Evidence for the activation of pyroptotic and apoptotic pathways in RPE cells associated with NLRP3 inflammasome in the rodent eye

Abstract

BackgroundAge-related macular degeneration (AMD) is a devastating eye disease causing irreversible vision loss in the elderly. Retinal pigment epithelium (RPE), the primary cell type that is afflicted in AMD, undergoes programmed cell death in the late stages of the disease. However, the exact mechanisms for RPE degeneration in AMD are still unresolved. The prevailing theories consider that each cell death pathway works independently and without regulation of each other. Building upon our previous work in which we induced a short burst of inflammasome activity in vivo, we now investigate the effects of prolonged inflammasome activity on RPE cell death mechanisms in rats.MethodsLong-Evans rats received three intravitreal injections of amyloid beta (Aβ), once every 4 days, and were sacrificed at day 14. The vitreous samples were collected to assess the levels of secreted cytokines. The inflammasome activity was evaluated by both immunohistochemistry and western blot. The types of RPE cell death mechanisms were determined using specific cell death markers and morphological characterizations.ResultsWe found robust inflammasome activation evident by enhanced caspase-1 immunoreactivity, augmented NF-κB nuclear translocalization, increased IL-1β vitreal secretion, and IL-18 protein levels. Moreover, we observed elevated proteolytic cleavage of caspase-3 and gasdermin D, markers for apoptosis and pyroptosis, respectively, in RPE-choroid tissues. There was also a significant reduction in the anti-apoptotic factor, X-linked inhibitor of apoptosis protein, consistent with the overall changes of RPE cells. Morphological analysis showed phenotypic characteristics of pyroptosis including RPE cell swelling.ConclusionsOur data suggest that two cell death pathways, pyroptosis and apoptosis, were activated in RPE cells after exposure to prolonged inflammasome activation, induced by a drusen component, Aβ. The involvement of two distinct cell death pathways in RPE sheds light on the potential interplay between these pathways and provides insights on the future development of therapeutic strategies for AMD.Electronic supplementary materialThe online version of this article (10.1186/s12974-018-1062-3) contains supplementary material, which is available to authorized users.

Caspase-1-dependent inflammasomes mediate photoreceptor cell death in photo-oxidative damage-induced retinal degeneration

“…Inflammasome-mediated inflammation and cell death are widely accepted to be associated with both wet and dry forms of AMD 1,3,17,23,33,34,51 , with in vivo inhibition of inflammasome-activated pro-inflammatory cytokine IL-1β shown to greatly improve the survivability of the retina following photo-oxidative damage 14 . However, while much of the current literature has focused on investigating the role of inflammasome sensor receptor NLRP3 in propagating this damage, little work has been done on other components of inflammasome pathways, in particular on the role of pro-inflammatory-cleavage protease CASP-1.…”

“…Several studies have been conducted to investigate if and how NLRP3 may be activated in AMD disease progression 21,[27][28][29][31][32][33][34][35][36] . However, to date studies using animal models have been focused on wet-AMD 21 , while those which investigate the role of NLRP3 in dry-AMD pathogenesis have been largely cell culture-based and focused on the RPE 19,21,22,27,28,31,32 .…”

Can dexamethasone prevent the seizures induced by SARS-CoV-2 infection?

“…A recent trial suggested that dexamethasone reduces mortality in these patients [8] . Interestingly, in a refractory model of epilepsy, dexamethasone was able to abrogate neuroinflammatory signs and improve astrocyte function [9] ; in fact, this anti-inflammatory steroid has been proposed as an adjuvant therapy in cases of refractory epilepsy [10] . Therefore, we speculate that dexamethasone, beyond reducing mortality, could be useful for preventing or mitigating convulsive manifestations in COVID-19 patients.…”

Novel Programmed Cell Death as Therapeutic Targets in Age-Related Macular Degeneration?

“…In 2013, NLRP3 was first detected in RPE and drusen in AMD patients. Using human RPE cells, the study also provided the evidence that lysosomal destabilization triggered NLRP3-mediated inflammation [ 111 ]. However, markers of pyroptosis were not examined in this study.…”