Effects of modified LDL and HDL on retinal pigment epithelial cells: a role in diabetic retinopathy?

Abstract

Aims/hypothesis Blood–retina barrier leakage in diabetes results in extravasation of plasma lipoproteins. Intra-retinal modified LDL have been implicated in diabetic retinopathy (DR), but their effects on retinal pigment epithelial (RPE) cells and the added effects of extravasated modified HDL are unknown. Methods In human retinas from individuals with and without diabetes and DR, immunohistochemistry was used to detect ApoB, ApoA1 and endoplasmic reticulum (ER) stress markers. In cell culture, human RPE cells were treated with native LDL (N-LDL) or heavily-oxidised glycated LDL (HOG-LDL) with or without pretreatment with native HDL (N-HDL) or heavily-oxidised glycated HDL (HOG-HDL). Cell viability, oxidative stress, ER stress, apoptosis and autophagy were assessed by Cell Counting Kit-8 assay, dichlorofluorescein assay, western blotting, immunofluorescence and TUNEL assay. In separate experiments, RPE cells were treated with lipid oxidation products, 7-ketocholesterol (7-KC, 5–40 µmol/l) or 4-hydroxynonenal (4-HNE, 5–80 µmol/l), with or without pretreatment with N-HDL or HOG-HDL. Results ApoB, ApoA1 staining and RPE ER stress were increased in the presence of DR. HOG-LDL but not N-LDL significantly decreased RPE cell viability and increased reactive oxygen species generation, ER stress, apoptosis and autophagy. Similarly, 4-HNE and 7-KC decreased viability and induced ER stress. Pretreatment with N-HDL mitigated these effects, whereas HOG-HDL was less effective by most, but not all, measures. Conclusions/interpretation In DR, extravascular modified LDL may promote RPE injury through oxidative stress, ER stress, autophagy and apoptosis. N-HDL has protective effects, but HOG-HDL is less effective. Extravasation and modification of HDL may modulate the injurious effects of extravasated modified LDL on the retinal pigment epithelium.

Immune complex formation in human diabetic retina enhances toxicity of oxidized LDL towards retinal capillary pericytes

“…Consistent with a general neurovascular retinal insult in DR ( 18 ), we also found evidence of a broad array of cytotoxic effects: "highly oxidized, glycated LDL" promoted oxidative stress, endoplasmic reticulum (ER) stress, infl ammation and abnormal gene expression, and decreased viability, not only in retinal vascular cells (endothelial cells, pericytes), but also in Müller glia and retinal pigment epithelial cells (RPEs) (9)(10)(11)(12)(13)(14)(15).…”

“…In brief, pericytes were trypsinized, washed twice with cold disease ( 7 ). We therefore hypothesized that the dominant effects of lipoproteins in DR occur not in plasma, but rather after extravasation through leaking blood-retina barriers (BRBs) (8)(9)(10)(11)(12)(13)(14)(15); the extent of this leakage may be more important than plasma concentrations of lipoproteins. We further hypothesized that extravasated intra-retinal lipoproteins undergo extensive modification (glycation, oxidation), rendering them cytotoxic ( 8 ).…”

Prevalence of diabetic retinopathy in screening-detected diabetes mellitus: results from the Gutenberg Health Study (GHS)

“…In a study of the prevalence of and risk factors for diabetic retinopathy in people with newly diagnosed type 2 diabetes mellitus using Scottish national data, diabetic retinopathy was associated with male sex, systolic blood pressure, time to screening and obesity [27]. In terms of dyslipidaemia, intraretinal modified LDLs have been implicated in diabetic retinopathy, and it has been shown that extravascular modified LDLs may promote retinal pigment epithelium injury through oxidative stress, endoplasmic reticulum autophagy and apoptosis, whereas modified HDLcholesterol had protective effects [28,29]. The same holds true for other novel risk markers such as serum apolipoprotein AI [30].…”

Biomarkers in Diabetic Retinopathy

“…-Inflammation -Oxidative stress -Blood clotting -Fibrosis -Cytotoxicity -Pro-and anti-angiogenic actions -Effects on cell-signaling and molecular pathways AGE-based modification of circulating proteins and extravasated proteins such as LDL enhances their pathogenicity, also in the retina (reviewed in [162][163][164][165][166][167]). In the DCCT/EDIC cohort, we demonstrated that baseline levels of AGE-LDL and oxidized LDL (oxLDL) within circulating immune complexes were independent predictors for retinopathy progression several years later [26].…”

“…Lyons' team has shown that extravasated and modified LDL and immune-complexed oxLDL are present in the retina of diabetic patients. They have also demonstrated that glycated LDL and/or oxLDL exert cytotoxicity to cultured human retinal capillary endothelial cells [192], pericytes [166,[192][193][194][195], retinal pigment epithelium [165], and Muller glial cells [196]. Finally, these glycated LDL could be shown to cause changes in cell signaling, gene expression, cell apoptosis, and autophagy [165,192,193,195,196].…”