Low-density Lipoprotein-mediated Retinal Pigment Epithelium Inflammation And Underlying Mechanisms

Purpose:Native and oxidized（OX）low-density lipoprotein（LDL）may contribute to the pathogenesis of age-related macular degeneration（AMD）.In this study,we investigated the effects of lipoproteins,including n-LDL and OX-LDL,on the expression of inflammation factors,interleukin-6（IL-6）and interleukin-1β（IL-1β）,in vivo and in cultured retinal pigment epithelial（RPE）cells.The potential role of Toll-like receptor 4（TLR4）was preliminarily explored.Methods:Fifteen male Sprague-Dawley rats were randomized into three groups and injected intravenously with PBS,low n-LDL（1mg/kg）,and high n-LDL（4mg/kg）for 14 days.Immunohistochemistry analysis of retina sections was conducted to detect IL-6 and IL-1β.ARPE-19 cells were incubated with 10-100 mg/mL n-LDL or OX-LDL for 24h.Reverse transcription polymerase chain reaction（RT-PCR）was used to detect IL-6,IL-1βand TLR4 mRNA levels in ARPE-19.IL-6 and IL-1βprotein expression was measured by enzyme-linked immune sorbent assay（ELISA）.Activation of TLR4 and extracellular signal-regulated kinase（ERK）protein were evaluated by western blot analysis.RPE cells of wild and gene knock-out(TLR4^-/-)C57 mice were primary cultured in vitro with enzyme digestion.The cultured RPE cells were identified with immunocytochemical staining.RPE cells were incubated with 10-100mg/mL native-LDL（n-LDL）or OX-LDL for 24h.IL-6 and IL-1βprotein in the supernatant was measured by ELISA.Western blot analysis and RT-PCR were used to detect TLR4 protein and mRNA levels in RPE cells.One-way analysis of variance was used to compare differences.Results:Circulating LDL increased both IL-6 and IL-1βexpression in rat retina tissue.OX-LDL treatment increased IL-6 and IL-1βexpression in ARPE-19 cells,and activated TLR4-ERK signaling pathway.OX-LDL treatment increased IL-6 and IL-1βsecretion in wild mouse RPE cells,with TLR4 mRNA and protein expression activated.There was no significant IL-6 and IL-1βsecretion increase in TLR4-/-mouse RPE cells.Conclusions:LDL activates inflammation cytokines in rat retina.OX-LDL induces inflammation promotion through TLR4 upregulation.