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Jing Z Cui, Jiangyuan Gao, Eleanor To, Joanne A Matsubara; XIAP’s Association with NLRP3 Inflammasome in Human Donor Eyes. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3461.
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X-linked inhibitor of apoptosis (XIAP) is a potent anti-apoptotic factor, whose neuroprotective role has been demonstrated in several retinal degeneration animal models. However, a number of recent studies have expanded our knowledge of XIAP’s biological functions by showing its involvement in cell signaling and immune response regulation, but not in retinal pigment epithelium (RPE) cells. Previously, we showed an age-dependent decrease of XIAP protein in RPE tissues from normal human donor eyes. We also showed a surge of XIAP immunoreactivity in RPE tissues from patients with geographic atrophy (GA) (Gao et al IOVS 2013;54;E-abstract 160). In this study, we aim to understand XIAP’s potential role in regulating NLRP3 inflammasome activity, a key immune response underlying GA.
The same set of donor eyes from previous XIAP study were used here. The eyes were categorized into three groups, a normal Young group (< 57 years of age), a normal Old group (> 70 years of age), and a GA group (averaging 83.7 years of age). Antibodies against phosphorylated NF-κB p65 subunit, NLRP3 and cleaved Caspase-1 p10 subunit were applied to assess the markers’ immunoreactivity in RPE layer. Nuclear immunolabeling of phosphorylated NF-κB p65 in all groups were counted and analyzed by One-Way ANOVA. Cytoplasmic labeling of NLRP3 and cleaved Caspase-1 p10 were analyzed semi-quantitatively following established protocols.
In contrast to XIAP’s age-dependent decrease, the immunoreactivity of phosphorylated NF-κB p65 and NLRP3 in normal RPE tissues increased with age. Moreover, parallel to the elevated XIAP level in the GA group, there was an augment in cleaved Caspase-1 p10 subunit and NLRP3 immunoreactivity in the GA group compared to the Old group. However, the phosphorylated NF-κB p65 level was reduced in the GA group compared to the Old group.
In this study, we correlated the changes in immunoreactivity of XIAP and markers of the NLRP3 inflammasome pathway using the same set of donor eyes. We showed an inverse relationship between XIAP and NF-κB activation, an inflammasome priming signal. Intriguingly, our findings also indicated a parallel correlation between XIAP and two inflammasome components, NLRP3 and Caspase-1 p10, suggesting XIAP’s potential involvement in inflammasome regulation. Future experiments using cell culture and animal models will provide mechanistic insights to fully understand such interaction.
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