Abstract 11500: Lysosomal Nitrosative Stress Contributes to Hepatic Insulin Resistance in Obesity

Obesity greatly increases risk for a wide range of diseases including diabetes, fatty liver disease and cardiovascular disease. The lysosome is an acidic organelle that plays a central role in maintaining organelle and metabolic homeostasis in the liver. Obesity results in a chronic inflammation of the liver, but how this affects lysosomal function and contributes to the disruption of glucose and lipid homeostasis is largely unknown. Here we show that obesity activates lysosome-localized inducible nitric oxide synthase (iNOSL) and elevates lysosomal arginine level, leading to accumulation of lysosomal nitric oxide (NO) in the liver. Our studies have also shown that obesity impairs activity of hepatic S-nitrosoglutathione reductase (GSNOR), a major cellular denitrosylase. Together, these outcomes result in increased S-nitrosylation of lysosomal enzymes, impairing the activity of lysosomal enzymes and thus lysosomal function, and engendering lysosomal nitrosative stress. Consistent with these findings, liver-specific deletion of GSNOR increases lysosomal nitrosative stress and impairs autophagy, worsening obesity-associated hepatic insulin resistance, steatosis and systemic glucose intolerance. Conversely, both liver-specific overexpression of GSNOR and iNOS deletion in diet-induced obese (DIO) markedly enhance lysosomal function and improve insulin action and glucose homeostasis, ameliorate steatosis. Moreover, expression of S-nitrosylation-resistant lysosomal enzymes, or treatment with autophagy enhancers leads to improved insulin sensitivity in GSNOR-deficient primary hepatocytes and livers, indicating that lysosomal nitrosative stress contributes directly to defects in autophagy and hepatic insulin resistance in obesity. Notably, analysis of human liver has shown that NAFLD and diabetes are accompanied by decreases in hepatic GSNOR activity and lysosomal nitrosative stress, revealing that this mechanism is conserved and relevant to human disease. Taken together, our findings provide the first insight into the inflammatory mechanisms that compromise lysosomes in obesity, and how this defect affects hepatic insulin sensitivity. This will be relevant for developing therapeutics for many obesity-associated diseases including cardiovascular disease.