Chronic liver disease and impaired hepatic glycogen metabolism in argininosuccinate lyase deficiency

Abstract

BACKGROUND. Liver disease in urea cycle disorders (UCDs) ranges from hepatomegaly and chronic hepatocellular injury to cirrhosis and end-stage liver disease. However, the prevalence and underlying mechanisms are unclear. METHODS. We estimated the prevalence of chronic hepatocellular injury in UCDs using data from a multicenter, longitudinal, natural history study. We also used ultrasound with shear wave elastography and FibroTest to evaluate liver stiffness and markers of fibrosis in individuals with argininosuccinate lyase deficiency (ASLD), a disorder with high prevalence of elevated serum alanine aminotransferase (ALT). To understand the human observations, we evaluated the hepatic phenotype of the Asl Neo/Neo mouse model of ASLD. RESULTS. We demonstrate a high prevalence of elevated ALT in ASLD (37%). Hyperammonemia and use of nitrogen-scavenging agents, 2 markers of disease severity, were significantly (P < 0.001 and P = 0.001, respectively) associated with elevated ALT in ASLD. In addition, ultrasound with shear wave elastography and FibroTest revealed increased echogenicity and liver stiffness, even in individuals with ASLD and normal aminotransferases. The Asl Neo/Neo mice mimic the human disorder with hepatomegaly, elevated aminotransferases, and excessive hepatic glycogen noted before death (3-5 weeks of age). This excessive hepatic glycogen is associated with impaired hepatic glycogenolysis and decreased glycogen phosphorylase and is rescued with helper-dependent adenovirus expressing Asl using a liverspecific (ApoE) promoter. CONCLUSION. Our results link urea cycle dysfunction and impaired hepatic glucose metabolism and identify a mouse model of liver disease in the setting of urea cycle dysfunction. TRIAL REGISTRATION. This study has been registered at ClinicalTrials.gov (NCT03721367, NCT00237315).

Beclin-1-mediated activation of autophagy improves proximal and distal urea cycle disorders

“…To this end, Asl Neo/Neo mice received protein-restricted diet and daily administration of Na-benzoate and L-Arg in combination with either TB-1 or vehicle, started on day ten of life and lasting for 3 weeks. Consistent with previous data (Ashley et al, 2018;Baruteau et al, 2018;Burrage et al, 2020;Erez et al, 2011), vehicle-treated Asl Neo/Neo mice showed vacuolated hepatocyte cytoplasm by hematoxylin and eosin (H&E) staining in contrast to WT mice, whereas TB-1 treatment markedly improved the microscopic changes of liver architecture (Fig. 3A).…”

“…3E). Moreover, glycogen accumulation in Asl Neo/Neo mice resulted in displacement of organelles to the cell membrane as previously reported (Burrage et al, 2020), that is relieved by TB-1 ( Fig. 3E).…”

“…To investigate the efficacy of autophagy enhancement for therapy of argininosuccinic aciduria (ASA), the second most frequent UCD (Baruteau et al, 2019a), we investigated TB-1 treatment in the hypomorphic murine model of ASL deficiency (Asl Neo/Neo ) that expresses approximately 16% of residual enzyme activity and recapitulates the main biochemical and clinical abnormalities of ASA patients (Baruteau et al, 2018;Burrage et al, 2020;Kho et al, 2018;Nagamani et al, 2012). Besides impaired urea synthesis and ammonia detoxification, systemic manifestations of ASA, such as reduced body weight, increased blood pressure, and reduced survival are also associated with nitric oxide (NO)-deficiency (Baruteau et al, 2018;Erez et al, 2011;Kho et al, 2018;Nagamani et al, 2012).…”

“…Chronic hepatocellular injury is a common complication in patients with ASL deficiency (Baruteau et al, 2017;Mori et al, 2002;Ranucci et al, 2019;Yaplito-Lee et al, 2013). Despite the underlying mechanism triggering the liver disease remains unclear, evidence in human and mouse suggests that it is related to massive accumulation of cytoplasmic glycogen (Badizadegan & Perez-Atayde, 1997;Bigot et al, 2017;Burrage et al, 2020). Moreover, because activation of autophagy was found to be effective in clearance of glycogen storage in glycogen storage diseases (Ashe et al, 2010;Farah et al, 2016;Martina et al, 2014;Spampanato et al, 2013), we investigated whether TB-1 promotes glycogen clearance in ASA livers.…”

“…Glycogen in hepatocytes is catabolized either in cytosol by the coordinated action of enzymes involved in glycogenolysis or in the lysosome by the acid glucosidase (Prats et al, 2018). Hepatic expression of glycogen phosphorylase (PYGL), the enzyme that catalyzes the rate limiting step of glycogenolysis, was recently found to be reduced in Asl Neo/Neo mice, suggesting a mechanism responsible for aberrant glycogen accumulation in ASA (Burrage et al, 2020). We confirmed reduced PYGL protein levels in livers of Asl Neo/Neo mice, but they were unaffected by TB-1 ( Fig.…”