ABSTRACT
Age-related macular degeneration (AMD) is the leading cause of legal blindness in the elderly in industrialized countries. AMD is a multifactorial disease influenced by both genetic and environmental risk factors. Progression of AMD is characterized by an increase in the number and size of drusen, extracellular deposits, which accumulate between the retinal pigment epithelium (RPE) and Bruch's membrane (BM) in outer retina. The major pathways associated with its pathogenesis include oxidative stress and inflammation in the early stages of AMD. Little is known about the interactions among these mechanisms that drive the transition from early to late stages of AMD, such as geographic atrophy (GA) or choroidal neovascularization (CNV). As part of the innate immune system, inflammasome activation has been identified in RPE cells and proposed to be a causal factor for RPE dysfunction and degeneration. Here, we will first review the classic model of inflammasome activation, then discuss the potentials of AMD-related factors to activate the inflammasome in both nonocular immune cells and RPE cells, and finally introduce several novel mechanisms for regulating the inflammasome activity.
Subject(s)
Carrier Proteins/metabolism , Inflammasomes/metabolism , Macular Degeneration/metabolism , Animals , Bruch Membrane/metabolism , Bruch Membrane/pathology , Humans , Macular Degeneration/pathology , NLR Family, Pyrin Domain-Containing 3 Protein , Retinal Pigment Epithelium/metabolism , Retinal Pigment Epithelium/pathologyABSTRACT
Chronic inflammation is a key pathogenic process in age-related macular degeneration (AMD). Amyloid-beta (Aß) is a constituent of AMD drusen and promotes the activation of NLRP3 inflammasome which facilitates the production of cytokines. We investigated the role of transcription factor NF-κB in the activation of inflammasome in the RPE and the effect of vinpocetine, a dietary supplement with inhibitory effect on NF-κΒ. ARPE19/NF-κB-luciferase reporter cells treated with Aß demonstrated enhanced NF-κB activation that was significantly suppressed by vinpocetine. Intraperitoneal injection of vinpocetine (15 mg/kg) inhibited NF-κB nuclear translocation and reduced the expression and activation of NLRP3, caspase-1, IL-1ß, IL-18, and TNF-α in the RPE of adult rats that received intraocular Αß, as measured by retinal immunohistochemistry and Western blot. Cytokine level in the vitreous was assayed using multiplex suspension arrays and revealed significantly lower concentration of MIP-3α, IL-6, IL-1α, IL-1ß, IL-18, and TNF-α in vinpocetine treated animals. These results suggest that the NF-κB pathway is activated by Aß in the RPE and signals the priming of NLRP3 inflammasome and the expression of pro-inflammatory cytokines including the inflammasome substrates IL-1ß and IL-18. NF-κB inhibition may be an effective approach to stem the chronic inflammatory milieu that underlies the development of AMD. Vinpocetine is a potentially useful anti-inflammatory agent that is well-tolerated in long term use.
Subject(s)
Amyloid beta-Peptides/antagonists & inhibitors , Cytokines/metabolism , Inflammasomes/metabolism , NF-kappa B/metabolism , Retinal Pigment Epithelium/drug effects , Vasodilator Agents/pharmacology , Vinca Alkaloids/pharmacology , Amyloid beta-Peptides/pharmacology , Animals , Blotting, Western , Carrier Proteins , Cell Line , Enzyme-Linked Immunosorbent Assay , Female , Humans , Injections, Intraperitoneal , NLR Family, Pyrin Domain-Containing 3 Protein , Rats , Rats, Long-Evans , Receptors, Cytoplasmic and Nuclear/metabolism , Retinal Pigment Epithelium/metabolism , Vitreous Body/metabolismABSTRACT
PURPOSE: Drusen are hallmarks of age-related macular degeneration (AMD). Amyloid-beta 1-40 (Aß 1-40), a constituent of drusen, is known to stimulate inflammatory pathways in RPE; however, its effect in vivo is not known. The purpose of this study was to examine the effect of Aß 1-40 on cytokine expression and inflammasome activation relevant to AMD in an animal model. METHODS: Wild-type rats received intravitreal injections of Aß 1-40, and eyes were taken at days 1, 4, 14, and 49 postinjection. The RPE, neuroretina, and vitreous were analyzed for cytokine expression, inflammasome activation, and microglial response via RT-PCR, immunohistochemistry, and suspension array assay. Retinal cell loss was assessed via apoptotic markers and retinal thickness. RESULTS: Aß 1-40 stimulated upregulation of IL-6, TNF-α, IL-1ß, IL-18, caspase-1, NLRP3, and XAF1 genes in the RPE/choroid and the neuroretina. Increased IL-1ß and IL-6 immunoreactivity was found in retinal sections, and elevated levels of IL-1ß and IL-18 were found in the vitreous of Aß-injected eyes. Aß 1-40 induced a moderate increase in CD11b/c-reactive cells on day 1 postinjection only. No evidence of the proapoptotic XAF1 protein, p53, TUNEL immunoreactivity, or retinal thinning was observed. CONCLUSIONS: These results confirm earlier in vitro work and support the proinflammatory role of drusen component Aß 1-40 in the RPE and retina. Inflammasome activation may be responsible for this effect in vivo. This model is useful for understanding cellular triggers of inflammasome activation and proposed early inflammatory events in the outer retina associated with the etiology of AMD.
