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Yvette Wooff, Nilisha Fernando, Josephine Wong, Catherine Dietrich, Riemke Aggio-Bruce, Joshua Aaron Chu-Tan, Sarah Doyle, Avril Robertson, Si Ming Man, Riccardo Carlo Natoli; Inhibition of NLRP3 does not protect against photo-oxidative damage-induced retinal degeneration. Invest. Ophthalmol. Vis. Sci. 2019;60(9):2798.
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The inflammasome is a key innate immune pathway that has been implicated in the progression of retinal degenerations such as Age-Related Macular Degeneration (AMD). However, evidence implicating the most widely studied inflammasome receptor protein, NOD-, LRR- and pyrin domain-containing 3 (NLRP3), is inconclusive. This study aimed to investigate, in vivo, the role of key components of the NLRP3 inflammasome including NLRP3, apoptosis-associated speck-like protein containing a CARD (ASC) and protease Caspase 1 (CASP1), in photoreceptor degeneration using photo-oxidative damage
Adult C57BL/6J, Nlrp3-/-, Asc-/-, Casp11-/- and Casp1/11-/- mice, as well as inhibitors of NLRP3 including siRNA for Nlrp3 (1µg/µL) and specific inhibitor MCC950 (20 and 100µM) were used in this study (N=6). The expression of inflammasome components (Nlrp3, Asc, Casp1, and interleukin-1β (Il-1β) was investigated over a protracted time-course (1, 3, 5 and 7 days) photo-oxidative damage (PD) (100k lux) in mice. The expression and localization of NLRP3, CASP1 and IL-1β was compared using western blot and immunohistochemistry (IHC). Retinas were analysed for function (electroretinography), photoreceptor loss (Optical Coherence Tomography, TUNEL and photoreceptor row counts), and inflammation (IBA-1 IHC for microglia/macrophages, and IL-1β ELISA.
Following 5 days PD, Nlrp3-/- mice had improved retinal function compared to WT controls (P<0.05), however, C57BL6/J mice injected with either MCC950 or Nlrp3 siRNA showed unchanged (P>0.05), or lower retinal function (P<0.05) compared to controls. In addition, there was no improvement in photoreceptor cell death or inflammation measured by IL-1β ELISA, and IBA-1+ cell counts in either Nlrp3-/- mice or NLRP3-inhibited retinas (P>0.05). While neither Asc-/- nor Casp11-/- mice showed any retinal protection compared to controls, Casp1/11-/- mice had significantly improved retinal function, fewer TUNEL+ and IBA-1+ cells in the outer retina, reduced levels of IL-1β and increased photoreceptor rows (P<0.05).
Inhibition of NLRP3 did not protect against PD-induced retinal degeneration. However, our data from Casp1/11-/- mice demonstrated that CASP1 may be critical in mediating inflammation and subsequent photoreceptor cell death in the degenerating retina. Therapeutic strategies that target CASP1 may therefore be beneficial in slowing the progression of AMD.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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