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Mingyuan Wu, Shihe Yang, Michael H. Elliott, Dongxu Fu, Kenneth Wilson, Jing Zhang, Mei Du, Junping Chen, Timothy J. Lyons; High Oxidized Glycated Low Density Lipoprotein Induces Apoptosis in Human Retinal Muller Cells via Activation of Oxidative Stress and Endoplasmic Reticulum Stress. Invest. Ophthalmol. Vis. Sci. 2011;52(14):510.
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We have previously discovered that modified low density lipoprotein has been associated with pathogenesis of diabetic retinopathy (DR) including apoptotic pericyte loss. In this work, we investigate whether modified low density lipoprotein induced apoptosis in human retinal Muller cells and whether oxidative stress and endoplasmic reticulum (ER) stress are implicated in this process.
Human Muller cell line MIO-M1 were treated with highly oxidized glycated low density lipoprotein (HOG-LDL) or native LDL (N-LDL) at 200 mg/L for 1,6,12 and 24h. In separate experiments, Muller cells were pretreated for 1 hr with NAC (a blocker of oxidative stress) and 4-PBA (a blocker of ER stress) before spiking HOG-LDL or N-LDL. Cell counting kit-8, western blot for caspase related proteins, and TUNEL immunostaining were performed to detect apoptosis. Western blots were conducted to detect oxidative stress and ER Stress.
HOG-LDL induced apoptosis as shown by deceased cell viability, increased TUNEL positive cells, and increased protein levels of Caspase 3, Caspase 12, Bax and decreased protein levels of Bcl-2. HOG-LDL also increased oxidative stress as shown by increased levels of 3-nitrotyrosine and SOD2. In parallel, HOG-LDL induced ER stress as shown by increased levels of ER stress markers eIF2-a, KDEL, ATF6, and Chop. In addition, pretreatment with NAC or 4-PBA partially attenuated apoptosis, oxidative stress and ER stress. In comparison, N-LDL did not induce apoptosis, oxidative stress, and ER stress.
The data suggest that modified LDL is implicated in apoptotic Muller cell death, supporting our main hypothesize that, in addition to hyperglycemia, oxidation of extravasated lipoproteins may contribute to the development of DR.
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