Leveraging arginase biology against metabolic disease

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ABSTRACT Intermittent fasting and caloric restriction are effective therapies against insulin resistance, non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH). Yet, intensive lifestyle modifications are rarely sustainable. We made the provocative discovery that modulating systemic arginine status is sufficient to mimic the therapeutic effects of generalized caloric restriction on hepatic steatosis. This is clinically significant, because targeting arginine is a tractable pathway through which to treat metabolic disease. Accordingly, our long-term goal is to define the signaling cascades underlying adaptive hepatic glucose fasting, so that we can identify new therapies that leverage these pathways against NAFLD and NASH. Our unbiased transcriptomic screening in fasting mice identified a novel glucose fasting-induced effector: the amino acid hydrolase, arginase 2 (Arg2). Our new data demonstrate that forced hepatocyte-specific Arg2 expression reduces peripheral insulin resistance, hepatic steatosis, and inflammation in diabetic mice. Because hepatocyte arginine fate depends upon competition between Arg2 and the lysosomal arginine sensing machinery that dictate autophagic flux, and the pro-inflammatory enzyme, inducible nitric oxide synthase (iNOS), we hypothesize that fasting-induced hepatocyte Arg2 attenuates hepatic steatosis and inflammation by depleting hepatocyte arginine. To test this, we will: 1) examine pleiotropic therapeutic mechanisms of Arg2 action against insulin resistance and hepatic inflammation; 2) examine small-molecule and advanced biological therapeutics that mimic the therapeutic actions of Arg2 activation and 3) define their mechanistic underpinnings. Completing these aims will: 1) establish arginine status as a determinant of metabolic homeostasis; 2) identify how modulating arginase activity impacts cellular lysosomal sensing and its physiological outcomes; and 3) examine efficacy and mechanisms of novel therapies to NAFLD, NASH and insulin resistance.