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Chi-Chao Chan, DeFen Shen, Yujuan Wang, Xi Chu, Mones Abu-Asab, Jingsheng Tuo; Inflammasomes in human eyes with AMD and mouse retinas with focal retinal degeneration. Invest. Ophthalmol. Vis. Sci. 2013;54(15):315.
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Inflammasome, a component of innate immune system, is multiprotein oligomers consisting of caspase 1, PYCARD and NLRP. Inflammasomes recognize the inflammatory induced stimuli including pathogen-associated molecular patterns (PAMPs) that are predominantly found in microbes, and damage-associated molecular patterns (DAMPs) that are released due to perturbation of tissue homeostasis. Inflammasomes typically activate IL-1β and IL-18. Recently, the role of inflammasomes has expanded from infection and inflammation to diabetes, obesity, artherosclerosis and age-related macular degeneration. In this study, we evaluated the expression of NLRP3 and IL-18 in the retinas of age-related macular degeneration (AMD) patients and Ccl2-/-/Cx3cr1-/- on rd8 background (DKO rd8), a model that develops progressive AMD-like retinal lesions including focal retinal degeneration, A2E accumulation and immune dysregulation, in addition to retinal dystrophy.
The macular and the peripheral retina and choroid of 16 paraffin-embedded, archived human AMD eyes (8 geographic atrophy (GA) and 7 neovascular (n) AMD) and 3 age-matched normal eyes were microdissected. Their RNA was isolated (Paradise RNA isolation system) for cDNA synthesis (SuperScript II RT system). The DKO rd8 and C57BL/6N mouse eyes, of ages 1, 5 and 12 months old were collected and their RNA was isolated with Trizol for cDNA synthesis. NLRP3 and IL-18 mRNA were quantitated by real time PCR monitored with SYBR Green fluorescence.
The relative expression of transcript levels of NLRP3 (AMD, 161.4±83.6; normal, undetectable; p<0.0001) and IL-18 (AMD, 210.5±35.9, GA AMD, 242.7±46.0, nAMD, 173.6±56.1; normal, undetectable; p<0.0001) were found significantly higher in AMD lesions compared to the normal macula. Expression of both NLRP3 and IL-18 in the periphery was barely detected or below detectable levels in both AMD and normal peripheries. In the mice, both Nlrp3 and Il-18 transcripts elevated with age. The relative expression of Nlrp3 and Il-18 transcripts were also significantly higher in DKO rd8 eyes compared with that in C57BL/6N eyes throughout changes in aging.
Higher levels of inflammasome and related cytokine are expressed in human AMD macula and DKO rd8 mouse eyes compared to the controls. These findings support the aforementioned hypothesis that the innate immune system may play a role in AMD pathogenesis.
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