A positive feedback loop between nitric oxide and amyloid beta (1-42) accelerates mitochondrial damage in human lens epithelial cells

摘要

We have reported that excessive nitric oxide (NO), like other reactive oxygen species (ROS), causes a decrease in cytochrome c oxidase (CCO) activity and ATP levels (mitochondrial damage) resulting in lens opacity. In addition, previous reports have shown that oxidative stress caused by ROS enhances amyloid 13 (A beta) production in mammalian lenses, and that A beta(1-42) stimulates inducible nitric oxide synthase (iNOS) promoter activity. Based on these reports, we investigated the relationship between NO and A beta(1-42) production in human lens epithelial (HLE) cells. iNOS was induced by the co-incubation of HLE cells with 1000 IU interferon-gamma (IFN-gamma) and 100 ngiml lipopolysaccharide (LPS) for 48 h. This led to enhanced NO release, an increase in the gene expression levels of proteins related to A beta production, and the cellular accumulation of A beta(1-42) . Moreover, both aminoguanidine (AG, a selective inhibitor of iNOS) and diethyldithiocarbamate (DDC, a nuclear factor-kappa B (NF kappa B) inhibitor) attenuated these changes in IFN-gamma and LPS stimulated HLE cells. Based on our finding that A beta(1-42) accumulation is induced by co incubation of HLE cells with both IFN-gamma and LPS, we prepared a HLE cell model with A beta(1-42) accumulation (A beta-accumulated-HLE cell model) by pre-stimulating cells with IFN-gamma and LPS for 48 h. A beta(1-42) accumulation caused NO production via iNOS, resulting in an enhancement in the mRNA levels for enzymes necessary for the proteolysis of amyloid precursor protein (APP) to AS in HLE cells. In addition, excessive NO produced in response to A beta(1-42) accumulation led to a decrease in CCO activity and ATP levels. Taken together, we hypothesize that excessive NO production in the lens epithelium enhances A beta(1-42) production, and that this enhancement accelerates NO release. The enhancement in NO production in the lens epithelium based on positive feedback (NO-A beta positive feedback loop, a vicious cycle) may promote the onset of cataracts (lens opacification) via the decrease in CCO activity and ATP levels. These findings provide significant information that can be used to design further studies aimed at developing anti-cataract drugs. (C) 2017 Elsevier B.V. All rights reserved.