increased in 8 month old Tg-Myoc mice with chronic IOP elevation. Immunohistochemistry of rat eyes exposed to transient IOP elevation identified a rise in IL-1β protein in the inner retina, and in horizontal bands throughout the optic nerve head consistent with astrocytes. In isolated optic nerve head astrocytes, message for IL-1β increased with moderate stretch and swelling. The rise of IL-1β in astrocytes was prevented by P2X7 receptor antagonists BBG and A839977, but P2X7R agonist BzATP did not increase expression of IL-1β in astrocytes. Swelling, but not BzATP, activated transcription factor NFkB in isolated astrocytes, while the swelling activated rise of IL-1β in astrocytes was prevented by NFkB inhibitor Bay 11-7082.
Moderate elevation of IOP primes inflammasome components, particularly IL-1β. Stimulation of the P2X7R contributes to this increase, suggesting the IOP-induced release of agonist ATP may influence the inflammatory response.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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