Inducible Arginase 1 Deficiency in Mice Leads to Hyperargininemia and Altered Amino Acid Metabolism

Yuan Yan Sin,Laurel L. Ballantyne,Tim St. Amand,Lianna Kyriakopoulou,Colin D. Funk,Andreas Schulze,Kamalika Mukherjee,Hervé Guillou

doi:10.1371/journal.pone.0080001

Yuan Yan Sin, Laurel L. Ballantyne + Show 6 more

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https://doi.org/10.1371/journal.pone.0080001

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Abstract

Arginase deficiency is a rare autosomal recessive disorder resulting from a loss of the liver arginase isoform, arginase 1 (ARG1), which is the final step in the urea cycle for detoxifying ammonia. ARG1 deficiency leads to hyperargininemia, characterized by progressive neurological impairment, persistent growth retardation and infrequent episodes of hyperammonemia. Using the Cre/loxP-directed conditional gene knockout system, we generated an inducible Arg1-deficient mouse model by crossing “floxed” Arg1 mice with CreERT2 mice. The resulting mice (Arg-Cre) die about two weeks after tamoxifen administration regardless of the starting age of inducing the knockout. These treated mice were nearly devoid of Arg1 mRNA, protein and liver arginase activity, and exhibited symptoms of hyperammonemia. Plasma amino acid analysis revealed pronounced hyperargininemia and significant alterations in amino acid and guanidino compound metabolism, including increased citrulline and guanidinoacetic acid. Despite no alteration in ornithine levels, concentrations of other amino acids such as proline and the branched-chain amino acids were reduced. In summary, we have generated and characterized an inducible Arg1-deficient mouse model exhibiting several pathologic manifestations of hyperargininemia. This model should prove useful for exploring potential treatment options of ARG1 deficiency.

Highlights

The urea cycle disorders (UCDs) are a group of rare inborn errors of hepatic metabolism causing malfunction in the nitrogen clearance system
There are two isoforms of arginase which are present at distinct intracellular sites: arginase 1 (ARG1) and arginase 2 (ARG2)
The induced Arg1 knockout mice showed an approximately 1.5–2.3-fold increase in citrulline and guanidinoacetic acid (GAA), whereas proline was reduced about 50% compared to the control vehicle-treated mice

Summary

Introduction

The urea cycle disorders (UCDs) are a group of rare inborn errors of hepatic metabolism causing malfunction in the nitrogen clearance system. Deficiency in any of the enzymes in the urea cycle results in perturbation of ureagenesis, thereby leading to incomplete removal of ammonia from the blood stream and to variable degrees of hyperammonemia. ARG1, which is expressed predominantly in the cytoplasm of the liver, hydrolyzes arginine into ornithine and urea, where the latter is excreted through the kidneys in the urine [1,2]. The second isoform, mitochondrial ARG2 is distributed in extrahepatic tissues, such as kidney and prostate, with lower levels in brain, gastrointestinal tract and macrophages [2,3]. In patients with ARG1 deficiency and hyperammonemic episodes, there is often a compensatory increase in ARG2 activity in the kidney [4]. The exact mechanism is not known, the augmented expression of ARG2 may mitigate the phenotypic deterioration via residual ureagenesis [1,4]

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