1. NO to Lysosomes: A Signal for Insulin Resistance in Obesity
- Author
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Abhinav Diwan and Ali Javaheri
- Subjects
HFD, high-fat diet ,medicine.medical_specialty ,Atg7, autophagy related 7 ,CQ, chloroquine ,CTSB, cathepsin B ,mTOR, mammalian target of rapamycin ,030204 cardiovascular system & hematology ,Nitric Oxide ,Signal ,PTIO, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide ,RD, regular diet ,03 medical and health sciences ,0302 clinical medicine ,Insulin resistance ,IR, insulin resistance ,SNAP, S-Nitroso-N-acetylpenicillamine ,Internal medicine ,Autophagy ,medicine ,Humans ,LC3, microtubule-associated protein 1A/1B-light chain 3 ,TFEB, transcription factor EB ,Obesity ,Original Research ,030304 developmental biology ,NO, nitric oxide ,TNF, tumor necrosis factor ,0303 health sciences ,KO, knockout ,Hepatology ,business.industry ,Gastroenterology ,OA, oleic acid ,DIO, diet-induced obesity ,medicine.disease ,Lysosome ,WT, wild-type ,Inducible Nitric Oxide Synthase ,iNOSL, inducible nitric oxide synthase pool localized at lysosomes ,Endocrinology ,iNOS, inducible nitric oxide synthase ,LPS, lipopolysaccharide ,EBSS, Earle's balanced salt solution ,Insulin Resistance ,Lysosomes ,business - Abstract
Background & Aims The lysosome is an acidic organelle that is important for maintaining cellular and metabolic homeostasis in hepatocytes. Lysosomal dysfunction and chronic inflammation coexist, and both contribute to obesity-associated hepatic insulin resistance. However, in the context of obesity, the interplay between inflammatory signals and hepatic lysosomal function remains largely unknown. Inducible nitric oxide synthase (iNOS) is a hallmark for inflammation, and is activated in obesity. The aim of this study is to understand the molecular link between iNOS-mediated lysosomal nitric oxide (NO) production, hepatic lysosomal function, and autophagy in the context of obesity-associated insulin resistance. Methods The role of iNOS in hepatic autophagy, as related to insulin and glucose homeostasis were studied in mice with diet-induced obesity (DIO). The effects and mechanisms of iNOS-mediated lysosomal NO production on lysosomal function and hepatic autophagy were studied in primary hepatocytes as well as in a mouse model of DIO. Results We demonstrate that obesity promotes iNOS localization to the lysosome and decreases levels of lysosomal arginine, resulting in an accumulation of NO in hepatic lysosomes. This lysosomal NO production is attenuated by treatment with a NO scavenger, while co-overexpression of mTOR and a lysosomal arginine transporter (SLC38A9) enhances lysosomal NO production and suppresses autophagy. In addition, we show that deletion of iNOS ameliorates lysosomal nitrosative stress in the livers of DIO mice, promotes lysosomal biogenesis by activating transcription factor EB (TFEB), and enhances lysosomal function and autophagy. Lastly, deletion of iNOS in mice with DIO improves hepatic insulin sensitivity, which is diminished by suppression of TFEB or autophagy related 7 (Atg7). Conclusions Our studies suggest that lysosomal iNOS-mediated NO signaling disrupts hepatic lysosomal function, contributing to obesity-associated defective hepatic autophagy and insulin resistance., Graphical abstract
- Published
- 2019
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