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Anitha Krishnan, Malvika Dua, Claire H Mitchell, Wennan Lu, Meredith S Gregory-Ksander; Pharmacologic inhibition of the NLRP3 inflammasome - a novel neuroprotective therapy for glaucoma. Invest. Ophthalmol. Vis. Sci. 2019;60(9):2256. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Glaucoma is a multifactorial neurodegenerative disease causing irreversible blindness. Recent evidence suggests early axon damage in the optic nerve head (ONH) is linked to glial reactivity and NLRP3 inflammasome activation, a critical regulator of inflammation. We previously reported that NLRP3 knockout mice were protected from axon degeneration and death of RGCs in the microbead-induced model of glaucoma. We now determined whether treatment with a small molecule inhibitor of NLRP3 (MCC950) could provide similar neuroprotection to RGCs and their axons in glaucoma.
NLRP3 expression in the ONH was confirmed in WT B6 mice by western blot (WB) analysis. To identify which cells express NLRP3, ONH astrocytes were isolated and also analyzed by WB. To determine the timing of IOP-induced inflammasome activation, intracameral injection of microbeads or saline (negative control) was used to elevate IOP and WB analysis of cleaved caspase-1 in the ONH was performed at 7 and 14 days post microbead injection. Neuroprotective effects of the NLRP3 inhibitor MCC950 were assessed in the microbead model of glaucoma. WT B6 mice received one ip injection of MCC950 (20mg/kg) when microbeads were injected and then every 2 days for 28 days. Rebound tonometry monitored IOP and at 28 days, the mice were euthanized and the ONH and retina were processed for RGC and axon counts.
WB analysis confirmed constitutive expression of NLRP3 in the ONH astrocytes of B6 mice with normal IOP. Significant inflammasome activation, as determined by cleaved Caspase-1, was detected in the ONH at 14 days post microbead injection. As previously demonstrated, intracameral injection of microbeads induced elevated IOP for up to 21 days, resulting in a 25-30% loss of RGCs and axons in B6 mice as compared to saline controls. Systemic treatment with MCC950 by ip injection had no significant effect on the elevation of IOP, which was equal to vehicle-treated mice. However, systemic MCC950 treatment provided significant neuroprotection, with RGC and axon densities equal to that of non-glaucomatous controls.
These results (i) implicate NLRP3 inflammasome activation in ONH astrocytes as a potential initiator of neuroinflammation and axon damage following elevated IOP and (ii) provide proof-of-concept that pharmacologic inhibition of NLRP3 can be used as a neuroprotective therapy in glaucoma.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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